The effects of a- and b-adrenergic blocking agents on postresuscitation myocardial dysfunction and myocardial tissue injury in a rat model of cardiac arrest MIN YANG, XIANWEN HU, XIAOYE LU, XIAOBO WU, JIEFENG XU, ZHENGFEI YANG, JIE QIAN, SHIJIE SUN, JENA CAHOON, and WANCHUN TANG RANCHO MIRAGE, LOS ANGELES, AND SAN DIEGO, CALIFORNIA; AND HEFEI, CHINA
We investigated the relationship between the severity of postresuscitation (PR) myocardial tissue injury and myocardial dysfunction after the administration of epinephrine as well as the protective effects of a- and b-adrenergic blocking agents. Forty male Sprague-Dawley rats were randomized into 6 groups: (1) placebo; (2) epinephrine; (3) epinephrine pretreated with a1-blocker (prazosin); (4) epinephrine pretreated with a2-blocker (yohimbine); (5) epinephrine pretreated with b-blocker (propranolol); and (6) epinephrine pretreated with b- plus a1-blocker (propranolol and prazosin). Cardiopulmonary resuscitation was initiated after 8 minutes of untreated ventricular fibrillation and continued for an additional 8 minutes. The myocardial function and the serum concentrations of troponin I (Tn I) and N-terminal probrain natriuretic peptide (NT-proBNP) were measured at baseline and after resuscitation. After resuscitation, both Tn I and NT-proBNP were significantly increased in all groups, especially in the epinephrine and epinephrine pretreated with a2-blocker groups. Significantly better PR myocardial function and neurologic deficit score were observed in epinephrine pretreated with the a1- or b-blocker with decreased releases of Tn I and NT-proBNP. However, the most significant improvements were observed in the animals pretreated with b- plus a1-blocker. The present study demonstrated that myocardial stunning may not be the only mechanism of PR myocardial dysfunction. Administration of epinephrine increased the severity of PR myocardial tissue injury and dysfunction. The b- and b- plus a1-blocker pretreatment significantly reduced the severity of PR myocardial tissue injury and myocardial dysfunction with better neurologic function and prolonged duration of survival. (Translational Research 2015;165:589–598) Abbreviations: CO ¼ cardiac output; CPP ¼ coronary perfusion pressure; CPR ¼ cardiopulmonary resuscitation; EF ¼ ejection fraction; ETCO2 ¼ end-tidal CO2; MPI ¼ myocardial performance index; NDS ¼ neurologic deficit score; PC ¼ precordial compression; PR ¼ postresuscitation; ROSC ¼ return of spontaneous circulation; VF ¼ ventricular fibrillation
From the Weil Institute of Critical Care Medicine, Rancho Mirage, California; The Second Hospital of Anhui Medical University, Hefei, China; The Keck School of Medicine, University of Southern California, Los Angeles, California; Department of Emergency Medicine, UC San Diego School of Medicine, San Diego, California. Submitted for publication August 12, 2014; revision submitted October 15, 2014; accepted for publication October 17, 2014.
Reprint requests: Wanchun Tang, Weil Institute of Critical Care Medicine, 35100 Bob Hope Drive, Rancho Mirage, CA 92270; e-mail: [email protected]. 1931-5244/$ - see front matter Ó 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.trsl.2014.10.012
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AT A GLANCE COMMENTARY Yang M, et al. Background
Cardiac arrest remains a significant health issue with poor outcomes. Myocardial dysfunction is one of the most causes of death after return of spontaneous circulation. We investigated the relationship between the severity of PR myocardial dysfunction and myocardial injury biomarkers after epinephrine and epinephrine with adrenergic blockers in a rat model of cardiopulmonary resuscitation. Translational Significance
The troponin I and N-terminal probrain natriuretic peptide are significantly correlated with the severity of PR myocardial dysfunction and prognosis. Administration of epinephrine increased the severity of myocardial tissue injury and dysfunction but combined with b- or b- plus a1adrenergic blocker may provide a better therapeutic strategy for resuscitation and PR.
INTRODUCTION
Sudden cardiac death remains a significant health issue with poor long-term outcomes. In the United States, approximately 300,000 patients suffer out-ofhospital sudden cardiac arrest annually and the average survival-to-hospital discharge is 7.9%.1 The most common cause of death after resuscitation is because of myocardial dysfunction and brain injury.2 The severity of postresuscitation (PR) myocardial dysfunction with the impairments of both systolic and diastolic functions is a major cause of early death after successful resuscitation. Animal and clinical studies indicated that the severity of PR myocardial dysfunction is closely related to the duration of ischemia, number of electrical defibrillations, and the dose of epinephrine.3-5 Previous studies further indicated that the mechanism of PR myocardial dysfunction is myocardial stunning with a reversible mechanical myocardial dysfunction.6 However, the underlying mechanisms of PR myocardial dysfunction especially whether there is predominant myocardial tissue injury after global myocardial ischemia of cardiac arrest remains controversial. Epinephrine has been used as a first-line vasopressor agent during cardiopulmonary resuscitation (CPR) for more than 50 years. Animal and clinical studies have demonstrated that epinephrine improves the rate of re-
turn of spontaneous circulation (ROSC). Several studies have demonstrated that the efficacy of epinephrine in aiding ROSC is because of a-adrenergic receptor stimulation.7,8 However, epinephrine significantly increases the severity of PR myocardial dysfunction and reduces the duration of survival.3,9 The detrimental effects of epinephrine during the PR phase are closely related to its b- and a1-actions.10,11 However, whether epinephrine causes myocardial tissue injury remains to be investigated. In the present study, we investigated the relationship between the severity of PR myocardial dysfunction and myocardial injury biomarkers after epinephrine and epinephrine with adrenergic blockers. We hypothesized that epinephrine increases the severity of PR myocardial dysfunction and myocardial tissue injury. When epinephrine is administrated with a1-, b-, or b- plus a1-blocker, the severity of PR myocardial dysfunction and myocardial injury tissue biomarkers are reduced with an improved duration of survival. MATERIALS AND METHODS
This study was approved by the Animal Care and Use Committee of the Weil Institute of Critical Care Medicine. All animals received humane care in compliance with the Principles of Laboratory Animal Care formulated by the National Society for Medical Research and the National Institute of Health publication on the Use of Laboratory Animals prepared by the Institute of Laboratory Animal Resources. Animal preparation. Healthy male Sprague-Dawley rats, aged 6–8 months, weighing between 450 and 550 g, were supplied by a single source breeder (Harlan Sprague-Dawley Inc, Livermore, California). All animals were fasted overnight except for free access to water. The animals were anesthetized by intraperitoneal injection of pentobarbital (45 mg/kg) and additional doses (10 mg/kg) were administrated at intervals of 1 hour, except for 30 minutes before the induction of cardiac arrest. The trachea was orally intubated with a 14-G cannula mounted on a blunt needle with a 145 angled tip. Endtidal CO2 (ETCO2) was continuously monitored with a side-stream infrared CO2 analyzer (End-Tid IL 200; Instrument Laboratory, Lexington, Massachusetts). A conventional lead II electrocardiogram was continuously monitored. The animals were breathing room air spontaneously during preparation. A polyethylene (PE) catheter (PE-50; BectonDickinson, Franklin Lakes, New Jersey) was advanced into the descending aorta from the surgically exposed left femoral artery for the measurement of arterial
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pressure and collection of blood samples for blood gas and biomarkers. Through the left external jugular vein, another PE-50 catheter was advanced into the right atrium for the measurement of right atrial pressure and drug injection. Aortic and right atrial pressures were measured with reference to the midchest with high-sensitivity transducers (model 42584-01; Abbott Critical Care Systems, North Chicago, Illinois). A thermocouple microprobe (9030-12-D-34; Columbus Instruments, Columbus, Ohio) was inserted into the inferior cava vena from the left femoral vein for the measurement of blood temperature. A 3-F PE catheter (model C-PMS-301J; Cook Critical Care, Bloomington, Indiana) was advanced through the right external jugular vein into the right atrium. A precurved guide wire was then advanced through the catheter into the right ventricle for inducing ventricular fibrillation (VF), and the position of the catheter was confirmed by an electrocardiogram. All catheters were flushed intermittently with saline containing 2.5 IU/mL of crystalline bovine heparin. During the experiment, the blood temperature of all rats was maintained between 36.8 C and 37.2 C with a heating lamp. Experimental procedures. Twenty minutes before inducing VF, the animals were randomized into 6 groups with 6 rats in each group by the sealed envelope method: (1) placebo group: saline in the same volume of adrenergic blocking agents and epinephrine were administered as bolus injections into the right atrium at 15 minutes before inducing VF and 5 minutes after the start of precordial compression (PC) separately; (2) epinephrine group: saline in the same volume of adrenergic blocking agents and epinephrine (20 mg/ kg) were administered as bolus injections into the right atrium at 15 minutes before inducing VF and 5 minutes after the start of PC separately; (3) epinephrine pretreated with a1-blocker group: prazosin (0.5 mg/kg) and epinephrine (20 mg/kg) were administered as bolus injections into the right atrium at 15 minutes before inducing VF and 5 minutes after the start of PC separately; (4) epinephrine pretreated with a2-blocker group: yohimbine (100 mg/kg) and epinephrine (20 mg/kg) were administered as bolus injections into the right atrium at the same time points; (5) epinephrine pretreated with b-blocker group: propranolol (1 mg/kg) and epinephrine (20 mg/kg) were administered as bolus injections into the right atrium at the same time points; (6) epinephrine pretreated with b- plus a1-blocker group: propranolol (1 mg/kg), prazosin (0.5 mg/kg), and epinephrine (20 mg/kg) were administered as bolus injections into the right atrium at the same time points.12-14 The experimental procedures are shown in Fig 1. Thirty-minutes before inducing VF, baseline measure-
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Fig 1. Experimental outline and procedure. BL, baseline; VF, ventricular fibrillation; PC, precordial compression; DF, defibrillation; PR, postresuscitation; h 5 hour; HR, heart rate; AP, arterial pressure; RA, right atrial pressure; ETCO2, end-tidal CO2; Blood Temp, blood temperature; Echo, echocardiology; BG, blood gas; NDS, neurologic deficit score.
ments and arterial blood gases were obtained. Fifteen minutes before inducing VF, mechanical ventilation was established at a tidal volume of 0.60 mL/100 g of body weight and a frequency of 100 breaths/min. The inspired O2 fraction was maintained at 0.21. VF was then induced through a guide wire advanced into the right ventricle. A progressive increase at 60-Hz current from 2.7 mA to a maximum of 5 mA was then delivered to the right ventricular endocardium. The current was continued for 3 minutes to prevent spontaneous defibrillation. Mechanical ventilation was discontinued after the onset of VF. PC together with mechanical ventilation (tidal volume 0.60 mL/100 g body weight, 100 breaths/min, inspired O2 fraction 1.0) was initiated after 8 minutes of untreated VF with a pneumatically driven mechanical chest compressor. PC was maintained at a rate of 200 breaths/min and synchronized to provide a compression-to-ventilation ratio of 2:1 with equal compression-relaxation for a duration of 8 minutes. The depth of compressions was initially adjusted to decrease the anteroposterior diameter of the chest by 25% and maintain coronary perfusion pressure at 22 6 2 mm Hg and ETCO2 at 11 6 2 mm Hg without the use of epinephrine. Fifteen minutes before the induction of VF, adrenergic blockers or placebo were injected into the right atrium. At 5 minutes after the start of PC, epinephrine or placebo was injected into the right atrium. Resuscitation was attempted with up to 3 two-joule counter shocks. ROSC is defined as the return of spontaneous circulation with a mean aortic pressure .50 mm Hg for 5 minutes. If ROSC was not achieved, a 30-second interval of PC was performed before attempting a subsequent sequence of up to 3 shocks.
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The procedure was repeated for a maximum of 3 cycles. If ROSC was not achieved, the resuscitation maneuvers were terminated. After ROSC, mechanical ventilation was continued with 100% inspired oxygen for 1 hour, 50% for the second hour, and 21% thereafter. During this time, the animals uniformly recovered from anesthesia. After the experiment, all catheters including the endotracheal tube were removed. Butorphanol (0.4 mg/kg) was injected intramuscularly if discomfort was identified. The animals were then returned to their cages equipped with a heated pet mat (Allied Precision Industries, Inc, Elburn, Illinois) to maintain the temperature in the cage at 24 C–26 C. All animals were euthanized by intraperitoneal injection of pentobarbital (150 mg/ kg) after a 72-hour observation period. A necropsy was routinely performed to identify any traumatic injuries of the thoracic and abdominal organs. Measurements. Heart rate, aortic and right atrial pressures, electrocardiogram, blood temperature, and ETCO2 values were continuously recorded on a personal computer–based data-acquisition system supported by Common Ocean Data Access System hardware and software (DataQ, Akron, Ohio). At baseline, 1, 2, 3, and 4 hours after ROSC, ejection fraction (EF), cardiac output (CO), and myocardial performance index (MPI) were measured with an echocardiography (Model HD11XE; Philips Medical Systems, Eindhoven, Netherlands) with a 12.5 Hz transducer. CO and EF were used to estimate myocardial contractility. MPI, which combines time intervals related to systolic and diastolic functions and reflecting the global myocardial function, was also calculated using the formula (a 2 b)/b, where a 5 mitral closure-to-opening interval (time interval from cessation to the onset of mitral inflow) and b 5 ET (aortic flow ejection time, obtained at the left ventricular outflow tract), was used to estimate left ventricular systolic and diastolic function.15 A 0.3 mL of artery blood sample was withdrawn for the measurement of arterial oxygen partial pressure, CO2 partial pressure, pH, and lactate at baseline and every hour after ROSC using a conventional blood gas analyzer (Phox, Stat Profile; Nova Biomedical Corporation, Waltham, Massachusetts). A 1.2 mL of artery blood sample was withdrawn for serum concentrations of troponin I (Tn I) and N-terminal probrain natriuretic peptide (NT-proBNP) at baseline, 1, and 4 hours after ROSC. The equivalent arterial blood from a donor rat of the same colony was transfused into the femoral artery after blood drawing. Serum concentrations of Tn I and NT-proBNP were measured with the commercial enzyme-linked immunosorbent assay kits according to the manufacturer’s instructions (Cat. No. 2010-2-US; Life Diagnostics,
Inc and Cat. No. MBS164802; MyBioSource, Inc, respectively). Levels of consciousness, brain stem function, and overall performance were examined and scored according to a neurologic deficit score (normal 5 0 and dead or brain dead 5 500) at baseline, 24, 48, and 72 hours of PR if they survived. The neurologic deficit score was confirmed by 2 investigators blinded to the treatment.16,17 The duration of survival was also recorded. Statistical analysis. The experimental data were analyzed by Microsoft Excel 2007 (Redmond, Washington) and Statistical Product and Service Solutions 13.0 (Chicago, Illinois). Measurements were reported as the mean 6 standard deviation. Comparisons between time-based measurements within each group were performed with repeated measurement of variance and Scheffe ’s multiple comparison techniques were used. The relationship between myocardial injury biomarkers, indicators of echocardiography, and the duration of survival time were analyzed with the Pearson correlation analysis. A value of P , 0.05 was regarded as significant. RESULTS
Forty rats were used in this study. Thirty-six experiments were completed and included. Four rats were excluded because of experimental instruments or technical failure during animal preparation and resuscitation. Body weight and baseline measurements including hemodynamic data, blood temperature, blood gas, myocardial function, and serum levels of Tn I and NTproBNP did not differ significantly among the 6 groups (Table I). All animals except for 1 in the placebo group were resuscitated. Coronary perfusion pressure was significantly greater in the 5 groups that received epinephrine at PC 6 minutes when compared with the placebo group (P , 0.05) (Table II). The number of defibrillations that were required to restore ROSC were significantly higher in the epinephrine group than epinephrine pretreated with b- and b- plus a1-blocker groups (P , 0.05) (Table II). After resuscitation, the serum concentrations of Tn I and NT-proBNP were significantly increased in all groups (Fig 2). The serum concentration of Tn I was significantly greater in the epinephrine, epinephrine with a2-blocker, and placebo groups than the epinephrine pretreated with b- or b- plus a1-blocker groups (P , 0.05) (Fig 2). The animals pretreated with a2blocker had significantly greater levels of Tn I than the animals pretreated with a1-blocker at PR 1 and 4 hours (P , 0.05) (Fig 2). The lowest levels of Tn I
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Table I. Baseline characteristics Group
Placebo
Epinephrine
Epinephrine with a1-blocker
Epinephrine with a2-blocker
Epinephrine with b-blocker
Epinephrine with b- plus a1-blocker
Body weight, g Heart rate, bpm MAP, mm Hg ETCO2, mm Hg RA, mm Hg Temperature, C CO, mL/min EF, % MPI Lactate, mmol/L Tn I, ng/L NT-proBNP, ng/L
506.0 6 21.2 362.5 6 14.6 133.6 6 6.0 40.4 6 2.4 1.2 6 0.2 36.8 6 0.3 117.1 6 4.9 68.6 6 2.7 0.69 6 0.02 0.7 6 0.2 0.02 6 0.01 84.7 6 53.5
516 6 22.3 351.8 6 20.3 134.6 6 6.8 40.7 6 3.2 1.3 6 0.1 36.6 6 0.2 117.3 6 2.4 69.2 6 1.3 0.71 6 0.04 0.7 6 0.1 0.03 6 0.02 90.6 6 53.8
500.8 6 15.2 359.7 6 11.1 141.1 6 11.9 41.8 6 4.5 1.2 6 0.1 36.6 6 0.2 119.5 6 3.0 70.5 6 1.6 0.70 6 0.01 0.8 6 0.1 0.03 6 0.01 98.3 6 18.1
521.3 6 26.2 363.7 6 21.6 132.3 6 10.1 39 6 2.2 1.1 6 0.1 36.5 6 0.1 115.8 6 2.8 68 6 2.8 0.70 6 0.03 0.7 6 0.1 0.04 6 0.03 82.1 6 38.5
511.8 6 12.7 352.2 6 18.3 130.6 6 3.4 41.4 6 2.3 1.3 6 0.2 36.6 6 0.3 115.9 6 7.9 70.1 6 1.9 0.71 6 0.03 0.8 6 0.2 0.03 6 0.02 86.9 6 24.5
504.3 6 16.1 347.2 6 25.5 135.2 6 9.0 40.9 6 1.7 1.2 6 0.1 36.7 6 0.2 116.7 6 3.5 70.4 6 2.2 0.70 6 0.02 0.8 6 0.1 0.02 6 0.01 97.6 6 21.8
Abbreviations: CO, cardiac output; EF, ejection fraction; ETCO2, end-tidal CO2; MAP, mean aortic pressure; MPI, myocardial performance index; NT-proBNP, N-terminal probrain natriuretic peptide; RA, right atrial pressure; Tn I, troponin I. Values are presented as the mean 6 standard deviation.
Table II. Coronary perfusion pressure and the number of defibrillations Group
Placebo
Epinephrine
Epinephrine with a1-blocker
Epinephrine with a2-blocker
Epinephrine with b-blocker
Epinephrine with b- plus a1-blocker
CPP, mm Hg PC1 PC5 PC6 The number of defibrillations
22.4 6 0.8 22.3 6 1.3 22.3 6 1.0 2.8 6 3.3
23.1 6 1.9 22.5 6 1.5 31.4 6 1.4* 2.2 6 1.0†
22.4 6 0.4 22.6 6 0.6 33.1 6 1.2* 1.2 6 1.0
22.6 6 0.0 22.1 6 1.4 31.9 6 3.2* 2.0 6 3.5
22.1 6 0.9 22.6 6 0.8 31.2 6 3.3* 1.0 6 0.6
22.7 6 0.6 23.1 6 0.8 32.3 6 0.6* 0.8 6 0.4
Abbreviations: CPP, coronary perfusion pressure; PC1, 1 minute after precordial compression; PC5, 5 minutes after precordial compression; PC6, 6 minutes after precordial compression. Values are presented as the mean 6 standard deviation. *P , 0.05 vs placebo group. † P , 0.05 vs epinephrine with b-blocker group and epinephrine with b- plus a1-blocker group.
were observed in the epinephrine pretreated with b- plus a1-blocker group. The serum concentration of NTproBNP was significantly greater in the epinephrine, epinephrine with a2-blocker, and placebo groups than the epinephrine pretreated with a1-, b-, and b- plus a1-blocker groups at PR 1 and 4 hours (P , 0.05) (Fig 2). Again, the lowest levels of NT-proBNP were observed in the epinephrine pretreated with b- plus a1-blocker group. The serum concentration of NTproBNP was significantly greater in the epinephrine group than the placebo group at PR 1 hour (P , 0.05) (Fig 2). PR myocardial function as measured by CO, EF, and MPI was significantly impaired in all groups when compared with the baseline (Table III). The b- plus a1-blocker pretreatment significantly improved the severity of PR myocardial function when compared with the other 5 groups (P , 0.05) (Table III). The epinephrine and epinephrine pretreated with a2-blocker increased the severity of PR myocardial dysfunction when compared with the placebo group (P , 0.05) (Table III).
A significantly improved duration of survival was observed in the animals pretreated with b- or b- plus a1-blocker when compared with the epinephrine and placebo groups (P , 0.05) (Table IV). The a2-blocker significantly reduced the duration of survival compared with epinephrine pretreated with a1-, b-, and b- plus a1-blocker groups (P , 0.05) (Table IV). The animals pretreated of with b- or b- plus a1-blocker demonstrated a significantly reduced severity of PR neurologic dysfunction when compared with the other 4 groups (P , 0.05) (Table IV). The increases in serum concentrations of Tn I and NT-proBNP were significantly correlated with MPI (P , 0.01) (Fig 3). The severity of PR myocardial tissue injury and mechanical dysfunction as measured by Tn I, NT-proBNP, and MPI at 1 hour after ROSC was significantly correlated with the duration of survival (r 5 20.683, P , 0.01; r 5 20.475, P , 0.01; and r 5 20.613, P , 0.01, respectively). There were no gross abnormalities or surgical injuries observed at necropsy.
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Fig 2. Serum concentration of Tn I and NT-proBNP. Tn I, troponin I; NT-proBNP, N-terminal probrain natriuretic peptide; BL, baseline; PR1h, 1 hour after postresuscitation; PR4h, 4 hours after postresuscitation. *P , 0.05 vs epinephrine with b-blocker group and epinephrine with b- plus a1-blocker group; ※P , 0.05 vs epinephrine with b- plus a1-blocker group; ＃P , 0.05 vs epinephrine with a1-blocker group; §P , 0.05 vs placebo group.
DISCUSSION
The present study demonstrated that 8 minutes of global myocardial ischemia and 8 minutes of low flow reperfusion of CPR produced significant myocardial tissue injury and PR myocardial mechanical dysfunction. We further demonstrated that the administration of epinephrine increased the severity of myocardial tissue injury and dysfunction. Pretreatment with b- or b- plus a1-adrenergic blocker significantly decreased the severity of myocardial tissue injury and PR myocardial dysfunction, with improved neurologic function and the duration of survival. The early stage of PR myocardial tissue injury biomarkers (Tn I and NT-proBNP) was significantly correlated with the severity of PR myocardial dysfunction and prognosis. In the present study, we demonstrated that the serum levels of Tn I and NT-proBNP increased significantly from 1 hour after resuscitation in all animals with 16 minutes of global myocardial ischemia–reperfusion injury. McDonough JL et al demonstrated that 15 minutes of mild ischemia was enough to cause the release of Tn I from an isolated rat heart.18 Earlier studies demonstrated that Tn I and NT-proBNP significantly increased from 2 hours after resuscitation in a rabbit model of CPR.19 The mechanism of early release of Tn I in a rat model of CPR is that global myocardial ischemia/ reperfusion injury results in an initial release of cytosol Tn followed by the gradual release of myofibril-bound Tn complexes through increased permeability of the cell membrane and microvasculature.20,21 Evidence indicates that NT-proBNP is related to various myocar-
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dial diseases and myocardial tissue injury, including mild ischemia/reperfusion injury.22,23 These results are consistent with our findings in which Tn I and NT-proBNP were increased significantly after 16 minutes of global ischemia and reinfusion of cardiac arrest and resuscitation. Our results indicated that myocardial stunning may not be the only mechanism of PR myocardial dysfunction. The PR myocardial stunning was considered the most important mechanism of PR myocardial dysfunction, a reversible mechanical myocardial dysfunction without myocardial necrosis.24-26 Several animal experimental studies demonstrated a full recovery of PR myocardial stunning, which was observed at 48– 72 hours after ROSC11,24. Pellis et al11 demonstrated that the values of Tn I significantly increased from PR 1 hour and returned to baseline at PR 72 hours in a porcine model of CPR. However, clinical research indicates that early PR deaths occur during the first 24 hours after ROSC, which is associated with a persistent low cardiac index.27 Therefore, the poor prognosis of CPR is incompatible with characteristics of PR myocardial stunning. Whether there is myocardial cell death after resuscitation that contribute to the severity of myocardial dysfunction is still a controversial issue. Our results indicated that the higher levels of Tn I and NT-proBNP were significantly related to severe PR myocardial dysfunction and poor prognosis. Tn I is highly sensitive to myocardial stunning, apoptosis, and necrosis induced by ischemia-reperfusion injury.21,28-30 Currently, there are no studies to address the relationship between NT-proBNP and ischemic myocardial stunning. However, the level of NTproBNP was closely correlated with diagnosis and prognosis of heart failure and acute myocardial infarction; both have the pathologic characteristics of apoptosis and necrosis.31-33 Our group has previously demonstrated that apoptosis was not involved in the mechanism of PR myocardial dysfunction in a rat model of CPR.34 A recent study, however, indicated that caspase 3–mediated mitochondrial apoptosis is activated in PR myocardial dysfunction at 12 and 24 hours after ROSC in a porcine model of CPR, which may reflect the differences in animal species.35 Our results support that PR myocardial stunning is just one of the mechanisms of PR myocardial dysfunction. The myocardial tissue injury plays an important role in the mechanisms of PR myocardial dysfunction and needs to be further investigated. In the present study, we demonstrated that the administration of epinephrine increases the severity of myocardial tissue injury and PR myocardial dysfunction. However, the accurate relationship between the duration of global myocardial ischemia, epinephrine,
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Table III. CO, EF, and MPI Placebo
Epinephrine
Epinephrine with a1-blocker
Epinephrine with a2-blocker
Epinephrine with b-blocker
Epinephrine with b- plus a1-blocker
117.10 6 4.90 75.38 6 4.51*,†,z 69.06 6 7.20*,†,z 62.42 6 9.84*,† 66.42 6 10.41*,†
117.30 6 2.40 65.28 6 5.99*,†,§ 58.52 6 7.91*,†,§ 52.33 6 5.45*,† 58.27 6 6.27*,†
119.50 6 3.00 86.68 6 3.68i 87.28 6 3.88i 82.50 6 11.16i 85.00 6 12.14i
115.80 6 2.80 62.57 6 4.61*,† 58.85 6 4.15*,† 54.33 6 5.98*,† 57.40 6 6.97*,†
115.90 6 7.90 91.18 6 7.01 89.45 6 5.79 86.07 6 8.44i 92.27 6 3.28i
116.70 6 3.50 92.37 6 1.79 95.93 6 6.26 98.40 6 7.86 100.72 6 3.15
68.60 6 2.70 49.04 6 5.05*,†,z 46.58 6 4.91*,†,z 44.48 6 4.58*,† 44.58 6 4.57*,†
69.20 6 1.30 44.08 6 3.37*,† 41.50 6 1.81*,†,§ 40.02 6 0.86*,†,§ 39.90 6 2.60*,†
70.50 6 1.60 54.52 6 2.63*,z 53.90 6 2.47*,z 52.67 6 2.79*,z 55.07 6 3.93*,z
68.00 6 2.80 43.37 6 1.78* 41.83 6 1.25* 40.25 6 2.33* 39.17 6 3.65*
70.10 6 1.90 60.45 6 1.23 58.15 6 1.92i 57.47 6 1.87i 60.23 6 1.23i
70.40 6 2.20 61.23 6 0.62 61.63 6 2.24 62.32 6 1.94 63.63 6 1.51
0.69 6 0.02 1.10 6 0.11*,† 1.19 6 0.09*,† 1.27 6 0.10*,† 1.25 6 0.10*,†,z
0.71 6 0.04 1.21 6 0.05*,†,§ 1.32 6 0.05*,†,§ 1.44 6 0.06*,†,§ 1.34 6 0.10*,†
0.70 6 0.01 1.10 6 0.07*,z 1.12 6 0.07*,z 1.17 6 0.12z,i 1.11 6 0.09*,z
0.70 6 0.03 1.28 6 0.07* 1.38 6 0.08* 1.44 6 0.07* 1.39 6 0.13*
0.71 6 0.03 0.98 6 0.04 1.02 6 0.03i 1.07 6 0.06i 1.01 6 0.06i
0.70 6 0.02 0.95 6 0.03 0.95 6 0.04 0.95 6 0.05 0.89 6 0.03
Group
CO, mL/min BL PR1h PR2h PR3h PR4h EF, % BL PR1h PR2h PR3h PR4h MPI BL PR1h PR2h PR3h PR4h
Abbreviations: BL, baseline; CO, cardiac output; EF, ejection fraction; MPI, myocardial performance index; PR1h, 1 hour after postresuscitation; PR2h, 2 hours after postresuscitation; PR3h, 3 hours after postresuscitation; PR4h, 4 hours after postresuscitation. Values are presented as the mean 6 standard deviation. *P , 0.05 vs epinephrine with b-blocker group and epinephrine with b- plus a1-blocker group. † P , 0.05 vs epinephrine with a1-blocker group. ‡ P , 0.05 vs epinephrine with a2-blocker group. § P , 0.05 vs placebo group. i P , 0.05 vs epinephrine with b- plus a1-blocker group.
Table IV. Survival time and NDS after resuscitation Group
Placebo
Epinephrine
Epinephrine with a1-blocker
Epinephrine with a2-blocker
Epinephrine with b-blocker
Epinephrine with b- plus a1-blocker
Survival time, h NDS PR24h PR48h PR72h
34.4 6 34.6* 300 6 200* 360 6 192i 380 6 168i
22.8 6 26.4* 408 6 150*,† 461 6 96* 473 6 67*
55.2 6 22.5 158 6 172 208 6 238 258 6 265i
24.8 6 13.5*,† 410 6 101*,† 480 6 49*,† 500 6 0*,†
67.8 6 10.2 58 6 58 108 6 196 125 6 209
72.0 6 0 33 6 26 17 6 26 060
Abbreviations: NDS, neurologic deficit score; PR24h, 24 hours after postresuscitation; PR48h, 48 hours after postresuscitation; PR72h, 72 hours after postresuscitation. Values are presented as the mean 6 standard deviation. NDS: normal 5 0; dead or brain dead 5 500. *P , 0.05 vs epinephrine with b-blocker group and epinephrine with b- plus a1-blocker group. † P , 0.05 vs epinephrine with a1-blocker group. i P , 0.05 vs epinephrine with b- plus a1-blockers group.
and the severity of PR myocardial tissue injury remains to be validated in an experimental CPR model with a different duration of ischemia and dose of epinephrine. We have previously demonstrated that the administration of b- or b- plus a1-blocker with epinephrine was associated with the reduction of the severity of PR myocardial dysfunction in animal models of CPR.3,36,37 In this study, we confirmed that epinephrine combined with b- or b- plus a1-adrenergic blocker significantly improved the severity of PR myocardial tissue injury, myocardial dysfunction, and the duration of survival. Studies have demonstrated
during the early phase of PR, the level of endogenous catecholamine and abnormity status of a1- and b-adrenergic receptor in myocardium are related to PR myocardial dysfunction.38-41 The present study demonstrated that blocking a1-adrenergic receptors reduced the severity of PR myocardial dysfunction to the same extent as b-blocker. The propranolol and prazosin have the half-life of 2–4 and 3–4 hours, respectively. The protective effect of a1-, b-, and b- plus a1-blocker may involve multiple mechanisms including improving the impaired a1- and b-receptor signaling and attenuate the release and effect of endogenous
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Fig 3. Pearson correlation analysis between myocardial tissue injury biomarkers and MPI. Tn I, troponin I; NT-proBNP, N-terminal probrain natriuretic peptide; MPI, myocardial performance index; r, Pearson correlation coefficient.
catecholamine after resuscitation. Therefore, longer half-lives of a1- and b-adrenergic blocker given during CPR may be beneficial for ROSC and PR myocardial dysfunction. Experimental studies have demonstrated that the cardioprotective mechanism of adrenergic blocker (carvedilol) is to prevent apoptosis of cardiomyocytes induced by regional and global myocardial ischemiareperfusion injury.42-44 To this extent, these results also support that myocardial stunning is not the only mechanism of PR myocardial dysfunction and apoptosis may also be involved. In addition, Ristagno et al13 demonstrated that the adverse effect of epinephrine on cerebral microvascular blood flow is mediated by its a1-agonist action, and when combined with prazosin and propranolol pretreatment could improve the severity of cerebral ischemia induced by epinephrine during CPR in a porcine model. Clinical reports have also highlighted that multiple doses of epinephrine decreased the chance of survival and good neurologic outcomes in patients.9 Our results demonstrated that combined with b- and a1-blocker pretreatment, the most significant improvement is the severity of PR neurologic dysfunction and the duration
of survival was observed. We believe its mechanism is related to the protective effects of b- and a1-blockers on cardiac and neurologic adverse effects of epinephrine during CPR and PR. The research evidence gives us 2 suggestions. First, serial measurements of myocardial injury biomarkers are very important to predict the severity of PR myocardial dysfunction and prognosis. The mechanism of PR myocardial tissue injury and specific diagnostic value of myocardial injury markers needs to be studied further. Second, epinephrine combined with b- or bplus a1-adrenergic blocker may provide a better therapeutic strategy for resuscitation and PR, which could reduce the PR cardiac and neurologic dysfunction and improve prognosis. However, the reasonable selection and use of adrenergic blockers still requires further research. Limitation of this research. There were a few limitations in our study. First, the experiments were performed in animals without any underlying disease. Second, based on previous animal research and pharmacokinetics of prazosin, yohimbine, and propranolol, the drugs were administered as a pretreatment 15 minutes before VF. Third, 4 hours of observation after ROSC was only a representation of the early stage of PR myocardial dysfunction. Finally, this experiment did not serially measure the myocardial function (CO, EF, and myocardial tissue injury biomarkers) from 4 to 72 hours after ROSC. On the basis of the related references and classic definition of myocardial stunning, we assume the myocardial dysfunction of animals that were still alive after 72 hours observation was because of PR myocardial stunning and less myocardial tissue injury. CONCLUSIONS
The present study demonstrated that 16 minutes of global myocardial ischemia/reperfusion injury produced significant myocardial tissue injury and myocardial mechanical dysfunction in a rat model of CPR. The myocardial stunning may not be the only mechanism of PR myocardial dysfunction. Administration of epinephrine increased the severity of PR myocardial tissue injury and dysfunction. The a1-, b-, and b- plus a1-blocker pretreatment, especially b- and b- plus a1-blocker significantly reduced the severity of PR myocardial tissue injury and myocardial dysfunction, with better neurologic function and prolonged duration of survival. The myocardial tissue injury at the early stage of PR is closely related to the severity of PR myocardial dysfunction and prognosis. The mechanism of PR myocardial tissue injury and specific diagnostic value of myocardial injury markers needs to be studied further with serial measurements.
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ACKNOWLEDGMENTS
Conflicts of Interest: All authors have read the journal’s policy on disclosure of potential conflicts of interest and have none to declare. The authors have no financial or personal relationships with organizations stated in this article. The study was funded by the Weil Institute of Critical Care Medicine. Lisa Luna contributed to the editing of this manuscript. All authors have reviewed and approved the manuscript.
REFERENCES
1. Lloyd-Jones D, Adams R, Carnethon M, et al., American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Heart disease and stroke statistics—2009 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation 2009;119:e21–181. 2. Peberdy MA, Callaway CW, Neumar RW, et al. Part 9: postcardiac arrest care: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2010;122:S768–86. 3. Tang W, Weil MH, Sun S, Noc M, Yang L, Gazmuri RJ. Epinephrine increases the severity of postresuscitation myocardial dysfunction. Circulation 1995;92:3089–93. 4. Palmer BS, Hadziahmetovic M, Veci T, Angelos MG. Global ischemic duration and reperfusion function in the isolated perfused rat heart. Resuscitation 2004;62:97–106. 5. Yamaguchi H, Weil M, Tang W, Kamohara T, Jin X, Bisera J. Myocardial dysfunction after electrical defibrillation. Resuscitation 2002;54:289–96. 6. Kern KB, Hilwig RW, Rhee KH, Berg RA. Myocardial dysfunction after resuscitation from cardiac arrest: an example of global myocardial stunning. J Am Coll Cardiol 1996;28: 232–40. 7. Yakaitis RW, Otto CW, Blitt CD. Relative importance of alpha and beta adrenergic receptors during resuscitation. Crit Care Med 1979;7:293–6. 8. Holmes HR, Babbs CF, Voorhees WD, Tacker WA Jr, de Garavilla B. Influence of adrenergic drugs upon vital organ perfusion during CPR. Crit Care Med 1980;8:137–40. 9. Hagihara A, Hasegawa M, Abe T, Nagata T, Wakata Y, Miyazaki S. Prehospital epinephrine use and survival among patients with out-of-hospital cardiac arrest. JAMA 2012;307: 1161–8. 10. Ditchey RV, Rubio-Perez A, Slinker BK. Beta-adrenergic blockade reduces myocardial injury during experimental cardiopulmonary resuscitation. J Am Coll Cardiol 1994;24:804–12. 11. Pellis T, Weil MH, Tang W. Evidence favoring the use of an alpha2-selective vasopressor agent for cardiopulmonary resuscitation. Circulation 2003;108:2716–21. 12. Sun S, Tang W, Song F, et al. The effects of epinephrine on outcomes of normothermic and therapeutic hypothermic cardiopulmonary resuscitation. Crit Care Med 2010;38:2175–80. 13. Ristagno G, Tang W, Huang L, et al. Epinephrine reduces cerebral perfusion during cardiopulmonary resuscitation. Crit Care Med 2009;37:1408–15. 14. Sun S, Weil MH, Tang W, Kamohara T, Klouche K. alphaMethylnorepinephrine, a selective alpha2-adrenergic agonist for cardiac resuscitation. J Am Coll Cardiol 2001;37:951–6.
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15. Xu T, Tang W, Ristagno G, Sun S, Weil MH. Myocardial performance index following electrically induced or ischemically induced cardiac arrest. Resuscitation 2008;76:103–7. 16. Hendrickx HH, Rao GR, Safar P, Gisvold SE. Asphyxia, cardiac arrest and resuscitation in rats. I. Short term recovery. Resuscitation 1984;12:97–116. 17. Hendrickx HH, Safar P, Miller A. Asphyxia, cardiac arrest and resuscitation in rats. II. Long term behavioral changes. Resuscitation 1984;12:117–28. 18. McDonough JL, Arrell DK, Van Eyk JE. Troponin I degradation and covalent complex formation accompanies myocardial ischemia/reperfusion injury. Circ Res 1999;84:9–20. 19. Hu CL, Li H, Xia JM, et al. Ulinastatin improved cardiac dysfunction after cardiac arrest in New Zealand rabbits. Am J Emerg Med 2013;31:768–74. 20. Mair J. Tissue release of cardiac markers: from physiology to clinical applications. Clin Chem Lab Med 1999;37:1077–84. 21. White HD. Pathobiology of troponin elevations. J Am Coll Cardiol 2011;57:2406–8. 22. Baggish AL, Van Kimmenade RR, Januzzi JL Jr. The differential diagnosis of an elevated amino-terminal pro-B-type natriuretic peptide level. Am J Cardiol 2008;101:43–8. 23. Goetze JP, Christoffersen C, Perko M, et al. Increased cardiac BNP expression associated with myocardial ischemia. FASEB J 2003;17:1105–7. 24. Kern KB, Hilwig RW, Rhee KH, Berg RA. Myocardial dysfunction after resuscitation from cardiac arrest: an example of global myocardial stunning. J Am Coll Cardiol 1996;28:232–40. 25. Kern KB. Postresuscitation myocardial dysfunction. Cardiol Clin 2002;20:89–101. 26. Chalkias A, Xanthos T. Pathophysiology and pathogenesis of post-resuscitation myocardial stunning. Heart Fail Rev 2012;17: 117–28. 27. Laurent I, Monchi M, Chiche JD, et al. Reversible myocardial dysfunction in survivors of out-of-hospital cardiac arrest. J Am Coll Cardiol 2002;40:2110–6. 28. Foster DB, Van Eyk JE. In search of the proteins that cause myocardial stunning. Circ Res 1999;85:470–2. 29. Van Eyk JE, Murphy AM. The role of troponin abnormalities as a cause for stunned myocardium. Coron Artery Dis 2001;12:343–7. 30. Jaffe AS, Babuin L, Apple FS. Biomarkers in acute cardiac disease. J Am Coll Cardiol 2006;48:1–11. 31. Brito D, Matias JS, Sargento L, Cabral MJ, Madeira HC. Plasma N-terminal pro-brain natriuretic peptide: a marker of left ventricular hypertrophy in hypertrophic cardiomyopathy. Rev Port Cardiol 2004;23:1557–82. 32. Richards AM, Nicholls MG, Espiner EA, et al. B-type natriuretic peptides and ejection fraction for prognosis after myocardial infarction. Circulation 2003;107:2786–92. 33. Eggers KM, Lagerqvist B, Venge P, Wallentin L, Lindahl B. Prognostic value of biomarkers during and after non-STsegment elevation acute coronary syndrome. J Am Coll Cardiol 2009;54: 357–64. 34. Song F, Shan Y, Cappello F, et al. Apoptosis is not involved in the mechanism of myocardial dysfunction after resuscitation in a rat model of cardiac arrest and cardiopulmonary resuscitation. Crit Care Med 2010;38:1329–34. 35. Gu W, Li CS, Yin WP, Guo ZJ, Hou XM, Zhang D. Apoptosis is involved in the mechanism of postresuscitation myocardial dysfunction in a porcine model of cardiac arrest. Am J Emerg Med 2012;30:2039–45. 36. Huang L, Weil MH, Sun S, Tang W, Fang X. Carvedilol mitigates adverse effects of epinephrine during cardiopulmonary resuscitation. J Cardiovasc Pharmacol Ther 2005;10:113–20.
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37. Huang L, Weil MH, Cammarata G, Sun S, Tang W. Nonselective beta-blocking agent improves the outcome of cardiopulmonary resuscitation in a rat model. Crit Care Med 2004;32:S378–80. 38. Niemann JT, Garnerb D. Post-resuscitation plasma catecholamines after prolonged arrest in a swine model. Resuscitation 2005;65:97–101. 39. Prengel AW, Lindner KH, Anh€aupl T, Vogt J, Lurie KG. Regulation of right atrial beta-adrenoceptors after cardiopulmonary resuscitation in pigs. Resuscitation 1996;31:271–8. 40. Ji XF, Wang S, Yang L, Li CS. Impaired b-adrenergic receptor signalling in post-resuscitation myocardial dysfunction. Resuscitation 2012;83:640–4. 41. Wu J, Li L, Zhang YL, Yan G. Changes in a1-adrenoreceptors in heart and kidney pre- and post- cardiopulmonary resuscita-
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tion in rats. Zhongguo Wei Zhong Bing Ji Jiu Yi Xue 1998;10: 386–9. 42. Yue TL, Ma XL, Wang X, et al. Possible involvement of stressactivated protein kinase signaling pathway and Fas receptor expression in prevention of ischemia/reperfusion-induced cardiomyocyte apoptosis by carvedilol. Circ Res 1998;82:166–74. 43. Schwarz ER, Kersting PH, Reffelmann T, et al. Cardioprotection by carvedilol: antiapoptosis is independent of beta-adrenoceptor blockage in the rat heart. J Cardiovasc Pharmacol Ther 2003;8: 207–15. 44. Yeh CH, Chen TP, Wang YC, Lin YM, Fang SW. Carvedilol treatment after myocardial infarct decreases cardiomyocytic apoptosis in the peri-infarct zone during cardioplegia-induced cardiac arrest. Shock 2013;39:343–52.
We investigated the relationship between the severity of postresuscitation (PR) myocardial tissue injury and myocardial dysfunction after the administration of epinephrine as well as the protective effects of a- and b-adrenergic blocking agents. Forty male Sprague-Dawley rats were randomized into 6 groups: (1) placebo; (2) epinephrine; (3) epinephrine pretreated with a1-blocker (prazosin); (4) epinephrine pretreated with a2-blocker (yohimbine); (5) epinephrine pretreated with b-blocker (propranolol); and (6) epinephrine pretreated with b- plus a1-blocker (propranolol and prazosin). Cardiopulmonary resuscitation was initiated after 8 minutes of untreated ventricular fibrillation and continued for an additional 8 minutes. The myocardial function and the serum concentrations of troponin I (Tn I) and N-terminal probrain natriuretic peptide (NT-proBNP) were measured at baseline and after resuscitation. After resuscitation, both Tn I and NT-proBNP were significantly increased in all groups, especially in the epinephrine and epinephrine pretreated with a2-blocker groups. Significantly better PR myocardial function and neurologic deficit score were observed in epinephrine pretreated with the a1- or b-blocker with decreased releases of Tn I and NT-proBNP. However, the most significant improvements were observed in the animals pretreated with b- plus a1-blocker. The present study demonstrated that myocardial stunning may not be the only mechanism of PR myocardial dysfunction. Administration of epinephrine increased the severity of PR myocardial tissue injury and dysfunction. The b- and b- plus a1-blocker pretreatment significantly reduced the severity of PR myocardial tissue injury and myocardial dysfunction with better neurologic function and prolonged duration of survival. (Translational Research 2015;165:589–598) Abbreviations: CO ¼ cardiac output; CPP ¼ coronary perfusion pressure; CPR ¼ cardiopulmonary resuscitation; EF ¼ ejection fraction; ETCO2 ¼ end-tidal CO2; MPI ¼ myocardial performance index; NDS ¼ neurologic deficit score; PC ¼ precordial compression; PR ¼ postresuscitation; ROSC ¼ return of spontaneous circulation; VF ¼ ventricular fibrillation
From the Weil Institute of Critical Care Medicine, Rancho Mirage, California; The Second Hospital of Anhui Medical University, Hefei, China; The Keck School of Medicine, University of Southern California, Los Angeles, California; Department of Emergency Medicine, UC San Diego School of Medicine, San Diego, California. Submitted for publication August 12, 2014; revision submitted October 15, 2014; accepted for publication October 17, 2014.
Reprint requests: Wanchun Tang, Weil Institute of Critical Care Medicine, 35100 Bob Hope Drive, Rancho Mirage, CA 92270; e-mail: [email protected]. 1931-5244/$ - see front matter Ó 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.trsl.2014.10.012
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AT A GLANCE COMMENTARY Yang M, et al. Background
Cardiac arrest remains a significant health issue with poor outcomes. Myocardial dysfunction is one of the most causes of death after return of spontaneous circulation. We investigated the relationship between the severity of PR myocardial dysfunction and myocardial injury biomarkers after epinephrine and epinephrine with adrenergic blockers in a rat model of cardiopulmonary resuscitation. Translational Significance
The troponin I and N-terminal probrain natriuretic peptide are significantly correlated with the severity of PR myocardial dysfunction and prognosis. Administration of epinephrine increased the severity of myocardial tissue injury and dysfunction but combined with b- or b- plus a1adrenergic blocker may provide a better therapeutic strategy for resuscitation and PR.
INTRODUCTION
Sudden cardiac death remains a significant health issue with poor long-term outcomes. In the United States, approximately 300,000 patients suffer out-ofhospital sudden cardiac arrest annually and the average survival-to-hospital discharge is 7.9%.1 The most common cause of death after resuscitation is because of myocardial dysfunction and brain injury.2 The severity of postresuscitation (PR) myocardial dysfunction with the impairments of both systolic and diastolic functions is a major cause of early death after successful resuscitation. Animal and clinical studies indicated that the severity of PR myocardial dysfunction is closely related to the duration of ischemia, number of electrical defibrillations, and the dose of epinephrine.3-5 Previous studies further indicated that the mechanism of PR myocardial dysfunction is myocardial stunning with a reversible mechanical myocardial dysfunction.6 However, the underlying mechanisms of PR myocardial dysfunction especially whether there is predominant myocardial tissue injury after global myocardial ischemia of cardiac arrest remains controversial. Epinephrine has been used as a first-line vasopressor agent during cardiopulmonary resuscitation (CPR) for more than 50 years. Animal and clinical studies have demonstrated that epinephrine improves the rate of re-
turn of spontaneous circulation (ROSC). Several studies have demonstrated that the efficacy of epinephrine in aiding ROSC is because of a-adrenergic receptor stimulation.7,8 However, epinephrine significantly increases the severity of PR myocardial dysfunction and reduces the duration of survival.3,9 The detrimental effects of epinephrine during the PR phase are closely related to its b- and a1-actions.10,11 However, whether epinephrine causes myocardial tissue injury remains to be investigated. In the present study, we investigated the relationship between the severity of PR myocardial dysfunction and myocardial injury biomarkers after epinephrine and epinephrine with adrenergic blockers. We hypothesized that epinephrine increases the severity of PR myocardial dysfunction and myocardial tissue injury. When epinephrine is administrated with a1-, b-, or b- plus a1-blocker, the severity of PR myocardial dysfunction and myocardial injury tissue biomarkers are reduced with an improved duration of survival. MATERIALS AND METHODS
This study was approved by the Animal Care and Use Committee of the Weil Institute of Critical Care Medicine. All animals received humane care in compliance with the Principles of Laboratory Animal Care formulated by the National Society for Medical Research and the National Institute of Health publication on the Use of Laboratory Animals prepared by the Institute of Laboratory Animal Resources. Animal preparation. Healthy male Sprague-Dawley rats, aged 6–8 months, weighing between 450 and 550 g, were supplied by a single source breeder (Harlan Sprague-Dawley Inc, Livermore, California). All animals were fasted overnight except for free access to water. The animals were anesthetized by intraperitoneal injection of pentobarbital (45 mg/kg) and additional doses (10 mg/kg) were administrated at intervals of 1 hour, except for 30 minutes before the induction of cardiac arrest. The trachea was orally intubated with a 14-G cannula mounted on a blunt needle with a 145 angled tip. Endtidal CO2 (ETCO2) was continuously monitored with a side-stream infrared CO2 analyzer (End-Tid IL 200; Instrument Laboratory, Lexington, Massachusetts). A conventional lead II electrocardiogram was continuously monitored. The animals were breathing room air spontaneously during preparation. A polyethylene (PE) catheter (PE-50; BectonDickinson, Franklin Lakes, New Jersey) was advanced into the descending aorta from the surgically exposed left femoral artery for the measurement of arterial
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pressure and collection of blood samples for blood gas and biomarkers. Through the left external jugular vein, another PE-50 catheter was advanced into the right atrium for the measurement of right atrial pressure and drug injection. Aortic and right atrial pressures were measured with reference to the midchest with high-sensitivity transducers (model 42584-01; Abbott Critical Care Systems, North Chicago, Illinois). A thermocouple microprobe (9030-12-D-34; Columbus Instruments, Columbus, Ohio) was inserted into the inferior cava vena from the left femoral vein for the measurement of blood temperature. A 3-F PE catheter (model C-PMS-301J; Cook Critical Care, Bloomington, Indiana) was advanced through the right external jugular vein into the right atrium. A precurved guide wire was then advanced through the catheter into the right ventricle for inducing ventricular fibrillation (VF), and the position of the catheter was confirmed by an electrocardiogram. All catheters were flushed intermittently with saline containing 2.5 IU/mL of crystalline bovine heparin. During the experiment, the blood temperature of all rats was maintained between 36.8 C and 37.2 C with a heating lamp. Experimental procedures. Twenty minutes before inducing VF, the animals were randomized into 6 groups with 6 rats in each group by the sealed envelope method: (1) placebo group: saline in the same volume of adrenergic blocking agents and epinephrine were administered as bolus injections into the right atrium at 15 minutes before inducing VF and 5 minutes after the start of precordial compression (PC) separately; (2) epinephrine group: saline in the same volume of adrenergic blocking agents and epinephrine (20 mg/ kg) were administered as bolus injections into the right atrium at 15 minutes before inducing VF and 5 minutes after the start of PC separately; (3) epinephrine pretreated with a1-blocker group: prazosin (0.5 mg/kg) and epinephrine (20 mg/kg) were administered as bolus injections into the right atrium at 15 minutes before inducing VF and 5 minutes after the start of PC separately; (4) epinephrine pretreated with a2-blocker group: yohimbine (100 mg/kg) and epinephrine (20 mg/kg) were administered as bolus injections into the right atrium at the same time points; (5) epinephrine pretreated with b-blocker group: propranolol (1 mg/kg) and epinephrine (20 mg/kg) were administered as bolus injections into the right atrium at the same time points; (6) epinephrine pretreated with b- plus a1-blocker group: propranolol (1 mg/kg), prazosin (0.5 mg/kg), and epinephrine (20 mg/kg) were administered as bolus injections into the right atrium at the same time points.12-14 The experimental procedures are shown in Fig 1. Thirty-minutes before inducing VF, baseline measure-
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Fig 1. Experimental outline and procedure. BL, baseline; VF, ventricular fibrillation; PC, precordial compression; DF, defibrillation; PR, postresuscitation; h 5 hour; HR, heart rate; AP, arterial pressure; RA, right atrial pressure; ETCO2, end-tidal CO2; Blood Temp, blood temperature; Echo, echocardiology; BG, blood gas; NDS, neurologic deficit score.
ments and arterial blood gases were obtained. Fifteen minutes before inducing VF, mechanical ventilation was established at a tidal volume of 0.60 mL/100 g of body weight and a frequency of 100 breaths/min. The inspired O2 fraction was maintained at 0.21. VF was then induced through a guide wire advanced into the right ventricle. A progressive increase at 60-Hz current from 2.7 mA to a maximum of 5 mA was then delivered to the right ventricular endocardium. The current was continued for 3 minutes to prevent spontaneous defibrillation. Mechanical ventilation was discontinued after the onset of VF. PC together with mechanical ventilation (tidal volume 0.60 mL/100 g body weight, 100 breaths/min, inspired O2 fraction 1.0) was initiated after 8 minutes of untreated VF with a pneumatically driven mechanical chest compressor. PC was maintained at a rate of 200 breaths/min and synchronized to provide a compression-to-ventilation ratio of 2:1 with equal compression-relaxation for a duration of 8 minutes. The depth of compressions was initially adjusted to decrease the anteroposterior diameter of the chest by 25% and maintain coronary perfusion pressure at 22 6 2 mm Hg and ETCO2 at 11 6 2 mm Hg without the use of epinephrine. Fifteen minutes before the induction of VF, adrenergic blockers or placebo were injected into the right atrium. At 5 minutes after the start of PC, epinephrine or placebo was injected into the right atrium. Resuscitation was attempted with up to 3 two-joule counter shocks. ROSC is defined as the return of spontaneous circulation with a mean aortic pressure .50 mm Hg for 5 minutes. If ROSC was not achieved, a 30-second interval of PC was performed before attempting a subsequent sequence of up to 3 shocks.
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The procedure was repeated for a maximum of 3 cycles. If ROSC was not achieved, the resuscitation maneuvers were terminated. After ROSC, mechanical ventilation was continued with 100% inspired oxygen for 1 hour, 50% for the second hour, and 21% thereafter. During this time, the animals uniformly recovered from anesthesia. After the experiment, all catheters including the endotracheal tube were removed. Butorphanol (0.4 mg/kg) was injected intramuscularly if discomfort was identified. The animals were then returned to their cages equipped with a heated pet mat (Allied Precision Industries, Inc, Elburn, Illinois) to maintain the temperature in the cage at 24 C–26 C. All animals were euthanized by intraperitoneal injection of pentobarbital (150 mg/ kg) after a 72-hour observation period. A necropsy was routinely performed to identify any traumatic injuries of the thoracic and abdominal organs. Measurements. Heart rate, aortic and right atrial pressures, electrocardiogram, blood temperature, and ETCO2 values were continuously recorded on a personal computer–based data-acquisition system supported by Common Ocean Data Access System hardware and software (DataQ, Akron, Ohio). At baseline, 1, 2, 3, and 4 hours after ROSC, ejection fraction (EF), cardiac output (CO), and myocardial performance index (MPI) were measured with an echocardiography (Model HD11XE; Philips Medical Systems, Eindhoven, Netherlands) with a 12.5 Hz transducer. CO and EF were used to estimate myocardial contractility. MPI, which combines time intervals related to systolic and diastolic functions and reflecting the global myocardial function, was also calculated using the formula (a 2 b)/b, where a 5 mitral closure-to-opening interval (time interval from cessation to the onset of mitral inflow) and b 5 ET (aortic flow ejection time, obtained at the left ventricular outflow tract), was used to estimate left ventricular systolic and diastolic function.15 A 0.3 mL of artery blood sample was withdrawn for the measurement of arterial oxygen partial pressure, CO2 partial pressure, pH, and lactate at baseline and every hour after ROSC using a conventional blood gas analyzer (Phox, Stat Profile; Nova Biomedical Corporation, Waltham, Massachusetts). A 1.2 mL of artery blood sample was withdrawn for serum concentrations of troponin I (Tn I) and N-terminal probrain natriuretic peptide (NT-proBNP) at baseline, 1, and 4 hours after ROSC. The equivalent arterial blood from a donor rat of the same colony was transfused into the femoral artery after blood drawing. Serum concentrations of Tn I and NT-proBNP were measured with the commercial enzyme-linked immunosorbent assay kits according to the manufacturer’s instructions (Cat. No. 2010-2-US; Life Diagnostics,
Inc and Cat. No. MBS164802; MyBioSource, Inc, respectively). Levels of consciousness, brain stem function, and overall performance were examined and scored according to a neurologic deficit score (normal 5 0 and dead or brain dead 5 500) at baseline, 24, 48, and 72 hours of PR if they survived. The neurologic deficit score was confirmed by 2 investigators blinded to the treatment.16,17 The duration of survival was also recorded. Statistical analysis. The experimental data were analyzed by Microsoft Excel 2007 (Redmond, Washington) and Statistical Product and Service Solutions 13.0 (Chicago, Illinois). Measurements were reported as the mean 6 standard deviation. Comparisons between time-based measurements within each group were performed with repeated measurement of variance and Scheffe ’s multiple comparison techniques were used. The relationship between myocardial injury biomarkers, indicators of echocardiography, and the duration of survival time were analyzed with the Pearson correlation analysis. A value of P , 0.05 was regarded as significant. RESULTS
Forty rats were used in this study. Thirty-six experiments were completed and included. Four rats were excluded because of experimental instruments or technical failure during animal preparation and resuscitation. Body weight and baseline measurements including hemodynamic data, blood temperature, blood gas, myocardial function, and serum levels of Tn I and NTproBNP did not differ significantly among the 6 groups (Table I). All animals except for 1 in the placebo group were resuscitated. Coronary perfusion pressure was significantly greater in the 5 groups that received epinephrine at PC 6 minutes when compared with the placebo group (P , 0.05) (Table II). The number of defibrillations that were required to restore ROSC were significantly higher in the epinephrine group than epinephrine pretreated with b- and b- plus a1-blocker groups (P , 0.05) (Table II). After resuscitation, the serum concentrations of Tn I and NT-proBNP were significantly increased in all groups (Fig 2). The serum concentration of Tn I was significantly greater in the epinephrine, epinephrine with a2-blocker, and placebo groups than the epinephrine pretreated with b- or b- plus a1-blocker groups (P , 0.05) (Fig 2). The animals pretreated with a2blocker had significantly greater levels of Tn I than the animals pretreated with a1-blocker at PR 1 and 4 hours (P , 0.05) (Fig 2). The lowest levels of Tn I
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Table I. Baseline characteristics Group
Placebo
Epinephrine
Epinephrine with a1-blocker
Epinephrine with a2-blocker
Epinephrine with b-blocker
Epinephrine with b- plus a1-blocker
Body weight, g Heart rate, bpm MAP, mm Hg ETCO2, mm Hg RA, mm Hg Temperature, C CO, mL/min EF, % MPI Lactate, mmol/L Tn I, ng/L NT-proBNP, ng/L
506.0 6 21.2 362.5 6 14.6 133.6 6 6.0 40.4 6 2.4 1.2 6 0.2 36.8 6 0.3 117.1 6 4.9 68.6 6 2.7 0.69 6 0.02 0.7 6 0.2 0.02 6 0.01 84.7 6 53.5
516 6 22.3 351.8 6 20.3 134.6 6 6.8 40.7 6 3.2 1.3 6 0.1 36.6 6 0.2 117.3 6 2.4 69.2 6 1.3 0.71 6 0.04 0.7 6 0.1 0.03 6 0.02 90.6 6 53.8
500.8 6 15.2 359.7 6 11.1 141.1 6 11.9 41.8 6 4.5 1.2 6 0.1 36.6 6 0.2 119.5 6 3.0 70.5 6 1.6 0.70 6 0.01 0.8 6 0.1 0.03 6 0.01 98.3 6 18.1
521.3 6 26.2 363.7 6 21.6 132.3 6 10.1 39 6 2.2 1.1 6 0.1 36.5 6 0.1 115.8 6 2.8 68 6 2.8 0.70 6 0.03 0.7 6 0.1 0.04 6 0.03 82.1 6 38.5
511.8 6 12.7 352.2 6 18.3 130.6 6 3.4 41.4 6 2.3 1.3 6 0.2 36.6 6 0.3 115.9 6 7.9 70.1 6 1.9 0.71 6 0.03 0.8 6 0.2 0.03 6 0.02 86.9 6 24.5
504.3 6 16.1 347.2 6 25.5 135.2 6 9.0 40.9 6 1.7 1.2 6 0.1 36.7 6 0.2 116.7 6 3.5 70.4 6 2.2 0.70 6 0.02 0.8 6 0.1 0.02 6 0.01 97.6 6 21.8
Abbreviations: CO, cardiac output; EF, ejection fraction; ETCO2, end-tidal CO2; MAP, mean aortic pressure; MPI, myocardial performance index; NT-proBNP, N-terminal probrain natriuretic peptide; RA, right atrial pressure; Tn I, troponin I. Values are presented as the mean 6 standard deviation.
Table II. Coronary perfusion pressure and the number of defibrillations Group
Placebo
Epinephrine
Epinephrine with a1-blocker
Epinephrine with a2-blocker
Epinephrine with b-blocker
Epinephrine with b- plus a1-blocker
CPP, mm Hg PC1 PC5 PC6 The number of defibrillations
22.4 6 0.8 22.3 6 1.3 22.3 6 1.0 2.8 6 3.3
23.1 6 1.9 22.5 6 1.5 31.4 6 1.4* 2.2 6 1.0†
22.4 6 0.4 22.6 6 0.6 33.1 6 1.2* 1.2 6 1.0
22.6 6 0.0 22.1 6 1.4 31.9 6 3.2* 2.0 6 3.5
22.1 6 0.9 22.6 6 0.8 31.2 6 3.3* 1.0 6 0.6
22.7 6 0.6 23.1 6 0.8 32.3 6 0.6* 0.8 6 0.4
Abbreviations: CPP, coronary perfusion pressure; PC1, 1 minute after precordial compression; PC5, 5 minutes after precordial compression; PC6, 6 minutes after precordial compression. Values are presented as the mean 6 standard deviation. *P , 0.05 vs placebo group. † P , 0.05 vs epinephrine with b-blocker group and epinephrine with b- plus a1-blocker group.
were observed in the epinephrine pretreated with b- plus a1-blocker group. The serum concentration of NTproBNP was significantly greater in the epinephrine, epinephrine with a2-blocker, and placebo groups than the epinephrine pretreated with a1-, b-, and b- plus a1-blocker groups at PR 1 and 4 hours (P , 0.05) (Fig 2). Again, the lowest levels of NT-proBNP were observed in the epinephrine pretreated with b- plus a1-blocker group. The serum concentration of NTproBNP was significantly greater in the epinephrine group than the placebo group at PR 1 hour (P , 0.05) (Fig 2). PR myocardial function as measured by CO, EF, and MPI was significantly impaired in all groups when compared with the baseline (Table III). The b- plus a1-blocker pretreatment significantly improved the severity of PR myocardial function when compared with the other 5 groups (P , 0.05) (Table III). The epinephrine and epinephrine pretreated with a2-blocker increased the severity of PR myocardial dysfunction when compared with the placebo group (P , 0.05) (Table III).
A significantly improved duration of survival was observed in the animals pretreated with b- or b- plus a1-blocker when compared with the epinephrine and placebo groups (P , 0.05) (Table IV). The a2-blocker significantly reduced the duration of survival compared with epinephrine pretreated with a1-, b-, and b- plus a1-blocker groups (P , 0.05) (Table IV). The animals pretreated of with b- or b- plus a1-blocker demonstrated a significantly reduced severity of PR neurologic dysfunction when compared with the other 4 groups (P , 0.05) (Table IV). The increases in serum concentrations of Tn I and NT-proBNP were significantly correlated with MPI (P , 0.01) (Fig 3). The severity of PR myocardial tissue injury and mechanical dysfunction as measured by Tn I, NT-proBNP, and MPI at 1 hour after ROSC was significantly correlated with the duration of survival (r 5 20.683, P , 0.01; r 5 20.475, P , 0.01; and r 5 20.613, P , 0.01, respectively). There were no gross abnormalities or surgical injuries observed at necropsy.
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Fig 2. Serum concentration of Tn I and NT-proBNP. Tn I, troponin I; NT-proBNP, N-terminal probrain natriuretic peptide; BL, baseline; PR1h, 1 hour after postresuscitation; PR4h, 4 hours after postresuscitation. *P , 0.05 vs epinephrine with b-blocker group and epinephrine with b- plus a1-blocker group; ※P , 0.05 vs epinephrine with b- plus a1-blocker group; ＃P , 0.05 vs epinephrine with a1-blocker group; §P , 0.05 vs placebo group.
DISCUSSION
The present study demonstrated that 8 minutes of global myocardial ischemia and 8 minutes of low flow reperfusion of CPR produced significant myocardial tissue injury and PR myocardial mechanical dysfunction. We further demonstrated that the administration of epinephrine increased the severity of myocardial tissue injury and dysfunction. Pretreatment with b- or b- plus a1-adrenergic blocker significantly decreased the severity of myocardial tissue injury and PR myocardial dysfunction, with improved neurologic function and the duration of survival. The early stage of PR myocardial tissue injury biomarkers (Tn I and NT-proBNP) was significantly correlated with the severity of PR myocardial dysfunction and prognosis. In the present study, we demonstrated that the serum levels of Tn I and NT-proBNP increased significantly from 1 hour after resuscitation in all animals with 16 minutes of global myocardial ischemia–reperfusion injury. McDonough JL et al demonstrated that 15 minutes of mild ischemia was enough to cause the release of Tn I from an isolated rat heart.18 Earlier studies demonstrated that Tn I and NT-proBNP significantly increased from 2 hours after resuscitation in a rabbit model of CPR.19 The mechanism of early release of Tn I in a rat model of CPR is that global myocardial ischemia/ reperfusion injury results in an initial release of cytosol Tn followed by the gradual release of myofibril-bound Tn complexes through increased permeability of the cell membrane and microvasculature.20,21 Evidence indicates that NT-proBNP is related to various myocar-
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dial diseases and myocardial tissue injury, including mild ischemia/reperfusion injury.22,23 These results are consistent with our findings in which Tn I and NT-proBNP were increased significantly after 16 minutes of global ischemia and reinfusion of cardiac arrest and resuscitation. Our results indicated that myocardial stunning may not be the only mechanism of PR myocardial dysfunction. The PR myocardial stunning was considered the most important mechanism of PR myocardial dysfunction, a reversible mechanical myocardial dysfunction without myocardial necrosis.24-26 Several animal experimental studies demonstrated a full recovery of PR myocardial stunning, which was observed at 48– 72 hours after ROSC11,24. Pellis et al11 demonstrated that the values of Tn I significantly increased from PR 1 hour and returned to baseline at PR 72 hours in a porcine model of CPR. However, clinical research indicates that early PR deaths occur during the first 24 hours after ROSC, which is associated with a persistent low cardiac index.27 Therefore, the poor prognosis of CPR is incompatible with characteristics of PR myocardial stunning. Whether there is myocardial cell death after resuscitation that contribute to the severity of myocardial dysfunction is still a controversial issue. Our results indicated that the higher levels of Tn I and NT-proBNP were significantly related to severe PR myocardial dysfunction and poor prognosis. Tn I is highly sensitive to myocardial stunning, apoptosis, and necrosis induced by ischemia-reperfusion injury.21,28-30 Currently, there are no studies to address the relationship between NT-proBNP and ischemic myocardial stunning. However, the level of NTproBNP was closely correlated with diagnosis and prognosis of heart failure and acute myocardial infarction; both have the pathologic characteristics of apoptosis and necrosis.31-33 Our group has previously demonstrated that apoptosis was not involved in the mechanism of PR myocardial dysfunction in a rat model of CPR.34 A recent study, however, indicated that caspase 3–mediated mitochondrial apoptosis is activated in PR myocardial dysfunction at 12 and 24 hours after ROSC in a porcine model of CPR, which may reflect the differences in animal species.35 Our results support that PR myocardial stunning is just one of the mechanisms of PR myocardial dysfunction. The myocardial tissue injury plays an important role in the mechanisms of PR myocardial dysfunction and needs to be further investigated. In the present study, we demonstrated that the administration of epinephrine increases the severity of myocardial tissue injury and PR myocardial dysfunction. However, the accurate relationship between the duration of global myocardial ischemia, epinephrine,
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Table III. CO, EF, and MPI Placebo
Epinephrine
Epinephrine with a1-blocker
Epinephrine with a2-blocker
Epinephrine with b-blocker
Epinephrine with b- plus a1-blocker
117.10 6 4.90 75.38 6 4.51*,†,z 69.06 6 7.20*,†,z 62.42 6 9.84*,† 66.42 6 10.41*,†
117.30 6 2.40 65.28 6 5.99*,†,§ 58.52 6 7.91*,†,§ 52.33 6 5.45*,† 58.27 6 6.27*,†
119.50 6 3.00 86.68 6 3.68i 87.28 6 3.88i 82.50 6 11.16i 85.00 6 12.14i
115.80 6 2.80 62.57 6 4.61*,† 58.85 6 4.15*,† 54.33 6 5.98*,† 57.40 6 6.97*,†
115.90 6 7.90 91.18 6 7.01 89.45 6 5.79 86.07 6 8.44i 92.27 6 3.28i
116.70 6 3.50 92.37 6 1.79 95.93 6 6.26 98.40 6 7.86 100.72 6 3.15
68.60 6 2.70 49.04 6 5.05*,†,z 46.58 6 4.91*,†,z 44.48 6 4.58*,† 44.58 6 4.57*,†
69.20 6 1.30 44.08 6 3.37*,† 41.50 6 1.81*,†,§ 40.02 6 0.86*,†,§ 39.90 6 2.60*,†
70.50 6 1.60 54.52 6 2.63*,z 53.90 6 2.47*,z 52.67 6 2.79*,z 55.07 6 3.93*,z
68.00 6 2.80 43.37 6 1.78* 41.83 6 1.25* 40.25 6 2.33* 39.17 6 3.65*
70.10 6 1.90 60.45 6 1.23 58.15 6 1.92i 57.47 6 1.87i 60.23 6 1.23i
70.40 6 2.20 61.23 6 0.62 61.63 6 2.24 62.32 6 1.94 63.63 6 1.51
0.69 6 0.02 1.10 6 0.11*,† 1.19 6 0.09*,† 1.27 6 0.10*,† 1.25 6 0.10*,†,z
0.71 6 0.04 1.21 6 0.05*,†,§ 1.32 6 0.05*,†,§ 1.44 6 0.06*,†,§ 1.34 6 0.10*,†
0.70 6 0.01 1.10 6 0.07*,z 1.12 6 0.07*,z 1.17 6 0.12z,i 1.11 6 0.09*,z
0.70 6 0.03 1.28 6 0.07* 1.38 6 0.08* 1.44 6 0.07* 1.39 6 0.13*
0.71 6 0.03 0.98 6 0.04 1.02 6 0.03i 1.07 6 0.06i 1.01 6 0.06i
0.70 6 0.02 0.95 6 0.03 0.95 6 0.04 0.95 6 0.05 0.89 6 0.03
Group
CO, mL/min BL PR1h PR2h PR3h PR4h EF, % BL PR1h PR2h PR3h PR4h MPI BL PR1h PR2h PR3h PR4h
Abbreviations: BL, baseline; CO, cardiac output; EF, ejection fraction; MPI, myocardial performance index; PR1h, 1 hour after postresuscitation; PR2h, 2 hours after postresuscitation; PR3h, 3 hours after postresuscitation; PR4h, 4 hours after postresuscitation. Values are presented as the mean 6 standard deviation. *P , 0.05 vs epinephrine with b-blocker group and epinephrine with b- plus a1-blocker group. † P , 0.05 vs epinephrine with a1-blocker group. ‡ P , 0.05 vs epinephrine with a2-blocker group. § P , 0.05 vs placebo group. i P , 0.05 vs epinephrine with b- plus a1-blocker group.
Table IV. Survival time and NDS after resuscitation Group
Placebo
Epinephrine
Epinephrine with a1-blocker
Epinephrine with a2-blocker
Epinephrine with b-blocker
Epinephrine with b- plus a1-blocker
Survival time, h NDS PR24h PR48h PR72h
34.4 6 34.6* 300 6 200* 360 6 192i 380 6 168i
22.8 6 26.4* 408 6 150*,† 461 6 96* 473 6 67*
55.2 6 22.5 158 6 172 208 6 238 258 6 265i
24.8 6 13.5*,† 410 6 101*,† 480 6 49*,† 500 6 0*,†
67.8 6 10.2 58 6 58 108 6 196 125 6 209
72.0 6 0 33 6 26 17 6 26 060
Abbreviations: NDS, neurologic deficit score; PR24h, 24 hours after postresuscitation; PR48h, 48 hours after postresuscitation; PR72h, 72 hours after postresuscitation. Values are presented as the mean 6 standard deviation. NDS: normal 5 0; dead or brain dead 5 500. *P , 0.05 vs epinephrine with b-blocker group and epinephrine with b- plus a1-blocker group. † P , 0.05 vs epinephrine with a1-blocker group. i P , 0.05 vs epinephrine with b- plus a1-blockers group.
and the severity of PR myocardial tissue injury remains to be validated in an experimental CPR model with a different duration of ischemia and dose of epinephrine. We have previously demonstrated that the administration of b- or b- plus a1-blocker with epinephrine was associated with the reduction of the severity of PR myocardial dysfunction in animal models of CPR.3,36,37 In this study, we confirmed that epinephrine combined with b- or b- plus a1-adrenergic blocker significantly improved the severity of PR myocardial tissue injury, myocardial dysfunction, and the duration of survival. Studies have demonstrated
during the early phase of PR, the level of endogenous catecholamine and abnormity status of a1- and b-adrenergic receptor in myocardium are related to PR myocardial dysfunction.38-41 The present study demonstrated that blocking a1-adrenergic receptors reduced the severity of PR myocardial dysfunction to the same extent as b-blocker. The propranolol and prazosin have the half-life of 2–4 and 3–4 hours, respectively. The protective effect of a1-, b-, and b- plus a1-blocker may involve multiple mechanisms including improving the impaired a1- and b-receptor signaling and attenuate the release and effect of endogenous
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Fig 3. Pearson correlation analysis between myocardial tissue injury biomarkers and MPI. Tn I, troponin I; NT-proBNP, N-terminal probrain natriuretic peptide; MPI, myocardial performance index; r, Pearson correlation coefficient.
catecholamine after resuscitation. Therefore, longer half-lives of a1- and b-adrenergic blocker given during CPR may be beneficial for ROSC and PR myocardial dysfunction. Experimental studies have demonstrated that the cardioprotective mechanism of adrenergic blocker (carvedilol) is to prevent apoptosis of cardiomyocytes induced by regional and global myocardial ischemiareperfusion injury.42-44 To this extent, these results also support that myocardial stunning is not the only mechanism of PR myocardial dysfunction and apoptosis may also be involved. In addition, Ristagno et al13 demonstrated that the adverse effect of epinephrine on cerebral microvascular blood flow is mediated by its a1-agonist action, and when combined with prazosin and propranolol pretreatment could improve the severity of cerebral ischemia induced by epinephrine during CPR in a porcine model. Clinical reports have also highlighted that multiple doses of epinephrine decreased the chance of survival and good neurologic outcomes in patients.9 Our results demonstrated that combined with b- and a1-blocker pretreatment, the most significant improvement is the severity of PR neurologic dysfunction and the duration
of survival was observed. We believe its mechanism is related to the protective effects of b- and a1-blockers on cardiac and neurologic adverse effects of epinephrine during CPR and PR. The research evidence gives us 2 suggestions. First, serial measurements of myocardial injury biomarkers are very important to predict the severity of PR myocardial dysfunction and prognosis. The mechanism of PR myocardial tissue injury and specific diagnostic value of myocardial injury markers needs to be studied further. Second, epinephrine combined with b- or bplus a1-adrenergic blocker may provide a better therapeutic strategy for resuscitation and PR, which could reduce the PR cardiac and neurologic dysfunction and improve prognosis. However, the reasonable selection and use of adrenergic blockers still requires further research. Limitation of this research. There were a few limitations in our study. First, the experiments were performed in animals without any underlying disease. Second, based on previous animal research and pharmacokinetics of prazosin, yohimbine, and propranolol, the drugs were administered as a pretreatment 15 minutes before VF. Third, 4 hours of observation after ROSC was only a representation of the early stage of PR myocardial dysfunction. Finally, this experiment did not serially measure the myocardial function (CO, EF, and myocardial tissue injury biomarkers) from 4 to 72 hours after ROSC. On the basis of the related references and classic definition of myocardial stunning, we assume the myocardial dysfunction of animals that were still alive after 72 hours observation was because of PR myocardial stunning and less myocardial tissue injury. CONCLUSIONS
The present study demonstrated that 16 minutes of global myocardial ischemia/reperfusion injury produced significant myocardial tissue injury and myocardial mechanical dysfunction in a rat model of CPR. The myocardial stunning may not be the only mechanism of PR myocardial dysfunction. Administration of epinephrine increased the severity of PR myocardial tissue injury and dysfunction. The a1-, b-, and b- plus a1-blocker pretreatment, especially b- and b- plus a1-blocker significantly reduced the severity of PR myocardial tissue injury and myocardial dysfunction, with better neurologic function and prolonged duration of survival. The myocardial tissue injury at the early stage of PR is closely related to the severity of PR myocardial dysfunction and prognosis. The mechanism of PR myocardial tissue injury and specific diagnostic value of myocardial injury markers needs to be studied further with serial measurements.
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ACKNOWLEDGMENTS
Conflicts of Interest: All authors have read the journal’s policy on disclosure of potential conflicts of interest and have none to declare. The authors have no financial or personal relationships with organizations stated in this article. The study was funded by the Weil Institute of Critical Care Medicine. Lisa Luna contributed to the editing of this manuscript. All authors have reviewed and approved the manuscript.
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