ORIGINAL ARTICLE
Coronary Artery Bypass Grafting During Acute Coronary Syndrome Outcomes and Comparison of Off-Pump to Conventional Coronary Artery Bypass Grafting at a Veteran Affairs Hospital Dominic A. Emerson, MD,*Þ Conor F. Hynes, MD,Þ Michael D. Greenberg, MD,* and Gregory D. Trachiotis, MD*þ
Objective: The management of acute coronary syndrome (ACS) has evolved dramatically over the last 50 years. Currently, management includes a multidisciplinary approach potentially including catheterbased therapy, surgery, or purely medical management. Where surgical therapy is indicated, data regarding long-term outcomes are limited. In particular, little data exist regarding on-pump (conventional coronary artery bypass grafting, cCABG) versus off-pump (OPCABG) outcomes for this group. Methods: A retrospective review of prospectively collected data was undertaken. Patients undergoing isolated CABG from January 2000 to December 2011 with ACS were identified (n = 271); non-ACS patients (n = 854) were established as a control. Data were analyzed with a W2 or a t test, where appropriate. Survival was compared using KaplanMeier analysis and Cox proportional hazards model. Results: Thirty-day mortality between the ACS and the control groups was similar; however, long-term mortality was worse for the ACS group (P = 0.032; median follow-up, 5.5 years). Length of stay and composite morbidity were higher in the ACS group (P G 0.01). Subgroup analysis of ACS patients (OPCABG vs cCABG) demonstrated worse preoperative comorbidities in the OPCABG group, but similar 30-day and long-term mortality. However, the cCABG group had higher rates of reoperation (P = 0.034) and longer length of stay (P = 0.017) and operative time (P G 0.0001). Cox proportional hazards model was applied. Risk factors for the non-ACS cohort included age, diabetes, OPCABG, and ACS (P G 0.05). Among the ACS cohort, only age remained a statistically significant factor (P G 0.0001). Conclusions: ACS appears to negatively impact long-term, but not short-term, mortality. Within the ACS group, OPCABG compares
Accepted for publication January 14, 2015. From the *Veterans Affairs Medical Center; †Georgetown University Hospital; and ‡The George Washington University Hospital, Washington, DC USA. Presented at the Annual Scientific Meeting of the International Society for Minimally Invasive Cardiothoracic Surgery, May 28Y31, 2014, Boston, MA USA. Disclosure: The authors declare no conflicts of interest. Address correspondence and reprint requests to Gregory D. Trachiotis, MD, Division of Cardiothoracic Surgery, Veterans Affairs Medical Center, 50 Irving St., NW, Washington, DC 20422 USA. E-mail: [email protected]. Copyright * 2015 by the International Society for Minimally Invasive Cardiothoracic Surgery ISSN: 1556-9845/15/1003-0157
Innovations & Volume 10, Number 3, May/June 2015
favorably to cCABG in the long-term and also improves short-term morbidity. Key Words: Acute coronary syndrome, Coronary artery bypass grafting, Off-pump coronary artery bypass grafting. (Innovations 2015;10:157Y162)
T
he management of acute coronary syndrome (ACS) has evolved dramatically over the last 50 years. Currently, management includes a multidisciplinary approach involving interventional cardiology, surgery, and internal medicine, with the optimal treatment for an individual potentially including catheter-based therapy, surgery, or purely medical management. The aggressive management of ACS has greatly improved the outcomes of patients presenting to the hospital with evidence of ischemia. A cornerstone of management for this population has been early and routine invasive management, including coronary angiography and revascularization with catheter-based or surgical techniques.1 A subset of individuals presenting with ACS ultimately require surgical revascularization, and it has been shown that coronary artery bypass grafting (CABG) remains a viable option for the management of this population.2Y4 Despite the clear utility of CABG, there has been debate regarding the optimal surgical approach to surgical revascularization in this population, with multiple authors indicating that there may be benefit to performing surgical procedures off pump (OPCABG).5,6 At this point, however, there are only limited data regarding the longterm outcomes within the ACS population as stratified by surgical revascularization technique, and the length of follow-up for these studies are at most around 4 years.6 In this study, we examine the short- and long-term outcomes of patients undergoing surgical revascularization in the setting of ACS and further subdivide these patients into those undergoing conventional CABG (cCABG) with full cardiopulmonary bypass, and those undergoing OPCABG.
MATERIALS AND METHODS This study was approved following a review from the local institutional review board. A pre-existing in-house database based on the national Veterans Affairs database was
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queried to identify patients who underwent isolated CABG from January 2000 to December 2011 (n = 1125). Patients from this cohort who underwent CABG for ACS were then identified as follows: patients who were identified at the time of surgery as being an emergent case for ‘ongoing ischemia,’ or who were noted to have had a myocardial infarction within 7 days before surgery were placed into the ACS cohort (n = 153). For those not fitting this criteria, patients who were noted to have ST changes, to be New York Heart Association class III or IV, or to be Canadian Cardiovascular Society class IV were selected for additional review (n = 603). A focused retrospective chart review was then undertaken to identify patients from this group who had ACS during the same admission, and before surgical intervention. This was defined in accordance with previous guidelines7 and included diagnosis of ACS by attending surgeon, presence of unstable angina, ST-segment elevation myocardial infarction (STEMI), or non-STEMI (NSTEMI). In total, 271 patients with ACS were identified, and the remaining 854 were used as a control cohort (Fig. 1). Following the creation of the ACS and non-ACS cohorts, these 2 groups were further subdivided into those undergoing cCABG and those undergoing OPCABG. Statistical analyses were undertaken to compare demographics, risk factors, and outcomes between groups. The primary end point of mortality (both short- and long-term) was used, and secondary end points of length of stay (LOS), isolated and composite morbidity, and operative time were also examined. Statistical analyses were performed using Student t test for continuous data, a Fisher
Exact test for binomial data, or Mann-Whitney U test for ordinal data; Kaplan-Meier analysis and a log-rank test were used for mortality comparisons. Cox proportional hazards model was used for regression analysis. P = 0.05 was considered statistically significant throughout. Statistical analysis was performed using R (Vienna, Austria). All patients were operated on by 1 of 2 surgeons, with operative technique up to the discretion of the individual surgeon. No strict criteria were used for determining OPCABG versus cCABG. ACS patients were generally jointly managed preoperatively by both the cardiac surgery and internal medicine/cardiology teams. Standard postoperative dual antiplatelet therapy, consisting of aspirin and Plavix, was given to patients for a period of 1 year for ACS patients as described previously.8
RESULTS Fifty-nine percent (160) of the ACS cohort received OPCABG, as did 65% (297) of the control cohort (P = 0.070). Demographics compared between the ACS and control cohorts were generally similar and are presented on Table 1, with the exception of greater frequency of depressed ejection fraction (EF) in the ACS group. Operative variables were significantly different in terms of more frequent preoperative intra-aortic balloon pump (IABP) placement among ACS patients (23% vs 9%, P G 0.0001), but were otherwise similar as well. Conversion (from OPCABG to cCABG intraoperatively) was seen more frequently in the ACS cohort, but this was not statically significant (Table 1).
FIGURE 1. Creation of cohorts.
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CABG in ACS: Off-Pump Outcomes
TABLE 1. ACS versus Non-ACS Demographics ACS (n = 271) Age % Female Diabetes Yes-insulin Yes-not on insulin BSA Smoker COPD Creatinine CVD EF G 55 No. anastamoses OPCABG Preoperative IABP Operative time (min) Conversion (OPCABG only)
65.5 T 10.0 1.8% (5)
Non-ACS (n = 854) 64.5 T 9.4 0.8% (7)
P 0.1256 0.1742 0.5804
29.5% (80) 22.1% (189) 9.2% (25) 17.9% (153) 2.00 T 0.212 2.02 T 0.203 0.0516 33.6% (91) 30.0% (256) 0.2907 45.4% (123) 45.5% (389) 90.9999 1.40 T 1.19 1.30 T 0.98 0.1571 20.1% (55) 20.8% (178) 0.9315 65.3% (175, n = 268) 55.1% (467, n = 847) 0.0033* 2.26 T 0.83 2.22 T 0.85 0.4929 59% (160) 65% (297) 0.0700 23.2% (63) 8.8% (75) G0.0001* 330 T 78 325 T 70 0.2968 3.1% (5 of 160) 1.3% (7 of 557) 0.1044
*Statistically significant values.
FIGURE 2. Survival, ACS vs non-ACS.
Short-term outcomes between groups were significantly different in regards to rate of prolonged ventilation within the ACS group (12% vs 4%, P G 0.0001). However, despite this, 30-day mortality was not different between groups (P = 0.237) (Table 2). Long-term outcomes, as evaluated using KaplanMeier curves and a log-rank test, demonstrated worse survival among the ACS cohort, as expected (Fig. 2; P = 0.032; median follow-up, 5.5 years). The ACS cohort was then subdivided into cCABG and OPCABG cohorts, as described above. Baseline characteristics between the ACS cCABG and OPCABG groups demonstrated the OPCABG group to be worse in regards to renal function (P = 0.006) and American Society of Anesthesia scores (a score for general determination of fitness for surgery and risk) (P G 0.001), and preoperative EF (P = 0.0103), with other factors being similar (Table 3). Short-term outcomes between ACS cCABG and OPCABG revealed a lower rate of reoperation for bleeding (1.3% vs 6.3%, P = 0.034), shorter LOS (8.6 vs 11.3 days, P = 0.012), and shorter operative time (298 vs 377 minutes, P G 0.0001) among the ACS OPCABG cohort (Table 4). It should be noted that operative time in our database is defined as ‘‘door-to-door’’ operative time, and that the actual surgeon time, or ‘‘skin-to-skin’’ TABLE 2. ACS versus Non-ACS Outcomes Operative mortality 30-day mortality Mediastinitis Perioperative MI New renal failure Reop bleeding New CVA Prolonged vent LOS (days)
ACS (n = 271)
Non-ACS (n = 854)
P
0.4% (1) 2.2% (6) 1.1% (3) 1.1% (3) 0.7% (2) 3.3% (9) 0.4% (1) 12.2% (33) 9.72 T 8.79
0.1% (1) 1.2% (10) 0.5% (4) 0.5% (4) 0.5% (4) 1.4% (12) 0.4% (3) 4.1% (35) 8.78 T 11.37
0.4236 0.2373 0.3688 0.3688 0.6351 0.6635 90.9999 G0.0001* 0.2134
CVA indicates cerebral vascular accident. *Statistically significant values.
time, is significantly less but was not recorded. Despite an increased rate of short-term morbidity among the cCABG cohort, rates of 30-day mortality were similar between groups (Table 3). Finally, long-term outcomes were also evaluated between groups with a median follow-up of 5.0 years and did not demonstrate any significant difference in long-term survival between groups (Fig. 3, P = 0.447). Multivariate regression analysis was performed using Cox proportional hazards models. Among the entire population (ACS and non-ACS, OPCABG and cCABG), age, diabetes, OPCABG, creatinine, chronic obstructive pulmonary disease (COPD), and ACS were all significant risk factors for mortality (all P G 0.05). When applied only to the ACS cohort, only age and creatinine remained statistically significant factors (P G 0.05), with surgical technique not being a statistically significant contributor to risk (Table 5). TABLE 3. ACS, OPCABG versus cCABG Demographics
Age % Female Diabetes Yes-insulin Yes-not on insulin BSA Smoker COPD Creatinine CVD EF G 55% No. anastamoses Preoperative IABP Operative time (min)
ACS OPCABG (n = 160)
ACS cCABG (n = 111)
65.7 T 10.9 2.5% (4)
65.2 T 8.7 0.9% (1)
32.5% (52) 9.3% (15) 1.99 T 0.23 30.6% (49) 45.6% (73) 1.57 T 1.50 21.2% (34) 71.3% (114) 1.9 T 0.7 25.6% (41) 298.5 T 57.5
25.2% (28) 9.0% (10) 2.00 T 0.18 37.8% (42) 45.0% (50) 1.17 T 0.31 18.9% (21) 56.1% (60, n = 107) 2.7 T 0.8 19.8% (22) 377 T 80.5
P 0.7192 0.6515 0.1833
0.6469 0.2401 90.9999 0.0058* 0.7590 0.0108* G0.0001* 0.3071 G0.0001*
*Statistically significant values.
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CONCLUSIONS For patients presenting with ACS who require surgical intervention, OPCABG remains a viable option with similar short- and long-term survival in this subgroup. Postoperative LOS and the risk of bleeding appear to be less with OPCABG, indicating that, where appropriate, there may be benefits to this surgical approach; however, further research is required.
DISCUSSION Great strides have been made in the management of patients presenting with ACS over the last several decades, and indeed, survival for individuals receiving care for ACS today is better than at any time in history. This improvement in outcomes has arisen from an evolution of all areas of management, including prehospital care, in-hospital medical management, surgical or percutaneous revascularization strategies, and postdischarge care. With the widespread use of percutaneous coronary intervention (PCI), surgical revascularization for ACS has become much less commonplace; however, indications for CABG in ACS remain and include evolving ischemia refractory to medical therapy, complex coronary anatomy not amenable to PCI, left main or 3-vessel disease, ongoing ischemia despite attempts at PCI, or failed attempts at PCI. Although patients presenting with these indications are less common, they represent a unique challenge for the cardiac surgeon because of their potential fragility and higher risk for mortality and morbidity. In an effort to decrease potential morbidity and mortality within this population undergoing CABG, OPCABG has been proposed as a revascularization strategy with the goal of minimizing the documented morbidities associated with extracorporeal cardiopulmonary bypass, aortic manipulation and clamping, hemodilution, and hypothermia, as well as avoiding global myocardial ischemia and reducing ischemia-reperfusion injury potential. The use of this technique in ACS was further bolstered by early favorable results9Y11 indicating the feasibility of OPCABG in ACS. Despite early enthusiasm, technical challenges and ongoing debate regarding the long-term results of all patients undergoing OPCABG has limited application of this technique, including in patients presenting with ACS. A subject of ongoing debate regarding OPCABG as a whole has been the long-term outcomes of this technique, with much ongoing discussion within the literature and at national meetings. Multiple studies have been developed to address this
FIGURE 3. Survival of ACS patients receiving cCABG versus OPCABG.
issue and have demonstrated that in experienced hands, outcomes for OPCABG can be similar to those for cCABG.12 Long-term data within the subgroup of patients presenting with ACS have been limited, however, with long-term follow-up being generally around 1 year and extending up to 4 years. In addition, no data set has yet to examine the outcomes specific to the United State veteran population. This study demonstrates that within our veteran population, patients presenting with ACS have similar short- and long-term survival after receiving cCABG or OPCABG, despite having increased preoperative rates of renal dysfunction and depressed EF. In addition, postoperative LOS and the risk of bleeding appear to be less with OPCABG. These outcomes are similar to those identified by other authors previously,6,7,10,13 with the added benefit of being demonstrated over a significantly longer period of time, and within the veteran population specifically. In addition to the end points examined, the OPCABG technique itself potentially confers several advantages over TABLE 5. Regression Analysis
TABLE 4. ACS, OPCABG versus cCABG Outcomes
Operative mortality 30-day mortality Mediastinitis Perioperative MI New renal failure Reop bleeding New CVA Prolonged vent LOS (days)
ACS OPCABG (n = 160)
ACS cCABG (n = 111)
P
0.6% (1) 3.8% (6) 0.6% (1) 1.3% (2) 1.3% (2) 1.3% (2) 0.6% (1) 11.9% (19) 8.61 T 5.37
0% (0) 0% (0) 1.8% (2) 0.9% (1) 0% (0) 6.3% (7) 0% (0) 12.6% (14) 11.32 T 11.98
90.9999 0.0845 0.5696 90.9999 0.5146 0.0346* 90.9999 0.8525 0.0121*
CVA indicates cerebral vascular accident. *Statistically significant values.
160
All patients
Demographics
HR
CIs
P
ACS Age COPD Creatinine Diabetes OPCABG
1.33 1.05 1.52 1.18 1.47 1.32
1.04Y1.70 1.03Y1.06 1.21Y1.91 1.11Y1.25 1.17Y1.84 1.03Y1.70
0.0255* G0.0001* 0.0003* G0.0001* 0.0009* 0.0273*
Age COPD Creatinine Diabetes OPCABG
1.07 1.49 1.15 1.41 1.06
1.04Y1.09 0.97Y2.31 1.02Y1.31 0.92Y2.15 0.68Y1.64
G0.0001* 0.0707 0.0207* 0.1149 0.7937
ACS only
*Statistically significant values.
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cCABG that were not specifically examined with this retrospective study. Multiple authors have demonstrated a reduction in stroke risk with OPCABG and reduced aortic manipulation,14 in our data set the overall stroke risk was low (less than 1%), and the study was not powered sufficiently to examine this potential advantage. In addition, although the observed decreased LOS and risk of bleeding did not translate into an improved survival benefit, the potential for reduced cost and reduction of risk associated with prolonged hospital stay and postoperative bleeding should be emphasized. Although not conferring a difference in the long-term to individual patient’s survival, the reduction in cost and system resources associated with this, as well as additional reductions associated with the shorter operative time observed, are likely significant and need to be examined further. The observed mortality rate for patients presenting with ACS in this study is relatively low, at 2.2% for 30-day, and 0.4% for operative mortality. These rates are favorable when compared with previously published data for this typically fragile population,15Y18 although comparisons are difficult as previous studies often enrolled only a subset of patients presenting with ACS. Our favorable mortality rates likely represent a general improvement in management of these patients from a variety of standpoints, rather than any specific difference inherent to this institution. In addition, our analysis is subject to inherent bias as there was no intent-to-treat analysis, and there was obviously a fraction of individuals who were too sick to tolerate surgery and died without surgical intervention. The relatively poor long-term survival, with a 30.96% mortality rate at 5 years for the ACS group, is consistent with previous reports and is expected given the overall burden of systemic disease that is inherent to this population. Regarding the feasibility of OPCABG in the challenging subpopulation of ACS patients, our experience indicates that this population tolerates the manipulation involved in OPCABG nearly as well as the non-ACS population. The conversion rate of 3% seen in the ACS population is higher than both the control group, at 1%, and our historic rate of just under 1% (unpublished data). This acceptable rate is facilitated by careful selection, surgeon experience, and perhaps most importantly, an excellent anesthesia team well experienced with managing hemodynamic changes that occur during this procedure. Because of the low number of patients in the ‘‘converted’’ subgroup (n = 12), an outcomes analysis was not conducted. This study has the obvious limitations that are innate to any retrospective study, including lack of randomization and inherent bias, including an admitted bias towards performing OPCABG by the surgeons included here. In addition, the ACS OPCABG group had higher rates of baseline renal dysfunction and need for preoperative IABP, which was not controlled for; however, this should have biased toward worse outcomes for this group. Furthermore, there is no intent-to-treat analysis for this study, although those converted from OPCABG to cCABG represented a small fraction of individuals, and the effect on outcomes is likely minimal. Finally, it should be noted that this study was conducted within a center that performs a high percentage of cases off-pump (approximately 70%), and that the results seen here may not be applicable to lower-volume centers.
CABG in ACS: Off-Pump Outcomes
REFERENCES 1. Mehta SR, Cannon CP, Fox KA, et al. Routine vs selective invasive strategies in patients with acute coronary syndromes: A collaborative metaanalysis of randomized trials. JAMA. 2005;293:2908Y2917. 2. Solodky A, Behar S, Boyko V, et al. The outcome of coronary artery bypass grafting surgery among patients hospitalized with acute coronary syndrome: The Euro Heart Survey of acute coronary syndrome experience. Cardiology. 2005;103:44Y47. 3. Thielmann M, Neuha¨user M, Marr A, et al. Predictors and outcomes of coronary artery bypass grafting in ST elevation myocardial infarction. Ann Thorac Surg. 2007;84:17Y24. 4. Hillis LD, Smith PK, Anderson JL, et al. 2011 ACCF/AHA Guideline for Coronary Artery Bypass Graft Surgery. A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol. 2011;58:e123Ye210. 5. Ben-Gal Y, Stone GW, Smith CR, et al. On-pump versus off-pump surgical revascularization in patients with acute coronary syndromes: Analysis from the Acute Catheterization and Urgent Intervention Triage Strategy trial. J Thorac Cardiovasc Surg. 2011;142:e33Ye39. 6. Biancari F, Mahar MA, Mosorin M, et al. Immediate and intermediate outcome after off-pump and on-pump coronary artery bypass surgery in patients with unstable angina pectoris. Ann Thorac Surg. 2008;86:1147Y1152. 7. Eagle KA, Guyton RA, Davidoff R, et al. ACC/AHA 2004 guideline update for coronary artery bypass graft surgery: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1999 Guidelines for Coronary Artery Bypass Graft Surgery). Circulation. 2004;110:e340Ye343. 8. Trachiotis GD. Early antiplatelet therapy in coronary artery bypass grafting: A calculated benefit. Innovations. 2010;5:317Y325. 9. Locker C, Shapira I, Paz Y, et al. Emergency myocardial revascularization for acute myocardial infarction: Survival benefits of avoiding cardiopulmonary bypass. Eur J Cardiothorac Surg. 2000;17:234Y238. 10. Ochi M, Hatori N, Saji Y, et al. Application of off-pump coronary artery bypass grafting for patients with acute coronary syndrome requiring emergency surgery. Ann Thorac Cardiovasc Surg. 2003;9:29Y35. 11. Kerendi F, Puskas JD, Craver JM, et al. Emergency coronary artery bypass grafting can be performed safely without cardiopulmonary bypass in selected patients. Ann Thorac Surg. 2005;79:801Y806. 12. Puskas JD, Williams WH, O’Donnell R, et al. Off-pump and on-pump coronary artery bypass grafting are associated with similar graft patency, myocardial ischemia, and freedom from reintervention: Long-term follow-up of a randomized trial. Ann Thorac Surg. 2011;91:1836Y1842. 13. Fattouch K, Guccione F, Dioguardi P, et al. Off-pump versus on-pump myocardial revascularization in patients with ST-segment elevation myocardial infarction: a randomized trial. J Thorac Cardiovasc Surg. 2009; 137:650Y656. 14. Brizzio ME, Zapolanski A, Shaw RE, et al. Stroke-related mortality in coronary surgery is reduced by the off-pump approach. Ann Thorac Surg. 2010;89:19Y23. 15. Boden WE, O’Rourke RA, Crawford MH, et al. Outcomes in patients with acute non-Q-wave myocardial infarction randomly assigned to an invasive as compared with a conservative management strategy. Veterans Affairs Non-Q-Wave Infarction Strategies in Hospital (VANQWISH) Trial Investigators. N Engl J Med. 1998;338:1785Y1792. 16. Fox KA, Poole-Wilson PA, Henderson RA, et al. Interventional versus conservative treatment for patients with unstable angina or non-ST-elevation myocardial infarction: The British Heart Foundation RITA 3 randomized trial. Lancet. 2002;360:743Y751. 17. Senanayake EL, Howell NJ, Evans J, et al. Contemporary outcomes of urgent coronary artery bypass graft surgery following non-ST elevation myocardial infarction: urgent coronary artery bypass graft surgery consistently outperforms Global Registry of Acute Coronary Events predicted survival. Eur J Cardiothorac Surg. 2012;41:e87Ye91. 18. Rastan AJ, Eckenstein JI, Hentschel B, et al. Emergency coronary artery bypass graft surgery for acute coronary syndrome: Beating heart versus conventional cardioplegic cardiac arrest strategies. Circulation. 2006;114: I477YI485.
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CLINICAL PERSPECTIVE This is an interesting report from Dr. Emerson and his group at the Veteran Affairs Medical Center in Washington, DC USA. In this retrospective case series, they examined their experience with coronary artery bypass grafting (CABG) in patients with acute coronary syndrome (ACS). They compared 271 patients with ACS to 854 patients who did not have ACS. While 30-day mortality was similar between the two groups, the long-term mortality was significantly worse for the ACS group at a median followup of 5.5 years. Not surprisingly, length of stay and composite morbidity were also higher in the ACS group. The authors then performed a subgroup analysis looking at just the acute ACS patients and stratified them by whether they had conventional coronary artery bypass grafting (CABG) or off-pump coronary artery bypass grafting (OPCABG). They demonstrated similar 30-day and late mortality in this group. However, the conventional CABG group had higher rates of reoperation, longer length of stay and a longer operative time. They concluded that OPCABG compared favorably to conventional CABG within the ACS group. This study has numerous limitations. First of all, it is a retrospective case series and thus subject to both selection bias and the fact that the two groups had significant differences in preoperative co-morbidities. There were also relatively few patients in the OPCABG and conventional CABG ACS groups, thus greatly limiting the power of the study. The suggestion that OPCABG may be more successful in the ACS group than in the non-ACS group would need to be proven in a prospective, randomized study. It is important to point out to the readers that in the non-ACS group, OPCABG was a significant risk factor for mortality in multivariate analysis.
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Coronary Artery Bypass Grafting During Acute Coronary Syndrome Outcomes and Comparison of Off-Pump to Conventional Coronary Artery Bypass Grafting at a Veteran Affairs Hospital Dominic A. Emerson, MD,*Þ Conor F. Hynes, MD,Þ Michael D. Greenberg, MD,* and Gregory D. Trachiotis, MD*þ
Objective: The management of acute coronary syndrome (ACS) has evolved dramatically over the last 50 years. Currently, management includes a multidisciplinary approach potentially including catheterbased therapy, surgery, or purely medical management. Where surgical therapy is indicated, data regarding long-term outcomes are limited. In particular, little data exist regarding on-pump (conventional coronary artery bypass grafting, cCABG) versus off-pump (OPCABG) outcomes for this group. Methods: A retrospective review of prospectively collected data was undertaken. Patients undergoing isolated CABG from January 2000 to December 2011 with ACS were identified (n = 271); non-ACS patients (n = 854) were established as a control. Data were analyzed with a W2 or a t test, where appropriate. Survival was compared using KaplanMeier analysis and Cox proportional hazards model. Results: Thirty-day mortality between the ACS and the control groups was similar; however, long-term mortality was worse for the ACS group (P = 0.032; median follow-up, 5.5 years). Length of stay and composite morbidity were higher in the ACS group (P G 0.01). Subgroup analysis of ACS patients (OPCABG vs cCABG) demonstrated worse preoperative comorbidities in the OPCABG group, but similar 30-day and long-term mortality. However, the cCABG group had higher rates of reoperation (P = 0.034) and longer length of stay (P = 0.017) and operative time (P G 0.0001). Cox proportional hazards model was applied. Risk factors for the non-ACS cohort included age, diabetes, OPCABG, and ACS (P G 0.05). Among the ACS cohort, only age remained a statistically significant factor (P G 0.0001). Conclusions: ACS appears to negatively impact long-term, but not short-term, mortality. Within the ACS group, OPCABG compares
Accepted for publication January 14, 2015. From the *Veterans Affairs Medical Center; †Georgetown University Hospital; and ‡The George Washington University Hospital, Washington, DC USA. Presented at the Annual Scientific Meeting of the International Society for Minimally Invasive Cardiothoracic Surgery, May 28Y31, 2014, Boston, MA USA. Disclosure: The authors declare no conflicts of interest. Address correspondence and reprint requests to Gregory D. Trachiotis, MD, Division of Cardiothoracic Surgery, Veterans Affairs Medical Center, 50 Irving St., NW, Washington, DC 20422 USA. E-mail: [email protected]. Copyright * 2015 by the International Society for Minimally Invasive Cardiothoracic Surgery ISSN: 1556-9845/15/1003-0157
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favorably to cCABG in the long-term and also improves short-term morbidity. Key Words: Acute coronary syndrome, Coronary artery bypass grafting, Off-pump coronary artery bypass grafting. (Innovations 2015;10:157Y162)
T
he management of acute coronary syndrome (ACS) has evolved dramatically over the last 50 years. Currently, management includes a multidisciplinary approach involving interventional cardiology, surgery, and internal medicine, with the optimal treatment for an individual potentially including catheter-based therapy, surgery, or purely medical management. The aggressive management of ACS has greatly improved the outcomes of patients presenting to the hospital with evidence of ischemia. A cornerstone of management for this population has been early and routine invasive management, including coronary angiography and revascularization with catheter-based or surgical techniques.1 A subset of individuals presenting with ACS ultimately require surgical revascularization, and it has been shown that coronary artery bypass grafting (CABG) remains a viable option for the management of this population.2Y4 Despite the clear utility of CABG, there has been debate regarding the optimal surgical approach to surgical revascularization in this population, with multiple authors indicating that there may be benefit to performing surgical procedures off pump (OPCABG).5,6 At this point, however, there are only limited data regarding the longterm outcomes within the ACS population as stratified by surgical revascularization technique, and the length of follow-up for these studies are at most around 4 years.6 In this study, we examine the short- and long-term outcomes of patients undergoing surgical revascularization in the setting of ACS and further subdivide these patients into those undergoing conventional CABG (cCABG) with full cardiopulmonary bypass, and those undergoing OPCABG.
MATERIALS AND METHODS This study was approved following a review from the local institutional review board. A pre-existing in-house database based on the national Veterans Affairs database was
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queried to identify patients who underwent isolated CABG from January 2000 to December 2011 (n = 1125). Patients from this cohort who underwent CABG for ACS were then identified as follows: patients who were identified at the time of surgery as being an emergent case for ‘ongoing ischemia,’ or who were noted to have had a myocardial infarction within 7 days before surgery were placed into the ACS cohort (n = 153). For those not fitting this criteria, patients who were noted to have ST changes, to be New York Heart Association class III or IV, or to be Canadian Cardiovascular Society class IV were selected for additional review (n = 603). A focused retrospective chart review was then undertaken to identify patients from this group who had ACS during the same admission, and before surgical intervention. This was defined in accordance with previous guidelines7 and included diagnosis of ACS by attending surgeon, presence of unstable angina, ST-segment elevation myocardial infarction (STEMI), or non-STEMI (NSTEMI). In total, 271 patients with ACS were identified, and the remaining 854 were used as a control cohort (Fig. 1). Following the creation of the ACS and non-ACS cohorts, these 2 groups were further subdivided into those undergoing cCABG and those undergoing OPCABG. Statistical analyses were undertaken to compare demographics, risk factors, and outcomes between groups. The primary end point of mortality (both short- and long-term) was used, and secondary end points of length of stay (LOS), isolated and composite morbidity, and operative time were also examined. Statistical analyses were performed using Student t test for continuous data, a Fisher
Exact test for binomial data, or Mann-Whitney U test for ordinal data; Kaplan-Meier analysis and a log-rank test were used for mortality comparisons. Cox proportional hazards model was used for regression analysis. P = 0.05 was considered statistically significant throughout. Statistical analysis was performed using R (Vienna, Austria). All patients were operated on by 1 of 2 surgeons, with operative technique up to the discretion of the individual surgeon. No strict criteria were used for determining OPCABG versus cCABG. ACS patients were generally jointly managed preoperatively by both the cardiac surgery and internal medicine/cardiology teams. Standard postoperative dual antiplatelet therapy, consisting of aspirin and Plavix, was given to patients for a period of 1 year for ACS patients as described previously.8
RESULTS Fifty-nine percent (160) of the ACS cohort received OPCABG, as did 65% (297) of the control cohort (P = 0.070). Demographics compared between the ACS and control cohorts were generally similar and are presented on Table 1, with the exception of greater frequency of depressed ejection fraction (EF) in the ACS group. Operative variables were significantly different in terms of more frequent preoperative intra-aortic balloon pump (IABP) placement among ACS patients (23% vs 9%, P G 0.0001), but were otherwise similar as well. Conversion (from OPCABG to cCABG intraoperatively) was seen more frequently in the ACS cohort, but this was not statically significant (Table 1).
FIGURE 1. Creation of cohorts.
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CABG in ACS: Off-Pump Outcomes
TABLE 1. ACS versus Non-ACS Demographics ACS (n = 271) Age % Female Diabetes Yes-insulin Yes-not on insulin BSA Smoker COPD Creatinine CVD EF G 55 No. anastamoses OPCABG Preoperative IABP Operative time (min) Conversion (OPCABG only)
65.5 T 10.0 1.8% (5)
Non-ACS (n = 854) 64.5 T 9.4 0.8% (7)
P 0.1256 0.1742 0.5804
29.5% (80) 22.1% (189) 9.2% (25) 17.9% (153) 2.00 T 0.212 2.02 T 0.203 0.0516 33.6% (91) 30.0% (256) 0.2907 45.4% (123) 45.5% (389) 90.9999 1.40 T 1.19 1.30 T 0.98 0.1571 20.1% (55) 20.8% (178) 0.9315 65.3% (175, n = 268) 55.1% (467, n = 847) 0.0033* 2.26 T 0.83 2.22 T 0.85 0.4929 59% (160) 65% (297) 0.0700 23.2% (63) 8.8% (75) G0.0001* 330 T 78 325 T 70 0.2968 3.1% (5 of 160) 1.3% (7 of 557) 0.1044
*Statistically significant values.
FIGURE 2. Survival, ACS vs non-ACS.
Short-term outcomes between groups were significantly different in regards to rate of prolonged ventilation within the ACS group (12% vs 4%, P G 0.0001). However, despite this, 30-day mortality was not different between groups (P = 0.237) (Table 2). Long-term outcomes, as evaluated using KaplanMeier curves and a log-rank test, demonstrated worse survival among the ACS cohort, as expected (Fig. 2; P = 0.032; median follow-up, 5.5 years). The ACS cohort was then subdivided into cCABG and OPCABG cohorts, as described above. Baseline characteristics between the ACS cCABG and OPCABG groups demonstrated the OPCABG group to be worse in regards to renal function (P = 0.006) and American Society of Anesthesia scores (a score for general determination of fitness for surgery and risk) (P G 0.001), and preoperative EF (P = 0.0103), with other factors being similar (Table 3). Short-term outcomes between ACS cCABG and OPCABG revealed a lower rate of reoperation for bleeding (1.3% vs 6.3%, P = 0.034), shorter LOS (8.6 vs 11.3 days, P = 0.012), and shorter operative time (298 vs 377 minutes, P G 0.0001) among the ACS OPCABG cohort (Table 4). It should be noted that operative time in our database is defined as ‘‘door-to-door’’ operative time, and that the actual surgeon time, or ‘‘skin-to-skin’’ TABLE 2. ACS versus Non-ACS Outcomes Operative mortality 30-day mortality Mediastinitis Perioperative MI New renal failure Reop bleeding New CVA Prolonged vent LOS (days)
ACS (n = 271)
Non-ACS (n = 854)
P
0.4% (1) 2.2% (6) 1.1% (3) 1.1% (3) 0.7% (2) 3.3% (9) 0.4% (1) 12.2% (33) 9.72 T 8.79
0.1% (1) 1.2% (10) 0.5% (4) 0.5% (4) 0.5% (4) 1.4% (12) 0.4% (3) 4.1% (35) 8.78 T 11.37
0.4236 0.2373 0.3688 0.3688 0.6351 0.6635 90.9999 G0.0001* 0.2134
CVA indicates cerebral vascular accident. *Statistically significant values.
time, is significantly less but was not recorded. Despite an increased rate of short-term morbidity among the cCABG cohort, rates of 30-day mortality were similar between groups (Table 3). Finally, long-term outcomes were also evaluated between groups with a median follow-up of 5.0 years and did not demonstrate any significant difference in long-term survival between groups (Fig. 3, P = 0.447). Multivariate regression analysis was performed using Cox proportional hazards models. Among the entire population (ACS and non-ACS, OPCABG and cCABG), age, diabetes, OPCABG, creatinine, chronic obstructive pulmonary disease (COPD), and ACS were all significant risk factors for mortality (all P G 0.05). When applied only to the ACS cohort, only age and creatinine remained statistically significant factors (P G 0.05), with surgical technique not being a statistically significant contributor to risk (Table 5). TABLE 3. ACS, OPCABG versus cCABG Demographics
Age % Female Diabetes Yes-insulin Yes-not on insulin BSA Smoker COPD Creatinine CVD EF G 55% No. anastamoses Preoperative IABP Operative time (min)
ACS OPCABG (n = 160)
ACS cCABG (n = 111)
65.7 T 10.9 2.5% (4)
65.2 T 8.7 0.9% (1)
32.5% (52) 9.3% (15) 1.99 T 0.23 30.6% (49) 45.6% (73) 1.57 T 1.50 21.2% (34) 71.3% (114) 1.9 T 0.7 25.6% (41) 298.5 T 57.5
25.2% (28) 9.0% (10) 2.00 T 0.18 37.8% (42) 45.0% (50) 1.17 T 0.31 18.9% (21) 56.1% (60, n = 107) 2.7 T 0.8 19.8% (22) 377 T 80.5
P 0.7192 0.6515 0.1833
0.6469 0.2401 90.9999 0.0058* 0.7590 0.0108* G0.0001* 0.3071 G0.0001*
*Statistically significant values.
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CONCLUSIONS For patients presenting with ACS who require surgical intervention, OPCABG remains a viable option with similar short- and long-term survival in this subgroup. Postoperative LOS and the risk of bleeding appear to be less with OPCABG, indicating that, where appropriate, there may be benefits to this surgical approach; however, further research is required.
DISCUSSION Great strides have been made in the management of patients presenting with ACS over the last several decades, and indeed, survival for individuals receiving care for ACS today is better than at any time in history. This improvement in outcomes has arisen from an evolution of all areas of management, including prehospital care, in-hospital medical management, surgical or percutaneous revascularization strategies, and postdischarge care. With the widespread use of percutaneous coronary intervention (PCI), surgical revascularization for ACS has become much less commonplace; however, indications for CABG in ACS remain and include evolving ischemia refractory to medical therapy, complex coronary anatomy not amenable to PCI, left main or 3-vessel disease, ongoing ischemia despite attempts at PCI, or failed attempts at PCI. Although patients presenting with these indications are less common, they represent a unique challenge for the cardiac surgeon because of their potential fragility and higher risk for mortality and morbidity. In an effort to decrease potential morbidity and mortality within this population undergoing CABG, OPCABG has been proposed as a revascularization strategy with the goal of minimizing the documented morbidities associated with extracorporeal cardiopulmonary bypass, aortic manipulation and clamping, hemodilution, and hypothermia, as well as avoiding global myocardial ischemia and reducing ischemia-reperfusion injury potential. The use of this technique in ACS was further bolstered by early favorable results9Y11 indicating the feasibility of OPCABG in ACS. Despite early enthusiasm, technical challenges and ongoing debate regarding the long-term results of all patients undergoing OPCABG has limited application of this technique, including in patients presenting with ACS. A subject of ongoing debate regarding OPCABG as a whole has been the long-term outcomes of this technique, with much ongoing discussion within the literature and at national meetings. Multiple studies have been developed to address this
FIGURE 3. Survival of ACS patients receiving cCABG versus OPCABG.
issue and have demonstrated that in experienced hands, outcomes for OPCABG can be similar to those for cCABG.12 Long-term data within the subgroup of patients presenting with ACS have been limited, however, with long-term follow-up being generally around 1 year and extending up to 4 years. In addition, no data set has yet to examine the outcomes specific to the United State veteran population. This study demonstrates that within our veteran population, patients presenting with ACS have similar short- and long-term survival after receiving cCABG or OPCABG, despite having increased preoperative rates of renal dysfunction and depressed EF. In addition, postoperative LOS and the risk of bleeding appear to be less with OPCABG. These outcomes are similar to those identified by other authors previously,6,7,10,13 with the added benefit of being demonstrated over a significantly longer period of time, and within the veteran population specifically. In addition to the end points examined, the OPCABG technique itself potentially confers several advantages over TABLE 5. Regression Analysis
TABLE 4. ACS, OPCABG versus cCABG Outcomes
Operative mortality 30-day mortality Mediastinitis Perioperative MI New renal failure Reop bleeding New CVA Prolonged vent LOS (days)
ACS OPCABG (n = 160)
ACS cCABG (n = 111)
P
0.6% (1) 3.8% (6) 0.6% (1) 1.3% (2) 1.3% (2) 1.3% (2) 0.6% (1) 11.9% (19) 8.61 T 5.37
0% (0) 0% (0) 1.8% (2) 0.9% (1) 0% (0) 6.3% (7) 0% (0) 12.6% (14) 11.32 T 11.98
90.9999 0.0845 0.5696 90.9999 0.5146 0.0346* 90.9999 0.8525 0.0121*
CVA indicates cerebral vascular accident. *Statistically significant values.
160
All patients
Demographics
HR
CIs
P
ACS Age COPD Creatinine Diabetes OPCABG
1.33 1.05 1.52 1.18 1.47 1.32
1.04Y1.70 1.03Y1.06 1.21Y1.91 1.11Y1.25 1.17Y1.84 1.03Y1.70
0.0255* G0.0001* 0.0003* G0.0001* 0.0009* 0.0273*
Age COPD Creatinine Diabetes OPCABG
1.07 1.49 1.15 1.41 1.06
1.04Y1.09 0.97Y2.31 1.02Y1.31 0.92Y2.15 0.68Y1.64
G0.0001* 0.0707 0.0207* 0.1149 0.7937
ACS only
*Statistically significant values.
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Innovations & Volume 10, Number 3, May/June 2015
cCABG that were not specifically examined with this retrospective study. Multiple authors have demonstrated a reduction in stroke risk with OPCABG and reduced aortic manipulation,14 in our data set the overall stroke risk was low (less than 1%), and the study was not powered sufficiently to examine this potential advantage. In addition, although the observed decreased LOS and risk of bleeding did not translate into an improved survival benefit, the potential for reduced cost and reduction of risk associated with prolonged hospital stay and postoperative bleeding should be emphasized. Although not conferring a difference in the long-term to individual patient’s survival, the reduction in cost and system resources associated with this, as well as additional reductions associated with the shorter operative time observed, are likely significant and need to be examined further. The observed mortality rate for patients presenting with ACS in this study is relatively low, at 2.2% for 30-day, and 0.4% for operative mortality. These rates are favorable when compared with previously published data for this typically fragile population,15Y18 although comparisons are difficult as previous studies often enrolled only a subset of patients presenting with ACS. Our favorable mortality rates likely represent a general improvement in management of these patients from a variety of standpoints, rather than any specific difference inherent to this institution. In addition, our analysis is subject to inherent bias as there was no intent-to-treat analysis, and there was obviously a fraction of individuals who were too sick to tolerate surgery and died without surgical intervention. The relatively poor long-term survival, with a 30.96% mortality rate at 5 years for the ACS group, is consistent with previous reports and is expected given the overall burden of systemic disease that is inherent to this population. Regarding the feasibility of OPCABG in the challenging subpopulation of ACS patients, our experience indicates that this population tolerates the manipulation involved in OPCABG nearly as well as the non-ACS population. The conversion rate of 3% seen in the ACS population is higher than both the control group, at 1%, and our historic rate of just under 1% (unpublished data). This acceptable rate is facilitated by careful selection, surgeon experience, and perhaps most importantly, an excellent anesthesia team well experienced with managing hemodynamic changes that occur during this procedure. Because of the low number of patients in the ‘‘converted’’ subgroup (n = 12), an outcomes analysis was not conducted. This study has the obvious limitations that are innate to any retrospective study, including lack of randomization and inherent bias, including an admitted bias towards performing OPCABG by the surgeons included here. In addition, the ACS OPCABG group had higher rates of baseline renal dysfunction and need for preoperative IABP, which was not controlled for; however, this should have biased toward worse outcomes for this group. Furthermore, there is no intent-to-treat analysis for this study, although those converted from OPCABG to cCABG represented a small fraction of individuals, and the effect on outcomes is likely minimal. Finally, it should be noted that this study was conducted within a center that performs a high percentage of cases off-pump (approximately 70%), and that the results seen here may not be applicable to lower-volume centers.
CABG in ACS: Off-Pump Outcomes
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CLINICAL PERSPECTIVE This is an interesting report from Dr. Emerson and his group at the Veteran Affairs Medical Center in Washington, DC USA. In this retrospective case series, they examined their experience with coronary artery bypass grafting (CABG) in patients with acute coronary syndrome (ACS). They compared 271 patients with ACS to 854 patients who did not have ACS. While 30-day mortality was similar between the two groups, the long-term mortality was significantly worse for the ACS group at a median followup of 5.5 years. Not surprisingly, length of stay and composite morbidity were also higher in the ACS group. The authors then performed a subgroup analysis looking at just the acute ACS patients and stratified them by whether they had conventional coronary artery bypass grafting (CABG) or off-pump coronary artery bypass grafting (OPCABG). They demonstrated similar 30-day and late mortality in this group. However, the conventional CABG group had higher rates of reoperation, longer length of stay and a longer operative time. They concluded that OPCABG compared favorably to conventional CABG within the ACS group. This study has numerous limitations. First of all, it is a retrospective case series and thus subject to both selection bias and the fact that the two groups had significant differences in preoperative co-morbidities. There were also relatively few patients in the OPCABG and conventional CABG ACS groups, thus greatly limiting the power of the study. The suggestion that OPCABG may be more successful in the ACS group than in the non-ACS group would need to be proven in a prospective, randomized study. It is important to point out to the readers that in the non-ACS group, OPCABG was a significant risk factor for mortality in multivariate analysis.
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