REVIEW ARTICLES Paul G. Barash, MD Giovanni Landoni, MD Section Editors

Strategies for Temporary Cardiac Pacing in Pediatric Patients With Postoperative Junctional Ectopic Tachycardia Andreas Entenmann, MD, and Miriam Michel, MD

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OSTOPERATIVE JUNCTIONAL ectopic tachycardia (JET) occurs in 6% to 14% of all pediatric patients after surgery for repair of congenital heart defects.1 In combination with postoperative systolic and diastolic ventricular dysfunction, the tachycardia and the absence of synchrony of atrial and ventricular contraction result in relevant hemodynamic compromise. Without adequate treatment, such rhythm disorder is associated with increased morbidity and mortality.1,2 Therapy for JET comprises administration of antiarrhythmic drugs, deep sedation, and induced hypothermia.3 Temporary pacing is a further important pillar of treatment. Different techniques of temporary pacing exist that aim either to reduce the effective heart rate or to resynchronize atrial and ventricular contraction.4 The aim of this article is to describe 4 different strategies of external cardiac pacing in pediatric patients with postoperative JET (atrial demand pacing [AAI], dual-chamber pacing [DDD], paired ventricular pacing [PVP], and ventricular-triggered atrial pacing [AVT]). Advantages and disadvantages of the described strategies will be discussed.

CHARACTERISTICS OF POSTOPERATIVE JUNCTIONAL ECTOPIC TACHYCARDIA

Postoperative JET is a focal supraventricular tachycardia caused by abnormal automaticity arising from the compact atrioventricular (AV) node or the bundle of His. In the absence of a branch block, the QRS complexes remain narrow. Postoperative JET is associated with either atrioventricular dissociation, resulting in the ventricular rate exceeding the atrial rate, or retrograde 1:1 or variously blocked conduction to the atria. Retrograde 1:1 conduction may be most detrimental to hemodynamics as atrial contraction regularly occurs against closed atrioventricular valves.5 The definition of postoperative JET often is based on a critical heart rate (eg, 170 beats/min)6 to discriminate between an accelerated junctional rhythm against junctional ectopic tachycardia. Significantly, there is an acceleration phase with an initial increase in frequency of heart rate at the onset of JET. Either spontaneously or therapeutically, the heart rate peaks and then begins to slow down during the deceleration phase. Applying external pacing, the time point when the patient´s spontaneous pulse rate becomes less than the critical heart rate, as well as the reconstitution of atrioventricular synchrony, can be reached earlier than the return of sinus rhythm (Fig 1).

ATRIAL DEMAND PACING

According to the Generic Pacemaker Code, the type of a pacemaker is described by 3 characteristics: the pacing site, the sensing site, and pacing mode.7 The pacing mode can be either triggered (T), inhibited (I), dual (D) or none of the above (0). In atrial demand pacing (AAI pacing), the pacing and sensing sites are located within the atrium, and sensed atrial activity inhibits atrial stimulation by the pacemaker. In the context of postoperative JET, AAI pacing is used to overdrive the patient’s ventricular heart rate to establish a pacemakerdriven atrial rhythm with atrioventricular synchrony (Fig 1). The applied mode could be described more correctly as AAO pacing, because the aim is not to sense atrial activity, but rather to overdrive it. To use this method, the pacing rate must be slightly higher (5-10 beats/min) than the patient’s heart rate.8 Advantages of AAI pacing are that it commonly is used and easy to apply. A single-chamber external pacemaker is suitable as long as pacing rates higher than the patient´s ventricular rate can be obtained. The main disadvantages are: (1) this method requires intact atrioventricular conduction, which often is disturbed in patients with postoperative JET;9 (2) the pacing rate must be greater than the patient’s heart rate, which implies an even shorter diastolic filling time; (3) several readjustments may be necessary, particularly during the acceleration phase; and (4) the decrease in heart rate during the deceleration phase may not be recognized during AAI pacing. In a recently published study, Barker et al investigated the impact of postoperative AAI pacing in pediatric patients not exhibiting tachycardia after congenital heart surgery.10 Patients were paced at a stimulation rate that was 15% higher than the patient’s sinus rhythm. The authors detected a decrease in tissue oxygenation on head and flank near-infrared

From the Department of Pediatrics, Innsbruck Medical University, Anichstrasse 35, 6020 Innsbruck, Austria. Address reprint requests to Andreas Entenmann, MD, Department of Pediatrics, Innsbruck Medical University, Anichstrasse 35, 6020 Innsbruck, Austria. E-mail: [email protected] © 2015 Elsevier Inc. All rights reserved. 1053-0770/2601-0001$36.00/0 http://dx.doi.org/10.1053/j.jvca.2015.03.011 Key words: pediatric cardiac surgery, junctional ectopic tachycardia, temporary pacing, AVT pacing

Journal of Cardiothoracic and Vascular Anesthesia, Vol ], No ] (Month), 2015: pp ]]]–]]]

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phase I

phase II

250

Heart rate (bpm)

AAI pacing 200 critical heart rate ROSR

150

100 Time after surgery (h) Fig 1. A schematic diagram of the heart rate course in postoperative junctional ectopic tachycardia. The heart rate increases during the acceleration phase (phase I) and decreases during the deceleration phase (phase II). In AAI pacing, the stimulation rate has to be higher than the patient´s ventricular heart rate. Abbreviations: bpm, beats per minute; AAI, atrial demand pacing; ROSR, return of sinus rhythm.

spectroscopy and a decrease in mean arterial pressure. Therefore, AAI pacing with a stimulation rate higher than the patient’s heart rate may have objective effects on the postoperative course of patients who do not develop arrhythmia. The negative impact of increasing the heart rate in the presence of a tachycardic rhythm disorder has to be considered carefully against the benefit of atrioventricular synchrony. Even though AAI pacing is recommended as an important therapeutic measure in postoperative JET, there is no published systematic clinical evaluation confirming the positive effects of the therapy. DUAL-CHAMBER PACING

Dual-chamber pacing (DDD pacing) presents an alternative option in patients in whom AAI pacing is not possible due to atrioventricular conduction disturbances (Fig 2). In such patients, DDD pacing can provide effective sequential atrioventricular stimulation. Moreover, the technique and specific settings associated with this pacing mode are familiar to most physicians. As in AAI pacing, the pacing rate must exceed the

patient’s heart rate. However, in contrast to the automatic focus in JET, the site of ventricular stimulation in DDD pacing is not located within the conduction system. Prolonged and dyssynchronous ventricular activation may negatively influence the ventricular performance.11 With respect to hemodynamic status, DDD pacing may not always be beneficial in patients with JET. Therefore, patients have to be monitored carefully during the pacing procedure to identify unfavorable effects. PAIRED VENTRICULAR PACING

In the context of postoperative JET, the sophisticated pacing mode, PVP, first was described by Waldo et al in 1976.12 Originally, PVP was developed for the treatment of adult patients with severe heart failure but was deemed unfeasible for this purpose.13 The aim of PVP is to halve the patient’s mechanical heart rate (rate of myocardial contraction) by the implementation of an artificial myocardial refractory period. The PVP method requires the use of a stimulator for electrophysiologic studies. Those stimulators offer the option of eRP mRP S1

eRP S2

eRP mRP S1

V

A

JET

JET

JET

PM

Fig 2. Dual-chamber pacing (DDD). In postoperative junctional ectopic tachycardia, the atria are paced via the pacemaker´s atrial output channel with a stimulation rate higher than the patient´s heart rate. At the end of the adjustable AV delay, ventricles are paced via the ventricular output channel with the same stimulation rate. Abbreviations: PM, pacemaker; A, atrial channel; V, ventricular channel.

AoP Fig 3. Paired ventricular pacing. Two ventricular stimuli (S1, S2) are used to implement a myocardial refractory period. The rate of effective cardiac contractions is halved. Abbreviations: eRP, electric refractory period; mRP, myocardial refractory period; JET, junctional ectopic tachycardia; AoP, aortic pressure.

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CARDIAC PACING IN PEDIATRIC PATIENTS

selecting 2 different stimulation intervals in a continuous S1-S2-S1-S2 sequence. A one-pulse ventricular stimulus (S1) then is set followed by a premature second stimulus (S2). Initially, the duration of the S1-S2-S1 sequence is adjusted to twice the length of the arrhythmic cycle and then gradually is decreased. By shortening the S1-S2 interval to reach an electrical capture without mechanical contraction, the decrease in effective heart rate is achieved (Fig 3). This phenomenon is possible because the durations of the mechanical and electrical refractory periods differ. The PVP method prevents effective myocardial contraction at the time of the S2 stimulus. In practice, the S1-S2 interval is adjusted by simultaneously monitoring the electrical stimulus on the electrocardiogram and arterial pressure curve until the tracing shows no cardiac output after the S2 stimulus. In 1999, Kohli et al retrospectively analyzed the clinical data of 5 patients with postoperative JET treated with PVP.14 Administration of PVP was successful in all patients and resulted in an instantaneous increase in blood pressure. PVP is uniquely capable of instantly decreasing the patient’s heart rate and, thus, increasing the diastolic filling time. Despite the good study results, PVP has not become accepted as a standard pacing strategy. Problems with PVP include (1) the complex technique that requires a high level of experience, (2) the requirement of specific equipment, (3) stimulation close to the vulnerable phase may increase the risk of ventricular fibrillation, (4) permanent readjustments are necessary to maintain safe and effective pacing, and (5) atrioventricular synchrony is not accomplished. Because of these disadvantages, PVP is considered outdated and rarely used any longer. AVT PACING

Table 1. Maximum Length of AV Delay in Dependence of MTR in AVT pacing14 MTR (bpm)

AV delay (ms)

230 220 210 200 190 180 170 160 150 140 130 120 110 100

190 200 210 220 240 260 280 300 320 350 390 400 400 400

Abbreviations: MTR, maximum tracking rate; bpm, beats per minute; AVT, ventricular triggered atrial (pacing); ms, milliseconds.

et al introduced a modified, commercially available pacemaker capable of AVT pacing in 2003.16 The technique was based on switching the external pacing wires at the input channels of the pacemaker (Fig 4). Thus, the pacemaker is able to sense the ventricles via the atrial input channel and pace the atrium via the ventricular output channel. In the technique described by Janousek et al, a commercial pacemaker (PACE 203, Osypka Medical, La Jolla, CA) was modified to allow a total postventricular atrial refractory period (PVARP) of 100 ms and a maximum tracking rate (MTR) of 230 beats/min. Software versions from version 1.10jj onward provide these features and are suitable for AVT

R-wave synchronized atrial (AVT) pacing first was described by Till and Rowland in 1991.15 In AVT pacing, the atria are paced, the ventricles are sensed, and the atrial pacing is triggered by the ventricular-sensed signals. The aim of AVT pacing is to sense the ventricular R-wave and trigger an atrial stimulation immediately before the following QRS complex. The method remained experimental until Janousek

AP–VS VS

sensing VS window

AP

AV delay

PVARP cycle length

V

A PM

Fig 4. AVT pacing. Atrial and ventricular pacing wires are switched at the pacemaker’s inputs. The ventricles are sensed via the atrial channel, and the atria are paced via the ventricular channel. An AVT capable pacemaker is required (PACE 203, Osypka Medical, La Jolla, CA). Abbreviations: PM, pacemaker; A, atrial channel; V, ventricular channel.

Fig 5. Intervals and settings in AVT pacing (PACE 203, Osypka Medical, La Jolla, CA). A ventricular event (VS) is seen by the pacemaker as an atrial event. The AV delay of the pacemaker acts as an effective VA delay due to the switch of pacing wires. The atria are paced via the ventricular output channel (AP) before the following QRS complex. The AP-VS interval is not directly adjustable and reflects the effective atrioventricular interval. The PVARP has the role of a postatrial refractory period and should prevent sensing the atrial stimulus as an electrical activity in the ventricle. In AVT pacing the PVARP has to be short (100 ms) to allow a sufficient sensing window even in heart rates 4200 beats/min. Abbreviations: AP, atrial pacing; VS, ventricular sensing; AV, atrioventricular; PVARP, postventricular atrial refractory period.

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V

A

P

S ePM

PM

Fig 6. AVT pacing in patients without intact pacing wires. Sensing of the ventricles is performed via surface electrocardiogram electrodes and stimulation of the atria is achieved with an esophageal pacemaker connected in series (PACE 50E, Osypka Medical, La Jolla, CA). Abbreviations: PM, pacemaker; ePM, esophageal pacemaker; A, atrial channel; V, ventricular channel; S, sensing input; P, pacing output.

pacing. To establish R-wave synchronized atrial pacing, the operator must adjust the pacemaker´s VAT mode. The maximum tracking rate of the pacemaker has to be selected 10 to 20 beats/min higher than the patient’s heart rate. The atrioventricular delay (AV delay, effective VA delay) then is set to the maximum allowed value in dependence of the MTR (Table 1). The PVARP (effective PAVRP) is adjusted to 100 ms and ventricular (effective atrial) sensitivity is set infinitely (Fig 5). Janousek et al evaluated their AVT pacing technique in a retrospective study of 10 pediatric patients with postoperative JET and found a significant increase in blood pressure during treatment. Thus, they recommended that R-wave synchronized atrial pacing should be implemented in the standard protocol for management of postoperative JET.16

The advantages of AVT pacing include (1) the method can be performed using a commercially available standard external pacemaker, (2) the patient’s heart rate is not increased, (3) the natural course of the heart rate can be observed, and (4) the ventricles are not paced. Although AVT pacing initially appears to be simple to perform, it is rather complex, with many detailed aspects. For example, readjustments of the pacemaker are necessary, primarily during the acceleration phase, to acquire effective pacing results. AVT pacing can induce pacemaker-associated tachycardia. Apparently, adverse short intervals between atrial pacing and ventricular sensing (AP-VS) can be observed in clinical practice. These ultrashort AP-VS intervals may be responsible for counterpulsations if the atria and ventricles do contract simultaneously. As the minimum AP-VS time is given by the shortest possible PVARP of 100 ms, ultrashort AP-VS intervals should not occur in theory. Long intra-atrial and interatrial conduction in some patients, however, may lead to suboptimal mechanical AV synchrony due to late atrial contraction. This can be corrected by a decrease in the sensed AV (effective VA) delay. AVT pacing also may be inefficient in patients with retrograde 1:1 conduction to the atria. In this situation, the ventricular-triggered atrial pacing might face atrial activation and pace the atrium in its own refractory period. AVT pacing at relative low heart rates may interact with the remigrating sinus rhythm and atrioventricular synchrony is not achieved. Restitution of sinus rhythm has to be checked for regularly by switching off the pacemaker once JET rate has decreased. Therefore, AAI pacing might provide more stable results and prove to be superior to AVT pacing in patients with heart rates o160 beats/min. VARIANTS OF AVT PACING

In some patients, external pacing wires become defective due to damage or dislocation. If the ventricular pacing wires

Table 2. Synopsis of the Various Modalities of Temporary Pacing in Postoperative Junctional Ectopic Tachycardia AAI

Equipment

Complexity Risk of VT induction Applicable in patients with AV-block Ventricular pacing Stimulation rate higher than patient´s HR Off-label use Readjustments necessary AV synchrony Applicable with defective atrial wires Applicable with defective ventricular wires

DDD

PVP

AVT

Basic external pacemaker Basic external (single chamber) *** pacemaker (dual chamber) *** Low*** Low*** Low*** Acceptable** No* Yes***

Electrophysiology stimulator*

AVT capable external pacemaker **

High* High* Yes***

Moderate** Low*** Yes***

No*** Yes*

Yes* Yes*

Yes* No***

No*** No***

No*** Regularly** Yes (natural)*** No*

No*** Regularly** Yes (artificial)** No*

Yes* Permanently* No* Yes***

Yes** Occasionally*** Yes (artificial)** Yes (complex)**

Yes***

No*

No*

Yes (easy)***

Abbreviations: AAI, atrial demand pacing; DDD, dual-chamber pacing; PVP, paired ventricular pacing; AVT, ventricular-triggered atrial pacing; VT, ventricular tachycardia; AV, atrioventricular; HR, heart rate. A high number of asterisks are in favor of the pacing modality (AAI, DDD, PVP, AVT).

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malfunction, AVT pacing can be performed easily by sensing ventricular excitation via surface electrocardiogram electrodes, as described by Janousek et al in 2003.16 In the case of defective atrial pacing wires, atrial stimulation can be achieved through the aid of a synchronized esophageal pacemaker.17 By combining both methods, AVT pacing is possible without any intact pacing wire (Fig 6). However, AVT pacing by means of transesophageal pacing remains challenging and requires distinct technical expertise and specialized equipment. Esophageal stimulation may harm the esophageal mucosa and might be painful to the patient, requiring supplemental analgesia.18 This method still is considered an experimental approach, and its benefit is unproven. CONCLUSIONS

In the context of postoperative JET, 4 different pacing techniques are described in the literature. AAI pacing is relatively simple to implement, but requires a pacing rate higher than the patient’s heart rate. The same is true for DDD pacing, which is suitable for use in patients with atrioventricular conduction disturbances. A disadvantage of DDD

pacing is that the ventricles are paced and not spontaneously activated. PVP leads to an instant and significant reduction in effective heart rate. Unfortunately, PVP is technically complex and does not accomplish atrioventricular resynchronization. AVT pacing is a useful technique in pediatric patients with JET associated with very high heart rates. The patient´s heart rate is not increased by AVT pacing and the ventricles are not paced. Furthermore, this method can be used for patients with defective atrial or ventricular pacing wires. The published data indicate that this method is both safe and effective (Table 2). Although AVT pacing has been proposed as the standard therapy by the inventors of the method,16 a systematic review is necessary to verify its effectiveness and superiority to other pacing techniques. The question, whether early and consequent AVT pacing of patients with postoperative JET is capable of reducing the extent of other therapeutic measures necessary to terminate the arrhythmia, still is to be answered. ACKNOWLEDGMENTS

The authors thank Prof. Dr. W. Entenmann for his kind support in preparing the figures with MetaPost.

REFERENCES 1. Mildh L, Hiippala A, Rautiainen P, et al: Junctional ectopic tachycardia after surgery for congenital heart disease: Incidence, risk factors and outcome. Eur J Cardiothorac Surg 39:75-80, 2011 2. Andreasen JB, Johnsen SP, Ravn HB: Junctional ectopic tachycardia after surgery for congenital heart disease in children. Intensive Care Med 34:895-902, 2008 3. Kovacikova L, Hakacova N, Dobos D, et al: Amiodarone as a first-line therapy for postoperative junctional ectopic tachycardia. Ann Thorac Surg 88:616-622, 2009 4. Janousek J, Vojtovic P, Chaloupecký V, et al: Hemodynamically optimized temporary cardiac pacing after surgery for congenital heart defects. Pacing Clin Electrophysiol 23:1250-1259, 2000 5. Walsh EP, Saul JP, Sholler GF, et al: Evaluation of a staged treatment protocol for rapid automatic junctional tachycardia after operation for congenital heart disease. J Am Coll Cardiol 29: 1046-1053, 1997 6. Imamura M, Dossey AM, Garcia X, et al: Prophylactic amiodarone reduces junctional ectopic tachycardia after tetralogy of Fallot repair. J Thorac Cardiovasc Surg 143:152-156, 2012 7. Bernstein AD, Daubert JC, Fletcher RD, et al: The revised NASPE/BPEG generic code for antibradycardia, adaptive-rate, and multisite pacing. North American Society of Pacing and Electrophysiology/British Pacing and Electrophysiology Group. Pacing Clin Electrophysiol 25:260-264, 2002 8. Haas NA, Camphausen CK: Impact of early and standardized treatment with amiodarone on therapeutic success and outcome in pediatric patients with postoperative tachyarrhythmia. J Thorac Cardiovasc Surg 136:1215-1222, 2008 9. Paech C, Flosdorff P, Dähnert I, et al: Temporary AV block as a predictor of postoperative junctional ectopic tachycardia, abstract P3. 44th Annual Meeting of the German Society of Pediatric Cardiology, Weimar, Germany, 2012. Available at: http://www.kinderkardiologie.

org/Tagungen/djpk44/Abstracts_DGPK2012.pdf. Accessed November 16, 2014. 10. Barker GM, Affolter J, Saenz J, et al: Temporary atrial pacing for cardiac output after pediatric cardiac surgery. Pediatr Cardiol 34: 1605-1611, 2013 11. Pap R, Gallardo R, Rónaszéki D, et al: The role of pacinginduced dyssynchrony in left ventricular remodeling associated with long-term right ventricular pacing for atrioventricular block. J Electrocardiol 45:357-360, 2012 12. Waldo AL, Krongrad E, Kupersmith J, et al: Ventricular paired pacing to control rapid ventricular heart rate after open heart surgery. Observations on ectopic automaticity. Report of a case in a four-monthold patient. Circulation 53:176-181, 1976 13. Braunwald E, Ross J Jr, Frommer PL, et al: Clinical observations on paired electrical stimulation of the heart. Effects on ventricular performance and heart rate. Am J Med 37:700-711, 1964 14. Kohli V, Young ML, Perryman RA, et al: Paired ventricular pacing: an alternative therapy for postoperative junctional ectopic tachycardia in congenital heart disease. Pacing Clin Electrophysiol 22: 706-710, 1999 15. Till JA, Rowland E: Atrial pacing as an adjunct to the management of post-surgical His bundle tachycardia. Br Heart J 66:225-229, 1991 16. Janousek J, Vojtovic P, Gebauer RA: Use of a modified, commercially available temporary pacemaker for R wave synchronized atrial pacing in postoperative junctional ectopic tachycardia. Pacing Clin Electrophysiol 26:579-586, 2003 17. Entenmann A, Reineker K, Kramer HH: R-wave synchronized atrial pacing in post-operative junctional ectopic tachycardia using a transoesophageal pacemaker. Cardiol Young 23:763-765, 2013 18. Arzbaecher R, Jenkins JM: A review of the theoretical and experimental bases of transesophageal atrial pacing. J Electrocardiol 35 (suppl):137-141, 2002 (suppl)

Strategies for Temporary Cardiac Pacing in Pediatric Patients With Postoperative Junctional Ectopic Tachycardia.

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