Sudden cardiac arrest (SCA) is among the leading causes of death worldwide and is responsible for 250,000-450,000 deaths per year in the United States alone.¹ Coronary artery disease (CAD) is a major risk factor for SCA, especially when left ventricular ejection fraction (LVEF) is reduced. In response to the morbidity and mortality imposed by SCA, prophylaxis has been developed in the form of the implantable cardioverter-defibrillator (ICD). Multiple randomized controlled trials in patients with ischemic cardiomyopathy have shown that ICD implantation results in mortality reduction over the long term.^2,3

SCA has a higher incidence in those with reduced LVEF in the months after acute myocardial infarction (MI) and/or following revascularization.^4-7 From this, one could expect that ICD implantation during the period immediately after MI or revascularization would save lives. However, two randomized controlled trials, DINAMIT (Defibrillator in Acute Myocardial Infarction) and IRIS (Immediate Risk Stratification Improves Survival), showed definitively that early ICD implantation does not reduce mortality.^5,6 In both of those trials, the reduction in arrhythmic death effected by the presence of an ICD was counteracted by a concomitant increase in death due to other causes. Similarly, the only trial examining ICD implantation at the time of coronary artery bypass surgery showed ICDs to be ineffective for patients with preoperative LVEF ≤35%, though the epicardial ICDs tested in that trial differed significantly from the transvenous endocardial ICD systems of today.⁸ Unfortunately, no equivalent randomized trial has been performed in patients with ischemic cardiomyopathy undergoing percutaneous revascularization for stable CAD.

Although the precise reasons for ICDs' lack of efficacy in the immediate post-MI and post-revascularization periods are unclear, some hypotheses have been advanced. One contributing factor is that the mortality risk from nonarrhythmic causes (e.g., progressive congestive heart failure, ventricular septal defects, ventricular free wall rupture, and recurrent MI) makes arrhythmic prophylaxis unlikely to help. In the setting of these competing risks, ICD-related reduction in SCA is nullified by nonarrhythmic risks. In addition, the stress of the ICD implantation procedure itself or postoperative complications (e.g., perforation, infection, and adverse drug effects), may play a role in increasing non-SCA risk. Inappropriate shocks, which occur at a low but not insignificant rate in patients with ICDs, have also been shown to correlate with increased mortality.^9-11

Conversely, in the current era of effective acute revascularization, the post-MI short-term SCA risk may be lower than it was in the prerevascularization era due to percutaneous revascularization's rescuing "stunned" myocardium and resulting in mitigation of long-lasting LVEF depression. In support of this theory, recent data from PREDICTS (the Prediction of ICD Treatment Study) revealed a high rate of eventual LVEF recovery among survivors of acute MI with an initial LVEF ≤35%, 84% of whom underwent percutaneous revascularization.¹² At 3 months post-MI, 57% of patients had LVEF recovery to ≥35%, with 26% achieving LVEF ≥50%. Similarly, in patients with stable but obstructive CAD, chronically ischemic or "hibernating" myocardium may awaken following revascularization. As shown recently by Lewis et al., revascularization of stable CAD may lead to significant LVEF recovery in a remarkably similar fraction of such patients: 56%.¹³ Clearly, LVEF improvement to levels that obviate ICD implantation is possible following revascularization, even when the initial LVEF is significantly depressed.

At present, ICD implantation for primary prophylaxis is usually deferred for 3 months following revascularization. This approach is justified based on the evidence outlined above. Only when the patient qualifies for ICD implantation based on other indications (e.g., cardiac arrest outside of any acute ischemia and inherited arrhythmogenic disease) should this waiting period be curtailed.¹⁴ Of course, if any noncardiac comorbidity limits life expectancy such that ICD therapy would not be expected to extend life, ICD therapy is contraindicated.^14,15 During the 3-month delay between revascularization and ICD implantation, the use of a wearable cardioverter-defibrillator vest may be considered. The ongoing randomized VEST (Vest Prevention of Early Sudden Death Trial) is evaluating this strategy in the post-MI population.¹⁶

In summary, in patients with ischemic cardiomyopathy undergoing revascularization, a 3-month waiting period is appropriate prior to ICD implantation for primary prophylaxis of sudden death. During this 3-month period, the LVEF of many such patients may improve enough such that ICD implantation is not required. If the LVEF remains low after the 3-month wait, the evidence favors implantation at that time. During the waiting period, the wearable cardioverter-defibrillator vest may be considered for temporary protection from sudden death due to ventricular tachyarrhythmia.

References

1. Myerburg RJ, Junttila MJ. Sudden cardiac death caused by coronary heart disease. Circulation 2012;125:1043-52.
2. Moss AJ, Zareba W, Hall WJ, et al. Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction. N Engl J Med 2002;346:877-83.
3. Bardy GH, Lee KL, Mark DB, et al. Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure. N Engl J Med 2005;352:225-37.
4. Solomon SD, Zelenkofske S, McMurray JJ, et al. Sudden death in patients with myocardial infarction and left ventricular dysfunction, heart failure, or both. N Engl J Med 2005;352:2581-8.
5. Hohnloser SH, Kuck KH, Dorian P, et al. Prophylactic use of an implantable cardioverter-defibrillator after acute myocardial infarction. N Engl J Med 2004;351:2481-8.
6. Steinbeck G, Andresen D, Seidl K, et al. Defibrillator implantation early after myocardial infarction. N Engl J Med 2009;361:1427-36.
7. Zishiri ET, Williams S, Cronin EM, et al. Early risk of mortality after coronary artery revascularization in patients with left ventricular dysfunction and potential role of the wearable cardioverter defibrillator. Circ Arrhythm Electrophysiol 2013;6:117-28.
8. Bigger JT Jr. Prophylactic use of implanted cardiac defibrillators in patients at high risk for ventricular arrhythmias after coronary-artery bypass graft surgery. Coronary Artery Bypass Graft (CABG) Patch Trial Investigators. N Engl J Med 1997;337:1569-75.
9. Proietti R, Labos C, Davis M, et al. A systematic review and meta-analysis of the association between implantable cardioverter-defibrillator shocks and long-term mortality. Can J Cardiol 2015;31:270-7.
10. Moss AJ, Greenberg H, Case RB, et al. Long-term clinical course of patients after termination of ventricular tachyarrhythmia by an implanted defibrillator. Circulation 2004;110:3760-5.
11. Poole JE, Johnson GW, Hellkamp AS, et al. Prognostic importance of defibrillator shocks in patients with heart failure. N Engl J Med 2008;359:1009-17.
12. Brooks G, Lee BK, Rao R, et al. Predicting Persistent Left Ventricular Dysfunction Following Myocardial Infarction: The PREDICTS Study. J Am Coll Cardiol 2016;67:1186-96.
13. Lewis GF, Harless AC, Vazquez L, et al. Natural History and Implantable Cardioverter-Defibrillator Implantation After Revascularization for Stable Coronary Artery Disease With Depressed Ejection Fraction. Clin Cardiol 2015;38:715-9.
14. Kusumoto FM, Calkins H, Boehmer J, et al. HRS/ACC/AHA expert consensus statement on the use of implantable cardioverter-defibrillator therapy in patients who are not included or not well represented in clinical trials. Heart Rhythm 2014;11:1271-303.
15. Epstein AE, Dimarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for device-based therapy of cardiac rhythm abnormalities. Heart Rhythm 2008;5:e1-62.
16. Olgin JE, Pletcher MJ, Lee BK. Vest Prevention of Early Sudden Death Trial and VEST Registry (ClinicalTrials.gov website). 2016. Available at: https://clinicaltrials.gov/ct2/show/NCT01446965. Accessed 02/09/ 2016.

Keywords: Cardiomyopathies, Cause of Death, Comorbidity, Coronary Artery Bypass, Coronary Artery Disease, Death, Sudden, Cardiac, Defibrillators, Implantable, Depression, Fibrinogen, Heart Failure, Heart Rupture, Heart Septal Defects, Ventricular, Life Expectancy, Myocardial Infarction, Myocardium, Postoperative Complications, Risk Factors, Stroke Volume, Tachycardia, Ventricular, Angina, Stable

< Back to Listings