Defibrillators Post Revascularization
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Synopsis: In patients with ischemic left ventricular dysfunction, the efficacy of ICD therapy after coronary revascularization(CR) is time dependent, with a significant life-saving benefit in patients receiving device implantation more than 6 months after CR.
Source: Goldenberg I, et al. Time Dependence of Defibrillator Benefit After Coronary Revascularization in the Multicenter Automatic Defibrillator Implantation Trial (MADIT)-II. J Am Coll Cardiol. 2006;47:1811-1817.
The appropriateness of implantable cardioverter defibrillator (ICD) therapy in patients with recent coronary revascularization has remained controversial. In this paper, Goldenberg and colleagues analyzed the effects of time from most recent revascularization on ICD effectiveness in the MADIT-II study. MADIT-II was a randomized study of patients with documented prior myocardial infarction and a left ventricular ejection fraction < 0.30 who were randomized to either a prophylactic ICD for primary prevention of sudden death vs conventional medical therapy in a 3:2 ratio. Patients were not eligible for enrollment if they had undergone coronary revascularization within the previous 3 months.
The entire study included 1232 patients. Of these, 951 had undergone coronary artery bypass grafting or a percutaneous coronary intervention at some time prior to enrollment. Of these 951, 130 had undergone coronary revascularization within less than 6 months, 414 within the time period of 7 to 60 months, and 407 more than 60 months prior to enrollment. Seventy-four percent of the patients who had undergone coronary revascularization had coronary artery bypass graft surgery (CABG) at some time, 57% had undergone a percutaneous intervention, and both procedures had been performed in 31%. Patients in the late (> 60 months) and intermediate (7-60 months) post coronary revascularization subgroup were more likely to be older, male, and have had CABG as their last revascularization procedure. Survival after enrollment was analyzed for the early, intermediate, and late post revascularization groups. Significant variables affecting outcome were incorporated into a Cox proportional hazards regression model to adjust for differences between the populations.
Among patients enrolled during the early post revascularization period, the 2-year Kaplan-Meier estimates of all-cause mortality between ICD and conventional therapy were similar. However, in both the intermediate and the late post revascularization groups, all-cause mortality rates were lower in the ICD group than in the conventional therapy groups. ICD therapy was associated with a 30% reduction in the risk of all-cause mortality in the entire group. Among the post revascularization subgroups, no survival benefit with ICD therapy was shown in the early group. In the intermediate and late post revascularization groups, there was an overall 36% reduction in the risk of all-cause mortality. The overall benefit of ICD therapy was due to a decrease in the incidence of sudden cardiac death. However, no benefit was seen in the patients in the early post revascularization group (HR = 2.01) in contrast to a marked benefit in the intermediate and late post revascularization groups (HR = 0.34). Analysis and mortality showed that the intermediate and late post revascularization groups had a much higher ratio of sudden to non-sudden deaths (60%) compared to the early post revascularization group (17%), perhaps explaining these observations.
Goldenberg and colleagues conclude that ICD therapy has a time dependent beneficial effect in patients who have undergone coronary revascularization. Patients in the early post revascularization period are at relatively low risk for arrhythmic mortality, but this risk increases over time.
Commentary
The interactions between coronary revascularization, recurrent ischemia, and ICD therapy have remained an active subject for investigation. In the CABG-Patch Trial, epicardial ICD systems were implanted at the time of coronary surgery in patients with depressed left ventricular ejection fractions and a positive single-averaged ECG. In that study, the overall hazard ratio was slightly higher (1.07) in the ICD group. In the DINAMIT study, defibrillators were implanted in patients with a recent myocardial infarction. Again, no benefit from ICD therapy was seen during follow-up. Other studies have shown a benefit of coronary revascularization on arrhythmic mortality. In both the Coronary Artery Surgery Study and the European Coronary Surgery Study, there were reductions in sudden cardiac death with surgical revascularization vs medical therapy in patients with chronic coronary disease. It has also been shown that ischemia is an important trigger for sudden death. For example, in the ATLAS trial, almost two-thirds of those patients who underwent autopsy after death had evidence for an acute coronary syndrome in the period immediately prior to their event. As confirmed by Goldenberg et al, mortality in the early phase after a revascularization procedure is dominated by deaths due to either complications of their procedure or nonarrhythmic causes. In this time period, an ICD produces little benefit. As disease progresses late after revascularization, recurrent ischemic events may serve to trigger sudden death episodes. It is during these latter time periods that the ICD will most likely be effective.
The appropriateness of implantable cardioverter defibrillator (ICD) therapy in patients with recent coronary revascularization has remained controversial.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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