A sub-study of the SCD-HeFT trial found no evidence that ICD benefit varies with time from MI to device implantation and that single lead ICD benefit is not restricted to patients with a remote MI ( >18 months). The sub-study, published in the March edition of Heart Rhythm, also showed that ICD therapy post-MI decreases the chances of sudden cardiac death immediately after a post-infarct period of zero to 40 days.
“The implantable cardioverter-defibrillator (ICD) is an effective therapy for preventing sudden cardiac death (SCD) in patients with prior myocardial infarction (MI) and reduced left ventricular function; however, the optimal timing of ICD implantation after MI remains unknown,” the authors wrote.
To better understand the risks and benefits of ICDs in MI survivors, Jonathan P. Piccini, MD, of division of cardiology at the Duke University Medical Center in Durham, N.C., and colleagues compared time to all-cause death and SCD between ICD and placebo arms of the SCD-HeFT (Sudden Cardiac Death in Heart Failure) trial to assess whether the benefit of single-lead programmed ICD therapy varies as a function of time from MI to ICD implantation within the sub-study.
The SCD-HeFT study included 2,521 patients from the U.S., Canada and New Zealand who were randomized to receive single lead, shock-only ICD therapy, amiodarone or placebo. ICD therapy significantly decreased the relative risk of mortality by 23 percent.
Piccini et al found that of the 712 patients with a history of MI evaluated, 274 died and 68 of these deaths were sudden cardiac deaths. The researchers reported that shocks were more common when time increased after MI; however, there was no evidence of differential mortality benefit with ICD implantation as a function of time after MI.
Of the 330 patients who were randomized to ICD therapy, 20.9 percent experienced one or more appropriate shocks for ventricular tachycardia or ventricular fibrillation at rates of 188 bpm or greater.
Piccini et al divided patients into three tertiles according to time from MI to implantation. Patients with the longest period of time between their last MI and enrollment were older, more often male, more likely to have a QRS duration equal to or greater than 120 ms and less likely to be administered a beta-blocker or statin.
The researchers reported that patients randomized to ICD were less likely to have experienced SCD when compared to those randomized to receive placebo in all three tertiles: 6.2 percent versus 14.2 percent within the first 2.11 years, 5.8 percent versus 10.3 percent between 2.11 and 7.31 years, and 2.5 percent versus 17.4 percent over 7.31 years.
“The risk of SCD is greatest immediately after MI and declines in the weeks to months after infarction,” the authors wrote. “Very simply, conservatively programmed devices, as in SCD-HeFT, may prove valuable early post-MI (outside of 40 days).
Therefore, device therapy should not be restricted to those patients remote from MI [ >18 months]. Future, prospective trials are needed to determine the optimal time for ICD implantation after MI and the optimal programming of primary prevention devices,” Piccini and colleagues concluded.
The authors said the limitations of the study stem from the fact that patients with MI, unstable angina or coronary revascularization within the last 30 days were not eligible for enrollment and only 10 percent of the patients within the analysis were within six months of their most recent MI.