Study: ICD Therapy Beneficial Regardless of Time From Heart Attack


March 4, 2011

March 4, 2011 – According to a retrospective sub-study of the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT), there is no evidence that implantable cardioverter defibrillator (ICD) benefit varies with time from myocardial infarction (MI) to device implantation. Accordingly, single lead ICD benefit is not restricted to patients with a remote MI (more than 18 months).

The study, published in HeartRhythm, the official journal of the Heart Rhythm Society, suggests that ICD therapy post-MI decreases the chances of SCD starting immediately after the post-infarct period of up to 40 days.

In SCD-HeFT, 2,521 patients across the United States, Canada and New Zealand were randomly assigned to single lead, shock-only ICD therapy, amiodarone or placebo (double blind). The trial analyzed the use of ICDs in patients who experienced MI, yet had no previous life-threatening arrhythmia. The purpose was to determine the efficacy of ICDs as a primary prevention therapy for patients with moderate heart failure. It found that ICD therapy significantly decreased the relative risk of mortality by 23 percent.

The retrospective sub-study, led by Jonathan Piccini, M.D., MHS, analyzed the outcomes of ICD therapy in post-MI patients to determine whether mortality benefit varied as a function of time. Data from 712 patients were analyzed and divided into tertiles based on the amount of time that had passed between MI and the implantation of a single-lead ICD.

Analysis revealed that patients randomized to ICD therapy (vs. placebo) were less likely to experience SCD in all three groups: 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. A sensitivity analysis was also conducted and revealed that there was no evidence that ICD benefit varied between implantation within the first 18 months or after.

“It is widely known that the risk of SCD is most common in people immediately following a heart attack, yet some evidence suggests that the benefits of ICD therapy may be restricted to those patients who are more than a year after their MI,” Piccini said. “However, the SCD-HeFT results show that the benefit of single lead, conservatively programmed ICD therapy is not limited to those patients remote from a myocardial infarction. Ensuring that eligible patients receive primary prevention defibrillator therapy is likely to be more important than when the device is implanted, outside of 40 days.”

Although future, prospective trials are needed, the analysis has shown there is no evidence that ICD benefit varied with time from MI to implantation. Therefore, ICD implantation, at least as implemented in SCD-HeFT, should not be restricted to patients with remote MI (more than 18 months), as previously suggested. The differences in outcome between SCD-HeFT and prior studies are not clear but the use of a simpler more conservatively programmed ICD may be responsible.

There are also some important limitations to the SCD-HeFT analysis. Patients with MI, unstable angina, or coronary revascularization within the last 30 days were not eligible for enrollment in SCD-HeFT. Additionally, only 10 percent of the patients in the SCD-HeFT analysis were within six months of their most recent MI.

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