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ICDs and Survival in Patients With/Without Improved EF
Study Questions:
What is the efficacy of implantable cardioverter-defibrillator (ICD) therapy in reducing risk of all-cause mortality and sudden cardiac death among patients with an ejection fraction (EF) ≤35% at baseline, with or without an improvement in EF to >35% during follow-up?
Methods:
This was a retrospective analysis of a data set provided by SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial), which had randomly assigned 2,521 patients to placebo, amiodarone, or ICD. A subset of 1,902 subjects (75.4%) of the SCD-HeFT had a repeated assessment of EF a mean (standard deviation) of 13.5 (6) months after randomization. These patients were stratified by EF ≤35% and >35% based on the first repeated EF measurement after randomization. All-cause mortality was compared between 649 patients randomized to placebo versus 624 patients randomized to ICD. Follow-up started with the repeated EF assessment.
Results:
Of the included 1,273 patients, the mean age was 59 years, 77% were male, and 79% were white. Repeated EF was >35% in 186 participants (30%) randomized to ICD and 185 participants (29%) randomized to placebo. During a median follow-up of 30 months, the all-cause mortality rate was lower in the ICD versus placebo group, both in patients whose EF remained ≤35% (7.7 vs. 10.7 per 100 person-year follow-up) and in those whose EF improved to >35% (2.6 vs. 4.5 per 100 person-year follow-up). Compared with placebo, the adjusted hazard ratio for the effect of ICD on mortality was 0.64 (95% confidence interval [CI], 0.48-0.85) in patients with a repeated EF of ≤35% and 0.62 (95% CI, 0.29-1.30) in those with a repeated EF >35%. There was no interaction between treatment assignment and repeated EF for predicting mortality.
Conclusions:
Among participants in the SCD-HeFT who had a repeated EF assessment during the course of follow-up, those who had an improvement in EF to >35% accrued a similar relative reduction in mortality with ICD therapy as those whose EF remained ≤35%. Prospective randomized clinical trials are needed to test ICD efficacy in patients with an EF >35%.
Perspective:
Improvement in EF occurs in up to 25% of patients with ischemic cardiomyopathy and 50% of patients with nonischemic cardiomyopathy. Patients with recovered left ventricular (LV) function have a lower risk of receiving appropriate ICD shocks, but still receive them. Because of lack of a control group (i.e., patients without an ICD), prior studies do not provide data to definitively establish whether ICD therapy reduces mortality in patients whose EF improves to above 35%. This is germane to patients whose ICD generator has reached elective replacement indicator, and whose EF has improved to the point that they would no longer be candidates for primary prevention ICD. This study provides some support for the notion that these patients are still likely to benefit from the generator replacement. This study, however, does not specifically address patients whose LVEF has normalized (>55%), who have never had their EF ≤35%, or who may have nonischemic cardiomyopathy with no myocardial scar. Likely, there are differences among these patient groups. According to the data analysis presented in this paper, 10.6 patients whose EF remained ≤35% versus 12.6 patients whose EF improved to >35% need to be implanted with ICD to save one life over a 5-year period.
Keywords: Amiodarone, Arrhythmias, Cardiac, Cardiomyopathies, Death, Sudden, Cardiac, Defibrillators, Implantable, Geriatrics, Heart Failure, Primary Prevention, Stroke Volume, Survival, Ventricular Function, Left
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