Adding ICD Therapy to CRT on Basis of Myocardial Substrate

Study Questions:

What is the impact of additional implantable cardioverter-defibrillator (ICD) over cardiac resynchronization therapy (CRT) in a large study group of primary prevention heart failure patients?

Methods:

An observational multicenter consortium data network from France, Sweden, and the United Kingdom was queried. The cohort consisted of 5,307 patients with nonischemic dilated cardiomyopathy (DCM) or ischemic cardiomyopathy (ICM), no history of sustained ventricular arrhythmias, who underwent CRT implantation with a defibrillator (CRT-D, n = 4,037) or without a defibrillator (CRT-P, n = 1,270). Propensity score and cause-of-death analyses were used to compare outcomes.

Results:

After a mean follow-up of 41 months, ICM patients had better survival when implanted with CRT-D compared with CRT-P (hazard ratio for mortality, 0.76; 95% confidence interval, 0.62-0.92), whereas in DCM patients, no such difference was observed (hazard ratio, 0.92; 95% confidence interval, 0.73-1.16). Compared to CRT-D patients, the excess mortality in CRT-P recipients was related to sudden cardiac death in 8% among the ICM patients, but only in 0.4% of the DCM patients.

Conclusions:

In the setting of heart failure patients with CRT indication, DCM patients do not appear to benefit from additional primary prevention ICD therapy, as opposed to those with ICM.

Perspective:

Patients with DCM have a lower risk of sudden cardiac death than patients with ICM, and they are known to better respond to CRT than ICM patients. The widely accepted indications for ICD in patients with DCM were derived from studies, which while showing decreased mortality risk for all patients, failed to show statistically significant reduction in death rates in the subsets of patients with DCM. At least two meta-analyses of these trials, however, did find the mortality benefit. The recently published DANISH trial, which enrolled only DCM patients (N Engl J Med 2016;375:1221-30) likewise failed to show decreased mortality with an ICD, although the overall mortality in the trial was lower than expected. The current study is likely to continue to fuel the controversy about the putative additional benefit from an ICD in CRT patients or lack thereof; unfortunately, given its observational character, it cannot be definitive.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Prevention, Implantable Devices, EP Basic Science, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure

Keywords: Arrhythmias, Cardiac, Cardiac Resynchronization Therapy, Cardiomyopathies, Cardiomyopathy, Dilated, Death, Sudden, Cardiac, Defibrillators, Implantable, Electric Countershock, Heart Failure, Primary Prevention, Risk, Survival


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