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Letter by Littmann Regarding Article, "Association Between Use of Primary-Prevention Implantable Cardioverter-Defibrillators and Mortality in Patients With Heart Failure: A Prospective Propensity Score-Matched Analysis From the Swedish Heart Failure Registry".

Circulation. 2020;141:e646–e647. DOI: 10.1161/CIRCULATIONAHA.119.045175 e646 Laszlo Littmann, MD, PhD To the Editor: To reduce the risk of death in patients with heart failure with reduced ejection fraction, current guidelines recommend the use of a prophylactic implanted cardioverter-defibrillator (ICD). This recommendation was based on studies performed decades ago. Over the last 20 years, however, the rate of sudden cardiac death in such patients has decreased by more than 40%, possibly negating the benefit of ICD seen in older trials. In a study published in 2016 (DANISH [Danish ICD Study in Patients With Dilated Cardiomyopathy]), there was no mortality benefit from prophylactic ICD in patients with nonischemic cardiomyopathy.1 In a recent issue of Circulation, Schrage et al2 presented the results of a propensity score–matched analysis from the Swedish Heart Failure Registry (SwedeHF). In contrast to DANISH, they found that ICD use was associated with significant reduction in all-cause mortality within 1 year and 5 years. The results were consistent in all subgroups, including patients with nonischemic cardiomyopathy. The patient groups with and without ICDs were well matched for baseline variables. What could be behind the opposing results of DANISH and SwedeHF? One of the explanations proposed was that the DANISH trial might have been underpowered. This, however, would not explain the divergent results, because the number of patients with nonischemic cardiomyopathy was almost identical in the negative DANISH and the positive SwedeHF trials (1116 and 1126, respectively). The argument that meta-analyses continue to demonstrate benefit from ICDs is also problematic because most trials included in the analyses were performed when β-blockers were not used consistently and mineralocorticoid receptor antagonists were essentially not used. These 2 classes of drugs dramatically reduce the risk of sudden cardiac death. In observational studies, even when patient groups are apparently well matched for baseline variables, there is always a risk of residual confounders. In SwedeHF, such a confounder may very well have been differences in quality of care of patients with and without ICDs. In SwedeHF, only 10% of eligible patients had an ICD implanted. It seems possible and even probable that a higher percentage of patients who were referred for ICD implantation were originally treated by cardiologists and heart failure specialists compared with those who were not referred for ICD. Moreover, patients who had an ICD implanted were then more likely to be followed by a cardiologist than were patients without ICDs. Several studies have demonstrated that patients with heart failure treated by cardiologists rather than generalists are more likely to achieve target doses of evidence-based medications, resulting in improved outcomes.3–5 In SwedeHF, the patient groups were well-matched for classes of medications used, but the doses achieved were not reported. © 2020 American Heart Association, Inc. LETTER TO THE EDITOR Letter by Littmann Regarding Article, “Association Between Use of Primary-Prevention Implantable Cardioverter-Defibrillators and Mortality in Patients With Heart Failure: A Prospective Propensity Score-Matched Analysis From the Swedish Heart Failure Registry” Circulation