Individuals with heart failure (HF) and diabetes generally have more severe HF and more comorbidities than those with HF and no diabetes, and the former may therefore have an increased risk of competing causes of death to arrhythmic death.

In the DANISH trial (The Danish Study to Assess the Efficacy of Implantable Cardioverter Defibrillators [ICDs] in Patients With Nonischemic Systolic Heart Failure on Mortality), primary prophylactic ICD implantation, compared with usual care, significantly reduced the rate of sudden cardiovascular death, but not all-cause mortality.1 We have previously examined the effect of ICD implantation according to diabetes status in the DANISH trial and found no statistically significant interaction between diabetes and the effect of ICD implantation.2 However, given that diabetes is a chronic disease, which can cause various systemic adverse effects over the long term, we conducted an extended follow-up study of the DANISH trial, adding 4 years of additional follow-up, to examine the long-term effects of primary prophylactic ICD implantation, according to diabetes status.

The data that support the findings of this study are available from the corresponding author on reasonable request. The design of the DANISH trial has been published and described previously.1,3 In brief, 1116 patients with nonischemic HF with reduced ejection fraction (HFrEF) were enrolled from 5 ICD-implanting centers in Denmark and randomized in a 1:1 ratio to ICD implantation or usual care. In the present analysis with extended follow-up, patients were followed from randomization until death or May 18, 2020, whichever came first, and no patients were lost to follow-up. The primary outcome was death from any cause, and secondary outcomes were cardiovascular death and sudden cardiovascular death. The protocol was approved by the ethics committee in the Capital Region of Denmark (H-D-2007-0101), and all participants gave written informed consent.

The effect of ICD implantation versus usual care was evaluated using the Kaplan-Meier estimator, Aalen-Johansen estimator, and Cox proportional hazards regression models, stratified according to center and status with respect to cardiac resynchronization therapy implantation. Data were analyzed according to the intention-to-treat principle. A P-value of 0.05 was considered statistically significant.