New data from the Swedish Heart Failure Registry indicate the use of an implantable cardioverter defibrillator (ICD) in patients with heart failure with reduced ejection fraction (HFrEF) is associated with a significant reduction in all-cause mortality at both one and five years. This finding is in keeping with current European Society of Cardiology (ESC) guidelines for heart failure, which advocate using ICDs for the primary prevention of sudden cardiac death in patients with HFrEF.
Speaking at the ESC Congress (ESC 2019; 31 August–4 September, Paris, France), study investigator Benedikt Schrage (Department of General and Interventional Cardiology, University Heart Center Hamburg, Hamburg, Germany) said that the current ESC recommendations of ICD use “were based on trials that were initiated ≥20 years ago and might not represent characteristics and treatments of a contemporary HFrEF cohort”. He added that a decline in the incidence of sudden cardiac death alongside improved outcomes in patients with HFrEF “have raised further questions regarding the benefits of primary prevention with ICD”.
Therefore, the aim of the present study—which was simultaneously published in Circulation—was to review the association between the use of ICD for primary prevention and all-cause mortality in a contemporary and large HFrEF cohort. Using data from the Swedish Heart Failure Registry, Schrage and colleagues identified 16,702 patients who (according to ESC guidelines) were eligible for primary prevention with an ICD. Of these, 10% had actually been treated with an ICD. The investigators then used propensity matched scoring to compare outcomes of 1,305 ICD patients with 1,305 non-ICD patients. The primary outcomes were the one-year and five-year rates of all-cause mortality. Secondary outcomes included the one- and five-year rates of cardiovascular death.
At one year, significantly fewer ICD patients had died than non-ICD patients, with absolute risk reduction of 4.2%. All-cause mortality was also reduced in the ICD group at the five-year point but the absolute risk reduction was lower (2.1%). Gerhard Hindricks (Department of Electrophysiology, Heart Center Leipzig at University of Leipzig, Leipzig, Germany), in the discussion following the presentation of the study, said the finding that the benefit on all-cause mortality appeared to decrease after a year was “difficult to explain”. He noted: “Other ICD studies have shown that if there is an effect [with ICD primary prevention], it is consistent over time.”
According to Schrage, ICD use was also associated with a significant reduction in cardiovascular mortality at one year (but not at five years). Furthermore, the results of the study were consistent in all evaluated subgroups (including women and patients with ejection fraction ≤30%).
However, he said that there were some important limitations to the study; these included “the potential impact of residual and unmeasured confounders”, and that “the limited sample size of the matched cohort might have prevented the observation of significant differences in the subgroup analyses”. The most important limitation though, Schrage explained, was that the study was observational and, therefore, showed an “association between exposure and outcome; it did not show causality”.
“These findings support current ESC guideline recommendation for primary prevention with ICD in patients with HFrEF. Furthermore, these findings call for better implementation of primary prevention with ICD in clinical practice,” he concluded.
For Hindricks, the study was interesting but raised more questions than it answered; he added that a randomised controlled trial was needed to provide answers. He went on to announce that the European Commission is to fund a new, industry-independent, trial—PROFIT—of ICD for primary prevention in the setting of heart failure post myocardial infarction.
Schrage told Cardiac Rhythm News: “In the past, concerns regarding the benefit in patients treated with guideline-recommended heart failure medications and high perception of contraindications could have reduced use of ICDs. The results of our study might thus encourage better implementation in clinical practice.”