The Optimal Timing of Primary Prevention Implantable Cardioverter-Defibrillator Referral in the Rapidly Changing Medical Landscape

The use of implantable cardioverter-defibrillators (ICDs) significantly reduces the risk of mortality in patients with heart failure with reduced ejection fraction (HFrEF). Current guidelines, which are based on seminal clinical trials published nearly 2 decades ago, recommend that patients be on optimal medical therapy for HF for a minimum of 3 months before referral for prophylactic ICD. This waiting period allows for left ventricular reverse remodelling and improvement in HF symptoms, which may render primary prevention ICD implantation unnecessary. However, medical therapy for HFrEF has significantly evolved since the publication of these landmark trials. Given the plethora of medical therapy options now available for HFrEF, it is appropriate to reassess the duration of this waiting period. In the present review, we examine the landmark randomised trials in primary prevention of sudden cardiac death in patients with HFrEF, summarise the novel medical therapies (sacubitril-valsartan, sodium-glucose cotransporter 2 inhibitors, ivabradine, vericiguat, and omecamtiv mecarbil) that have emerged since the publication of those trials, discuss the optimal timing of ICD referral, and review subtypes of nonischemic cardiomyopathy where timing of ICD insertion is guided by alternative criteria. With the steps now needed to optimise medical therapy for HFrEF, in terms of both classes of drugs and doses of each agent, it can easily take up to 6 months to achieve optimisation. Following that, waiting periods of 3 months for ischemic cardiomyopathy and 6 months for nonischemic cardiomyopathy may be required to allow adequate reverse remodelling before reevaluating for ICD implantation.