Adherence to Guidelines in Patients with Heart Failure and reduced Ejection Fraction before defibrillator implantation.

Background Guideline-directed medical therapy (GDMT) improves outcomes in patients with heart failure and reduced ejection fraction (HFrEF). Nonetheless, real-world adherence before implantable cardioverter-defibrillator (ICD) for primary prevention remains suboptimal. To evaluate adherence to GDMT among HFrEF patients referred for primary prevention ICD implantation at the Montreal Heart Institute (MHI); to identify treatment gaps at time of implantation, and to assess whether further optimization occurs afterward. Methods We retrospectively reviewed 364 patients with HFrEF who underwent first-time ICD implantation between 2018 and 2020. GDMT optimization was defined as achieving the target or maximally tolerated dose of beta-blockers (BB), mineralocorticoid receptor antagonists (MRA), and renin–angiotensin system inhibitors (ACEI, ARB, or ARNI). Results The cohort was predominantly male (80%), with a mean age of 64 years and mostly ischemic cardiomyopathy (63%). Although overall GDMT prescription rates were high (BB 94.6%, MRA 71.6%, ACEI/ARB/ARNI 87.6%), only about 10% were at target doses at baseline. After 12 months, optimization improved markedly for BB (96.9%) and MRA (91.4%), while rates for ACEI/ARB/ARNI remained unchanged. Arrhythmic events were comparable across groups, though slightly more frequent in patients optimized on ACEI/ARB/ARNI (12.7% vs. 5.1%, p=0.0308). Conclusion Most patients receive suboptimal GDMT at the time of ICD implantation, yet substantial optimization occurs afterward. Early ICD implantation in undertreated patients did not reduce arrhythmic events, highlighting the need to ensure comprehensive GDMT optimization before device implantation to improve outcomes and avoid unnecessary procedures.