We appreciate the comments from Dr. Canpolat. He proposes a strategy involving early physiologic resynchronization and cardiac magnetic resonance (CMR) imaging-guided risk stratification to identify patients who may benefit from implantable cardioverter-defibrillator (ICD) therapy.

Over the past two decades, recommendations for ICD implantation in patients with nonischemic heart failure and reduced ejection fraction (HFrEF) have varied. The DANISH (Danish Study to Assess the Efficacy of ICDs in Patients with non-ischemic Systolic Heart Failure on Mortality) trial, with median follow-up periods of 5.6 and 13.2 years, respectively, found that ICD implantation did not reduce all-cause mortality in patients, although it did significantly reduce the risk of sudden cardiac death (SCD).1,2 Consequently, the 2021 ESC heart failure guidelines downgraded ICD implantation in nonischemic HFrEF to a Class IIa recommendation, whereas US guidelines maintained a Class I recommendation.3,4 In the 2022 AHA/ACC/HFSA guideline, ICD therapy is recommended for the primary prevention of SCD in patients with nonischemic HFrEF (LVEF <35%), NYHA Class II or III symptoms despite chronic guideline-directed medical therapy (GDMT), and an expectation of meaningful survival exceeding one year.4

Recently, we reported a case in which left bundle branch area pacing (LBBAP) reversed left bundle branch block (LBBB) and improved left ventricular (LV) dysfunction in a patient with nonischemic heart failure and reduced ejection fraction (HFrEF) and LBBB.5 Over the past two years, the patient received treatment with a beta-blocker, sacubitril/valsartan, metformin, and dapagliflozin. Despite this, the patient's ejection fraction (EF) decreased from normal to 38% in the past year, indicating that guideline-directed medical therapy (GDMT) has not adequately improved cardiac function. Further decline in EF may occur if the current treatment regimen continues. Therefore, in accordance with the 2022 AHA/ACC/HFSA guideline,4 we believe ICD implantation is a reasonable consideration for this patient.

Optimized drug therapy and cardiac resynchronization therapy (CRT) significantly improve outcomes and can mitigate the benefit of an ICD, underscoring the importance of careful patient selection for ICD implantation. In patients with LBBB and nonischemic HFrEF, CRT has the potential to reverse LBBB and restore normal cardiac function, thereby obviating the need for ICD implantation. However, approximately one-third of patients do not respond to left bundle branch pacing (LBBP),6 raising the question of routine ICD implantation in patients eligible for CRT. The HeartSync-LBBP randomized clinical trial by Chen et al., 83% of patients with LBBP, received routine ICD implantation.7

Given the challenges in identifying patients most likely to benefit from ICD therapy, cardiac MRI has been used for risk stratification. In patients with nonischemic systolic heart failure, late gadolinium enhancement (LGE) predicted all-cause mortality. However, ICD therapy did not improve survival in patients with LGE,8 suggesting that the absence of LGE on CMR can identify low-risk patients with LBBB and nonischemic cardiomyopathy who may not require ICD implantation9 and LGE did not identify patients who would benefit from ICD implantation.8 Further work is required to identify patients who are more likely to benefit from ICD implantation.

We thank Dr. Canpolat for encouraging a reconsideration of these important issues, and we would like to use this strategy in our practice.