Conduction system pacing showed inferior outcomes compared to biventricular pacing in adults with heart failure and left bundle-branch block.

IMPORTANCE: Conduction system pacing (CSP) is a promising and potentially cost-effective alternative to biventricular pacing (BiVP) in patients with heart failure with reduced ejection fraction (HFrEF) and left bundle-branch block (LBBB), but its impact on heart failure (HF) outcomes remains uncertain. OBJECTIVE: To compare CSP vs BiVP on an HF-related outcome in patients with HFrEF and LBBB. DESIGN, SETTING, AND PARTICIPANTS: PhysioSync-HF (Conduction System Pacing Versus Biventricular Resynchronization in Patients With Chronic Heart Failure) was an investigator-initiated, multicenter, noninferiority randomized clinical trial enrolling participants from November 2022 to December 2023 with 12 months of follow-up at 14 hospitals across all regions of Brazil. Adults with symptomatic HFrEF (New York Heart Association NYHA] classes II through III), left ventricular ejection fraction (LVEF) of 35% or less, and LBBB (QRS duration ≥130 milliseconds) were eligible for inclusion. Data were analyzed from May to August 2025. INTERVENTION: Patients were randomized 1:1 to either CSP (preferentially left bundle-branch area pacing) or BiVP. MAIN OUTCOMES AND MEASURES: The primary outcome was a hierarchical composite of death, HF hospitalizations, urgent HF visits, and change in LVEF at 12 months. The prespecified noninferiority margin for the odds ratio (OR) was 1.2. RESULTS: A total of 173 patients (median [IQR] age, 62 years [56-68]; 86 female patients [49.7%]; 115 (66.5%) with dilated cardiomyopathy; median [IQR] LVEF, 26% [22%-31%]; median [IQR] QRS, 180 milliseconds [170-200]) were included. At 12 months, CSP failed to meet noninferiority and was inferior to BiVP for the primary end point (OR, 2.36; 95% CI, 1.37-4.06; P = .99 for noninferiority; P = .002 for between-group difference). The time-to-event composite of death, HF hospitalizations, or urgent HF visits was higher in CSP (hazard ratio, 2.35; 95% CI, 0.99-5.61). Mean (SD) LVEF increased to 35% (12%) with CSP and 39% (12%) with BiVP (mean difference, 3.8%; 95% CI, 0.3%-7.3%). Relative to baseline, both groups had comparable improvements in QRS duration, Kansas City Cardiomyopathy Questionnaire Overall Summary Score, NYHA class, and natriuretic peptide levels. Total direct medical cost related to the procedure and heart failure care was the equivalent of $7090 (95% CI, $5779-$8648) lower in patients randomized to CSP at 12 months. CONCLUSIONS AND RELEVANCE: In patients with HFrEF and LBBB, CSP was inferior to BiVP for a composite of death, HF hospitalizations, urgent HF visits, and change in LVEF at 12 months. These findings do not support the routine use of CSP as the first-line resynchronization strategy in this population. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT05572736.