Clinical Response to Resynchronization Therapy

BACKGROUND: Randomized studies comparing conduction system pacing (CSP) with biventricular pacing (BiVP) are scarce and do not include clinical outcomes. OBJECTIVES: The CONSYST-CRT (Conduction System Pacing vs Biventricular Resynchronization Therapy in Systolic Dysfunction and Wide QRS) trial aimed to test the noninferiority of CSP as compared with BiVP in patients with an indication for cardiac resynchronization therapy, with respect to a combined clinical endpoint at 1-year follow-up. METHODS: A total of 134 patients with cardiac resynchronization therapy indication were randomized to BiVP or CSP and followed up for 12 months. Crossover was allowed when the primary allocation procedure failed. The atrioventricular interval was optimized to obtain fusion with intrinsic conduction. The primary combined endpoint was all-cause mortality, cardiac transplant, heart failure hospitalization, or left ventricular ejection fraction (LVEF) improvement <5 points at 12 months. Secondary endpoints were LVEF increase, LV end-systolic volume (LVESV) decrease, echocardiographic response (≥15% LVESV decrease), QRS shortening, septal flash correction, NYHA functional class improvement, and a combined endpoint of all-cause mortality, cardiac transplantation, and heart failure hospitalization. RESULTS: Sixty-seven patients were allocated to each group. Eighteen patients (26.9%) crossed from CSP to BiVP; 5 (7.5%) crossed over from BiVP to CSP. Noninferiority (NI) was observed for CSP compared with BiVP for the primary endpoint (23.9% vs 29.8%, respectively; mean difference -5.9; 95% CI: -21.1 to 9.2; P = 0.02) and for the combined endpoint of all-cause mortality, cardiac transplantation, and heart failure hospitalization (11.9% vs 17.9%; P < 0.01 NI); echocardiographic response (66.6% vs 59.7%; P = 0.03 NI); NYHA functional class (P < 0.001 NI); and QRS shortening (P < 0.01). LVEF, LVESV, and septal flash endpoint values were similar, but noninferiority was not met (14.1% ± 10% vs 14.4% ± 10%, -27.9% ± 27% vs -27.9% ± 28%, -2.2 ± 2.7 mm vs -2.7 ± 2.4 mm, respectively). CONCLUSIONS: CSP was noninferior to BiVP in achieving clinical and echocardiographic response, suggesting that CSP could be an alternative to BiVP. (Conduction System Pacing vs Biventricular Resynchronization Therapy in Systolic Dysfunction and Wide QRS [CONSYST-CRT]; NCT05187611).