Conduction system pacing vs biventricular pacing in patients with left bundle branch block and resynchronization therapy indication. CONSYST-CRT trial secondary findings

Abstract Background Randomized studies comparing conduction system pacing (CSP) with biventricular pacing (BiVP) are scarce and do not include clinical outcomes. Moreover, the percentage of crossover from CSP to BiVP is high. Crossover rate in the CONSYST-CRT trial was 26.9% (18/67) from CSP to BiVP and 7.5% (5/67) from BIVP to CSP. Purpose As half of the crossovers from CSP to BiVP in the CONSYST-CRT trial presented intraventricular conduction disease (IVCD), a superiority subanalysis in the left bundle branch block (LBBB) group (n=75) was performed. The objective was to test if CSP was superior to BiVP in LBBB patients. Methods CONSYST-CRT is a randomized, controlled, noninferiority trial (NCT05187611). 134 patients with CRT indication were randomized to BiVP or CSP and followed up for 12 months. Crossover was allowed when the primary allocation procedure failed. The AV interval was optimized with fusion. LBBB was defined according with Strauss criteria. Non-prespecified analysis in patients with LBBB (without AV block) was performed. Primary combined endpoint was all-cause mortality, cardiac transplant, heart failure hospitalization, or left ventricular ejection fraction (LVEF) improvement <5 points at 12-month. Secondary endpoints were: LVEF increase; LV end-systolic volume (LVESV) decrease; echocardiographic response (≥15% LVESV decrease); a combined endpoint of all-cause mortality, cardiac transplant, heart failure hospitalization; QRS shortening; septal flash correction; and NYHA functional class. Intention-to-treat analysis. Results Seventy-five patients presented LBBB (37 in the CSP arm and 38 in the BiVP arm). Mean age was 68 ± 9 years, 36% (27/75) were women, and 24% (18/75) had ischemic cardiomyopathy. At baseline, LVEF was 27 ± 7% and baseline QRS interval was 176 ± 24 ms. Mean NYHA class was 2.3 ± 0.7. The only difference between groups was a higher percentage of patients with ischemic cardiomyopathy in de BiVP group 34.2% (13/38) compared to CSP 13.5% (5/37) (p=0.04). Percentage of crossovers was 13.5% (5/37) and 7.8% (3/38) in the CSP and BiVP arm, respectively. Incidence of the primary endpoint was 10.8% (4/37) and 26.3% (10/38) for CSP and BiVP respectively (p=0.08, for superiority). Superiority was not demonstrated for any of the secondary endpoints however, there was a trend towards better results with CSP. The combined endpoint of all-cause mortality, cardiac transplant and heart failure hospitalization had an incidence of 5.4% (2/37) vs 18.4% (7/38) (p=0.08). Intention-to-treat, per-protocol and treatment-received analysis showed similar results. Figure and Table. Conclusion Superiority of CSP in patients with LBBB and resynchronization therapy indication was not demonstrated; although there was a tendency towards more improvement with CSP compared to BiVP. CONSYST Endpoints LBBB