Effectiveness of cardiac resynchronization therapy in adult congenital heart disease: A meta-analysis of biventricular and conduction system pacing outcomes

BACKGROUND: Patients with adult congenital heart disease (ACHD) often develop heart failure (HF). Cardiac resynchronization therapy (CRT) may provide benefit, but evidence is limited to observational studies and guidelines are extrapolated from acquired HF. OBJECTIVE: This study aimed to systematically evaluate the effects of CRT in ACHD, including both biventricular pacing (BiV) and conduction system pacing (CSP) strategies, on electrocardiographic, functional, and clinical outcomes. METHODS: We conducted a systematic review and meta-analysis following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines (PROSPERO CRD420251036152). PubMed, Embase, Web of Science, CINAHL, and Cochrane were searched until February 2025. Primary outcomes were changes in QRS duration, systemic ventricular function (SVF), and New York Heart Association (NYHA) class; secondary outcomes were HF hospitalizations and all-cause mortality. RESULTS: 25 studies (n = 796; 723 BiV, 73 CSP) were included. CRT was associated with significant QRS duration reduction (-23.1 ms; 95% confidence interval -31.6 to -14.7), SVF improvement (+7.8%; 5.9-9.6), and NYHA class reduction (-0.9; -1.2 to -0.5). Benefits extended to patients with a systemic right ventricle (QRS -27.7 ms; SVF +8.5%; NYHA -1.0). Pooled incidence rates of HF hospitalization and mortality were 4.3 and 3.2 per 100 patient-years, respectively. Early data suggest that CSP achieves comparable QRS narrowing with BiV, although long-term outcomes remain scarce. CONCLUSION: CRT in ACHD is associated with significant improvements in electrocardiographic, functional, and clinical outcomes, including patients with a systemic right ventricle. Although most evidence pertains to BiV, early reports on CSP are encouraging. Prospective, phenotype-specific studies with standardized outcomes are needed to optimize patient selection and pacing strategies.