Background: There are limited data regarding cardiac resynchronization therapy (CRT) in adult congenital heart disease (ACHD). We aimed to assess early and late outcomes of CRT amongst patients with ACHD.

Methods: We retrospectively studied ACHD patients receiving CRT (2004-2017). Clinical and echocardiographic data were analyzed at baseline, early (1.8±0.8 years) and late (4.7±0.8 years) follow-up after CRT.

Results: Fifty-four ACHD patients (median age 46 years, range 18-73 years, 74% male) had CRT (biventricular paced >90%) and were followed for 5.7±3.0 years.
Compared to baseline, CRT was associated with significant improvement at early follow-up in NYHA functional class, QRS duration and cardiothoracic ratio (P<0.05 for all); improvement in NYHA class was sustained at late follow-up.
Amongst patients with a systemic left ventricle (LV; n=39), there was significant increase in LV ejection fraction (LVEF) and reduction in LV end-systolic volume at early and late follow up (P<0.05 for both). For patients with a systemic right ventricle (RV; n=15), there was a significant early but not late reduction in systemic RV basal and longitudinal diameters.
Eleven patients died and 2 had heart transplantation unrelated to systemic ventricular morphology. Thirty-five (65%) patients responded positively to CRT but only baseline QRS duration was predictive of a positive response.

Conclusions: CRT results in sustained improvement in functional class, systemic LV size and function. Patients with a systemic LV and prolonged QRS duration, independent of QRS morphology, were most likely to respond to CRT.