Abstract Introduction Cardiac resynchronization therapy (CRT) is a recommended therapeutic measure for patients with heart failure. Heart failure is a major morbidity amongst patients with adult congenital heart disease (ACHD). However, the data on the efficacy and safety of CRT amongst ACHD is limited. Methods Data was analyzed from a retrospective cohort of patients with a known diagnosis of ACHD and implantation of CRT between 2015-2022. The primary outcome was echocardiographic response to CRT. This was defined as either:1) an increase in systemic ventricular ejection fraction (EF) of ≥5% in patients with EF <50% (therapeutic) or 2) maintenance of EF in patients with EF≥50% (preventative). Secondary outcomes included change in QRS duration, heart failure admissions, death and CIED (cardiovascular implantable electronic devices) infection during follow up. The outcomes were also assessed by subgroup of systemic left or right ventricle systemic ventricle. Results Our cohort included 46 patients, 96% male and average age was 54±14 years. 26 patients had a systemic left ventricle (56.6%) and 20 patients had a systemic right ventricle (44.4%). The indication for CRT implantation was 1) Reduced EF with wide QRS (n=10, 22%), 2) Reduced EF and RV (right ventricular) pacing (n=22, 49%), and 3) Normal EF with RV pacing (n=14, 33%). 25 patients (55%) had an implanted defibrillator at baseline. Primary outcome amongst patients with preserved EF at baseline was achieved in 22/32 patients (68.7%) and was achieved in 12/14 patients (85.7%) amongst patients with reduced EF at baseline. During follow up, QRS duration was shortened in 68.7%, 13 patients had heart failure admissions (30%), 4 patients underwent heart transplants/mechanical support device implantation (8.6%), death occurred in 11 patients (24%) and 3 had CIED infection (7%). There was no significant difference in complication or efficacy rates between the left systemic and right systemic group. Conclusion CRT is effective in patients with ACHD both as a therapeutic and as a preventative measure for heart failure. There was no difference in clinical response to CRT between patients with SRV compared to SLV. The percentage of patients with a safety outcome was relatively high in this subpopulation due to advanced ACHD.
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