Electrical similarity, myocardial divergence: a comparative study of isolated and CHD-associated complete AV block

Background Congenital complete atrioventricular block (CCAVB) is a rare condition that occurs either in isolation or in association with structural congenital heart disease (CHD). Although the electrical abnormality is shared, the underlying pathophysiology and long-term prognosis may differ significantly. A direct, comprehensive comparison of the clinical characteristics and outcomes of these two distinct patient populations is lacking, as CHD cases are often excluded from larger studies. Purpose To compare the clinical characteristics, electrophysiological profile, growth, and biventricular function between patients with isolated CCAVB and those with CHD-associated CCAVB. Methods We conducted a retrospective, single-center analysis including 60 CCAVB patients, of whom 31 had isolated CCAVB and 29 had CHD-associated CCAVB. We systematically compared baseline presentation and medium-term follow-up data, with a specific focus on Holter monitoring, growth Z-scores, and serial echocardiographic assessment of ventricular size and function. Results The two groups were comparable in age, sex, and symptoms. Holter parameters showed no significant differences at baseline or follow-up, indicating a similar electrical disease burden. Growth parameters were also similar. However, striking differences emerged in myocardial structure and function. At presentation, the CHD group had significantly higher rates of impaired systemic ventricular function (20% vs. 0%; p=0.01), ventricular ectopy (18% vs. 3%; p=0.04), and right ventricular dilation (17% vs. 0%; p=0.01). These disparities widened at a median follow-up of 4 years, with the CHD group exhibiting higher rates of impaired systemic ventricular function (40% vs. 7%; p=0.01) and progressive RV dilation (28% vs. 0%; p=0.01). Subgroup analysis revealed that patients with L-Transposition of the Great Arteries (L-TGA) carried the highest burden of ventricular dysfunction (6/9, 66%). In contrast, those with patent ductus arteriosus (PDA) showed better preservation of systolic function, with all PDA cases maintaining preserved ejection fraction. The need for pacing also varied by subtype, being most frequent in L-TGA (5/9, 56%) and atrial septal defect (ASD) patients (4/7, 57%). Conclusion This study affirms a dual management paradigm for CCAVB: standardized electrical surveillance for all, complemented by anatomy-specific myocardial monitoring. The profoundly elevated risk in patients with L-TGA identifies systemic right ventricle anatomy as a critical priority for proactive heart failure and pacing management, underscoring that their prognosis is dictated by the vulnerable substrate, and may be worsened by the bradycardia.