Twin atrioventricular nodes and accessory pathways in congenital heart diseases with abnormal atrioventricular connections: Association with the developmental hierarchy of cardiac morphology.

Twin atrioventricular (AV) nodes (TWAVNs) are common in heterotaxy syndrome. The purpose of this study was to investigate the presence and implications of TWAVNs and accessory pathways in congenital heart diseases (CHDs) with abnormal AV connections. A retrospective study of a 1980-2022 cohort with sufficient electrocardiographic (ECG) data for review was conducted. We enrolled 136 patients with heterotaxy syndrome, 70 with congenitally corrected transposition of the great arteries (ccTGA) (4 with Ebstein anomaly), 47 with double-inlet ventricle (DIV), and 63 with isolated AV canal defect. TWAVNs, detected in the same ECG (18%), in separate ECGs (70.8%), or after electrophysiological study (11.2%), were present in 43.4% of heterotaxy, 10.6% of DIV, 10% of ccTGA, and 1.6% of AV canal defect cases. Accessory pathways were noted in 11.4% of ccTGA and 4.4% of heterotaxy cases, but none of the DIV and AV canal cases. Actuarial incidence of supraventricular tachycardia (SVT) by age 10 was 0.354, 0.121, 0.022, and 0 in heterotaxy, ccTGA, DIV, and AV canal, respectively. In patients with TWAVNs, the risk of SVT varies according to the rate of TWAVNs in each CHD type, with risks of 65.5%, 58.3%, and 0% for TWAVNs rates >50%, 10%-50%, and <10%, respectively. Onset age of tachycardia did not differ between those with TWAVNs and those with accessory pathways. In CHD with abnormal AV connections, evidence suggested a developmental hierarchy in the propensity to exhibit TWAVNs, but not for accessory pathways. The earlier cardiac developmental errors occur, the higher the likelihood of TWAVNs and the greater the chance of SVT.