Baseline electrocardiographic characteristics before occurrence of complete atrioventricular block following transcatheter aortic valve replacement

Background Complete atrioventricular block (CAVB) following transcatheter aortic valve replacement (TAVR) is primarily associated with mechanical compression of the penetrating portion of the His bundle, its branches, or less commonly the atrioventricular (AV) node. However, no prior systematic electrocardiogram (ECG) studies have investigated the site of the block or the origin of the escape rhythm (ER) in CAVB after TAVR. Aim To assess ECG characteristics of stable ERs during CAVB in patients who underwent TAVR. Methods Cases from 3 institutions were retrospectively analysed using 12-lead ECGs obtained before TAVR (ECG1), after TAVR but before CAVB (ECG2) and during CAVB (ECG3). ERs in ECG3 were defined as similar to the QRS in ECG2 if QRS morphology was similar in ≥10/12 leads, QRS durations differed by <10msec, and frontal QRS axes differed by <30°. The mechanism of ER was classified as "Junctional" if QRS morphology, duration and axis were similar between ECG 2 and 3, and as "Ventricular" if there were differences. In cases where ECG2 was unavailable, ERs in ECG3 were compared to ECG1, and were classified as "junctional" if similar, or "Unknown" if not. Results Of 58 cases included 60% were female, with a mean age of 81 years. Self-expandable valves were implanted in 64% of cases. At baseline (ECG1), 57% of patients had no conduction disturbances, 17% of patients had right bundle branch block (RBBB), and 9% had left bundle branch block (LBBB). After TAVR (ECG2), LBBB was observed in 70%, and RBBB in 17%. Two different ER morphologies were identified in 14% of patients. The first ER (ECG3) was presumed to have a junctional origin 41% of patients and a ventricular origin in 59%. Of patients with a presumed junctional origin to their ER, ECG2 had a LBBB pattern in 58%, and a RBBB pattern in 32%. Of patients with a presumed ventricular origin to their ER, ECG2 had a LBBB pattern in 78%, and a RBBB pattern in 7%. Conclusion ECG characteristics during and before CAVB provide insight regarding the site of conduction block following TAVR. Consistent with the anatomical regions typically affected by the prosthetic valve, a significant proportion of patients exhibited an ER presumably originating from the AV junctional area, with some likely involving the His bundle. Some presumed ventricular ERs also appeared to originate near the AV junctional area. Localizing the block to the AV junctional area, and particularly to the His bundle, may support the use of conduction system pacing in CAVB following TAVR.