Among patients undergoing TAVR, the characteristics and mechanisms causing atrioventricular (AV) conduction block during the procedure differed from those after the procedure, according to a study published Dec. 10 in JAMA Cardiology.

Jonathan W. Waks, MD, et al., conducted a single-center, prospective cohort study of 409 patients (mean age, 78.5 years; 44.5% women) with severe aortic stenosis and without a pre-existing pacemaker who underwent TAVR. Most (90%) patients received a balloon-expandable valve; the remainder (10%) received a self-expanding valve.

A 12-lead electrocardiogram (ECG) was recorded before and after TAVR and daily until discharge. Additionally, an electrophysiologic (EP) study was performed immediately before and after the valve placement. The primary endpoint, development of new high-grade AV conduction block, was defined as either complete heart block or Mobitz II second-degree AV block.

Results showed that overall, 40 patients developed heart block requiring permanent pacemakers. Of these, 15 developed heart block during TAVR, which remained persistent in all patients. Of the 25 blocks that developed after TAVR (delayed block), 20 were paroxysmal and relatively brief. Findings also revealed that block localized to the AV node in six patients during TAVR, which all resolved, and in three patients after TAVR. Infranodal block occurred in seven patients during TAVR and in 22 patients after TAVR.

Notably, the only ECG or EP predictor for block during, but not after, TAVR was pre-existing right bundle branch block. For delayed heart block, the best predictors included His-ventricular interval of ≥80 milliseconds, PR interval >300 milliseconds, and AV Wenckebach cycle length of ≥500 milliseconds, all at the end of the procedure.

In an accompanying editorial comment, Kristen K. Patton, MD, FACC, and Stephan Windecker, MD, write that the study results "support consideration of a more selective, physiology-guided strategy, which may include shorter observation for transient block, targeted monitoring for newly prolonged conduction intervals, and potential reduction in unnecessary pacemaker implantation."