Abstract 4136989: Association of alternating PR intervals with paroxysmal atrioventricular block in patients with right bundle branch block following cardiac surgery

Background: We previously observed a positive correlation between QRS duration and the preceding RP interval in sinus rhythm in certain patients experiencing new onset left bundle branch block (LBBB) after transcatheter aortic valve replacement (TAVR). This unique phenomenon, termed inverse decremental conduction ( IDC ) or Yan conduction, prompted us to investigate whether IDC in the left bundle could manifest as AV conduction in an IDC pattern in patients with preexisting right bundle branch block (RBBB) and its association with atrioventricular block (AVB). Methods: 12 lead ECGs, available in-patient telemetry and mobile cardiac outpatient telemetry were reviewed in patients with sinus rhythm and preexisting RBBB who developed paroxysmal AVB requiring temporary or permanent pacemaker within 7 days following any types of cardiac surgery from 2014 to 2023 in Lankenau Medical Center. Results: A total of 9 patients (5 males) with a mean age of 71±15 years were identified to exhibit PR interval changes consistent with IDC prior to paroxysmal AVB. Among these patients, 6 had undergone TAVR, while the remaining 3 had undergone surgical aortic valve replacement, mitral valve repair, and ventricular septal defect repair, respectively. Specifically, PR interval alternation in the setting of RBBB occurred during sinus rhythm in a pattern that the longer RP interval is followed by a longer PR interval (Figure 1). This pattern exhibits the following features: 1) 8 of 9 patients had RBBB plus left anterior fascicular block (LAFB); 2) PR alternation occurred at sinus rates from 68 to 91 bpm within 5 days following surgical procedures; 3) proximal AVB occurred within 1 to 12 hours after PR interval alternation began. A positive correlation was established between PR and preceding RP interval in 2 of 9 patients whose telemetry data were available for analysis ( Figure 2A ). In a patient with RBBB who developed paroxysmal AVB without IDC changes in the PR interval post TAVR, intracardiac recording showed a decrease in AH interval but an increase in HV interval with slowing heart rates ( Figure 2B ), indicating that decremental conduction in AV node can mask IDC in Purkinje system. Conclusion: 1) PR alternation with longer PR following longer preceding RP interval in presence of RBBB, likely due to IDC in left bundle, heralds paroxysmal AVB; 2) PR interval changes resulting from IDC in left bundle in the setting of RBBB may be masked by decremental conduction in AV node.