From benign to significant: adverse outcomes in patients with first degree AV block and syncope

Abstract Background First-degree atrioventricular (AV) block is traditionally considered benign; however, it is increasingly recognized as a marker for adverse outcomes, including pacemaker implantation. Patients with syncope and first-degree AV block represent a particularly challenging subgroup due to the difficulty predicting which patients are at risk for adverse outcomes, with current guidelines providing limited guidance for risk stratification. Purpose To address this knowledge gap by evaluating predictors of pacemaker implantation and adverse outcomes in patients with first-degree AV block and syncope. Methods The multicenter, prospective cohort study (BASEL IX) recruited patients >40 years presenting with syncope to the emergency department (ED) across 14 hospitals in nine countries. The SRS study, a US-based cohort enrolling patients ≥60 years with syncope, was used for external validation. Multivariable regression models were used to identify predictors of pacemaker implantation. Outcomes included pacemaker implantation and a composite of recurrent syncope, life-threatening arrhythmias, pacemaker implantation, and death. Subgroup analyses assessed the impact of PQ interval duration and beta-blocker use on the risk of pacemaker implantation and adverse clinical outcomes. Results First-degree AV block was present in 16.5% (329/2000) of patients and associated with higher rates of pacemaker implantation (28% vs. 12.9%, HR 3.8, 95% CI: 2.7–5.2, p<0.001) and serious adverse outcomes (45.3% vs. 25.7%, HR 2.2, 95% CI: 1.8–2.7, p<0.001) over a 2-year follow-up period. Key predictors of pacemaker implantation included right bundle branch block (RBBB), left anterior fascicular block (LAFB), prolonged QTc interval, diabetes, recurrent syncope and head injury. Patients requiring pacemakers within two years had median PR intervals of 240 ms at initial presentation, challenging guidelines focused on extreme PR prolongation. Beta-blocker use was not associated with adverse outcomes. Findings were consistent in the validation cohort with a 30-day follow-up, where first-degree AV block was present in 16% (272/1748) of patients and associated with a threefold increase in pacemaker implantation (HR 3.0, 95% CI 1.6–5.6, p<0.001). Conclusion First-degree AV block in patients presenting with a syncope is associated with a substantial risk of adverse outcomes, even when PR intervals are moderately prolonged. Subgroup with first-degree AV block