Marked first-degree AV block may lead to complete AV block development

Abstract

Abstract Funding Acknowledgements Type of funding sources: None. Background First-degree atrioventricular (AV) block (PR interval >200 ms) is considered a benign condition with rare progression to a higher degree AV block. The site of block is determined with electrophysiological (EP) study and measurement of His-ventricular (HV) interval, with normal values below 55 ms. Prolonged HV interval > 70 ms is predictive of higher-grade AV block development. Marked first-degree AV block with a PR > 300 ms may lead to symptoms such as fatigue, poor exercise tolerance and palpitations. When symptoms are correlated to the conduction delay, permanent pacemaker (PPM) implantation to restore AV synchrony should be considered. In the Framingham heart study, patients with first-degree AV block had a threefold higher risk of PPM implantation. However, there is no data on the HV intervals and the rate of progression of conduction disorder in patients with marked first-degree AV block. Purpose To assess the predictive value of HV interval measurement in patients with marked first-degree AV block for progression to a higher-degree conduction disorder. Methods We prospectively evaluated consecutive patients with symptomatic marked first-degree AV block that underwent a PPM implantation. His electrograms were recorded during the implantation, and HV intervals were measured from the first deflection of the His signal to the earliest onset of ventricular activation on a 12-lead surface ECG. Patients were followed for 6 months with three out-patient visits, during which the PPM was temporarily inhibited to check for intrinsic AV conduction. Results Seventeen patients were evaluated between January 2020 and September 2022. Ten patients (59%) were male, and 7 (41%) were female, with an average age of 61 ± 19 years. All patients had markedly prolonged PR interval (383 ± 47 ms) and narrow QRS complex (100 ± 16 ms). Three patients (17%) had intermittent type 1 second-degree AV block, right bundle branch block was recorded in two (12%) and left anterior fascicular block in four (24%) patients. Except for one patient with a corrected atrial septal defect, there were no echocardiographic signs of structural heart disease with a left ventricular ejection fraction of 61 ± 5%. The HV intervals were on the upper limit of normal values at 54 ± 6ms and no patient had an HV interval above 70 ms. Two patients (12%) developed complete AV block during follow-up: one female, and one male, 28 and 83 years old, respectively, with a PR interval 392 and 363 ms, QRS 104 and 94 ms, and HV 57 and 48 ms. None of the two had any additional conduction blocks at the time of PPM implant. Conclusion In our cohort of patients with symptomatic first-degree AV block (PR>300 ms), two patients (12%) developed complete AV block despite normal HV intervals at the time of implant. Closer monitoring, beyond only EP measurements, of patients with markedly prolonged PR intervals is warranted for the potential progression of conduction disorder.