Clinical and Electrophysiologic Characteristics Before and After Radiofrequency Ablation of Sustained Slow Atrioventricular Nodal Pathway Conduction

Objectives: This study examined the clinical and electrocardiographic characteristics and electrophysiologic determinants of sustained slow pathway conduction (SSPC) during sinus rhythm.

Background: SSPC during sinus rhythm in presence of dual atrioventricular (AV) nodal pathways has not been thoroughly studied.

Methods: We studied 30 consecutive patients (19 men), whose median age was 31 years (interquartile range: 22 to 48 years); their electrocardiograms revealed 2 different PR intervals during nearly identical sinus rates. We measured the short and long PR intervals and their differences and examined the electrophysiologic determinants of SSPC during slow pathway (SP) ablation in 12 patients.

Results: Among the 30 patients, 21 (70%) complained of major symptoms. The short and long PR intervals measured 202 ± 42 ms and 472 ± 110 ms, respectively, and their mean difference measured 270 ± 101 ms. During electrophysiologic studies, dual AV nodal and SSPC were observed in all patients. A markedly prolonged refractory period (593 ± 116 ms) and retrograde conduction block over the fast pathway (FP) were observed over a range of sinus cycle lengths (CLs). Ablation of the SP in 11 patients promoted FP conduction and shortened its effective refractory period from 593 ± 116 ms to 288 ± 90 ms. Over a median follow-up of 2 years (interquartile range: 1 to 3 years), all patients remained asymptomatic and without recurrences of SSPC or AV block.

Conclusions: Two distinct PR intervals during sinus rhythm indicated the presence of dual AV nodal pathways. SSPC was promoted by a markedly impaired bidirectional conduction over the FP at critical sinus CL. SP ablation safely and effectively eliminated SSPC in symptomatic patients.