A simplified approach for evaluating sustained slow pathway conduction for diagnosis and treatment of atrioventricular nodal reentry tachycardia in children and adults

Purpose: During incremental atrial pacing in patients with atrioventricular nodal reentrant tachycardia, the PR interval often exceeds the RR interval (PR > RR) during stable 1:1 AV conduction. However, the PR/RR ratio has never been evaluated in a large group of patients with pacing from the proximal coronary sinus and after isoproterenol challenge. Our study validates new site of pacing and easier method of identification of PR > RR. Material and methods: A prospective protocol of incremental atrial pacing from the proximal coronary sinus was carried out in 398 patients (AVNRT 228 and control-170). The maximum stimulus to the Q wave interval (SQ = PR), SS interval (S-S), and Q-Q (RR) interval were measured at baseline and 10 min after successful slow pathway ablation and after isoproterenol challenge (obligatory). Results: The mean maximum PR/RR ratios at baseline were 1.17 +/- 0.24 and 0.82 +/- 0.13 (p < 0.00001) in the AVNRT and controls respectively. There were no PR/RR ratios >= 1 at baseline and after isoproterenol challenge in 12.3% of the AVNRT group and in 95.9% of the control group (p < 0.0001). PR/RR ratios >= 1 were absent in 98% of AVNRT cases after slow pathway ablation/modification in children and 99% of such cases in adults (P = NS). The diagnostic performance of PR/RR ratio evaluation before and after isoproterenol challenge had the highest diagnostic performance for AVNRT with PR/RR > = 1 (sensitivity: 88%, specificity: 96%, PPV-97%, NPV-85%). Conclusions: The PR/RR ratio is a simple tool for slow pathway substrate and AVNRT evaluation. Eliminating PR/RR ratios >= 1 may serve as a surrogate endpoint for slow pathway ablation in children and adults with AVNRT.