The atrioventricular interval during pre-excited tachycardia: A simple way to distinguish between decrementally or rapidly conducting accessory pathways

Background Recognition of the presence and role of decremental fibers during wide QRS tachycardia requires carefully executed intracardiac studies. Objective This study sought to determine the value of the atrioventricular (AV) conduction time during pre-excited tachycardia to differentiate a fast from a decrementally conducting accessory pathway (AP). Methods Fifty-one patients with 56 pre-excited tachycardias were included in the study: Group I: 27 patients with 31 antidromic tachycardia (ADT) using an atriofascicular pathway, Group II: 2 patients with pre-excited tachycardia due to bystander AV conduction, Group III: 3 patients with ADT and a short AV Mahaim fiber, and Group IV: 19 patients with 21 ADT using a fast conducting right-sided AP. The AV interval was measured in the His bundle electrogram and related to the tachycardia cycle length (TCL) by making an AV/TCL index. Results An AV interval ≥ 150 ms during pre-excited tachycardia yielded a 91% sensitivity, 90% specificity, positive predictive value of 94%, and negative predictive value of 83% for AV conduction over a decrementally conducting pathway, whereas a ≥0.55 AV/TCL index yielded a sensitivity of 89%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 84%. In 3 of 4 patients with Mahaim fibers and a Conclusions An AV interval ≥150 ms during pre-excited tachycardia is a fast and reliable method for detecting a decrementally conducting AP. Correcting the AV interval by the tachycardia cycle length improved specificity and positive predictive accuracy.