The effect of anomalous pathway (AP) location and conduction time on the cycle length (CL) and sustainability of paroxysmal A-V reentrant tachycardia was studied in 15 dogs, using an anomalous pathway simulator (APS). The APS was a programmable digital electronic circuit with ability for unidirectional conduction, ventricular sensing, adjustable delay, and atrial stimulation. Contiguous pairs of ventricular sensing electrodes were placed along the A-V ring in each dog at the following sites: anterior, posterior, and lateral right (AR, PR, and LR) and anterior, posterior, and lateral left (AL, PL, and LL) and septal (S). There were significant differences in the CL of tachycardias among the tested sites (P less than 0.01). The CL of tachycardias from the LL site was significantly longer and from the PR site significantly shorter than that from the other sites (P less than 0.05). These differences in CL of tachycardias in relation to the AP location were explicable in terms of corresponding variation in conduction times of the various components of the tachycardia circuit (e.g., intra-atrial, A-V nodal, intraventricular conduction times). The differences in magnitude of the CL of tachycardias, although significant, were small. It was also found that all sites allowed maintenance of tachycardias up to an AP conduction time of 10 ms. In 27% of experiments, atrial refractoriness prevented sustained tachycardias at pathway delays of 1 ms. The relationship between AP conduction time and CL of tachycardias was exponential.
Effects of Verapamil and Ibutilide on Atrial Fibrillation and Postfibrillation Atrial Refractoriness
