Mapping in the atrioventricular junction.

Ectopic conduction is defined as the premature exit of the cardiac impulse from the specialized conduction system across a damaged Purkinje-ventricular muscle interface. This anomalous form of atrioventricular (AV) conduction was induced in the dog heart by lidocaine injection of the His bundle-interventricular septum interface and by ischemic damage of the AV junction subsequent to anterior septal artery ligation in the dog heart. The electrocardiogram (ECG) manifestation of ectopic conduction is the loss of initial forces and replacement of the Q waves with delta waves. In order to verify these effects, the authors devised a multi-electrode, malleable plaque (63 electrode sites) that could be secured at the AV junction during venous occlusion in the open-chest, anesthetized dog. Preliminary maps indicated a dramatic change in activation that proceeded from apex to base of the heart in the control state and reversed after ischemic damage to the His bundle. In vitro, it was possible to induce ectopic conduction by lidocaine injection at the interface of the right bundle branch and septal muscle. Microelectrode studies demonstrated that foot potentials, for example, electrotonic, or subthreshold potentials mediated the connection from Purkinje to muscle in the damaged zone. In a recent set of experiments in vivo, subthreshold stimulation (STS) was delivered to simulate electrotonic potentials to the His bundle region, and right ventricular apex, using multipolar electrode catheters. In the normal heart, STS delivered as DC constant current or pulse trains (1000 Hz, 50 ms pulse duration) induced shortened P-R intervals and delta waves with or without bundle branch block patterns.(ABSTRACT TRUNCATED AT 250 WORDS)