Demonstration of an Excitable Gap in the Common Form of Atrioventricular Nodal Reentrant Tachycardia

Premature ventricular depolarizations were introduced during sustained atrioventricular nodal reentrant tachycardia ("slow-fast" type) in a single patient during electrophysiological study. Preexcitation of the atrium with retrograde His bundle capture occurred over an 85 msec range of coupling intervals between the last antegmde His bundle depolarization and the first retrograde His bundle depolarimtion associated luith the premature beat (H₁ - H₂ interval). The interval between the retrograde His bundle depolarization (H₂) and the retrograde atrial depolarization (A₂) remained constant over this 85 msec excitable gap as the H₁-H₂ interval decreased. This indicates the presence of fully excitable tissue luithin the retrograde fast pathway of the reentrant circuit during the tachycardia and demonstrates the utility of this technique for defining the extent and conduction properties of the excitable gap in reentrant arrhythmias