Stability of an experimental atrioventricular reentrant tachycardia in dogs.

The factors leading to spontaneous block and instability of a reentrant tachycardia were studied with a computer model and in eight anesthetized dogs with an electronically simulated atrioventricular (AV) bypass tract. The bypass tract delay could be changed in a programmed sequence. AV nodal refractoriness in the dogs was increased with verapamil. Stability of the reentrant tachycardia was assessed by noting how rapidly cycle-length changes from a transient alteration in the bypass-tract delay time would dampen out and the tendency of the reentrant tachycardia to spontaneously block. There was close agreement between computer model predictions and experimental results. After a transient change in bypass tract delay time, dampened oscillations of the cycle length were noted. The degree of dampening was related to the slope of the AV nodal refractory curve. When the reentrant tachycardia operated on a steep portion of the refractory curve (slope steeper than -1), spontaneous oscillations and block developed. In the dog, the reentrant tachycardias terminated spontaneously either by an increase in amplitude of oscillations or by an increase in AV nodal refractoriness. We conclude that, for stable reentry, a reentrant circuit must have no conduction block and must be able to dampen out transient perturbations.