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(Circulation. 1999;99:949-962.)
© 1999 American Heart Association, Inc.

Basic Science Reports

Differential Effects of a Segment of Slow Conduction on Reentrant Ventricular Tachycardia in the Rabbit Heart

Kai Haberl, MD; Maurits Allessie, MD, PhD

From the Department of Physiology, Cardiovascular Research Institute Maastricht, Maastricht University, Netherlands.

Correspondence to Prof Dr M.A. Allessie, Department of Physiology, Cardiovascular Research Institute Maastricht, Maastricht University, PO Box 616, 6200 MD Maastricht, Netherlands.

Background—The purpose of this study was to compare differential effects of a segment of slow conduction during ventricular tachycardia (VT) due to depression of the action potential and electrical uncoupling.

Methods and Results—In 33 Langendorff-perfused rabbit hearts, a ring of anisotropic left ventricular subepicardium was created by a cryoprocedure. Reentrant VT was produced by incremental pacing. Slow conduction in a segment of the ring was created by selective perfusion of the LAD with 10 mmol/L potassium or 0.75 mmol/L heptanol. As a result, VT cycle length increased from 193±34 to 235±37 ms (potassium) and 227±42 ms (heptanol). Reset curves were made by applying premature stimuli proximal to the area of depressed conduction. In a ring of uniform anisotropic tissue, the reset curve was almost completely flat. Electrical uncoupling of part of the ring (nonuniform anisotropy) resulted in a mixed reset curve. In both substrates, early premature beats failed to terminate VT. Depression of part of the ring by increasing K⁺ resulted in a completely sloped reset curve, indicating a gap of partial excitability. Under these conditions, in 19 of 24 hearts, premature beats terminated VT by conduction block in the high K⁺ area.

Conclusions—The nature of the area of slow conduction determines the type of reset response and the ability to terminate VT.

Key Words: tachycardia • conduction • ventricles • electrophysiology