Anisotropic reentry in a perfused 2-dimensional layer of rabbit ventricular myocardium

Background-Anisotropy creates nonuniformity in electrical propagation and m ay contribute to the occurrence of unidirectional conduction block and reen try. We describe the characteristics of reentrant tachycardia in a 2D layer of anisotropic ventricular myocardium. Methods and Results-A Langendorff-perfused epicardial sheet (1.0+/-0.4 mm, n=35) was created by freezing the intramural layers of the rabbit left vent ricle. Epicardial activation maps were constructed by use of different high -resolution mapping arrays connected to a mapping system. In 5 experiments, monophasic action potentials were recorded. In the intact left ventricle, no arrhythmias except VF could be induced. After freezing, programmed elect rical stimulation or rapid pacing led to the induction of sustained VT (cyc le length 130+/-11 ms). VT was caused by reentry around a functional line o f block oriented parallel to the epicardial fiber direction. Action potenti al recordings demonstrated that the central line of block was kept refracto ry by electrotonic currents generated by the depolarization waves propagati ng at either side of the line of block. At the pivot points of the line of block, the pronounced curvature of the turning wave and abrupt loading chan ges created an excitable gap of 30 ms in the reentrant pathway. Conclusions-In uniform anisotropic myocardium, reentry around a functional Z-shaped line of block may occur. The core of the circuit is kept refractor y by electrotonic currents. The pronounced wave-front curvature and abrupt loading changes at the pivot points cause local conduction delay and create a small excitable gap.