VENTRICULAR-FIBRILLATION IS NOT ALWAYS DUE TO MULTIPLE WAVELET REENTRY

Introduction: It is not known whether ventricular fibrillation (VF) is always caused by multiple wavelet reentry, or if it could also be cau sed by a single wandering reentrant wavefront. Activation mapping of t he entire ventricles during VF is practically impossible. Methods and Results: We studied VF in a two-dimensional sheet of left ventricular subepicardial tissue of isolated, Langendorff-perfused pig hearts. Lef t and right endocardial cryoablation via probes filled with liquid nit rogen caused coagulation necrosis of the right ventricle, interventric ular septum, and most of the left ventricular wall, leaving a thin sub epicardial layer intact. Left ventricular epicardial activation patter ns were constructed based on simultaneous recording of 128 unipolar ex tracellular electrograms. Regular pacing through a central electrode b efore and after freezing revealed that, following cryoablation, the ac tivation pattern no longer showed evidence of involvement of the Purki nje system, and that it was compatible with propagation through a two- dimensional anisotropic tissue sheet. VF was induced by burst pacing. When the mass of surviving subepicardium was < 10 g, no VF could be in duced; when it was between 10 and 20 g, VF was nonsustained; when it w as > 20 g, VF was sustained. Unipolar extracellular electrograms durin g VF before and after cryoablation could not be distinguished from eac h other; however, epicardial activation patterns were markedly differe nt. In the intact left ventricle, up to six different wavefronts were simultaneously present during a 100-msec time window. In the ''frozen heart,'' during a period of about 0.5 seconds, at most two wandering r eentrant waves were simultaneously present; sometimes only one reentra nt wave was seen in a 100-msec time window. Conclusion: The extracellu lar waveform during VF can be caused by different forms of reentry: mu ltiple wavelet reentry (on the order of six different wavefronts), two independent wandering reentrant waves, and a single wandering reentra nt wave.