Abstract 1358: Reentry within the Working Myocardium is not the Sole Mechanisms by which Ventricular Fibrillation is Maintained
Background: For well over 50 years, it has been assumed that ventricular fibrillation (VF) is maintained solely by reentry in the working myocardium. This hypothesis has never been tested by recording VF with electrodes spaced sufficiently close together to map activation sequences in 3-dimensions.
Methods and Results: We recorded for 10 min during VF from the region of insertion of the anterior papillary muscle in the left ventricle of 4 open-chest pigs. A 3-D transmural unipolar electrode array consisting of a 9×9 array of needles with 2-mm spacing and 6 electrodes 2 mm apart on each needle was used to record from the working myocardium. The numbers of wavefronts, foci and reentrant circuits per sec were counted. A focus was identified when a wavefront appeared de novo within the central portion of the mapped region, insuring that it did not arise from another wavefront nor propagate into the mapped region from outside it. While intramural reentry was present early but not late during VF in the mapped region, foci were numerous and increased as VF continued (Figure⇓).
Conclusion: Intramural foci are present during VF in pigs and, as VF continues, increase in incidence while the incidence of reentry in working myocardium decreases. These results suggest that, particularly after the first 2 min of VF, mechanisms other than reentry in the working myocardium maintain VF. It remains to be determined if these mechanisms consist of abnormal automaticity, afterdepolarizations, or reentry in which Purkinje fibers form all or part of the circuit.