Role of Structural Complexities of Septal Tissue in Maintaining Ventricular Fibrillation in Isolated, Perfused Canine Ventricle

INTRODUCTION: It is unclear how the patterns of wavelet propagation during ventricular fibrillation (VF) vary between structurally different tissues. We hypothesized that the structural complexities of septal tissue influence the maintenance of reentrant wavelets in the ventricle. METHODS AND RESULTS: Endocardial activation patterns during VF were analyzed in the isolated, perfused canine right ventricular (RV) free wall (n = 9), interventricular septum (n = 5), and left ventricular (LV) free wall (n = 6) using a computerized mapping system (2-mm resolution) with 120-msec consecutive windows. Each tissue sample was cut progressively to reduce the tissue mass until the VF was terminated. More wavelets were seen in the septa than in the RV and LV free walls at baseline (P = 0.004), and VF in the septa displayed a shorter cycle length than in the RV and LV free walls (P = 0.017). As the tissue mass decreased, VF became successively more organized in all regions: the number of wavelets decreased and the cycle length of VF lengthened. Single and "figure-of-eight" stationary, reentrant wavelets often were mapped after tissue mass reduction in the RV free walls and rarely in the LV free walls, but they were not observed in the septa. Less critical mass was required to maintain VF in the septa than in the RV and LV free walls (P = 0.0006). Gross anatomic and histologic examinations indicated that the tissue structure of the septa is more complex than that of the RV and LV free walls. CONCLUSION: VF activation patterns with progressive reduction of tissue mass differ for the septum and the ventricular free walls. The structural complexities of the septal tissue influence the maintenance of fibrillation in the ventricle.