Aims

Conflicting data exist supporting differing mechanisms for sustaining ventricular fibrillation (VF), ranging from disorganised multiple-wavelet activation to organised rotational activities (RAs). Abnormal gap junction (GJ) coupling and fibrosis are important in initiation and maintenance of VF. We investigated whether differing ventricular fibrosis patterns and the degree of GJ coupling affected the underlying VF mechanism.
Methods and Results

Optical mapping of 65 Langendorff-perfused rat hearts was performed to study VF mechanisms in control hearts with acute GJ modulation, and separately in three differing chronic ventricular fibrosis models; compact (CF), diffuse (DiF) and patchy (PF). VF dynamics were quantified with phase mapping and frequency dominance index (FDI) analysis, a power ratio of the highest amplitude dominant frequency in the cardiac frequency spectrum.

Enhanced GJ coupling with rotigaptide (n = 10) progressively organised fibrillation in a concentration-dependent manner; increasing FDI (0nM: 0.53±0.04, 80nM: 0.78±0.03, p < 0.001), increasing RA sustained VF time (0nM:44±6%, 80nM: 94±2%, p < 0.001) and stabilised RAs (maximum rotations for a RA; 0nM:5.4±0.5, 80nM: 48.2±12.3, p < 0.001). GJ uncoupling with carbenoxolone progressively disorganised VF; the FDI decreased (0µM: 0.60±0.05, 50µM: 0.17±0.03, p < 0.001) and RA-sustained VF time decreased (0µM: 61±9%, 50µM: 3±2%, p < 0.001).

In CF, VF activity was disorganised and the RA-sustained VF time was the lowest (CF: 27±7% versus PF: 75±5%, p < 0.001). Global fibrillatory organisation measured by FDI was highest in PF (PF: 0.67±0.05 versus CF: 0.33±0.03, p < 0.001). PF harboured the longest duration and most spatially stable RAs (patchy: 1411±266ms versus compact: 354±38ms, p < 0.001). DiF (n = 11) exhibited an intermediately organised VF pattern, sustained by a combination of multiple-wavelets and short-lived RAs.
Conclusion

The degree of GJ coupling and pattern of fibrosis influences the mechanism sustaining VF. There is a continuous spectrum of organisation in VF, ranging between globally organised fibrillation sustained by stable RAs and disorganised, possibly multiple-wavelet driven fibrillation with no RAs.
Translational perspective

Multiple competing mechanisms have been proposed for sustaining VF. We reframed conflicting mechanisms reported in sustaining fibrillation and defined them as part of a continuum of varying global organisation, with some sustained by stable rotationalactivities. The underlying cardiac electroarchitecture, namely gap junction coupling and fibrosis, were important determinants of the VF mechanism. Characterising the VF mechanism and its relationship to the cardiac electroarchitecture may facilitate a patient-tailored treatment approach towards VF prevention in VF survivors. Organised fibrillation sustained by stable rotational activities could be considered for targeted ablation. Disorganised fibrillation dynamics may be better suited for conventional pharmacotherapy.