4969Enhanced gap junction coupling organised and terminated acute ventricular fibrillation in ex-vivo perfused hearts

Abstract

Abstract Background The underlying mechanism of ventricular fibrillation (VF) remains unclear. There are both experimental and clinical data to support the existence of rotational drivers (RDs), though other opposing studies suggest that VF is the result of disorganized myocardial activation. Abnormal electrical coupling between cardiomyocytes through gap junctions (GJ) has been considered an important factor in the genesis and maintenance of VF and pre-treatment with GJ couplers, rotigaptide (RTG), has been shown to reduce VF inducibility. Purpose We hypothesized that the degree of GJ coupling determines the underlying mechanism of VF, and that changes in GJ coupling can shift or modify the predominant mechanism of fibrillation along the spectrum between disorganised activity and organised drivers. We proposed that increased organisation of VF is critical to its termination. Methods Thirty Sprague-Dawley rat hearts were explanted, perfused ex-vivo and acute VF was induced with burst pacing and 30μM pinacidil. Optical mapping of transmembrane potential was performed at baseline and the effects of GJ coupling on VF dynamics were studied in an acute VF model by perfusing with increasing concentrations of a GJ uncoupler; carbenoxolone (0–50μM, CBX, n=10) or a GJ coupling-enhancer; RTG (0–80nM, n=10). A chronic diffuse fibrosis model (n=10) was generated with 4 weeks of in-vivo angiotensin infusion (500nm/kg/min). Fibrillation dynamics were quantified using phase analysis, phase singularity (PS) tracking and our novel method of global fibrillation organisation quantification, frequency dominance index (FDI), which is a power ratio of highest amplitude dominant frequency in the frequency spectrum. Results RTG increased average rotations per RD (Baseline: 2.86±0.10 vs 80nM: 5.66±0.43, p<0.001) whilst CBX caused a reduction (Baseline: 3.77±0.39 vs 50μM: 0.26±0.26, p<0.001). Maximum rotations for a RD increased with RTG (5.4±0.45 vs 48.20±12.32, p<0.001) and decreased with CBX (8.0±1.3 vs 0.3±0.3, p<0.001). Proportion of time PSs were detected in VF increased with RTG (0.44±0.06 vs 0.93±0.02, p<0.001) and decreased with CBX (0.61±0.9 vs 0.03±0.02, p<0.001). RTG reduced meander of longest duration RD (20.6±1.68 vs 11.51±0.77 pixels, p<0.001) for PS >5 rotations. FDI increased with RTG (0.53±0.04 vs 0.78±0.3, p<0.001) and decreased with CBX (0.60±0.05 vs 0.17±0.03, p<0.001). In the diffuse fibrosis group, in comparison to baseline RTG 80nM increased FDI (0.35 vs 0.65, p<0.001) and terminated VF in 40% of hearts. Conclusion The degree of GJ coupling is a key determinant of the underlying mechanism of VF. RTG organised fibrillation and stabilised RDs in a concentration-dependent manner whilst CBX disorganised VF. Enhancing GJ coupling with RTG in diseased hearts with fibrosis can terminate VF and may be a potential therapeutic target in acute VF. Acknowledgement/Funding BHF Programme Grant PG/16/17/32069