Panoramic Imaging Reveals Mechanisms of Resistance to Ventricular Arrhythmias Under Blebbistatin as Compared to 2,3-Butanedione Monoxime (BDM)

Abstract

Unlike other excitation-contraction uncouplers (such as BDM), blebbistatin does not have apparent side effects, and is increasingly used in cardiac electrophysiology studies using optical mapping. However, the effects of blebbistatin on restitution and ventricular arrhythmia remain unknown. Determining these effects is important for the use of blebbistatin and a better understanding of the mechanisms of arrhythmia. Monophasic action potentials at various cycle lengths were measured before and after the application of blebbistatin in Langendorff-perfused rabbit hearts (n=5). Optical mapping experiments were conducted in rabbit hearts (n=7) which were sequentially perfused with BDM and blebbistatin. Action potential duration (APD) restitution, conduction velocity (CV) restitution, and vulnerability to shock-induced arrhythmia were measured. Panoramic imaging system was used to optically record the action potentials and the reentry circuits from the entire ventricular epicardium. Application of blebbistatin did not change the APD restitution. In contrast, BDM significantly decreased the APD and flattened the APD restitution. BDM also significantly decreased the CV at both longitudinal and transverse directions, and thus decreased the wavelength (APD × CV). Vulnerability to shock-induced arrhythmia was much higher under BDM compared with that under blebbistatin (inducibility of sustained arrhythmia: 23/99 vs. 2/123). Stable reentry was responsible for the sustained arrhythmia under BDM, while wave breaks and wave extinctions were frequent and facilitated the self-termination of shock-induced arrhythmia under blebbistatin. In conclusion, blebbistatin has no significant effect on the APD restitution in the normal rabbit heart, and is associated with low sustainability of shock-induced arrhythmias. Low dynamic instability under BDM facilitates the maintenance of stable reentrant arrhythmia, while the combination of relatively high dynamic instability and long wave length under blebbistatin facilitates the self-termination of reentrant arrhythmia and thus explains the resistance to arrhythmia.