A Computational Cardiac Modeling Approach to Study Directional Shock Vectors in Terminating and Modulating Rotors

Sudden Cardiac Death (SCD) is one among the leading causes of death worldwide. In an analysis, 56 % of the SCD is on account of Out-of-Hospital Cardiac Arrest (OHCA). In the United States, annually, about 356,000 patients experience OHCA, most of them being Ventricular Fibrillation (VF) or pulseless Ventricular Tachycardia (VT). Studies have shown the presence of spatio-temporally organized electrical activities called rotors during VF, and terminating these rotor-like activities can modulate or terminate VF in an in-hospital scenario or research set up. But this approach cannot be implemented in an OHCA scenario. In an OHCA scenario, where the timely intervention is very critical, electrical defibrillation is the main treatment option, and the shock delivered should be optimal, as a lower magnitude shock may not be able to terminate the arrhythmia. Similarly, a higher magnitude of shock than the threshold can lead to myocardial and neurological damages. In this work, the rotor termination approaches are extended into an OHCA scenario, and evaluated whether the effectiveness of the shock in an OHCA can be improved by targeting rotor-like activities or patterns. The hypothesis is that the direction of shock vector orientation has an impact on rotor termination and thereby can improve shock success. To test the hypothesis, a bidomain porcine cardiac model that can simulate rotor activities and defibrillation was developed. The results indicate that, the highest average likelihood of rotor termination is when the defibrillator pads are placed in perpendicular direction with respect to rotor (0.99 +/- 0.03), with an average current density of 7.2A/m2, compared to the parallel direction (0.76 +/- 0.26), and oblique direction (0.08 +/- 0.12). The voltage gradients for the termination were obtained in the acceptable range, and varied as 3.25, 4.71 and 5.37 V/cm for perpendicular, parallel and oblique directions respectively. As a summary, a computational model was used to demonstrate that the rotors are more likely to be terminated by optimizing the orientation of the defibrillation. Further, the results indicate that optimal defibrillator pad orientation combined with sufficient current density magnitude could improve the likelihood of rotor termination, thereby improving defibrillation success in an OHCA scenario.