INFLUENCE OF ANISOTROPY ON LOCAL AND GLOBAL MEASURES OF POTENTIAL GRADIENT IN COMPUTER-MODELS OF DEFIBRILLATION

A heart-torso model including fiber orientation is used to calculate e lectric field strength in an active-can transvenous defibrillation sys tem and estimate errors due to inadequate description of the anisotrop y of the myocardium. Using a minimum potential gradient (5 V/cm) in a critical mass (95%) of the tissue, the estimated defibrillation voltag e threshold for a right ventricular transvenous lead placement differs by only 4.5% when using isotropic myocardial conductivity compared to a model with realistic fiber architecture, in addition: point-wise co mparisons of the two solutions reveal differences of 10.8% rms in pote ntial gradient strength and 31.6% rms in current density magnitude in the myocardium, resulting in a change in the location of the low gradi ent regions. These results suggest that if a minimum potential gradien t throughout the heart is necessary to avoid reinitiation of fibrillat ory wave fronts, then isotropic models are adequate for modeling the e lectric field in the heart. Alternatively, the model demonstrates the use of physiologically based descriptions of anisotropy and fiber orie ntation, which will soon allow simulations of shock induced membrane p olarization during defibrillation. (C) 1998 Biomedical Engineering Soc iety.