Fieldtheoretical approach to the origin of the monophasic action potential for optimizing geometry of implantable leads

This study investigates by a fieldtheoretical approach the origin of the monophasic action potential (MAP) and the ventricular evoked response (VER) from the transmembrane potential (TAP). The results were correlated with experiments for geometric optimizing of implantable leads. The quasistatic, anisotropic, bidomain model was calculated in small unity volume Vi where the TAP #, is constant and represented by the current density J'. Two solutions for electrode positions inside the heart 47t heart $ou'*ie = -~ q j ~ V ( ~ )wdeSre achieved. By a; +o; r superposition of each solution 6,' the summed potential at the electrode position are calculated. During experiments several lead geometries (tip surface: 1.3 to 12 mm'; distance Jip-ring: 0.8 mm to 25 mi; ring surface: 1.8"' to 40 mm') were investigated in endo- and epicardial position in 12 dogs (17*9 kg). MAP and VER were recorded during several interventions and correlated with MAP measured using Ag/AgCI MAP catheters. Distance tip-ring smaller than 5 mm with an ring surface not larger than the tip (<5 mm') showed no disturbing of the repolarization course by signals proportional to 6'0"t.