Transmembrane Voltage Changes During Unipolar Stimulation of Rabbit Ventricle

Abstract

Abstract This study tested the prediction of bidomain models that unipolar stimulation of anisotropic myocardium produces transmembrane voltage changes (ΔV m s) of opposite signs away from the electrode on perpendicular axes. Stimulation with a strength of 0.1 to 40 mA was applied from a point electrode on the left or right ventricle of isolated perfused rabbit hearts at 37°C to 38°C stained with the potentiometric dye di-4-ANEPPS. A laser scanner system recorded V m -sensitive fluorescence at 63 spots in an 8×8-mm region around the electrode. Cathodal stimulation in the refractory period produced regions of −ΔV m 1 to 5 mm away from the electrode on an axis oriented parallel to the fast propagation axis to within 1.8±11° ( P ≥.7 for difference versus zero, n=7). Recording spots in these regions underwent +ΔV m when anodal stimulation was used. At recording spots on the slow propagation axis, cathodal stimulation produced +ΔV m and anodal stimulation produced −ΔV m . During diastolic stimulation, early excitation occurred near the electrode for cathodal stimulation or on the fast propagation axis as far as 2.8±1 mm away from the electrode for anodal stimulation. A “dog-bone” region of +ΔV m that included tissue near and away from the electrode on the slow propagation axis occurred when cathodal stimulation was given in diastole. Regions of +ΔV m occurred away from the electrode on the fast propagation axis when anodal stimulation was given in diastole. Thus, ΔV m differs in regions along and across myocardial fibers, indicating that ΔV m depends on anisotropic bidomain properties. Sites of early excitation are those where +ΔV m occurs, indicating that membrane channel excitation depends on the distribution of ΔV m .