Effect of nontransmural necrosis on epicardial potential fields. Correlation with fiber direction.

Abstract

The effect of nontransmural necrosis on epicardial potential distributions was studied in 13 dogs. In previous studies, left ventricular epicardial pacing generated epicardial potential maps at QRS onset with a negative central area and two positive areas that faced the portions of the wavefront propagating along fibers. Subsequently, the positive areas expanded in a counterclockwise direction by 900 to 120°. In those studies, the rotatory expansion of the positive areas was tentatively attributed to the spread of excitation through deep myocardial layers, where fiber direction rotated counterclockwise from epicardium to endocardium. To test this hypothesis, we tried to interrupt the counterclockwise expansion of the positive area by creating localized, nontransmural necrosis at various depths in the left ventricular wall by injection of formalin or application of laser energy. Epicardial potential maps were obtained from a grid of 12 x 15 electrodes on a 44 x56-mm area. Epicardial pacing from selected sites generated epicardial maps in which some positive areas were missing compared with controls. The direction of the straight line joining the pacing site to the site of missing positivity correlated well with the average fiber direction in the necrotic mass (r=0.82, p<0.01). Angle between epicardial fiber direction and the straight line described above correlated well with the average depth of the necrosis, expressed as percent of the wall thickness (r=0.95, p<0.01). These data support the hypothesis that the counterclockwise expansion of the epicardial positivity occurring after epicardial pacing results from excitation spreading along deep fibers. The findings are consistent with the oblique dipole layer model of the excitation wavefront. The results may be useful for localizing nontransmural necrosis from epicardial maps. (Circulation 1990;82:2115-2127 In previous studies,1-6 epicardial pacing of exposed dog ventricles generated epicardial potential distributions at the beginning of QRS with a negative central area and two potential maxima. The direction of the straight line joining the two maxima correlated well with the direction of subepicardial muscle fibers near the pacing site.1-6 This finding is consistent with the "oblique dipole layer" model of the excitation wavefront.7 The model assigns greater dipole strength per unit area to the portions of a wavefront that propagate along fibers

Effect of myocardial fiber direction on epicardial potentials.

“…These effects have been observed in superfused myocardial laminas,3 on the epicardial and endocardial surfaces,4-7 and in volume conductors surrounding an isolated heart.8 The counterclockwise (CCW) rotation of fiber direction from epicardium to endocardium9-1 further affected wave front shapes and potential distributions both on the epicardium and in the ventricular walls. 5,6,[12][13][14] On the basis of the above studies, we made the hypothesis that epicardial potential patterns recorded in the initial stages of a paced beat, when excitation spreads through quasi-parallel fibers, would reveal the orientation of the fibers near the site of pacing, even when the pacing site was intramural or subendocardial and, importantly, even before the arrival of excitation at the epicardial surface. A second hypothesis to be tested was that in later stages of ventricular excitation, intramural propagation through rotating fibers would also affect epicardial potentials in a recognizable way.…”

Noninvasive ECG Imaging of Electrophysiologically Abnormal Substrates in Infarcted Hearts

“…1 Experimental and clinical data from infarcted hearts have helped to define measures for identifying abnormal EP substrates [2][3][4][5] and for stratifying their arrhythmogenic potential. 6,7 Identification of arrhythmogenic substrates before an arrhythmia occurs could reduce the risk of sudden death by indicating the need for device, drug, or ablation therapy.…”

Extracardiac effects of myocardial electrical anisotropy

“…Positive potentials and potential maxima are predominantly recorded from those ventricular areas toward which excitation spreads along fibers. Islands of missing positivity in epicardial potential maps obtained during ventricular pacing reveal non-transmural necroses [6]. This potential distribution affects the shape and polarity of intracardiac and epicardial clectrograms [3].…”