A solid angle analysis of the epicardial ischemic TQ-ST deflection in the pig. A theoretical and experimental study.

The solid angle theory has long been applied to the interpretation of the ECG; however, quantitative evaluation of its applicability has been minimal. We applied solid angle analysis to the interpretation of the TQ-ST deflection during acute ischemia. Five anesthetized pigs were studied 1--3 hours after coronary occlusion. Multiple unipolar tracings were recorded from precisely determined positions on the epicardium overlying the ischemic and normal zones. The geometry of the hearts and ischemic zones was preserved, the margins of ischemia being defined as the outer border of Thioflavin S nonfluorescence. Wax replicas of the hearts with ischemic zones removed were constructed. Solid angles subtended at electrode positions on the replicas were calculated. A linear relationship (r = 0.84 - 0.97, P less than 0.001) was shown to exist between the observed TQ-ST deflection and the calculated solid angle. A small but patterned deviation from exact fit of the TQ-ST deflection with the calculated solid angle led us to investigate the possibility that dipole moment strength (phi) is not confined to the ischemic margins. Computations using idealized heart models with ischemic zones cylindrical and transmural in shape allowed us to distribute phi arbitrarily within the ischemic zone, comparing this predicted pattern of TQ-ST deflection with that observed experimentally. The experimental data appear most consistent with the condition in which phi is distributed over a 1-cm border region during the first several hours of ischemia. We conclude that the solid angle theory provides a rational basis for interpretation of the ischemic TQ-ST deflection; however, phi may be distributed over a marginal zone.