Threshold in Dogs

The relation between ventricular fibrillation threshold (VFT) and cardiac surface QRST area distributions was studied in eight pentobarbital-anesthetized dogs. Unipolar epicardial electrograms were recorded from 64 sites evenly distributed on the right and left ventricles. Localized areas of short repolarization properties were produced by directing five intensities of light onto the surface of the anterior right ventricle through apertures of three sizes. VFT, measured at the center of the lesion, decreased during warming and had a high negative correlation to the change (warming-control) in QRST area (AQRST1) in the electrogram recorded from the center of the lesion. This correlation was independent of lesion size. For the six experiments, the correlation coefficients for 400-, 800-, and 1,600-mm2 lesions averaged -0.95, -0.94, and -0.96, respectively. The correlation between VFT and AQRST1 without regard to lesion size averaged -0.88. VFT also had a negative correlation to root mean square (RMS)AQRST because of warming. RMSAQRST was calculated from the change in QRST areas (warming control) in all 64 electrograms. The correlation between VFT and RMSAQRST was dependent on lesion size. For all experiments, the correlation between VFT and RMSAQRST averaged -0.97, -0.93, and -0.93 for 400-, 800-, and 1,600-mm2 lesions, respectively. The correlation between VFT and RMSAQRST without regard to lesion size, however, was considerably lower, -0.59. The results of this study provide the first direct evidence that VFT is correlated with cardiac surface QRST area distributions. (Circulation, 1988;78:171-177)