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The Electrocardiographic Recognition of Cardiac States at High Risk of Ventricular Arrhythmias: An Experimental Study in Dogs

Recognition of states in which the heart is vulnerable to arrhythmia would be a helpful guide to prophylaxis. The possibility of recognizing such states from the ECG is suggested by the already established relations between abnormally disparate recovery to both vulnerability to arrhythmia and ECG waveform. In this study, canine QRS, T, and QRST isoarea maps were determined from ECGs recorded at 192 body sites during control states and conditions of enhanced susceptibility to arrhythmia. Vulnerable states were produced by ouabain intoxication, hypothermia, premature beats, and epinephrine infusion. A hypothetical series of QRST isoarea maps that would be expected to occur without increased local inequalities of recovery was derived by adding the control QRS isoarea map to a fraction (α) of the control T isoarea map and allowing the fraction to vary from α = 1 to α =−1. One QRST isoarea map selected from the derived series was subtracted from a QRST isoarea map during each state of enhanced arrhythmia vulnerability. Derived maps were selected to minimize the average amplitude of the residual maps. RMS values of the residual maps systematically increased with increasing prematurity of depolarization, with time after a toxic injection of a dose of ouabain, with increasing hypothermia, and during the first 3 minutes of epinephrine infusion. Also, the RMS values of the residual maps decreased in hypothermic dogs during rewarming. Our findings suggest that states of vulnerability to arrhythmia due to increased disparity of recovery can be identified by analysis of ECG waveforms recorded from lead systems sensitive to electrical activity in local cardiac regions.