Electrophysiologic effects of left ventricular hypertrophy in the intact cat

Electrophysiologic abnormalities have been described in isolated, hypertrophied left ventricular tissue removed from animals exposed to a chronic pressure load. However, changes in electrical properties of intact hypertrophied hearts have not been described. To study this question, 15 cats underwent supraventricular aortic banding and five underwent a sham procedure. After ten weeks, the animals were anesthetized and instrumented using paired transmural plunge electrodes and endocardial quadripolar pacing catheters. Measurement of pacing threshold, refractoriness, inducibility of ventricular arrhythmias (using programmed electrical stimulation), and vulnerability to ventricular fibrillation (ventricular fibrillation threshold) were made in both groups. Mean left ventricular mass was significantly greater in the banded compared with sham-operated animals (2.5 +/- 0.9 v 2.1 +/- 0.5 g/kg body weight; P less than .05). Pacing thresholds and refractory periods measured at multiple left and right ventricular sites were similar in both groups, and there was no difference in the extent of site-to-site differences in refractoriness (dispersion). Six banded but no sham animals had inducible ventricular tachycardia or fibrillation using programmed stimulation. Furthermore, left ventricular mass was significantly greater in animals with inducible arrhythmias compared with those noninducible (P less than .05). Ventricular fibrillation thresholds, measured in milliamperes (mA), in the banded animals were significantly lower in the left ventricle (13.5 +/- 1.3 mA) than in the right (21.7 +/- 3.2 mA; P less than .05) and was also lower than the thresholds obtained in either the left or right ventricle of the sham-operated animals (18.3 +/- 1.9 mA and 20.1 +/- 1.1 mA, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)