Effects of tachycardia with normal and ectopic ventricular activation on S-T segment potential and patterns in the dog.

Tachycardia induced by atrial pacing in the dog increases the intensity of potentials recorded on the body surface during the ST-T interval. The effects of tachycardia caused by ectopic right or left ventricular stimulation on ventricular recovery potentials were studied in 30 dogs. Rate was increased in a stopwise manner from 90 to 250 beats per minute by atrial pacing (ten dogs), or by left atrial-right ventricular sequential pacing (ten dogs), or by left atrial-left ventricular sequential pacing (ten dogs). ECG effects were determined by construction of body surface isopotential maps from voltages registered from 84 torso electrodes using a P-R segment baseline. Ectopic stimulation intensified the repolarization maximum and shifted its location to correspond with sites of epicardial stimulation. These findings reflect a reduced cancellation of transventricular differences in recovery times, with earliest recovery occurring at earliest activated sites. Increasing rate with any one activation pattern linearly increased potential extrema magnitudes without further changes of spatial features. This singular response to tachycardia regardless of activation sequence is consistent with an increase in the apparent moment of a repolarization dipole without alteration of its orientation.