Study of the Electrophysiological Effects of Early or Subendocardial Ischaemia with Intracavitary Electrodes in the Dog

Abstract

The early electrophysiological patterns of regional subendocardial ischaemia were studied by using the paced endocardial evoked response and simultaneous endocardial monophasic action potential recordings in 16 experiments in open chested dogs. Ischaemia was produced by transient (1-3 min) coronary artery occlusion. Regional subendocardial isochaemia caused asynchronous activation due to differential conduction delay and shortened repolarization as evaluated by the duration of the paced evoked response from 175 +/- (SD) 18.7 ms to 167 +/- 16 ms (P less than 0.001). These changes occurred within 60 s of occlusion and reversed rapidly after release of the occlusion. In simultaneous endocardial monophasic action potentials there was a decrease in plateau amplitude and the duration of repolarization shortened from 180 +/- (SD) 21.2 ms to 167 +/- 20.4 ms (P less than 0.001). The delay in endocardial activation after 2 min ischaemia was 5.5 ms, which is considerably shorter than the conduction delay previously reported in the subepicardial layers. The calcium-channel blocking drug verapamil (infused at 0.4 mg/kg) altered the rate at which shortening of repolarization and asynchronous activation occurred during ischaemia in six experiments. These experiments suggest that intracavitary electrodes could provide earlier and more sensitive detection of regional subendocardial ischaemia and may permit the assessment of therapy on the early electrical changes in the intact heart.

Differential effects of ischaemia and hyperkalaemia on myocardial repolarization and conduction times in the dog.

“…The changes in monophasic action potentials duration and conduction time, although crude estimations of refractoriness and conduction velocity, are relevant to the assessment of the electrophysiological alterations during ischaemia on the intact heart. We have shown previously that these clinically applicable intracardiac recordings can detect and monitor the early electrophysiological changes of ischaemia (Donaldson et al 1983). The duration of the paced endocardial evoked response and monophasic action potentials normally represent a measure of the local refractory period of the myocardium.…”

“…Studies employing K+-sensitive electrodes have shown Intracavitary recordings of the paced endocardial evoked response and monophasic action potentials are sensitive indices of the electrophysiological changes produced by regional myocardial ischaemia (Donaldson, Taggart, Nashat, Abed, Rickards & Noble, 1983). Using this technique we have evaluated the differential effects of ischaemia and hyperkalaemia on ventricular repolarization and conduction times in open-chested dogs.…”