Changed Duration of Ventricle Repolarization in Dog Heart under Conditions of Increased Preload

The duration of repolarization of subendocardial, intramural, and epicardial layers of dog ventricles was studied under conditions of volume overload of the heart in situ. Increased preload was modeled by rapid intravenous infusion of saline and rheopolygluquine. The activation-recovery interval was measured by flexible intramural electrodes inserted into the right and left ventricles. The level of preload was evaluated by the increase in left-ventricular end-diastolic pressure. The increase in preload from 11±6 to 26±10 mm Hg led to a significant (p<0.05) prolongation of the activation-recovery interval in the subepicardial layers of apex, all layers of the lateral wall, and subepicardial and intramural layers of the base of the left ventricle and in subendocardial layers of the apex and base of the right ventricle. Further elevation of the end-diastolic pressure to 34±11 mm Hg led to shortening of the activation-recovery interval (p<0.05) in the subepicardial layers of the apex and lateral wall of the left ventricle and in the subepicardial layers of right-ventricular base and left-ventricular lateral wall. Hence, different areas of the myocardium differently react to volume overload of the heart. Changes in repolarization length in response to preload increase are biphasic.