Local ventricular bulging after acute coronary occlusion

In open-chest dogs, anesthetized with Nembutal, under positive pressure respiration, the coronary arteries were dissected out, and an umbilical ligature was placed about the left coronary artery, the anterior descendens, or the circumflex artery. Strain-gauge arches were sutured directly to the myocardium both in and out of the distribution of the occluded coronary artery. Blood pressure and ECG were also recorded before, during, and after arterial occlusion, which lasted for periods varying from 10 sec to 20 min. During occlusion of a large coronary artery the force of contraction of the affected myocardium decreased, and with continued occlusion the ischemic area no longer contracted but bulged during ventricular systole. Lead II of the ECG remained unchanged during ventricular bulging. After several successive occlusions, ventricular bulging became more pronounced and occurred more promptly after occlusion. A slight increase in blood pressure was noticed on the initial occlusion and could be abolished in a fresh preparation by bilateral vagotomy. Also, pulsus alternans was frequently noticed without electrical alternans. Restoration of contraction in the ischemic segment was observed in all instances of occlusion of 1 min or less. Upon release of occlusion, the force of contraction in the ischemic segment was markedly greater than control, with apparently complete recovery during the following 1–3 min.