Polarographic oxygen, the epicardial electrocardiogram and muscle contraction in experimental acute regional ischemia of the left ventricle.

This study is the first attempt to correlate nivocardial oxygen availability by the polaro-graphic method with direct electrocardiographic leads and cinematographic records of muscle contraction during experimental acute coronary branch occlusion and narrowing. The comparative insensitivity and slowness of the epicardial electrocardiogram as an index of acute regional ischemia is demonstrated. Special attention is given to the rates of myocardial oxygen change immediately following attainment of a significant degree of coronary obstruction, the effects of pure oxygen inhalation on the experimental situations, and alterations in coronary vein color following release of arterial occlusion. I N PREVIOUS studies 1 ' 2 it has been shown that measurements of oxygen availability by the platinum electrode provide stable values in nonischemic myocardium as well as sensitive indices of ischemia produced by coronary occlusion. The borders of ischemic areas responded to oxygen inhalation by significant rises of myocardial oxygen, whereas the centers failed to show such a response. A "physi-ologic" classification for ischemic muscle, based on the depth of myocardial oxygen fall, distinguished central zones (levels 25 per cent or less of the control) from border zones (levels 25 to 85 per cent of the control). This classification was roughly consistent with the anatomic extent of the ischemic area as judged from inspection. In these experiments we did not attempt to determine the rate of change in myocardial oxygen or to correlate electrocardiographs or muscle contraction changes with the polarographic findings. The present communication will describe the sequence of events that follow acute obstruction of a coronary branch as reflected by rapid, semicontinuous polarographic oxygen determinations, epicardial electrocardiograph-ic records and cinematographic color records of muscle contraction. The behavior during ischemia and oxygen inhalation of each of these parameters of myocardial function will fii-st be described and commented on individually. Their interrelationships and the general implications of the experiments will then be considered. METHODS Acute regional ischemia was produced in 22 dogs weighing from 15 to 20 Kg. by an experimental teehnic previously described. 1 Under morphine-pentobarbital-dial-urethane anesthesia, 1 the heart wns exposed, a coronary branch isolated, and an array of oxygen electrodes inserted, so as to sample muscle within and, insofar as possible, beyond the vessel's apparent left ventricular distribution. We utilized medium-sized or small arterial branches, which in these experiments were always derivatives of the left anterior descending. We considered a small branch to be any of the terminal surface rami beyond the …