EFFECT OF ACUTE REGIONAL MYOCARDIAL ISCHEMIA ON THE ANGIOGRAPHIC ANATOMY OF CORONARY-ARTERIES

Twenty-eight anesthetized dogs were studied to investigate the effects of regional myocardial ischemia on the angiographic appearance of large coronary arteries. Left ventricular (LV) and left coronary angiograms were recorded before and after the diameter of the left anterior descending coronary artery (LAD) was reduced by 60-70%. The left ventricular end-diastolic pressure (LVEDP) and the epicardial ECG showed no regional dyskinesia or ischemia. After the LAD was narrowed, we produced regional ischemia with atrial pacing in eight dogs and with 0.4 mg of ergonovine maleate i.v. in five dogs. Repeat angiograms during each episode of ischemia showed that the LAD associated with the dyskinetic segment transiently failed to opacify. This was reversed by intravenous nitroglycerin. In another five dogs, we produced regional ischemia by injecting microspheres into the LAD. Repeat angiograms showed narrowed vessels and impaired opacification of the associated segment of the LAD. This was partially reversed by intravenous nitroglycerin. A dynamic assessment of changes in regional myocardial perfusion was recorded in 10 more dogs using krypton-81 m. Stenosis (60-70%) of the LAD produced no changes in regional perfusion. Atrial pacing produced an immediate redistribution with increases in perfusion (112 ± 14% [mean ± SD] to remote myocardium and decreases (78 ± 9.0%) in the affected segment. These experiments showed that when several interventions are used to produce acute regional myocardial ischemia, the angiographic appearance of the coronary arteries changes. This change consisted of a transient failure to opacify the length of the artery associated with the ischemic segment. This suggests that the reversible disappearance of a large coronary artery during an episode of myocardial ischemia may not necessarily be due to coronary spasm.