Severity of Contraction Abnormalities

In order to determine the severity of contraction abnormalities in acute myocardial infarction and their response to sublingual nitroglycerin, 23 patients were studied by radionuclide angiography within 6-24 hours after the onset of chest pain. Radionuclide angiograms were obtained in the right anterior oblique projection before and after nitroglycerin and segmental shortening was determined using a hemiaxis method in the central and lateral chords of the infarcted and nonischemic zones. All 23 patients had asynergy in the zone of acute infarction. Mean hemiaxis shortening of the ischemic zone was depressed after acute myocardial infarction and improved after sublingual nitroglycerin (p < 0.001). Nonischemic zone hemiaxis shortening also improved after nitroglycerin. In another group of 16 patients with documented remote myocardial infarction (more than I year old) the response to nitroglycerin of contraction abnormalities in acute and remote myocardial infarcts was studied. Hemiaxis shortening in the zone of infarction was 14.8 ± 11.2% and did not improve after nitroglycerin. Nonischemic zone hemiaxis shortening improved with nitroglycerin from 29.9 ± 20.2% to 37.6 ± 22.8% (p < 0.02). Ejection fraction improved slightly but not significantly in both the acute and remote infarction groups after nitroglycerin. In the acute group, ejection fraction increased from 33.4 ± 10.8 to 36.4 ± 10.8% and in the remote group from 38.6 ± 15.9 to 41.2 ± 14.3%. Thus, the data indicate that zones of both acute and remote infarction are characterized by a significant reduction in hemiaxis shortening. However, 6-24 hours after acute myocardial infarction, increased hemiaxis shortening is demonstrable in the area of infarction after nitroglycerin administration. No such change occurred in the infarct zone of patients with remote infarction.