Myocardial imaging with extractable cations and inert tracers: the effects of flow and metabolism

Patterns of disturbed myocardial perfusion in patients with coronary artery disease. Regional myocardial perfusion in angina pectoris

Fifty patients who presented with angina pectoris were studied to examine the disturbances of regional myocardial perfusion during stress. Each patient underwent 16-point precordial mapping of the ECG during an exercise test, and coronary and left ventricular angiography. Regional myocardial perfusion was assessed using an atrial pacing test and a short-lived radionuclide, krypton-81m. Eleven patients had negative exercise tests and uniform increases in myocardial activity of krypton-81m of 98 +/- 18.0% during pacing. Ten patients performed 30,000-43,000 J in positive exercise tests. These patients showed abnormal coronary anatomy and increases in myocardial activity of krypton-81m to remote and jeopardized myocardium at the onset of pacing. However, further pacing produced a decrease in activity in the affected segment of 68.0 +/- 9.0% accompanied by ST-segment depression and angina. Twelve patients achieved 26,000-32,000 J in positive exercise tests and had significant coronary artery disease. Atrial pacing produced increased activity of krypton-81m to remote myocardium. The jeopardized segment at first showed no change and then a decrease in regional activity of krypton-81m (89.0 +/- 17%) accompanied by ST-segment depression and chest pain. Seventeen patients achieved only 7000-22,000 J in positive exercise tests. These patients showed abnormal coronary anatomy and developed decreases in regional activity of krypton-81m to the affected segment of myocardium starting at the onset of atrial pacing and decreasing by 88 +/- 0 7.0% below control. We conclude that different patterns of disturbed myocardial distribution of krypton-81m are present during stress-induced ischemia in patients with coronary artery disease. There was a close temporal relationship between these disturbances and ST-segment depression.

Myocardial infarction in the dog: effects of intravenous propranolol

The effects of propranolol on myocardial perfusion and metabolism during acute myocardial infarction were studied in 18 mongrel dogs. A reversible snare was placed on the left anterior descending coronary artery; regional myocardial perfusion was continuously measured using the short-lived isotope krypton-81m, and myocardial metabolism was assessed using the epicardial electrocardiogram and measurement of release of creatine kinase activity from the affected segment of myocardium. Six dogs with no arterial occlusion acted as "sham operated" dogs; six others in which the snare was occluded acted as a control group and a third group of six were given propranolol, 0.5 mg/kg, 30 minutes after coronary occlusion. All variables were recorded before and for 5 hours after coronary occlusion. Dogs treated with propranolol showed a significant improvement in regional myocardial perfusion to the affected segment, decreased loss of electrically active myocardium at the end of each experiment for any given degree of early S-T segment elevation and a delay in the local release of creatine kinase activity compared with that in the control dogs. These results suggest that propranolol exerts a beneficial effect on the progress of ischemic myocardial damage when given shortly after the onset of infarction.

The effects of propranolol on myocardial perfusion and metabolism during acute regional ischaemia

The unique physical properties of the short-lived inert and freely diffusing isotope 81mkrypton allow a continuous observation to be made of regional myocardial perfusion. Eighteen dogs were anaesthetised and a reversible snare placed on the left anterior descending coronary artery (LAD). 81mKrypton was used to study regional myocardial perfusion, and myocardial metabolism was assessed using the epicardial ECG and release of creatine kinase activity (CK). Six dogs did not undergo LAD occlusion ("sham operated"); in six other dogs the LAD was occluded (controls), and another six dogs were given propranolol, 0.5 mg/kg, 20 min after LAD occlusion. All the parameters were measured before and for 5 h after LAD occlusion. When compared to controls, dogs treated with propranolol showed significant improvement (p less than 0.01) in regional myocardial perfusion; smaller loss of electrically active myocardium for any given degree of early ST-segment elevation; and a delay in the release of CK activity from a local coronary vein. These results suggest that propranolol exerts a beneficial effect following the development of acute myocardial infarction.