Radionuclide studies in patients with stress-induced ST-segment elevation after acute myocardial infarction

The meaning of a stress-induced ST-segment elevation (ΔST) after acute myocardial infarction is still controversial. Some studies show it is related to asynergy, and other studies show it is related to ischemia. However, no study has compared the ΔST with both stress-induced ischemia and stress-induced asynergy in the same group of patients. With this purpose, 88 patients were studied 16 ± 4 days after acute myocardial infarction. They were submitted to a dobutamine stress test on two different occasions 1 to 2 days apart. Dobutamine was infused up to 40 μg/kg/min with blood pressure and electrocardiographic controls. Thallium-201 single-photon emission computed tomography was performed during the highest dobutamine dose and 3 to 4 hours later. Equilibrium radionuclide ventriculography was performed at rest and during the highest dobutamine dose. Global and regional (hypokinetic area) ejection fractions were quantified. The ST segment was elevated ≥ 1 mm in 33 patients at rest and in 71 during stress. A stress-induced ΔST was seen in 66 patients. Redistribution was detected in 65 patients. Multiple regression analysis showed a significant correlation between ST elevation and thallium defect score both at rest and during stress. No correlation was found between ΔST and redistribution score. However, a significant inverse linear correlation was found between the ΔST and the change in regional ejection fraction: the greater the ΔST, the smaller the change in regional ejection fraction with dobutamine. In conclusion, a stress-induced ΔST is not related to ischemia but to stress-induced left ventricular asynergy.