Comparison of echocardiography with electrocardiography in detecting myocardial viability

ST-segment changes in pathologic Q-wave leads during stress testing may reflect contractile reserve, inducible ischemia or passive mechanical stretching. Dobutamine echocardiography allows the detection of contractile reserve at low dose and inducible ischemia at high dose. We evaluated dobutamine stress ECG for detecting potentially reversible contractile dysfunction or residual ischemia in the infarct-related area. We utilized low and high doses of dobutamine in 49 patients with previous Q-wave myocardial infarction and analyzed the relation between ST-T segment changes in pathologic Q-wave leads and regional myocardial contraction. At low-dose dobutamine, regional contraction improved in the infarct-related area in 23 patients. New or further ST segment elevation and pseudonormalization of negative T waves developed at low dose more frequently in patients with contractile reserve than in those without (both p < 0.001), giving, respectively, a sensitivity of 44% and 61% and a specificity of 100% and 96%. At high-dose dobutamine (43 patients), new or further ST segment elevation and pseudonormalization of negative T waves, occurring beyond those observed at low dose, had a low predictive accuracy for contractile reserve (sensitivity: 10% and 14%; specificity: 68% and 82%, respectively). Pseudonormalization of negative T waves at high-dose dobutamine was 100% specific (though only 25% sensitive) for homozonal ischemia. In conclusion, ST segment elevation and/or pseudonormalization of negative T waves are indicative of contractile reserve in the infarct-related area when they develop at low-dose dobutamine, but they may be associated with worsening or no change in contractile function at high dose.