Twenty-four-hour thallium-201 imaging enhances the detection of myocardial ischemia and viability after myocardial infarction: a comparison study with echocardiography follow-up.

Background: To explore the value of 24 hour late Tl-201 imaging for detection of myocardial ischemia/viability after myocardial infarction.
Materials and Methods: Thirty-eighty patients with myocardial infarction underwent immediate, 3 hour redistribution and 24-hour late imaging after intravenous injection of 5 mCi Tl-201. Image quality analysis was performed using a 4-grade model. The immediate/redistribution, redistribution/late, and immediate/late Tl-201 images were analyzed double-blinded. The capability of detection of myocardial ischemia/viability was compared between the 3 hour redistribution and the 24-hour late imaging. Thirty-two patients underwent coronary angiography and successful revascularization of stenotic coronary arteries. The relationship between the severity of coronary artery stenosis and the time to completed redistribution of myocardial perfusion defects after resting injection of Tl-201 was investigated. The sensitivity, specificity, and accuracy for predicting an improvement in function post revascularization were compared between the 24-hour late imaging and the 3-hour redistribution imaging by way of a follow-up echocardiography.
Results: Three hour redistribution and 24-hour late imaging showed no significant differences in image quality according to the 4-grade model (P = 0.3580). Of 194 abnormal segments based on immediate Tl-201 imaging, redistribution imaging showed 60 reversible segments, taking up 31% (60/94), and late imaging showed 86 reversible segments, taking up 44% (86/194), with a significant difference (P = 0.0064). Of 128 severely abnormal segments, redistribution imaging showed 32 reversible segments, taking up 25% (32/128), and late imaging showed 48 reversible segments, taking up 38% (48/128), with a significant difference (P = 0.0310). Of 66 mildly abnormal segments, redistribution imaging showed 28 reversible segments, taking up 42% (28/66), and late imaging showed 38 reversible segments, taking up 58% (38/66), with no significant difference. Twenty-four hour late imaging showed an additional 30 reversible segments, taking up 22% (30/134) among 134 abnormal segments based on the immediate Tl-201 imaging, which did not improve on 3-hour redistribution imaging. The coronary arteries supplying the reversible segments detected by the 24-hour late imaging were more severe in diameter stenosis than those supplying the reversible segments detected by the 3-hour redistribution imaging. The sensitivity, specificity, and accuracy for predicting the functional improvement after the revascularization were 93% and 83%, 80% and 78%, 86% and 78%, respectively, by the 24-hour late imaging and the 3-hour redistribution imaging correspondingly, with the former being superior to the latter on the basis of the evaluation results of 9.90 +/- 3.62 months of follow-up echocardiography (chi = 10.8655, P = 0.0010).
Conclusion: Twenty-four hour late Tl-201 imaging, with satisfactory image quality, enhances the detection of myocardial ischemia/viability after myocardial infarction.