Detection of viable tissue in healed infarcted myocardium by dipyridamole thallium-201 reinjection and regional wall motion studies

Screening for coronary artery disease

Unidentified coronary artery disease remains a significant cause of premature death and morbidity during the prime of life. The availability of effective interventions for the management of ischemia has provoked new interest in screening for this condition in asymptomatic patients, in the hope of reducing the burden of this condition. Although widespread use of stress testing is ineffective, the use of imaging techniques may offer better accuracy for detection of ischemia. Other tests that identify evidence of atheroma in the peripheral or coronary circulation may be useful to identify patients at risk.

Detection of myocardial viability in the prediction of improvement in left ventricular function after successful coronary revascularization by using the dobutamine stress echocardiography and quantitative SPECT rest-redistribution-reinjection 201TI imaging after dipyridamole infusion

The aim of this study was to assess the feasibility, safety, and respective diagnostic accuracy of low-dose dobutamine infusion and rest-redistribution-reinjection thallium 201 single photon emission computed tomography (SPECT) after dipyridamole infusion (Th-DIP), in the prediction of functional improvement of asynergic infarcted zones, after successful revascularization in patients with chronic ischemic heart disease. Thirty-one patients with a previous myocardial infarction and left ventricular dysfunction (mean ejection fraction: 41 +/- 5.8%) were studied. The regional wall motion of the left ventricle was evaluated by basic echocardiography before and 14 +/- 1.7 weeks after successful revascularization (19 by percutaneous transluminal coronary angioplasty and 12 by coronary artery bypass grafting). Dobutamine stress echocardiography (DSE) was performed in all patients with dobutamine infusion of 5 and 10 micrograms/kg/minute over five minutes. Within three days after DSE and prior to revascularization, all patients underwent Th-DIP for myocardial viability assessment. A 16-ventricular-segment model was used for basic, DSE, and Th-DIP images. Viability was assessed by applying the standard criteria for each technique. In the 31 patients, 496 segments were analyzed. By basic echocardiography, 164 (33%) of them were classified as asynergic. The DSE detected viable tissue in 69/496 (14%) segments, whereas Th-DIP identified viability in 95/496 (19%) segments. When the postrevascularization basic echocardiographic study was used as the gold standard in identifying myocardial viability, the sensitivity and specificity for the DSE and Th-DIP were 86.5%, 94.4% and 90.5%, 69%, respectively. No major side effects were observed with both techniques. In conclusion, DSE seems to be an accurate method for identifying viable but asynergic myocardium in patients with chronic ischemic heart disease, whereas Th-DIP overestimates the postrevascularization recovery. Detection of hibernating myocardium can be obtained by these two noninvasive methods. However, DSE seems to be more useful in determining the prospective selection of patients who are going to benefit from revascularization.

Nitrate-augmented myocardial imaging for assessment of myocardial viability

201Tl myocardial perfusion imaging is presently done by several possible strategies. Stress/delayed redistribution, stress/redistribution/reinjection, and rest/redistribution imaging can be useful in the clinical assessment of myocardial viability. Unfortunately, the extent of myocardial viability may still be underestimated even by 201Tl reinjection imaging, compared with 18F-fluorodeoxyglucose positron emission tomography. 99mTc-labeled sestamibi imaging provides results similar to those of 201Tl imaging in the detection of coronary artery disease, but several previous studies suggest that stress/rest 99mTc-labeled sestamibi imaging significantly underestimates myocardial viability. Recently it has been reported that the administration of nitrates, before 201Tl reinjection, improves detection of defect reversibility. Several studies also suggested that administration of nitrates before the injection of 99mTc-labeled sestamibi significantly improved detection of reversibility with this agent, whereas additional studies showed further that this combination improves the predictive accuracy for recovery of left ventricular function and perfusion after coronary revascularization, compared with a standard rest 99mTc-labeled sestamibi study. Nitrate administration before the injection of 201Tl and 99mTc-labeled sestamibi may thus be a potentially attractive alternative for the evaluation of myocardial viability. Although the available results are encouraging, further studies are needed to evaluate the clinical value of 201Tl and 99mTc-labeled sestamibi imaging, in combination with nitrates, for predicting recovery of left ventricular dysfunction.

Dobutamine-induced ST-segment elevation in patients with healed myocardial infarction. A marker of myocardial viability

The purpose of this study was to determine the significance of transient ST-segment elevation during dobutamine infusions in patients with healed Q wave myocardial infarction. Twenty-seven patients with previous Q wave myocardial infarction were studied prospectively with dobutamine-thallium-201 single-photon emission computed tomography. The presence of ST-segment elevation in leads with Q waves was related to thallium reversibility at 4-hour redistribution imaging or after reinjection, to residual flow, as well as to wall motion abnormalities in the infarcted zone. ST-segment elevation in infarct-related leads was observed in 15 patients; 11 (73%) showed viability by thallium-201 in the infarcted zone. In patients without ST-segment elevation, viability was shown less frequently (33%, P < .05). Hypokinesis in infarcted segments was present in 60% of patients with ST-segment elevation and in 25% of patients without ST-segment elevation (.05 < P < .1). Finally, infarct-related artery was patent and/or collaterals were present in 10 patients with ST-segment elevation (67%) and in 4 patients without (33%, .05 < P < .1). In conclusion, ST-segment elevation during dobutamine infusion is a marker of residual viability in infarcted segments.