Objective: Dobutamine echocardiography and thalium 201 are useful in the assessment of myocardial viability, but both techniques frequently yield conflicting results. The objective of this study was to determine the minimum mass of viable myocardium that each test could detect and compare the agreement of dobutamine echocardiography and thallium 201 to detect viability.
Methods: Dobutamine echocardiography and thallium 201 were performed in 10 patients scheduled for cardiac transplantation. In each patient, 15 segments were studied. After transplantation these segments were analyzed by the pathologist measuring by a computer system the total area of each segment, the necrotic + fatty mass, and area (%) of viable myocytes per segment. The percentage of viable tissue was estimated ([Total mass - (Necrotic + Fatty tissue)]/Total mass x 100) on each segment, which was compared with the result (viable or not viable) obtained by echocardiography or thallium 201.
Results: Dobutamine echocardiography defined 90 segments (60%) as viable versus 117 (78%) in thallium (kappa 0.49, 95% CI 0.36-0.63). The minimum percent of viable tissue per segment defined as viable by thallium was 43% versus 49% by echocardiography. With use of thallium, the highest accuracy of the test to detect viability was when the percent of necrotic tissue of the segment analyzed was 40% (positive and negative likelihood ratio 2.2 and 3.6, respectively). By use of echocardiography, the highest accuracy of the test was observed when the percent of necrotic tissue of the segment analyzed was 31% (positive and negative likelihood ratio 5.5 and 7.7, respectively).
Conclusion: The discrepant results of dobutamine echocardiography and thallium 201 are due to differences in the minimum mass of live myocytes required by each technique to detect viability.