Revascularization and prognosis after acute myocardial infarction (AMI) depend on the assessment of myocardial viability. Thus, after AMI, the myocardium may still be viable, though with contractile dysfunction. This study was aimed at comparing three tomographic methods, that is, dobutamine echocardiography (DE), thallium scintigraphy after i.v. nitrate bolus (SPET) and MRI at rest, in the assessment of viable tissue. The viability standard was post-revascularization functional recovery, as assessed with echocardiography at rest. Twenty-four patients with previous AMI (3-6 months earlier) were examined: 384 segments in all; 106 segments were a-dyskinetic and they make up our study group. At first follow-up (30-45 days), 38 segments exhibited functional recovery and were considered viable; sensitivity and specificity rates follow: 68% and 75% for DE, 75% and 55% for SPET, and 95% and 34% for MRI, respectively.
In conclusion: 1) this is the first study comparing three different tomographic methods with the same myocardial segmentation for viability assessment; 2) MRI exhibited very high sensitivity, which means no false negatives; 3) SPET and MRI exhibited low specificity, due to their intrinsic limitations, but also to the inadequacy of functional recovery as a viability parameter, as indicated by PET; 4) the authors expect better results from MRI with low-dose dobutamine and first-pass ultrafast MRI with Gd-DTPA for the assessment of myocardial perfusion.