Diagnostic Accuracy of Delayed Enhanced MRI for Predicting Myocardial Viability in Acute and Chronic Myocardial Infarction: Thickness of Non-enhanced Myocardium is a Better Predictor of Functional Recovery
Purpose: Previous reports indicated that delayed contrast enhanced MRI overestimates the size of acute myocardial infarction (MI). The purposes of this study were to evaluate serial changes of delayed enhanced tissue and non-enhanced myocardium in the left ventricular (LV) wall in patients after MI, to determine whether thickness of non-enhanced myocardium is a better predictor of functional recovery than transmural extent of delayed enhancement, and to assess the diagnostic value of delayed enhanced MRI in patients early after onset of MI.
Methods and Materials: Fifteen patients with acute MI (9 men and 6 women; mean 60.5±8.7 years) were enrolled in this study. Breath-hold inversion recovery MR images were acquired 15-20 minutes after administration of Gd-contrast medium in acute phase (4.7±1.4 days after onset) and chronic phase (9.7±4.4 months after onset) in all patients. The area and mean thickness of enhanced tissue and non-enhanced myocardium were quantitatively determined by using a 30-segment model. Systolic wall thickening on follow-up cine MR was used for evaluating the recovery of regional myocardial contraction.
Results: The infarct size determined by delayed enhancement significantly decreased from acute phase to chronic phase (19.8±8.9g versus 13.5±6.3g, p<0.001). The averaged thickness of non-enhanced myocardium in the infract segments significantly increased (5.2±3.1mm versus 6.5±3.2mm, p<0.001). The ROC analysis indicated that thickness of non-enhanced myocardium (Az 0.923) in each LV segment is a better predictor of functional recovery than transmural extent of delayed enhancement (Az 0.827, p<0.001). When thickness of non-enhanced myocardium equal to or greater than 5.0mm was used as a diagnostic criterion, the sensitivity, specificity, and accuracy of contrast-enhanced MRI were 64.5%, 90.0% and 72.8% in acute phase and 84.6%, 90.0% and 86.4% in chronic phase, respectively.
Conclusion: The diagnostic performance of delayed enhanced MRI for predicting functional recovery of regional myocardial contraction can be significantly improved by measuring thickness of non-enhanced myocardium rather than transmural extent of delayed enhancement. Preserved thickness of non-enhanced myocardium (³5mm) reliably indicates regional myocardial viability in patients early after onset of MI as well as those with chronic MI.