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Signal intensity of myocardial scars at delayed-enhanced mri

Background: Traditionally, unrecognized myocardial infarction (UMI) is defined as the appearance, in a non-acute setting, of a new diagnostic Q wave. In the recent past, delayed-enhanced magnetic resonance imaging (DE-MRI) has provided a new imaging method for evaluating myocardial viability and to detect myocardial scars. Purpose: To investigate differences in tissue characteristics between UMI and recognized myocardial infarction (RMI) scars, by assessing the signal intensity (SI) detected by DE-MRI. Material and Methods: A randomized subgroup of 259 subjects from the Prospective Investigation of the Vasculature of Uppsala Seniors (PIVUS) study was submitted to cardiac magnetic resonance imaging (MRI). DE-MRI-detected myocardial scars were divided in two groups, UMI and RMI, according to the hospital medical records. The scars detected by DE-MRI were analyzed by measuring SI ratio of scar tissue to normal myocardium. Results: The mean SI ratio in the UMI group (4.5±3.0, mean±SD) was lower than in the RMI group 8.9±5.1 (P-value = 0.001). This difference was still significant (P<0.0001) after adjustment for gender, body mass index, time of image acquisition after gadolinium administration, scar transmurality, or total myocardial infarction mass. Conclusion: The difference in the SI ratio of the scars between the two groups most likely reflects a different contrast distribution volume of the tissues, which might indicate that UMI and RMI tissues diverge in tissue composition.