Signal intensity of myocardial scars at delayed-enhanced MRI

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.

To investigate differences in tissue characteristics between UMI and recognized myocardial infarction (RMI) scars, by assessing the signal intensity (SI) detected by DE-MRI.

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.

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.

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.