SUBJECTS AND METHODS: Thirty eight consecutive patients with acute myocardial infarction were enrolled in this study. MRI and coronary angiography were performed in all patients during their admission. A 32 segment model was used to analyze the MRI findings. Just before MRI, the electrocardiograms of all the patients were checked and the presence of the pathologic Q wave evaluated. The ischemic territories in each patient were quantified by the number of dysfunctional segments. Myocardial necrosis was determined by the area of delayed hyperenhancement in contrast enhanced MRI, and the myocardial necrosis index per segment was defined as the ratio of the hyperenhanced area to that of the entire segment. The total necrosis index was defined as the sum of all the myocardial necrosis indices in a patient, and the average necrosis index of dysfunctional segment (ANI) was calculated from the total necrosis index/number of dysfunctional segments in a patient. The transmurality of infarction was also assessed.

RESULTS: Of all 38 patients, 26 showed a pathologic Q wave on ECG (Group A), whereas the other 12 did not (Group B). The number of dysfunctional segments, total necrosis index and frequency of transmural infarction (defined by infarct transmurality> or = 75% of wall thickness) were no different between the two groups. The infarct transmurality over 25 or 50% and ANI were significantly different between the two groups. In a multivariate analysis, an infarct transmurality over 50% and ANI were significant factors in determining the presence of a pathologic Q wave.

CONCLUSION: By an in vivo analysis of myocardial necrosis, as determined by MRI in acute myocardial infarction, an infarct transmurality over 50% and average necrosis index of dysfunctional segments (ANI) might be significant factors in the genesis of a pathologic Q wave.