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MRI of reperfused myocardial infarct in dogs
Abstract:
The current study evaluated the capability of magnetic resonance imaging (MRI) to detect acutely injured myocardium in the first 5 hr after a 1-hr period of occlusion followed by reperfusion of the coronary artery and to determine if magnetic relaxation times could be used to differentiate injured from normal myocardium. Fourteen dogs underwent left anterior descending coronary arterial occlusion for 1 hr, followed by reperfusion. Electrocardiographic gated MRI was performed before and during coronary artery occlusion and immediately after reperfusion, and serially up to 5 hr postreperfusion. In all dogs with postmortem evidence of myocardial infarction (n = 7), regional increase of signal intensity was observed in the anterior wall of the left ventricle as early as 30 min after reestablishing blood flow to the jeopardized myocardium. The area of increased signal intensity in the myocardium conformed to the site of myocardial infarction found at autopsy. The signal intensities of the jeopardized myocardium were significantly (p less than 0.01) greater than those of normal myocardium at 30 to 300 min postreperfusion. The T2 (spin-spin) relaxation time was significantly (p less than 0.05-p less than 0.01) prolonged in the region of the reperfused myocardial infarct at 30 min (59.6 +/- 13.1 msec) and remained prolonged up to 300 min (62.6 +/- 12 msec) postreperfusion compared with the T2 of normal myocardium (40.6 +/- 5.2 msec). Of the remaining seven dogs, four developed fatal arrhythmias during the reperfusion procedure and three dogs had no evidence of myocardial infarction at pathologic examination. Signal intensities and T2 relaxation times in these three dogs did not change during the experiment. Thus, acutely infarcted and reperfused myocardium can be detected by in vivo gated MRI, using the spin-echo technique, as early as 30 min after reperfusion. The jeopardized myocardium is characterized by a prolonged T2 relaxation time and, therefore, best visualized on T2-weighted images.
Insights
Magnetic resonance imaging (MRI) can detect acute myocardial infarction within 30 minutes of reperfusion. Prolonged T2 relaxation times in injured heart muscle are key indicators, differentiating it from healthy tissue.
Area of Science:
- Cardiovascular Imaging
- Diagnostic Radiology
- Biomedical Engineering
Background:
- Early detection of myocardial infarction is crucial for timely intervention.
- Assessing myocardial injury post-reperfusion remains a clinical challenge.
- Magnetic resonance imaging (MRI) offers non-invasive visualization of cardiac tissue.
Purpose of the Study:
- To evaluate MRI's capability in detecting acute myocardial injury within 5 hours post-reperfusion.
- To determine if magnetic relaxation times can differentiate injured from normal myocardium.
- To assess the early detection of myocardial infarction using MRI.
Main Methods:
- Fourteen dogs underwent 1-hour coronary artery occlusion followed by reperfusion.
- Electrocardiographic-gated MRI was performed serially before, during, and up to 5 hours post-reperfusion.
- Spin-echo MRI sequences were utilized to measure signal intensity and T2 relaxation times.
Main Results:
- Increased signal intensity in the anterior wall myocardium was observed as early as 30 minutes post-reperfusion in infarcted dogs.
- Signal intensities in jeopardized myocardium were significantly higher than normal myocardium (p<0.01).
- T2 relaxation times were significantly prolonged in the infarct region (59.6±13.1 ms at 30 min, 62.6±12 ms at 300 min) compared to normal myocardium (40.6±5.2 ms).
Conclusions:
- In vivo gated MRI with spin-echo technique can detect acutely infarcted and reperfused myocardium as early as 30 minutes post-reperfusion.
- Prolonged T2 relaxation times characterize jeopardized myocardium, making it best visualized on T2-weighted images.
- MRI is a valuable tool for early diagnosis and characterization of myocardial infarction and reperfusion injury.