Computerized tomographic (CT) appearance of the myocardium after reversible and irreversible ischemic injury

Computerized tomographic abnormalities have been observed within hours after coronary occlusion. It has not been determined whether these CT changes are always indicative of irreversible myocardial damage or whether they can be produced by reversible myocardial injury. Accordingly, in the current study, the circumflex coronary arteries of 16 dogs were occluded for 20 minutes (reversible injury) or 40 minutes (irreversible injury) and then reperfused. The animals were sacrificed 24 hours later. Ten minutes prior to sacrifice, eight of the dogs received contrast material intravenously. The electron microscopic changes in the 20-minute occlusion group consisted of reversible damage, while those in the 40-minute group were irreversible. Two of the animals in the 20-minute group showed slightly decreased X-ray density of the infarct in the absence of contrast media, but none showed contrast enhancement of the infarct in the presence of contrast media. All the animals in the 40-minute group showed decreased X-ray density, and all animals that received contrast media had contrast enhancement of the area of ischemic damage. The results of the current study suggest that the decreased X-ray density of the area of ischemic damage on CT scans is due to cellular edema and may be observed in reversible myocardial injury, while delayed contrast enhancement is only associated with, and is indicative of, irreversible myocardial injury.