MRI may hold clue to second AMIs
Microvascular obstruction predicts damage
Whether magnetic resonance imaging (MRI) plays a role in your chest pain unit's future is a matter of speculation, but investigators from Johns Hopkins University School of Medicine in Baltimore ran a study recently to see whether profound microvascular obstruction after heart attack can predict two-year cardiovascular morbidity and mortality.1 Using contrast-enhanced MRI, they scanned 44 post-heart attack patients and found 11 with partially blocked heart capillaries. Nearly half had complications later, including a second acute myocardial infarction (AMI), congestive heart failure, stroke, or death. Only about 10% with normal MRIs had complications.
The researchers' conclusion: Yes. After infarction, obstruction does predict frequent complications, and the extent of total myocardial ischemic injury - infarct size - relates directly to the risk of cardiovascular complications and long-term prognosis. The investigators write, "The ability to combine microvascular perfusion studies with direct measurements of infarct extent illustrates the potential of MRI to study the heart after acute coronary thrombosis."
Karen N. Elder, RN, MSN, coordinator of case management practices at Vanderbilt University Medical Center in Nashville, TN, and consulting editor of Cost Management in Cardiac Care, says she thinks it impractical to perform MRIs on chest pain patients: "I can't see MRI being used on any regular basis for AMI diagnosis. Indeed, the tool can be used to rule out aortic dissection, but for one thing, the MRI machine is very large and cumbersome, and chest pain patients typically have a lot of IV drips." Robert Eisner, PhD, co-director of nuclear cardiology at Crawford-Long Hospital in Atlanta, agrees: "Some machines are more open than others, but none do well with metal around them." He suggests having an echo machine close by the patient instead of using MRI to look at wall motion for tissue viability and function. "I don't see the advantage of MRI," he says.
Reference
1. Wu KC, Zerhouni EA, Judd RM, et al. Prognostic significance of microvascular obstruction by magnetic resonance imaging in patients with acute myocardial infarction. Circulation 1998;97:765-772.
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