Delayed enhancement cardiovascular magnetic resonance to detect non-Q wave heart attacks
Apr 25, 2009 - 3:09:44 PM
In a paper published by PLoS Medicine, Han W. Kim and colleagues from the Duke Cardiovascular Magnetic Resonance Center, United States of America, use a recently developed technique to detect heart damage in patients who don't have symptoms or abnormalities in the electrocardiogram (ECG) that are usually associated with a heart attack ( myocardial infarction ). They show that the prevalence of this type of heart attack which doesn't display ECG abnormalities is more than three times higher than heart damage which does display ECG abnormalities.
Although coronary artery disease is the leading cause of death among adults in developed countries, up to 40 60% of heart attacks are not preceded by typical symptoms and are not immediately identified by patients or physicians, if at all. Therefore, these heart attacks are known as unrecognized myocardial infarctions (UMIs). The diagnosis of UMI is currently based on the appearance of changes in the ECG, leading to so-called Q-waves . However, not all UMIs result in Q-waves. Han Kim and colleagues therefore used a technique known as delayed enhancement cardiovascular magnetic resonance (DE-CMR) to detect heart damage in patients whose Q-waves were absent.
The researchers studied 185 patients with suspected coronary artery disease but with no history of heart attacks. They then followed the patients for 2 years to discover whether a diagnosis of non-Q-wave UMI predicted their likelihood of dying from any cause including from a heart problem. They found that non-Q-wave UMI occurred more than three times as often in patients with suspected coronary artery disease than Q-wave UMI. They also found that patients with this silent heart damage had an 11-fold higher risk of death from any cause and a 17-fold higher risk of death from a heart problem than patients without heart damage.
The clinical implications of the study are discussed in an expert commentary by Clara Kayei Chow from the Population Health Research Institute, McMaster University, Canada, and The George Institute for International Health, University of Sydney, Australia, who was not involved in the study. This important new study has two key clinical implications. First, previous non-Q-wave UMI is potentially being missed in patients with suspected coronary artery disease. Second, non-Q-wave UMI is important because it is significantly associated with increased mortality, she says. She also points out, however, that the results are from a small select group of patients and that further studies need to be done to evaluate the determinants of the increased mortality in patients with non-Q wave UMI. In addition the study will need repeating in other groups of patients. Finally, two of the authors are named on a US patent on the technique used in this study, Delayed Enhancement CMR. The patent itself is owned by Northwestern University.
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