Cardiac MR imaging with delayed gadolinium enhancement can detect silent myocardial infarction in diabetic patients and predict the chances these patients will suffer a future cardiac event, according to a study presented at the 2007 Society for Cardiac Magnetic Resonance meeting in Rome. Findings suggest the technique could play a role in screening diabetic patients.
Diabetes hits more than 20 million people in the U.S. alone, according to the American Diabetes Association. A third of them are unaware of their disease. While most people who have a heart attack can feel its effects, many diabetics cannot. Most suffer from some form of autonomic dysfunction and may not feel any pain, said senior investigator Dr. Raymond Kwong, codirector of cardiac MRI and CT at Brigham and Women's Hospital in Boston.
"Not all people who suffer heart attacks have typical symptoms. That includes the elderly, people with renal disease, or women. But diabetics are at especially high risk of silent MI," he said.
Kwong and colleagues performed late-enhancement CMR in 133 diabetic patients with no previous history of MI. Clinical indications included myocardial ischemia. The investigators included more than 50 diabetic patients with a history of MI as controls. Patients also underwent left ventricular ejection fraction and ECG testing.
The investigators found that late-enhancement CMR could detect scarred myocardial tissue previously undiagnosed by other exams. They also found the test could predict the likelihood of another adverse cardiac event, including heart attack, unstable angina, congestive heart failure, and death.
Data showed that late enhancement was the strongest predictor for either an adverse cardiac event or death. While diabetic patients with abnormal enhancement face about three times the risk of suffering another heart attack, their chance of dying could be almost four times higher than that of other patients, Kwong said.
More than 30% of patients in the study showed abnormal late enhancement by CMR. After an average of 17 months follow-up (range, six months to five years), 39 patients experienced adverse events, including 17 deaths. Researchers used a 1.5T scanner and included steady-state free precession cine imaging and late-enhancement imaging with T1-weighted fast gradient-echo sequences.
The association between late gadolinium enhancement results and a bad prognosis is much stronger than that indicated by clinical tests currently available, Kwong said. ECG Q waves did not find signs of silent MI in these patients. Albeit powerful to predict outcomes in patients with known MI, left ventricular ejection fraction testing did not provide useful information in this subset of patients.
"Now we have a technique that shows that diabetic patients are at substantial risk, even though they may not have a history of heart disease, and there is a way to detect an abnormal myocardium, which tells us these people are at risk. The next question we have is, Should we use this technique to screen for these patients and refer them for existing treatments, such as cardiac catheterization or other treatments? That will require a large-scale trial," Kwong said.
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