According to the researchers, defibrillators are prescribed when tests show abnormalities in the heart's ejection fraction (ability to squeeze blood to the rest of the body) and/or its resistance to electrical impulses that try to stimulate an arrhythmia.
"Our MRI technique has significant advantages over existing methods because it avoids the risks of infection that come with surgery, it is noninvasive, there are no catheters, and it is relatively easy to perform, taking only 45 minutes," says study co-author and cardiologist Joo Lima, M.D., an associate professor of medicine and radiology at Hopkins.
Lima notes that a patient with an ejection fraction of 60 percent has normal pumping ability, but anything less than 30 percent for a period of nine months or longer is considered low and an immediate risk factor for arrhythmia. He adds that if a patient has an ejection fraction that is slightly above 30 percent, then an electrophysiology test is used to determine if a patient requires a defibrillator. In this test, a thin catheter is inserted into the heart to try to induce an arrhythmia, something that will fail if the heart is healthy and not at risk. However, if it happens once, it is known to be two to four times more likely to happen again, he says.
Twenty-six patients from the Baltimore area participated in the study, which took place from July 2003 to February 2005. Participants were men and women, with an average age of 53, referred by community physicians to Hopkins for cardiac assessment. None had previous signs of coronary artery disease, another leading cause of sudden cardiac death, yet were experiencing other symptoms of heart disease, such as shortness of breath, instant fatigue and the inability to walk up stairs.
As part of a baseline MRI, the researchers used a technique developed at Hopkins to
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Contact: David March
dmarch1@jhmi.edu
410-955-1534
Johns Hopkins Medical Institutions
1-Nov-2005