Having a hole in the upper chamber of the heart is not as significant in causing stroke in the general population as previous studies have suggested, finds a new Mayo Clinic study. The findings call into question the need for surgeries to close the holes in many such patients.
Known as patent foramen ovale (PFO), a small hole in the upper chamber of the heart is present in one-fourth to one-third of all people. In recent years numerous studies have suggested that PFOs commonly cause stroke by allowing blood clots to pass through the heart, bypass the lungs and go to the brain.
Mayo's study, published in the May issue of Mayo Clinic Proceedings, contradicts previous PFO studies. Past studies may have overestimated the relationship between PFOs and stroke risk due to a variety of biases, Mayo physicians say, including selective referral of cases.
Past studies have led to an increasing use of anticoagulants or PFO closure procedures in patients who have a stroke or warning of a stroke, but when doctors can't identify another cause. Such strokes are known as cryptogenic strokes (strokes of unknown cause) and afflict about 200,000 Americans annually. As many as 50,000 or more of these stroke victims have a PFO.
"Our study indicates that in the majority of these patients, the PFO and the stroke are unrelated," says George Petty, M.D., lead author of the study published in Mayo Clinic Proceedings.
Mayo's population-based study on the relationship between PFOs and cryptogenic strokes involved 1,072 Olmsted County, Minn., residents who underwent transesophageal echocardiography between 1993 and 1997.
The new findings should prompt patients with PFOs and their physicians to carefully consider whether a closure procedure is necessary, says study author, Bijoy Khandheria, M.D. He expects the findings to be controversial in part because PFO closure procedures totaling $2 billion are performed annually.
The study's findings indicate that, in the general population and particularly those over age 55, traditional cardiovascular risk factors are more important than PFO in contributing to cryptogenic strokes. In younger patients, however, PFO may play a more important role in causing cryptogenic stroke. Larger population-based studies are needed to determine the magnitude and nature of the risk for those patients, say Mayo physicians.
Other authors of the PFO study are Irene Meissner, M.D., and David Wiebers, M.D., from Mayo Clinic's Division of Cerebrovascular Diseases and Department of Health Sciences Research; and Jack Whisnant, M.D.; Walter Rocca, M.D.; Teresa Christianson; JoRean Sicks; Michael O'Fallon, Ph.D.; and Robyn McClelland, Ph.D., all from Mayo's Department of Health Sciences Research.
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