New research at the prestigious Mayo Clinic in the US has questioned the need for surgery to close the congenital heart defect called foramen ovale - a small hole between the two upper chambers of the heart - to prevent a stroke. Such a hole was discovered in former prime minister Ariel Sharon after his harmless ischemic stroke on January 4 that led to his anxiety about having surgery under general anesthesia and his being given a "cocktail" of anti-clotting drugs by Hadassah-University Medical Center cardiologists. It was the "cocktail" that apparently led to his suffering a devastating hemorrhagic stroke soon after. Hadassah doctors have said that they recommended the surgery to close the hole - which was never performed because Sharon's first stroke occurred the night before the scheduled operation - on the basis of medical literature, experience and recommendations in Israel and abroad. They said they gave Sharon the "cocktail" of anticoagulants to prevent him from developing more clots and suffering another ischemic stroke. The presence of the anticoagulants in his bloodstream, however, made it very difficult for neurosurgeons to halt the bleeding in his brain from his hemorrhagic stroke, from which he has never recovered. The May issue of the journal Mayo Clinic Proceedings reached its conclusion without referring to the famous Sharon case. Dr. George Petty, the lead author of the study, said that 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. He noted that the team's findings called 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 at birth 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. The Mayo Clinic journal's study contradicts previous PFO studies, noting that past studies may have "overestimated the relationship" between PFOs and stroke risk due to a variety of "biases," including selective referral of cases. Previous studies have led to an increasing use of anticoagulants or PFO closure procedures in patients who have a stroke or warning of a stroke and when doctors can't identify another cause. Such strokes are known as cryptogenic strokes (strokes of unknown cause) and annually afflict about 200,000 people in the US alone; 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," said Petty, whose research involved 1,072 residents of Olmsted County, Minnesota who underwent transesophageal echocardiography between 1993 and 1997. The new findings should induce patients with PFOs and their physicians to carefully consider whether a closure procedure is necessary, said study co-author Dr. Bijoy Khandheria. He added that he expected the findings to be controversial, partly because PFO closure procedures totaling $2 billion are performed each year in the US alone. Asked to comment, Prof. Dan Tzivoni, chief of cardiology at Jerusalem's Shaare Zedek Medical Center and head of the Israel Heart Society, told the Post he believes that in the past there had been "too much enthusiasm abroad and in Israel" for sealing PFOs in patients who had migraine or other conditions. "But the situation is different for certain patients who have already had an ischemic stroke and a PFO is discovered," said Tzivoni. "Saline solution is introduced while the patient has transesophageal echocardiography, and you can see microsopic bubbles passing from one side of the heart septum to the other. If there is free movement of many bubbles rather than only a few, it is usually advisable to close the hole, because the hole is much more likely to have caused the stroke," Tzivoni said. "I don't know for a fact if Sharon's echocardiography showed many bubbles passing through, but rumor has it that it did. I agree," he continued, "that the closing of PFOs should be carried out only in selected cases, such as those showing a lot of bubbles. I think studies like this will reduce the number of such operations but not eliminate them completely." The Hadassah Medical Organization declined to allow its cardiologists to be interviewed on the subject, but spokeswoman Yael Bossem-Levy said: "The Mayo Clinic article is one of many that presents an approach. It deals with one issue related to PFOs and not with other factors that were involved in the decision-making of Hadassah doctors who treated Ariel Sharon. The article is not relevant to his treatment." She did not say whether Sharon's echocardiography showed a large free flow of bubbles or not. The Mayo Clinic Proceedings study indicates that in the general population and particularly for 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 strokes. Larger population-based studies were needed to determine the magnitude and nature of the risk for those patients, say Mayo physicians. Broad interpretations exist on data related to PFOs and whether they cause stroke, wrote Dr. Harold Adams Jr. of the University of Iowa's neurology department as a commentary on the Minnesota study. Lacking, he said, were good estimates of overall risks or variables that could affect prognosis. Adams noted that the study serves as a reminder to physicians to exercise caution when a "new" cause of a common disease such as stroke is described. Additional research would help determine the best course of treatment for patients with PFOs, Adams wrote, and would give physicians and patients the necessary data to make educated treatment decisions.