Israeli Prime Minister Ariel Sharon suffered a significant Hemorrhagic stroke today, according to a hospital here. He had been scheduled to undergo repair of a patent foramen ovale defect tomorrow.

Shlomo Mor-Yosef, M.D., the hospital’s director general, said that Sharon, 77, had suffered a cerebral hemorrhage with “massive bleeding” and was undergoing brain surgery.

The fact that Sharon was taken to surgery is not a good sign, said Anthony Furlan, M.D., head of the section of stroke and neurocritical care at the Cleveland Clinic Foundation.

“In fact the clinical trials comparing surgery to medical therapy for treatment of Hemorrhagic stroke didn’t show an advantage of surgery,” he said. “So the only reason that we would take a person to surgery would be that this is life threatening situation.”

Dr. Furlan said that therapy for Hemorrhagic stroke has changed as “we learned more about it. At one time we believed that once a hemorrhage occurs in the brain-that’s it. A one time, bleed and it’s over. Now we know that bleeding can continue for the first 24 to 48 hours.”

Larry Goldstein, M.D., a professor of medicine and director of the Duke Center for Cardiovascular Disease in Durham, N.C., said that surgery can only be done if the bleeding is an area that makes surgical evacuation possible.

Dr. Goldstein said that the brain stem, which is the area that is reportedly affected in Sharon, is one of the areas in which surgery would be attempted. When the hemorrhage is related to use of blood thinners, “vitamin K or fresh platelets can be tried to overcome the effect of the Coumadin.”

Sharon suffered what was called a minor stroke last month. At that time doctors discovered a patent foramen ovale defect, the so-called hole-in-the-heart defect that is thought to be a risk factor for ischemic stroke.

Dr. Goldstein noted that although patent foramen is not associated with Hemorrhagic stroke there are a number of factors that could have triggered a cerebrovascular bleeding event in Sharon.

“I’m told he was on blood thinners, so that could be a contributing factor,” he said. “But hypertension is a major risk factor and it is possible that he has high blood pressure.” Dr. Goldstein said that following an ischemic stroke patients may be put on aspirin or more potent blood thinners such as Coumadin (warfarin).

Chaim Lotan, M.D., chief of cardiology at Hadassah University Medical Center here, said the patent foramen ovale had been discovered during Sharon’s hospitalization and apparently contributed to the minor stoke on Dec. 18. The hole, Dr. Lotan said, is less than an eighth of an inch wide.

Although a patent foramen ovale is not considered to be a heart defect and does not increase cardiac workload, it can be the source of a stroke under certain rare circumstances, according to the American Heart Association. For example, a thrombus can travel from the venous system to the right atrium, and if right-sided pressures exceed left-sided pressures, across the patent foramen ovale, into the left atrium, and then into the cerebral circulation, resulting in a stroke.

It is hypothesized that when there is a change in the normal pressure gradient within the heart, which can occur, for example, during a Valsalva’s maneuver, blood can be shunted from the right atrium into the left. If this counter-flow carries debris or a thrombus with it, the clot or material can be pumped out into the systemic circulation and cause an embolic cerebrovascular event such as a transient ischemic attack or stroke.

Alternatively, if the inter-atrial septum is particularly mobile, it could allow a clot to form on the site of the patent foramen ovale itself, Dr. Tuzcu said.

Sharon’s doctors elected a catheter-based approach to seal the patent foramen ovale. They described it as involving a percutaneous placement of an umbrella-like device that seals the hole in the heart wall. It becomes a permanent implant and often avoids the long-term use of Coumadin (warfarin).