Hardening Of The Aorta Increases The Risk Of Stroke

"This is the first prospective, long-term study of the relationship between atherosclerosis in the aorta and risk of stroke and death. We found that as this important vessel becomes diseased, long-term risk increases dramatically," says Victor G. Davila-Roman, M.D., principal investigator and associate professor of medicine and anesthesiology. "Now that we've identified patients at risk the next step is to identify treatments that can lower the risk."

Davila-Roman and colleagues studied 1,957 patients undergoing cardiac surgery. During the surgery, the researchers made images of the ascending aorta using a technique called epiaortic ultrasound. After evaluating those images to detect the presence and severity of atherosclerosis, they followed the study patients for an average of three and a half years.

Stroke is a major problem in patients undergoing cardiac surgery. Depending upon patient age and other risk factors, up to 15 percent have strokes during or soon after surgery. These investigators previously had shown that hardening of the aorta was a risk factor for those strokes. This new study wanted to learn whether the risk would decrease with time or remain high in patients with hardening of the aorta.

More than half of the patients in this study had no signs of atherosclerosis. About 24 percent had mild disease, while 13 percent were classified as moderate. The remaining 5 percent had severe atherosclerosis in the aorta.

"When I went to medical school, we were taught that the aorta was pretty much spared from hardening of the arteries, but this study and others show that notion was wrong," says Benico Barzilai, M.D., co-investigator and associate professor of medicine.

Although some patients from all four groups suffered neurologic events or died in the years after their surgery, the rates were significantly higher in those with the most advanced atherosclerosis. In patients with normal aortas or mild atherosclerosis, about 4 percent suffered strokes or brief, stroke-like events called transient ischemic attacks (TIAs) in the three years after surgery. Some 15 percent of patients with normal aortas died of various causes during follow-up, and 22 percent of those with mild disease died.

In patients with moderate disease, the incidence of stroke or TIA rose to 5.6 percent, and 31 percent died during follow-up. Those with severe atherosclerosis suffered strokes or TIAs at a rate of just over 10 percent, and more than 43 percent died during the follow-up period.

In all, the risk of a neurologic event or death increased one and a half times as the severity of the atherosclerosis increased from normal or mild to moderate. And there was more than a 300 percent increase in the incidence of both as the severity of disease progressed from normal or mild to severe.

"Other factors increase the risk of stroke and mortality too," Davila-Roman says. "The age of the patient is closely related, as are high cholesterol levels, diabetes, smoking and blockages in the carotid arteries that carry blood to the brain. But our study clearly shows that atherosclerosis in the ascending aorta is an independent and significant risk factor."

Most stroke-causing blood clots form in the heart or in the carotid arteries leading to the brain, but the source of about 40 percent of strokes is unknown. Davila-Roman and Barzilai believe that diseased aortas could explain some of them.

"During surgery, the surgeon manipulates the aorta quite a bit. If you can imagine an aorta full of plaque, you can see that in patients with atherosclerosis, one of those plaques might break loose as the vessel is moved around. Or perhaps it could break free weeks or years later and migrate toward the brain to cause a stroke," Davila-Roman explains.

Or maybe hardening of the aorta is a sign of disease throughout the body, the researchers say. In that case, plaques in the aorta might not cause a stroke but might signal the presence of disease in other vessels. In an earlier study, the researchers found that hardening of the aorta is linked to kidney failure, presumably through the same mechanism that could cause strokes.

"Our imaging technique allows us to put the ultrasound probe right onto the vessel and look directly at the ascending aorta," says Barzilai. "It's easy to imagine that if plaques break loose, they can potentially travel downstream toward the blood vessels that feed the brain or kidneys or other organs. But it's also likely that patients with the disease in this very early part of the aorta also have atherosclerosis throughout the body."

The investigators hope to test available therapies to learn whether they can lower the risk of stroke and death with aspirin, warfarin or other anti-platelet and blood-thinning drugs.

This research was supported in part by a grant from the American Heart Association.

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