Hospitals Performing More Heart Valve Surgeries

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Hospitals that perform more heart valve replacement surgeries are far more likely to insert the type of aortic valve considered safest for most older patients, according to a study reported in Circulation: Journal of the American Heart Association.

"Our analyses showed that where you receive your valve replacement appears to be more important than your medical condition or other factors in determining what kind of valve you will receive," said lead author Erik B. Schelbert, M.D., a fellow in the division of cardiovascular diseases at the University of Iowa in Iowa City.

The aortic valve opens and closes with each heartbeat to allow oxygen-rich blood to flow from the heart's main pumping chamber (the left ventricle) to the aorta. As the body's largest artery, the aorta then carries blood to the rest of the body. Aortic valve disease is a malfunction of the aortic valve. This disease is more common in men, smokers, and people with high blood pressure and high levels of cholesterol in their blood.

When an aortic valve must be replaced, surgeons choose between two types. Bioprosthetic valves (BPVs), made from human or animal tissue, can wear out and may need to be replaced within 10 years. Mechanical valves, made of metal, are more durable, so a patient is less likely to require a second operation to replace the valve. However, patients who have mechanical valves are at heightened risk of blood clot formation. For that reason, they must take powerful blood-thinning medications, such as warfarin, which can result in dangerous bleeding. In selecting a valve, the risks of each option must be weighed, along with the patient's preferences and other medical considerations.

In 1998, the American Heart Association and the American College of Cardiology issued guidelines about the choice of valves. They recommended that most patients 65 and older would be better off with BPVs because the risks of complications from blood-thinning therapy is greater than the risk that they will require a second valve replacement.

In the current study, the researchers examined the valve choices made during the three years after the AHA/ACC guidelines were released. Their study was based on national Medicare data in 80,470 patients, each at least 65 years old (average 76), who underwent aortic valve replacement (with or without coronary artery bypass surgery) at 1,045 different hospitals.

Although the guidelines would suggest that most of these patients would receive a BPV, overall less than half of older patients (48 percent) did. The older a patient, the more the balance of risks shifts in favor of utilizing a BPV, according to the guidelines. In the study, older patients were significantly more likely to receive the BPV, given to 60 percent of patients over 90 but only 36 percent of patients between 65 and 69 years of age.

Use of BPVs increased each year, from 44 percent in 1999 to 52 percent in 2001, but was still much lower than anticipated.

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"The apparently large percentage of people over age 65 receiving mechanical valves is troubling, because it suggests unnecessary exposure to anticoagulation as well as the associated risks of blood clots," said Schelbert.

Valve choice was strongly associated with the number of valve replacement surgeries performed in the hospital. When hospitals were divided into 10 groups, based on the number of surgeries, patients who had surgery at the highest-volume hospitals were 2.3 times as likely to receive a BPV (68 percent) as those at the lowest-volume hospitals (28 percent).

"The finding that hospital volume was a very strong predictor of BPV use suggests that most of the variation in BPV use was attributable to where the surgery occurred, rather than any characteristic of the patient. To us, this was a very provocative finding, and we were surprised by the magnitude of the association. I think that hospital valve surgery volume was a proxy for doctors' experience, and our findings suggest that those with less experience in taking care of patients in need of aortic valve replacement do not adhere to the guidelines as well as those with more experience," explained Schelbert.

In the study, most surgery in the nation was performed at low-volume hospitals. In previous studies, hospital volume has been linked with mortality rates following heart surgery, but this study suggests that it might be important to study the relationship of volume with other quality indicators as well.

"Schelbert's article serves as a reminder that what is published in generally accepted guidelines may not necessarily be translated to real-world practice," wrote Lawrence H. Cohn, M.D., professor of cardiac surgery at Brigham and Women's Hospital in Boston, in an accompanying editorial from the same issue. At his hospital, data from 1992-2004 indicates that 81 percent of patients 65 and older received BPVs in their replacement surgeries.

Because the data came from Medicare claim forms, rather than a clinical study, the researchers caution that they cannot verify the accuracy of the forms' data on valve type, although they find no reason to suspect that coding mistakes would favor one type over another.

"We also could not capture the patients' wishes regarding which valve type they would prefer, although I would guess that most would follow the advice of their doctors," says Schelbert.

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Statements and conclusions of study authors that are published in the American Heart Association scientific journals are solely those of the study authors and do not necessarily reflect association policy or position. The American Heart Association makes no representation or warranty as to their accuracy or reliability. http://www.americanheart.org - DALLAS, April 26

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