Patients at low risk of dying after coronary artery bypass graft surgery fare better with high-volume surgeons

Aug 11 2004

Patients at low risk of dying after coronary artery bypass graft (CABG) surgery have a significantly better chance of survival when treated by surgeons and hospitals that handle many cases, researchers report in today’s rapid access issue of Circulation: Journal of the American Heart Association.

In a study of more than 57,000 bypass patients in New York, those at low-risk who were treated at hospitals performing at least 200 bypass procedures a year had a 47 percent lower in-hospital death rate compared to those treated at hospitals where fewer than 200 procedures are performed annually. The death rate for moderate- and high-risk patients was 38 percent lower at higher-volume hospitals compared to hospitals with annual CABG volumes less than 200.

The researchers divided hospitals into volume groups based on a threshold for annual number of bypass operations at 200, 300, 400, 500 or 600. “For both risk groups, patients in hospitals with a volume above any threshold consistently had lower observed mortality rates than those in hospitals with a volume below a threshold,” said lead author Chuntao Wu, M.D., Ph.D., a research scientist and an assistant professor of epidemiology in the School of Public Health at the State University of New York in Albany.

Surgeons were grouped according to thresholds set at 50, 75, 100, 125 or 150.

Researchers found that low-risk patients treated by surgeons who perform at least 125 procedures per year at higher-volume hospitals had a 48 percent lower risk of death in the hospital compared to patients treated by surgeons who performed fewer than 125 bypass surgeries per year in hospitals with CABG volumes less than 600 per year.

At most volume thresholds examined, high provider volume was associated with a significantly lower in-hospital death rate for patients at all levels of risk.

“For all patients, not just those at high risk of mortality, high-volume providers — both hospitals and surgeons — are associated with a lower risk of death,” said Wu.

The new findings could have a major influence on debates about where bypass surgery should be performed, researchers said.

Previous studies have found that the benefit of high-volume hospitals is limited to high-risk patients. This has led to the suggestion that only high-risk patients be referred to high-volume hospitals.

“Our findings support applying a volume-based referral to all bypass patients, not just those at high risk, when there are no better quality indicators available,” Wu said. “But performing most bypass surgeries in high-volume hospitals could overburden them and cause hardships for many patients.”

He and colleagues from 10 medical institutions said it would be better to improve the quality of care at all hospitals than to send most bypass patients to high-volume medical centers. They note that a volume-based referral could increase the travel difficulties and expenses for many patients, and further reduce the number of patients treated at low-volume hospitals.

“Thus, it is preferable to improve outcomes by identifying processes of care associated with superior outcomes, and implementing these processes in both high-volume and low-volume hospitals rather than to refer all patients to high-volume centers,” Wu said.

The researchers examined the records of 57,150 patients who had bypass surgery without other major heart procedures during 1997–99. They used data collected by the New York State Cardiac Surgery Reporting System, which has registered bypass patients operated on in the state since 1989.

Patients were divided into two groups: Low-risk patients had a lower than 2 percent risk of dying in the hospital, and moderate-to-high-risk patients had a 2 percent chance or higher. There were 39,491 low-risk patients and 17,659 moderate-to-high-risk patients.

Risk factors for in-hospital death include age, female gender, a previous heart attack, a patient’s ejection fraction (the amount of blood the heart pumps with each beat), and a variety of other conditions. “Older people and women are at higher risk of dying in the hospital after bypass surgery,” Wu said.

Among all the patients, 1,260 (2.2 percent) died in the hospital — 312 (0.79 percent) low-risk patients and 948 (5.37 percent) moderate-to-high-risk patients.

“Our observations are based on average outcomes,” Wu said. “If you look at individual hospitals, not all low-volume hospitals have poor outcomes and not all high-volume hospitals have good outcomes.”

Co-authors of the report are Edward L. Hannan, Ph.D.; Thomas J. Ryan, M.D.; Edward Bennett, M.D.; Alfred T. Culliford, M.D.; Jeffrey P. Gold, M.D.; O. Wayne Isom, M.D.; Robert H. Jones, M.D.; Barbara McNeil, M.D., Ph.D.; Eric A. Rose, M.D.; and Valavanur A. Subramanian, M.D.