Smaller hospitals OK for heart bypass surgery - if your risk is small

November 30, 2001

First study to combine patient health status with hospital bypass results challenges earlier findings

High-risk patients still better off at high-volume hospitals, but others can stick closer to home

ANN ARBOR, MI - Learning you have to have a heart bypass operation is scary enough. But now, a new study may take some of the fear out of choosing where to have the operation.

Researchers from the University of Michigan Health System report today a finding that challenges the perception that all bypass patients should go to the biggest medical center they can, no matter how far away from home, to get a surgical team that does hundreds of bypasses.

This "practice makes perfect" effect on patient survival was popularized in recent years by several studies that found better results for patients who had their bypass surgery at big hospitals that do many such operations a year, versus patients treated at smaller local hospitals.

But, the U-M researchers report in the December Journal of the American College of Cardiology, those generalizations about differences between hospitals overlooked the differences between patients themselves. When you factor in the patients' own health risks, the picture changes.

In fact, the U-M team finds, patients whose overall health is good - aside from their clogged arteries - do fine if they have a bypass at a hospital that does less than 200 of them a year. But moderate- and high-risk patients, such as those with high blood pressure, diabetes or other health problems that could make an operation tricky, should be sure to seek out a major medical center whose surgical teams do hundreds of bypasses a year, in order to lower their chance of dying.

"It may seem strange for physicians from a major hospital to do a study that finds you don't necessarily have to come to us or our peers for your surgery, but our results strongly suggest this," says senior author Kim Eagle, M.D., the Albion Walter Hewlett Professor of Internal Medicine and UMHS chief of clinical cardiology. "While higher-risk patients should find the most experienced team they can, those low risk can rest assured that a smaller hospital closer to home can care for them very well, with similar costs and time in the hospital."

The new results, says an accompanying editorial, are important and should influence further study and policy debate over the proposed "regionalization" of non-emergency bypass surgery that would limit complex surgeries to hospitals that perform a high number of the procedures.

Such a move, says lead author and U-M cardiology fellow Brahmajee Nallamothu, M.D., M.P.H., would inconvenience patients and their family, and cut their health care choice and access. And, he says, it would further overload the already stressed medical staffs at major medical centers, while putting at risk the ability of small hospitals to sustain surgical and emergency services. "The question has been, would the drawbacks be worth the lives saved?," he explains.

Based on the new results, the U-M team instead proposes "targeted regionalization", in which lower-volume hospitals take the lowest-risk cases and refer trickier ones to major centers that handle more - and more complex - patients. If such a strategy had been used for patients in their study, the analysis found, only four more patients would have died than if full regionalization system had been used, but 1,659 fewer patients would have faced a transfer to other hospitals.

Eagle, Nallamothu and their colleagues from UMHS and the Department of Veterans Affairs Ann Arbor Healthcare System made the finding using data on 13,644 patients over the age of 35 who had non-emergency coronary artery bypass grafts at 56 hospitals across the United States in 1997. The researchers set their cutoff point between "low volume" and "high volume" hospitals at 200 bypasses per year, but also looked at thresholds of 100 and 300 cases.

For each patient, the team looked not only at where they had their surgery, but also at their age and gender, the severity of their heart disease, the urgency of their need for a bypass, their other health risks and the interaction between these factors. Based on this information, the researchers assigned each patient a minimal, low, moderate, high or severe risk of dying during surgery or in the hospital, with odds ranging from less than 2 percent for minimal and low risk, to 5 percent for moderate risk, to 20 percent for high risk and above 20 percent for severe risk.

For example, Nallamothu says, a middle-aged man with no other health conditions and having a bypass electively to prevent possible problems would be minimal-risk. But an 80-year-old woman with diabetes and kidney problems who needs a bypass urgently would be high-risk.

In all, 2,029 of the patients had their operations at one of 25 hospitals that did fewer than 200 bypasses in 1997, while the other 11,615 went to 31 hospitals that performed 200 or more. The study recorded how many of them died before leaving the hospital, then cross-referenced their outcomes with their pre-surgery risks. The data came from a national health care database.

"Those patients whose initial risk had been seen as minimal or low did just as well at the low-volume hospitals as at the high-volume ones," says Nallamothu. "But those whose risk was moderate or high were about twice as likely to die in the hospital if they had their operations at low-volume hospitals," with an in-hospital death rate of more than 5 percent versus 2.2 percent for moderate risk and 22.6 percent versus 11.9 percent for high risk.

As for those whose pre-operative risk was severe, the study is inconclusive. Though the actual survival of these patients was the same at both types of hospital, Eagle attributes this to a statistical fluke caused by the low number of such patients seen at low-volume hospitals.

Overall, the cost of caring for the patients, and the number of days they each spent in the hospital, was roughly similar no matter where they were treated. And a lower or higher threshold between high- and low-volume hospitals didn't make a difference.

Says Harold S. Luft of the University of California, San Francisco in the editorial, "The underlying concept is an important step forward; the empirical implementation may suffer from some weaknesses, but despite this, the policy implications are worthy of serious discussion."
Besides Eagle and Nallamothu, the study's authors include: Sanjay Saint, M.D., M.P.H., Scott Ramsey, M.D., Ph.D., Timothy Hofer, M.D. MSc., and Sandeep Vijan, M.D., MSc.

University of Michigan Health System

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