High risk patients less likely to die if they undergo stress testing before surgery but low risk patients may be harmed

29/01/2010

Patients scheduled for major surgery sometimes undergo specialized heart tests (or stress tests) before surgery to help determine whether they have heart disease. Physicians can use the information from these tests to improve the care of patients undergoing major surgery. Researchers at the Institute for Clinical Evaluative Sciences (ICES) found that specific types of patients who underwent stress testing before major surgery had a lower chance of dying within one-year after surgery, as well as a shorter hospital stay, than people who did not.

The study of 271,082 patients who had major surgery in Ontario between April 1, 1994 and March 31, 2004 found:

Nearly 9 per cent of all patients underwent non-invasive stress testing within 180 days before surgery.
If patients had risk factors for heart complications after surgery, they had a lower chance of dying within one-year, as well as a shorter hospital stay, if they underwent stress testing before major surgery.
For patients with one to two risk factors, one death could have been prevented for 156 tests that were performed.
For patients with three or more risk factors, one death could have been prevented for every 38 tests that were performed. It is presumed that the test itself is not therapeutic, but it identifies patients who need more active treatment to prepare for surgery.
On the other hand, patients who had stress testing despite having no risk factors had a slightly higher chance of dying within one-year after surgery. For these patients, one extra death may have resulted for every 179 tests that were performed. The reasons for this increase are unclear, but may be due to unnecessary, and potentially harmful, interventions that occur because of these tests.
Important risk factors for heart-related complications after surgery include known heart disease, heart failure, stroke, diabetes, kidney disease, and high-risk operations. High-risk operations include abdominal or chest surgery.

“Stress testing in high risk patients enables physicians to manage that risk and yields real benefits for patients. Paradoxically, in patients who don’t have risk factors for heart complications, the adverse outcomes from testing and treatment outweigh any benefit. Accordingly, tests are most helpful for people who have three or more such risk factors. Our results are largely consistent with current guidelines that also suggest that only patients with risk factors for heart complications should undergo stress testing before surgery,” says principal investigator and a researcher at ICES, Dr. Duminda Wijeysundera.

The study “Non-invasive cardiac stress testing before elective major non-cardiac surgery: a population-based cohort study” is in the current issue of the British Medical Journal (BMJ).

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.