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EDs that treat more heart attack patients are less likely to miss the diagnosis


A new study from the Institute for Clinical Evaluative Sciences (ICES) shows that emergency departments (EDs) that treat a high volume of heart attack patients are less likely to miss the diagnosis compared to EDs that treat lower volumes of heart attack patients.

“It’s estimated that heart attacks are missed in about two to three per cent of patients who come to EDs in the U.S. and Canada. Failure to accurately diagnose a heart attack leads to delays in the initiation of appropriate treatments, potentially increased mortality, and is responsible for more money recovered in malpractice lawsuits than any other condition,” said Dr. Michael Schull, ICES scientist and lead author of the study.

“Previous studies to identify what may cause a missed heart attack diagnosis have mainly focused on patient factors; however, physician and hospital characteristics may also be important.”

To further investigate this issue, ICES scientists linked the records of all heart attack patients admitted to an Ontario hospital between April 1, 2002 and March 31, 2003, to their ED visit records in the seven days preceding admission. The investigators then assessed whether the annual volume of admitted heart attack patients seen in the ED was associated with missed heart attack diagnoses.

In a secondary analysis, investigators surveyed Ontario EDs to assess whether hospital characteristics, such as triage practices, use of diagnostic tests, and availability of cardiology or internal medicine specialist consultation, explained any ED volume association. And finally, they measured whether missed heart attacks were associated with increased mortality.

Of the 19,663 heart attack patients admitted to hospital during the study period, 419, or 2.1%, had a missed heart attack diagnosis. This rate varied from 1.8%, on average, in the very high volume EDs, to 3.6%, on average, in the very low volume EDs. After adjusting for patient differences, lower volume EDs had up to twice the risk of missed heart attack diagnosis compared with very high volume EDs.

Lower volume EDs were also more likely to assign lower urgency triage scores to heart attack patients, were less likely to have diagnostic tests available around-the-clock, and were less likely to have specialist consultation available in the ED. However, missed heart attacks were not associated with an increased risk of mortality at 30 days or one year following hospital admission for heart attack.

“The relationship between higher volume and better outcomes has been demonstrated for some elective surgeries, and it’s possible to regionalize such procedures to higher volume centres only in order to improve quality. But this can’t be done for the care of emergency conditions like heart attacks; people have to be able to go to their local ED to be cared for in such cases,” said Dr. Schull.

“Since most of the EDs in Ontario are lower volume sites, our results have broad implications for reducing overall rates of missed heart attacks and improving cardiac care. The focus should be on finding solutions suitable for these lower volume institutions. Such measures could include appropriately timed and sensitive diagnostic tests, as well as easier access to specialist consultation through the use of telemedicine links.”

The study, “The risk of missed diagnosis of acute myocardial infarction associated with emergency department volume”, is in the December 2006 issue of the Annals of Emergency Medicine.

Author affiliations: ICES (all authors); Clinical Epidemiology Unit (Drs. Schull and Stukel), and Department of Emergency Services (Dr. Schull), Sunnybrook Health Sciences Centre; Department of Medicine (Dr. Schull), and Department of Health Policy, Management and Evaluation (Dr. Schull and Ms. Vermeulen), University of Toronto.

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.


  • Julie Dowdie
  • Media Relations Officer, ICES
  • (416) 480-4780 or cell (416) 432-8143


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