Cardiology and vascular/original research
The Risk of Missed Diagnosis of Acute Myocardial Infarction Associated With Emergency Department Volume

https://doi.org/10.1016/j.annemergmed.2006.03.025Get rights and content

Study objective

Missed diagnosis of acute myocardial infarction is associated with adverse clinical outcomes and more dollars recovered in malpractice suits than any other condition. The rate of missed diagnosis varies between emergency departments (EDs); we hypothesized that it is associated with the volume of acute myocardial infarction patients treated in an ED and that the association can be explained by other hospital characteristics.

Methods

We linked the records of all acute myocardial infarction patients admitted to an Ontario hospital in 2002 to 2003 to their ED visit records in the 7 days preceding admission. Acute myocardial infarctions were defined as missed if the diagnosis on the previous visit matched a list of cardiac symptoms and illnesses. We assessed whether annual volume of admitted acute myocardial infarction patients treated in the ED (grouped as 0 to 49; 50 to 99; 100 to 199; 200 to 299; and ≥300) was associated with missed acute myocardial infarction, adjusting for age, sex, teaching hospital status, and acute myocardial infarction severity. In a secondary analysis, we used data from a survey of Ontario EDs to assess whether hospital characteristics (triage practices, use of diagnostic tests, and consultant availability) explained the volume association.

Results

Of 19,663 acute myocardial infarction patients, mean age (68.3 years), sex (63% men), and predicted 1-year mortality (mean 0.21; SD 0.18) were similar across volume groups. The rate of missed acute myocardial infarction was 2.1% (95% confidence interval [CI] 1.9% to 2.3%) and varied from 0% to 29% across EDs. Compared with very high-volume EDs, the adjusted odds ratio of missed acute myocardial infarction was 2.0 in very low- (95% CI 1.5 to 2.7) and 1.6 in low- (95% CI 1.1 to 2.3) volume EDs. Consultant availability partially explained the volume effect.

Conclusion

Lower-volume EDs have up to 2-fold higher odds of missed acute myocardial infarctions compared with highest-volume ones after controlling for patient factors. Many current technologies designed to increase diagnostic sensitivity are feasible only in higher-volume centers. Efforts to reduce overall rates of missed acute myocardial infarctions should instead focus on simpler solutions appropriate for lower-volume EDs, such as telemedicine to improve access to consultant expertise.

Introduction

Patients with symptoms suggestive of acute myocardial infarction should promptly seek medical evaluation, yet the diagnosis is missed in about 2% to 3% of acute myocardial infarction patients presenting to emergency departments (EDs) in the United States1 and Canada2 and about 6% of patients in the United Kingdom.3 Failure to accurately diagnose an acute myocardial infarction leads to delays in the initiation of appropriate treatments, may increase mortality,1, 3, 4 and is responsible for more dollars recovered in malpractice suits than any other condition.3, 5, 6, 7

Studies to identify predictors of missed acute myocardial infarction have focused on patient-level factors.1, 8 However, predictors that have been identified, such as nonwhite race and a normal ECG,1 are of limited clinical utility and lack specificity. Interventions designed to reduce the risk, such as specialized chest pain observation units, are not widely used outside the United States9, 10, 11, 12 and may be practical only in larger EDs.9, 13, 14

Although previous studies have assumed that patient factors predominantly predict the risk of missed acute myocardial infarction, physician and hospital characteristics may also be important. For example, high-volume surgical centers are known to have lower perioperative mortality than low-volume centers,15, 16, 17 and physician decisionmaking varies for acute cardiac patients, depending on the availability of hospital resources.18 Small hospital EDs have been found to have missed acute myocardial infarction rates that were substantially higher than those of teaching hospital EDs.19 We hypothesized that high-volume EDs have lower rates of missed acute myocardial infarction than centers that treat fewer acute myocardial infarctions. We also explored whether ED factors such as triage procedures and the availability of consultants and diagnostic resources are associated with missed acute myocardial infarction risk. Finally, we assessed whether missed acute myocardial infarction was associated with increased mortality.

Section snippets

Theoretical Model of the Problem

Patient outcomes may be determined by characteristics inherent to the patient, the care provider, and the context in which the care is provided. The risk of missed acute myocardial infarction diagnosis may be influenced by a patient’s age, sex, and clinical features, including ECG and laboratory findings. Provider characteristics could include ED nurse and physician experience and training. Finally, contextual factors include the type of hospital, its experience as a whole with acute myocardial

Results

We identified 19,663 patients admitted to hospital for an acute myocardial infarction who were treated at 171 EDs in the province (17 teaching hospitals and 154 community hospitals); 63.4% of patients were men, and their mean age was 68.3 years. The largest proportion of patients arrived in the ED in the daytime (43.0%), and 14.2% of patients had a history of acute myocardial infarction. Comorbidities present at the time of admission and known to be associated with acute myocardial infarction

Limitations

We relied on population-based administrative health databases to identify and characterize acute myocardial infarction patients, as has been done in previous acute myocardial infarction research.27 This strategy had the advantage of greater numbers of cases but the disadvantage of less clinical detail than is typical in prospective studies, clinical registries, or medical record reviews. Carrying out a volume-outcome study that was sufficiently large by medical record review or clinical

Discussion

The volume of acute myocardial infarction patients treated in an ED is an important predictor of the risk of missed acute myocardial infarction. Overall, 2.1% of acute myocardial infarction patients were missed during an ED visit in the previous 7 days before hospitalization. Very low-volume EDs exhibited about a doubling of the rate of a missed diagnosis of acute myocardial infarction compared with high-volume EDs, whereas those with low volume had about a 1.6 times higher odds. These results

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    Supervising editor: Robert L. Wears, MD, MS

    Author contributions: MJS originated the hypothesis and took primary responsibility for study design and analysis for manuscript writing. MJV and TAS helped with study design, analysis, and manuscript writing. MJS takes responsibility for the paper as a whole.

    Funding and support: Supported by a grant from the Peter Lougheed Medical Research Foundation. Dr. Schull has a Career Award from the Canadian Institutes of Health Research.

    Reprints not available from the authors.

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    Copyright © 2006 American College of Emergency Physicians. Published by Mosby, Inc. All rights reserved.