The new definition of myocardial infarction - Diagnostic and prognostic implications in patients with acute coronary syndromes

Background: The clinical implications of the recently revised criteria for diagnosis of acute myocardial infarction (AMI) in patients with suspected acute coronary syndromes are unknown. Methods: To evaluate the prognostic implications of the new diagnostic criteria for AMI, we studied 493 consecutive patients with suspected acute coronary syndromes admitted to University of Michigan, Ann Arbor, between May 1, 1999, and January 1, 2000. Patients with positive cardiac enzymes and symptoms suggestive of coronary ischemia (n=275) were divided into 2 groups: group A, with elevated peak creatine kinase-MB fraction and/or new electrocardiographic changes suggestive of AMI regardless of troponin status (diagnosed as AMI by old criteria), and group B, with normal peak creatine kinase-MB fraction but elevated troponin I level (additional patients diagnosed as having AMI by new criteria). Results: As compared with group A (n=224), patients in group B (n=51) were older women, with increased comorbidities such as previous stroke or aortic stenosis, and had fewer in-hospital procedures. In-hospital adverse events (reinfarction, heart failure, shock, and mortality) were similar between the groups, whereas 6-month mortality was higher among group B patients (16.3% vs 5.8%; P=.03). This difference was not statistically significant after adjustment for differences in baseline characteristics between the groups (odds ratio, 1.6; 95% confidence interval, 0.5-5.9). Conclusions: The new criteria result in a substantial increase in the diagnosis of AMI. Furthermore, they help to identify patients with acute coronary syndromes who have greater comorbidities and worse 6-month outcomes who are otherwise missed by the old criteria. Additional studies are needed to confirm these preliminary findings and to determine the financial implications of the new criteria.