Objective: To evaluate how the use of different biochemical markers of myocardial injury affects the recorded numbers of cases of diagnosed acute myocardial infarction (AMI) and unstable angina pectoris (UAP) and also the observed in-hospital mortality of AMI.
Design: 442 patients admitted with suspected acute coronary syndrome (ACS) were studied. Based on the World Health Organization (WHO) criteria, the patients were classified into five categories: acute Q-wave myocardial infarction (QMI): acute non-Q-wave myocardial infarction (NQMI); UAP; stable angina pectoris; and chest pain of non-cardiac origin.
Results: Using total creatine kinase (tCK) as the "gold standard" for diagnosis, we found 172 AMI. 100 UAP and 170 with other diagnoses. If we used CK-MB (>6 microg/L) or cTnl (> 1 microg/L) for diagnosing AMI, the numbers of AMI increased significantly by 50 (29%) and 64 (37%), respectively. Using tCk, CK-MB or cTnl for diagnosing AMI, the observed in-hospital mortality was 14%, 11% and 10%, respectively. The group of patients with elevated cTnl but negative tCK had similar long-term survival as the group of patients with cTnI >30 microg/L, comprising 95% of the patients with the diagnosis AMI based on tCK.
Conclusion: The introduction of new biochemical markers for detection of AMI may lead to significant changes in the recorded incidence and in-hospital mortality of AMI. New biochemical markers of myocardial injury must be validated against the traditional markers as they are introduced into clinical practice by the new diagnostic criteria.