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BACKGROUND: Lowering the diagnostic threshold for troponin is controversial because it may disproportionately increase the diagnosis of myocardial infarction in patients without acute coronary syndrome. We assessed the impact of lowering the diagnostic threshold of troponin on the incidence, management and outcome of patients with type 2 myocardial infarction or myocardial injury.
METHODS: Consecutive patients with elevated plasma troponin I concentrations (≥50 ng/L; n=2,929) were classified as type 1 (50%) myocardial infarction, type 2 myocardial infarction or myocardial injury (48%) and type 3-5 myocardial infarction (2%) before and after lowering the diagnostic threshold from 200 to 50 ng/L with a sensitive assay. Event-free survival from death and recurrent myocardial infarction was recorded at one year.
RESULTS: Lowering the threshold increased the diagnosis of type 2 myocardial infarction or myocardial injury more than type 1 myocardial infarction (672 versus 257 additional patients, P<0.001). Patients with myocardial injury or type 2 myocardial infarction were at higher risk of death compared to type 1 myocardial infarction (37% versus 16%; RR 2.31, 95%CI 1.98-2.69), but had fewer recurrent myocardial infarctions (4% versus 12%; RR 0.35, 0.26-0.49). In patients with troponin concentrations 50-199 ng/L, lowering the diagnostic threshold was associated with increased healthcare resource utilization (P<0.05) that reduced recurrent myocardial infarction and death for patients with type 1 myocardial infarction (31% versus 20%; RR 0.64, 0.41-0.99), but not type 2 myocardial infarction or myocardial injury (36% versus 33%; RR 0.93, 0.75-1.15).
CONCLUSION: Following implementation of a sensitive troponin assay, the incidence of type 2 myocardial infarction or myocardial injury disproportionately increased and is now as frequent as type 1 myocardial infarction. Outcomes of patients with type 2 myocardial infarction or myocardial injury are poor and do not appear to be modifiable following reclassification despite substantial increases in healthcare resource utilization.