Clinical Characteristics and Outcomes of Patients with Myocardial Infarction, Myocardial Injury, and Nonelevated Troponins

Abstract

Background: Cardiac troponins have emerged as the preferred biomarkers for detecting myocardial necrosis and diagnosing myocardial infarction. However, current cardiac troponin assays do not discriminate between ischemic and nonischemic causes of myocardial cell death. Thus, when an increased troponin value is encountered in the absence of obvious myocardial ischemia, a careful search for other clinical conditions is crucial.

Methods: In 2010 to 2011, we prospectively studied hospitalized patients who had cardiac troponin I measured on clinical indication. An acute myocardial infarction was diagnosed in cases of a cardiac troponin I increase or decrease pattern with at least 1 value >30 ng/L (99th percentile) together with myocardial ischemia. Myocardial injury was defined as cardiac troponin I values >30 ng/L, but without signs or symptoms indicating overt cardiac ischemia. Patients with peak values ≤30 ng/L were classified as nonelevated cardiac troponin I. Follow-up was at least 3 years with all-cause mortality as the sole clinical end point.

Results: A total of 3762 patients were included. Of these, 488 (13%) had acute myocardial infarction, 1089 (29%) had myocardial injury, and 2185 (58%) had nonelevated cardiac troponin I values. Patients with myocardial injury frequently presented with dyspnea, were older, and had more comorbidity than patients in the 2 other groups. During a median follow-up of 3.2 years, 1342 patients died. Mortality differed significantly between groups: 39% in those with myocardial infarction, 59% in those with myocardial injury, and 23% in those with nonelevated cardiac troponin I (log-rank test; P < .0001). No significant difference in mortality between patients with type 2 myocardial infarction and patients with myocardial injury was observed (63% and 59%, respectively).

Conclusions: Patients with myocardial injury are older and have more comorbidity than those with acute myocardial infarction. Both groups exhibit a poorer prognosis than patients with nonelevated cardiac troponin I values. Of note, a very high long-term mortality is observed in patients with type 2 myocardial infarction and patients with myocardial injury.

Keywords: Myocardial infarction; Myocardial injury; Prognosis; Troponins; Type 2 myocardial infarction.