Implications of a new clinical classification of acute myocardial infarction

Abstract Background The Universal Definition of Myocardial Infarction has provided standardisation of the diagnostic criteria for myocardial infarction. However, there remain significant challenges in adopting some of the current recommendations in practice. The diagnostic criteria for type 2 myocardial infarction identify a heterogenous group of patients with variable clinical outcomes and no clear treatment implications to date. Purpose To determine the implications of a new clinical classification for myocardial infarction with more objective diagnostic criteria using cardiac imaging.(1) Methods In a prospective cohort study,(2) patients with type 2 myocardial infarction underwent coronary angiography and cardiac magnetic resonance imaging or echocardiography. The new classification was applied to identify (a) spontaneous myocardial infarction due to acute coronary pathology, (b) secondary myocardial infarction precipitated by acute illness in the presence of obstructive coronary artery disease, a new regional wall motion abnormality or infarct pattern scarring, and (c) no myocardial infarction in the absence of obstructive disease or new myocardial abnormality. The diagnostic outcome was the proportion of patients with type 2 myocardial infarction reclassified as having spontaneous, secondary or no myocardial infarction by the new clinical classification. The prognostic outcome was a composite of all-cause death, any recurrent myocardial infarction, or heart failure hospitalisation during follow up. Results In 100 patients (65 years, 43% women) with type 2 myocardial infarction, the new classification identified 25 and 31 patients with spontaneous and secondary myocardial infarction, respectively, and 44 without myocardial infarction (Figure 1). Compared to patients without myocardial infarction, those with secondary myocardial infarction were older, had more risk factors, and higher troponin concentrations (P<0.05 for all). In patients who underwent cardiac magnetic resonance imaging, there was evidence of infarct-pattern late gadolinium enhancement in 95% (19/20) and 60% (15/25) of patients with spontaneous and secondary myocardial infarction, respectively, which was more likely to be transmural in the former. In patients reclassified as secondary myocardial infarction, just 45% and 58% were established on aspirin or a lipid lowering therapy. During a median follow up of 4.4 years, death, myocardial infarction or heart failure hospitalization was more common in secondary myocardial infarction compared to those without myocardial infarction (55% [17/31] versus 16% [7/44], P<0.001; Figure 2). Conclusions A new clinical classification of myocardial infarction informed by cardiac imaging would reduce the diagnosis of myocardial infarction in acute illness and identify those patients at highest risk who are most likely to benefit from treatment.Figure 1:Alluvial plotFigure 2:Kaplan Meier curve