AIM: The diagnostic criteria for type 2 myocardial infarction identify a heterogenous group of patients with variable outcomes and no clear treatment implications. We aimed to determine the implications of a new clinical classification for myocardial infarction with more objective diagnostic criteria using cardiac imaging. METHODS: In a prospective cohort study, 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. 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. 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). 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). 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. CLINICAL TRIAL REGISTRATION: https://clinicaltrials.gov/ct2/show/NCT03338504.