Assessment and Treatment of Patients With Type 2 Myocardial Infarction and Acute Nonischemic Myocardial Injury

Abstract

Although coronary thrombus overlying a disrupted atherosclerotic plaque has long been considered the hallmark and the primary therapeutic target for acute myocardial infarction (MI), multiple other mechanisms are now known to cause or contribute to MI. It is further recognized that an MI is just one of many types of acute myocardial injury. The Fourth Universal Definition of Myocardial Infarction provides a taxonomy for acute myocardial injury, including 5 subtypes of MI and nonischemic myocardial injury. The diagnosis of MI is reserved for patients with myocardial ischemia as the cause of myocardial injury, whether attributable to acute atherothrombosis (type 1 MI) or supply/demand mismatch without acute atherothrombosis (type 2 MI). Myocardial injury in the absence of ischemia is categorized as acute or chronic nonischemic myocardial injury. However, optimal evaluation and treatment strategies for these etiologically distinct diagnoses have yet to be defined. Herein, we review the epidemiology, risk factor associations, and diagnostic tools that may assist in differentiating between nonischemic myocardial injury, type 1 MI, and type 2 MI. We identify limitations, review new research, and propose a framework for the diagnostic and therapeutic approach for patients who have suspected MI or other causes of myocardial injury.

Keywords: heart injuries; myocardial infarction; myocardial ischemia.

Figure 1.

Myocardial injury taxonomy.

Figure 2.

All-cause mortality in cohort studies of patients with type 1 myocardial infarction (MI), type 2 MI, or myocardial injury. Size of bubble indicates the number of patients in the study (small <1000, medium <3000, large >3000) with color representing diagnosis (type 1 MI=red, type 2 MI=blue, myocardial injury=purple). Label indicates lead author from cohort. *In most of the depicted studies, the category of myocardial injury was aimed at capturing acute nonischemic myocardial injury.

Figure 3.

Peak cardiac troponin concentration among patients with type 1 myocardial infarction (MI), type 2 MI, or nonischemic myocardial injury.^,,, Boxes represent medians and interquartile ranges, whiskers display the maximum and minimum values. All units standardized to micrograms per liter with y axis transformed as log₁₀. *In most of the depicted studies, the category of myocardial injury was aimed at capturing acute nonischemic myocardial injury.

Figure 4.

Systematic approach to the evaluation, classification, and treatment of patients presenting with evidence of myocardial injury. Gradation of coloring represents the gradation of assessed probability of myocardial ischemia (orange) and type 1 MI (red), with darker coloring representing higher likelihood.ASCVD indicates atherosclerotic cardiovascular disease; CAD, coronary artery disease; CMR, cardiac magnetic resonance imaging; cTn, cardiac troponin; HF, heart failure; MI, myocardial infarction; and UDMI, Universal Definition of Myocardial Infarction.

Figure 5.

Proposed conceptual paradigm for the evaluation and treatment of patients presenting with symptoms and signs of myocardial infarction. Gradation of coloring represents the gradation of assessed probability of type 1 myocardial infarction (MI; red) and diagnostic iatrogenic risk (blue), with darker coloring representing higher likelihood. Dotted lines represent how different combinations of different pretest probabilities of type 1 MI and risk of a diagnostic modality or treatment may impact selection of diagnostic modalities or empiric treatments. For example, patients with a low pretest probability of type 1 MI and a high risk of bleeding or contrast-induced nephropathy should not receive the same diagnostic evaluation and empiric antithrombotic treatment as a patient with a high probability of type 1 MI and a low risk for bleeding or contrast-induced nephropathy. Decisions on patients not at these extremes are more nuanced. CAD indicates coronary artery disease; cTN, cardiac troponin; GI, gastrointestinal; NSAID, nonsteroidal anti-inflammatory drug; and PCI, percutaneous coronary intervention.