Assessment and Treatment of Patients With Type 2 Myocardial Infarction and Acute 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.

Myocardial infarction (MI) is defined pathologically as myocardial cell death attributable to prolonged myocardial ischemia (inadequate oxygen supply to the myocardium). Each year, >8 million Americans present to the hospital with signs and symptoms suggestive of acute MI.1 Approximately 700 000 are ultimately diagnosed with MI.1,2 Although coronary thrombus overlying a disrupted atherosclerotic plaque remains the hallmark and primary therapeutic target for MI, multiple other mechanisms are now known to contribute to MI and nonischemic causes of myocardial injury (Table 1, Table I in the online-only Data Supplement, Figure 1); however, optimal diagnostic and treatment strategies for patients with myocardial injury attributable to these nonthrombotic mechanisms have yet to be defined.

Table 1.

Classification	Definition
Acute MI	Clinical evidence of acute myocardial injury as evident from detection of a rise and/or fall of cTn values with at least one value >99th percentile URL and at least one of the following symptoms of myocardial ischemia: Symptoms of acute myocardial ischemia New ischemic ECG changes Development of pathological Q waves Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality in a pattern consistent with an ischemic etiology Identification of a coronary thrombus by angiography or autopsy (not for type 2 MI)
Type 1 MI	MI caused by atherothrombotic coronary artery disease and usually precipitated by atherosclerotic plaque disruption (rupture or erosion)
Type 2 MI	MI caused by a mismatch between oxygen supply and demand by a pathophysiological mechanism other than coronary atherothrombosis (type 1 MI)
Acute nonischemic myocardial injury	Acute myocardial injury (rise and fall in biomarkers [cTn]) in the absence of a primary ischemic cause (ie, absence of MI)
Chronic myocardial injury	Chronic myocardial injury (cTn >99th percentile URL without an acute change)

cTn indicates cardiac troponin; MI, myocardial infarction; and URL, upper reference limit.

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Figure 1. Myocardial injury taxonomy.

Invasive Imaging

Coronary angiography is considered the gold standard for defining coronary anatomy and is used widely to identify patients with evidence of plaque rupture and coronary thrombosis among patients with suspected type 1 MI