Type 2 versus type 1 myocardial infarction: a comparison of clinical characteristics and outcomes with a meta-analysis of observational studies

In 2007, a joint task force of the American College of Cardiology (ACC), the American Heart Association (AHA), the European Society of Cardiology and the World Heart Federation proposed the Universal Definition of myocardial infarction (MI), which was an expert consensus document categorizing MI into five subtypes (1). The Third Universal Definition released in 2012, was an update to the 2007 document and backed the MI subtype classification as per the 2007 Universal Definition (2). Type 1 MI is caused by an acute atherothrombotic coronary event following plaque rupture. Type-2 MI is an entity where a condition other than coronary artery disease (CAD) contributes to a critical imbalance between oxygen supply (such as hypoxemia, anemia, or hypotension) and demand (such as tachycardia, tachyarrhythmias, or hypertension). In clinical practice it may be difficult to distinguish type 2 MIs from other non-ischemic conditions, such as Takotsubo cardiomyopathy and myocarditis (3). This difficulty resulted in significant variation in the prevalence of type 2 MI across studies, ranging from 1.6% to 29.6% (4-7). Although evidence-based treatment recommendations are established for type-1 MI, there is a lack of similar recommendations for type 2 MI. Recent studies have shown that compared to type 1 MI, noninvasive strategies are more often followed in type 2 MI and these patients also receive fewer cardioprotective drugs (8,9). While some studies have shown that type 2 MI is associated with higher mortality rates (10), others have shown mortality comparable to type 1 MI after multivariate adjustment (11). Although isolated studies comparing outcomes between type 1 and type 2 MI exist, a meta-analysis of these studies will provide useful information