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

Background: Type 2 myocardial infarction (MI) is an imbalance between myocardial oxygen demand and supply, leading to myocardial ischemia. It is not due to plaque rupture, and is usually caused by a condition other than coronary artery disease (CAD). However, limited data are available comparing the prevalence of traditional coronary risk factors and mortality between type 1 and type 2 MI. We hypothesize that type 2 MI carries a higher mortality than type 1. Methods: We searched the databases of PubMed, EMBASE, CENTRAL, and MEDLINE for studies comparing type 1 MI with type 2 MI. The baseline variables were compared in each cohort. Summary risk ratios and 95% confidence intervals were calculated using the random effects model to compare mortality between the two groups. Results: The included studies yielded 25,872 patients of whom 2,683 (10%) had type 2 MI. Compared to the type 1 cohort, the type 2 cohort had significantly higher inpatient (15% vs. 4.7%, P<0.00001), 30-day (17.6% vs. 5.3%, P<0.00001) and 1-yr mortality (27% vs. 13%, P<0.00001), as well as higher 30-day major adverse cardiovascular events (20% vs. 9%, P<0.0001). Operative stress (20%) was the most common trigger of type 2 MI, followed by sepsis (19%), arrhythmia (18.63%), heart failure (15%), and anemia (12%). Conclusions: Type 2 MI is a common entity and is more common in females, older age groups, and in patients with multiple comorbidities: it also tends to result in higher mortality.