Variations on classification of main types of myocardial infarction: a systematic review and outcome meta-analysis

Abstract

Objective: Classifying myocardial infarction into type 1 (T1MI) or type 2 (T2MI) remains a challenge in clinical practice. We aimed to identify factors contributing to variation in the classifications of MI into type 1 or type 2. In addition, pooled analyses of long-term mortality and reinfarction outcomes were performed.

Methods: We searched Medline, Embase and Web of Science through January 2018 for observational studies or clinical trials classifying patients as either T1MI or T2MI. Studies with baseline characteristics allowing a comparison between both groups were included. Inverse variance random-effects models were used to pool risk ratios (RR).

Results: Overall, 93,194 patients from 20 included observational studies were classified as T1MI and 9291 as T2MI; corresponding to 87.9% and 8.8% of all patients diagnosed with MI. Inclusion of ST-elevation MI patients was inconsistent among studies. Coronary angiography was performed in 77.7% and 31.5% of all patients with T1MI and T2MI, respectively. From a subgroup of 11 studies, percutaneous coronary intervention was performed in 79.2% of all patients classified as T1MI (range 44.2-93.0%) and 40.2% of all T2MI patients (range 0-87.5%). A meta-analysis of 6 studies (44,366 in total) on 2-year mortality showed worse outcome among T2MI patients (RR: 1.52, CI 1.07-2.17, P = 0.02; I² = 92%). Risk of reinfarction at 1.6 years was higher among T2MI patients (RR: 1.68, CI 1.22-2.31, P = 0.001; I² = 9%).

Conclusions: Classification of T1MI and T2MI varies widely among studies. A standardized approach with clear definitions is needed to avoid misclassification and ensure appropriate patient management.

Keywords: Acute coronary syndrome; Classification; Type 1 myocardial infarction; Type 2 myocardial infarction; Universal definition.