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

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.

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).

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%).

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.