Association of follow-up time and all-cause mortality in type 2 myocardial infarction: a systematic review and meta-analysis

Currently, the classification of type 2 myocardial infarction (T2MI) is contentious, with no consensual management or treatment strategy available. Therefore, patients with T2MI have poorer clinical outcomes, especially higher all-cause mortality, compared with type 1 myocardial infarction (T1MI) patients. Online databases, such as PubMed, Web of Science, Medline, EmBase, and Cochrane Library, were systematically searched. The search strategy included the terms "type 2 myocardial infarction", "follow-up time", and "mortality". All studies were reviewed from January 1, 2007 to December 31, 2016. Nine eligible retrospective cohort studies involving 23914 patients with T1MI or T2MI were included. The total pooled risk ratios for in-hospital, 30-day, and 1-year all-cause mortality, respectively, were 2.80 (95% CI 1.93-4.04; P<0.01), 2.44 (95% CI 1.82-3.27; P<0.01), 2.21 (95% CI 1.92-2.54; P<0.01) in the fixed-effects model, with no significant heterogeneity. In subgroup analysis, the pooled risk ratio (RR) for 150 to 180 day all-cause mortality showed no significant difference between the T2MI and T1MI groups (RR 1.25; 95% CI 0.80-1.94; P=0.33) in the fixed-effects model, with no significant heterogeneity. The pooled RR for 1-year all-cause mortality extracted from two studies was 1.81 (95% CI 1.64-2.00; P<0.01) in the fixed-effects model, with no significant heterogeneity. After multivariable adjustment, no significant difference was found between T2MI and T1MI. Follow-up time is negatively correlated with all-cause mortality in T2MI. The risk of mortality in T2MI was twice the value obtained for T1MI. More studies are required to confirm the association of follow-up time and all-cause mortality in T2MI.