Incidence and outcomes of type 2 myocardial infarction: a cohort study of a national population-based registry

Abstract Background/introduction Type 2 myocardial infarction (T2MI), caused by myocardial oxygen supply/demand mismatch without acute thrombotic plaque disruption, makes up 2-25% of reported MI. T2MI may be triggered by conditions such as arrhythmias, anaemia, sepsis, heart failure, but the incidence, outcomes and predictors of poor outcomes post-T2MI requires further study. Aims In this study, we characterised the incidence, outcomes and predictors of poor outcomes in T2MI in Singapore. Methods We performed an ambidirectional cohort study of 10720 consecutive T2MI patients from January 2012 to December 2018 from the national Singapore MI Registry (SMIR). The primary outcome was major adverse cardiovascular events (MACE; composite of MI, stroke and mortality) within 30 days and 1 year. The secondary outcomes were all-cause mortality, cardiovascular death and stroke. Results Of 10,724 patients with T2MI, 3852 (35.9%) had MACE within 30 days and 5947 (51.4%) had MACE within 1 year (Table 1). The incidence of T2MI increased from 20 per 100,000 residents in 2012 to 80 per 100,000 residents in 2017 (Figure 1A). Significant independent predictors of MACE at 30 days on multivariable analysis include age (hazard ratio [HR] 1.01, 95% confidence interval (CI) 1.00-1.01), history of hypertension (HR 1.23, 95% CI 1.06-1.42) or diabetes mellitus (HR 1.32, 95% CI 1.17-1.48), Killip classes 2-4 and left ventricular ejection fraction <50% during hospitalization. Low hemoglobin (Hb) 8-9 (HR 1.42, 95% CI 1.07-1.88) and 10-11 (HR 1.36, 95% CI 1.05-1.76) compared to Hb 14-15, were predictors of MACE at 30 days and Hb <13 showed significant associated with MACE at 1 year. Hb <12 was also significantly associated with all-cause mortality at 1 year, but not cardiovascular death or stroke. Significant predictors of stroke at 1 year included current smoking (HR 1.53, 95% CI 1.04-2.23) and atrial fibrillation (AF) (HR 1.54, 95% CI 1.21-1.97). Troponin levels were not significantly associated with MACE at 30 days or 1 year. Conclusions The incidence of T2MI has been increasing since 2012, with generally poor outcomes within 1 year. Predictors of poor outcomes include age, history of cardiovascular risk factors, AF, reduced LVEF during hospitalization, and low hemoglobin. A higher target Hb may be needed post-T2MI, and further research is needed to establish this.