Medical Therapy for Secondary Prevention and Long-Term Outcome in Patients With Myocardial Infarction With Nonobstructive Coronary Artery Disease

BACKGROUND: Myocardial infarction with nonobstructive coronary arteries (MINOCA) occurs in 5% to 10% of all patients with myocardial infarction. Clinical trials of secondary prevention treatment in MINOCA patients are lacking. Therefore, the aim of this study was to examine the associations between treatment with statins, renin-angiotensin system blockers, β-blockers, dual antiplatelet therapy, and long-term cardiovascular events. METHODS: This is an observational study of MINOCA patients recorded in the SWEDEHEART registry (the Swedish Web-system for Enhancement and Development of Evidence-based care in Heart disease Evaluated According to Recommended Therapy) between July 2003 and June 2013 and followed until December 2013 for outcome events in the Swedish Cause of Death Register and National Patient Register. Of 199 162 myocardial infarction admissions, 9466 consecutive unique patients with MINOCA were identified. Among those, the 9136 patients surviving the first 30 days after discharge constituted the study population. Mean age was 65.3 years, and 61% were women. No patient was lost to follow-up. A stratified propensity score analysis was performed to match treated and untreated groups. The association between treatment and outcome was estimated by comparing between treated and untreated groups by using Cox proportional hazards models. The exposures were treatment at discharge with statins, angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, β-blockers, and dual antiplatelet therapy. The primary end point was major adverse cardiac events defined as all-cause mortality, hospitalization for myocardial infarction, ischemic stroke, and heart failure. RESULTS: At discharge, 84.5%, 64.1%, 83.4%, and 66.4% of the patients were on statins, angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, β-blockers, and dual antiplatelet therapy, respectively. During the follow-up of a mean of 4.1 years, 2183 (23.9%) patients experienced a major adverse cardiac event. The hazard ratios (95% confidence intervals) for major adverse cardiac events were 0.77 (0.68-0.87), 0.82 (0.73-0.93), and 0.86 (0.74-1.01) in patients on statins, angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, and β-blockers, respectively. For patients on dual antiplatelet therapy followed for 1 year, the hazard ratio was 0.90 (0.74-1.08). CONCLUSIONS: The results indicate long-term beneficial effects of treatment with statins and angiotensin-converting enzyme inhibitors/angiotensin receptor blockers on outcome in patients with MINOCA, a trend toward a positive effect of β-blocker treatment, and a neutral effect of dual antiplatelet therapy. Properly powered randomized clinical trials to confirm these results are warranted.