Introduction: Myocardial infarction without obstructive coronary artery disease (MINOCA) is a heterogeneous clinical condition presenting with myocardial necrosis not due to an obstruction of a major coronary artery. Recently, a relevant role of coronary microvascular dysfunction (CMD) in the pathogenesis of MINOCA has been suggested; however, data on this is scarce. Furthermore, it is unclear if CMD is equally present in all subtypes of MINOCA, or differentially identifies one or more of these conditions. Therefore, the aim of this study was to assess CMD in all three coronary vessels of MINOCA patients, correlating it with the clinical subtype.

Methods: In 61 patients with MINOCA, we retrospectively assessed coronary microvascular function in all three coronary territories by means of angiography-based index of microvascular resistance (aIMR). Patients were compared with a control group of 28 patients undergoing coronary angiography due to stable symptoms and showing no evidence of myocardial ischemia nor obstructive coronary artery disease. To further assess the association of CMD with MINOCA subtypes, MINOCA patients were subdivided according to clinical data in takotsubo (n=12), ischemic cause (n=12), infiltrative or inflammatory cardiomyopathy (n=13) or unclear (n=27).

Results: Patients with MINOCA showed a significantly elevated average aIMR compared to control patients (29.8±5.6 vs. 22.1±5.9, p<0.001) as marker of a relevant CMD; these data were consistent in all vessels. Among MINOCA subtypes, no significant difference in average aIMR could be detected between patients with takotsubo cardiomyopathy (30.4±6.6), ischemic cause (29.5±3.9) or unclear cause (30.6±5.8), whereas MINOCA patients with infiltrative or inflammatory cardiomyopathy showed a trend towards a lower aIMR (26.5±5.4, p=0.061).

Conclusion: Coronary microvascular dysfunction is a hallmark of all MINOCA subtypes. This study adds to the pathophysiological understanding of MINOCA and sheds light into the role of CMD in MINOCA.