Coronary microvascular dysfunction in patients with acute coronary syndrome and no obstructive coronary artery disease

Background: Between 10 and 15% of patients admitted for non-ST-segment elevation acute coronary syndrome (NSTE-ACS) show no obstructive coronary artery disease (NO-CAD) at angiography. Coronary microvascular spasm is a possible mechanism of the syndrome, but there are scarce data about coronary microvascular function in these patients. Objectives: To assess coronary microvascular function in patients with NSTE-ACS and NO-CAD. Methods: We studied 30 patients (67 ± 10 years, 19 female) with NSTE-ACS and NO-CAD. Specific causes of NSTE-ACS presentation (e.g., variant angina, takotsubo disease, tachyarrhythmias, etc.) were excluded. Coronary blood flow (CBF) velocity response to IV ergonovine (6 µg/kg up to a maximal dose of 400 µg) was evaluated before discharge by transthoracic Doppler echocardiography. CBF response to IV adenosine (140 μg/kg/min) and cold pressor test (CPT) was also assessed after 1 month. Ten age- and sex-matched patients with non-cardiac chest pain served as controls. Vasoactive tests were repeated after 12 months in 10 NSTE-ACS patients. Results: The ergonovine/basal CBF velocity ratio was 0.79 ± 0.09 and 0.99 ± 0.01 in patients and controls, respectively (p < 0.001). The adenosine/basal CBF velocity ratio was 1.46 ± 0.2 and 3.25 ± 1.2 in patients and controls, respectively (p < 0.001), and the CPT/basal CBF velocity ratio was 1.36 ± 0.2 and 2.43 ± 0.3 in the 2 groups, respectively (p < 0.001). In 10 patients assessed after 12 months, CBF velocity responses to ergonovine, adenosine, and CPT were found to be unchanged. Conclusions: Patients with NSTE-ACS and NO-CAD exhibit a significant coronary dysfunction, which seems to involve both an increased constrictor reactivity, likely mainly involving coronary microcirculation, and a reduced microvascular dilator function, both persisting at 12-month follow-up.