AbstractAimsCoronary microvascular dysfunction (CMD) has been proposed as an important pathophysiological mechanism in Takotsubo syndrome (TTS). Our aims were (i) to evaluate and compare levels of CMD in patients with TTS and patients with ischaemia and no obstructive coronary arteries (INOCA) and (ii) to investigate associations between CMD and clinical parameters, left ventricular function, and coronary atherosclerosis in TTS.Methods and resultsWe conducted a prospective study of 27 female TTS patients and an equally sized, age‐ and gender‐matched, cohort of INOCA patients. Coronary microvascular function was quantified invasively using the index of microcirculatory resistance (IMR), coronary flow reserve (CFR), and resistive reserve ratio (RRR). CMD was defined as IMR ≥ 25 and/or CFR ≤ 2. In the TTS patients, left ventricular function was assessed with echocardiography and cardiovascular magnetic resonance (CMR) imaging, and coronary atherosclerosis was visualized with intravascular ultrasound with near‐infrared spectroscopy (IVUS‐NIRS). The incidence of CMD was higher in the TTS patients than in the INOCA cohort (78% vs. 44%, P = 0.01), with higher IMR (30 vs. 14, P = 0.002), lower CFR (1.8 vs. 2.8, P = 0.009), and lower RRR (2.1 vs. 3.5, P = 0.003). In apical compared with midventricular TTS, IMR was numerically higher (50 vs. 28, P = 0.20), whereas CFR and RRR were lower (1.5 vs. 2.5, P = 0.003 and 1.6 vs. 2.7, P = 0.01, respectively). Global longitudinal strain and global circumferential strain, assessed with CMR imaging, were more impaired in apical than in midventricular TTS (−11 vs. −14, P < 0.001 and −12 vs. −15, P = 0.049, respectively). In the TTS patients, CFR and RRR correlated with echocardiography‐derived (R² = 0.15, P = 0.002 and R² = 0.18, P = 0.007, respectively) and CMR‐derived (R² = 0.09, P = 0.025 and R² = 0.10, P = 0.038, respectively) ejection fraction. CFR and RRR correlated inversely with CMR‐derived end‐diastolic volume index, end‐systolic volume index, and left ventricular mass index. IMR, CFR, and RRR were not associated with measures of coronary atherosclerosis derived by IVUS‐NIRS.ConclusionsCoronary microvascular dysfunction is common in patients with TTS and more frequent than in patients with INOCA. CMD in TTS is more severe in the apical compared with the midventricular phenotype of the syndrome, is associated with left ventricular function, but is unrelated to coronary atherosclerosis. Our results support the notion of CMD as a key mediator in TTS.