ObjectivePatients with Takotsubo syndrome (TTS) present an acute microvascular dysfunction that leads to an impaired myocardial perfusion and, in more severe forms, an impaired epicardial flow. However, clinical relevance of a delayed coronary flow, the coronary slow flow (CSF), has never been investigated. We studied the prognostic value of CSF occurring in the acute phase of TTS.MethodsThis cohort study prospectively evaluated patients with a diagnosis of TTS. CSF was defined as angiographically non-obstructive coronary arteries with thrombolysis in myocardial infarction-2 flow. The incidence of overall mortality and major adverse cardiovascular events (MACEs), defined as the composite of TTS recurrence, cardiac rehospitalisation, cerebrovascular events and mortality, was assessed at follow-up.ResultsWe enrolled 101 patients (mean age 71.0±11.1 years, 86 (85.1%) female); CSF occurred in 18 (17.8%) patients. At admission, patients with CSF presented more frequently with Killip class III/IV, moderate-to-severe left ventricle systolic dysfunction and right ventricle dysfunction. During the index admission, patients with CSF had a higher rate of intrahospital complications (12 (66.7%) vs 28 (33.7%), p=0.01). At long-term follow-up, patients with CSF had a significantly higher occurrence of overall mortality (9 (50%) vs 19 (22.9%), p=0.011), mainly due to non-cardiac causes (89.3%), and a higher rate of MACE (10 (55.5%) vs 27 (32.5%), p=0.06). At multivariable Cox regression, CSF was independently associated with death from any causes.ConclusionsPatients with TTS presenting with CSF have a worse clinical presentation with a higher rate of intrahospital complications and a poor long-term clinical outcome.