The Role of Coronary Microvascular Dysfunction in Improving Left Ventricular Systolic Function Using Registry for Evaluation of Factors associatEd With Heart Failure With Reduced Ejection Fraction Caused by Non-ischemic Etiology (REFERENCE).

HF is a clinical syndrome characterized by dyspnea or exertional limitation due to impairment of ventricular filling or ejection of blood or both. HFrEF occurs when the left ventricular ejection fraction (LVEF) is 40% or less and is accompanied by progressive left ventricular dilatation and adverse cardiac remodeling. Among them, a substantial portion of patients had non-ischemic etiology.4 The CMD, defined by impaired coronary flow reserve (CFR), is commonly observed in patients with cardiomyopathies caused by non-ischemic etiology and is well-known to be associated with poor prognosis independently of the degree of left ventricular functional abnormality. However, the presence of CMD can be more specifically evaluated by invasive physiologic assessment using both CFR and the index of microcirculatory resistance (IMR) than by non-invasive methods (doppler echocardiography, positron emission tomography, or cardiac magnetic resonance imaging [MRI]) measuring CFR alone. Considering that CMD, defined by depressed CFR with elevated IMR, reflects the impaired myocardial flow and microvascular damages, there was a possibility that it may be a predictor of irreversible myocardial damages in HFrEF patients with non-ischemic etiology. Nevertheless, there has been limited data regarding the association between the improvement of LV function and CMD for patients with HFrEF caused by non-ischemic etiology after guideline-directed medical treatment (GDMT). Therefore, the investigators sought to evaluate the incidence of CMD and its prognostic implication for the improvement of left ventricular function after GDMT in patients who have been diagnosed with HFrEF caused by non-ischemic etiology.