This study aims to evaluate the incidence of coronary microvascular dysfunction (CMD) and its prognostic implication for the improvement of left ventricular function in patients who have been diagnosed with heart failure with reduced ejection fraction (HFrEF) caused by non-ischemic etiology.

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.

Inclusion Criteria:

• a) Subject must be at least 19 years of age. b) Subject with symptoms or signs of HF (NYHA ≥2 dyspnea) and reduced ejection fraction (LVEF ≤ 40%) c) Subject who clinically need coronary angiography d) Subject who can voluntarily sign informed consent form

Exclusion Criteria:

• a) Subject with significant coronary artery stenosis on coronary angiography (diameter stenosis ≥90% or 50-90% with fractional flow reserve [FFR] ≤0.80) b) Subject scheduled for cardiac replacement therapy (heart transplantation or left ventricular assisted device [LVAD] implantation) c) HF due to restrictive cardiomyopathy, active myocarditis, or constrictive pericarditis d) Significant valvular heart disease requiring surgery e) Subject who have non-cardiac co-morbid conditions with life expectancy <1 year

Patients with heart failure with reduced ejection fraction (HFrEF) without significant coronary artery disease (non-ischemic cardiomyopathy)