Abnormal coronary microvascular vasodilation has been demonstrated in patients with diabetes and metabolic syndrome, but the role of insulin resistance in its pathogenesis is not clear. The aim of this study is to invasively assess coronary microcirculation and to investigate the relationship of insulin resistance with coronary microvascular dysfunction.

A pressure temperature-sensor-tipped coronary wire will be advanced in coronary arteries without significant lumen reduction. Thermodilution-derived coronary flow reserve (CFR) will be calculated as resting mean transit time (Tmn) divided by hyperemic Tmn (obtained with a 5-min i.v. infusion of adenosine 140 mg/kg/min). An index of microvascular resistance (IMR) will be calculated as the distal coronary pressure at maximal hyperemia divided by the inverse of the hyperemic Tmn. FFR will be calculated by the ratio of Pd/Pa at maximal hyperemia. Insulin resistance (IR) will be assess by the homeostasis model assessment (HOMA) index and plasma IL-6 and TNF-alpha levels will be measured in addition to routine blood examinations before the procedure.

Inclusion Criteria:

• Patients with stable angina or inducible myocardial ischemia
• Coronary arteries without high-grade epicardial stenoses (angiographic stenosis < 50% and fractional flow reserve [FFR] > 0.75)

Exclusion Criteria:

• Significant renal insufficiency (serum creatinine > 1.5 mg/dL), a recent (< 1 week) acute coronary syndrome, heart failure, severe valvular disease, or hypertrophic cardiomyopathy.