The significance of insulin resistance and hyperlipidemia in microvascular angina (syndrome X)

Patients with chest pain and normal epicardial coronary arteries are characterized by an impairment of myocardial perfusion reserve. Functional and morphological abnormalities of the intramyocardial arterioles are suggested to be responsible for this, possibly as a consequence of hypertension and/or left ventricular hypertrophy. In an attempt to isolate predisposing factors of microvascular angina we investigated 34 patients (15 f, 19 m) with a mean age of 53±7 years. They were diagnosed as microvascular angina without hypertension or left ventricular hypertrophy. Parameters such as plasma insulin, glucose, cholesterol, LDL-cholesterol, triglycerides, (VLDL-cholesterol) and fibrinogen were determined for a metabolic profile. Furthermore, insulin and glucose were measured after an oral glucose load of 100 g glucose (OGTT) over 3 h. All parameters were compared to a control group of 15 healthy people matched for age and body mass index. In the study population systolic blood pressure was within normal limits at 137±17 mm Hg and thus higher than control at 124±11 mm Hg (p<0.02). Furthermore, diastolic blood pressure was 85±7 mm Hg compared to 78±9 mm Hg in controls (p<0.02). Insulin was significantly elevated in patients with microvascular angina 90 min (median: 101 vs 54 μU/ml; p<0.01) and 120 min (median: 88 vs 51 μU/ml; p<0.05) after ingestion of 100 g glucose. The fasting glucose was elevated at 98±12 compared to 87±7 mg/dl in controls (p<0.01). Glucose concentration was also elevated after 30 min at 176±28 compared to 148±33 mg/dl (p<0.02), after 45 minutes (198±35 compared to 152±53 mg/dl) (p<0.01) and 60 minutes (193±44 compared to 145±54 mg/dl) (p<0.01). In microvascular angina parameters such as total cholesterol: (244±46 vs 199±29 mg/dl (p<0.01)), LDL-cholesterol (157±41 vs 122±18 mg/dl (p<0.01)) and fibrinogen: (377±150 vs to 285±69 mg/dl (p<0.03)) were elevated. These findings suggest a pathogenetic role of insulin resistance, hyperlipoproteinemia and elevated levels of fibrinogen for impaired myocardial coronary reserve. This metabolic constellation as well as exhaustion of coronary reserve is often found in hypertensive patients and may identify microvascular angina as an early stage of hypertensive heart disease before manifest hypertension has developed