Insulin resistance in microvascular angina (syndrome X)

Patients with microvascular angina (syndrome X) may be insulin resistant. We designed a study to establish whether this is the case. 11 patients with microvascular angina were compared with 9 matched subjects with noncardiac chest pain. Patients and controls were evaluated by coronary sinus catheterisation, and by isotopic measurement of glucose turnover, indirect calorimetry, and forearm technique during a 3 h baseline period after overnight fast and during a 2 h hyperinsulinaemic euglycaemic clamp. Pace-induced increase in coronary sinus blood flow was less in patients than in controls, whereas forearm blood flow did not differ between groups. Baseline measures of glucose metabolism were normal. During the clamp, glucose production and lipolysis were equally suppressed in both groups. Mean (SE) total insulin-induced glucose uptake was significantly impaired in patients compared with controls (3.9 [0.7] vs 6.4 [0.7] mg/kg per min; p < 0.01), and insulin-stimulated glucose uptake in the forearm was significantly reduced in patients (0.88 [0.10] vs 1.6 [0.30] mmol/L; p < 0.001). Reduced oxidative and nonoxidative metabolism accounted for the defect in overall glucose uptake in patients. No correlation between changes in coronary sinus blood flow and total body glucose uptake was seen. We found that microvascular angina was associated with substantial insulin resistance. Whether this relation is causal or coincidental is as yet unsettled.