Abnormal myocardial glucose handling in patients with syndrome X: Effect of beta-adrenergic blockade

The present study was designed to test the hypothesis that patients with angina, positive exercise test and angiographically smooth coronary arteries (syndrome X), may exhibit abnormal myocardial glucose handling, as assessed by fluorodeoxyglucose (FDG) and positron emission tomography (PET) and to investigate the possibility that this abnormality could be reversed by treatment with betablockers, the drugs of choice in most patients with syndrome X. Eight consecutive patients (4 females, age 53 +/- 4 yrs) with syndrome X were studied. Off therapy, they underwent stress/rest 99m-TcMIBI SPET (360 degrees) and assessment of resting glucose metabolism by PET. PET studies were again performed after a 10 day treatment period on oral atenolol (100 mg/o.d.). All patients exhibited significant fasting FDG uptake in 2 or more myocardial regions. Overall, there were 28 of 48 segments (58%) with abnormal tracer uptake. On atenolol, there were only 5 segments with persistent FDG uptake (10%) in 2 patients. At rest, 7 patients exhibited perfusion defects in 14 myocardial segments. With stress performed in pharmacological wash-out, 5 patients developed perfusion defects in 10 myocardial segments. Eight of these segments were already underperfused at rest, and showed further reduction in perfusion after stress. All hypoperfused segments showed abnormal FDG uptake when the PET study was performed off therapy. The results suggest that, in patients with syndrome X, imbalance of the demand/supply ratio, either caused by limited coronary flow reserve or by primary vasoconstriction with reduction in myocardial perfusion, may determine a sustained metabolic shift towards anaerobic glycolysis. The mechanism by which atenolol improves metabolism in these patients could be simply related to reduction in O2 consumption.