Endothelium-Dependent and -Independent Perfusion Reserve and the Effect of l -Arginine on Myocardial Perfusion in Patients With Syndrome X

Impaired vasodilatation capacity in patients with angina pectoris and a normal coronary arteriogram (syndrome X [SX]) has been reported. Most studies report on the response in epicardial vessels. This does not necessarily reflect compromised myocardial microcirculation. Lack of the NO precursor L-arginine has been suggested as a possible cause.Myocardial blood flow (MBF) was measured, using PET, at rest (MBF-rest) and during intravenous dipyridamole (MBF-DIP) in 25 women (mean age 53+/-7 years) with SX. Thirty healthy volunteers served as controls. One group (A) consisted of 15 age-matched female volunteers (54+/-10 years). The other control group consisted of 15 young healthy women (B; 24+/-5 years). In 12 SX patients, MBF-rest and MBF during cold pressor testing were also measured after infusion of L-arginine (6.7 g/min for 45 minutes). The increase in MBF after cold pressor testing was similar in the SX group compared with controls. L-arginine did not affect MBF-rest (0.83+/-0.14 versus 0.89+/-0.13 mL. g-1. min-1) or MBF after cold pressor test (0.95+/-0.10 versus 1. 03+/-0.17 mL. g-1min-1). In contrast, the hyperemic response to DIP was blunted compared with the group A controls (1.68+/-0.49 versus 2. 34+/-0.45 mL. g-1. min-1, P<0.05); this resulted in a significant reduction of the coronary flow reserve in SX patients relative to controls (2.03+/-0.53 versus 2.96+/-0.63 mL. g-1. min-1, P<0.01).In patients with SX, the microcirculatory response to cold, reflecting the endothelium function, is normal and unaltered by intravenous L-arginine. This suggests preserved microcirculatory endothelial function. However, a markedly attenuated hyperemic flow and flow reserve after DIP suggest a dysfunction of the adenosine-mediated endothelium-independent vasodilatation at the microcirculatory level in these patients.