Effects of atrial pacing on coronary sinus endothelin-1 and nitric oxide levels in patients with myocardial bridging.

Myocardial bridging (MB) is associated with clinical and metabolic evidence of ischaemia. In the present study, we aimed to evaluate the extent of atherosclerosis and endothelial dysfunction in patients with MB. The study population consisted of 15 patients with MB [9 women (60%), aged 56 +/- 9 years] and 14 control subjects [8 women (57%), aged 54 +/- 10 years]. All patients underwent coronary angiography. The femoral artery and coronary sinus endothelin-1 (ET-1) and nitric oxide (NOx) plasma levels were measured before and after right atrial pacing in all subjects. Also, intravascular ultrasonography was performed in 13 patients with MB. With right atrial pacing, coronary sinus ET-1 levels increased significantly in patients with MB compared with baseline levels (5.77 +/- 6.76 versus 11.32 +/- 9.40 pg/ml, p < 0.05). The coronary sinus ET-1 levels remained unchanged in controls with pacing (3.99 +/- 4.00 versus 4.19 +/- 7.15 pg/ml, p > 0.05). There was no significant difference between the two groups according to the increase in NOx levels with atrial pacing. Ten (77%) of the 13 patients had plaque formation in the segments proximal to the bridge with an area stenosis of 37 +/- 21% (12% to 75%). In patients with MB, post-pacing levels of coronary sinus ET-1 correlated significantly with the cross-sectional area of the plaque (r = 0.65, p = 0,04). Increased ET-1 levels and the pathological data of intravascular ultrasonography may be associated with endothelial dysfunction and atherosclerosis development in patients with MB. The presence of atherosclerosis in the proximal segments to the bridge may contribute to the myocardial ischaemia detected in these patients.