Background: Neurostimulation techniques have been shown to be beneficial in patients with angina and syndrome X but the mechanism remains unclear. We examined the effect of transcutaneous electrical nerve stimulation (TENS) on coronary artery blood flow in a group of patients with syndrome X.
Methods: Coronary blood flows were measured in 11 patients with angiographically normal coronary arteries, positive results from exercise tests and angina (syndrome X) using intracoronary Doppler catheters combined with quantitative coronary angiography.
Results: The mean coronary flow velocity did not increase in any patient during TENS therapy; in fact, there was a fall from 5.2 +/- 2.8 to 4.3 +/- 1.9 cm/s (P = 0.02) and the coronary blood flow index fell from 47 +/- 22 to 38 +/- 16 cm/s per mm2 (P = 0.007). This was associated with a fall in the rate x pressure product from 0.92 +/- 0.22 to 0.83 +/- 0.18 mmHg/min (P = 0.038). The coronary vascular resistance rose from 2.4 +/- 1.1 to 3.0 +/- 1.6 mmHg/cm per s per mm2 (P = 0.041). There were no major changes in the epicardial coronary artery diameter during TENS and there was no significant effect on the response to the cold-pressor test.
Conclusions: In this group of patients with syndrome X, TENS produced a small but significant fall in coronary artery blood flow associated with a reduction in the rate x pressure product. TENS had no significant effect on coronary vasomotion during sympathetic stimulation by the cold-pressor test. Thus, TENS is unlikely to have a direct effect on coronary artery vasomotion or haemodynamics in syndrome X but reduces the rate x pressure product and thus myocardial oxygen consumption.