Background: Spinal cord stimulation (SCS) has proven antianginal and antiischemic effects in severe coronary artery disease patients, minimizing frequency, intensity, and duration of pain. The mechanism explaining these effects has been detected in a sympathicolytic effect of the SCS. We monitored 30-minute-long recordings of the heart rate variability (HRV) and its spectral power parameters to evaluate the influence of SCS on the sympathetic/parasympathetic balance.
Methods and results: Eight patients underwent HRV recordings in controlled environmental conditions. The patients were seated in a relaxed position and isolated from external contacts. During three consecutive 30-minute periods, the SCS was programmed, in a randomized fashion, to stimulate at a level generating paresthesias (ON), at a subliminal level (SUB, amplitude 80% of ON), or switched off (OFF). The low-frequency/high-frequency ratio during stimulation (ON) was significantly lower compared to that found while the SCS was turned OFF (0.54, 0.35-1.04 vs 1.21, 0.80-2.48; P = 0.036). The stimulation resulted in a median 52% (33-65%) reduction of the sympathetic activity compared to basal (ON vs OFF, P = 0.049).
Conclusion: No difference emerged instead comparing OFF versus SUB (P = 0.575). The stimulation effect was not influenced by the randomized sequence. Thirty-minute SCS significantly influenced the sympathetic/parasympathetic balance reducing sympathetic modulation.