Spinal cord stimulation normalizes abnormal cortical pain processing in patients with cardiac syndrome X

Cardiac syndrome X (CSX) is characterized by effort angina, ST-segment depression during stress tests and normal coronary arteries. Abnormal nociception was suggested in these patients by studies showing a reduced cardiac pain threshold; furthermore, we recently found a lack of habituation to pain stimuli using recording of laser evoked potentials (LEPs). In CSX patients with severe angina, spinal cord stimulation (SCS) was shown to improve symptoms. In this study we investigated whether, in these patients, SCS has any effects on the excitability of the nociceptive system, assessed by LEPs recording. We studied 16 CSX patients (61.6 ± 7 years; 4 men) who underwent SCS for refractory angina. Cortical LEPs were recorded during stimulation of the chest and right-hand during active SCS (SCS-ON) and in the absence of SCS (SCS-OFF), using a randomized cross-over design. Three sequences of painful stimuli were applied at each site during each test. During the first sequence of chest stimuli, the N2/P2 LEP amplitude was higher during the SCS-ON, compared to the SCS-OFF phase (18.2 ± 7.8 vs. 11.5 ± 4.4 μV, P = 0.006). The N2/P2 amplitude did not change significantly across the three stimulation sequences during the SCS-OFF phase (P = 0.22), whereas it decreased progressively during the second and third sequence (to 87.1 ± 29.5% and 76.4 ± 24.1%, respectively) compared with the first sequence, during the SCS-ON phase (P = 0.014). Similar results were observed during right-hand stimulation. Our study shows that in CSX patients SCS is able to restore habituation to peripheral pain stimuli. This effect might contribute to restore the ability of CSX patients to better tolerate cardiac pain.