In patients with cardiac syndrome X (CSX) who present with refractory angina episodes, spinal cord stimulation (SCS) has beneficial effects. The mechanisms of SCS, however, remain speculative. We assessed the effects of SCS on cardiac sympathetic function in these patients.
METHODS AND RESULTS: We studied 11 CSX patients treated by SCS for refractory angina (mean age, 60 +/- 9 years; 5 men and 6 women), both during SCS therapy (SCS-ON) and after withdrawal of SCS therapy (SCS-OFF), using a randomized crossover design. Planar and single photon emission computed tomography iodine 123 metaiodobenzylguanidine (MIBG) myocardial scintigraphy and technetium 99m sestamibi (MIBI) bicycle exercise stress testing were performed at the end of each period. Compared with 10 healthy control subjects, CSX patients showed a lower heart-mediastinum ratio for MIBG uptake (2.19 +/- 0.3 vs 1.69 +/- 0.3, P = .001) and a higher cardiac MIBG uptake score (4.0 +/- 2.5 vs 19.7 +/- 27, P = .08). There were no differences in CSX patients during the SCS-ON and SCS-OFF phases of the study in heart-mediastinum ratio (1.74 +/- 0.3 vs 1.69 +/- 0.3, P = .13), cardiac washout rate of MIBG (42.9% +/- 14% vs 43.3% +/- 14%, P = .08), or MIBG defect score (18.7 +/- 25 vs 19.7 +/- 27, P = .22). Reversible perfusion defects during the SCS-OFF phase were detected in 8 patients; an improvement in perfusion defects was observed in 2 patients (25%) during the SCS-ON phase.
CONCLUSIONS: Our data confirm the presence of abnormal cardiac adrenergic nerve function in CSX patients. SCS was unable to result in significant improvement of cardiac MIBG uptake abnormalities, suggesting that its therapeutic effects are unlikely to be mediated by modulation of cardiac adrenergic nerve activity