Modulation of intrinsic cardiac neurons by spinal cord stimulation: implications for its therapeutic use in angina pectoris

Objective: Electrical stimulation of the dorsal aspect of the upper thoraci c spinal cord is used increasingly to treat patients with severe angina pec toris refractory to conventional therapeutic strategies. Clinical studies s how that spinal cord stimulation (SCS) is a safe adjunct therapy for cardia c patients, producing anti-anginal as well as anti-ischemic effects. Howeve r, little information is yet available about the underlying mechanisms invo lved. Methods: In order to determine its mechanism of action, the effects o f SCS on the final common integrator of cardiac function, the intrinsic car diac nervous system, was studied during basal states as well as during tran sient (2 min) myocardial ischemia. Activity generated by intrinsic cardiac neurons was recorded in 9 anesthetized dogs in the absence and presence of myocardial ischemia before, during and after stimulating the dorsal T1-T2 s egments of the spinal cord at 66 and 90% of motor threshold using epidural bipolar electrodes (50 Hz; 0.2 ms; parameters within the therapeutic range used in humans). Results: The SCS suppressed activity generated by intrinsi c cardiac neurons. No concomitant change in monitored cardiovascular indice s was detected. Neuronal activity increased during transient ventricular is chemia (46%), as well as during the early reperfusion period (68% compared to control). Despite that, activity was suppressed during both states by SC S, Conclusions: SCS modifies the capacity of intrinsic cardiac neurons to g enerate activity. SCS also acts to suppress the excitatory effects that loc al myocardial ischemia exerts on such neurons. Since no significant changes in monitored cardiovascular indices were observed during SCS, it is conclu ded that modulation of the intrinsic cardiac nervous system might contribut e to the therapeutic effects of SCS in patients with angina pectoris. (C) 2 000 Elsevier Science B.V. All rights reserved.