Spinal Cord Activation Differentially Modulates Ischaemic Electrical Responses to Different Stressors in Canine Ventricles

Spinal cord stimulation (SCS) represents an acceptable treatment modality for patients with chronic angina pectoris refractory to standard therapy, but its mechanism of action remains unclear. To develop an experimental paradigm to study this issue, ameroid (AM) constrictors were implanted around the left circumflex coronary artery (LCx) in canines. Six weeks later, unipolar electrograms were recorded from 191 sites in the LCx territory in the open-chest, anesthetized state under basal pacing at 150 beats/min. We investigated the effect of SCS on ST segment displacements induced in the collateral-dependent myocardium in response to two stressors: (i) transient bouts of rapid ventricular pacing (TRP: 240/min for 1 min) and (ii) angiotensin II administered to right atrial neurons via their coronary artery blood supply. ST segment responses to TRP consisted of ST segment elevation in central areas of the LCx territory and ST depression at more peripheral areas. Such responses were unchanged when TRP was applied under SCS. Shortening of repolarization intervals in the metabolically compromised myocardium in response to TRP was also unaffected by SCS. In contrast, ST segment responses to intracoronary angiotensin II, which consisted of increased ST elevation, were attenuated by SCS in 6/8 preparations. The modulator effects of SCS were greatest at sites at which the greatest responses to angiotensin II occurred in the absence of SCS. These data indicate that spinal cord stimulation may attenuate the deleterious effects that stressors exert on the myocardium with reduced coronary reserve, particularly stressors associated with chemical activation of the intrinsic cardiac nervous system