To the Editor:--We would like to congratulate Kamibayashi et al. on their interesting paper. However, we wish to offer an alternative view to one of their conclusions. The authors stated, "Sympathetic activity to the heart in epidurally anesthetized animals was significantly attenuated, while parasympathetic activity was not affected. Therefore, the activity in the parasympathetic nerve may be relatively dominant to sympathetic tone after epidural treatment, and this situation is similar to vagal nerve stimulation." Although it is intuitive to suggest that, when the sympathetic efferent nerves are blocked, a relative vagal dominance would exist, clinically this is not the case. Rather, in patients with a cardiac sympathectomy after high spinal block (T4-C7), [2,3]spectral analysis of heart rate variability results in a loss of both sympathetic and vagal components. This indicates a state of reduced sympathetic and vagal outflow and probably results from sympathetic afferent blockade to central neural centers. Therefore, the vagal outflow, which was not directly blocked by the anesthetic, was not sufficient to maintain normal heart rate variability. In their dog model of thoracic sympathectomy, the baroreceptor pressor response after epinephrine probably created a vagal dominant state, but we submit that this state would not exist in the absence of systemic hypertension. Therefore, we believe that sympathectomy of the heart alone does not necessarily result in a state of vagal dominance but that vagal dominance exists only after sympathetic blockade in the presence of vagal stimulation.
R.P.S. Introna, M.D., J.K. Pruett, Ph.D., D.C. Martin, M.D., E.H. Yodlowski, Ph.D., E. Grover, R.S. Crumrine, M.D., Department of Anesthesiology, Medical College of Georgia, Augusta, Georgia 30912.
(Accepted for publication April 4, 1995.)