Right‐sided Vagus Nerve Stimulation

To the Editor: We enjoyed the recent article entitled “Right-sided vagus nerve stimulation as a treatment for refractory epilepsy in humans” by McGregor et al. (1). We agree that right vagus nerve stimulation may be used in humans with epilepsy, as prior reports of cardiac effects after right-sided vagus nerve stimulation were based on experiments in dogs (2). Although complications with vagus nerve stimulation are low, as found in our report of 74 children undergoing this procedure (3), as surgeons, the option of left versus right side for vagus nerve stimulation is appealing, especially in cases of concomitant left-sided ventriculoperitoneal shunts, so that additional hardware (i.e., vagus nerve stimulator) is moved farther away from the shunt system, thus decreasing the risk of infection of the shunt. Our experience also has shown that another cardiovascular nerve (the carotid sinus nerve) can be stimulated on both left and right sides in a dog model with equal effect on causing cessation of cortically induced seizures (4). Furthermore, we found no significant cardiovascular effects when this nerve (carotid sinus nerve) was stimulated with parameters comparable to those used for vagus nerve stimulation in humans (4). Interestingly, both of these nerves synapse proximally in the cardiorespiratory part of the nucleus tractus solitarius. After right-sided vagus nerve stimulation, we have been unable to alter the cardiorespiratory system in a porcine model (5). These data imply, whether with vagus or carotid sinus nerve stimulation, that nerve stimulation responses (e.g., right-sided cardiorespiratory responses) may be species specific. We also agree with the authors' statement that the right vagus nerve may be desired for stimulation when a left-sided vagus nerve has been used and removed after infection. Indeed, we have shown in a single case that a left-sided vagus nerve that was often stimulated and removed at autopsy had severe demyelination (6).