Response: Right‐sided Vagus Nerve Stimulation

To the Editor: We appreciate the interest in our article by Drs. Tubbs and Blount. We were intrigued by the concept of stimulation of the carotid sinus nerve to abort seizures. Their dog model showed no effect on cardiac function with either left or right carotid sinus nerve stimulation. However, stimulation of the carotid sinus nerve has been shown to have cardiac effects in humans, which may limit its usefulness as a therapeutic measure for epilepsy. In the 1960s, cardiac stimulation was developed as a new treatment for angina pectoris. Braunwald (1) described two patients in whom he stimulated both carotid sinus nerves simultaneously to treat angina that was unrelieved by medical management. He used a transmitter unit that generated 50 pulses/s at 1.5 to 8.0 volts for 0.3 ms. Braunwald theorized that angina relief was due to “a reduction in sympathetic stimulation to the heart and arterial bed” causing a decrease in heart rate and arterial pressure, which resulted in decreased oxygen consumption. Epstein (2) later reported 17 similar cases using a transmitting unit that generated 20 to 80 pulses/s at 0.5 to 8 volts for 0.3 ms. Both studies showed that heart rate and blood pressure decreased in proportion to the intensity of stimulation. This suggests that stimulation of the carotid sinus nerve in humans for the treatment of seizures may be limited by cardiac effects. This reflects the variable response on cardiac function, which appears to be species dependent. The development of peripheral stimulators must continue to have safety screening performed in animals and rigorous safety monitoring in human trials.