BRADYCARDIA INDUCED BY INTRAVASCULAR VERSUS DIRECT STIMULATION OF THEVAGUS NERVE

Background. Electrical stimulation of the parasympathetic nervous syst em results in slowing of the heart. We sought to determine whether car diac vagal efferent axons can be stimulated adequately to induce brady cardia without disturbing the integrity of the thorax. Methods. Cardio depressor effects elicited by direct stimulation of a vagus nerve in a nesthetized dogs and pigs were compared with those generated when the same nerve was stimulated indirectly through bipolar electrodes placed in the adjacent superior vena cava. Results. The heart rate of dogs d ecreased by about 80% when electrical stimuli were delivered to the ri ght thoracic vagus at the level of the thoracic outlet through bipolar electrodes placed either in the adjacent superior vena cava (intravas cular method) or directly on the nerve (direct method). Maximal respon ses were achieved with 10-V, 5-ms, and 20-Hz stimuli. In anesthetized pigs, similar bradycardia occurred when the right cervical vagus or th e right cranial thoracic vagus was stimulated either directly or indir ectly through the intravascular method. Atrial dysrhythmias occurred w hen the stimulating electrodes were placed by either method within 1 c m of the right atrium in both animal models. Conclusions. Controlled b radycardia can be induced during operation without the risk of generat ing cardiac dysrhythmias using electrical stimuli (10 V, 5 ms, and 10 to 20 Hz) delivered to the right cervical vagus nerve or the right cra nial thoracic vagus nerve through adjacent intravascular electrodes. ( C) 1998 by The Society of Thoracic Surgeons.