Conversion of hemiblock to complete heart block by intraoperative motor-evoked potential monitoring

Intraoperative monitoring of nervous system pathways, including assessing the integrity of descending motor pathways with motor-evoked potentials, is often performed in intracranial and spine operations to reduce the risk of iatrogenic neurological impairment. We present a case in which intraoperative monitoring with motor-evoked potentials resulted in complete heart block in a patient with a history of hemiblock. Neuromonitoring has been associated with arrhythmias in patients with ostensibly normal conduction systems, and we propose that monitoring personnel, anesthesiologists, and surgeons need to be aware of this risk and exercise caution when monitoring motor-evoked potentials in patients with known conduction deficits.