Ventricular oversensing from monopolar electrosurgery (ESU) causes pacing inhibition

A 61-year-old woman undergoing a T10 vertebrectomy who was pacing-dependent due to third-degree AV block had a Medtronic Kappa 401 dual-chamber pacemaker in the left pectoral position. During surgery, a monopolar ESU was used, with the current dispersion pad placed on the thigh. Note the lack of ventricular pacing for five seconds due to EMI during monopolar ESU use, which caused ventricular oversensing (ie, energy entering the system via the ventricular lead caused cessation of all pacing output).
The two arrows represent native P-waves that were unconducted due to the patient's AV block. The circle shows an atrial pace without a following ventricular pace because of fluctuating noise, a common issue with monopolar ESU. The event occurring at * is a "ventricular safety pace," which results from an electrical signal occurring on the ventricular channel shortly after an atrial pace (after 60 to 90 msec, depending upon manufacturer). This pacemaker emits a ventricular pace 110 msec after the atrial pace since it cannot determine whether the early event is a native ventricular event or noise.