Monopolar Radiofrequency Energy’s Effect On Pacemaker Function: Practical Implications

Henry R Govekar, MD, Thomas N Robinson, MD FACS, Guillaume Girard, MS, Greg V Stiegmann, MD FACS, Paul D Varosy, MD. University of Colorado School of Medicine

Introduction: Recommended use of monopolar “bovie” energy in patients with pacemakers is based on expert opinion and small case series. Current guidelines recommend to use low monopolar power settings in short/intermittent bursts, to avoid proximity of the active electrode to the pacemaker, to position the dispersive electrode (“grounding pad”) so the current vector avoids the pacemaker and to use bipolar instead of monopolar energy. The PURPOSE of this study was to challenge current guidelines regarding the use of monopolar electrosurgery in the setting of a pacemaker in an in vivo animal model. The SPECIFIC AIMS were to quantify pacer inhibition resulting from monopolar energy by altering: (1) generator power setting; (2) generator mode (cut versus coagulation); (3) distance between active electrode and pacemaker; (4) location of dispersive electrode; (5) activation technique (intermittent bursts versus continuous); (6) energy modality (monopolar versus bipolar).
Methods: The effect of monopolar radiofrequency energy on a trans-venous ventricular lead pacemaker was tested in vivo (porcine model). The native heart rate (85 beats/minute) was overdrive paced with the pacemaker (110 beats/minute). The primary outcome variable was pacer inhibition (quantified as the number of beats dropped by the pacemaker during a 5 second monopolar energy activation).
Results: (1) Lowering generator power setting from 60 to 30 Watts decreased the number of dropped paced events (2.3±1.2 versus 1.6±0.8; p=0.045. (2) On 30 Watts, the cut mode decreased the number of dropped paced beats in comparison to coagulation mode (0.6±0.5 versus 1.6±0.8; p=0.015). (3) On 30 Watts coagulation, firing the active electrode at different distances from the pacemaker generator (3.75 cm, 7.5 cm, and 15 cm) did not change the number of dropped paced beats (1.8±1.3, 1.6±0.8 and 2.2±1.3; ANOVA p=0.612). (4) When placing the dispersive electrode in four locations (right/left gluteus, right/left shoulder), more paced beats were dropped when the current vector travelled through the pacemaker/leads (e.g., the current crossed through the pacemaker and/or leads as it travelled from the active to dispersive electrode) than when the current vector did not travel through the pacemaker/leads (1.5±1.0 versus 0.2±0.4; p<0.001). (5) Intermittent “bovie” use (1 second on and 1 second off for a total of 10 seconds) versus continuous activation (one continuous 5 second activation) decreased the number of dropped paced beats (0.9±0.6 versus 1.6±0.8; p=0.001). (6) On 30 and 60 Watts power, bipolar energy dropped no paced beats (p<0.001 versus monopolar energy at both power settings).
Conclusions: Placement location of the dispersive electrode to avoid current vector traversing the generator/leads is critical to minimizing monopolar energy’s disruptive effect on pacemaker function. Varying distance of the active electrode from the pacemaker generator was not a significant factor in pacemaker disruption when the variable of whether or not the current vector was traversing the generator/leads was held constant (a finding that contradicts current guidelines). Cut mode causes less pacemaker disruption than coagulation mode (a finding not included in current guidelines). Current recommendations to use a lower power settings, short/intermittent monopolar energy activations and bipolar energy were confirmed.