Safety of a permanent unipolar rate adaptive pacemaker during prolonged helicopter travel.

Environmental interference with implanted rhythm management devices may result in inappropriate pacemaker inhibition and bradycardia or inappropriate stimulation and tachycardia. In permanent rate adaptive pacemakers with motion-based activity sensors or unipolar electrodes, this interference may be particularly problematic. We report the first case of repeated, prolonged exposure of a unipolar, motion-based rate adaptive pacemaker system in a pacemaker-dependent patient without sequelae. The patient is a 36-year-old woman, a registered flight nurse who underwent implantation of a permanent dualchamber pacemaker at age 21 for congenital third-degree block manifested as dizziness without syncope. At that time, a Medtronic Pulse Generator 7005 was implanted using unipolar atrial and ventricular electrodes. She developed pacemaker-mediated tachycardia that required treatment with beta blockers. Referred for pulse-generator replacement for end-of-life parameters at age 32, she was found to be pacemaker-dependent. Operative findings included P wave of 3, atrial threshold of 1 volt measured at 0.5 ms, and an atrial impedance of 400 ohms. Ventricular threshold was 1 volt at 0.5 ms with no underlying ventricular rhythm and a ventricular impedance of 430 ohms. These leads were retained and connected to an Intermedics 493-03 pulse generator programmed in the DDDR mode. Postventricular atrial refractory period (PVARP) was extended, and pacemaker-medicated tachycardia resolved without drug therapy. Two years later, she presented for cardiac clearance for flight nurse service on a twin-engine Agusta 109 helicopter equipped with a four-blade main rotor system. She remained pacemaker dependent without escape rhythm at a lower rate of 30 in the pacemaker clinic, but histograms showed intermittent atrial and ventricular sensed cycles. Reprogramming the atrial output to 8.1 volts and the ventricular sensitivity to 1.5 mv showed no evidence of crosstalk. No oversensing of myopotentials could be provoked. In the DDDR mode, pocket manipulation at rest showed minimal increase in pacing rate. Final programmed parameters were DDDR 60-120, PVARP 350 ms, atrial and ventricular outputs 3.5 v and 0.45 ms, atrial sensitivity 0.8 ms, and ventricular sensitivity 3.5 mv. A Holter monitor worn during a 4-hour flight at these parameters showed normal pacemaker function with evidence of atrial sensing and pacing and ventricular pacing without spontaneous ventricular activity. No oversensing or pacemaker-medicated tachycardia was present. Appropriate P wave tracking was documented to rates of 110 bpm. No sensor-driven atrial pacing was present. Similar evaluations have been performed at 3-month intervals without further Holter monitoring with similar findings. Histogram reviews have shown P wave tracking to rates of 110. No high rate ventricular episodes above 120 have occurred. To date she has completed 56 patient flights and 200 hours of flight time without cardiac symptoms. Rate-adaptive pacemakers with vibration sensors have been reported to demonstrate increased sensor-driven pacing rates in response to nonactivity and environmentally related stimuli during air travel. 1-3 This result presumably is related to the pacemaker misinterpreting vibration of the aircraft and classifying it as cardiac electrical activity. These studies, however, involved pacemakers externally attached to volunteers’ chests rather than studies of permanently implanted pacemakers. We failed to observe inappropriate increase in sensor-driven pacing resulting from rapid helicopter acceleration or deceleration, rapid vertical or lateral flight, or rotational maneuvers.