Toff, William Daniel; (1994) Cardiac pacemaker function in the aviation environment. Doctoral thesis (M.D), UCL (University College London).

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Abstract

Experience suggests that patients with implanted cardiac pacemakers may travel safely by air but the exacting medical standards for pilots invite special consideration, as pacemaker failure may result in subtle or sudden incapacitation that might jeopardise flight safety. Potential hazards in the aviation environment were assessed, with particular regard to the risk of electromagnetic interference (EMI). Occasional inhibition was noted in explanted unipolar pacemakers during flight tests and a systematic study was therefore undertaken. Electromagnetic field strengths were measured in 10 aircraft under operational conditions and explanted and implanted pacemakers were exposed to comparable fields. The effect of aircraft vibration on activity-sensing, rate-adaptive pacemakers was also assessed by monitoring the rate-response during flights. Aircraft field strengths ranged from 0.20-1.12Vm-1, 0.20-35.00Vm-1 and 1.60-18.00Vm-1 in the HF, VHF and microwave bands respectively. Explanted unipolar devices were all affected in comparable fields, with thresholds (mean±sd) for interference and failure (cessation of pacing ≥30s) respectively of 3.2±1.9Vm-1 and 7.7±1.5Vm-1 in HF and 5.7±3.0Vm-1 and 11.2±6.6Vm-1 in VHF fields. Modulation with pulsing increased HF susceptibility (0.49±0.2Vm-1 and 1.5±0.93Vm-1). Only one device showed sustained interference in microwave fields (1-2GHz at 16Vm-1) but susceptibility was increased by pulsing. Bipolar devices were less susceptible although one device showed interference and failure in modulated HF fields at 18.5Vm-1 and 30Vm-1 respectively and another showed interference in VHF fields at 27Vm-1. Implanted unipolar devices were unaffected. Activity-sensing devices showed increased pacing rates during flight. In fixed-wing aircraft, these were modest and confined to specific periods (take-off, turbulence and landing) but in helicopters and hovercraft, they were marked and sustained. It is concluded that, whilst explanted unipolar pacemakers are susceptible to EMI in radio-frequency fields comparable to those in aircraft, clinically significant effects are unlikely in implants. These findings may serve to reassure patients with pacemakers who wish to fly as passengers but the remote risk of EMI and the small inherent risk of spontaneous failure make unrestricted certification to fly inappropriate for pilots with implants. Certification restricted to multi-crew operations may, however, be considered for selected subjects, in whom bipolar systems are preferable. Activity-sensing devices are acceptable in fixed-wing aircraft but inappropriate in helicopters and hovercraft.

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