Effects of an increased air gap on the in vitro interaction of wireless phones with cardiac pacemakers.

Several clinical and laboratory studies have demonstrated electromagnetic interaction between implantable cardiac pacemakers and hand-held wireless phones operated in close proximity. Current FDA and HIMA labeling guidelines indicate that a minimum separation of 6 in (15 cm) should be maintained between a hand-held wireless phone and an implanted pacemaker. This separation requirement does not distinguish between lateral locations on the chest and a perpendicular air gap. Evidence is provided here for a substantially reduced separation threshold when measured across an air gap rather than near the saline conductive media of a simulated torso. Twenty pacemaker-phone combinations involving 6 pacemakers and 9 phones were evaluated in vitro under worst-case conditions with respect to phone output power and pacemaker sensitivity. The phones represented CDMA, TDMA-11 Hz, TDMA-22 Hz, TDMA-50 Hz, and TDMA-217 Hz digital wireless technologies. Small increases in the perpendicular air gap between the phone and the saline surface resulted in a dramatic reduction in interaction. Approximately half of the 208 test runs exhibiting interaction at an air gap of 1 cm no longer resulted in interaction when the gap was increased to 2 cm. At a gap of 7.4 cm, the percentage of runs with interaction decreased to 1.4%. The overall interaction rate, considering a total of 8296 test runs from an earlier study, was less than 0.07% at a total perpendicular distance of 8.6 cm from the saline surface to the phone antenna axis. The perpendicular distance threshold of 8.6 cm was significantly less than the horizontal plane projection threshold of 19 cm previously reported. This difference is a function of the electromagnetic field coupling to the saline bath rather than field strength changes along the axis of the phone antenna. The results have implications for those making recommendations to pacemaker patients who may be unaware of this distinction.