Dose rate dependence of incorrect sensing and triggering of defibrillation in cardiac implantable electronic devices: single manufacturer result with kV beam.

An incorrect triggering condition owing to irradiation of a cardiac implantable electronic device (CIED) with a defibrillation function has not yet reached consideration. This study aimed to experimentally examine the dose rate dependence on incorrect sensing and triggering for defibrillation, as either direct or indirect irradiation of a CIED requires numerical explanation by the dose rate. Four devices were directly irradiated by X-ray beams of 160 kV at dose rates to the device surfaces of 50- 3600 cGy/min. The devices were set to a VVI mode of 60 bpm, where the function for defibrillation was deactivated for safety reasons. Wave signals monitored on an electrocardiogram were recorded as a movie. During the 15-second irradiation time, the number and the time interval of incorrect sensing caused by irradiation were counted. The dose rate, considering the attenuation effect in the titanium case, was calculated as 11 - 800 cGy/min. It has been clearly observed that the ratio of incorrect sensing and the reach rate of incorrect triggering for defibrillation depend on the dose rate as well as on the sensing threshold level. The dose dependence was well reproduced by an error function. Extrapolation of the present result from a single manufacturer's result predicts that an incorrect triggering of shock therapy would not occur if the sensing threshold level were set at higher than 0.9 mV for X-ray kV beams at a dose rate of 600 cGy/min. This was therefore the first study of a safe condition against incorrect defibrillation caused by direct irradiation.