Testing has shown that for devices which incorporate an accelerometor for rate responsive activity-based pacing, if the activity sensor is programmed "on" while continuous diagnostic X-ray exposure (e.g. CT scanning) is performed, if the beam of energy is directly over the implanted device, there may be a temporary increase in pacing rate during the exposure. The pacing rate will return to baseline pacing after the X-ray exposure is terminated. If increased rates occur, the pacing rate will be limited to the programmable Maximum Sensor Rate which is generally determined by the patient's physician as the safe maximum rate to be achieved during exercise. To prevent any potential transient rate increase, the clinician may want to consider programming the rate responsive sensor to Passive or OFF, if appropriate, prior to the X-ray procedure and then reprogram the parameter as desired after the diagnostic imaging is completed.Read the rest for the details.
Medtronic's statement regarding the same issue is included here (pdf).
I cannot recall ever seeing an interaction like the one they're describing, but the implications are that we'll have to be more cautious as CT scanners become more powerful, especially as patients have chest CT's that might scan the pacemaker implant sight. For the great majority of patients, I just do not see this as a "biggie" for patient care. Anyone else with thoughts?