Runaway atrioventricular sequential pacemaker after radiation therapy.

Pacemaker malfunction manifested as a runaway circuitry occurred in two patients after they received radiation therapy for treatment of carcinoma. Both pacemakers were programmable atrioventricular sequential units (DVI) with complementary metal oxide semiconductor circuitry. One pacemaker was directly in the radiation field, whereas the other was not directly within the radiation port. Thus, direct irradiation of an implanted pacemaker should be avoided. It is advisable that a pacemaker be shielded even when the pacemaker is not in the direct field of radiation.