Pacemakers (PMs) and implantable cardioverter defibrillators (ICDs) may develop malfunction during external beam radiotherapy (RT). We aimed to describe clinical practice in PM/ICD patients undergoing RT and to assess the rate and predictors of device malfunctions.

We reviewed medical records of all PM/ICD patients undergoing RT at four centers in Western Denmark during 2003-2012. Logistic regression was applied to identify predictors of PM/ICD malfunctions.

Five hundred sixty patients were included. The annual rate of RT courses in PM/ICD patients increased by 199% from 1.45 treatments per 100,000 person-years in 2003 to 4.33 in 2012. Safety measures included supplementary evaluations of PM/ICD (38.3%), reprogramming (1.5%), relocation of the device (3.5%), and application of a magnet to the ICD during RT (10.8%). At device evaluations after the RT (n = 453), malfunctions were detected in 10 (2.5%) PMs and four (6.8%) ICDs. Electrical resets constituted 11 (78.6%) of the malfunctions, and no failures were life-threatening or warranted PM/ICD removal. Factors associated with device malfunctions in logistic regression analysis were beam energy ≥15 MV (odds ratio [OR] 5.73; 95% confidence interval [CI], 1.58-20.76) and location of tumor below the diaphragm (OR 4.31; 95% CI, 1.42-13.12). However, the effect of tumor location declined (OR 2.27; 95% CI, 0.65-7.95) after adjustment for beam energy.

Although the rate of RT in PM/ICD patients is increasing, the damaging effects of RT on the devices seem to be usually transient. Our data suggest that high beam energy plays the pivotal role in inducing impairments in these devices.