Unpredictable Effects of Cancer Radiotherapy on Cardiac Devices Prompts Call to Action

Patrice Wendling

May 06, 2016

SAN FRANCISCO, CA — Radiotherapy (RT) in cancer patients with modern cardiac implantable electronic devices (CIEDs) appears safe but can prompt some devices to switch into a fallback mode even if the radiation is far from the device, a small study shows[1].

"We really need to check them after every RT, even if it's like 40 times, because the effect is not predictable," lead investigator Dr Julia Vogler (University Heart Centre Hamburg, Germany) told heartwire from Medscape.

Dr Julia Vogler

Her center began checking CIEDs after every RT after an implantable cardioverter-defibrillator (ICD) switched into fallback mode after multiple RT sessions in a patient with prostate cancer and had to be reprogrammed with the manufacturer.

Between March 2012 and November 2015, device evaluations were performed after every RT session in 43 patients and once a week in four patients with prostate cancer. The cumulative radiation dose in the two groups was 44.9 Gy and 57.8 Gy, respectively. In all, 33 had a pacemaker, 12 had an ICD, and two had  cardiac resynchronization therapy with a defibrillator (CRT-D).

Battery capacity, lead impedance, sensing, and threshold levels remained stable during the entire RT, Vogler reported in a poster at the Heart Rhythm Society (HRS) 2016 Scientific Sessions.

In three patients with a pacemaker treated with RT for rectal cancer, endometrial carcinoma, and oral cancer, however, the device switched into the VVI-fallback mode during one of the RT sessions. In one patient this happened twice.

"We had one patient with a Biotronic device and when they got into fallback mode it was unipolar sensing, which in a patient who is pacemaker-dependent can result in a problem," she said. "If you don't recognize this and if you do the [CIED] interrogation a week later and he's unipolar sensing, that might result in asystole."

After resetting the device, no further complications occurred. No device malfunctions or premature battery depletions were observed. The fallback events occurred in Biotronic and St Jude Medical devices, but the study also included devices from Boston Scientific, Medtronic, and Sorin/Livanova, Vogler said.

Significant Knowledge Gap

Even though the number of patients with CIEDs undergoing cancer therapy is on the rise, "in the field of cardiology and radiation oncology there is a significant lack of knowledge regarding the safe handling of cardiac implantable electronic devices during RT," according to national guidelines for RT in patients with CIEDs, published last year by the German Society of Radiation Oncology and the German Society of Cardiology.

They say this is reflected by a recent UK poll suggesting many physicians still use the now-outdated 1994 American Association of Physicists in Medicine recommendations.

Modern CIEDs, however, may be more sensitive than older devices to the effects of ionizing radiation because they use complementary metal oxide semiconductors (CMOS), thinner housing with less shielding, and random access memory (RAM), which holds patient-related data by small amounts of highly volatile increments in energy that, when damaged, can lead to complete loss of CIED function.

The guidelines recommend that devices should never be located in the beam, beam energy should be limited to 6 to 10 MV, and the cumulative scatter-radiation dose should be limited to 2 Gy.

Beam energies above this threshold can cause excess formation of secondary neutrons that can harm the device, particularly its RAM or CMOS, Vogler pointed out. Publications also suggest that the effect of RT is additive, "which is why you have to do all the interrogations. It could have an effect 2 years later."

She acknowledged that the study was limited by small patient numbers and follow-up and said they would like to reach out to the manufacturers for additional data on file.

"RT seems to be safe in patients with modern CIEDs concerning battery longevity and lead measurements. However, the observed device resets into fallback mode do underlie the unpredictable effect of RT and therefore the necessity of CIED interrogations after every RT session," the investigators conclude.

The authors reported no relevant financial relationships.

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