Reduced Shock Efficacy With Some Boston Scientific Defibrillation Leads

Certain Boston Scientific defibrillation leads are subject to potential shock coil calcification that can result in reduced shock efficacy, according to an alert released by the company, the Heart Rhythm Society (HRS), and the European Heart Rhythm Association (EHRA) on July 29.

The issue affects all Reliance G single- or dual-coil leads with shock coils coated by Gore expanded polytetrafluoroethylene (ePTFE), which were made between 2002 and 2021 and are no longer being distributed. Boston Scientific estimates that about 354,000 of these leads remain in use, including 250,000 in the United States.

Calcification on the coils may gradually increase low-voltage shock impedance, which reduces shock efficacy, and “instances of failed shock therapy have been reported,” lead author Molly Sachdev, MD (WashU Medicine, St. Louis, MO), and colleagues write in the alert. They add that “sensing and pacing performance of these leads are not known to be compromised.”

In an alert issued August 6, the US Food and Drug Administration said “the most common harm is early lead replacement and the most serious harm is death or need for cardiac resuscitation due to nonconversion of a sustained ventricular arrhythmia from a reduced shock energy due to high impedance.” The agency noted that as of July 24, Boston Scientific had reported 386 serious injuries and 16 patient deaths tied to the issue.

On that date, the company, after completing its investigation, sent a letter to physicians detailing the potential for calcification on these leads. That prompted the health policy and regulatory affairs committee of the HRS, in collaboration with Boston Scientific and EHRA, to convene a “rapid response team” to address the issue.

“The ePTFE leads were initially developed to prevent tissue ingrowth. However, it has now been recognized that the ePTFE membrane allows for cell debris, proteins, and minerals to enter, which can lead to dystrophic calcification over time,” the alert’s authors note. “The accumulation of a calcific encapsulant over the shock coils may reduce the electrical conductivity and increase both low and high voltage shock impedances,” which may reduce shock efficacy.

Boston Scientific has estimated that the risk of life-threatening harm due to arrhythmic death among all patients with these leads is 0.0021%, or one out of every 47,500 leads at 10 years.

“Ten deaths due to failure to convert a sustained ventricular arrhythmia in the last 10 years have been associated with this phenomenon,” the alert states, noting that there also has been harm associated with extracting these leads reported in some patients.

Both Boston Scientific and the professional societies recommend weighing the risks and benefits of lead extraction if replacement is planned. “Based on implant time and likely coil calcification, these leads may pose an increased risk of extraction-related complications,” the HRS notes. “However, this must be balanced by potential complications of abandoned leads and that extraction risk may be higher with longer lead dwell times.”

The authors acknowledge that it’s unclear whether these leads, in fact, do carry greater risks associated with extraction compared with others, but add: “When appropriate, alternative strategies such as a nonvascular ICD system or addition of another transvenous lead should be considered.”

The HRS also encourages its members to read Boston Scientific’s letter on the calcification issue. “Given the highly technically nuanced nature of this advisory, clinicians should maintain a low threshold to discuss lead concerns with [the company’s] technical services for additional guidance to support informed lead replacement decision-making,” they say.

The FDA said it is currently reviewing information about this issue and will keep the public apprised of any new developments.