A new device can detect dangerously abnormal heart rhythms and deliver shocks to restore a normal heartbeat without relying on wires that connect to the heart, according to research reported in the American Heart Association journal, Circulation.
Traditional implantable cardiac defibrillators (ICDs) use electrical conducting wires inserted into blood vessels. These leads are in direct contact with the heart.
Instead of wires to the heart, the first subcutaneous implantable cardiac defibrillator (S-ICD®), uses a lead placed under the skin along the left side of the breast bone. This alleviates many genuine concerns about ICD lead complications, including broken lead wires, vessel damage, vessel infection and scarring.
“The lead is the most common failure mechanism for a transvenous ICD system, and patients often outlive the useful life of the lead,” the authors wrote. The complications from the leads provide “a rationale to develop a totally subcutaneous ICD (S-ICD),” they added. “The S-ICD System senses, detects, and treats malignant ventricular tachycardia/ventricular fibrillation but leaves the heart and vasculature untouched.”
“This new system was developed over a dozen years to combine some of the best aspects of traditional implanted ICDs and external defibrillators,” said the study’s senior author Martin C. Burke, D.O., professor of medicine at the University of Chicago and director of the medical center’s Heart Rhythm Center.
While the added distance from the heart requires a more powerful shock (about 2.5 times stronger than traditional ICDs), the power is “well within a safe range,” Burke said. And patients should experience fewer of those shocks, thanks to an improved monitoring system that measures more complex heart rhythm characteristics to separate out dangerous cardiac events from false positives.
The Food and Drug Administration approved the device on September 28, 2012, for patients who do not require a pacemaker or pacing therapy.“The S-ICD System provides an alternative for treating patients with life-threatening heart arrhythmias for whom the routine ICD placement procedure is not ideal,” said Christy Foreman, director of the Office of Device Evaluation at FDA’s Center for Devices and Radiological Health, in the release announcing their approval. “Some patients with anatomy that makes it challenging to place one of the implantable defibrillators currently on the market may especially benefit from this device.”
In their Circulation paper, the researchers extended the data presented to the FDA. In the 33-site study, 330 patients (average age 52) were evaluated and 314 had the S-ICD® implanted. During an average 11 month follow-up, 21 patients spontaneously developed 38 episodes of ventricular fibrillation or tachycardia (an abnormally fast heartbeat). All were successfully restored to a normal heart rhythm. Forty-one patients (13.1 percent) received shocks that were determined to be inappropriate because they were not preceded by a dangerous heart rhythm.
“The rate of inappropriate shocks is similar to the most recent data for traditional ICDs, but it can still be improved,” Burke said.
Ninety-nine percent of the S-ICDsremained free of complications 180 days following implantation. When tested by a purposely-induced abnormal rhythm following implantation, the S-ICD® was more than 90 percent effective at consistently detecting and reversing ventricular fibrillation.
The S-ICD® has been available in Europe and New Zealand since 2009. The first U.S. patient to receive the device was Brooke Bergeron, 38 at the time, on March 3, 2010. She was 37 weeks pregnant when she suffered a heart attack, a rare complication of her fourth pregnancy. After the child was delivered via caesarian section and the mother underwent an emergency double-bypass operation, Burke recommended an implantable defibrillator.
Because of her young age, normal heart rate and high risk of cardiac arrest, Bergeron was an ideal candidate for a device without leads, which can be damaged over time.
“I wasn’t sure if I wanted to be a test dummy,” Bergeron said in 2010. But one month after the procedure she went on a family vacation to the Gulf of Mexico. She rode a jet ski.
“The S-ICD® is not a replacement for other defibrillators,” Burke said. “For some patients, like Mrs. Bergeron, it will be ideal, for others inappropriate, and the vast proportion in the middle will be able to select the type of system they want.”
“Although the subcutaneous ICD is defeatured and exists only to defibrillate, it does represent a major engineering feat for an entirely subcutaneous system,” wrote Leslie Saxon, MD, in an accompanying editorial in Circulation.
Saxon was troubled by the deliberate simplicity of the device, compared to the completely featured, Internet-connected transvenous systems used in the latest generation of ICDs. But, in the best of all possible worlds,” she suggested, “the subcutaneous ICD will grow and evolve into a device whose design supports the growth of features and capabilities that can evolve with the patient’s condition.”
Should patients request this type of implant?
Patients should be given a balanced presentation of data and rationale for both the single-chamber transvenous ICD and the subcutaneous ICD,” Burke said. Patients in this study understood the difference and “took preference with the subcutaneous ICD system,” he said. This was especially true for patients who were implanted after transvenous device infection and recall failure.
As part of the approval, the FDA is requiring the manufacturing company to conduct a post market study to assess the long-term safety and performance of the device and to assess differences in effectiveness across genders. The study will follow 1,616 patients for five years.
Weiss R., Knight B.P., Gold M.R., Leon A.R., Herre J.M., Hood M., Rashtian M., Kremers M., Crozier I. & Lee K.L. & (2013). Safety and Efficacy of a Totally Subcutaneous Implantable-Cardioverter Defibrillator, Circulation, 128 (9) 944-953. DOI: 10.1161/CIRCULATIONAHA.113.003042