Subcutaneous Defibrillator Passes First Test

nejmoa0909545f1Last month, we told you about a new cardiac defibrillator device that was implanted for the first time in the United States here at the University of Chicago Medical Center. That procedure – performed by Martin Burke, professor of cardiology, on 38-year-old mother of four Brooke Bergeron – was also the first of a global clinical trial that hopes to test the subcutaneous implantable cardioverter-defibrillator (S-ICD) in more than 300 people. But a new medical device doesn’t just jump straight to the world-testing stage; the current trial was built on the foundation of several smaller trials that worked out the kinks of the device and proved its effectiveness in smaller pools of patients.

The data from those trials were published this week in the New England Journal of Medicine, and portray an instructive case study in how a new device is developed and tested without endangering the patient. In trials conducted in New Zealand and Europe over the last 10 years, different configurations of the device were compared, software was refined, and a slow, careful roll-out of the S-ICD in more and more patients was achieved. With a majority of successes along the way, the researchers set the stage for the wider testing of the device currently in progress while exciting many in the field of cardiology.

“This could be a game changer, if indeed this is the direction this technology goes,” Richard Page, president of the Heart Rhythm Society, told Bloomberg News.

Interestingly, the first step was an engineering challenge – figuring out the best configuration for the device’s leads, which both sense the heart’s rhythms and deliver the shock if necessary. The classic implantable defibrillators have an advantage in this respect, since the leads are actually placed inside the heart. But with subcutaneous leads placed under the skin near the sternum, the same task can be accomplished from farther away with a stronger, but still safe, shock. All the same, the device’s designers wanted to minimize the amount of electricity required to reset the heart’s rhythm, and thus tested four different configurations (pictured above) to find the one that performs its function with the least firepower.

The winner was the top left design, with the lead running parallel along the left side of the sternum and the device monitor placed outside the ribs near the left armpit. That model was then moved to the next stage, where patients were implanted with both the classic, transvenous device and a subcutaneous device. The double-implant allowed researchers to directly compare the shocking power needed to restore normal heart rhythm in each ICD. As expected, the S-ICD needed a threefold higher shock to jolt the heart back to normal. However, because the subcutaneous device was removed after those initial tests, researchers could not compare long-term effectiveness of the two approaches.

Finally, the research could advance to permanent implantation of the S-ICD, first in a small pilot study of six and then in a larger clinical trial of 55 patients. For the original six, doctors were able to monitor the patients for more than year following the procedure, but did not see any spontaneous heart problems that necessitated defibrillation – good news for the patients, but frustrating for those looking to test the device. Still, the devices never fired inappropriately, and no complications from the implantation were observed either – two intermediate successes.

In the larger permanent study, the device had a chance to go to work: 12 spontaneous incidents of tachycardia, an accelerated heart rate, were detected and successfully treated. The larger study also picked up some complications, including one patient where “lead dislodgement occurred at 6 months, during vigorous physical activity.” That led to the designers coming up with a new “anchoring sleeve” and implantation methods to make sure the leads don’t drift from their intended position.

Combined, the results suggest a promising start for the device. But the authors emphasize that it’s just a start: until subcutaneous and transvenous ICDs can be directly tested, it’s impossible to say whether the new model is an improvement upon the old. The authors also noted that subcutaneous ICDs are also limited in that they cannot function as long-term pacemaking devices, narrowing the eligible patient pool for the new devices. But if trials continue to produce encouraging results, and FDA approval is eventually granted, the S-ICD could offer a safer and more effective long-term safeguard for heart issues.

“There is no question that the entire system, from implanting to programming to postoperative care for patients, is simpler,” Burke told HealthDay News.

(For more coverage, see Reuters, the Wall Street Journal, and the New York Times)

About Rob Mitchum (512 Articles)
Rob Mitchum is communications manager at the Computation Institute, a joint initiative between The University of Chicago and Argonne National Laboratory.

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