UNTOUCHED: Inappropriate Shocks Cut by Subcutaneous ICD Improvements

Mitchel L. Zoler

May 09, 2020

FROM HEART RHYTHM 2020

Patients with an indication for an implantable cardiac defibrillator for primary prevention of sudden cardiac death and a sharply reduced left ventricular ejection fraction of 35% or less safely received treatment from a refined, subcutaneous device that produced one of the lowest rates of inappropriate cardiac shocks ever seen in a reported ICD study, in a single-arm trial with 1,111 patients followed for 18 months.

The results showed "high efficacy and safety with contemporary devices and programming" despite being "the 'sickest' cohort studied to date" for use of a subcutaneous ICD (S-ICD), Michael R. Gold, MD, said at the annual scientific sessions of the Heart Rhythm Society, held online because of COVID-19.

The 3.1% 1-year rate of patients who received at least one inappropriate shock was "the lowest reported for the S-ICD, and lower than in many transvenous ICD device studies," and was also "the lowest 1-year rate reported to date for a multicenter ICD trial," said Dr. Gold, a cardiac electrophysiologist and professor of medicine at the Medical University of South Carolina, Charleston. The upshot is that these data may help convince clinicians to be more liberal about offering a S-ICD device to patients with left ventricular function in this low range who need an ICD and do not need pacing.

The study's primary endpoint was the rate of freedom from inappropriate shocks during 18 months of follow-up, which happened in 95.9% of patients and was highly statistically significant for meeting the prespecified performance goal of 91.6% that had been set using "standard Food and Drug Administration benchmarks," with particular reliance on the performance shown in the MADIT-RIT trial (N Engl J Med. 2012 Dec 13;367[24]:2275-83).

S-ICDs Maintain 'Niche' Status Despite Advantages

The S-ICD first received Food and Drug Administration clearance for U.S. use in 2012, but despite not requiring placement of a transvenous lead and thus eliminating the possibility for lead complications and deterioration, it so far has had very modest penetration into American practice. Recently, roughly 4% of U.S. patients who've received an ICD have had a subcutaneous model placed, relegating the S-ICD to "niche device" status, noted Andrea M. Russo, MD, director of electrophysiology and arrhythmia services at Cooper University Health Care in Camden, N.J.

A major limitation of S-ICD devices is that they cannot provide chronic pacing and so aren't an option for the many patients who also need this function in addition to protection from life-threatening ventricular arrhythmias.

"We have had a bias for whom we place an S-ICD," explained Dr. Gold. "They have mostly been used in younger patients with less heart disease," but when used in the current study cohort with markedly depressed heart function, the results showed that "we didn't appear to harm patients in any way," including no episodes of syncope because of an arrhythmia. Compared with other S-ICD studies, the patients in the new study, UNTOUCHED, had "lower ejection fractions, more heart failure diagnoses, and a higher rate of ischemic etiology."

The tested S-ICD device appears to have safety and efficacy that is "just as good, and perhaps better" than many ICDs that use transvenous leads, "which was very surprising to us," said Dr. Gold during a press briefing. "I think it will change practice" for ICD placement in patients who do not need pacing. "We found the device works even in the sickest patients."

"This was a classic ICD population, with a low ejection fraction, and the results showed that the device performed well," commented Dr. Russo, who served on the steering committee for the study. "I agree that the results will help" increase use of this device, but she added that other factors in addition to concerns about the inappropriate shock rate and the lack of most pacing functions have hobbled uptake since the device came on the market.

These notably include a somewhat different placement approach that operators need to learn. The device is not always offered as an option to patients by their clinicians "in part because of their lack of familiarity, and concern about inappropriate shocks," she said in an interview. That's despite the clear attractions of a leaderless device, which obviates issues of lead deterioration, lead placement complications like perforations and pneumothorax, and sizing issues that can come up for women with narrower veins, as well as cutting the risk both for infections overall and for infections that progress to bacteremia, noted Dr. Russo, who is president of the Heart Rhythm Society.

Device Improvements Boost Performance

The low 1-year and 18-month rates of inappropriate shocks likely occurred because of new filtering and programming incorporated into the tested device. "By changing the filter, we could make it more like a transvenous device" that is not fooled by T wave over sensing. The programing also included a high beat threshold, with a conditional zone above 200 beats per minute and an "aggressive shock zone" of 250 bpm, Dr. Gold said. This helped make the tested S-ICD more immune to inappropriately shocking a supraventricular arrhythmia; the study recorded no inappropriate shocks of this type, he reported.

The UNTOUCHED study enrolled 1,116 patients at any of 110 sites in the United States and elsewhere who had a need for primary prevention of sudden cardiac death, a left ventricular ejection fraction of 35% or less, no need for pacing, and had successfully passed an S-ICD screening test. The investigators were able to include 1,111 of these patients in their endpoint analysis. Patients averaged 56 years of age, a quarter were women, and their average ejection fraction was 26%.

In addition to the primary endpoint and the 1-year inappropriate-shock rate, the results also showed an all-cause shock-free rate of 90.6% during 18-months' follow-up, which significantly surpassed the prespecified performance goal for this metric of 85.8%. The tested device also appeared to successfully apply appropriate shocks when needed, delivering a total of 64 of these with just 1 shock failure, a case where the patient spontaneously reverted to normal rhythm.

During the study period, 53 patients died (5%), including 3 arrhythmia-related deaths: 1 caused by asystole and 2 from pulseless electrical activity.

"The data show that in a standard ICD population, the device worked well, and was safe and effective," Dr. Russo said. "These data say, at least consider this device along with a transvenous device" for appropriate patients. "It's a great option for some patients. I've seen so may lead problems, and this avoids them."

UNTOUCHED was sponsored by Boston Scientific, the company that markets the tested S-ICD. Dr. Gold has been a consultant to Boston Scientific and Medtronic and has been an investigator for trials sponsored by each of these companies. Dr. Russo served on the steering committee for UNTOUCHED but received no compensation and has no financial disclosures.

This story originally appeared on MDedge.com.

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