Conference Coverage

UNTOUCHED: Inappropriate shocks cut by subcutaneous ICD improvements



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.

Michael R. Gold

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.”

Dr. Andrea Russo

“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 than 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.


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