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SAN FRANCISCO -- Candidates for an implantable cardioverter-defibrillator (ICD) found that a subcutaneous device dramatically slashed the major lead-related complications seen with transvenous devices, though trends suggested worse ICD performance without meeting statistical significance.

In the ATLAS trial of more than 500 patients, major lead-related complications occurred in 0.4% of those who had a subcutaneous ICD (S-ICD) implanted versus 4.8% of those following implantation of a standard transvenous ICD (TV-ICD; OR 0.08, 95% CI 0.00-0.55), reported Jeff Healey, MD, of Hamilton Health Sciences and McMaster University in Ontario.

ICD performance was not significantly different between the groups. However, rates of inappropriate shocks (6.4% vs 2.8%) and failed appropriate ICD shock and/or arrhythmic death (1.7% vs 1.1% per year) did numerically favor TV-ICDs.

"The S-ICD can be considered an alternative to the TV-ICD, particularly when prevention of lead-related complications is desired," Healey said during his presentation at the Heart Rhythm Society (HRS) annual meeting.

In a secondary 6-month safety analysis of ATLAS, 4.4% of the S-ICD group experienced a composite of the primary endpoint -- lead-related complications including hemothorax, cardiac perforation, pericardial effusion, lead dislodgement, and new moderate-to-severe tricuspid insufficiency, among others -- plus device-related infections requiring surgical revision, significant wound hematoma, myocardial infarction, stroke, and death versus 5.6% of the TV-ICD group (OR 0.78, 95% CI 0.35-1.75).

ATLAS follows in the footsteps of the PRAETORIAN trial that showed the noninferiority of the S-ICD to the TV-ICD.

This second large trial of S-ICDs is significant for including more young people and other patients who are considered to be more likely to have lead complications, noted session discussant Christine Albert, MD, MPH, a cardiac electrophysiologist at Cedars-Sinai Medical Center in Los Angeles and previous president of HRS.

In contrast, PRAETORIAN had enrolled a more general ICD population, she pointed out.

S-ICDs were designed to sit under the skin without needing leads to be placed into the heart. This minimizes the lead-related complications associated with standard ICDs, which are used to prolong survival in people at high risk of life-threatening arrhythmias.

As ATLAS showed, however, S-ICDs do not completely eliminate lead complications.

The trial randomized 503 people to subcutaneous or transvenous ICDs. Eligible participants were adults with a standard indication for ICD or those who met criteria such as an inherited arrhythmia syndrome or prior pacemaker or ICD removal for infection. Exclusion criteria included need for cardiac pacing for bradycardia, a clinical indication for biventricular pacing, PR intervals over 240 milliseconds, and an existing permanent pacemaker implant.

The randomized cohort had a mean age of 49 years, and 74.2% were men. At baseline, 22.5% had had a previous cardiac arrest. The most prevalent cardiac conditions were coronary artery disease (36.4%), dilated cardiomyopathy (23.1%), hypertrophic cardiomyopathy (18.5%), and idiopathic ventricular fibrillation (16.7%).

The groups appeared to be well matched at baseline. All patients had a study echocardiogram prior to implant and 6 months post-implant.

Healey reported that the S-ICD group had no significant reduction in ICD or lead-related re-operations at 3 years. Follow-up averaged 2.5 years by the time of his report at HRS, and is ongoing.

Albert stressed the importance of longer-term monitoring of the ATLAS cohort, given the wide confidence intervals around the inappropriate shock endpoint that did not favor S-ICDs.

The FDA approved Boston Scientific's first-generation S-ICD in 2012 and the second-generation Emblem S-ICD in 2015.

Emblem S-ICD was recalled in 2020 due to a manufacturing snafu that made it possible for devices to short circuit and .

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