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The Watchman FLX met primary safety and effectiveness endpoints in an observational study of the next-generation transcatheter left atrial appendage (LAA) closure device.

Designed to improve upon the ease of delivery and safety profile of the original Watchman, the newer device left 100% of patients with no peri-device flow exceeding 5 mm on transesophageal echocardiography (TEE) at 12 months, exceeding the 97.0% efficacy goal of the study (P<0.0001), according to Shephal Doshi, MD, of Providence Saint John's Health Center at Pacific Heart Institute in Santa Monica, California.

Moreover, 89.5% of people had a complete seal with no TEE-identifiable leak at all at that time, Doshi noted in presenting the PINNACLE FLX study at this year's of the Heart Rhythm Society (HRS).

In comparison, in the PROTECT-AF and PREVAIL trials, the original Watchman had a 99.3% rate of jet size ≤5 mm and 66% complete seal at 12 months after implant.

Doshi reported that safety events within 7 days of LAA occlusion or hospital discharge (whichever was later) occurred in 0.5% of Watchman FLX recipients, well below the goal of 4.21% set by the PREVAIL and CAP2 trials (P<0.0001). Among those events were two ischemic strokes (both occurring 1-2 days post-procedure) but no death or systemic embolism.

"My initial impressions about the Watchman FLX study are very positive. Although this was a single-arm prospective study in 400 patients, without a randomized comparison group, this second-generation device performed well," HRS president Andrea Russo, MD, of Cooper Medical School of Rowan University in Camden, New Jersey, told MedPage Today in an email.

The FLX appeared to show improved device performance and procedural safety over its predecessor, agreed Sanjay Kaul, MD, of Cedars-Sinai Medical Center in Los Angeles, who was not involved with the study.

"However, we still need longer-term results regarding ischemic stroke. In addition, data regarding hard clinical outcomes (such as long-term stroke prevention), rather than just measuring 'leak,' will be important to determine in future studies," Russo urged.

The most important change in the Watchman redesign was making it deploy from the catheter as a ball instead of with its legs sticking out, which was hoped to be less traumatic to the LAA, Doshi explained during an HRS press conference.

Additionally, the FLX has less metal exposure, the ability to be fully recaptured and repositioned, more struts for better sealing, and dual-row anchors to increase device engagement of LAA tissue.

"One thing this device does is it significantly reduces operator anxiety around the procedure," Doshi said. "I can see operators being more willing to put patients under invasive procedure of LAA occlusion with this device"

Notably, the newer device has had European regulatory clearance , although previously pulled because of high embolic rates.

First-generation Watchman gained FDA approval for stroke risk reduction in nonvalvular atrial fibrillation in 2015. The idea was that the implant would prevent thrombus embolization from the LAA in affected patients.

The PINNACLE FLX single-arm study enrolled 400 patients at 29 U.S. sites. Average age was 73.8 years, and 35.5% of the participants were women. Mean CHA₂DS₂-VASc and HAS-BLED scores were 4.2 and 2.0, respectively.

Participants had to be eligible for anticoagulation therapy, as their antithrombotic regimen consisted of a direct oral anticoagulant (DOAC or NOAC, most commonly apixaban [Eliquis]) plus aspirin for the first 45 days after the procedure, followed by clopidogrel (Plavix) plus aspirin until the 6-month mark, then aspirin alone thereafter.

"Compared with prior Watchman studies, the current study is different in that it uses NOACs (rather than warfarin) post-procedure, which is better representative of current clinical practice," Russo noted.

Doshi reported an implant success rate of 98.8%, with an average of 1.2 Watchman FLX devices used per patient.

Follow-up is ongoing, as the study's secondary efficacy endpoint is ischemic stroke or systemic embolism at 24 months.

"The long-term efficacy data are key, and so far we see 25 deaths, 10 ischemic strokes, one systemic embolism, four device or procedural complications requiring intervention, and 31 bleeding events," Kaul noted.

"I realize that follow-up is incomplete and sample size is low, nonetheless I would have liked to see some comparative data against PREVAIL, CAP 2, or EWOLUTION to get some insights," he said.

The rate of device-related thrombus was 1.8%. All seven of these patients were on dual antiplatelet therapy or aspirin at the time the thrombus was detected, and two of these individuals suffered an ischemic stroke or systemic embolism, Doshi reported.

Device-related thrombus was "a potential area of concern" for Kaul, who said that the long-term efficacy and safety of the Watchman FLX is ultimately best evaluated in a randomized trial against a DOAC control arm.

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