Limited Flow Across Watchman LAA Occluder Common, Safe

March 05, 2012

March 5, 2012 (Washington, DC) — It seems safe to withdraw warfarin from patients with atrial fibrillation who are implanted with the Watchman (AtriTech) left-atrial-appendage (LAA) closure device even if there's some residual flow across it, an analysis suggests [1].

The post hoc finding comes from the randomized PROTECT-AF trial, in which thromboembolic outcomes in patients with AF implanted with the percutaneous device were "noninferior" to those who maintained conventional warfarin therapy [2], as previously reported by heartwire. The current analysis was published in the March 6, 2012 issue of the Journal of the American College of Cardiology.

Whither the Watchman?

The Watchman is available in Europe but remains investigational in the US following an FDA decision two years ago that the PROTECT-AF trial was insufficient as basis for approval. The rejection came a year after a 7-to-5 advisory panel vote to recommend approval based on the trial.

Watchman LAA closure device [Source:Atritech]

Some supporters of approval on the panel wanted at least a postmarket registry to monitor safety. The FDA took it further and demanded a predecision prospective superiority trial. Randomization in that trial, called PREVAIL, started "less than a year ago," Dr Juan F Viles-Gonzalez (Mount Sinai School of Medicine, New York, NY), lead author of the current retrospective analysis, told heartwire.

The Watchman is seeking approval, at least initially, for patients with an indication for chronic anticoagulation, such as those with paroxysmal or persistent AF or others with an elevated CHADS score "but who also have some contraindication for anticoagulation," Viles-Gonzalez said.

"That can be a history of gastrointestinal bleeding or a history of hemorrhagic stroke or other hemorrhagic complications." He estimated that would include about 30% of patients with AF, although "some of those will also have an appendage that isn't suitable for [Watchman] closure because of the shape [of the LAA ostium], for example."

Although the circular device comes in several sizes and bends to conform somewhat to the LAA ostium's oval shape, sometimes the implantation leaves gaps that allow blood through, according to Viles-Gonzalez. In PROTECT-AF, implantation was considered successful even if there was a limited amount of residual flow.

"Clinically reassuring"

The current analysis came out of concerns that such residual peridevice flow will encourage formation of potentially embolic thrombi. Residual flow was common; almost a third of Watchman recipients showed some degree of peridevice flow at 12-month transesophageal echocardiography (TEE). But, he said, "Based on our results, it looks like there just isn't an interaction between [peridevice] flow and clinical embolic events. That risk seems to be similar in patients with minimal peridevice flow and those with no such flow whatsoever."

It's "clinically reassuring" that Watchman implantation doesn't have to be technically perfect to give good results, that such residual flow is safe even without anticoagulation, according to Viles-Gonzalez--"although the data need to be corroborated prospectively."

Impact of residual peridevice flow on the primary thromboembolic end point in PROTECT-AF, hazard ratio (HR, 95% CI)

End point HR (95% CI)
Minor peridevice vs no peridevice flow 0.85 (0.11–6.40)
Moderate peridevice vs no peridevice flow 0.83 (0.33–2.09)
Major peridevice vs no peridevice flow 0.48 (0.11–2.09)
Any peridevice flow and continued warfarin (vs no peridevice flow and discontinued warfarin) 0.63 (0.14–2.71)

 

In PROTECT AF, the protocol called for the 485 patients implanted with the Watchman to be on warfarin but to go off anticoagulation (and initiate clopidogrel) if 45-day TEE demonstrated LAA closure. "Closure" allowed for residual peridevice flow indicated on TEE by a jet of no more than 5 mm.

For every 1-mm increase in residual flow jet dimensions, the hazard ratio (HR) for the primary end point of stroke, cardiovascular death, or systemic embolism was 0.84 (95% CI 0.62–1.14, p=0.256).

If the Watchman is to PREVAIL . . . 

The phase 3 trial specified by the FDA is using a revised version of the Watchman, one without the anchoring tines of the PROTECT-AF version, "which were thought to be too rough and related to perforations that were sometimes seen in the initial study," according to Viles-Gonzalez. "The new device is theoretically going to be much safer."

The methods and primary efficacy and safety end points of PREVAIL, which has a target enrollment of 475, are similar to those of the noninferiority PROTECT-AF. But enrollment is going slowly, he said, in part because the AF patients can't have an absolute contraindication to warfarin. Also, eligibility requires a CHADS score of at least 2, except that CHADS 1 is allowed if there are any of four additional risk factors: female aged 75 or older; baseline LVEF ≥ 30% and < 35%; aged 65 to 74 with diabetes or coronary artery disease; or aged ≥ 65 with heart failure.

PROTECT-AF was supported by Atritech; Viles-Gonzalez had no disclosures. Disclosures for the coauthors are listed in the paper.

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