In March, Boston Scientific got the trial result it had spent years working toward. CHAMPION-AF, a 3,000-patient study the company funded, found its Watchman FLX heart implant no worse than blood thinners at preventing strokes, cardiovascular death and embolism over three years. On October 28, CEO Mike Mahoney reported that US Watchman sales fell 7% in the third quarter, and that procedures where a patient came in for Watchman alone dropped by a high-teens percentage. Boston has cut its 2026 sales forecast three times this year. In February it expected growth of 10.5% to 11.5%; it now expects about 4.25%, and Watchman is one of the two businesses it has named as a cause.
Boston is answering with education. Across the second and third quarters it ran more than 200 medical education events for over 2,000 referring and implanting doctors, and it is working toward a label change Mahoney hopes to have approved by 2028. I think the evidence that hurt Watchman came from CLOSURE-AF, an independent trial presented in November 2025, months before the first forecast cut. It studied patients much closer to the ones Watchman treats today, while Boston’s own trial studied the patients it wants to reach next.
Two trials, two sets of patients
Watchman seals off the left atrial appendage, a small pouch in the heart where most stroke-causing clots form in people with atrial fibrillation. The procedure is called left atrial appendage closure. Watchman’s FDA indication today covers patients who can’t tolerate long-term blood thinners, usually because they have bled before or are likely to.
CHAMPION-AF enrolled patients who could take blood thinners safely. The average patient was 72, with a low bleeding-risk score of 1.3. At three years, 5.7% of the Watchman group and 4.8% of the drug group had a stroke, cardiovascular death or embolism, a gap small enough to meet the trial’s noninferiority margin. Watchman patients bled less outside the procedure itself, 10.9% against 19%. They also had more ischemic strokes, the kind caused by a blocked artery: 3.2% against 2%.
CLOSURE-AF ran at 42 German centers without industry funding and enrolled about 900 patients, average age 79. Their average bleeding-risk score was 3.0, which puts them far nearer the high-bleeding-risk patients the current label describes. About half got a Watchman and most of the rest got Abbott’s Amulet. Counting strokes, embolism, deaths and major bleeding, including bleeding from the procedure, closure did worse than best medical care.
Who reads which trial
Mahoney tied the slowdown mainly to changes in which patients get identified and referred, as physicians assess the clinical evidence published over the last year. He didn’t name a trial, so the link to CLOSURE-AF is my inference, and CHAMPION-AF’s own excess of ischemic strokes may weigh on doctors too. Either way, the decision sits with a referring cardiologist. Deciding whether to send a frail 80-year-old for a standalone Watchman, that cardiologist is looking at someone who resembles CLOSURE-AF’s patients, and CHAMPION-AF describes a younger, sturdier patient the cardiologist isn’t sending.
The Watchman procedures that skip that referral are growing. Cases done during an ablation, the catheter treatment for atrial fibrillation itself, rose about 35%. The doctor doing the ablation already has the patient on the table, so adding the implant needs no second doctor to weigh the evidence. For standalone cases, Boston’s early outlook for 2027 assumes demand stays at its fourth-quarter level despite the education push and the planned label change.
Evidence for the market you already have
A company planning a pivotal or label-expansion study chooses its patients to win the indication it wants next, and the FDA submission rewards that choice. The market it already sells into keeps whatever evidence exists for it, and an academic group with a grant and a few dozen hospitals can add a trial to that record without asking. Boston ran 3,000 patients for its next market. German investigators ran 900 on its current one.
A founder with a cleared product should know which studies the doctors who refer or approve purchases are reading this year, and whether any of those studies enrolled the customers the company has now.
Dave’s take
CHAMPION-AF is a solid result, and Boston may well get its label change. A study on the patients a company already treats can come back looking like CLOSURE-AF, and that risk is the reason to run it early: a bad answer from your own trial arrives while you can still adjust the label you ask for, and a bad answer from someone else’s arrives on an earnings call. If I were budgeting a client’s evidence plan, that study would come first.
From Dave’s video library
Today's Teardown: why Watchman procedures done during an ablation grew while standalone cases fell, and who decides whether a patient gets referred.
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Dave Saunders is the founder of Base Reality Group and a Fractional CPO for product companies. He was a founder and operator at Galen Robotics, where the surgical-robotics platform earned FDA De Novo authorization in 2023, and he managed a 35-patent portfolio licensed from Johns Hopkins. He wrote Founders Who Finish and publishes The Build. More about Dave →