CHAMPION-AF study of the WATCHMAN FLX™ Left Atrial Appendage Closure Device as a first-line therapy for stroke risk reduction meets all primary and secondary safety and efficacy endpoints

Rhea-AI Summary

Boston Scientific (NYSE: BSX) announced that the CHAMPION-AF trial of the WATCHMAN FLX left atrial appendage closure device met all primary and secondary safety and efficacy endpoints at 36 months. The randomized trial enrolled 3,000 NVAF patients and showed reduced bleeding and non-inferior efficacy versus NOACs.

Key metrics: non-procedural major and clinically relevant non-major bleeding 10.9% vs 19.0% (45% relative reduction), combined procedural+non-procedural bleeding 12.8% vs 19.0% (34% reduction), efficacy composite 5.7% vs 4.8% (non-inferior), 99% procedural success, ongoing follow-up to five years.

Positive

• Non-procedural bleeding reduced by 45% (10.9% vs 19.0%)
• Procedural+non-procedural bleeding reduced by 34% (12.8% vs 19.0%)
• Net clinical benefit superior (15.1% vs 21.8%)
• Large randomized trial with 3,000 NVAF patients
• Procedural success rate of 99%

Negative

• Primary efficacy event rate higher with device (5.7% vs 4.8%) despite non-inferiority
• Key outcomes require continued assessment through 5-year follow-up for long-term durability

Key Figures

Trial enrollment: 3,000 patients Primary safety bleeding: 10.9% vs 19.0%; P<0.001 Bleeding incl. procedural: 12.8% vs 19.0%; P<0.001 +5 more

8 metrics

Trial enrollment 3,000 patients CHAMPION-AF NVAF population suitable for anticoagulation

Primary safety bleeding 10.9% vs 19.0%; P<0.001 Non-procedural major and clinically relevant non-major bleeding at 36 months

Bleeding incl. procedural 12.8% vs 19.0%; P<0.001 Major and clinically relevant non-major bleeding at 36 months

Primary efficacy 5.7% vs 4.8%; P<0.001 Stroke, CV/unexplained death or systemic embolism at 36 months

Net clinical benefit 15.1% vs 21.8%; P<0.001 Composite of CV death, stroke, systemic embolism and non-procedural bleeding

Procedural success 99% WATCHMAN FLX implant success rate across 141 global sites

AF population 59 million people Estimated global prevalence of atrial fibrillation

LAA clot proportion More than 90% Heart-related blood clots in NVAF forming in left atrial appendage

Market Reality Check

Price: $69.17 Vol: Volume 15,755,871 is 24% ...

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$69.17 Last Close

Volume Volume 15,755,871 is 24% above the 20-day average of 12,683,169 shares. normal

Technical Shares at $69.17 are trading below the $94.95 200-day moving average and 36.83% under the 52-week high.

Peers on Argus

BSX is down 1.43%, while key peers SYK, MDT, EW, ABT and PHG are also negative (...

BSX is down 1.43%, while key peers SYK, MDT, EW, ABT and PHG are also negative (-1.57% to -3.01%), indicating broader medical device pressure despite the positive trial data.

Historical Context

5 past events · Latest: Mar 12 (Negative)

Pattern 5 events

Date	Event	Sentiment	Move	Catalyst
Mar 12	Litigation news	Negative	-1.6%	Lawsuit alleging executives misrepresented U.S. electrophysiology volumes.
Mar 06	Investor conference	Positive	-2.3%	Announcement of ACC investor event to discuss key clinical data.
Feb 25	M&A and earnings	Neutral	-2.2%	Penumbra earnings tied to its proposed acquisition by Boston Scientific.
Feb 23	Board changes	Neutral	-0.3%	Election of Cathy Smith and Christophe Weber to the Board.
Feb 13	Conference participation	Neutral	+0.8%	Planned participation at TD Cowen’s health care conference.

Pattern Detected

Recent BSX headlines, including legal and conference items, have often coincided with modest negative price reactions, even when news was neutral or constructive.

Recent Company History

Over the last few months, Boston Scientific has faced a mix of legal, strategic and investor‑relations developments. A lawsuit alleging misrepresentation of U.S. electrophysiology volumes on Mar 12, 2026 saw shares fall modestly. The company has been active on the conference circuit, including ACC and TD Cowen events, and progressed its proposed Penumbra acquisition, yet these items generally drew small negative or muted reactions. Against this backdrop, today’s strong CHAMPION‑AF trial results add significant clinical momentum to the WATCHMAN franchise.

Market Pulse Summary

This announcement details CHAMPION-AF, a 3,000-patient trial in which WATCHMAN FLX met all primary a...

Analysis

This announcement details CHAMPION-AF, a 3,000-patient trial in which WATCHMAN FLX met all primary and secondary safety and efficacy endpoints versus NOACs over 36 months, with significant bleeding reduction and non-inferior stroke prevention. It reinforces WATCHMAN as a potential first-line option in NVAF and adds to a long clinical history with more than 600,000 implants. In context of recent legal, governance and M&A activity, this trial represents a key clinical milestone for Boston Scientific’s structural heart portfolio.

Key Terms

left atrial appendage closure, non-vitamin k antagonist oral anticoagulants, atrial fibrillation, left atrial appendage

4 terms

left atrial appendage closure medical

"the WATCHMAN FLX™ Left Atrial Appendage Closure (LAAC) Device compared to"

A medical procedure that seals off the left atrial appendage, a small pouch in the heart where blood can pool and form clots in people with irregular heartbeats; sealing it is like plugging a gutter so debris can’t collect and cause a downstream flood. It matters to investors because devices, hospitals, and insurers involved in the procedure create revenue streams and regulatory or adoption changes can affect sales, costs and long‑term market size for related medical technology.

non-vitamin k antagonist oral anticoagulants medical

"compared to non-vitamin K antagonist oral anticoagulants (NOACs) as a first-line"

Oral medications that prevent blood clots by blocking specific steps in the clotting process instead of interfering with vitamin K. Think of them as placing a targeted roadblock at a particular junction of clot formation rather than shutting down the whole highway; they are used to reduce stroke and clot risk in people with irregular heartbeats or prior clots. Investors track them because prescribing trends, safety records, patent status and approvals directly affect drug sales, market share and long‑term revenue potential.

atrial fibrillation medical

"Atrial fibrillation (AF) is an increasingly common heart rhythm disorder that"

Atrial fibrillation is a common heart rhythm problem in which the heart’s upper chambers quiver instead of delivering steady, strong pumps, like a washing machine on an unbalanced cycle. It matters to investors because it increases use of medications, medical devices, hospital care and long‑term monitoring, drives demand for new treatments and diagnostics, and can affect healthcare costs, regulatory decisions and revenue prospects across drug, device and insurance markets.

left atrial appendage medical

"more than 90% of heart-related blood clots form in the left atrial appendage"

The left atrial appendage is a small, pouch-like outcrop on the left upper chamber of the heart that can trap blood clots, especially when the heart beats irregularly. For investors, it matters because treatments that close, remove, or influence clot formation in this pouch — either with devices, procedures, or drugs — can drive demand, regulatory review, reimbursement decisions, and clinical trial outcomes tied to related medical products and services.

AI-generated analysis. Not financial advice.

Data highlights the WATCHMAN FLX device provided statistically superior protection from bleeding, demonstrated similar efficacy compared to blood thinners in patients with non-valvular atrial fibrillation

Late-breaking findings presented at ACC.26 and simultaneously published in The New England Journal of Medicine

MARLBOROUGH, Mass. and NEW ORLEANS, March 28, 2026 /PRNewswire/ -- Boston Scientific Corporation (NYSE: BSX) today announced that the CHAMPION-AF global clinical trial met all primary and secondary safety and efficacy endpoints. The study evaluated the WATCHMAN FLX™ Left Atrial Appendage Closure (LAAC) Device compared to non-vitamin K antagonist oral anticoagulants (NOACs) as a first-line option for stroke risk reduction in a broad population of patients with non-valvular atrial fibrillation (NVAF). Key results were presented as a late-breaking clinical trial at the American College of Cardiology's Annual Scientific Session & Expo and simultaneously published in The New England Journal of Medicine.

Atrial fibrillation (AF) is an increasingly common heart rhythm disorder that affects approximately 59 million people worldwide¹ and increases stroke risk by five times compared to people with a normal heart rhythm.² In patients with NVAF, more than 90% of heart-related blood clots form in the left atrial appendage (LAA).³ An alternative to long-term NOACs – considered the leading contemporary blood thinners for stroke risk reduction in patients with NVAF – the WATCHMAN technology is designed to permanently close off the LAA and is implanted in a single procedure.

"The success of the landmark CHAMPION-AF trial represents a meaningful milestone that will undoubtedly transform the treatment approach to stroke risk reduction in a broader population of patients who historically have needed to rely on medication," said Martin Leon, M.D., study co-chair and Mallah Family professor of cardiology, chief innovation officer and director, Cardiovascular Data Science Center, Columbia University Medical Center.* "These results should give clinicians confidence in the potential of the WATCHMAN FLX device to become a first-line treatment option for reducing the risk of stroke for a rapidly growing number of patients with AF."

The randomized, controlled trial enrolled 3,000 patients with NVAF who were suitable for oral anticoagulation therapy across a broad spectrum of stroke and bleeding risk. At 36 months:

• The primary safety endpoint was met with data demonstrating the WATCHMAN FLX device was statistically superior to NOACs (10.9% vs. 19.0%; P<0.001) for non-procedural major and clinically relevant non-major bleeding, achieving a 45% relative reduction in non-procedural bleeding risk.
  • When including procedural bleeding in a secondary analysis, the WATCHMAN FLX device performance was consistent with the primary safety endpoint, demonstrating a significant reduction in bleeding compared to NOACs (12.8% vs. 19.0%; P<0.001) for major and clinically relevant non-major bleeding, representing a 34% relative reduction in procedural and non-procedural bleeding risk.
• The primary efficacy endpoint, defined as occurrence of stroke, cardiovascular or unexplained death or systemic embolism, was met with the WATCHMAN FLX device achieving statistical non-inferiority compared to NOACs (5.7% vs. 4.8%; P<0.001).

The study's secondary safety endpoint underscored the WATCHMAN FLX device is statistically non-inferior to NOACs at 36 months for procedural and non-procedural major bleeding (5.9% vs. 6.4%; P<0.001). Additionally, a secondary combined safety and efficacy endpoint highlighted a net clinical benefit with the device demonstrating statistical superiority to NOACs for the occurrence of cardiovascular death, stroke, systemic embolism and non-procedural major bleeding and clinically relevant non-major bleeding (15.1% vs. 21.8%; P<0.001).  

CHAMPION-AF is the largest clinical trial comparing an LAAC device to NOACs for patients with NVAF to date and included 141 sites in the U.S., Canada, Europe, Japan and Australia, which implanted the devices with a 99% procedural success rate. Patient follow-up in the CHAMPION-AF trial will continue through five years and will include additional primary and secondary endpoints.

"These positive data, which have the potential to support updated clinical guidelines globally, will be used in our submission to expand the indication and coverage for the well-established WATCHMAN platform as a first-line stroke risk reduction option, providing physicians with more choices in care for a wider range of patients who have atrial fibrillation," said Brad Sutton, M.D., chief medical officer, Atrial Fibrillation Solutions, Boston Scientific. "Today, 40% of patients with AF who are prescribed blood thinners for stroke risk reduction are not taking their medications consistently, significantly increasing their risk of stroke.⁴ The CHAMPION-AF data add to Boston Scientific's robust body of clinical evidence supporting the WATCHMAN device as a one-time implant that helps provide stroke risk protection over a patient's lifetime."

More than 600,000 people have been treated with the WATCHMAN implant, which is the most implanted and studied LAAC device on the market. The WATCHMAN LAAC device was first introduced to the European market in 2009 and was approved by the U.S. Food and Drug Administration (FDA) in 2015. The latest-generation WATCHMAN FLX™ Pro LAAC Device was approved in the U.S. in 2023 and is currently being studied in several clinical trials, including the SIMPLAAFY randomized controlled trial, which is evaluating single-drug alternatives to dual anti-platelet therapy as a post-procedural regimen.

For more information about the CHAMPION-AF trial, visit watchman.com/CHAMPION

About Boston Scientific
Boston Scientific transforms lives through innovative medical technologies that improve the health of patients around the world. As a global medical technology leader for more than 45 years, we advance science for life by providing a broad range of high-performance solutions that address unmet patient needs and reduce the cost of healthcare. Our portfolio of devices and therapies helps physicians diagnose and treat complex cardiovascular, respiratory, digestive, oncological, neurological and urological diseases and conditions. Learn more at www.bostonscientific.com and follow us on LinkedIn.  

Cautionary Statement Regarding Forward-Looking Statements

This press release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934.  Forward-looking statements may be identified by words like "anticipate," "expect," "project," "believe," "plan," "estimate," "intend" and similar words. These forward-looking statements are based on our beliefs, assumptions and estimates using information available to us at the time and are not intended to be guarantees of future events or performance. These forward-looking statements include, among other things, statements regarding our business plans, product performance and impact, clinical trials, and new and anticipated product approvals and/or indications or coverage expansions. If our underlying assumptions turn out to be incorrect, or if certain risks or uncertainties materialize, actual results could vary materially from the expectations and projections expressed or implied by our forward-looking statements. These factors, in some cases, have affected and in the future (together with other factors) could affect our ability to implement our business strategy and may cause actual results to differ materially from those contemplated by the statements expressed in this press release. As a result, readers are cautioned not to place undue reliance on any of our forward-looking statements. 

Factors that may cause such differences include, among other things: economic conditions, including the impact of foreign currency fluctuations; future U.S. and global political, competitive, reimbursement and regulatory conditions, including changing trade and tariff policies; geopolitical events, conflicts and tensions; manufacturing, distribution and supply chain disruptions and cost increases; disruptions caused by cybersecurity events; disruptions caused by public health emergencies or extreme weather or other climate change-related events; labor shortages and increases in labor costs; variations in outcomes of ongoing and future clinical trials and market studies; new product introductions; expected procedural volumes; the closing and integration of acquisitions; demographic trends; intellectual property; litigation; financial market conditions; the execution and effect of our business strategy, including our cost-savings and growth initiatives; and future business decisions made by us and our competitors. All of these factors are difficult or impossible to predict accurately and many of them are beyond our control. For a further list and description of these and other important risks and uncertainties that may affect our future operations, see Part I, Item 1A – Risk Factors in our most recent Annual Report on Form 10-K filed with the Securities and Exchange Commission, which we may update in Part II, Item 1A – Risk Factors in Quarterly Reports on Form 10-Q we have filed or will file hereafter.  We disclaim any intention or obligation to publicly update or revise any forward-looking statements to reflect any change in our expectations or in events, conditions or circumstances on which those expectations may be based, or that may affect the likelihood that actual results will differ from those contained in the forward-looking statements, except as required by law. This cautionary statement is applicable to all forward-looking statements contained in this document.

CONTACTS:
Kirsten Lesak-Greenberg
Media Relations
+1 (763) 300-9254
Kirsten.Lesak-Greenberg@bsci.com

Lauren Tengler
Investor Relations
+1 (508) 683-4479
BSXInvestorRelations@bsci.com

*Dr. Martin Leon is a paid consultant of Boston Scientific Corporation. He has not been compensated in connection with this press release.
1 Linz, Dominik, et al. Atrial fibrillation: epidemiology, screening and digital health. Lancet Reg Health Eur. 2024 Feb 1:37:100786. https://www.thelancet.com/journals/lanepe/article/PIIS2666-7762(23)00205-3/fulltext. Accessed Feb. 3, 2026.
2 FAQ About AFib. American Heart Association, Inc., 2023. https://www.heart.org/-/media/Files/Health-Topics/Atrial-Fibrillation/FAQ-About-AFib.pdf. Accessed Feb. 3, 2026.
3 Blackshear JL, Odell JA. Appendage obliteration to reduce stroke in cardiac surgical patients with atrial fibrillation. Ann Thorac Surg. 1996;61:755-759.
4 Tarn, D, Shih, K, Tseng, C. et al. Reasons for Nonadherence to the Direct Oral Anticoagulant Apixaban: A Cross-Sectional Survey of Atrial Fibrillation Patients. JACC Adv. 2023 Jan, 2 (1). https://doi.org/10.1016/j.jacadv.2022.100175.

 

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SOURCE Boston Scientific Corporation

FAQ

What did CHAMPION-AF report about bleeding outcomes for WATCHMAN FLX (BSX) at 36 months?

WATCHMAN FLX showed a substantial bleeding reduction versus NOACs, with non-procedural bleeding 10.9% versus 19.0%. According to Boston Scientific, this represents a 45% relative reduction; combined procedural and non-procedural bleeding was also lower (12.8% vs 19.0%).

Did the CHAMPION-AF trial show WATCHMAN FLX (BSX) is as effective as NOACs for stroke prevention?

The device achieved statistical non-inferiority versus NOACs for the composite efficacy endpoint (5.7% vs 4.8%). According to Boston Scientific, the trial met the primary efficacy endpoint at 36 months but did not show superiority.

How many patients and sites were in the CHAMPION-AF trial for WATCHMAN FLX (BSX)?

CHAMPION-AF randomized 3,000 patients across 141 sites globally. According to Boston Scientific, enrollment included centers in the U.S., Canada, Europe, Japan and Australia with a 99% procedural success rate reported.

What is the clinical significance of the WATCHMAN FLX (BSX) net clinical benefit reported in CHAMPION-AF?

The trial reported a superior net clinical benefit (15.1% vs 21.8%) for the device versus NOACs. According to Boston Scientific, this combined measure included cardiovascular death, stroke, systemic embolism and non-procedural major and clinically relevant non-major bleeding.

Will CHAMPION-AF results change WATCHMAN FLX (BSX) labeling or guidelines?

The company intends to use these data to support expanded indications and coverage for WATCHMAN FLX as a first-line option. According to Boston Scientific, submissions to update labeling and guideline consideration are planned based on the results.