Boston Scientific's Watchman LAA Closure Device Demonstrates Reduced Stroke Risk for AF Patients

May 11, 2012—Boston Scientific Corporation (Natick, MA) announced that Vivek Reddy, MD, presented results from the ASA Plavix (ASAP) study of the company's percutaneously implanted Watchman left atrial appendage (LAA) closure device during a late-breaking session at the Heart Rhythm Society's 33rd annual scientific sessions in Boston, Massachusetts. The device was developed by Atritech, Inc. (Plymouth, MN), which Boston Scientific acquired in March 2011.

Boston Scientific stated that the Watchman device is designed to close the LAA, thereby preventing clots from forming, which could dislodge and potentially cause a stroke. This approach is an alternative to long-term anticoagulation in patients who are eligible for anticoagulant therapy. The Watchman is contraindicated in patients who are not eligible for anticoagulation therapy.

Data showed a reduction in the risk of ischemic stroke by 75% in patients with atrial fibrillation who have a contraindication to oral anticoagulants such as warfarin. Dr. Reddy, who is the Director of Cardiac Arrhythmia Service at Mount Sinai Medical Center in New York City, serves as the ASAP study's Coordinating Investigator.

"Findings from the ASAP study are promising in that closure of the LAA with the Watchman device produced a significant reduction in the expected ischemic stroke rate for this patient population,” commented Dr. Reddy in the Boston Scientific press announcement. "These results are very impressive and show potential for an effective device-based solution for higher-risk patients with limited pharmacologic options to reduce their risk of stroke."

The prospective multicenter ASAP study evaluated 150 patients with contraindications to warfarin. The patients received the Watchman device and a 6-month postprocedure regimen of dual-antiplatelet therapy (DAPT: acetylsalicylic acid and clopidogrel [Plavix, Bristol-Myers Squibb/Sanofi Pharmaceuticals Partnership, New York, NY]). The patients were followed for a mean average of 14.4 months.

The study employed the CHADS₂ risk stratification score accounting for congestive heart failure, hypertension, age (≥ 75 years), diabetes mellitus, and previous stroke or transient ischemic attack. The CHADS₂ score provides a clinical prediction tool for estimating the risk of stroke in patients with atrial fibrillation and is regularly used to determine whether treatment is required with anticoagulation or antiplatelet therapy.

Boston Scientific reported that for patients in the ASAP study, the average baseline CHADS₂ score of 2.8 equated to a predicted ischemic stroke rate of approximately 7.1% per year. The observed rate of ischemic stroke for patients implanted with the Watchman device was 1.7% per year, which is a 75% reduction in stroke risk from the predicted stroke rate based on the CHADS₂ score (P < .01). The corresponding upper confidence bound yielded a stroke rate of 4.4% per year, lower than the predicted stroke rate of 7.1%.

In its press release, Boston Scientific noted that the stroke rates in the ASAP study were similar to those observed in the PROTECT AF study, which assessed similar subjects not contraindicated to warfarin. In the multicenter, randomized PROTECT AF trial, the Watchman device proved to be noninferior to warfarin and demonstrated a 38% relative risk reduction for stroke, cardiovascular death, and systemic embolism compared to long-term warfarin therapy in 707 patients.

The Watchman device was approved for marketing in Europe and other CE Mark countries in 2009. In the United States, it is an investigational device, limited by applicable law to investigational use and not available for sale.

The company is currently enrolling patients in the United States in the PREVAIL confirmatory study, which is designed to gain US Food and Drug Administration approval. Enrollment expected to be completed in the second quarter of 2012.