Watchman device shows 75% reduction in stroke risk in patients with atrial fibrillation not eligible for oral anticoagulation therapy


On 11 May, Vivek Reddy, director of Cardiac Arrhythmia Service at Mount Sinai Medical Center, New York presented results from the ASA Plavix (ASAP) study of the Watchman Left Atrial Appendage Closure (LAAC) device (Boston Scientific) during a late-breaking session at the Heart Rhythm Society’s 33rd Annual Scientific Sessions in Boston, USA. The data showed a reduction in the risk of ischaemic stroke by 75% in patients with atrial fibrillation who have a contraindication to oral anticoagulants such as warfarin.

The prospective multicentre ASAP study evaluated 150 patients with contraindications to warfarin, who were implanted with the Watchman device and treated with dual antiplatelet therapy for six months post-procedure. Subjects were followed for a mean average of 14.4 months. The study employed the widely recognised CHADS2 risk stratification score, which provides a clinical prediction tool for estimating the risk of stroke in patients with atrial fibrillation. The CHADS2 score has been validated by numerous studies and is regularly used to determine whether treatment is required with anticoagulation or antiplatelet therapy.

“Findings from the ASAP study are promising in that closure of the LAA with the Watchman device produced a significant reduction in the expected ischaemic stroke rate for this patient population,” said Reddy. “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.”

“Watchman is the most studied LAA closure device with more than 2,000 patients enrolled in prospective studies and nearly 4,000 patient-years of follow up,” said Keith D Dawkins, global chief medical officer, Boston Scientific. “This novel device has been well received in more than 30 countries where it offers a safe and effective alternative to long-term treatment with oral anticoagulants.”

For patients in the ASAP study, the average baseline CHADS2 score of 2.8 equated to a predicted ischaemic stroke rate of approximately 7.1% per year. The observed rate of ischaemic stroke for patients implanted with the Watchman device was 1.7% per year, a 75% reduction in stroke risk from the predicted stroke rate based on the CHADS2 score (p<0.01). The corresponding upper confidence bound yielded a stroke rate of 4.4% per year, lower than the predicted stroke rate of 7.1%.

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 multicentre, randomised PROTECT AF trial, the Watchman device proved to be non-inferior 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.

About the Watchman device

The Watchman device is an alternative to long-term anticoagulation in patients eligible for anticoagulant therapy. It is designed to close the LAA, thereby preventing clots forming within the appendage and being dislodged into the bloodstream where they can potentially cause a stroke.

The device was approved for marketing in Europe and other CE Mark countries in 2009. Boston Scientific is currently enrolling US patients in the PREVAIL study, a confirmatory study designed to gain FDA approval. Enrolment is expected to be completed in the second quarter of 2012. The device was developed by Atritech, which Boston Scientific acquired in March 2011.