Watching WATCHMAN

Dear Readers, Bleeding will always be a concern when using oral anticoagulation to prevent stroke in patients with atrial fibrillation (AF). Therefore, there remains a strong interest in left atrial appendage (LAA) occlusion to prevent stroke. Encouraging results and new concepts related to LAA closure continue to be reported. Recently, Friedman et al published the use of a device with a snare and a pair of forceps to ligate the LAA via an epicardial approach in animals.¹ However, the system that has come closest to market approval in the United States is the WATCHMAN device, made by Atritech, Inc., recently acquired by Boston Scientific. The WATCHMAN device was initially evaluated in the pivotal PROTECT AF study, but was not approved by the U.S. Food and Drug Administration because of the high incidence of acute procedural complications. However, much progress toward a better understanding of this device has been made in the past year. In follow-up to PROTECT AF, the Prospective Randomized EVAluation of the WATCHMAN LAA Closure Device In Patients with Atrial Fibrillation Versus Long Term Warfarin Therapy (PREVAIL) trial, the WATCHMAN device will be evaluated in another large randomized trial. This trial began enrollment in November 2010, and has the potential to result in device approval from the FDA by April 2013. The results of this study will be much anticipated by patients, physicians, and investors. Registry data can also provide useful information regarding new medical technology. After completion of the PROTECT AF trial, participating centers with high enrollment rates were permitted to participate in a Continued Access Protocol (CAP). Data from 460 patients implanted during the CAP study were compared to 542 patients in the PROTECT AF study, to determine if operator experience and improvements in technique had an effect on complication rates. The findings from this analysis were published by Reddy et al in February 2011.² Fortunately, although not surprisingly, procedure- or device-related adverse event rates within 7 days decreased from 10.0% during the first half of the PROTECT AF trial, to 5.5% during the second half of the trial, and further to 3.7% during the CAP study. These data are reassuring in terms of the potential for the device to help patients. However, it does not address the concern that many patients could be exposed to serious complications at the time of commercial availability in the United States, where the device would likely be implanted by a large number of physicians with minimal experience or training. Under further evaluation are different patient populations and next generations of the WATCHMAN device itself. The safety of device implantation in patients who have a contraindication to warfarin is currently being evaluated in Europe in the Aspirin Plavix (ASAP) registry, and preliminary data have already been published.³ Although 1/78 patients required treatment with subcutaneous fractionated heparin for two months after being found to have a device-related thrombus detected during a follow-up transesophageal echocardiogram, no patient has experienced a stroke. The newest version of WATCHMAN devices is being evaluated in the EVOLVE trial. There is still no commercially available left atrial appendage occlusion device in the United States, but there has been continued positive progress toward this goal. However, even if such a device were shown to be safe and effective, several questions will remain. These questions include: which patients would be the best candidates for the device, who should be implanting them, how much training should be required before credentialing is granted, and how often will oral anticoagulation still be needed after device implantation in the long term?

References

1. Bruce CJ, Stanton CM, Asirvatham SJ, et al. Percutaneous epicardial left atrial appendage closure: Intermediate-term results. J Cardiovasc Electrophysiol 2011;22:64–70.
2. Reddy VY, Holmes D, Doshi SK, et al. Safety of percutaneous left atrial appendage closure. Results from the Watchman left atrial appendage system for embolic protection in patients with atrial fibrillation (PROTECT AF) clinical trial and the Continued Access Registry. Circulation 2011;123:417–424.
3. Sievert H, et al. Left atrial appendage closure using the Watchman device in patients with contraindications to warfarin. Preliminary results from the “ASA Plavix Registry” (ASAP). (Abstract) J Am Coll Cardiol 2010;56:B109.