New concerns about the WATCHMAN device
AUSTIN, TEXAS. The formation of cardiac emboli (blood clots) in the left atrium and left atrial appendage (LAA) is a major cause of ischemic stroke in atrial fibrillation (AF) patients with risk factors for stroke. It is estimated that 90% of these emboli are formed in the LAA due to poor circulation in and out of this small pouch attached to the left atrium. Thus it is not surprising that electrophysiologists (EPs) and cardiovascular surgeons have been experimenting with either removing or closing off the LAA.

The latest entry in the market for devices used to close off the LAA is the WATCHMAN device. This is a nitinol (nickel-titanium alloy) cage covered with a polyethylene membrane and having barbs for anchoring it to the inside of the LAA. The device is inserted with a special catheter entering the left atrium through the femoral vein – a procedure similar to that used in pulmonary vein ablation procedures. The first trial of the device involved 66 patients with AF and one or more risk factors for ischemic stroke; it was performed at the Mayo Clinic. After 45 days, 93% of participants had achieved satisfactory sealing of the LAA and 92% were able to discontinue warfarin.

Preliminary results of a larger trial indicated that 87% of patients were able to discontinue warfarin after 45 days and the Mayo Clinic researchers concluded that the WATCHMAN device is "non-inferior" to warfarin treatment as far as the risk of stroke and bleeding is concerned. This despite the fact that 5% of the trial participants required intervention to deal with pericardial effusion occurring during the procedure. NOTE: Both the Mayo Clinic and the authors of the article have a direct financial interest in Atritech, the manufacturer of the WATCHMAN device.[1]

Researchers at McMaster University in Canada question the conclusion that the WATCHMAN device will eliminate the need for warfarin therapy. They state, "No conclusive evidence exists to demonstrate that LA exclusion reduces stroke in AF patients". They also point out that there is evidence that removing or isolating the LAA may decrease cardiac function, impair hemodynamic response to volume and pressure changes, impede thirst, and promote heart failure. Thus, it is by no means certain that eliminating LAA function is a benign procedure. Some studies involving surgical closure of the LAA have shown that stroke risk can actually increase if the LAA is not completely isolated.

Now a group of EPs at St. David's Medical Center reports that gaps may develop between the edge of the WATCHMAN device and the wall of the LAA thus allowing blood from the LAA to seep into the left atrium and (presumably) vice versa. Their study involved 58 AF patients who had a WATCHMAN device implanted at St. David's between November 2008 and June 2010. The average age of the patients was 74 years, 64% were male, and 74% had a CHADS2 score of 2 or higher – in other words, of intermediate risk for stroke. Transesophageal echocardiography (TEE) was used to guide the initial placement of the device. TEE was also used to check its position and look for gaps 45 days and 12 months after implantation. All patients were maintained on warfarin (INR between 2.0 and 3.0) for the first 45 days, after which, 55 (95%) discontinued anticoagulation.

Although TEE at the end of the insertion procedure showed tight closure and no gaps in 72% of patients, notable gaps were observed in the remaining 28%. At the 45-day TEE an additional 12% had developed new gaps, but some of these had closed and others had opened at the 12-month TEE examination. All told, at the 12-month follow-up, 65% of patients had no visible gaps, while the remaining 35% had one or more. During 26 months of follow-up, 1 patient (1.7%) had a stroke (4.7 months after the implantation). No device dislodgement occurred during follow-up. The authors conclude that incomplete LAA closure with gaps between the WATCHMAN device surface and the LAA wall is relatively common. They recommend further trials to determine whether the presence, persistence or variation in size of gaps is related to stroke risk.
Bai, R, Natale, A, et al. Intraprocedural and long-term incomplete occlusion of the left atrial appendage following placement of the WATCHMAN device. Journal of Cardiovascular Electrophysiology, Vol. 23, May 2012, pp. 455-61

Editor's comment: It would seem that there are still questions about the viability of LAA occlusion with a WATCHMAN device as an alternative to anticoagulation with warfarin. It should also be kept in mind that the LAA serves a useful function and that its "elimination" may have unintended consequences. For more on this see Left Atrial Appendage: Useless or Priceless? Fortunately, this is largely irrelevant to lone afibbers with no risk factors for stroke since they do not have an increased risk of stroke and would not benefit from either long-term warfarin therapy or LAA isolation or removal.
[1] Holmes, DR and Schwartz, RS. Does left atrial appendage occlusion eliminate the need for warfarin? Left atrial appendage occlusion eliminates the need for warfarin. Circulation, Vol. 120, November 10, 2009, pp. 1919-26