Does the WATCHMAN device prevent stroke?

ROCHESTER, MINNESOTA & HAMILTON, ONTARIO, CANADA. Patients with heart disease and atherosclerosis accompanied by paroxysmal or permanent AF have a substantially increased risk of suffering an ischemic stroke (stroke caused by a blood clot or a ruptured plaque). The risk increases with age from about 7% a year for patients aged 50 to 59 years to 36% for those between the ages of 80 to 89 years. NOTE: There is no evidence that people with no underlying heart disease (lone afibbers) or other risk factors for ischemic stroke (congestive heart failure, hypertension, diabetes, history of prior stroke or TIA, age over 75 years) have a greater stroke risk than that found in an age-matched population without AF.

A major cause of stroke in AF patients is the formation of cardiac emboli (blood clots) in the left atrium. It is estimated that 90% of these emboli are formed in the left atrial appendage (LAA) due to poor circulation in and out of this small pouch attached to the left atrium. Thus it is not surprising that 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 conclude 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.

In an accompanying article published in Circulation, researchers at McMaster University in Hamilton, Ontario question the conclusion that the implantation of 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. Furthermore, some studies involving surgical closure of the LAA have shown that stroke risk can actually increase if the LAA is not completely isolated.

In commenting specifically on the most recent WATCHMAN trial (707 patients) involving device implantation in 449 patients and comparison to 258 patients on warfarin they point out that 12.3% of patients experienced serious complications during the implantation procedure and that the rate of ischemic stroke during the follow-up period was actually 50% higher in the device group than in the warfarin group. Nevertheless, the total incidence of stroke (including hemorrhagic stroke) cardiovascular death, and systemic embolization was lower in the WATCHMAN group (3.4% a year) than in the warfarin group (5% a year). Their conclusion was, “the evidence of efficacy and safety is insufficient to recommend this approach for any patients other than those in whom long-term warfarin is absolutely contraindicated”.

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
Whitlock, RP, et al. Does left atrial appendage occlusion eliminate the need for warfarin? Left atrial appendage occlusion does not eliminate the need for warfarin. Circulation, Vol. 120, November 10, 2009, pp. 1927-32

Editor’s comment: Clearly there is no consensus on the merits of the WATCHMAN device. 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 need neither long-term warfarin therapy nor LAA isolation or removal.