Left Atrial Appendage Closure in Atrial Fibrillation

Mechanical methods to prevent stroke

Patient and doctor
Considering the alternatives. Hero Images/Getty Images

The greatest health risk faced by people who have atrial fibrillation is the risk of stroke. In people with atrial fibrillation, the risk of having a stroke is four to six times higher than it is in people without this arrhythmia. So when doctors treat a person with atrial fibrillation, one of their main goals is to take steps to reduce the risk of stroke.

Typically, this means taking anticoagulants (blood thinners). In patients with atrial fibrillation who have an increased estimated risk of stroke, anticoagulants will significantly reduce that risk. However, because anticoagulant drugs themselves can cause problems (mainly, the risk of bleeding), and because some patients cannot take them, researchers have been trying for a long time to find alternative ways to lower the risk of stroke in people with atrial fibrillation.

The most promising efforts so far has been the mechanical approach to stroke prevention - developing methods of separating the left atrial appendage from the rest of the left atrium.

Why Does Atrial Fibrillation Cause Stroke?

In atrial fibrillation, the the electrical signals in the atrial chambers, which normally spread across the atria in a smooth, organized fashion, instead become rapid, fragmented, and disorganized.

As a result, the the right and left atria cease to beat effectively, and instead begin to simply “quiver” ineffectively. This loss of normal beating causes the blood within the atrial chambers to swirl around, creating eddies and areas of pooling. In these areas of low blood flow, clots can form. If the clots within the left atrium break off, they can travel to the brain and produce a stroke.

Why Is The Left Atrial Appendage Important?

The left atrial appendage (LAA) is a small pouch that is formed in the left atrium during fetal development that is believed to have no important function after birth. We now know that in patients with atrial fibrillation the large majority of atrial blood clots develop in the LAA.

So if the LAA can be isolated in some way from the blood circulation, then any clots that form there will be unable to break loose and travel to the brain (or anywhere else in the body). Several methods have now been developed to isolate LAA.

Methods To Isolate The Left Atrial Appendage

Surgical closure or amputation. The LAA can be either removed entirely or ligated (tied off) surgically, so that it no longer communicates with the rest of the left atrium. Amputating or ligating (tying off) the LAA requires major surgery, and these procedures are never performed unless cardiac surgery is being done for some other reason. While clinical data with these surgical approaches are limited, available evidence indicates that they do indeed reduce the risk of subsequent stroke.

(LAA amputation appears more effective than ligation.) In fact, the American Heart Association/American College of Cardiology guidelines now recommend amputation of the LAA in patients who are having surgery for mitral stenosis or mitral regurgitation.

Catheter-Based LAA Closure Procedures. Since the early 2000s, companies have developed various devices that can be deployed during a catheterization procedure to isolate the LAA, in order to reduce the risk of stroke. Developing such a device has proven to be a big challenge, and several attempts have fallen to the wayside. However, significant progress has been made.

In 2015, the Watchman device (Boston Scientific) became the first LAA closure device to be approved in the U.S. by the Food and Drug Administration. This device is comprised of a nitinol wire cage, covered by a “fabric” made of polyethylene terephthalate. The device is inserted into a special catheter which is then advanced to the LAA, and the device is deployed. When fully opened, the Watchman resembles a parachute that covers the opening of the LAA, separating it from the left atrium. After about two months, normal tissue overgrows the “parachute” fabric to create a smooth surface - at which time the LAA is completely closed off. Anticoagulant drugs are required for these first two months, but after that, they can be discontinued.

The safety and effectiveness of the Watchman device was evaluated in the PROTECT AF study. A thousand patients with non-valvular atrial fibrillation were randomized to receive either the device or standard anticoagulation drug. After a follow-up of about two years, the risk of stroke was roughly similar between groups.

The major drawback of this device is the insertion procedure itself. Significant risks are involved including the risk of pericardial effusion, pericarditis, or death. Furthermore, the insertion procedure for the Watchman device is relatively difficult to perform, and also difficult to learn. Anyone considering this approach should only have the procedure done by a very experienced physician.

Similar devices from other companies are under development, and are being tested in the U.S. and elsewhere. At least one of them (the Amplatzer Cardiac Plug, St. Jude) has now been approved for use in Europe.

The Bottom Line

Feasible alternatives to long-term anticoagulation drug therapy are becoming available for patients with atrial fibrillation. However, because of the relative difficulty of these approaches - whether surgical or catheter-based - and because long-term outcomes are currently unknown, for the foreseeable future anticoagulant drugs will remain the mainstay of stroke prevention in atrial fibrillation.

Still, in patients with atrial fibrillation and a high risk of stroke who cannot take these drugs, LAA closure procedures ought to get serious consideration.

Sources:

Meier B, Blaauw Y, Khattab AA, et al. EHRA/EAPCI expert consensus statement on catheter-based left atrial appendage occlusion. Europace 2014; 16:1397.

Reddy VY, Sievert H, Halperin J, et al. Percutaneous left atrial appendage closure vs warfarin for atrial fibrillation: a randomized clinical trial. JAMA 2014; 312:1988.

Reddy VY, Möbius-Winkler S, Miller MA, et al. Left atrial appendage closure with the Watchman device in patients with a contraindication for oral anticoagulation: the ASAP study (ASA Plavix Feasibility Study With Watchman Left Atrial Appendage Closure Technology). J Am Coll Cardiol 2013; 61:2551.

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