Left atrial appendage occlusion
|Left atrial appendage occlusion|
Left atrial appendage occlusion is a treatment strategy to prevent blood clot formation in patients suffering from atrial fibrillation (AF). In this heart rhythm disorder, blood clots form in the left atrial appendage (LAA) in 10-20 % of cases. During cardiac catheterization, an expandable nitinol frame can be introduced into the appendage.
LAA occlusion can be used as an alternative for patients who cannot use oral anticoagulants such as warfarin, although it has been studied and approval is sought as an alternative in patients who are eligible for oral anticoagulants. Some patients can not take anticoagulants because of a recent or previous bleeding, non-compliance or pregnancy (17% in one study). A sizeable portion of patients (21% in the above mentioned study) eligible for anticoagulants are not offered them, or are not taking them. This applies particularly to the elderly, although studies have indicated that they can also benefit from anticoagulants.
Devices and alternatives
On April 23, 2009 an U.S. Food and Drug Administration Advisory panel voted 7 to 5 in favor of approval of the WATCHMAN device (by Atritech Inc., Plymouth, Minnesota) for use in patients with non-valvular AF in centers with heart surgery backup. The panel also advised creation of a registry and a certification program for physicians who implant the device. This decision was based on the results of the PROTECT-AF trial (presented at the 2009 American College of Cardiology Scientific Sessions), which showed less hemorrhagic stroke with the device compared to treatment with warfarin; stroke and all-cause mortality outcomes were non-inferior.
Another device termed PLAATO (percutaneous left atrial appendage transcatheter occlusion) was the first LAA occlusion device, although it is no longer being developed by its manufacturer (Appriva Medical, Inc. from Sunnyvale, CA). In 210 patients receiving the PLAATO device, there was an estimated 61% reduction in the calculated stroke risk.
Both LAA occlusion systems are introduced into the right atrium and are then passed into the left atrium through a patent foramen ovale or through a puncture hole. These small iatrogenic atrial septal defects usually disappeared within six months. Although these are catheter-based techniques, they are generally performed under general anaesthesia.
The Amplatzer device, used to close atrial septal defects, has also been used to occlude the left atrial appendage. This can be performed without general anaesthesia and without echocardiographic guidance. Transcatheter patch obliteration of the LAA has also been reported.
Other devices exhist to occlude the left atrial appendage from the inside of the heart such as the Wavecrest device  and the Lariat device. The latter technique entails closing a strangling noose around the LAA, which is advanced from the chest wall with a special sheath, after introducing a balloon in the LAA from the inside surface of the heart (endocardium)
The LAA can also be surgically removed simultaneous with other cardiac procedures such as the maze procedure or during mitral valve surgery. Finally, the left atrial appendage has been closed in a limited number of patients using a chest keyhole surgery approach.
Adverse events and limitations
The main adverse events related to this procedure are pericardial effusion, incomplete LAA closure, dislodgement of the device, blood clot formation on the device requiring prolonged oral anticoagulation, and the general risks of catheter-based techniques (such as air embolism). The left atrium anatomy can also preclude use of the device in some patients.
Following implantation, a transesophageal echocardiography has to be performed to judge completeness of closure and the presence of blood clots. Patients need to use low dose aspirin indefinitely, and prolonged clopidogrel can be prescribed as well; oral anticoagulants are needed following implantation of the WATCHMAN device to allow blood vessel lining to form around the device (endothelialization).
Theoretical concerns surround the role of the LAA in thirst regulation and water retention because it is an important source of atrial natriuretic factor. Preserving the right atrial appendage might attenuate this effect.
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