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Dr Diana R Holdright
MD, FRCP, FESC, FACC, MBBS, DA, BSc

Consultant Cardiologist

Dr Diana Holdright
 
 

August 2013

A novel alternative to warfarin and other anticoagulants (blood thinners) in atrial fibrillation

Atrial fibrillation is the most common change in the heart rhythm, affecting millions of patients worldwide.  The most serious consequence is a significantly increased risk of stroke,  up to five times the risk of someone with a normal heart rhythm.  The reason for this is that when the upper collecting heart chambers (atria) start to fibrillate the blood passes through less swiftly.   One particular part of the left atrium, called the left atrial appendage (LAA), a finger-like protuberance, is especially prone to stasis of blood and hence clot (thrombus) formation.  Should the clot dislodge it will travel into the main aorta and then into smaller arteries and ultimately lodge in and block a smaller artery.  If this happens in an artery to the brain the outcome is a stroke, so called embolic stroke, which is typically severe and associated with poor recovery. The risk of embolic stroke in the general population increases with age such that embolic stroke is one of the most important causes of stroke in older people.

Until recently the only way to reduce the risk of clot formation in patients with atrial fibrillation was with warfarin (rat poison) which, although effective, patients dislike for a number of reasons.  The effect of warfarin is sensitive to many factors, including other medicines and vitamin K in food substances.  High levels of vitamin K reduce the effect of warfarin and low levels do the opposite, such that patients need regular blood tests and run the risk of unexpected and unpredictable changes in the degree of blood thinning induced by warfarin.  Studies have shown that many patients taking warfarin spend a considerable amount of time with the blood either not thin enough, and so not effectively reducing the risk of stroke, or too thin, which predisposes to bleeding.  Bleeding can have devastating effects, especially if this occurs in the brain, causing haemorrhagic stroke with profound consequences.

More recently alternative drugs to warfarin, collectively known as the NOACs, were developed, offering a number of advantages and I written about them extensively elsewhere (please see links below).  However, all these drugs inevitably predispose to bleeding by virtue of their effects.  Moreover, a proportion of patients are predisposed to bleeding due to other medical problems and so would be placed at a far greater risk of bleeding if prescribed warfarin or one of the NOACs.  The benefits and risks of prescribing or not have to be carefully assessed in every case.

Some patients with atrial fibrillation have a particularly high risk of stroke but also a significant risk of bleeding, for example a history of a prior bleed in the bowel or brain, recurrent and severe nose bleeds, blood disorders, liver disorders and other conditions.  This unsatisfactory position had to be accepted until the more recent development of mechanical devices which can block off the LAA, the most common site of clot formation, and so markedly reduce the risk of embolic stroke.  Most studied is the WATCHMAN device, which can be inserted via keyhole surgery into the LAA. The WATCHMAN Device is a self-expanding nitinol frame structure with tiny barbs to help anchor it in position and a permeable polyester fabric that covers the atrial facing surface of the device. The device is preloaded within a delivery catheter, which is passed from the femoral vein at the top of the leg to the heart and then across the interatrial septum, which separates the right and left atria, and positioned in the LAA where it is deployed and the catheter removed.  The procedure takes about one hour and is undertaken under local anaesthesia with conscious sedation or general anaesthesia.  Patients can usually expect to be discharged the following day in most cases.

Studies of the WATCHMAN device have been encouraging and more techniques working along these lines are in development. The latest analysis of the PROTECT-AF1 trial comparing the WATCHMAN device to warfarin showed that it is a viable alternative in patients who cannot take warfarin.  As with all new techniques there is a learning curve and procedural complications lessen with increasing experience.

 1.       VY Reddy et al on behalf of the PROTECT AF Investigators. Percutaneous Left Atrial Appendage Closure for Stroke Prophylaxis in Patients With Atrial Fibrillation. 2.3-Year Follow up of the PROTECT AF (Watchman Left Atrial Appendage System for Embolic Protection in Patients With Atrial Fibrillation) Trial. Circulation 2013; 127: 720-729

Related pages:

Cardiac conditions - Atrial fibrillation

News - March 2013 - Three new alternatives to warfarin for atrial fibrillation - which to choose?

News - October 2012 - Yet another alternative to warfarin on its way in patients with atrial fibrillation

News - November 2011 - Dabigatran treatment in atrial fibrillation

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