Atrial Fibrillation – Part 2 – Blood thinners

By Julian Booker, MD

Although we identify only four chambers with a normal human heart, the left atrium has a small finger-like pouch attachment most commonly called the appendage.

Heart left atrial appendage transesophageal ec...

Heart left atrial appendage transesophageal echocardiography view (Photo credit: Wikipedia)

Blood flow within the appendage can be slower than the rest of the left atrium. Although many cardiologists would argue, the left atrial appendage does have value. It has been shown to help in the following ways:

  1. It acts as a decompression chamber to help the heart deal with unusually elevated pressures within the left atrium
  2. It produces atrial natriuretic peptide, which helps the body eliminate excess salt and water.
  3. Removal of the appendage has been shown to decrease cardiac output.

Unfortunately, when a patient has atrial fibrillation, there is a major downside. Relatively slow blood flow now becomes stagnant blood. We all know that stagnant blood becomes clotted blood. Blood clots within the heart are dangerous not so much because of any particular harm done to the heart but because the danger that a liberated blood clot poses to the remainder of the body, particularly the brain.

A person with atrial fibrillation is five times more likely to have a stroke than a person without atrial fibrillation. About 15% of stroke patients also have atrial fibrillation. The risk of stroke in the setting of atrial fibrillation is not equal across the board. Certain conditions have been found to increase your risk of stroke in the setting of atrial fibrillation.

  1. Increasing age
  2. The presence of congestive heart failure or a weak heart
  3. High blood pressure
  4. Diabetes
  5. A prior stroke, transient ischemic attack (sometimes called a TIA or mini stroke) or blood clot
  6. A prior history vascular disease, sometimes called hardening of the arteries. Some examples are Peripheral Artery Disease, blockages of your carotid arteries, prior heart attack, atherosclerosis of your aorta.
  7. Female gender

If you have one of the above conditions then the risk of blood thinners* should be weighed against the risk of bleeding. If you have none of the above risk factors then no anticoagulation or aspirin may be adequate. If you have only one risk factor then your doctor may give you the option of aspirin or a proper blood thinner. If you have more than one risk factor then blood thinners should be strongly considered. You may only need one risk factor if you older than 75 years or have had a prior stroke or TIA to be strongly considered. For patients with a history of rheumatic mitral stenosis or a prosthetic heart valve, your risk is significantly higher and blood thinners are highly recommended.

Currently there are three blood thinners for higher risk atrial fibrillation. Each has pros and cons that will be discussed here briefly. You will need to have an honest discussion with your health care provider to decide which is right for you.

Warfarin (Coumadin) –

Warning label on a tube of rat poison laid on ...

Warning label on a tube of rat poison laid on a dike of the Scheldt river in Steendorp, Belgium. The tube contains bromadiolone, a second-generation (“super-warfarin”) anticoagulant. (Photo credit: Wikipedia)

This medication is Old Faithful.  It started its illustrious career as a lowly rat poison but has reached heights that it never imagined. It is the blood thinner that patients are most curious about. Dosing is once daily, it has been available forever and we understand how to use it. Five decades of use have proven that this vitamin K antagonist reduces the risk of stroke in patients with atrial fibrillation. Unfortunately, warfarin is very finicky and can be difficult to find the correct dose for you. The target range of effect is very narrow which further makes dosing difficult. If you blood is too thick, you are not fully protected from stroke. If your blood is too thin, your risk of bleeding is higher. You will need frequent checks of your INR (a blood test to follow the blood’s thickness) to make sure that you are within range.

When dosed properly, warfarin can be a powerful ally but in the case of warfarin life can get in the way. There is a list of medications as long as my arm that has a direct effect on warfarin’s potency. Most result in increasing its potency and potentially place you in danger from bleeding.  Many foods we eat, especially green leafy vegetables, decrease its effectiveness and place you at risk of developing clots. If you are going to be on warfarin, you must meticulously keep track of what you put in your body.

There are some really good things about warfarin that may make it appealing to you. Because it is a really old drug, it can be very inexpensive. If the costs of lab work are excluded it can be as low as pennies per day. The other really good thing about warfarin is that it is reversible.  The “antidote” is vitamin K, a substance commonly found in green leafy foods. Should you have an issue with bleeding while on warfarin, we can correct you blood levels without issuing plasma.

Dabigatran (Pradaxa)

1127 Pradaxa (dabigatran) cápsula abierta con ...

1127 Pradaxa (dabigatran) cápsula abierta con gránulos (Photo credit: ec-jpr)

– This is an oral direct thrombin inhibitor that is not approved for atrial fibrillation associated with valvular heart disease. It was the first medication not named warfarin that the FDA gave the seal of approval for the anticoagulation of atrial fibrillation. Although dosing is twice daily, many patients find it more convenient than warfarin because there is no need to constantly follow-up with your health care provider for the pesky INR checks. There is also far fewer interaction with medications and food.

Rivaroxaban (Xarelto) and Apixaban (Eliquis) – These medications fall under the category of factor Xa inhibitors. They work at a different place in the clotting cascade than do Pradaxa but for your purposes, you can consider the thrombin inhibitors and Xa inhibitors as one in the same. Dosing is once daily in the case of Xarelto and twice daily for Eliquis.

As you might imagine, there are some downsides to direct thrombin and Xa inhibitors. Compared to warfarin, the medication can be quite expensive. For Pradaxa and Eliquis, dosing must be adjusted if you have kidney dysfunction. Failure to make the proper adjustments could result in too large a dose and bleeding complications. If you have severe kidney dysfunction, all three should probably be avoided. When bleeding does occur, it is not as easy to fix as with warfarin. The intervention for bleeding may be as simple as discontinuing the drug in most cases but can be as significant as short-term dialysis for rare cases.

I see all the law firm commercials on television about the risks of blood thinners. They are enough to frighten anyone. The decision to start anticoagulation because of a diagnosis of atrial fibrillation can be a difficult one. Talk with your doctor; it could save your life.

*These medicines do not actually thin your blood. They alter your clotting potential. Your blood viscosity of your blood remains the same 😉

About Julian Booker, MD

I am a noninvasive cardiologist at the University of Alabama at Birmingham specializing in multi-modality cardiovascular imaging and preventative medicine. My training was primarily at Baylor College of Medicine in Houston TX and the National Institutes of Health in Bethesda MD.
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