Blood Thinners and Adult Congenital Heart Disease (ACHD)

Some people with CHD have a higher chance of forming blood clots because of:

• Past damage to blood vessels
• Heart surgeries
• Implanted devices, like pacemakers, valves, or grafts
• Blood that moves slowly or unevenly
• Heart rhythm problems, like atrial fibrillation

In general, the more complex the heart condition, the higher the risk of clots. People with CHD are more likely to have a stroke or other problems caused by clots. In fact, the risk of stroke in CHD can be 10 to 100 times higher than in people without a CHD. That is why it is important to understand your risk of forming blood clots and, if needed, take medication(s) to prevent them. 

Blood clots are the body’s way of helping you heal. When a blood vessel is damaged, your body forms a clot to stop the bleeding. Sometimes, blood clots form when there is no damage, and this can be a problem. As an adult with CHD, you may need medicine to regulate the normal process of forming blood clots.

Normally, blood forms a stable clot when an injury occurs.

• First, tiny blood cells called platelets rush to the injured site where they clump together and form a plug to help stop bleeding. This is almost like the bricks of a building. But just as bricks need cement to bind them together, platelets are not stable enough to do this alone.
• This is where fibrin comes in. Fibrin is a protein that forms a sticky mesh, like cement, that holds the platelets together.
• These steps happen in a careful order called the clotting cascade. This is a chain reaction of signals from clotting factors, which are small proteins in the blood.

Together, platelets and fibrin make a stable clot. In some cases, platelets, fibrin, and the clotting cascade do not work properly, and blood clots form too easily.

Anticoagulants, antiplatelets, or both may be given to prevent or treat blood clots in those at high risk for them. Each medication works differently and dosing must be watched closely to decrease the chance of bleeding. Your treatment should be based on your specific needs.

• Anticoagulants are sometimes called blood thinners. They stop clots from forming in places they should not be.
• Antiplatelets prevent platelets (the bricks or plugs) from clumping and forming a clot.

Vitamin K Antagonists (VKAs) stop blood clots by blocking clotting factors that need vitamin K. The most common VKA is warfarin. It has been the mainstay in preventing dangerous and life-threatening clots for many years.

Warfarin is used most often in people with:

• Atrial fibrillation or flutter
• Mechanical heart valves
• To treat or prevent blood clots in the legs or lungs

Warfarin is highly effective, but some people find it hard to use. People who take warfarin need to:

• Take it once a day by mouth.
• Eat a consistent amount of vitamin K foods daily because vitamin K impacts how effective warfarin is. Foods that are high in vitamin K include spinach, broccoli, and green tea, among others.
• Have regular INR blood tests to measure how long it takes your blood to clot. This helps your doctor know the best dose of warfarin for you.
• Report other medications you take to your doctors. Warfarin interacts with some medications (for example, antibiotics and amiodarone).
• Understand that it can take up to a week for warfarin to reach a steady and effective level in your blood. It takes 3-4 days after stopping warfarin for warfarin’s blood-thinning properties to wear off.
• Understand that is one of the easiest and most predictable blood thinners to reverse in an emergency.

Direct Oral Anticoagulants (DOACs) are newer medications used to prevent blood clots. Like warfarin, they act directly on the clotting factors involved in the clotting cascade. Examples include Pradaxa (dabigatran), Eliquis (apixaban), and Xarelto (rivaroxaban). 

These are mostly used for: 

• Non-valvular atrial fibrillation
• Deep vein thrombosis
• Pulmonary embolism 

If you are taking DOACs, keep in mind that:

• Most are taken once or twice a day by mouth.
• They start working faster than warfarin and wear off faster.
• You do not need regular blood tests.
• The vitamin K in your diet does not need to be consistent because vitamin K does not affect how DOACs work.
• DOACs cannot be used in people with mechanical valves; only warfarin may be used.

Low molecular weight heparin (LMWH) prevents and treats blood clots like deep vein thrombosis and pulmonary embolism. They are given either under the skin or by IV. In people already taking warfarin, they are often used short term as a bridge to prevent blood clots when warfarin must be stopped before a procedure or surgery. Lovenox (enoxaparin) is an example. 

Unfractionated heparin is given intravenously (IV) in the hospital. Its effects are less predictable, but the medication wears off the fastest. Because of this, it is used right before procedures or surgeries or when bleeding risk is unknown or high. Frequent blood tests are needed to make sure the dosage is correct and to adjust it safely.

Antiplatelets make platelets less sticky and prevent the initial plug from forming. 
The most common antiplatelet medication is aspirin. Another example is Plavix (clopidogrel). 

• Aspirin is often used after a stent is placed or a device is used to close an atrial septal defect or ventricular septal defect.
• Plavix may be prescribed after a stent is placed.

Antiplatelets can increase your risk of bleeding. The bleeding can be mild or more severe. 

Anticoagulation treatment during pregnancy must be managed carefully. If you take an anticoagulant, it is important to let your ACHD team know before you become pregnant. 

• Warfarin crosses the placenta and can cause birth defects and other problems, including fetal death. 
• Little information is known about the safety of DOACs in pregnancy.
• If warfarin cannot be used during pregnancy, LMWH or unfractionated heparin may be used because they do not cross the placenta.

Women with mechanical valves have a higher risk of clotting, bleeding, pregnancy complications, and fetal loss. Decisions about valve type and timing of surgery should be made before pregnancy with your ACHD specialist.