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Why do I take anticoagulants/blood thinners? Do I have a problem with clotting, too?

Patients with PAH are more prone to blood clots in the pulmonary vessels. These blood clots are also called thrombi. Some blood clots originate in the lungs themselves, and some of the clots occur originally in the veins of the legs and travel up to the lungs via the veins draining the legs and these are called thromboemboli.

The thrombi can block blood flow to one or more parts of the lung, impairing lung function. There are several theories to the reason patients with PAH are more prone to thrombi. The cells that line the blood vessels (endothelial cells) of pulmonary vessels are altered in PAH in a way that they produce chemicals that create an environment favorable to formation of thrombi. In addition, as we've discussed elsewhere, in PAH, the right ventricle can become dilated. Any chamber of the heart that is dilated and does not contract normally has an increased risk of forming a thrombus there since blood flow will be more sluggish. Furthermore, many patients with PAH are more sedentary due to their symptoms. This predisposes to formation of blood clots in the veins of the legs because these veins depend on muscle activity to help keep the blood flowing. When blood flow slows down, there is a higher tendency for it to form clots.

Some small studies have shown a benefit with anticoagulation. These studies were done in what is called a retrospective fashion, meaning that patients' experiences were reviewed after the fact. The blood thinner most commonly used is called warfarin or coumadin. It is an oral medication. The dose of warfarin needs to be adjusted by monitoring a blood test called prothrombin time or international normalized ratio (PT-INR). Initially, your INR will need to be checked frequently (up to a few times a week), but once it is stabilized, it can be checked as infrequently as once monthly. Most patients with PAH who are started on anticoagulation remain on it indefinitely unless a reason to stop the medication (such as bleeding) develops.