How do you monitor clotting function if you have an artificial heart valve?
Artificial heart valves made of metallic components can induce clot formation on their surface. These clots can either cause obstruction to the valve or move away in the circulation and get lodged somewhere else. If it obstructs the valve, it can result in severe breathlessness or collapse. When the clot gets transferred to some other location, it can block a major blood vessel as in the brain and cause a stroke or other problems due to blood supply to the concerned organ. To prevent this those on mechanical heart valves need to take medicines which prevent clotting of blood life long. These medicines, popularly known as coumadin, need careful monitoring of clotting function of the blood. Usually this is done by monthly checking of blood clotting function by a test known as prothrombin time and calculation of the international normalized ration (PT-INR). In most cases, the target value of INR is between 2-3. In certain cases, the target INR is kept at 2.5-3.5 when the risk of clot formation is deemed higher.
It is worth remembering that coumadin group of drugs have a lot interactions with other medicines as well as with many types of food. Basically these drugs act by blocking the synthesis of clotting factors which are dependent on vitamin K. Hence if food containing a lot of vitamin K like green leafy vegetables are taken, the effect of these medications will be reduced and INR value falls. This can lead to clot formation over the mechanical heart valves.
Pain killer medications belonging to the group of non-steroidal anti-inflammatory drugs (NSAIDs) interfere with the binding of coumadin to proteins in the blood and consequently increase the effect of coumadin by making more free form available in blood. This can lead to elevated INR levels and increased risk of bleeding. Hence one should be cautious about taking any new medication or for that matter even any new type of food while coumadin medications are being taken. If there is any doubt, INR levels can be checked to make sure that there is neither an increase or decrease from the recommended range of values.