Oral anticoagulants (Blood thinners) for artificial heart valves
Blood thinners (oral anticoagulants) are mandatory for all patients who have had one of their heart valves replaced. Artificial heart valves are of two types
A mechanical valve is a heart valve substitute manufactured from metal alloy. It is long lasting, used in relatively younger patients (<< 65 years) and needs life long anticoagulation to prevent blood from clotting on it. A blood clot on an artificial heart valve impedes its opening and closing leading to potentially life threatening complications.
A tissue valve is made from the heart tissues of animals. Usually the cow (bovine tissue valve) or the pig (porcine tissue valve). Tissue valves have many structural similarities with human heart valves and so are less prone to thrombosis (blood clot formation). Anticoagulants are therefore need only for 8-12 weeks after implantation, after which they may be discontinued.
They are needed during the first 12 weeks to allow for “endothelialisation” to take place. Endothelialisation is a process by which the body lines any foreign surface in the circulatory system with a thin linig called endothelium. Presence of an endothelium on a surface prevents blood from clotting on that surface. Endothelialisation occurs on the surface of a tisue valve over a period of about 12 weeks.
Oral anticoagulants can therefore be discontinued after this process is complete without the fear of clot formation (thrombosis). Endothelialisation is never adequate on a mechanical valve and so life long oral anticoagulants are necessary whenever mechanical heart valves are implanted. Tissue valves are used in relatively older patients (>>65 years).
Tissue valves are not as durable as mechanical valves but have the distinct advantage of not needing long term anticoagulation beyond the first 12 weeks after implantation. Long term anticoagulants have some deleterious side effects especially in the elderly and so are best avoided in the elderly when possible. This makes a tissue valve the valve of choice in the elderly.
Oral anticoagulants (blood thinners) act by antagonising Vitamin K. Vitamin K is essential for the synthesis of a group of protiens collectively called coagulation factors which are important in the normal “clotting process” of the blood. Inhibition of these coagulation factors reduces the ability of the blood to clot. It therefore does not also clot on the artificial heart valve as well.
Whether one is on short term or long term oral anticoagulants, especially after heart valve surgery certain precautions are necessary to remain safe. A high dose of the drug and a high blood level of the drug could cause excessive bleeding due to the inability of the blood to clot. Conversely an inadequate dose of the drug and an inadequate blood level of the drug could result in a catastrophic clot formation on the artificial heart valve.
The optimum dose of the oral anticoagulant drug is vital for safety. The level of oral anticoagulants in the blood is monitored by a test called Prothrombin time (PT) and the International Normalised Ratio (INR). The adequate INR following a heart valve implantation is 3.0 – 4.5. An INR <3 predisposes to clot formation (thrombosis) on the valve. Conversly an INR >4.5 predisposes to bleeding.
The INR needs to be checked 2-3 times a week in the early postoperative period. After it stabilizes over a period of time it can be checked less frequently during long term follow up. The oral anticoagulant drug is best administered in the evening (around6-7pm). Its peak action is about 12 hours after administration. The INR is therefore best checked first thing in the morning to obtain an accurate estimate of the blood level of the previously administered oral anticoagulants.
Some important guidelines to follow are:
- Always take your oral anticoagulant at a fixed time. Preferably between 6pm and 7pm every day. If this practice is followed religiously, the INR can be done in the morning (12 hras after the last dose) on the following day when the results are likely to be most accurate.
- Always ensure that you have an emergency stock of your oral anticoagulants so that you NEVER have to miss a dose.
- Never skip a dose your oral anticoagulants
- If you accidentally skip a dose, DO NOT take a “double dose” on the following day. Report to your doctor. He will tell you what to do.
- If you accidentally miss more than two consecutive doses, report to your doctor immediately.
- If you are started on any new drug by any other doctor, always, first,inform the doctor who is monitoring your oral anticoagulation and obtain his concurrence. Oral anticoagulants interact with many drugs. Many drugs also augment or suppress the pharmacological effects of oral anticoagulants. The doctor monitoring your oral anticoagulant is the best judge to titrate the dose of these drugs for you for maximum safety.
- It is safe to avoid any physical activity that may cause injury and bleeding such as contact sports, motor car and bike racing etc.
- Always look out for signs of excessive bleeding, bruising which could indicate a very high blood level of your oral anticoagulant.
- Avoid combining herbal medications with oral anticoagulants except under exceptional circumstances and under close medical supervision.
- Carry yourwarfarin book with you at all times.
- Have a consistent intake of vitamin K.Recommended Dietary Allowance for adults is1microgram / Kg / per day.
- Avoid Vitamin supplements except under close medical supervision
- Avoid any thing that could alter the composition of the bacterial flora in your gut. These bacteria synthesise Vitamin K for you. Common things that could alter the intestinal gut flora include:
- All antibiotics (without consulting your doctor)
- Crash diets and fasting
- Binge drinking
- Avoid all green leafy vegetables.
Side effects of oral anticoagulants (blood thinners)
Side effects of oral anticoagulants are rare They include haemorrhage, skin necrosis, purple toe syndrome, hypersensitivity, rash, alopecia, diarrhoea, jaundice, hepatic dysfunction, nausea, vomiting and rarely pancreatitis.
Alcohol consumption and oral anticoagulants (blood thinners)
Its best to avoid alcohol when you are on oral anticoagulants. If you must drink, limit the number to two per day. A regular limited consumption is reported to have minimal effects on anticoagulation. This should preferably be combined with two alcohol-free days every week.