Gettysburg Medical New
 The Clinical View
 by P.E. Hoffsten, MD
 1 June 2005

PREVENTING BLOOD CLOTS

            The leading cause of death in the United States is blood clots that stop up arteries to the brain or to the heart or less frequently to other areas.  Fully 40% of all the people that die in the United States each year, die from blood clots forming in various organs.  As you might imagine, there are many medications directed to preventing blood clots from forming.  It is ironic that humans are equipped with very effective blood clotting mechanisms that prevent us from bleeding to death.  Bleeding to death from any cause is remarkably rare but our clotting system is so good, that with our current lifestyle clots are what kill us.

            As a first step in understanding how to deal with blood clots, a distinction needs to be made between arteries and veins.  Arteries carry blood away from the heart to the various parts of the body to provide oxygen and nourishment.  The arterial system is a high pressure system.  Normal blood pressures are 120/80 mm/Hg.  The arterial system is affected by all those things that you have been warned about for many years including high blood pressure, cholesterol, diabetes, cigarette smoking, and inactivity.  These risk factors lead to roughening of the arterial lining and blood clots begin to form at all the nooks and crannies that develop in the arterial system.  These clots eventually grow and then one day block the artery off completely causing the stroke or heart attack.

            On the opposite side is the venous system that carries blood back to the heart.  This is a low pressure system (5 mm/Hg) that is affected by injuries, inactivity, and rarely factors that make the blood clot too easily.  Blood clots in the venous system are common in travelers who sit on an airplane or in a car for hours without moving and are common in cross country truck drivers who are relatively inactive sitting in their cabs for hours at a time driving cross country.

            The strategy to prevent blood clots in the arterial system is very different than the strategy to prevent blood clots in the venous system.  Aspirin is the cheapest and most commonly used preventive for arterial clots.  It prevents heart attacks and strokes remarkably well.  There has been argument over the years about the right dose of aspirin to use.  Some authorities say to use 81 mg (1 grain) aspirin tablet or an adult low dose of aspirin at 162 mg (2 grains) or alternatively a 325 mg aspirin tablet (5 grains).  Many studies have shown that individuals can tolerate the lower doses of aspirin better than the higher doses of aspirin.  However, recent studies have shown clearly that at least 20% of our population derives no meaningful benefit from the low dose of aspirin.  The ability of some individuals to metabolize aspirin and get it out of the system is so effective that the low doses simply do not prevent strokes or heart attacks.  It is my personal recommendation that all individuals who can tolerate it use the 5 grain aspirin tablet daily.  As far as effectiveness is concerned there isn’t a particle of difference whether one takes the aspirin as a buffered product, a coated product or delayed release product.  All of those considerations are for personal comfort but have no impact on the effectiveness of the aspirin.  By the same token, the price of the aspirin has no impact on its effectiveness.  Five grains of aspirin are 5 grains of aspirin no matter what brand you by.

            The side effects of aspirin preventing some people from using it include sensitivity with asthma, rare allergic reactions, and sometimes stomach irritation.  To avoid aspirin in these situations is a personal choice.  In addition, aspirin should be stopped before some surgeries;   the surgeon will usually advise what he would like to have done at that time.

            Over the years, multiple other products have been sought to replace aspirin for those individuals who are allergic to it or perhaps to find a product that is even more effective than aspirin.  Persantine is still recommended by some neurologists for stroke prevention.  More recently a more expensive product called Plavix (clopidogrel) has gained favor for those individuals who are resistant to aspirin and have a stroke or heart attack in spite of taking aspirin.  These products do seem to be more effective and their use can be recommended on an individual basis by the healthcare provider.  These are most commonly used after a person has had coronary artery stents placed or had a “mini stroke” in spite of the use of aspirin.  In the past, a drug called Coumadin (warfarin) was used to prevent repeat mini-strokes but the use of Coumadin for that purpose has now been shown to be more dangerous than helpful. Plavix seems to be the best choice in this situation.

            Blood clots on the venous side of the circulation are dealt with through very different medications.  One type of medication is called heparin which is injectable.  It comes in multiple different forms including an unfractionated relatively cheap product and a much more expensive purified low molecular weight heparin.  There is slightly less risk of bleeding with the low molecular weight heparin but that risk/benefit is very expensive and beyond the means of many patients.  Heparin products are most commonly used when a person presents with a new sudden onset venous blood clot or as preventive measures when an individual has various types of orthopedic surgery such as hip replacement or knee replacement.  Heparin products are also the drug of choice for treatment of individuals who are pregnant.  In this context is the burden of monitoring the drug and the expense of the drug (thousands of dollars per month) can be a major consideration.

            The other drug that is most commonly used is called Coumadin (warfarin).  Whereas heparin has an immediate effect in preventing blood clots, warfarin takes 4-7 days before it begins to have significant effect.  Therefore, the use of heparin in someone with venous blood clots is often the initial treatment for 4-7 days until the warfarin has time to have an effect.  Whereas heparin acts upon blood clotting factors already in the blood, warfarin works by slowing the rate of production of blood clotting factors.  It interferes with the livers production of certain blood clotting factors.  These factors are slowly depleted from the blood over the first 4-7 days of warfarin treatment and with their depletion from the blood system, blood clots more slowly.  The most common use of warfarin is for individuals who have a condition called atrial fibrillation or individuals who have deep vein thrombosis and pulmonary emboli (lung blood clots).  Aspirin and Persantine and Plavix simply do not have a meaningful effect in dealing with venous blood clots.

            The problems of warfarin regulation are major.  One has to have blood tests at least monthly for most individuals.  Rarely an individual can go six weeks or two months without a check but this is a dangerous practice because the warfarin dosage changes so frequently and bleeding complications can occur.  The right dose  is dependent upon how much of the warfarin is removed by the liver and how much Vitamin K the person takes in.  Both of these are highly variable factors and in some individuals the regulation of warfarin is so erratic that it is more dangerous to use it than it is to pursue the natural history of the venous clotting problem.

            One of the most common questions asked is whether a person should take aspirin and warfarin together.  The handouts provided by the pharmacy always tell the patient as blanket advice now to use Coumadin and aspirin together.  Speaking for myself, I get very perturbed at what I consider to be inappropriate blanket advice.  Very frequently individuals have both arterial blood clot threats and venous blood clot threats.  The medications used for arterial clots (aspirin) do not prevent venous clots.  The medicines used for venous clots (warfarin) do not cover the need to prevent arterial clots.  Many times, the use of both warfarin and aspirin together is appropriate care.  This needs to be addressed on an individual basis by your healthcare provider.  Your local clinics are well versed on these problems and are equipped to monitor warfarin treatment by checking prothrombin times (INR’s) on an appropriate basis.