Athletes and Blood Clots
Stephan Moll, MD University of North Carolina, Chapel Hill, NC
Edward Libby, MD University of New Mexico, Albuquerque, NM
William Roberts, MD University of Minnesota Medical School, Minneapolis, MN
The diagnosis of deep vein thrombosis (DVT) or pulmonary embolism (PE) in athletes, who exhibit classic symptoms (table 1), may be delayed or even missed because such medical problems are often not considered by healthcare providers or by the affected athlete. No studies have been done to determine whether athletes are at a higher, the same, or lower risk for developing blood clots than non-athletes. Blood clots are uncommon in young, healthy individuals – and most athletes are young and healthy. So, for that reason, DVT, PE, and arterial clots in athletes are not the norm.
To understand the problematic issues facing an athlete and the attending caregiver it is important to first understand the condition terminology. Our body is composed of an endless tunnel of arteries and veins through which blood flows throughout the body. Arteries are the blood vessels through which the blood flows from the heart into the periphery: the brain, the internal organs, the legs, and the arms. A clot in an artery leads to stroke, heart attack, or limb threatening peripheral arterial clot causing a painful, cold, and pale extremity.
Many people think of blood clots as a problem occurring in elderly people, but not in young and apparently healthy individuals. Symptoms may, therefore, be misinterpreted as something less serious. The leg symptoms from DVT are often interpreted as “muscle tear,” a “Charlie horse,” a “twisted ankle,” or shin splints, while the chest symptoms from PE are attributed to a pulled muscle, costochondritis (inflammation of the joint between ribs and breast bone), bronchitis, or a “touch of pneumonia.”
Veins are the vessels through which blood is carried back to the heart. A clot in the deep veins of legs, arms, pelvis, abdomen, or around the brain is called a deep vein thrombosis (DVT). If a piece of clot breaks off from a leg or arm DVT it can travel into the lung causing a life threatening condition known as a pulmonary embolism (PE).
Athlete-Specific Risk Factors for Clots
Being apparently healthy and being an athlete does not prevent a person from developing blood clots. Several circumstances put the athlete, as well as the non-athlete, at increased risk for DVT and PE (table 2). Athletes, coaches and trainers should be particularly aware of these risk factors.
Blood clots can occur when:
- there is a disparity between the two systems that balance the clotting process in our blood; either (A) too much activity of the proteins and blood platelets that form clots (the procoagulant system), or (B) too little activity of the system that dissolves blood clots as they form (the fibrinolytic system);
- there is trauma to the blood vessel wall, as may occur after a bone fracture or in thoracic outlet obstruction (see discussion below);
- blood return from the extremities to the heart is impaired, such as when sitting with bent legs in cramped positions for a prolonged period of time;
- the blood is “thicker” than usual, as occurs when an athlete is dehydrated, using the drug erythropoietin (EPO), or has received excessive blood transfusions (blood doping).
Unfortunately, there are few studies investigating the influence that physical training has on blood clot formation and dissolution. So, the exact net effect of training on this equilibrium is unknown. It is known, for example, that blood levels of the clotting protein “factor VIII” increase with exercise and that the elevation persists during recovery. Theoretically, this could lead to an increased risk of blood clots in athletes. However, data also indicate that the fibrinolytic system that dissolves blood clots is overactive in people who exercise. With this over activity present, the athlete would be protected from having a blood clot. Yet, the net effect of these changes in the athlete is not known.
A detailed scientific discussion of the coagulation issues relevant to exercise and training can be found in a recently published review (reference 1). However, the conclusions are sparse and vague, because of a lack of data and conflicting results from different studies.
Risk Factors for DVT and PE in Athletes
The most common clots occurring in athletes are DVT of the leg and PE. Factors that increase the risk for an athlete, as well as the non-athlete, are listed in table 2. A few unique risk factors predisposing the young and the athlete to DVT and PE are:
Thoracic Outlet Obstruction
In some individuals an extra (cervical) rib or excess muscle or tendon tissue compress the big vein in the upper chest (subclavian vein) that drains the blood from the arm. This compression typically gets worse when the arm is lifted up. This obstruction, often combined with repeated trauma to the vein (due to throwing activities or gymnastics maneuvers), may cause a DVT to form in this area, extending into the arm veins. This is termed “effort thrombosis” or “thoracic outlet obstruction/syndrome.” If the DVT resolves, such as after clot buster treatment, resection of the extra rib or the excess tissue may be indicated to increase space in the thoracic outlet.
This is a common congenital anatomic variation that predisposes to DVT in the left leg, because the main left pelvic vein is compressed by the overlying main right pelvic artery. This increases the risk of clot formation at the site of this narrowing in the left pelvis with extension of clot down into the left leg. If the DVT resolves, such as after clot buster (thrombolytic) treatment, the narrowing can be opened up by a radiologist with a balloon angioplasty and then kept open by placing a stent.
Congenital Absence or Malformation of the Vena Cava
Congenital abnormalities of the anatomy of the big vein in the abdomen (vena cava) or pelvic veins can be a cause of DVT in young people. The abnormal anatomy probably leads to disturbed blood flow and an increased risk of clotting. Treatment decisions for people affected with blood clots must be individualized. This is particularly true for young, apparently healthy individuals, such as athletes. In the case of unexplained DVT, testing for an inherited or acquired clotting disorder may be appropriate. When first diagnosed with the DVT, clot buster medication (fibrinolytic or thrombolytic therapy) should be considered to quickly dissolve the clot. However, clot buster treatment has not been systematically studied to determine whether it really decreases the risk for long-term damage to the veins of the leg and arm, i.e. the postthrombotic syndrome.
Athlete-Specific c Challenges and Questions
Most often, an active individual – be it an athlete or one who remains physically fit through routine training and exercise – is suddenly stymied by the affects of his/her clotting incident. Questions, lots of questions, are poised to the care-giver. Of paramount importance for the athlete are particularly the two following issues:
a) Can I continue my sport while on warfarin?
A solid medical assessment should be made whether the person who has had a blood clot can come off warfarin or should remain on it. Being on warfarin increases the risk for bleeding. Therefore, contact sports and sports with a risk for serious injury, such as football, hockey, basketball, soccer, gymnastics, alpine skiing, or boxing should not be pursued by a person on warfarin. However, athletes such as runners, bicyclists or triathletes may be able to continue their sport, but they should adapt their activities to avoid trauma that might put them at risk for bleeding (avoid situations leading to bicycle crashes, etc.). Individual blood thinning treatment plans can also be designed, such as (a) a decrease in warfarin dosage a few days prior to athletic events that would otherwise put the person at increased risk for bleeding, (b) switching the athlete who should be on long-term blood thinners to low molecular weight heparin shots during the athletic season and interrupting the shots for competitions that pose a risk for bleeding, (c) stopping blood thinners during the season and accepting a higher risk for blood clots during that time, but restarting warfarin during the off season. Finally, an athlete may decide to switch from a high risk bleeding competitive sport to one with a lower risk. Obviously, these are all very individual treatment decisions that should be thoroughly discussed between the patient’s personal physician, the patient, and the team physician (if the patient is participating in a team sport)
b) How soon after a DVT or PE can I go back to training?
Patients with a DVT may have significant extremity swelling and pain which may improve only slowly over weeks and months. Some residual symptoms may persist long-term, this is termed “postthrombotic syndrome.” It appears that being highly active one month after a DVT is not detrimental; it may, actually be beneficial and lead to less symptoms of postthrombotic syndrome (reference 2). This can be used as an argument to encourage individuals to return to physical activity relatively soon after a DVT. Also, wearing individually fitted compression stockings decreases the long-term risk for postthrombotic syndrome.
No official guidelines exist as to when and how quickly an athlete might return to exercising. Each patient will need an individualized exercise plan (an example is described in reference 3). It seems appropriate to refrain from any athletic activities for the first 10-14 days after an acute DVT or PE until the clot is more adherent to the blood vessel wall and the risk of having the clot break loose (causing a PE) has decreased. To lessen deconditioning during this period of relative inactivity, the athlete may do some strength training – arm and trunk exercises in the case of a leg DVT, leg and trunk exercises in the case of an arm DVT. The athlete may then increase activity between week 2 and 4 and return to pre-clot activity levels by week 4.
Athletes need to appreciate that significant deconditioning can occur after a DVT or PE. Depression can also set in after such a life-changing event. This is not surprising, given that athletes often view themselves as healthy and, from a health point of view, invincible, and now suddenly realize that they are vulnerable, sick, and sometimes even disabled. Patient support groups may be helpful in this situation, as may antidepressants.
How to minimize the risk for clots
Measures that the athlete and, for that matter, the non-athlete should take to minimize the risk for DVT or PE are listed in table 3. For the athlete the most important ones are probably to (a) avoid dehydration, and (b) take breaks when traveling long distances.
El-Sayed MS et al: Exercise and training effects on blood haemostasis in health and disease: an update. Sports Med 2004;34(3):181-200.
Shrier I, Kahn SR: Effect of physical activity after recent deep venous thrombosis: a cohort study. Medicine and Science in Sports and Exercise 2005;37: 630-634.Roberts WO, Christie DM: Return to training and competition after deep venous calf thrombosis. Medicine and Science in Sports and Exercise 1992;24:2-