Today is World Thrombosis Day. On this day someone never to be forgotten is Rudolf Virchow [1821-1902]a German physician, pathologist and politician, called the ‘Pope of Medicine’ by his colleagues. His famous postulate that three factors are needed for blood to clot – stagnation, damage to the vessel wall and abnormalities in the clotting mechanism – remains undisputed to this day.
Understanding clotting
Clotting is important because it can be symptomless and yet cause sudden death. Clotting in the veins of the legs – acute deep vein thrombosis in medical terms – which sometimes floats to the lungs (pulmonary embolism) is the most preventable cause of hospital deaths and a source of significant long-term morbidity. About 120 out of every 1 lakh persons are affected by this disease.
The most common causes of thrombosis are prolonged immobility due to trauma, spinal cord injury resulting in paralysis, major neurosurgery, pelvic or orthopedic surgery, especially hip and knee replacement surgeries, and prolonged stays in intensive care units. Some diseases, such as cancer and certain viral infections, also disrupt the clotting cascade and can promote a clot. The common viral infection H1N1 causes a 23.3-fold higher incidence of pulmonary embolism and a 19.9-fold higher incidence of deep venous thrombosis. A number of patients recovering from chickenpox, a viral disease, also have clots in their legs. Drugs, including oral contraceptives, hormone replacement therapies, and some cancer drugs, also promote clots in the veins. Catheters left in the central veins for extended periods of time also promote clots. Physiological stagnation and clotting can also occur during pregnancy and the early postpartum period. Smoking is also a clear cause of atherosclerosis.
How clotting occurs
When a person is immobile, blood stagnates in the veins of the legs, the veins of the sole, and promotes the formation of clots in the valves present in those veins. This is aggravated by inactivity of the calf muscles. The calf muscles act like a pump and push blood up to the heart. They are considered the peripheral heart or the second heart. Any form of mobility, such as walking, climbing stairs, running or cycling, pumps venous blood from the lower extremities to the heart, and should therefore be strongly encouraged in normal populations, as well as in people recovering from various diseases or recovering from major surgeries.
There are many reasons why clots in the legs are bad: First, such a clot can detach itself from the walls of the leg veins, travel all the way to the lungs, suffocate them and cause sudden death. Usually this happens so suddenly that there is no time to even plan definitive treatment to save these patients. Second, these clots can recanalize the blood vessels of the lungs, but also cause narrowing. They may not end in sudden death, but can cause severe shortness of breath even with minimal exertion, which can lead to pulmonary hypertension. And finally, the leg veins and the valves where the clots form can become permanently damaged. They lose their ability to pump blood to the heart, leading to a constant pooling of blood in these veins. So the ‘second heart’ is damaged forever. In rare cases, massive thrombosis in the veins of the legs can result in gangrene of the extremities and even death. Therefore, prevention is the best primary choice, and in cases where a clot has developed, very early diagnosis and prompt treatment to prevent the growth and migration of the clots and prevent damage to the vein valves is essential.
Prevention and treatment
How do you prevent these terrible clots? Although preventing vessel wall damage or inherent defects in the clotting mechanism may not be possible, stagnation can certainly be avoided by aggressively promoting physical exercise and adequate hydration to keep the blood optimally diluted.
Any exercise, from a simple toe exercise to running, will help prevent stagnation. Prolonged immobility during a long-distance journey predisposes one to venous stagnation. Walking on an airplane, especially during long-haul flights, is a proven way to prevent clots, as is proper hydration. Avoid alcohol on long flights, as intoxication increases immobility. If it’s a road trip, break the trip every three or four hours, get out and walk around, and stay hydrated.
If surgery is planned, especially a knee or hip replacement, a discussion with the surgeon should take place regarding anticoagulation protocols and early ambulation. Similarly, for those who are bedridden for long periods of time, compression stockings and intermittent pneumatic compression devices are available. A doctor will be able to advise patients on which treatment is appropriate. In some cases, filters placed in the large vein, the inferior vena cava, can prevent the migration of clots from the legs to the heart. There are very specific indications for such procedures and the treating physician can best decide on this.
As soon as a clot is detected in the veins of the legs, prompt treatment is needed. In certain cases, clot-dissolving chemicals, commonly known as clot busters, can prevent damage to the veins and vein valves. In severe cases, surgical removal of the clots from the lower extremities or from the pulmonary blood vessels can be lifesaving. Depending on the case, a specialist is best placed to decide on treatment.
Move your limbs
As with all diseases and conditions, prevention is the best strategy. Stay hydrated, stay mobile and those who have inherent clotting factor abnormalities should continue clot prevention unless specifically stopped by the treating physician. Smoking and alcohol consumption promote arterial thrombosis and are best avoided.
(Dr. J. Amalorpavanathan is Director (Retired), Institute of Vascular Surgery, Madras Medical College. amalorpavanathanjoseph@gmail.com)
Published – Oct 13, 2025 2:01 PM IST
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