A thromboembolic event occurs when a blood clot, known as a thrombus, forms inside a blood vessel. The threat escalates if a piece of this clot breaks away, transforming into an embolus that travels through the bloodstream. This mobile clot then lodges in a vessel too small to pass through, obstructing blood flow and potentially causing tissue damage or organ failure. These events, which include Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE), require immediate medical attention.
How Blood Clots Form and Travel
A thromboembolic event involves two phases: thrombosis and embolism. Thrombosis is the initial formation of a blood clot (thrombus) within a vessel. This typically occurs due to damage to the vessel wall, altered blood flow, or changes in the blood’s composition that promote clotting. The thrombus remains fixed at its origin, impeding local circulation.
An embolism occurs when the fixed thrombus detaches and travels through the circulatory system as an embolus. The embolus causes an obstruction when it reaches a vessel too narrow to pass. The most common form of this event is venous thromboembolism (VTE), which encompasses Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE).
DVT involves a thrombus forming in a deep vein, most frequently in the legs or pelvis. If a piece of the DVT clot breaks loose, it travels through the right side of the heart and lodges in a lung artery, causing a PE.
PE is a life-threatening complication because it blocks blood flow to the lungs, restricting the body’s ability to oxygenate blood. DVT and PE are grouped under the term VTE because they are manifestations of the same underlying clotting process. Preventing DVT is the primary way to prevent PE.
Understanding the Primary Risk Factors
The likelihood of a thromboembolic event is determined by acquired and inherited risk factors. Acquired factors are conditions developed over a lifetime that create hypercoagulability, meaning the blood clots more easily. A major acquired factor is prolonged immobility, such as extended bed rest after surgery, hospitalization, or long-haul travel.
Major surgery, especially orthopedic procedures like hip or knee replacement, and significant trauma increase risk due to vessel damage and inflammation. Certain medical conditions, including cancer and its treatments, elevate the risk because cancer cells activate the body’s clotting system. Advanced age, generally considered over 40, is an independent risk factor, with incidence increasing substantially beyond age 60.
Hormonal factors are a significant acquired risk, particularly the use of hormonal birth control and hormone replacement therapy containing estrogen. Pregnancy is also a prothrombotic state; the enlarging uterus compresses veins, slowing blood flow, and hormonal changes increase clotting factors. The risk is highest during pregnancy and for approximately six weeks after childbirth.
Inherited risk factors involve genetic conditions that affect the balance of clotting and anti-clotting proteins. These genetic clotting disorders, or thrombophilias, include Factor V Leiden mutation and Prothrombin G20210A mutation. These mutations are common in certain populations and increase susceptibility to a clot, especially when combined with an acquired risk factor.
Other genetic deficiencies, such as those involving the natural anticoagulant proteins C, S, and Antithrombin, also predispose individuals to clot formation. These inherited conditions are often detected in individuals who experience recurrent or unprovoked VTE at a younger age.
Recognizing the Warning Signs
Symptoms differ depending on whether the clot is a DVT in a limb or a PE in the lung. DVT symptoms often affect the leg, but they can occur in the arm as well. The primary sign is sudden, unexplained swelling in one leg or arm that may not improve with elevation.
The affected limb may exhibit pain, tenderness, or cramping that often begins in the calf or thigh. The skin over the area may feel warm to the touch. There may also be a noticeable change in skin color, appearing red, purplish, or discolored.
Symptoms of a Pulmonary Embolism (PE) are systemic and acute. The most common symptom is the sudden onset of shortness of breath unexplained by physical exertion. This is often accompanied by chest pain or discomfort, which is sharp and worsens when taking a deep breath or coughing.
Other signs of PE include:
- A rapid heart rate.
- Palpitations.
- A feeling of lightheadedness.
- Sudden fainting.
- A sudden cough that may occasionally produce blood.
Because PE symptoms can mimic those of other heart or lung problems, any sudden, unexplained combination of these signs requires immediate medical attention.
Actionable Prevention Strategies
Prevention involves both lifestyle adjustments and targeted medical interventions, especially for those in high-risk situations. Maintaining an active lifestyle promotes healthy blood circulation and prevents blood from pooling in the deep veins of the legs. This is important during periods of prolonged sitting, such as long flights or car rides.
During travel, actions like walking every hour, performing ankle and calf muscle exercises while seated, and avoiding crossing the legs mitigate risk. Adequate hydration, primarily with water, is important because dehydration can cause blood to thicken, increasing the potential for clot formation. Weight management further reduces strain on the circulatory system.
In medical settings, prophylactic measures are employed for patients undergoing major surgery or experiencing extended hospital stays. Pharmacological prevention involves the use of anticoagulant medications to reduce the blood’s ability to clot. These may include low-molecular-weight heparins or other agents, prescribed for a specific duration to cover the period of highest risk.
Mechanical methods are also used, alone or with medications, to encourage blood flow in the legs. These include graduated compression stockings that apply pressure, or intermittent pneumatic compression devices that periodically inflate and deflate to mimic muscle action. Discussing VTE risk assessment with a healthcare provider before surgery or during hospitalization ensures appropriate preventative steps are taken.