Thromboembolism - Symptoms, Types, Causes, Complications & Prevention

Thromboembolism is a vascular disorder characterised by obstruction of blood vessels (arteries or veins) due to the formation of an embolus (movement of blood clot from one place to another place), which originates from a blood clot (thrombus).  Based on the location of blood clot formation, they are classified into venous thromboembolism (which occurs in veins) or arterial thromboembolism (which arises in arteries). Haematologists lead the healthcare team which diagnoses and treats thromboembolic disorders. 

While acute myocardial infarction (MI), atherothrombotic stroke and peripheral artery diseases (PAD) constitute thromboembolic arterial diseases, venous thromboembolism (VTE) includes deep venous thrombosis (DVT) and pulmonary embolism (PE).

Thromboembolism meaning 

While the thromboembolism definition explains the blood flow obstruction, the word thrombo is derived from the Greek word "thrombos", meaning blood clot, and embolism is derived from the Greek word "embolus", which defines the movement of a blood clot from one place to another place.

Globally, the numbers of ischemic stroke cases, deaths, and DALYs increased from 407, 204.9, and 4050 crores, respectively, in 1990 to 786, 315, and 6253 crores, respectively, in 2020.

According to a research study, the total incidence of myocardial infarction is 15%, with a maximum incidence of eight cases in the 51-60-year age group. This is consistent with the study, which found a 12.7% incidence of acute myocardial infarction in cerebrovascular accident patients.

Venous thromboembolism

Venous thromboembolism (VTE) refers to the formation of blood clots in the veins. This is a gradually developing disorder which is often underdiagnosed but can have serious consequences, such as disability and death. Nevertheless, it is a preventable medical condition if diagnosed accurately and early. 

Deep vein thrombosis: Deep vein thrombosis (DVT or venous thrombosis) is a medical condition referring to blood clot formation in the veins where the thrombus formation could occur due to either injured veins or the blood's hypercoagulability (increased coagulation affinity). Usually found in the lower extremities, such as the lower leg, thigh, etc. Deep vein thrombosis could cause partial or complete blockage to the blood flow to the respective organs.

Pulmonary thromboembolism: This is also known as pulmonary embolism, a medical condition that disrupts (blocks) the pulmonary arterial blood flow due to the embolus either in the pulmonary artery or its branches. Here, the thrombus is formed elsewhere in the circulatory system but gets detached and passes through the pulmonary artery or its capillaries.

The combination of disrupted pulmonary embolism and deep vein thrombosis is collectively called venous thromboembolism (VTE). Pulmonary emboli originate from deep venous thrombus and are responsible for the most common form of pulmonary thromboembolic disease. Based on the severity of the disease, the pulmonary embolism is of two types: 

• Acute pulmonary embolism: In acute embolism, the increased diameter of the pulmonary artery is observed.
• Chronic pulmonary embolism: In chronic embolism, narrowing of distal blood vessels is observed.

Arterial thromboembolism

Arterial embolism is an infarction (tissue death due to inadequate blood supply) of arteries in the blood vessels due to an embolus that adheres (attached) to the arterial wall that obstructs the blood flow. Arterial thromboembolism may lead to cerebral or another vital end-organ infarction.

Ischemic stroke: The deficiency (reduction)of blood supply to the brain is known as an ischaemic stroke. This is a serious condition as it causes the blockage of oxygen and nutrients to the brain, which could cause the death of neurons (brain cells) within minutes. Ischaemic stroke could be due to thrombosis (clot formation) or emboli (movement of blood clot from one place to another).

Myocardial Infarction: Known as a "heart attack," this myocardial infarction (MI) is a cardiac condition in which there is either a complete or a partial obstruction of blood flow to the myocardium (heart wall). Myocardial infarction due to atherosclerotic plaque (fat deposition in arteries) build-up in coronary arteries (blood taken to arteries), leading to a deficient supply of blood to the heart, if it is not treated, leads to sudden death. 

Other types of thromboembolism

Systemic thromboembolism: If the thromboembolism condition is observed in systemic arteries, it is considered systemic thromboembolism. Most systemic emboli (80%) are from intra cardiac mural thrombi; two-thirds are associated with left ventricular infarcts (deficient blood supply), and another 25% have dilated left atria (upper heart chamber). The remainder originate from aortic aneurysms (abnormal blood vessels); common arteriolar embolisation sites include the lower extremities (75%) and central nervous system (10%).

Cerebral thromboembolism: If the thromboembolism condition is observed in the cerebral arteries, it is known as cerebral thromboembolism. Cerebral thromboembolism is due to the artery-to-artery embolism. The intracranial arteries include the intracranial internal carotid, basilar, proximal segments of the basilar artery, and anterior cerebral artery, which are affected by cerebral thromboembolism.

Coronary thromboembolism: The thromboembolic forms in the coronary arteries which obstruct the arteries is known as coronary thromboembolism. Coronary embolism mainly affects the anterior descending artery in the regions of the distal epicardial portion and its intramural branches. 

Massive thromboembolism: Massive thromboembolism, which is usually observed in pulmonary embolism, defined as obstruction of at least 51% of pulmonary arteries, leads to acute and severe cardiopulmonary failure from right ventricular overload. 

Thromboembolism in spleen: Patients who are suffering from splenic vein thrombosis can be symptomatic (shows symptoms) or asymptomatic. These symptoms include abdominal pain, variceal bleeding, splenomegaly (enlarged spleen), and thrombocytopenia (decreased platelets). Splenectomy is a surgical intervention for specific indications, benign and malignant. This procedure could induce venous thromboembolism (VTE).

Thromboembolism after muscle injury: The partial ruptures of muscles in the leg lead to the formation of venous thrombosis. The presence of oedema or haematoma (collection of blood outside the blood vessel), caused by the ruptured muscles, may lead to compression of popliteal or gastrocnemius veins, thus determining the deep vein thrombosis (DVT).

Thromboembolic coagulopathy: Trauma-induced coagulopathy (TIC) (usually >24 hours after injury) is represented by a hypercoagulable state, which may result in thromboembolic events (e.g. deep venous thrombosis (DVT) and pulmonary embolism (PE)).

Cancer-associated thromboembolism: In cancer, coagulation and platelets are activated, which can induce cancer-associated thromboembolism.

Post-partum thromboembolism: The risk for post-partum (post-delivery state) venous thromboembolism (VTE) is higher during the first three weeks after delivery. Women with delivery complications are at a higher risk of post-partum venous thromboembolism, and this risk will be elevated throughout the first 12 weeks after delivery.

Thromboembolic renal disease: The thromboembolic renal disease occurs due to a thrombus in the veins of the renal system. The pathogenesis of thromboembolic renal disease is based on Virchow's triad, which includes vascular endothelial damage, stasis of blood flow, and hypercoagulability. 

The thromboembolism depends on the formation of thrombus or blood clot in arteries or veins.

• Etiology of venous thromboembolism (venous thromboembolism causes)
• Injury of the deep vein leads to the formation of a blood clot.
• Limited movement in physical activity, so there is a deficient supply of blood circulation in blood vessels, leads to the formation of a blood clot.
• Heavy usage of oestrogen leads to the formation of a blood clot. 

Etiology of arterial thromboembolism (arterial thromboembolism causes)

• Increased age
• Smoking
• Increased fibrinogen levels 
  

Thromboembolic disease in pregnancy:

Pregnancy, as such, is a prothrombotic state that enhances venous stasis (cessation of blood flow in veins) mainly due to obstructed venous flow by the enlarging uterus. During 25–29 weeks of gestation, venous flow velocity falls by nearly 50% in the legs. A reduction of venous flow velocity of almost 50% occurs in the legs by weeks 25–29 of gestation. This self-healing condition lasts until approximately 6 weeks post-partum (after delivery). Among pregnant and post-partum women, usually the lower part of the left leg is the most commonly affected site of deep vein thrombosis (DVT) 

Risk factors for thromboembolism in pregnancy, specifically for deep vein thrombosis (DVT)

Pregnancy is a prothrombotic state; there are various risk factors which increase the affinity for the development of deep vein thrombosis (DVT)

• Hospitalisation for caesarean delivery
• An inherited thrombophilia (e.g., factor V Leiden mutation, prothrombin gene mutation, or antithrombin III, protein C, or protein S deficiencies) increases the risk of thromboembolism .

Thromboembolic complications in pregnancy:

The risk of developing a thromboembolic disorder is high, during 6 weeks after delivery. Most of the complications due to formation of blood clots results from injuries of the blood vessels during labour(delivery) period. The caesarean deliveries are having higher risk than vaginal delivery.

Thromboembolism infant:

Neonates are at higher risk for development of venous thromboembolism. Central lines (supply of medicine through jugular vein), sepsis (body response improperly to infection), liver dysfunction, fluid fluctuations (imbalance of fluids), and inflammation are the risks for venous thromboembolism (VTE) development in ill neonates.