Thrombosis

Jump to navigation Jump to search

Thrombosis Microchapters

Home

Patient Information

Overview

Pathophysiology

Classification

Arterial
Venous
Arterial and Venous Thrombosis: Differences and Similarities

Causes

Site of Thrombosis

Arterial
Venous

Differentiating Thrombosis from other Diseases

Arterial
Venous

Risk Factors

Natural History, Complications and Prognosis

Diagnosis

Diagnostic Evaluation

Treatment

Risk Factor Modifications

Prevention

Thrombosis On the Web

Most recent articles

Most cited articles

Review articles

CME Programs

Powerpoint slides

Images

Ongoing Trials at Clinical Trials.gov

US National Guidelines Clearinghouse

NICE Guidance

FDA on Thrombosis

CDC onThrombosis

Thrombosis in the news

Blogs on Thrombosis

to Hospitals Treating Thrombosis

Risk calculators and risk factors for Thrombosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Thrombosis is the formation of a thrombus (medical term for a clot) inside a blood vessel. This can dislodge from the site it was formed and can move along the flow of blood to distant places in the body. A piece of thrombus that is transported in this way is called an embolus (plural emboli). This process of formation an emboli, from a thrombus is called thromboembolism. The term was coined in 1848 by Rudolph Carl Virchow.

The most important sites of thrombosis formation, based on their frequency and clinical effect are coronary arteries and deep veins of the legs. Former, the most important site of arterial thrombosis and latter the most important site of venous thrombosis.

Pathophysiology

Rudolf Virchow noted several factors affecting the clot formation, which are as follows:

1) Alterations in blood flow (stasis): Blood flows throughout the circulatory system, without significantly stopping or slowing any where. In certain pathological conditions where the blood flow slows down or stops, it causes:

  • Increase in platelet to endothelium contact
  • Decrease the dilution of clotting factors

This increases the risk of clot formation and form microthrombi, which further grow and propagate.

2) Injury to the vascular endothelium: Intrinsic or secondary to external trauma (eg, catheterization) can cause intimal damage and stimulates clot formation. See Coagulation.

3) Alterations in the constitution of blood (hypercoagulability): It is the propensity to develop thrombosis due to an abnormality in the system of coagulation.

These three conditions are collectively known as Virchow's triad and lead to intravascular coagulation, forming a mass of red blood cells, leukocytes, and fibrin.

Shown below is a table depicting the elements of Virchow's triad and their modern counterparts.

Virchow's Modern Notes
Phenomena of interrupted blood-flow "Stasis" or "venous stasis" The first category, alterations in normal blood flow, refers to several situations. These include turbulence, stasis, mitral stenosis, and varicose veins. The equivalence of Virchow's version and the modern version has been disputed.
Phenomena associated with irritation of the vessel and its vicinity "Endothelial injury" or "vessel wall injury" The second category, injuries and/or trauma to endothelium includes damage to the veins arising from shear stress or hypertension.
Phenomena of blood-coagulation "Hypercoagulability" The last category, alterations in the constitution of blood, has numerous possible risk factors such as hyperviscosity, deficiency of antithrombin III, nephrotic syndrome, changes after severe trauma or burn, disseminated cancer, late pregnancy and delivery, race, age, whether the patient is a smoker, and obesity. All of these risk factors lead to hypercoagulability.

Thrombus Formation

  • Usually there is a balance between the coagulation and fibrinolysis systems in order to not having abnormal thrombosis in the body.
  • Factors that increase the risk for a homeostatic imbalance include:

Thrombophilia

Immobilization

Trauma

Factors that serve as nidus for development stent thrombosis are:

Delayed endothelialization.

Inflammatory response to the stent material.

Hypersensitivity reaction around the stent material in DES serving as nidus for ST.

  • Pregnancy increases risk of having thrombosis in both veins and arteries because of hypercoagulate state .
  • Acquired risk factors for thrombosis are:

Oral contraceptive use,

Hormone replacement therapy

Advanced age

Surgery

Prolonged immobilization like hospitalization .

This video explains the process of thrombosis:

{{#ev:youtube|X_POCRsy7i4}}

Genetics

Genetic factors that play roles in causing thrombosis :

  • Non-O blood groups
  • Factor V Leiden mutation
  • Prothrombin G20210A gene variants
  • Polymorphisms in factors IX17 or XI

Gross Pathology

  • Dull appearance.
  • Zahn line from platelets and fibrin with layers of RBCs in pulmonary venous thromboembolism.
  • Gross picture of thrombosis is different in live and dead person.

In live person it is gray and firm.

In dead person it is dark purple or yellow elastic called "chicken fat".

Microscopic Pathology

  • lamination
  • Zahn line


Classification

There are two distinct forms of thrombosis:

Venous Thrombosis

Arterial Thrombosis

Classification of Embolism Based on Direction of Blood Flow

If a bacterial infection is present at the site of thrombosis, the thrombus may break down, spreading particles of infected material throughout the circulatory system (pyemia, septic embolus) and setting up metastatic abscesses wherever they come to rest.

Without an infection, the thrombus may become detached and enter circulation as an embolus, finally lodging in and completely obstructing a blood vessel (an infarction). The effects of an infarction depend on where it occurs.

The pathway of the embolism can be one of three types:

  • Anterograde
  • Retrograde
  • Paradoxical

In anterograde embolism, the movement of emboli is in the direction of blood flow. In retrograde embolism, however, the emboli move in opposition to the blood flow direction; this is usually significant only in blood vessels with low pressure (veins) or with emboli of high weight. In paradoxical embolism, also known as crossed embolism, an embolus from the veins crosses to the arterial blood system. This is generally found only with heart problems such as septal defects between the atria or ventricles.

Causes

Site of Thrombosis

Arterial | Venous

Differentiating Thrombosis from other Diseases

Arterial | Venous

Risk Factors

The following are the risk factors for thrombosis:

Natural History, Complications and Prognosis

Diagnosis

Diagnostic Evaluation

Treatment

Risk Factor Modifications | Prevention

Related Chapters

Template:WH Template:WS