The risk of VTE is increased in pregnancy by about five times because of a more hypercoagulable state, a likely adaptation against fatal postpartum hemorrhage. Additionally, pregnant women with genetic risk factors are subject to a roughly three to 30 times increased risk for VTE. Preventative treatments for pregnancy-related VTE in hypercoagulable women were suggested by the ACCP. Homozygous carriers of factor V Leiden or prothrombin G20210A with a family history of VTE were suggested for antepartum LMWH and either LMWH or a vitamin K antagonist (VKA) for the six weeks following childbirth. Those with another thrombophilia and a family history but no previous VTE were suggested for watchful waiting during pregnancy and LMWH or—for those without protein C or S deficiency—a VKA. Homozygous carriers of factor V Leiden or prothrombin G20210A with no personal or family history of VTE were suggested for watchful waiting during pregnancy and LMWH or a VKA for six weeks after childbirth. Those with another thrombophilia but no family or personal history of VTE were suggested for watchful waiting only. Warfarin, a common VKA, can cause harm to the fetus and is not used for VTE prevention during pregnancy.

The 2012 ACCP guidelines offered weak recommendations. For at-risk long-haul travelers—those with "previous VTE, recent surgery or trauma, active malignancy, pregnancy, estrogen use, advanced age, limited mobility, severe obesity, or known thrombophilic disorder"—suggestions included calf exercises, frequent walking, and aisle seating in airplanes to ease walking. The use of graduated compression stockings that fit below the knee and give 15–30 mm Hg of pressure to the ankle was suggested, while aspirin or anticoagulants were not. Compression stockings have sharply reduced the levels of asymptomatic DVT in airline passengers, but the effect on symptomatic VTE is unknown, as none of the individuals studied developed symptomatic VTE.

The most common cause of chronic venous insufficiency is reflux of the venous valves of superficial veins. This may in turn be caused by several conditions:

- Deep vein thrombosis (DVT), that is, blood clots in the deep veins. Chronic venous insufficiency caused by DVT may be described as postthrombotic syndrome.

- Superficial vein thrombosis.

- Phlebitis

- May–Thurner syndrome. This is a rare condition in which blood clots occur in the iliofemoral vein due to compression of the blood vessels in the leg. The specific problem is compression of the left common iliac vein by the overlying right common iliac artery. Many May-Thurner compressions are overlooked when there is no blood clot. More and more of them get nowadays diagnosed and treated (by stenting) due to advanced imaging techniques.

Deep and superficial vein thrombosis may in turn be caused by thrombophilia, which is an increased propensity of forming blood clots.

Arteriovenous fistula (an abnormal connection or passageway between an artery and a vein) may cause chronic venous insufficiency even with working vein valves.

Currently laboratory testing is not as reliable as observation when it comes to defining the parameters of Thrombotic Storm. Careful evaluation of possible thrombosis in other organ systems is pertinent in expediting treatment to prevent fatality.Preliminary diagnosis consists of evidence documented with proper imaging studies such as CT scan, MRI, or echocardiography, which demonstrate a thromboembolic occlusion in the veins and/or arteries. Vascular occlusions mentioned must include at least two of the clinic events:

- Deep venous thrombosis affecting one (or more) limbs and/or pulmonary embolism.

- Cerebral vein thrombosis.

- Portal vein thrombosis, hepatic vein, or other intra-abdominal thrombotic events.

- Jugular vein thrombosis in the absence of ipsilateral arm vein thrombosis and in the absence of ipsilateral central venous access.

- Peripheral arterial occlusions, in the absence of underlying atherosclerotic vascular disease,

- resulting in extremity ischemia and/or infarction.

- Myocardial infarction, in the absence of severe coronary artery disease

- Stroke and/or transient ischemic attack, in the absence of severe atherosclerotic disease and at an age less than 60 years.

- Central retinal vein and/or central retinal arterial thrombosis.

- Small vessel thrombosis affecting one or more organs, systems, or tissue; must be documented by histopathology.

In addition to the previously noted vascular occlusions, development of different thromboembolic manifestations simultaneously or within one or two weeks must occur and the patient must have an underlying inherited or acquired hypercoagulable state (other than Antiphospholipid syndrome)

The following factors increase the risk of developing PTS:

- age > 65

- proximal DVT

- a second DVT in same leg as first DVT (recurrent ipsilateral DVT)

- persistent DVT symptoms 1 month after DVT diagnosis

- obesity

- poor quality of anticoagulation control (i.e. dose too low) during the first 3 months of treatment

Thrombotic Storm has been seen in individuals of all ages and races. The initial symptoms of TS present in a similar fashion to the symptoms experienced in deep vein thrombosis. Symptoms of a DVT may include pain, swelling and discoloration of the skin in the affected area. As with DVTs patients with TS may subsequently develop pulmonary emboli. Although the presentation of TS and DVTs are similar, TS typically progresses rapidly, with numerous clots occurring within a short period of time. After the formation of the initial clot a patient with TS typically begins a “clotting storm” with the development of multiple clots throughout the body. Rapid progression within a short period of time is often seen, affecting multiple organs systems. The location of the clot is often unusual or found in a spot in the body that is uncommon such as the dural sinus. Patients tend to respond very well to anticoagulation such as coumadin or low molecular weight heparin but may become symptomatic when treatment is withheld.

While the key clinical characteristics of thrombotic storm are still being investigated, it is believed that the clinical course is triggered by a preexisting condition, known as a hypercoagulable state. These can include such things as pregnancy, trauma or surgery. Hypercoagulable states can be an inherited or acquired risk factor that then serves as a trigger to initiate clot formation. However, in a subset of patient with TS a trigger cannot be identified. Typically people with TS will have no personal or family history of coagulations disorders.

Despite ongoing research, the cause of PTS is not entirely clear. Inflammation is thought to play a role as well as damage to the venous valves from the thrombus itself. This valvular incompetence combined with persistent venous obstruction from thrombus increases the pressure in veins and capillaries. Venous hypertension induces a rupture of small superficial veins, subcutaneous hemorrhage and an increase of tissue permeability. That is manifested by pain, swelling, discoloration, and even ulceration.

Varicose veins are more common in women than in men, and are linked with heredity. Other related factors are pregnancy, obesity, menopause, aging, prolonged standing, leg injury and abdominal straining. Varicose veins are unlikely to be caused by crossing the legs or ankles. Less commonly, but not exceptionally, varicose veins can be due to other causes, as post phlebitic obstruction or incontinence, venous and arteriovenous malformations.

It is often caused by venous reflux. More recent research has shown the importance of pelvic vein reflux (PVR) in the development of varicose veins. Hobbs showed varicose veins in the legs could be due to ovarian vein reflux and Lumley and his team showed recurrent varicose veins could be due to ovarian vein reflux. Whiteley and his team reported that both ovarian and internal iliac vein reflux causes leg varicose veins and that this condition affects 14% of women with varicose veins or 20% of women who have had vaginal delivery and have leg varicose veins. In addition, evidence suggests that failing to look for, and treat pelvic vein reflux can be a cause of recurrent varicose veins.

There is increasing evidence for the role of incompetent perforator veins (or "perforators") in the formation of varicose veins. and recurrent varicose veins.

Varicose veins could also be caused by hyperhomocysteinemia in the body, which can degrade and inhibit the formation of the three main structural components of the artery: collagen, elastin and the proteoglycans. Homocysteine permanently degrades cysteine disulfide bridges and lysine amino acid residues in proteins, gradually affecting function and structure. Simply put, homocysteine is a 'corrosive' of long-living proteins, i.e. collagen or elastin, or lifelong proteins, i.e. fibrillin. These long-term effects are difficult to establish in clinical trials focusing on groups with existing artery decline. Klippel-Trenaunay syndrome and Parkes-Weber syndrome are relevant for differential diagnosis.

Another cause is chronic alcohol consumption due to the vasodilatation side effect in relation to gravity and blood viscosity.

Patient characteristics and predisposing factors for thrombophlebitis nearly mirror those for DVT; thrombophlebitis is a risk factor for the development of DVT, and vice versa.

Lower extremity superficial phlebitis is associated with conditions that increase the risk of thrombosis, including abnormalities of coagulation or fibrinolysis, endothelial dysfunction, infection, venous stasis, intravenous therapy and intravenous drug abuse.

History and examination by a physician with characteristic signs and symptoms are sufficient in many cases in ruling out systemic causes of venous hypertension such as hypervolemia and heart failure. An ultrasound (usually a lower limbs venous ultrasonography) can detect venous obstruction or valvular incompetence as the cause, and is used for planning venous ablation procedures, but it is not necessary in suspected venous insufficiency where surgical intervention is not indicated.

This condition is most common after age 50.

It is more prevalent in females.

There is a hereditary role.

It has been seen in smokers, those who have chronic constipation and in people with occupations which necessitate long periods of standing such as lecturers, nurses, conductors (musical and bus), stage actors, umpires (cricket, javelin, etc.), the Queen's guard, lectern orators, security guards, etc.

Some 125,000 cases a year have been reported in the United States, but actual incidence of spontaneous thrombophlebitis is unknown.

A fourfold increased incidence from the third to the eight decade in men and a preponderance among women of approximately 55-70%.

The average mean age of affected patients is 60 years.

Thrombophlebitis can develop along the arm, back, or neck veins, the leg is by far the most common site. When it occurs in the leg, the great saphenous vein is usually involved, although other locations are possible.

In treating pulmonary insufficiency, it should be determined if pulmonary hypertension is causing the problem to therefore begin the most appropriate therapy as soon as possible (primary pulmonary hypertension or secondary pulmonary hypertension due to thromboembolism). Furthermore, pulmonary insufficiency is generally treated by addressing the underlying condition, in certain cases, the pulmonary valve may be surgically replaced.

A very large range of medical conditions can cause circulatory collapse. These include, but are not limited to:

- Surgery, particularly on patients who have lost blood.

- Blood clots, including the use of some platelet-activating factor drugs in some animals and humans

- Dengue Fever

- Severe dehydration

- Shock (including, among other types, many cases of cardiogenic shock- e.g., after a myocardial infarction or during heart failure; distributive shock, hypovolemic shock, resulting from large blood loss; and severe cases of septic shock)

- Heart Disease (myocardial infarction- heart attack; acute or chronic congestive or other heart failure, ruptured or dissecting aneurysms; large, especially hemorrhagic, stroke; some untreated congenital heart defects; failed heart transplant)

- Superior mesenteric artery syndrome

- Drugs that affect blood pressure

- Drinking seawater

- As a complication of dialysis

- Intoxicative inhalants

Several studies have attempted to predict the survival of patients with Budd–Chiari syndrome. In general, nearly 2/3 of patients with Budd–Chiari are alive at 10 years. Important negative prognostic indicators include ascites, encephalopathy, elevated Child-Pugh scores, elevated prothrombin time, and altered serum levels of various substances (sodium, creatinine, albumin, and bilirubin). Survival is also highly dependent on the underlying cause of the Budd–Chiari syndrome. For example, a patient with an underlying myeloproliferative disorder may progress to acute leukemia, independently of Budd–Chiari syndrome.

Epidemiological data is elusive owing to the wide variety of clinical presentation. In the U.S., incidence is estimated to be at 5–10 cases per 100,000 per year. Minor compression of the inferior vena cava during pregnancy is a relatively common occurrence. It is seen most prevalently when women lie on their back or right side. 90% of women lying in the supine position during pregnancy experience inferior vena cava syndrome; however, not all of the women display symptoms.

The effects of a circulatory collapse vary based on the type of collapse it is. Peripheral collapses usually involve abnormally low blood pressure and result in collapsed arteries and/or veins, leading to oxygen deprivation to tissues, organs, and limbs.

Acute collapse can result from heart failure causing the primary vessels of the heart to collapse, perhaps combined with cardiac arrest.

The thrombi may dislodge and may travel anywhere in the circulatory system, where they may lead to pulmonary embolus, an acute arterial occlusion causing the oxygen and blood supply distal to the embolus to decrease suddenly. The degree and extent of symptoms depend on the size and location of the obstruction, the occurrence of clot fragmentation with embolism to smaller vessels, and the degree of peripheral arterial disease (PAD).

- Thromboembolism (blood clots)

- Embolism (foreign bodies in the circulation, e.g. amniotic fluid embolism)

Traumatic injury to an extremity may produce partial or total occlusion of a vessel from compression, shearing or laceration. Acute arterial occlusion may develop as a result of arterial dissection in the carotid artery or aorta or as a result of iatrogenic arterial injury (e.g., after angiography).

Acquired telangiectasia, not related to other venous abnormalities, for example on the face and trunk, can be caused by factors such as

- Acne rosacea

- Blepharitis

- Environmental damage such as that caused by sun or cold exposure

- Age

- Trauma to skin such as contusions or surgical incisions.

- Radiation exposure such as that experienced during radiotherapy for the treatment of cancer

- Chemotherapy

- Carcinoid syndrome

- Limited systemic sclerosis/scleroderma (a Scleroderma sub-type)

- Chronic treatment with topical corticosteroids may lead to telangiectasia.

- Spider angiomas are a radial array of tiny arterioles that commonly occur in pregnant women and in patients with hepatic cirrhosis and are associated with palmar erythema. In men, they are related to high estrogen levels secondary to liver disease.

- Tempi syndrome

- Smoking

In the past, people used to think that leg varicose veins or telangectasia were caused by high venous pressure or "venous hypertension". However it is now understood that venous reflux disease is usually the cause of these problems (see above for reference for "venous reflux".

Telangiectasia in the legs is often related to the presence of venous reflux within underlying varicose veins. Flow abnormalities within the medium-sized veins of the leg (reticular veins) can also lead to the development of telangiectasia.

Factors that predispose to the development of varicose and telangiectatic leg veins include

- Age: The development of spider veins may occur at any age but usually occurs between 18 and 35 years, and peaks between 50 and 60 years.

- Gender: It used to be thought that females were affected far more than males. However research has shown 79% of adult males and 88% of adult females have leg telangectasia (spider veins).

- Pregnancy: Pregnancy is a key factor contributing to the formation of varicose and spider veins. The most important factor is circulating hormones that weaken vein walls. There's also a significant increase in the blood volume during pregnancy, which tends to distend veins, causing valve dysfunction which leads to blood pooling in the veins. Moreover, later in pregnancy, the enlarged uterus can compress veins, causing higher vein pressure leading to dilated veins. Varicose veins that form during pregnancy may spontaneously improve or even disappear a few months after delivery.

- Lifestyle/occupation: Those who are involved with "prolonged sitting or standing" in their daily activities have an increased risk of developing varicose veins. The weight of the blood continuously pressing against the closed valves causes them to fail, leading to vein distention.

The cause can be found in more than 80% of patients.

- Primary Budd–Chiari syndrome (75%): thrombosis of the hepatic vein

- Hepatic vein thrombosis is associated with the following in decreasing order of frequency:

2. Polycythemia vera

1. Pregnancy

2. Postpartum state

3. Use of oral contraceptives

4. Paroxysmal nocturnal hemoglobinuria

5. Hepatocellular carcinoma

6. Lupus anticoagulants

- Secondary Budd–Chiari syndrome (25%): compression of the hepatic vein by an outside structure (e.g. a tumor)

Budd–Chiari syndrome is also seen in infections such as tuberculosis, congenital venous webs and occasionally in inferior vena caval stenosis.

Often, the patient is known to have a tendency towards thrombosis, although Budd–Chiari syndrome can also be the first symptom of such a tendency. Examples of genetic tendencies include protein C deficiency, protein S deficiency, the Factor V Leiden mutation, hereditary anti-thrombin deficiency and prothrombin mutation G20210A. An important non-genetic risk factor is the use of estrogen-containing (combined) forms of hormonal contraception. Other risk factors include the antiphospholipid syndrome, aspergillosis, Behçet's disease, dacarbazine, pregnancy, and trauma.

Many patients have Budd–Chiari syndrome as a complication of polycythemia vera (myeloproliferative disease of red blood cells). Patients suffering from paroxysmal nocturnal hemoglobinuria (PNH) appear to be especially at risk for Budd–Chiari syndrome, more than other forms of thrombophilia: up to 39% develop venous thromboses and 12% may acquire Budd-Chiari.

A related condition is veno-occlusive disease, which occurs in recipients of bone marrow transplants as a complication of their medication. Although its mechanism is similar, it is not considered a form of Budd–Chiari syndrome.

Other toxicologic causes of veno-occlusive disease include plant & herbal sources of pyrrolizidine alkaloids such as Borage, Boneset, Coltsfoot, T'u-san-chi, Comfrey, Heliotrope (sunflower seeds), Gordolobo, Germander, and Chaparral.

The pathophysiology is due to diastolic pressure variations between the pulmonary artery and right ventricle, differences are often very small, but increase regurgitation. An elevation in pulmonary insufficiency due to elevated intrathoracic pressure is relevant in ventilated patients (having acute restrictive right ventricular physiology). The reasons for changes in stiffness of the right ventricle's walls are not well understood, but such stiffness is thought to increase with hypertrophy of the ventricle.

The progression of HFpEF and its clinical course is poorly understood in comparison to HFrEF. Despite this, patients with HFrEF and HFpEF appear to have comparable outcomes in terms of hospitalization and mortality. Causes of death in patients vary substantially. However, among patients in more advanced heart failure (NYHA classes II-IV), cardiovascular death, including heart attacks and sudden cardiac death, was the predominant cause in population-based studies.

The prognosis of tricuspid insufficiency is less favorable for males than females. Furthermore, increased tricuspid insufficiency (regurgitation) severity is an indication of a poorer prognosis according to Nath, et al. It is also important to note that since tricuspid insufficiency most often arises from left heart failure or pulmonary hypertension, the person's prognosis is usually dictated by the prognosis of the latter conditions and not by the tricuspid insufficiency "per se".