How does pulmonary thrombosis form? Causes of pulmonary artery thrombosis

Thrombosis is a common disease in life, and the types of thrombosis we hear about, such as pulmonary thromboembolism, are the most common. There are many factors that cause thrombosis, and patients with heart disease are particularly prone to thrombosis. In addition, cancer patients and patients after childbirth should pay attention to preventing thrombosis, otherwise it will be detrimental to their physical recovery.

Causes

1. Thrombosis

Pulmonary embolism is often a complication of venous thrombosis. Emboli usually originate from the deep veins of the lower extremities and pelvis and circulate to the pulmonary arteries, causing embolism. But rarely they originate from the veins of the upper limbs, head, and neck. Blood stasis, increased blood coagulability and venous endothelial damage are factors that promote thrombosis. Therefore, trauma, long-term bed rest, varicose veins, venous catheterization, pelvic and hip surgery, obesity, diabetes, contraceptives or other reasons for hypercoagulation mechanism can easily induce venous thrombosis. The early thrombus is brittle, and coupled with the action of the fibrinolytic system, the risk of pulmonary embolism is highest in the first few days of thrombosis.

Modern concepts have proposed three elements of pulmonary thromboembolism: ① blood flow stagnation; ② blood hypercoagulable state; ③ blood vessel wall damage.

2. Heart disease

It is the most common cause of pulmonary embolism in my country, accounting for 40%. It is common in all kinds of heart diseases, with a higher incidence in patients with atrial fibrillation, heart failure and subacute bacterial endocarditis. The most common type of thrombosis is in the right heart cavity, but a few also originate from the venous system. In addition to subacute bacterial endocarditis, bacterial emboli can also be caused by pacemaker infection. In the former, infectious emboli mainly come from the tricuspid valve. Occasionally, mitral valve vegetation in patients with congenital heart disease can be shunt from the left heart into the right heart through the defect and reach the pulmonary artery.

3. Tumor

In my country, it is the second reason, accounting for 35%, which is much higher than 6% in foreign countries. Lung cancer, digestive system tumors, choriocarcinoma, leukemia, etc. are more common. Only about one-third of malignant tumors complicated by pulmonary embolism are tumor thrombi, and the rest are blood clots. It is speculated that thrombin and other substances that can activate the coagulation system, such as histones, cathepsins and proteases, may exist in the blood of cancer patients. Therefore, the incidence of pulmonary embolism is high in cancer patients and may even be the first symptom.

4. Pregnancy and childbirth

Pulmonary embolism occurs most frequently in pregnant women, several times more often than in age-matched nonpregnant women, and is most common postpartum and after cesarean delivery. During pregnancy, increased intra-abdominal pressure, hormonal relaxation of vascular smooth muscle and compression of pelvic veins can cause slow venous blood flow, change blood rheology properties, and aggravate venous thrombosis. In addition, coagulation factors and platelets increase, and the activity of the plasma proteolytic system decreases. However, these changes were not absolutely different from those in pregnant women without thromboembolism. Amniotic fluid embolism is also a serious complication during delivery.