Secondary pulmonary hypertension (PH) refers to any type of PH that is caused by an underlying health condition. This is in contrast to primary PH, which has an unknown cause.
Normally, the right side of the heart pumps blood through to the lungs, where it picks up oxygen. The newly oxygenated blood then gets pumped back through the left side of the heart so it can carry oxygen through the rest of the body.
In someone with PH, however, blood cannot properly flow through the pulmonary arteries (blood vessels in the lungs). This results in the right side of the heart working extra hard to pump blood, leading to high blood pressure and enlargement of the right side of the heart. Ultimately, this condition can result in right heart failure.
Although PH was originally classified as either primary or secondary, those terms are no longer widely used. Instead, the World Health Organization (WHO) now divides PH into five different groups depending on the cause:
Idiopathic pulmonary arterial hypertension (IPAH), included in group 1, might also be referred to as primary PH. All other forms of PH can be considered secondary PH.
Many conditions can lead to PH. Typically, it is a form of heart or lung disease. However, there are additional genetic risk factors, exposures, and other chronic conditions that are associated with PH.
Organs and tissues throughout the body are supported by connective tissue, which helps provide structure. The connective tissue can be affected by several autoimmune disorders caused by the immune system inappropriately attacking the tissue. Conditions that can lead to PH include:
PAH as a complication of connective tissue diseases is included in group 1 PH.
Mutations in certain genes are associated with an increased risk of PH. Genetic mutations can be inherited, which can cause PH to be more prevalent in some families.
Another known risk factor for PH is human immunodeficiency virus (HIV) infection. HIV can directly cause PH similar to other causes of group 1 PH or cause lung disease and other health problems that may lead to the development of PH.
High pressure in the liver caused by portal hypertension is linked to PH. This cause falls into the group 1 category.
PH is often associated with chronic heart disease. In some cases, this is congenital heart disease, which is a condition present at birth. PH associated with congenital heart disease is part of group 1.
One of the most common causes of PH is left heart disease, which causes a buildup of pressure in the pulmonary arteries due to left-side heart dysfunction. PH associated with left heart disease makes up the group 2 classification. It may also be called pulmonary venous hypertension or postcapillary PH.
Conditions that negatively affect lung function can also cause PH. PH-associated lung diseases include:
Some of these conditions can cause pulmonary fibrosis, a lung disease that occurs from tissue damage and scarring. PH caused by lung diseases corresponds to the group 3 category.
The group 4 classification includes chronic thromboembolic PH, which is PH caused by blood clots. In many cases, this is due to an acute pulmonary embolism, which occurs when a blood clot from a deep vein in the leg breaks off and travels to the lungs. In a small subset of patients with acute pulmonary embolism, the blood clots do not dissolve. Over time, this can lead to an increase in pulmonary artery pressure.
The group 5 category includes other rare diseases that are linked to PH in a way that isn’t well understood. Conditions in this category include:
For secondary PH, the initial treatment approach is generally to target the underlying condition that is causing the PH. This is referred to as primary treatment.
Oftentimes, however, PH will persist despite primary treatment and more advanced therapy may be required. After a diagnosis of PH, your health care provider will determine potential underlying causes and discuss a treatment approach that best suits your condition.
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