Pulmonary hypertension overview

# Overview
Pulmonary hypertension (PH) is a condition of elevated blood pressure (>25 mmHg at rest) within the pulmonary artery of the lungs, leading to myriad symptoms including shortness of breath, dizziness, syncope, chest pain, tachycardia and leg swelling. PH has several differing etiologies and is a progressive and fatal disease if left untreated. PH is classified by the World Health Organization (WHO) into 5 different groups, which will be discussed later on this page. Treatment is generally targeted toward the underlying etiology of disease. Pulmonary arterial hypertension (PAH) refers to group 1 PH in the updated WHO classification and pulmonary hypertension (PH) refers to any of group 2 PH through group 5 PH. PH is also used when referring to all five groups collectively.

# Historical Perspective
Pulmonary hypertension was first described by Ernst von Romberg, a German physician, in 1891.

# Classification
Pulmonary hypertension may be classified according to the mechanism leading to its development into 5 groups: pulmonary arterial hypertension, pulmonary hypertension due to left heart disease, pulmonary hypertension due to chronic lung diseases and/or hypoxia, and pulmonary hypertension due to embolic disease and miscellaneous causes.

# Pathophysiology
Pulmonary hypertension (PH) is a pathological condition of the pulmonary vasculature present in several disease states that presents with elevated mean pulmonary artery pressure (PAP) as measured by right heart catheterization at rest. The factors that are involved in the pathophysiology of the increase in the mean pulmonary arterial pressure are: increase in pulmonary vascular resistance, increase in the right-side cardiac output, and increase in the mean pulmonary venous pressure. Pulmonary arterial hypertension is characterized by endothelial dysfunction resulting from an imbalance between apoptosis and proliferation of pulmonary artery smooth muscle cells favoring the proliferation. The other types of pulmonary hypertension are caused by hemodynamic changes that result in increased pulmonary blood pressure or architectural changes to the lung or its vasculature that result in the same outcome.

# Causes
The World Health Organization (WHO) has classified PH based on etiology into five distinct groups: Group 1 (pulmonary arterial hypertension - which may be related to heritable PAH due to genetic defects, connective tissue diseases such as rheumatoid arthritis, systemic lupus erythematosus, Raynaud Disease, and mixed connective tissue disease, HIV, drugs and toxins, and parasitic infections such as schistosomiasis), Group 2 (PH due to left heart failure), Group 3 (PH due to chronic lung disease and/or hypoxemia), Group 4 (PH due to chronic thromboembolic disease), and Group 5 (PH due to multifactorial mechanisms such as chronic hemolytic anemia, sarcoidosis, chronic kidney disease, and myeloproliferative disorders).

# Differentiating Pulmonary hypertension from Other Diseases
One of the most common initial presentations of patients with pulmonary hypertension is dyspnea; therefore, the differential diagnosis is very broad. As the disease progresses with time, more symptoms related to right ventricular hypertrophy and failure occur; which further narrows down the differential diagnosis.

# Epidemiology and Demographics
Pulmonary arterial hypertension has been considered as a disease of young women. The mean age of patients in the U.S. registry was 36 years old and the overall female-to-male ratio was 1.7:1. The prevalence of pulmonary hypertension is approximately 1.5-5 per 100,000 individuals.

# Risk Factors
Pulmonary hypertension (PH) is a multifactorial disease involving genetic and environmental risk factors. Risk factors for pulmonary arterial hypertension include BMPR2 mutation, connective tissue disease, HIV infection, portal hypertension, fenfluramine use, and congenital heart disease with shunt. Left heart and lung diseases are risk factors for PH. Patients with a hypercoagulable state (such as the presence of lupus anticoagulant, deficiency of protein C, protein S, or antithrombin III, chronic inflammatory disorders, myeloproliferative syndromes, and splenectomy) are at an increased risk for chronic thromboembolic pulmonary hypertension.

# Screening
Patients with a known BMPR2 mutation, scleroderma, and portal hypertension undergoing evaluation for liver transplantation should receive periodic screening for pulmonary hypertension (PH) through a thorough assessment of the presence of symptoms, physical examination, a chest X ray, electrocardiography, and an echocardiogram.  Additional investigation with right heart catheterization should be performed if screening is suggestive of the presence of PH.

# Natural History, Complications and Prognosis
The most common initial symptoms of pulmonary hypertension are dyspnea, fatigue, and syncope. There was an estimated median survival of 2.8 years for symptomatic patients who do not receive any treatment, with the most common cause of death as cor pulmonale, but survival rates have been increasing as new forms of treatment become available. Despite such advances, prognosis is still poor.

# Diagnosis

## Diagnostic Study of Choice
Pulmonary hypertension is defined by a mean pulmonary arterial pressure higher than 25mmHg. It can be assessed by echocardiography, the diagnostic study of choice due to its low risk and useful information that it can provide, and right heart cardiac catheterization to confirm the diagnosis.

## History and Symptoms
The hallmark of pulmonary hypertension is progressive dyspnea. The most common symptoms of pulmonary hypertension include dyspnea, fatigue, chest pain and syncope or presyncope. Ortner syndrome may also be seen (characterized by hoarseness due to compression of the left laryngeal nerve caused by enlargement of the pulmonary artery).

## Physical Examination
Pulmonary hypertension (PH) can present with myriad physical findings that may be associated with PH or the underlying cause. Findings associated with pulmonary hypertension are usually associated with right heart failure or right heart overload, while other findings may be associated with underlying cause, such as thoracic deformities which may arise in the setting of COPD, or sclerodactyly that may be seen in patients with scleroderma. Some may develop on a spectrum corresponding to the severity of the disease.

## Laboratory Findings
There are no specific diagnostic lab findings associated with pulmonary hypertension. Despite that, several laboratory tests are required in the evaluation of a patient for pulmonary hypertension to assess its severity or possible associated causes. Biochemistry, hematology and thyroid function tests are required in all patients with pulmonary hypertension. They are important for the diagnosis of chronic hemolytic anemia, myeloproliferative disorders, thyroid disorders and chronic renal failure on dialysis.

## ECG
Elevated pulmonary pressures in pulmonary hypertension (PH) can lead to right ventricular hypertrophy (RVH) and right atrial enlargement which can sometimes be observed on an electrocardiogram (ECG). The ECG findings of PH include right axis deviation, right ventricular strain pattern, and P pulmonale. The ECG findings of PH are neither specific nor sensitive and their absence does not rule out the presence of PH.

## Chest X Ray
A chest X-ray is abnormal in the majority of patients with pulmonary hypertension (PH); however, there is no correlation between the severity of PH and the findings on a chest X-ray. Findings of PH on a chest X-ray include pulmonary artery dilatation and right-sided enlargement of the heart. A chest X-ray allows the exclusion of left heart disease and lung disease that can lead to group 2 and group 3 PH, respectively.

## CT
A lung CT scan is helpful in the differential diagnosis of pulmonary hypertension. Different types of CT imaging have been used to rule out certain etiologies of pulmonary hypertension and to evaluate the anatomy of the pulmonary vasculature.

## MRI
Thoracic MRI is helpful in the differential diagnosis of pulmonary hypertension as well as in the evaluation of the right ventricle function. It provides important prognostic indicators when assessing the right ventricle in patients with pulmonary hypertension. Findings that predict poor prognosis are: stroke volume 25ml/m^2, right ventricular end-diastolic volume 84ml/m^2 and left ventricular end-diastolic volume 40ml/m^2.

## Echocardiography or Ultrasound
Echocardiography may demonstrate right ventricular or atrial enlargement with a thickened interventricular septum in patients with pulmonary hypertension, decreased right ventricular function, or hypertrophy. Pulmonary artery systolic pressure can also be estimated using echocardiography. Right ventricular afterload may be suggested by a leftward septal displacement during systole. Pericardial effusions and diminished left ventricular cavity typically portend a dismal prognosis.

## Other diagnostic studies
Pulmonary hypertension diagnosis is made using right heart cardiac catheterization. It is mandatory for diagnosing pulmonary arterial hypertension. It confirms the diagnosis and evaluates for some causes such as valvular heart diseases. Other studies may also be performed. These studies include pulmonary function tests, overnight oximetry, and ventilation-perfusion studies (which is crucial to rule out chronic pulmonary thromboembolism).

# Treatment

## Medical Therapy
The choice of treatment for pulmonary hypertension (PH) requires the assessment of the clinical severity of the disease and the identification of any underlying cause. Patients who have PH secondary to a medical condition such as left heart failure, lung diseases, or thromboembolic disease (PH group 2, 3, and 4 respectively) should receive treatment for the underlying cause. Patients who have pulmonary arterial hypertension (PAH) must undergo vasoreactivity testing in order to assist in the selection of the optimal therapy which include calcium channel blockers, endothelin receptor antagonist, phosphodiesterase inhibitors, or prostanoids.

## Surgery
Patients with severe WHO functional class II or III pulmonary hypertension (PH) refractory to medical therapy are candidates for surgical intervention, such as atrial septostomy or lung transplantation. Pulmonary thromboendarterectomy (PTE) is a surgical procedure that is used for chronic thromboembolic pulmonary hypertension.

## Primary Prevention
Genetic and environmental factors are involved in pulmonary hypertension (PH); therefore, not all cases of PH are preventable. PH that is secondary to other diseases such as left heart failure, chronic lung disease, chronic liver disease, and collagen vascular diseases among others can be prevented by the early and optimal treatment of these medical conditions. Patients who are at elevated risk for developing pulmonary arterial hypertension (PAH) must be monitored for the occurrence of symptoms of PAH. Patients at risk for PAH include subjects with systemic sclerosis or with genetic predisposition.

## Secondary Prevention
The recommended measures for the secondary prevention are avoiding pregnancy, rigorous follow up in case of pregnancy, avoid unnecessary surgeries, multidisciplinary care in case of necessary surgery, avoid high altitude, supplemental oxygen in order to ensure a target oxygen saturation of 91% in case of exposure to high altitude, and up-to-date immunizations against influenza and pneumococcal pneumonia.