Secondary pulmonary hypertension

Overview

Increased blood pressure in blood vessels that carry deoxygenated blood from the heart to the lungs (pulmonary artery). The increased blood pressure is due to any of a number of diseases that restricts blood flow through the lung and hence builds pressure in the pulmonary artery leading to it.

Symptoms

• Breathing difficulty 
• Anxiety 
• Rapid breathing 
• Pulmonary artery dilatation 
• Shortness of breath during exertion 
• Fainting spells 
• Dizziness 
• Ankle swelling
• Leg swelling 
• Chest pain 
• Racing pulse

Diagnosis

In terms of the diagnosis of secondary pulmonary hypertension, dictates it can be of five major types, a series of tests must be performed to distinguish pulmonary arterial hypertension from venous, hypoxic, thromboembolic, or miscellaneous varieties.Further procedures are required to confirm the presence of pulmonary hypertension and exclude other possible diagnoses. These generally include pulmonary function tests; blood tests to exclude HIV, autoimmune diseases, and liver disease; electrocardiography (ECG); arterial blood gas measurements; X-rays of the chest (followed by high-resolution CT scanning if interstitial lung disease is suspected); and ventilation-perfusion or V/Q scanning to exclude chronic thromboembolic pulmonary hypertension. Clinical improvement is often measured by a "six-minute walk test", i.e. the distance a patient can walk in six minutes. Stability and improvement in this measurement correlate with better survival.

Diagnosis of PAH requires the presence of pulmonary hypertension. Although pulmonary arterial pressure can be estimated on the basis of echocardiography, pressure measurements with a Swan-Ganz catheter through the right side of the heart provide the most definite assessment. Diagnosis of PAH requires right-sided cardiac catheterization; a Swan-Ganz catheter can also measure the cardiac output, which is far more important in measuring disease severity than the pulmonary arterial pressure. Normal pulmonary arterial pressure in a person living at sea level has a mean value of 8–20 mm Hg (1066–2666 Pa) at rest. Pulmonary hypertension is present when mean pulmonary artery pressure exceeds 25 mm Hg (3300 Pa) at rest.

Physical examination

A physical examination is performed to look for typical signs of pulmonary hypertension. These include altered heart sounds, such as a second heart sound, a loud P₂ or pulmonic valve closure sound (part of the second heart sound), and pulmonary regurgitation. Other signs include an elevated jugular venous pressure, peripheral edema (swelling of the ankles and feet),ascites (abdominal swelling due to the accumulation of fluid), hepatojugular reflux, and clubbing.

Echocardiography

A meta-analysis of doppler echocardiography for predicting right heart catheterization reported a sensitivity and specificity of 88% and 56%, respectively.

Prognosis

The prognosis of secondary pulmonary hypertension has an untreated median survival of 2–3 years from time of diagnosis, with the cause of death usually being right ventricular failure (cor pulmonale). A recent outcome study of those patients who had started treatment with bosentan (Tracleer) showed that 89% patients were alive at 2 years. With new therapies, survival rates are increasing. For 2,635 patients enrolled in The Registry to Evaluate Early and Long-term Pulmonary Arterial Hypertension Disease Management (REVEAL Registry) from March 2006 to December 2009, 1-, 3-, 5-, and 7-year survival rates were 85%, 68%, 57%, and 49%, respectively. For patients with idiopathic/familial PAH, survival rates were 91%, 74%, 65%, and 59%. Levels of mortality are very high in pregnant women with severe pulmonary hypertension. Pregnancy is sometimes described as contraindicated in these women.

Treatment

Treatment of  secondary pulmonary hypertension is determined by whether the PH is arterial, venous, hypoxic, thromboembolic, or miscellaneous. The treatment is to optimize left ventricular function by the use of diuretics,digoxins, blood thinners, or to repair/replace the mitral valve or aortic valve. Patients with left heart failure or hypoxemic lung diseases (groups II or III pulmonary hypertension) should not routinely be treated with vasoactive agents including prostanoids, phosphodiesterase inhibitors, or endothelin antagonists, as these are approved for the different condition called pulmonary arterial hypertension. To make the distinction, doctors at a minimum will conduct cardiac catheterization of the right heart, echocardiography, chest CT, a six-minute walk test, and pulmonary function testing. Using treatments for other kinds of pulmonary hypertension in patients with these conditions can harm the patient and wastes substantial medical resources.

High dose calcium channel blockers are useful in only 5% of IPAH patients who are vasoreactive by Swan-Ganz catheter. Unfortunately, calcium channel blockers have been largely misused, being prescribed to many patients with non-vasoreactive PAH, leading to excess morbidity and mortality. The criteria for vasoreactivity have changed. Only those patients whose mean pulmonary artery pressure falls by more than 10 mm Hg to less than 40 mm Hg with an unchanged or increased cardiac output when challenged with adenosine, epoprostenol, or nitric oxide are considered vasoreactive. Of these, only half of the patients are responsive to calcium channel blockers in the long term.

Vasoactive substances

Many pathways are involved in the abnormal proliferation and contraction of the smooth muscle cells of the pulmonary arteries in patients with pulmonary arterial hypertension. Three of these pathways are important since they have been targeted with drugs — endothelin receptor antagonists, phosphodiesterase type 5 (PDE-5) inhibitors, and prostacyclin derivatives.

Prostaglandins

Prostacyclin (prostaglandin I₂) is commonly considered the most effective treatment for PAH. Epoprostenol (synthetic prostacyclin) is given via continuous infusion that requires a semi-permanent central venous catheter. This delivery system can cause sepsis and thrombosis. Prostacyclin is unstable, and therefore has to be kept on ice during administration. Since it has a half-life of 3 to 5 minutes, the infusion has to be continuous, and interruption can be fatal. Other prostanoids have therefore been developed. Treprostinil can be given intravenously or subcutaneously, but the subcutaneous form can be very painful. An increased risk of sepsis with intravenous Remodulin has been reported by the CDC. Iloprost is also used in Europe intravenously and has a longer half life. Iloprost was the only inhaled form of prostacyclin approved for use in the US and Europe, until the inhaled form of treprostinil was approved by the FDA in July 2009.

Endothelin receptor antagonist

The dual (ET_A and ET_B) endothelin receptor antagonist bosentan was approved in 2001. Sitaxentan (Thelin) was approved for use in Canada, Australia, and the European Union, but not in the United States. In 2010, Pfizer withdrew Thelin worldwide because of fatal liver complications. A similar drug, ambrisentan is marketed as Letairis in the U.S. by Gilead Sciences.

Phosphodiesterase type 5 inhibitors

The U.S. FDA approved sildenafil, a selective inhibitor of cGMP specific phosphodiesterase type 5 (PDE5), for the treatment of PAH in 2005. It is marketed for PAH as Revatio. In 2009, they also approved tadalafil, another PDE5 inhibitor, marketed under the name Adcirca. PDE5 inhibitors are believed to increase pulmonary artery vasodilation, and inhibit vascular remodeling, thus lowering pulmonary arterial pressure and pulmonary vascular resistance.

Tadalafil is taken orally, as well as sildenafil, and it is rapidly absorbed (serum levels are detectable at 20 minutes). The T_1/2 (biological half-life) hovers around 17.5 hours in healthy subjects. Moreover, if we consider pharmacoeconomic implications, patients that take tadalafil would pay ⅔ of the cost of sildenafil therapy. However, there are some adverse effects of this drug such as headache, diarrhea, nausea, back pain, dyspepsia, flushing and myalgia.

Activators of soluble guanykate cyclase

Soluble guanylate cyclase (sGC) is the intracellular receptor for NO. As of April 2009, the sGC activators cinaciguat and riociguat were undergoing clinical trials for the treatment of PAH.

Surgical

Atrial septostomy is a surgical procedure that creates a communication between the right and left atria. It relieves pressure on the right side of the heart, but at the cost of lower oxygen levels in blood (hypoxia).Lung transplantation cures pulmonary arterial hypertension, but leaves the patient with the complications of transplantation, and a post-surgical median survival of just over five years.

Pulmonary thromboendarterectomy (PTE) is a surgical procedure that is used for chronic thromboembolic pulmonary hypertension. It is the surgical removal of an organized thrombus (clot) along with the lining of the pulmonary artery; it is a very difficult, major procedure that is currently performed in a few select centers.

Monitoring

Established clinical practice guidelines dictate the frequency of pulmonary nodule evaluation and surveillance, patients are normally monitored through commonly available tests such as:

.