Pulmonary hypertension (PH) is a complicated, and potentially life threatening, disease that is defined as having a mean pulmonary artery pressure greater than or equal to 25 mm Hg at rest. It was first described in medical literature in 1891 by a German physician, Ernst von Romberg, who mentioned pulmonary vascular stenosis in an autopsy. While it is considered a rare disease, being seen in only 1-2 people out of every million across the United States and Europe, those of us practicing cardiac surgery at programs with advanced heart and lung failure patients will likely see a lot of this disease.
While there are several methods to gain information in order to diagnose PH, such as chest X-ray, echocardiogram, and EKG, the gold standard remains right heart catheterization. Once diagnosis is made, it is important that patients establish care with an advanced lung disease specialist, as PH can lead to heart failure, respiratory failure requiring lung transplant, and death.
PH has been divided into five different groups by the World Health Organization (WHO), based on etiology. Group 1, or pulmonary arterial hypertension, is caused by processes that cause thickening and/or stiffening of the walls of the pulmonary arteries. This narrows the vessels and, in turn, causes elevated pressures in the pulmonary arterial vasculature. Contributors to this group include idiopathic causes, genetic predisposition, drug and toxin exposure, and disease processes such as connective tissue disorders, HIV, and portal hypertension. Group 2 is the most common type of PH, and is caused by diseases of the left heart. Contributing diseases include coronary artery disease, hypertension, valvular disease of the heart, and advanced age. Group 3 PH is caused by diseases of the lungs, most commonly chronic obstructive pulmonary disease, and idiopathic pulmonary fibrosis. As these diseases progress, the destruction of the lung causes a gradual loss of blood vessels causing hypoxia which, in turn, causes elevation of pulmonary artery pressures. Group 4 is also known as chronic thromboembolic pulmonary hypertension (CTEPH). It is defined as a mean pulmonary artery pressure greater than or equal to 25 mm Hg that is persistent for greater than 6 months despite anticoagulation therapy. This category is unique in that it is caused by the presence of the thrombi themselves which form a physical barrier in the pulmonary arteries, and in the fact that it is potentially curable through pulmonary artery embolectomy surgery. The last type of PH is group 5 which is caused by unclear mechanisms. This is often related to disease processes that are not clearly understood, such as sarcoidosis, blood diseases such as sickle cell, and metabolic diseases such as thyroid disease.
Treatment of PH varies according to which group the disease belongs to. Generally, the only type that can be treated with medicine is Group 1. There are now several drugs that can be given to treat the narrowed pulmonary vasculature. Phosphodiasterase-5 inhibitors, such as sildenafil, work by relaxing pulmonary vascular smooth muscle, thus, dilating the blood vessels. Prostanoids, such as inhaled epoprostenol, are naturally occurring prostaglandins that dilate the pulmonary as well as the systemic arteries. Endothelin receptor antagonists, such as bosentan and ambrisentan, reduce endothelian in the blood. Endothelin causes constriction of blood vessels, and it is produced in increased amounts in patients with PH.
Treatment for Groups 2, 3 and 5 PH often involves treating the underlying disease process. When this no longer becomes effective, heart and or lung transplant surgery is the only remaining treatment. As previously mentioned, the treatment of Group 4 PH is unique because pulmonary thromboendarterectomy surgery can be performed on many patients. If the clot burden is removed from the lungs, this can be a curative surgery.
PH is a multi-faceted and complicated disease process in which many advances in therapy have been made. Practices with advanced heart and lung disease programs are likely very familiar with this disease already, however, it was my hope to provide a brief summary for those who aren’t able to take care of these patients on a regular basis.