Long-term Treatment for Pulmonary Artery Hypertension
Current therapy helps slow disease progression, increase functional ability and extend life in patients with this rare condition.
Pulmonary artery hypertension (PAH) is a rare condition in which the arteries within the lungs narrow and stiffen. As result, blood flowing from the heart meets resistance when it enters the pulmonary artery causing an increase in blood pressure within the vessel. As a consequence, the heart’s right pumping chamber (right ventricle) weakens and enlarges from the exertion of forcing blood into the noncompliant arteries. This leads to a potentially fatal condition known as right side heart failure.
Although the early symptoms of PAH—mainly shortness of breath during activity—are usually mild and easily over looked, the disease becomes more debilitating as it advances. PAH has a poor prognosis; the average life expectancy without treatment is 2.8 years from the time of diagnosis.
PAH is associated with a number of seemingly unrelated conditions such as connective tissue disease (lupus or scleroderma), HIV infection, and past use of certain weight loss medications. There is also an inherited form of the disease. Many times the origins of the condition are unknown. Regardless of the underlying factors, the common denominator of the disease is damage to the lining of the arteries in the lungs that causes an abnormal growth of cells on the interior surface of the vessels. Over time, this proliferation of cells progressively reduces the size of the arterial opening and obstructs blood flow to the lung tissue.
The current research into treatments for PAH has identified imbalances in a group of compounds that control the relaxation and constriction of the vessels, and the growth of the cells that make up the arterial lining. So far, three classes of drugs targeting these interactions have been approved by the Food and Drug Administration (FDA). These include: prostacyclin analogs and endothelin receptor antagonists, both of which dilate the blood vessels and help prevent overgrowth of the arterial lining; and phosphodiesterase type 5 (PDE-5) inhibitors, which increase nitric oxide in the blood and promote the relaxation of the arteries.
Because PAH is a rapidly progressing disease with a fatal outcome, there has been an urgency to bring these new therapies to patients as early as possible. Therefore, much of what is known about these drugs comes from small, uncontrolled studies lasting only a few months. With the goal of clarifying the long-term strengths and weakness of the approved PAH medications, researchers examined the results of studies on these drugs conducted between 1990 and 2010 that lasted more than one year and included at least 50 subjects. Their review article, published in the February 21, 2011 issue of the Journal of the American College of Cardiology focused on three key outcomes: exercise capacity; direct measurement of pressures in the pulmonary artery and vascular stiffness; and length of survival following diagnosis.
The analysis concluded that all three types of drugs produce clear benefits, especially in increasing exercise tolerance and lowering blood pressure in the pulmonary arteries. Both of these factors are linked to longer survival. However, the answer to whether long-term therapy with these drugs directly extended life was less definitive. The inconclusiveness was due primarily to the relatively short follow up periods of most of the studies. PAH treatment does appear to help patients live longer compared to predictions based on historical data collected on the disease, however.
The confirmation that current medical therapy for PAH can slow the progression of the disease, increase patients’ functional ability, and probably extend life is an important milestone. Researchers reiterate however, that long-term, properly controlled trials are still needed to refine and extend PAH therapy.
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