There has been considerable research into the causes of pulmonary arterial hypertension (PAH) over the past decade, and recent advances in our understanding of the mechanisms behind the development of the disease have led to major progress in treatment options for patients. While there is currently no cure for the disease, modern advanced PAH therapies can markedly improve a patient's symptoms and slow the rate of clinical deterioration. Research into therapies for PAH continues, and as clinical experience continues to grow, it is important to be aware of developments and recommendations in the field, including international guidelines (Fourth World Symposium, Dana Point Classification, 2008) and regional guidelines such as those provided by the European Society of Cardiology and European Respiratory Society (ESC/ERS), the American College of Chest Physicians (ACCP) and the American College of Cardiology Foundation and American Heart Association (ACCF/AHA).
The aims of treatment in patients with PAH are several-fold and range from symptomatic relief to improvement in the physical limitations imposed by their disease (such as improving functional class and delaying disease progression).
The management of PAH is complex and involves the use of a range of treatment options, including supportive and general measures, the assessment of vasoreactivity, and the optimal use of different drugs and interventions. Treatment options for PAH can be broadly broken down into four main categories:
General measures aim to limit any potentially deleterious effects of the patient's external circumstances on their PAH disease. These recommendations are largely based on expert opinion rather than controlled trials, and include measures such as avoiding pregnancy, prevention and prompt treatment of chest infections, and awareness of the potential effects of altitude.
A range of treatment approaches have been shown to provide some degree of symptomatic benefit to PAH patients. However, there is no evidence that they have an effect on the disease process or prognosis. Such measures include:
- Oxygen: For patients with dyspnoea associated with PAH, supplemental oxygen provides symptomatic relief and improves patient comfort, although there is no consistent evidence supporting any long-term benefit.1 It is generally considered important to maintain oxygen saturation above 90% at all times, and oxygen may be indicated in some patients
- Anticoagulants: clinical data supportive of the use of anticoagulant therapy in PAH are limited; however, improved survival has been reported with oral anticoagulation in patients with idiopathic PAH (IPAH),5,6 and because of high risk of in situ thrombosis within the small pulmonary arteries, there is a rationale for the use of oral anticoagulants in PAH patients.
- Diuretics: there are no randomised controlled trials (RCTs) of diuretics in PAH, however clinical experience shows clear symptomatic benefit in fluid-overloaded patients with decompensated right heart failure associated with PAH
- Calcium channel blockers (CCBs): CCBs may be of benefit in a small proportion of patients with PAH. Suitable patients are detected by acute vasoreactivity testing during right heart catheterisation. A positive vasoreactive response indicating potential suitability for CCB therapy is shown by around 10% of patients,1 and approximately 7% of these patients have a sustained response. Patients who respond to vasoreactivity testing and are subsequently treated with CCBs need regular assessment and repeat testing, as the vasoreactivity status may change.
PAH-specific therapies have been developed specifically to target one of three major pathways known to be involved in the development of PAH and have, to varying degrees, been shown to affect the disease process:
- Endothelin receptor antagonists (ERAs): endothelin is implicated in the pathogenesis of PAH through its actions on the pulmonary vasculature. Endothelin is elevated in patients with PAH and levels are directly related to disease severity and prognosis. Endothelin receptor antagonists are oral treatments that act by blocking the binding of endothelin to either one (single antagonist) or both (dual antagonist) of its receptors. Clinical trials have shown that treatment with ERAs has a beneficial effect on exercise capacity, WHO Functional Class (FC), haemodynamics and time to clinical worsening in patients with PAH.
- Prostacyclin therapy: synthetic prostacyclins and prostacyclin analogues act by helping to correct the deficiency of endogenous prostacyclin seen in patients with PAH. The clinical use of prostacyclins in patients with PAH has been extended by the synthesis of more stable anologs for intravenous infusion, as well as those that can be given by subcutaneous infusion or by inhalation.
- Phosphodiesterase-5 (PDE-5) inhibitors: these oral agents act on the nitric oxide (NO) pathway to induce vasodilation and also have antiproliferative effects on vascular smooth muscle cells. Clinical trials have shown that treatment with PDE-5 inhibitors has a beneficial effect on exercise capacity, haemodynamic parameters, and symptoms in patients with PAH.
For patients with severe PAH, for example those in WHO FC IV, who do not respond satisfactorily to treatment with advanced therapies, surgery may be the only option.
- Balloon atrial septostomy: atrial septostomy creates a small hole between the right and left atria, allowing blood to pass from the right atrium directly to the left, bypassing the restricted pulmonary circulation. This aims to increase the left ventricular preload and the systemic blood flow (cardiac output), resulting in an improved systemic oxygen transport, and to reduce the pressure and therefore the stress on the right heart, but at the cost of lower oxygen levels in the blood (hypoxaemia).
- Transplantation: lung transplantation or heart and lung transplantation are considered for patients who have failed medical therapy. Given the time needed to complete a transplant evaluation and the time spent on the transplant list awaiting suitable organs, it is currently recommended that patients with WHO FC III or IV symptoms (see section: Assessing the severity of PAH) should be referred for evaluation for transplantation while their response to therapy is being evaluated in order to avoid delays.1,20 Recent long-term survival studies have reported 10-year post-transplant survival rates of 42-66% in patients with IPAH and 70% in other groups of PAH patients.