Six-Minute Walk Test in Scleroderma-Associated Pulmonary Arterial Hypertension: Are We Counting What Counts?

Abstract

> Everything that can be counted does not necessarily count; > > Everything that counts cannot necessarily be counted > > —Albert Einstein Systemic scleroderma (SSc) is a multisystem disease with protean manifestations, but pulmonary involvement is the leading cause of mortality. Interstitial lung disease (ILD) and pulmonary arterial hypertension (PAH) are 2 serious pulmonary complications of SSc that commonly cause clinical symptoms of dyspnea and exercise intolerance, can be associated with severe functional limitation, and often have a poor prognosis for longterm survival. SSc-associated PAH (SSc-PAH) is a serious disease of progressive pulmonary vascular obliteration characterized by persistent elevation of pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR). Untreated SSc-PAH usually results in right-sided heart failure and high risk of death. The average survival in SSc patients diagnosed with PAH is 1–2 years1–3. Patients with SSc-PAH have a worse prognosis than most other PAH patients, including primary or idiopathic PAH (IPAH)4,5. Many new PAH-specific therapies have been studied and are available for the treatment of patients with SSc-PAH. These include prostacyclin derivatives (intravenous epoprostenol, subcutaneous or intravenous treprostinil), a novel family of oral endothelin receptor antagonists (bosentan, sitaxsentan, and ambrisentan), as well as an oral phosphodiesterase type 5 inhibitor (sildenafil)6. Treatment of PAH patients, including SSc-PAH, with these PAH-specific medications is associated with subjective and objective clinical benefit. Given that PAH is a disease of disturbed pulmonary hemodynamics, reductions in mean PAP and PVR, as well as improved right ventricular (RV) function, as evidenced by increased cardiac output, have been expectations of PAH therapy. However, repeated assessment of pulmonary hemodynamics by invasive rightheart catheterization is not feasible, and not necessarily indicated. Doppler echocardiographic assessment of RV systolic pressure (RVSP) is commonly used as a surrogate for systolic PAP. Moreover, other echo parameters, such … See Limitations to the 6-minute walk test in interstitial lung disease and pulmonary hypertension in scleroderma, page 330 Address reprint requests to Dr. S. Mehta, Division of Respirology, London Health Sciences Center-Victoria Hospital, Room E2.623, Professional Building, 800 Commissioner’s Road East, London, Ontario N6A 5W9, Canada. E-mail: sanjay.mehta{at}lhsc.on.ca