6-minute walk ‘not an accurate surrogate’ in systemic sclerosis-associated PAH

By Eleanor McDermid, Senior medwireNews Reporter

The 6-minute walk distance (6MWD) of patients with systemic sclerosis-associated pulmonary arterial hypertension (SSc-PAH) is not a suitable marker for tracking treatment-related haemodynamic changes, say researchers.

Although patients’ 6MWD was associated with their baseline cardiac output, changes in these measures did not correlate during follow-up, report David Launay (Université de Lille, France) and colleagues.

“Altogether, our data suggests 6MWD has a limited utility to assess haemodynamic severity and evolution under treatment in SSc-PAH”, the team writes in the Annals of the Rheumatic Diseases.

At baseline, before treatment commenced, 6MWD was significantly associated with all haemodynamic parameters, with the association with cardiac output remaining significant after adjusting for confounders.

The researchers studied two prospective patient cohorts. In the cohort of 83 French patients, baseline functional class was also independently associated with 6MWD, together with cardiac output explaining 28% of the variance in 6MWD.

In the second cohort – of 332 US patients entered into randomised clinical trials – age, gender, body mass index, mean pulmonary arterial pressure (mPAP) and cardiac output were independently associated with 6MWD, together explaining 16% of the variance.

In all, 68% of the US patients and 88% of the French cohort started on PAH-specific treatment, and were followed up after 12 weeks and an average of 27 weeks, respectively.

Although there were some associations between haemodynamic variables and 6WMD at the time of follow-up, changes in haemodynamic variables across the follow-up period were not reflected by changes in 6MWD.

However, associations were present in the 32% of the US cohort that received placebo, with changes in mPAP and mean right atrial pressure significantly correlating with changes in 6MWD.

Launay et al suggest that the difference between treated and untreated patients could be because “PAH-specific treatments also improve the 6MWD by extra-‘pulmonary vascular’ mechanisms.”

They say that their findings raise “concerns about the relevance of 6MWD as an outcome measure in SSc-PAH, beyond the potential inherent value of its increase.”

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