Submaximal exercise testing may be superior to the 6-min walk test in assessing pulmonary arterial hypertension disease severity

Introduction: Submaximal exercise testing (SET) assesses functional exercise capacity in pulmonary arterial hypertension (PAH) patients and provides additional physiologic information compared with the 6-min walk test (6MWT). The relative correlations of the 6MWT and SET using SHAPE-HF (TM) with other markers of PAH severity, particularly echocardiogram (ECHO)-derived mean pulmonary artery pressure (MPAP), have not been investigated. Objectives: (i) Examine the correlation between SHAPE measures with the 6-min walk distance (6MWD), and (ii) Compare SHAPE parameters and the 6MWD to clinical measures of PAH severity. Methods: Fifty-five consecutive group 1 PAH outpatients were evaluated in a single pulmonary hypertension referral center from March 2011 to June 2012. Data collected: World Health Organization (WHO) functional class (FC), brain natriuretic peptide (BNP), ECHO, 6MWD and SHAPE results. Data are reported using mean +/- standard deviation and Spearman correlation coefficients (r). Results: Nine patients were excluded. Of the 46 remaining patients, 78% were women and the average age was 61 +/- 13 years. PAH characteristics: WHO FC III-IV 48%; idiopathic PAH 52%; BNP 198 +/- 277 pg/mL; 6MWD 399 +/- 97 m; ECHO right atrial pressure (RAP) 7 +/- 4, pulmonary artery systolic pressure (PASP) 63 +/- 29 and MPAP 45 +/- 17 mmHg. SET with SHAPE results: mean partial pressure of end-tidal (P-ET) CO2 31 +/- 6 mmHg at end-exercise; ventilatory efficiency (VE/VCO2) 43 +/- 16. Significant correlations were found between the 6MWD and SHAPE variables: VE/VCO2 (r = -0.57, P < 0.0001) and end-exercise PETCO2 (r = 0.42, P = 0.004). VE/VCO2 correlated with WHO FC, BNP, RAP, MPAP and PASP and 6MWD only with WHO FC, BNP and PASP. Conclusion: SHAPE outperformed 6MWD in comparison with other measures of PAH disease severity.