Heart rate response during 6-minute walking testing predicts outcome in operable chronic thromboembolic pulmonary hypertension

Background: Six-minute walk test (6MWT) is routinely performed in chronic thromboembolic pulmonary hypertension (CTEPH) before pulmonary endarterectomy (PEA). However, the clinical relevance of heart rate response (Delta HR) and exercise-induced oxygen desaturation (EID) during 6MWT is remaining unknown. Methods: Patients undergoing PEA in our center between 03/2013-04/2014 were assessed prospectively with hemodynamic and exercise parameters prior to and 1 year post-PEA. Patients with symptomatic chronic thromboembolic disease (mean pulmonary artery pressure (mPAP) <25 mmHg) and clinical relevant obstructive pulmonary disease were excluded. The following definitions were used: Delta HR = (peak HR - resting HR), percent heart rate reserve (HRR) = (peak HR - rest HR)/(220 - age - rest HR) x 100 and EID= SpO(2) <= 88 %. Results: Thirty-seven patients (of 116 patients screened) with mPAP of 43.2 +/- 8.7 mmHg, pulmonary vascular resistance (PVR) of 605.5 +/- 228.7 dyn* s/cm(5), cardiac index (CI) of 2.4 +/- 0.5 l/min/m(2) and a 6MWT-distance of 404.7 +/- 148.4 m and a peak VO2 of 12.3 +/- 3.4 ml/min/kg prior to PEA were included. Baseline Delta HR during 6MWT was significantly associated with PVR 1 year post-PEA using linear regression analysis (r = 0.43, p = 0.01). Multivariate analysis indicated an association of HRR during 6MWT and residual PH with a hazard ratio of 1.06 (95 % Confidence interval for hazard ratio 0.99-1.14, p = 0.08). EID was observed commonly during 6MWT but no correlations to outcome parameters were found. Conclusions: This is the first prospective study to describe an association of Delta HR during 6MWT with pulmonary hemodynamics 1 year post-PEA. Our preliminary results indicate that HRR derived from 6MWT is of clinical significance. EID was commonly observed, albeit failed as a significant prognostic factor