11 Cpex testing detects subclinical cardiac limitation to exercise in early stage ckd

Abstract

INTRODUCTION AND AIMS: Effort tolerance is impaired in end stage kidney disease. Peak oxygen uptake (VO2peak) is a powerful predictor of survival in haemodialysis patients. A low percent predicted oxygen uptake at the anaerobic threshold (VO2AT) has also been associated with excess mortality in patients undergoing kidney transplantation. Data on effort tolerance and cardiovascular disease in early CKD are very sparse though it is well recognized that cardiovascular mortality begins to increase at an eGFR of about 75ml/min/m2. The aim of this study is to understand whether subclinical cardiac limitation, as measured by VO2peak and VO2AT, begins early in CKD independently of conventional cardiovascular risk factors. METHODS: This study examined effort tolerance, cardiac structure and function in 60 patients with CKD (stages 2 to 5) without known cardiovascular disease or diabetes. All patients underwent a cardiopulmonary exercise bicycle test using an individualised ramp protocol. Myocardial ischaemia was excluded by exercise stress echocardiography or 99m technetium tetrofosmin single photon electron computed tomography. Lung disease was excluded by formal lung function testing. Cardiac magnetic resonance imaging without gadolinium contrast was used to assess cardiac function and structure. The Kruskall Wallis test was used to compare the difference in mean values across stages of CKD. Correlation coefficients were measured to look for trends between continuous variables. RESULTS: Table 1 shows the baseline characteristics per CKD stage. Percent predicted peak VO2 was positively associated with eGFR (r=0.358, p=0.007) even after correction for age and haemoglobin (p=0.005). NT pro-BNP was negatively associated with eGFR (r=-0.586, p=0.001), even after similar correction (p<0.001). The percent predicted VO2 at the anaerobic threshold was also negatively associated with worsening eGFR (r=0.282, p=0.039). Exercise capacity (VO2AT) was negatively associated with increasing LV mass (r=-0.382, p=0.006) but there was no significant association with left ventricular (LV) size, ejection fraction or global longitudinal strain. CONCLUSIONS: Effort tolerance falls from the earliest stages of CKD in association with a progressive increase in LV mass and NT pro-BNP. This is the first study to examine exercise capacity in patients with early stage CKD in whom coronary artery disease has been excluded, and further study is needed to confirm whether the reduction in exercise capacity is a reflection of diastolic impairment and myocardial fibrosis that characterize end-stage kidney disease. (Table Presented).