Impact of physical activity on surrogate markers of cardiovascular disease in the haemodialysis population

Background and hypothesis

The haemodialysis population is sedentary with substantial cardiovascular disease risk. In the general population, small increases in daily step count associate with significant reductions in cardiovascular mortality. This study explores the relationship between daily step count and surrogate markers of cardiovascular disease, including left ventricular fraction (LVEF) and native T1 (a marker of diffuse myocardial fibrosis), within the haemodialysis population. 

Methods

 This was a post-hoc analysis of the association between daily step count and metabolic equivalent of task (MET) and prognostically important cardiac magnetic resonance imaging (CMR) parameters from the CYCLE-HD study (ISRCTN11299707). Unadjusted linear regression and multiple linear regression adjusted for age, body mass index, dialysis vintage, haemoglobin, hypertension and ultrafiltration volume were performed. Significant relationships were explored with natural cubic spline models with four degrees of freedom (five knots). 

Results 

107 participants were included; 56.3 ± 14.1 years, 79 (73.8%) males. Median daily step count was 2558 (IQR 1054–4352). There were significant associations between: steps and LVEF (β = 0.292; P = 0.009); steps and native T1 (β = -0.245; P = 0.035). Further modelling demonstrated most of the increase in LVEF occurred up to 2,000 steps per day and there was an inverse dose-response relationship between steps and native T1, with the most pronounced reduction in native T1 between ∼2,500 and 6,000 steps per day. 

Conclusions

 These results suggest an association between daily step count and parameters of cardiovascular health in the haemodialysis population. These findings support the recommendations for encouraging physical activity but they are not the justification. Further research should evaluate whether a simple physical activity intervention improves cardiovascular outcomes in individuals receiving maintenance haemodialysis.