Limited reliability of heart rate as a sympathetic marker in chronic kidney disease

BACKGROUND: Chronic kidney disease (CKD) is characterized by a pronounced sympathetic overactivity as documented by the marked increase in muscle sympathetic nerve traffic (MSNA) and in plasma norepinephrine reported in this condition. Whether and to what extent in CKD heart rate (HR) reflects the adrenergic overdrive remains undefined. It is also undefined the relative validity of the different adrenergic markers in reflecting renal dysfunction. MATERIALS AND METHODS: In 82 CKD patients, aged 58.4 ± 1.1 years (mean ± SEM), we measured resting clinic blood pressure, HR (EKG), venous NE (HPLC) and MSNA (microneurography). The same measurements were made in 24 age-matched healthy controls. RESULTS: HR was significantly greater in CKD than in controls (74.0 ± 1.1 versus 68.2 ± 1.8 bpm, P < 0.02) and significantly directly related to the elevated plasma norepinephrine and MSNA values (r = 0.22 and 0.39, P < 0.05 and <0.0003, respectively). Both MSNA and plasma norepinephrine were significantly and inversely related to the estimated glomerular filtration rate. The correlation did not achieve statistical significance for HR. Similar results were obtained examining the relationships with left ventricular mass index. CONCLUSION: Our data show that in CKD not only peripheral but also cardiac sympathetic drive is markedly enhanced and HR can be regarded as a marker of the adrenergic overdrive characterizing this condition. The reliability of HR as sympathetic marker appears to be limited, however, this variable being unable to closely reflect, at variance from MSNA and plasma norepinephrine, the interindividual differences in renal dysfunction and the accompanying structural cardiovascular alterations.