Relationships between sympathetic markers and heart rate thresholds for cardiovascular risk in chronic heart failure

Background: Results of recent clinical trials have shown that in heart failure (HF) heart rate (HR) values > 70 beats/minute are associated with an increased cardiovascular risk. No information is available on whether the sympathetic nervous system is differently activated in HF patients displaying resting HR values above or below this cutoff. Methods: In 103 HF patients aged 62.7 ± 0.9 (mean ± SEM) years and in 62 heathy controls of similar age we evaluated muscle sympathetic nerve traffic (MSNA, microneurography) and venous plasma norepinephrine (NE, HPLC assay), subdividing the subjects in different groups according to their resting clinic and 24-h HR values. Results: In HF progressively greater values of clinic or 24-h HR were associated with a progressive increase in both MSNA and NE. HR cutoff values adopted in large scale clinical trials for determining cardiovascular risk, i.e., 70 beats/minute, were associated with MSNA values significantly greater than the ones detected in patients with lower HR, this being the case also for NE. In HF both MSNA and NE were significantly related to clinic (r = 0.92, P < 0.0001 and r = 0.81, P < 0.0001, respectively) and 24-h (r = 0.91, P < 0.0001 and r = 0.79, P < 0.0001, respectively) HR. The behavior of sympathetic markers described in HF was specific for this clinical condition, being not observed in healthy controls. Conclusions: Both clinic and 24-h HR values greater than 70 beats/minute are associated with an increased sympathetic activation, which parallels for magnitude the HR elevations. These findings support the relevance of using in the therapeutic approach to HF drugs exerting sympathomoderating properties.