The effects of growth hormone therapy on heart rate variability in adults with growth hormone deficiency

Background. Growth hormone (GH) deficiency is associated with increased cardiovascular morbidity and mortality. Abnormalities in heart rate variability (HRV) (such as decreased cardiac sympathetic activity), which is a marker of cardiac autonomic tone, have been found in patients with GH deficiency. Objective: The purpose of this study was to investigate the effects of GH therapy on HRV in adults with GH deficiency. Methods: Adult patients with GH deficiency were eligible. HRV measurements were obtained by 24-hour measurements from Holter electrocardiography before and after 6 months of GH therapy in adult patients with GH deficiency. The following time domain parameters of HRV were calculated: the SD of the normal-to-normal (NN) interval (SDNN), the SD of the average NN interval (SDANN), the square root of the mean squared differences (RMSSD), and the proportion derived by dividing the number of interval differences of successive NN intervals >50 ms (NN50) by the total number of NN intervals (PNN50). Results: A total of 21 patients (7 men, 14 women; mean age, 46.0 +/- 11.2 years) were enrolled. Thirteen patients had panhypopituitarism and 8 had normal adrenocorticotropic hormone secretion. At the end of 6 months of GH therapy, the mean values of the sympathetically influenced parameters SDNN (before GH treatment, 134.5 +/- 6.0 ms; after GH treatment, 118.5 +/- 8.0 ms) and SDANN (before GH treatment, 121.2 +/- 6.0 ms; after GH treatment, 96.2 +/- 9.1 ms) decreased significantly (P < 0.05), but the parasympathetically influenced parameters RMSSD and PNN50 did not differ significantly from baseline. The mean heart rate and ventricular premature beats were not significantly different from baseline after GH therapy. Conclusions: In this patient population, cardiac sympathetic tone was increased, without an obvious arrhythmogenic effect, after 6 months of GH therapy.