The influence of growth hormone replacement on heart rate variability in adults with growth hormone deficiency

OBJECTIVE Growth hormone (GH) deficiency is associated with increased cardiovascular morbidity and mortality. Abnormalities in heart rate variability (HRV), a surrogate marker of cardiac autonomic tone, have also been found in untreated growth hormone deficient (GHD) patients. Similar abnormalities have been found in patients with complications postmyocardial infarction. DESIGN AND MEASUREMENTS This study was designed to investigate whether GH treatment leads to normalization of cardiac autonomic tone, HRV measurements were obtained from 15 minute resting ECG recordings in 11 untreated adult GHD patients (7 females; mean age 39.2 years), 10 GHD patients (6 females; mean age 46.2 years) reCENving GH replacement (mean duration, 52.7 months) and 12 healthy controls (7 females; mean age 44.6 +/- 2.9 years) who were all of similar age, weight and BMI. The untreated GHD patients were then commenced on GH and HRV measurements repeated after 3 and 6 months of treatment. RESULTS In accord with our previous findings, HRV analysis using Fast Fourier Transform (FFT) showed a distinct pattern of abnormality in GHD patients compared with controls. Specifically, there was an increase in nHF power (P = 0.04) and a reduction in nLF power (P = 0.04) (representing parasympathetic and sympathetic activity, respectively), a reduction in nVLF power (P = 0.03) and a 50% reduction in LF/HF ratio (P = 0.02) (a measure of sympathovagal balance) in GHD patients when compared with controls. HRV results in patients who have been on long-term GH replacement were indistinguishable from controls. After 3 months GH replacement in the untreated GHD patient group, nVLF power had increased by 28% (P = 0.03) at 3 months and this was sustained at 6 months. However, no significant changes in LF and HF power were seen. CONCLUSIONS These results suggest that abnormalities of the cardiac autonomic system in GHD patients may be correctable. Longer duration of prospective follow-up will be required to determine at what time point improvements in the other frequency bands occur.