Effect of Postmenopausal Hormone Replacement Therapy on Heart Rate Variability

Minimal research has addressed effects of postmenopausal hormone replacement therapy (HRT) on heart rate variability (HRV), a measure of cardiovascular autonomic balance and a predictor of cardiac morbidity/mortality. Using an exploratory, pre-test/post-test design to describe HRV in postmenopausal women (PMW) before/after six weeks of HRT, twenty-four Black (n=15) and White (n=9) women, (mean age=55±4 years), were recruited from two primary care clinics (n=20) and one church population (n=4) in a large urban midsouth community. Cardiovascular risk factors for the sample included chronic illnesses of DM (n=8), HRT (n=11), both DM and HRT (n=4), smoking (n=9), non-exercise (n=11), and obesity quantified by sample mean BMI (mean=28±7.5). Twenty-four hour Holter monitoring and HRV analyses were done at first visit and following six weeks of oral self-administration of PremPro™ (estrogen: 0.625 mg; medroxyprogesterone acetate: 2.5 mg). PMW demonstrated lower, but normal, HRV mean values than those for healthy female controls (n=118; age=35.6±11.8 years), Mean values were within normal limits established for the laboratory. Paired t-tests with significance at p? .10 demonstrated total group improvement for LowHertz (p=.06) and pNN50 (p=.10). HRV values improved for PMW with selected risk factors, consistently for values of TotalHertz and HighHertz, and, to a lesser extent, for values of PNN50 and rMSSD. Decreases in SDNN and SDANN were unexpected and merit further investigation. White PMW showed no significant differences before/after HRT ; Black PMW demonstrated significant improvement in TotalHertz (p=.01), LowHertz (p=.03), HighHertz (p=.01), and rMSSD (p=.05. Correlational analyses of relationship for pre-/post-test HRV values to CV risk factors demonstrated significant (p?.10) relationships across HTN and years of menopause. Pre-/post-test significant differences were found for PMW with HTN for TotalHertz (p=.08), HighHertz (p=.04), pNN50 (p=.03), and rMSSD (p=.006), and PMW * 9 years menopausal for TotalHertz (p=.07), LowHertz (p=.01), pNN50 (p=.08), and SD (p=.07). Previous research findings suggested that PMW not on estrogen have a higher sympathetic mediation of autonomic function. Blacks and PMW \u3c 55 years of age, following six-weeks of HRT, demonstrated a mediation in sympathetic/parasympathetic balance in post-test values. Because the study was exploratory with numerous analyses at p-value?.10, findings must be interpreted with caution