Effects of Early Hormone Replacement Therapy on Risk Factors for Sudden Cardiac Death: Autonomic Function and Ventricular Repolarization Heterogeneity ( A KEEPS Ancillary Study)

The parent study KEEPS, will be a randomized, placebo-controlled double blinded, prospective trial with two active groups and one placebo group. Only patients enrolled in KEEPS will be invited to participate in this ancillary study.Duration of the KEEPS study will be for 4 years after randomization for each study subject, with assessment of the primary endpoint, carotid CIMT, twice at baseline, 12, 24, 36 and 48 months. Ancillary to the KEEPS study, patients will undergo holter monitoring at baseline, 24 and 48 months.Data will be analyzed after 24 and 48 months (corresponding to data analysis of the primary endpoints.) Holter monitors will be put on during the scheduled KEEPS visits, will be worn for 24 hours and will be returned the following day. Effects of estrogen on heart rate variability (HRV) and repolarization parameters will be evaluated, and also correlated with clinical, quality of life, sleep and mood information gathered through the parent study. Anticipated enrollment from the parent study at this site is 90 study subjects. This ancillary does not involve the use of drugs or investigational devices.