We will investigate whether standard and newer indices of heart rate variability (HRV) enhance the prediction of clinical and functional outcomes in the Cardiovascular Health Study (CHS). The CHS, an NIH-sponsored population-based longitudinal study of the risk factors for coronary heart disease and stroke in 5,201 men and women aged 65 years and older, includes ambulatory ECG recordings on a subset of 1432 participants at baseline, repeated in 862 during exam year 7-8, and recordings in an additional 387 minority participants in exam year 5. Although measurement of HRV, which quantifies beat-to-beat changes in the normal rhythm of the heart, was among the original purposes of the ambulatory ECG monitoring, only a limited index (5-minute averaged time domain HRV) was determined, and beat-to-beat data were not saved. Thus a more in depth analysis of HRV is impossible without re-analyzing the tapes. Time domain indices of HRV provide generalized information about cardiac autonomic modulation, but frequency domain indices of HRV, because they partition the variance in the heart rate into distinct frequency bands, provide a more precise picture and can provide insights into circadian patterns of the autonomic modulation of the heart. Also, frequency domain HRV has been a better predictor of outcome than time domain HRV. Heart rate tachograms will be generated which reveal periodic and other heart rhythms. The prognostic value of newer HRV indices which provide information independent of that from standard HRV will be determined. To perform frequency domain and other analysis of HRV in the CHS, the tapes will be re-scanned and the beat-to-beat data saved in electronics format. In addition to determining if HRV enhances prediction of outcome in the CHS, the detailed relationship between cardiac autonomic modulation and clinical and functional health in the CHS will be investigated. The changes in HRV over time in healthy older adults will be determined. We will investigate whether there is an effect of gender or race on the relationship between HRV and aging in healthy adults. Clinical outcomes will include cardiovascular and non-cardiovascular morbidity and mortality. Health may also be defined as maintaining the ability to carry out activities of daily living for as long as possible. Therefore, we will also consider the predictive value of HRV for functional status and describe the detailed HRV profile of those who are functionally healthy at baseline and remain so upon follow up. Furthermore, the data generated will provide the basis for a number of studies about HRV and clinical and functional parameters that otherwise would require a large number of separate investigations.
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