Postural Response of Low-Frequency Component of Heart Rate Variability: Discussion

Major Findings
This study demonstrated that the postural response of HRV assessed under well-controlled conditions predicts the risk for cardiac death during long-term follow-up in patients with CAD. We observed that an increased postural response of the LF predicts an increased risk for cardiac death during 8-year follow-up of patients with CAD. The prognostic association was significant after an adjustment for cardiovascular risk factors and CAD severity. Furthermore, when the patients were stratified into three groups by postural LF responses (ie, large drop, small drop, and rise), the three groups were comparable in terms of cardiovascular risk factors and CAD severity at baseline; however, the 8-year cardiac mortality rate increased with increasing degrees of postural LF response. This study seems to provide a new prognostic aspect of HRV that is unique when compared with the earlier concept that prognostic information on HRV exists mainly in its long-term variability or in the components reflecting cardiac vagal function.
Earlier Observations and Strength of the Present Study
Much clinical evidence has been accumulated for the association of reduced HRV with adverse prognosis in patients after acute myocardial infarction and in those patients with congestive heart fail-ure.> Because experimental studies” have demonstrated that HRV is almost abolished by atropine, cardiac vagal dysfunction and/or the resulting relative sympathetic overactivity have been hypothesized as the mechanisms mediating adverse prognosis in patients with reduced HRV. canadian health care mall

However, convincing clinical evidence for this concept seems limited. In most of the earlier stud-ies- on the prognostic value of HRV, even those analyzing short-term HRV, data were collected by ambulatory ECG monitoring, mostly in patients receiving medications. Under these conditions, the autonomic neural activities are influenced by posture, food intake, wake-sleep cycle, and other physical and mental activities.

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