Clinical relevance of heart rate variability changes after heart transplantation.

Heart rate variability (HRV) of the healthy innervated heart is controlled and regulated by the autonomous nervous system and is influenced by respiratory frequency. Physiologically, there are slow and fast variations of heart rate which are of sympathetic or parasympathetic origin respectively. Spectral analysis of heart rate variability permits a selective quantification of these periodic influences of autonomous neural control. In the absence of neural influence on the pacemaker of the donor heart, we do not expect a high periodic heart rate variability (HRV). Due to the almost rigid heart rhythm we only anticipate a slight deviation of the R-R intervals from their mean value. Interventions such as valsalva maneuvers, controlled respiration and tilt table result in a very small but significant change of heart rate variability. These changes are most likely due to local influences at the donor sinus node. Neural influences from reinnervation may also play an important role in patients long after transplantation.