Spontaneous baroreflex sensitivity and heart rate turbulence parameters: parallel responses to orthostasis.

Premature ventricular contractions (PVC-s) induce baroreflex mediated arterial pressure and heart rate fluctuations. PVC-related RR interval fluctuations detected on Holter ECG recordings could be characterized by the heart rate turbulence (HRT) parameters, including early post-extrasystolic acceleration, described by turbulence onset, and late deceleration, described by turbulence slope (TS). We have determined the increasing and decreasing spontaneous baroreflex sequence sensitivity (up- and down-BRS) parameters in supine and in upright position in 12 patients with VVI pacemaker while in sinus rhythm. Five-five premature ventricular pacemaker extrastmuli were also applied in both body positions and HRT parameters were calculated. Up- and down-BRS values showed a very close relationship with TS both in the supine (R = 0.94, P < 0.001 and R = 0.92, P < 0.001, respectively), and upright position (R = 0.96, P < 0.001, and R = 0.94, P < 0.001, respectively). The BRS indices decreased significantly upon tilting, which was paralleled by a significant decrease in TS (from 21.6 to 13.9 ms/cycle, P = 0.02). Our findings confirm the close association between TS and spontaneous BRS indices. The relationship is further supported by the similar postural behavior of these parameters. Our results suggest that the confounding effect of posture should be considered when analyzing Holter recordings.