Heart rate turbulence and heart rate variability in patients with atrial synchronous ventricular pacing

Background: Heart rate turbulence (HRT) and heart rate variability (HRV) have been shown to be independent and powerful predictors of mortality in a specific group of cardiac patients. Pacing has unfavorable effects on autonomic function. Our aim is to investigate autonomic responses to atrial synchronous ventricular pacing (VDD) by evaluating HRT and HRV parameters. Methods and Results: The study groups comprised 12 control and 12 patients without organic heart disease and with normal sinus function who were implanted with a permanent VDD pacing system for high-degree atrioventricular block. The HRV and HRT analysis were assessed from a 24-hour Holter recording. There was no statistically significant difference between the two groups for HRV parameters. When HRT parameters were compared, turbulence onset was significantly higher in the cardiac paced group than the controls group (2.729 +/- 8.818 vs -1.565 +/- 8.301, P = 0.006), but no statistically significant difference was found between the two groups for turbulence slope (11.166 +/- 10.034 vs 31.675 +/- 28.107, P = 0.68). The number of patients who had abnormal HRT onset was significantly higher in the paced group than controls (9 vs 2, P = 0.004). Conclusion: Atrial synchronous pacing has unfavorable effects on autonomic function. Altered ventricular depolarization sequence may lead to changes in autonomic response. Although we found no difference in HRV parameters between the control and VDD patient groups, the HRT onset and number of patients with abnormal HRT onset was significantly higher in VDD patients. HRT onset can be a better way of noninvasive autonomic response predictor in VDD patients.