Background: This study tested the hypothesis that heart rate turbulence (HRT) following ventricular pacing trains depends on train cycle length, presence of retrograde ventriculoatrial (VA) conduction, and left ventricular (LV) function.
Methods: We analyzed digital recordings of programmed ventricular stimulation (PVS) performed in 82 patients (57 men) referred for electrophysiologic studies of ventricular arrhythmias, whose mean age was 64 +/- 12 years and LV ejection fraction (EF) was 47 +/- 15%. Profiles of sinus RR intervals after all available 8-beat ventricular pacing trains (600-and 400-ms) were averaged. Heart rate turbulence slope (HRTS) was analyzed as the maximum positive slope of a regression line through a sequence of 2-5 (HRTS2 - HRTS5) consecutive RR intervals within the first 5 RR intervals after the pacing train.
Results: Dynamics of RR intervals had biphasic and monophasic patterns, in patients with and without VA conduction, respectively. Sinus nodal response was less prominent after 600-ms than 400-ms pacing trains. After 400-ms pacing trains, HRTS was significantly shallower in patients with LVEF </= 40% than in those with LVEF > 40%. HRTS4 was the best discriminator between the two groups (6.8 +/- 8.6 ms/RR vs 19.6 +/- 26.0 ms/RR, P = 0.017).
Conclusion: In patients with VA conduction, HRT after ventricular pacing trains reflects a combination of vagal withdrawal due to transient hypotension and suppression of sinus node automaticity. Attenuation of vagal modulation was detected in patients with LV dysfunction during standard PVS.