Short-term HRV metrics as a method for intraoperative assessment of cardiac parasympathetic response to rapid atrial pacing

Introduction: Heart rate variability (HRV) is widely used to assess parasympathetic influence on cardiac function and has proven useful in evaluating long-term autonomic effects of cardioneuroablation (CNA). However, HRV has not yet been used intraoperatively to quantify dynamic, short-term changes in parasympathetic tone. Rapid atrial pacing (AP) is expected to provoke a brief parasympathetic reaction, but no standardized method exists to assess this response in real time during electrophysiological procedures. Aims: To evaluate HRV changes induced by rapid AP using RMSSD and the maximal-minimal PP interval difference (ΔPP), and to assess the feasibility of repeated intraoperative monitoring. Methods: This prospective observational study enrolled 50 patients (median age 39 years [IQR 31-52]) without structural heart disease referred for electrophysiological study. RMSSD and ΔPP were calculated from four PP intervals before pacing and reassessed immediately after 30-s atrial pacing at 100 bpm. Heart rate, Sinus node recovery time, cSNRT and Wenckebach point were also measured. All measurements were repeated 2 minutes later. Results: Rapid AP produced a significant increase in RMSSD (15.7 ms [9.7-23.7] vs. 41.7 ms [25.6-59.6], p < 0.001) and ΔPP (33 ms [19-56] vs. 90 ms [60-152], p < 0.001). The response was reproducible in the second pacing sequence (RMSSD 13.6→41.0 ms; ΔPP 24→107 ms; both p < 0.001; Wilcoxon signed-rank test with Bonferroni correction). HRV changes occurred independently of sinus cycle length modifications. No significant differences were observed in SNRT, cSNRT, or Wenckebach point. Conclusion: Rapid AP evokes a robust, repeatable parasympathetic response detectable using ultra-short HRV metrics-expressed as an increase in RMSSD and ΔPP. These parameters allow real-time intraoperative assessment of parasympathetic influence on the sinus node. This approach warrants validation in future studies involving CNA, atropine challenge, and ECVS.