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

## TL;DR

This study shows that short-term heart rate variability metrics can detect parasympathetic responses during rapid atrial pacing in real time during cardiac procedures.

## Contribution

The study introduces the use of ultra-short HRV metrics for intraoperative assessment of parasympathetic tone during rapid atrial pacing.

## Key findings

- Rapid atrial pacing significantly increased RMSSD and ΔPP, indicating a parasympathetic response.
- The parasympathetic response was reproducible in repeated pacing sequences.
- HRV changes occurred independently of sinus cycle length modifications.

## Abstract

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.

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.

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.

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.

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.