Autocorrelation of daily resting heart rate: A novel metric of postoperative recovery

Abstract

Purpose

Resting heart rate (RHR) is a sensitive indicator of an individual’s physiologic condition. However, its use in clinical practice has been limited due to the wide variation in baseline RHR based on multiple factors, including age, sex, cardiovascular fitness, and comorbidities. The study aims to develop a novel, clinically meaningful metric that is applicable across these conditions, based on day-by-day changes in RHR—the difference in autocorrelation of daily RHR (ACΔ-RHR). We present ACΔ-RHR in the context of monitoring post-discharge recovery for pediatric appendectomy patients.

Methods

Children 3–17 years old who underwent laparoscopic appendectomy for complicated appendicitis from 2019 to 2022 at a tertiary children’s hospital wore a Fitbit for twenty-one postoperative days (POD). Patients without complications were included to describe normative recovery. Using RHR on POD 1–3 as the baseline, autocorrelation of daily RHR was calculated (fixed lag = 1) for POD 3–21. Then, daily ACΔ-RHR was determined by subtracting autocorrelation values between the current and previous day. Means and standard deviations were calculated for daily RHR to estimate on which POD ACΔ-RHR stabilized at 0, representing general RHR stability and recovery from surgery for all patients. Subgroup analyses were performed by age (3–10 years old vs 11–17 years old) and sex.

Results

Thirty-one patients were included (58.1 % 3–10 years old, 41.9 % female, 67.7 % Hispanic). Whereas the mean daily RHR did not demonstrate clear trends, the mean ACΔ-RHR for the cohort first reached 0 on POD 12 and stabilized on POD 14 (95 % confidence interval: POD [11,17]). Subgroup analysis showed that ACΔ-RHR stabilized on POD 9 for age of 3–10 years, POD 12 for age of 11–17 years, POD 12 for females and POD 10 for males.

Conclusions

The ACΔ-RHR is a promising clinical metric that could enhance post-surgical patient monitoring, such as for children following laparoscopic appendectomy for complicated appendicitis.