Relationship Between Intraoperative and Preoperative Ambulatory Nighttime Heart Rates: A Secondary Analysis of a Prospective Observational Study

BACKGROUND: It remains unknown what constitutes physiologically relevant intraoperative bradycardia. Intraoperative bradycardia is usually defined using absolute heart rate thresholds, ignoring preoperative baseline heart rates. In contrast, we considered defining intraoperative bradycardia relative to preoperative ambulatory nighttime heart rate. Specifically, we hypothesized that the individual mean intraoperative heart rate is lower than the mean preoperative ambulatory nighttime heart rate. We, therefore, sought to investigate the relationship between the intraoperative and preoperative ambulatory nighttime heart rates in adults having noncardiac surgery with general anesthesia. Additionally, we sought to investigate the incidence of intraoperative bradycardia using relative versus absolute heart rate thresholds. METHODS: We conducted a secondary analysis of a database from a prospective study including preoperative ambulatory and intraoperative heart rates in 363 patients having noncardiac surgery with general anesthesia. RESULTS: The mean intraoperative heart rate was lower than the mean nighttime heart rate (mean difference, -9 bpm; 95% confidence interval CI, -10 to -8 bpm; P 30% lower than mean nighttime heart rate and 43% (95% CI, 38%-49%) when it was defined as intraoperative heart rate <45 bpm. CONCLUSIONS: The mean intraoperative heart rate is lower than the mean nighttime heart rate in about 9 of 10 patients. Intraoperative bradycardia might thus be physiologically and clinically important. Future research needs to investigate whether there is an association between intraoperative bradycardia and postoperative outcomes.