Low intraoperative heart rate volatility is associated with early postoperative mortality in general surgical patients: a retrospective case–control study

Heart rate volatility (HRVO) is hypothesized to be a physiological measure of sympathetic activity and is defined by the standard deviation (SD) of the heart rate (HR) in beats per minutes (BPM) over fixed time intervals. To investigate the relationship between low HRVO (SD < 0.5 BPM) during surgical procedures and mortality within 48 h post-procedure. We retrospectively reviewed all adult general surgical procedures performed at our center from January 1, 2003 through July 1, 2013 to identify patients who died within 48 h post-procedure. Demographic, heart rate, and mortality data were extracted from the electronic anesthesia record. Propensity score analysis was used to find matching controls based on age, gender, ASA score, anesthesia type, Charlson index, procedure type, emergency status, year, use of preoperative beta blocker, hypertension, diabetes, atrial fibrillation and heart failure. HRVO was calculated for each 5 min interval as the SD of all HR’s within that interval. Negative binomial regression was then used to model the count of intervals with HRVO < 0.5 BPM for the duration of the surgery. During the 10 year study period, 283 patients died within 48 h of procedure finish. These patients were matched to 566 patients who did not die within 48 h after procedure. Patients who died had a 39 % increase in frequency of low HRVO episodes compared to patients who survived (RR 1.39, 95 % CI 1.13–1.72; p = 0.003). Low HRVO during surgical procedure is associated with increased mortality risk within 48 h after procedure. Strategies to identify HRVO early and modify it may lead to improvement in outcomes.