Incidence and Risk Factors of Severe Bradycardia During Spinal Anesthesia with Chronic β-Blockade

Background: Severe bradycardia and asystole after spinal anesthesia was considered a serious side effect. Beta (β)-blockers lower blood pressure with decrease resting heart rate and left ventricular function. In this study, we retrospectively recorded the incidence of severe bradycardia and asystole during spinal anesthesia in patients medicated with β-blockers and investigated risk factors contributing to the incidence of severe bradycardia. Methods: Anesthesia chart of 693 cases were retrospectively examined. All patients receive elective surgery in our institute ith spinal anesthesia and received β-blockers until the day of operation. Bradycardia was defined as a heart rate <50 beats per minute for at least 1 minute. Ten variables as risk factors contributing to bradycardia were selected: gender, age, body mass index, spinal drug dose, and peak sensory block height, baseline heart rate, baseline systolic blood pressure, baseline diastolic blood pressure, baseline mean blood pressure, and history of diabetes. Results: Eighty six of the 693 (13.4%) patients experienced bradycardia. No asystole occurred. On univariate analysis, male gender, absence of diabetes, low baseline heart rate was associated with statistically higher incidence of bradycardia. In multivariate logistic regression, low baseline heart rate, absence of diabetes elevated the risk of bradycardia (Odds Ratio, 10.44 and 2.6 respectively). Conclusions: The incidence of severe bradycardia during spinal anesthesia was 13.4% in the patient receiving the β-blockers. Those with low baseline heart rate and absence of diabetes were more vulnerable to develop severe bradycardia.