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Prolonged PR Interval Is a Risk Factor for Bradycardia During Spinal Anesthesia
  1. Spencer Liu, M.D.*,
  2. Greg E. Paul, M.D.*,
  3. Randall L. Carpenter, M.D.*,
  4. Carol Stephenson, R.N.* and
  5. Rae Wu, M.D., M.P.H.
  1. *Department of Anesthesiology, Virginia Mason Medical Center,
  2. Virginia Mason Research Center, Seattle, Washington
  1. Reprint requests: Dr. Liu, Department of Anesthesiology, Virginia Mason Medical Center, 1100 Ninth Avenue, P.O. Box 900, Seattle, WA 98111.


Background and Objectives Bradycardia occurs during 9%-13% of spinal anesthetics and may lead to cardiac arrest. Several risk factors for the development of bradycardia have been identified, but the risk conferred by presence of abnormalities detected on preoperative electrocardiogram (ECG) has not been examined. The authors undertook the study to correlate abnormal ECG findings with the incidence of bradycardia.

Methods The database was previously collected from 952 patients undergoing spinal anesthesia. Patient records were reviewed and 537 had ECGs performed within 6 months of surgery. Intraoperative bradycardia was defined as a heart rate <50 bpm (plus >10% decrease from baseline). Abnormalities recorded from the ECG were prolonged PR interval (PR > 0.2 sec), atrial-ventricular conduction abnormalities, evidence of chamber hypertrophy, ischemia, and infarction. The findings were compared with incidence of bradycardia using contingency tables. Significant correlations were then evaluated with logistic regression. Significance was defined as P < .05.

Results The incidence of bradycardia in this population was 12%. Patients with a prolonged PR interval had an increased incidence of bradycardia (25%, P = .01). Other ECG abnormalities did not correlate with increased incidence of bradycardia. Duration of PR interval did correlate significantly (P = .001) but poorly (r 2 = 0.014) with baseline heart rate. However, logistic regression demonstrated that prolonged PR interval was a significant and independent predictor for bradycardia (odds ratio = 3.2, P = .01).

Conclusions Risk factors previously identified for the development of bradycardia during spinal anesthesia include: baseline heart rate <60 bpm, ASA physical status 1 versus 3 or 4, use of beta-blocking drugs, sensory block height ≥T5, and age <50. The results demonstrate that prolonged PR interval on the preoperative ECG is another significant and independent predictor for bradycardia.

  • anesthesia
  • spinal
  • adverse effects
  • heart rate
  • bradycardia
  • multivariate analysis

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  • Presented in part at the annual meeting of the American Society of Anesthesiologists, Washington, D.C., October 9-13, 1993.

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