What causes intraoperative bradycardia?

Causes of Intraoperative Bradycardia

Intraoperative bradycardia is most commonly attributable to sinus node dysfunction and only rarely attributable to worsening atrioventricular conduction, with multiple patient-related and procedure-related risk factors contributing to its development. 1

Patient-Related Risk Factors

• Age: Patients >60-65 years of age have significantly higher risk 1, 2
• Baseline vital signs: Lower heart rates (<60 bpm) or blood pressure (<110/60 mm Hg) at baseline 1, 2
• Comorbidities:
  • American Society of Anesthesia Class III or IV 1
  • Ischemic heart disease (increases risk by approximately 2-fold) 3
  • Pre-existing conduction disorders 1
• Medications:
  • Beta blockers 1, 2
  • Drugs that block the renin-angiotensin system (ACE inhibitors, ARBs) 1, 2
  • Vagotonic drugs used for general anesthesia 4

Procedure-Related Risk Factors

• Type of surgery:

  • Ear surgery (approximately 1.6-fold increased risk) 3
  • Carotid artery endarterectomy or stenting 1
  • Maxillofacial and ENT procedures 3
  • Laparoscopic procedures 4, 5

• Specific surgical maneuvers:

  • Rapid peritoneal insufflation during laparoscopy 4, 5
  • Abdominal insufflation during laparoscopic surgeries 1
  • Manipulation of regions innervated by the trigeminal nerve 1
  • Stretching of the peritoneum 4
  • Manipulation of the gallbladder/Calot's triangle 4

• Anesthesia factors:

  • Longer duration of anesthesia 3
  • Controlled hypotension (increases risk by approximately 2.2-fold) 3

• Physiological mechanisms:

  • Vagal stimulation due to hypoxia 6
  • Laryngeal stimulation during intubation 6
  • Peritoneal stretching causing vagal-mediated bradycardia 4, 5

Management Considerations

For patients at high risk of intraoperative bradycardia:

• Placement of transcutaneous pacing pads is reasonable (Class IIa recommendation) 1
• Avoid routine prophylactic temporary transvenous pacing in patients with LBBB who require pulmonary artery catheterization (Class III: Harm recommendation) 1
• Consider local anesthetic infiltration in areas prone to vagal stimulation (e.g., Calot's triangle during laparoscopic cholecystectomy) 4
• Monitor flow rate of CO2 during peritoneal insufflation in laparoscopic surgery 5

Acute Management of Intraoperative Bradycardia

• Stop the surgical stimulus causing bradycardia (e.g., deflate pneumoperitoneum) 4, 5
• Atropine may be used for symptomatic bradycardia 1, 7
  • Note: Use with caution in patients with glaucoma 4
  • Consider that atropine's elimination half-life is more than doubled in children less than 2 years of age 7
• For persistent symptomatic bradycardia, temporary transvenous or transcutaneous pacing may be required 1

Common Pitfalls and Caveats

• Failure to identify high-risk patients preoperatively using risk factors (HEART score components: Heart rate <60, preoperative hypotension <110/60 mm Hg, Elderly age >65 years, preoperative renin-Angiotensin blockade, Revised cardiac risk index ≥3 points, and Type of surgery) 2
• Not distinguishing between "stable" bradycardia (responds to re-oxygenation and pause in laryngoscopy) and "unstable" bradycardia 6
• Overlooking that controlled hypotension, while beneficial for surgical exposure, significantly increases the risk of bradycardia 3
• Failing to recognize that intraoperative bradycardia can potentially lead to cardiac arrest, particularly in hypertensive patients undergoing laparoscopic procedures 5

Remember that prompt recognition and management of intraoperative bradycardia is essential as it may be an early warning sign for cardiac arrest, especially during laparoscopic procedures with pneumoperitoneum 4, 5.