Bradycardia during General Anesthesia

Intraoperative bradycardia, defined by heart rate (HR) below 60 beats per minute (bpm), is common, affecting nearly 11 percent of patients under general anesthesia. While many of these arrhythmias are brief and clinically inconsequential, some may signify underlying issues, such as myocardial ischemia or electrolyte imbalances. Others may result from specific procedures or medications and, in rare cases, lead to hemodynamic instability during surgery.

Identification of factors contributing to bradycardia can occur during the preoperative period or be addressed in real-time during surgery. Certain medications, particularly beta blockers and negative chronotropic agents like calcium channel blockers, digoxin, and amiodarone, are recognized culprits for drug-induced sinus bradycardia. Notably, a 2019 meta-analysis revealed a higher incidence of clinically significant bradycardia and hypotension in noncardiac surgical patients receiving perioperative beta blockers.

The most prevalent form of bradyarrhythmia during general anesthesia is sinus bradycardia, characterized by a slow HR (<60 bpm) with normal atrial and ventricular depolarization. This can arise from various causes, including medication use, increased vagal tone, athletic conditioning, or intrinsic sinus node dysfunction outside the surgical context. Sinus bradycardia can also be induced by acetylcholinesterase inhibitors like neostigmine or edrophonium, commonly used to reverse the effects of nondepolarizing neuromuscular blocking agents. Proper dosing of anticholinergic agents, such as glycopyrrolate or atropine, is crucial to prevent severe bradycardia in these situations.

Mild sinus bradycardia in a stable patient (HR 40 to 60 bpm) typically doesn’t necessitate pharmacologic intervention, although addressing the underlying cause may be crucial. In contrast, severe sinus bradycardia with hemodynamic instability requires prompt intervention. Treatment options include pharmacologic approaches and temporary pacing.

Causes of sinus bradycardia include 1) vagal reflexes, 2) neuraxial anesthesia, and 3) medications. Surgical manipulations, such as those during eye surgery, laparoscopic abdominal surgery, or carotid endarterectomy, may trigger vagal reflexes leading to bradycardia. Immediate cessation of manipulation and, if necessary, administration of anticholinergic agents is crucial in these situations. High neuraxial anesthesia levels can cause sinus bradycardia and hypotension. Treatment involves beta-adrenergic agonists like ephedrine or epinephrine, with consideration for discontinuing epidural infusions. Certain medications, particularly those discussed earlier, may also contribute to sinus bradycardia.

Pharmacologic treatment of bradycardia is necessary for hemodynamically unstable patients, for example patients with abnormally low blood pressure. For hemodynamically unstable patients, intravenous atropine is administered, with the option for repeated doses every three to five minutes. For stable patients with severe sinus bradycardia, glycopyrrolate or small incremental doses of atropine are preferred to avoid undesirable tachycardia.

Temporary pacing may be required for patients experiencing recurrent or severe bradycardia with hemodynamic instability. Options include transcutaneous pacing, transvenous pacing, and pacing pulmonary artery catheters. Transcutaneous pacing is a rapid method in the perioperative setting, using external defibrillator pads to achieve pacing capture. However, it may be painful

for awake or mildly sedated patients. Transvenous pacing involves insertion of an introducer sheath into a central vessel, typically the right internal jugular vein, allowing for transvenous pacing. This method may be impractical during ongoing surgery as it requires cardiology consultation. Finally, specialized pulmonary artery catheters with pacing capability can be used with an external pacemaker. However, these may have less stable leads compared to dedicated transvenous pacing wires.

In conclusion, understanding the causes and management of bradycardia during general anesthesia, sedation, and neuraxial anesthesia is essential for anesthesiologists and perioperative care teams. Vigilance in identifying contributing factors, appropriate pharmacologic interventions, and access to temporary pacing options contribute to the comprehensive care of patients experiencing bradyarrhythmias during surgery.

References

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