Sinus bradycardia

Sinus bradycardia is a sinus node–driven heart rate of less than 60 beats/min. Unless there is severe underlying heart disease, hemodynamic changes are minimal. With very slow rates, atrial and ventricular ectopic escape beats or rhythms may occur.

1. Etiologies:
   1. Hypoxia.
   2. Intrinsic cardiac disease such as sick sinus syndrome or acute MI (particularly inferior wall MI).
   3. Medications such as succinylcholine (especially in young children via a direct cholinergic effect), anticholinesterases, β-adrenergic blockers, calcium channel blockers, digoxin, and synthetic narcotics (eg, fentanyl and remifentanil).
   4. Increased vagal tone occurs with traction on the peritoneum or spermatic cord; pressure on the globe via the oculocardiac reflex; pressure near the brainstem during craniotomies for posterior fossa lesions; direct pressure on the vagus nerve or carotid sinus during neck or intrathoracic surgery; acute distension of the peritoneal cavity during laparoscopy; centrally mediated vagal response from anxiety or pain (vasovagal reaction); and Valsalva maneuvers.
   5. Increased intracranial pressure (Cushing reflex).
   6. Reflex bradycardia. From baroreceptor reflex (eg, with phenylephrine administration), atrial stretch, or cardiopulmonary reflex.
2. Treatment of sinus bradycardia
   1. Verify adequate oxygenation and ventilation.
   2. Bradycardia due to increased vagal tone requires discontinuation of the provocative stimulus. The vagal reflex may fatigue with repeat stimulus or be less pronounced with deeper anesthesia. Atropine 0.5 mg IV or low-dose epinephrine 10 to 50 μg IV may be needed if the patient is hypotensive. Glycopyrrolate 0.2 to 0.6 mg IV or ephedrine 5 to 10 mg IV may be given for hemodynamically stable bradycardia.
   3. In patients with intrinsic cardiac disease, treatment should proceed with atropine 0.5 mg IV, chronotropes (eg, ephedrine, dopamine), or cardiac pacing.