Sinus Bradycardia

Rate	40-59 bpm
P wave	Sinus
QRS	Normal (.06-.12)
Conduction	P-R normal or slightly prolonged at slower rates
Rhythm	Regular or slightly irregular

The name of this rhythm indicates its origin, i.e., the sinus node. The normal rate of depolarization for the sinus node is 60 bpm to 100 bpm. This rhythm is often seen as a normal variation in athletes, during sleep, or in response to a vagal maneuver. If the bradycardia becomes slower than the SA node pacemaker, a junctional rhythm may occur.

Rhythm Analysis

Step 1 - Rhythm regularity, R-R distance does not vary more than 1.5 small boxes from one complex to the next ?
Step 2 - Rate < 60 ?
Step 3 - P wave in Lead II is associated with each QRS, rounded, upright ?
Step 4 - R-R interval 3-5 small boxes on all complexes ?
Step 5 - QRS all same normal shape, with duration 1.5 to 3 small boxes ?

Signs and symptoms vary: none, shortness of breath, chest pain (angina), fatigue, heart palpitations, memory or cognitive problems, dizziness, syncope, irritability, agitation or other personality changes.

Etiology - Nodal pathology, electrolyte deficiencies, hypothyroidsim, cardiac ischemia, infection, or inflammation, sick sinus syndrome, heart block, drugs, cardiac surgery, sleep apnea, etc.

Treatment (hemodynamically unstable patients):

Treat the underlying cause, e.g., electrolyte imbalance, hypothyroidism, etc.
Atropine, intravenous (IV) and injectable atropine for temporary treatment
Isuprel, or Isoproterenol ia a beta adrenergic agonist with similarities to epinephrine. It raises heart rate and cardiac output without vasoconstriction.
Artificial pacing if patient is hemodynamically compromised.

Instant Feedback:

Sinus bradycardia is always abnormal and must be treated.

Reference

Dakkak W, Doukky R. Sick Sinus Syndrome. [Updated 2023 Jul 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470599/

Jacobs, B., Robie, S., Monsalve, M. (2024). Chapter 8 - The Electrocardiogram and Cardiac Monitoring. In Shesser, R., Pourmand, A., & Keim, A., The Emergency Department Technician handbook. Elsevier. https://doi.org/10.1016/B978-0-323-83002-7.00008-5