Definition

There is considerable variation in the resting heart rate of healthy, asymptomatic populations.  Technically, a HR < 60bpm is considered bradycardia. Clinically, HR < 50 (some cardiologists use HR < 40) is bradycardia. Bradycardia generally requires acute intervention if it is symptomatic (e.g. lightheadedness, weakness, loss of consciousness) or unstable (hypotension).

Differential Diagnosis

Conduction System Abnormalities Causing Bradycardia:

• Sinus-node Dysfunction: sinus bradycardia, sinus arrest (pause >3sec), sinoatrial exit block, bradycardia-tachycardia syndrome (alternating atrial tachyarrhythmia and bradycardia).
• AV Conduction Disturbances: 1st degree AV block, Type I and Type II 2nd degree AV block, 2nd degree with high grade AV block (3:1 conduction), and 3rd degree AV block (complete heart block, AV dissociation).

Evaluation

• Determine if the patient is hemodynamically stable or unstable/symptomatic. Ask the nurse to get a full set of vital signs and a 12-lead EKG as you are on your way to the bedside. If concerned, have pacer pads and atropine at the bedside. (If unstable, see ACLS bradycardia)
• Determine whether this is sinus bradycardia (HR < 50) based on EKG.
• Review telemetry. Often the irregularity of atrial fibrillation will be misread as intermittent bradycardia on the monitor; and this typically does not require additional work-up or management. If the patient is truly having >3-second sinus pauses while awake, this indicates sinus node dysfunction and the patient potentially needs a pacemaker if symptomatic. In general, pauses can be common during sleep and are often not clinically relevant. Symptomatic pauses while awake are clinically significant.
• Take a history and examine the patient, pay attention to symptoms, vital sign abnormalities and mental status. Sinus bradycardia in the hospital can often be the result of a vagal event from pain, vomiting, or recent surgery.
• Evaluate the medication list including recently given medications (e.g. β-blocker, CCB) and obtain an electrolyte panel (especially K+), TSH if not done recently, and a Troponin to evaluate for an ischemic etiology.

Management

• Ensure that atropine and pacer pads are easily available (i.e. at the bedside if available per nursing protocol).
• If symptomatic or unstable bradycardia follow ACLS protocols for temporary pacing and consult cardiology for temporary pacing wire placement.
• Treat the underlying conditions i.e. inferior MI, medication overdoses, hypothyroidism (see Endocrine: Hypothyroidism), electrolyte abnormalities (especially K+).
• Atropine 0.5 mg IV (repeat every 3-5 minutes, maximum 3 mg) is first line for symptomatic/unstable bradycardia. Use with caution in patients with MI, as it may cause increased myocardial demand. Epinephrine and dopamine infusions are second line agents. Do not delay transcutaneous pacing.
• Medications are a common cause of bradycardia in the hospital, particularly beta blockers and calcium channel blockers. If stable, simply reducing or holding a dose may be sufficient. If unstable, administer atropine, consider the following reversal agents, and see Toxicology: Beta Blocker Overdose or Calcium Channel Blocker Overdose for more details.
  • For beta blocker: IV glucagon
  • For calcium channel blocker: IV calcium gluconate
• Transcutaneous pacing is uncomfortable and a transition to temporary transvenous pacing wire should be made if continuous pacing for > 12 hours is anticipated. These patients should be transferred to the ICU and cardiology should be consulted.

• For indications for pacemaker placement see Cardiology: Pacemakers.

Key points

• Asymptomatic bradycardia in a young, athletic patient can be normal, especially when asleep, but don’t ignore the call.
• It is important to identify the underlying rhythm in bradycardia as the management differs depending on the etiology.
• Medications are often the cause.
• Check electrolytes - pay close attention to the K.
• Inferior myocardial infarctions often cause bradycardia due to increased vagal tone and require pre-load for management of hypotension.
• Have atropine at the bedside for patients with clinically significant bradycardia.

Mangrum, J.M and DiMarco, J. “Management of bradycardia.” N Engl J Med 2000; 342:703-709

2015 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Part 7.17: Bradyarrhythmias. https://eccguidelines.heart.org/circulation/cpr-ecc-guidelines/