What to watch out for in bradycardia?

Key Aspects to Watch for in Bradycardia

When evaluating bradycardia, focus on identifying signs of hemodynamic instability, determining the underlying cause, and assessing for potential life-threatening complications that may require immediate intervention. 1

Definition and Initial Assessment

• Bradycardia is defined as a heart rate <60 beats per minute, but clinically significant bradycardia typically presents with a heart rate <50 beats per minute 1
• Assess for signs of increased work of breathing (tachypnea, intercostal retractions, suprasternal retractions, paradoxical abdominal breathing) and check oxyhemoglobin saturation via pulse oximetry 1
• Evaluate for symptoms of poor perfusion that may be caused by bradycardia, including altered mental status, ischemic chest discomfort, acute heart failure, hypotension, or other signs of shock 1

Critical Signs and Symptoms to Monitor

• Watch for signs of hemodynamic instability: hypotension, altered mental status, chest pain, dyspnea, syncope, or signs of shock 1, 2
• Monitor for potential progression to life-threatening conditions such as complete heart block or pulseless electrical activity 3
• Be vigilant for a >30% decrease in heart rate from baseline, which may indicate high risk for severe bradycardia leading to pulseless electrical activity 3

Types of Bradycardia to Recognize

• Sinus bradycardia: slow sinus rhythm with normal P waves 1
• Atrioventricular (AV) blocks 1:
  • First-degree AV block: prolonged PR interval (>0.20 second), generally benign
  • Second-degree AV block:
    • Mobitz type I (Wenckebach): progressive PR interval prolongation before blocked P wave, typically at AV node level
    • Mobitz type II: constant PR intervals before blocked P wave, typically infranodal and more concerning
  • Third-degree (complete) AV block: no impulses pass between atria and ventricles

High-Risk Features

• Mobitz type II second-degree AV block, especially in the setting of acute myocardial infarction 1
• Infranodal (distal) conduction system disease, which can progress rapidly and unpredictably and has been associated with sudden death 1
• BRASH syndrome: Bradycardia, Renal failure, AV nodal blockers, Shock, and Hyperkalemia - a potentially life-threatening synergistic condition 4
• Bradycardia-induced ventricular arrhythmias, which can be fatal without prompt intervention 5

Diagnostic Approach

• Obtain a 12-lead ECG to document rhythm, rate, and conduction, and to screen for structural heart disease or systemic illness 1
• Consider cardiac monitoring to identify rhythm, monitor blood pressure, and oxygen saturation 1
• For intermittent symptoms, select appropriate cardiac rhythm monitoring based on symptom frequency 1:
  • Holter monitor for frequent symptoms (within 24-72 hours)
  • Event monitor for symptoms likely to recur within 2-6 weeks
  • Implantable cardiac monitor for very infrequent symptoms (>30 days between episodes)

Management Considerations

• For symptomatic bradycardia, atropine remains the first-line drug (0.5 mg IV every 3-5 minutes to maximum total dose of 3 mg) 1, 6
• Be aware that atropine doses <0.5 mg may paradoxically worsen bradycardia 1
• For bradycardia unresponsive to atropine, consider second-line agents such as epinephrine (2-10 μg/min) or dopamine 7, 8
• In patients with head injuries, ensure adequate oxygenation and consider temporary pacing for persistent hemodynamically unstable bradycardia 7
• For patients with BRASH syndrome, standard atropine treatment may be ineffective; consider isoproterenol, fluid therapy, and management of hyperkalemia 4

Special Considerations

• Watch for medication-induced bradycardia, especially with beta-blockers, calcium channel blockers, and digoxin 1, 4
• Be cautious with atropine in patients after cardiac transplantation, as it may paradoxically cause high-degree AV block 8
• Consider that asymptomatic bradycardia may not require treatment, particularly in athletes or during sleep 1, 9
• Monitor for bradycardia-related cardiomyopathy, heart failure, and adverse effects on brain function in long-standing cases 5

By systematically evaluating these aspects of bradycardia, you can effectively identify patients requiring immediate intervention versus those who can be safely monitored or treated conservatively.