In this episode of "IM Basics," host Dr. Acker is joined by Dr. Harmandip Parmar, an intern with an interest in cardiology, to break down the essentials of heart block. They cover the full spectrum of atrioventricular (AV) blocks, from incidental findings on an ECG to symptomatic emergencies. Tune in to learn how to identify, investigate, and manage these crucial cardiac conditions.

What You'll Learn in This Episode:

• Patient Presentation:
  • While many patients with heart block are asymptomatic, some may present with symptoms like fainting (syncope), lightheadedness, or chest pain.
  • Myocardial infarction (MI) can be an underlying cause of these symptoms and the heart block itself.
• ECG Findings for Different Heart Blocks:
  • First-Degree AV Block: Identified by a prolonged PR interval of more than 0.20 seconds.
  • Second-Degree AV Block, Mobitz Type I (Wenckebach): Characterized by a PR interval that gets progressively longer until a QRS complex is "dropped".
  • Second-Degree AV Block, Mobitz Type II: Features a constant PR interval length with intermittently dropped beats. These patients are often more symptomatic.
  • Third-Degree (Complete) AV Block: Shows a complete dissociation between P waves and QRS complexes, with each marching out at its own regular rate.
• Investigating the Causes:
  • A thorough workup is essential to find the underlying cause.
  • Potential causes include MI, electrolyte imbalances (like hyperkalemia), and thyroid issues.
  • A patient's medication list should be reviewed for drugs like beta-blockers, digoxin, amiodarone, and certain calcium channel blockers.
  • Other causes can include Lyme disease, inherited conditions like sarcoidosis, or recent cardiac procedures.
• Treatment and Management:
  • First-Degree and Mobitz I: Often asymptomatic and may not require urgent intervention, aside from investigating the cause.
  • Mobitz Type II: These patients are at high risk of progressing to a third-degree block and require admission. Atropine should be avoided. Definitive treatment is often a permanent pacemaker.
  • Third-Degree Block: This is an urgent condition. Management includes:
    • Giving atropine.
    • Using beta-adrenergic agonists like dopamine or epinephrine.
    • Initiating temporary cardiac pacing, followed by evaluation for a permanent pacemaker.

    Special Cases: In patients with Lyme carditis, a permanent pacemaker is often avoided as the condition typically improves within weeks.

• Additional Insights:
  • The discussion touches on "Stokes-Adams attacks," which are episodes of fainting linked to heart block.
  • The hosts explore the theory that rate control in atrial fibrillation might bombard the AV node, potentially leading to third-degree heart block over time