Understanding 2nd Degree AV Block on ECG

Introduction

Second-degree atrioventricular (AV) block is a conduction abnormality where some electrical impulses from the atria fail to reach the ventricles. This can lead to dropped beats, causing symptoms such as dizziness or syncope. On an electrocardiogram (ECG), second-degree AV block is categorized into two types: Mobitz type I (Wenckebach) and Mobitz type II.

Types of 2nd Degree AV Block

Mobitz Type I (Wenckebach)

  • ECG Characteristics: Progressive prolongation of the PR interval until a beat is dropped.
  • Clinical Significance: Often benign and can be caused by increased vagal tone or medications like beta-blockers or calcium channel blockers.
  • Management: Usually does not require intervention unless symptomatic.

Mobitz Type II

  • ECG Characteristics: Sudden dropped QRS complexes without progressive PR prolongation.
  • Clinical Significance: More dangerous as it may progress to complete heart block.
  • Management: Requires close monitoring and often pacemaker implantation.

Causes of 2nd Degree AV Block

  • Medications (e.g., beta-blockers, digoxin)
  • Ischemic heart disease
  • Electrolyte imbalances
  • Structural heart disease (e.g., myocarditis, amyloidosis)

Treatment and Management

  • Asymptomatic Mobitz I: Monitor and correct reversible causes.
  • Symptomatic Mobitz I or any Mobitz II: Consider pacemaker placement, especially if there is hemodynamic instability.

Always consult a cardiologist for proper evaluation and management.

Source recommendations

1. American Heart Association Guidelines on Bradycardia and Conduction Disorders

  1. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/conduction-disorders
  2. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000628
  3. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia
  4. https://pubmed.ncbi.nlm.nih.gov/30412709/
  5. https://www.jacc.org/guidelines/bradycardia

2. European Society of Cardiology Guidelines on Cardiac Pacing and Resynchronization Therapy

  1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Cardiac-Pacing-and-Cardiac-Resynchronization-Therapy
  2. https://academic.oup.com/eurheartj/article/42/35/3427/6358547
  3. https://pubmed.ncbi.nlm.nih.gov/34455430/
  4. https://academic.oup.com/eurheartj/article/34/29/2281/401445
  5. https://pubmed.ncbi.nlm.nih.gov/23801827/

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