Second-Degree Atrioventricular Block on ECG

Introduction

Second-degree atrioventricular (AV) block is a conduction disorder of the heart where some atrial electrical impulses fail to reach the ventricles. This condition is diagnosed using an electrocardiogram (ECG) and can be classified into two main types: Mobitz type I (Wenckebach) and Mobitz type II.

Types of Second-Degree AV Block

1. Mobitz Type I (Wenckebach)

• Characterized by a progressive prolongation of the PR interval until a beat is dropped (P wave not followed by a QRS complex).
• Often caused by AV nodal dysfunction.
• Usually benign but may require monitoring.

2. Mobitz Type II

• PR interval remains constant, but sudden non-conducted P waves occur (dropped QRS complexes).
• Indicates a more serious conduction system disease, often below the AV node (His-Purkinje system involvement).
• Higher risk of progression to complete heart block.
• Generally requires a pacemaker for treatment.

ECG Findings

• Mobitz I: Progressive lengthening of PR interval before a dropped beat.
• Mobitz II: Constant PR interval with intermittent dropped QRS complexes.

Causes and Risk Factors

• Mobitz I: Normal aging, medications (beta-blockers, calcium channel blockers), increased vagal tone, inferior myocardial infarction.
• Mobitz II: More concerning causes include conduction system disease, anterior myocardial infarction, and infiltrative conditions (e.g., amyloidosis, sarcoidosis).

Diagnosis and Management

• Diagnosis: ECG/Holter monitoring, electrolyte tests, and possible electrophysiology study.
• Treatment:
  • Mobitz I: Usually no treatment required unless symptomatic (then atropine or pacemaker may be needed).
  • Mobitz II: Often requires a permanent pacemaker due to high risk of progression to complete heart block.

Conclusion

Recognizing second-degree AV block on ECG is crucial for early intervention. While Mobitz I is often benign, Mobitz II is a severe condition requiring prompt management, often with a pacemaker.

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/bradycardia--slow-heart-rate
4. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000627
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/