Second-Degree Atrioventricular Block on ECG

Introduction

Second-degree atrioventricular block (AV block) is a condition where there is intermittent failure of atrial impulses to reach the ventricles. This disorder is classified into two types: Mobitz type I (Wenckebach) and Mobitz type II.

ECG Characteristics of Second-Degree AV Block

Mobitz Type I (Wenckebach)

• Progressive prolongation of the PR interval until a dropped QRS complex occurs.
• After the dropped beat, the cycle repeats.
• The QRS complex is usually narrow unless there is underlying bundle branch disease.
• Often associated with impaired conduction in the AV node.

Mobitz Type II

• PR interval remains constant, but there are intermittent dropped QRS complexes.
• More serious than Mobitz I, as it can progress to complete heart block.
• Usually associated with disease of the His-Purkinje system.

Clinical Significance

• Mobitz I is often benign and may not require treatment unless symptomatic (e.g., dizziness, fatigue).
• Mobitz II is more dangerous and often requires pacemaker implantation due to the risk of complete AV block.

Management and Treatment

• Mobitz I: Often monitored unless symptoms develop. If symptomatic, atropine or a pacemaker may be needed.
• Mobitz II: Pacemaker implantation is generally required as this condition has a high risk of progressing to complete heart block.

Conclusion

Recognizing second-degree AV block on ECG is crucial in determining appropriate management. Mobitz I is generally benign, while Mobitz II is a more severe condition that often necessitates pacemaker therapy.

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/