Atrioventricular (AV) Blocks

Introduction

Atrioventricular (AV) block is a condition in which the electrical signals between the atria (upper chambers of the heart) and the ventricles (lower chambers) are partially or completely blocked. This can affect heart rhythm and lead to symptoms such as dizziness, fatigue, or even fainting. AV blocks are classified into three degrees of severity.

Types of AV Blocks

First-Degree AV Block

• The electrical impulse is delayed but still reaches the ventricles.
• The PR interval (time between atrial and ventricular contraction) is prolonged (>200 ms).
• Usually does not cause symptoms and requires no specific treatment, but monitoring is needed.

Second-Degree AV Block

There are two types of second-degree AV blocks:

• Mobitz Type I (Wenckebach Block)

  • Progressive lengthening of the PR interval until a beat is dropped.
  • Often benign but may cause symptoms like dizziness.
  • No treatment is needed unless symptoms are present.

• Mobitz Type II

  • Sudden dropped beats without PR interval prolongation.
  • More serious and may require a pacemaker as it can progress to complete block.

Third-Degree (Complete) AV Block

• No electrical signals pass from the atria to the ventricles.
• The atria and ventricles beat independently.
• Serious and often requires a pacemaker.

Causes of AV Block

AV blocks may be caused by conditions such as: - Aging (degeneration of electrical pathways) - Heart diseases (e.g., coronary artery disease, myocarditis) - Certain medications (e.g., beta-blockers, calcium channel blockers, digoxin) - Electrolyte imbalances (e.g., hyperkalemia) - Congenital conditions

Diagnosis

AV block is diagnosed using: 1. Electrocardiogram (ECG) – The primary tool for detecting AV block. 2. Holter Monitoring – If AV block is intermittent, a 24-hour ECG recording may be performed. 3. Electrophysiology Study – Used in some cases to evaluate conduction abnormalities.

Treatment

• First-degree AV block: Usually does not require treatment but needs monitoring.
• Mobitz Type I: No treatment unless symptomatic.
• Mobitz Type II and Third-Degree AV Block: Pacemaker implantation is often necessary to maintain proper heart function.

Conclusion

Atrioventricular blocks range from benign to life-threatening. If diagnosed, regular monitoring and appropriate treatment (such as a pacemaker for severe cases) are crucial to maintaining a healthy heart rhythm.

Source recommendations

1. American Heart Association Guidelines on Electrophysiology and Conduction Disorders

1. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000628
2. https://www.heart.org/en/health-topics/arrhythmia/prevention--treatment-of-arrhythmia/ablation-for-arrhythmias
3. https://pubmed.ncbi.nlm.nih.gov/30586772/
4. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/types-of-arrhythmia-in-children
5. https://newsroom.heart.org/news/aha-media-alert-information-and-resources-on-heart-rhythm-issues-and-pacemakers

2. European Society of Cardiology Guidelines on Cardiac Pacing and Electrophysiology

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Cardiac-Pacing-and-Cardiac-Resynchronization-Therapy
2. https://academic.oup.com/eurheartj/article/34/29/2281/401445
3. https://www.heartrhythmjournal.com/article/S1547-5271(23)02026-X/fulltext
4. https://www.escardio.org/static-file/Escardio/Guidelines/Scientific-Statements/guidelines-Heart-Rate-Variability-FT-1996.pdf
5. https://pubmed.ncbi.nlm.nih.gov/11583910/