Atrioventricular (AV) Block: Understanding the Condition

Introduction

Atrioventricular (AV) block is a condition affecting the electrical conduction system of the heart, leading to delayed or completely blocked electrical signals between the heart's upper (atria) and lower chambers (ventricles). This can result in various degrees of heart rhythm abnormalities, which may cause symptoms ranging from mild dizziness to severe cardiac arrest.

Types of AV Block

AV block is classified into three degrees:

First-Degree AV Block

• Description : A mild form where electrical impulses take longer than normal to travel from the atria to the ventricles.
• Symptoms : Typically asymptomatic and often found incidentally on an ECG.
• Treatment : Usually does not require treatment but may indicate an underlying heart condition.

Second-Degree AV Block

This type is further divided into:

1. Mobitz Type I (Wenckebach)

   • Description : The PR interval (time between atrial and ventricular contractions) progressively lengthens until a beat is dropped.
   • Symptoms : May cause dizziness or fatigue but is often benign.
   • Treatment : Usually not necessary unless symptoms appear.

2. Mobitz Type II

   • Description : Sudden failure of some electrical impulses to reach the ventricles without progressive lengthening of the PR interval.
   • Symptoms : Higher risk of fainting and severe heart complications.
   • Treatment : Often requires a pacemaker due to potential progression to complete AV block.

Third-Degree (Complete) AV Block

• Description : A complete disconnection between the atria and ventricles, with no electrical signals passing through.
• Symptoms : Severe bradycardia (slow heart rate), fatigue, dizziness, fainting, or even sudden cardiac arrest.
• Treatment : Pacemaker implantation is almost always required.

Causes and Risk Factors

• Aging-related degeneration of the heart's conduction system
• Heart diseases (e.g., coronary artery disease, myocarditis)
• Certain medications , such as beta-blockers and calcium channel blockers
• Electrolyte imbalances (e.g., high potassium levels)
• Congenital heart defects (inborn conditions)

Diagnosis

• Electrocardiogram (ECG) : The primary test to identify AV block.
• Holter monitor : Continuously records heart rhythm over 24-48 hours.
• Electrophysiology study : Evaluates electrical conduction in more detail.

Treatment Options

• Observation : For mild cases (e.g., first-degree AV block), no immediate treatment may be required.
• Medication adjustment : If drugs are causing AV block, modifying or stopping them may help.
• Pacemaker implantation : Essential in higher-degree AV blocks to restore normal heart rhythm.

Conclusion

AV block is a disorder affecting the heart's electrical conduction system, with varying severity levels. While mild cases may not require intervention, more severe forms may necessitate pacemaker implantation. If you experience symptoms like dizziness or fainting, seek medical attention promptly.

Source recommendations

1. American Heart Association Guidelines on Bradycardia

1. https://cpr.heart.org/-/media/cpr-files/cpr-guidelines-files/algorithms/algorithmacls_bradycardia_200612.pdf
2. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/bradycardia--slow-heart-rate
3. https://cpr.heart.org/en/resuscitation-science/cpr-and-ecc-guidelines/algorithms
4. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000628
5. https://pubmed.ncbi.nlm.nih.gov/30412710/

2. European Society of Cardiology Guidelines on Cardiac Pacing

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/23801822/