Third-degree atrioventricular block

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Third-degree atrioventricular block
File:CompleteHeartBlock.jpg Third-degree atrioventricular block
Synonyms	Complete heart block, AV block
Pronounce	N/A
Specialty	N/A
Symptoms	Bradycardia, fatigue, dizziness, syncope
Complications	Heart failure, cardiac arrest
Onset	Can occur at any age
Duration	Chronic
Types	N/A
Causes	Myocardial infarction, cardiomyopathy, congenital heart disease, medications
Risks	Age, coronary artery disease, heart surgery
Diagnosis	Electrocardiogram, Holter monitor
Differential diagnosis	Second-degree atrioventricular block, sick sinus syndrome
Prevention	Management of risk factors
Treatment	Pacemaker, medications
Medication	N/A
Prognosis	Variable, depends on underlying cause and treatment
Frequency	Rare
Deaths	N/A

Third-Degree Atrioventricular Block (AV Block)

Introduction

Third-degree atrioventricular block (AV block), also known as complete heart block, is a serious cardiac arrhythmia where the electrical impulse generated in the sinoatrial node (SA node) in the heart's atrium fails to propagate to the ventricles.

File:3rd degree heart block.PNG

Diagram of the heart's conduction system including the SA node

Pathophysiology

In third-degree AV block, the disruption in the heart's electrical conduction system prevents the atrial impulse from reaching the ventricles. As a result:

• An accessory pacemaker in the ventricles, typically the His-Purkinje system, initiates an escape rhythm.
• This leads to the atria and ventricles beating independently of each other, visible on an electrocardiogram (ECG).

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Causes

Possible causes of third-degree AV block include:

• Ischemic heart disease
• Cardiac surgery
• Certain medications
• Congenital heart defects
• Infiltrative diseases like sarcoidosis or amyloidosis

Symptoms

Symptoms can vary but may include:

• Fatigue
• Dizziness or lightheadedness
• Shortness of breath
• Fainting spells (syncope)
• Bradycardia (slow heart rate)

File:Bavc26 (CardioNetworks ECGpedia).jpg

ECG showing third-degree AV block

Diagnosis

Diagnosis involves:

• A thorough medical history and physical examination
• Electrocardiogram (ECG) revealing the independent atrial and ventricular rhythms
• Additional tests like echocardiography or cardiac MRI may be required

Treatment

Treatment options depend on the severity and underlying cause but may include:

• The implantation of a pacemaker
• Medication adjustments
• Addressing underlying conditions

Prognosis

The prognosis for third-degree AV block varies based on the underlying cause and treatment efficacy. Pacemaker implantation often significantly improves symptoms and quality of life.

Epidemiology

Third-degree AV block is relatively rare but can occur at any age, with increased prevalence in the elderly due to degenerative heart diseases.

References

• American Heart Association - Complete Heart Block
• Mayo Clinic - Heart Block
• National Center for Biotechnology Information - Atrioventricular Block

External Links

• Heart Rhythm Society - Heart Blocks
• Medscape - Third-Degree Atrioventricular Block