Third-degree atrioventricular block

Third-Degree Atrioventricular Block (AV Block)

Overview

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.

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)

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

Third-degree atrioventricular block Resources
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