Third-Degree Atrioventricular Block (AV Block)[edit | edit source]

Overview[edit | edit source]

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[edit | edit source]

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[edit | edit source]

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[edit | edit source]

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[edit | edit source]

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[edit | edit source]

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

The implantation of a pacemaker
Medication adjustments
Addressing underlying conditions

Prognosis[edit | edit source]

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[edit | edit source]

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[edit | edit source]

External Links[edit | edit source]

Third-degree atrioventricular block Resources
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