First-degree atrioventricular block

First-degree Atrioventricular Block

ECG showing first-degree AV block, characterized by a prolonged PR interval.

First-degree atrioventricular (AV) block is a type of heart block where the electrical conduction between the atria and ventricles of the heart is delayed but not interrupted. It is the mildest form of AV block and is often asymptomatic.

Pathophysiology

In first-degree AV block, the electrical impulse generated in the sinoatrial node is delayed at the atrioventricular node before it reaches the ventricles. This delay is reflected on an electrocardiogram (ECG) as a prolonged PR interval, which is greater than 200 milliseconds. The PR interval is the time from the onset of the P wave to the start of the QRS complex.

Causes

First-degree AV block can be caused by a variety of factors, including:

• Increased vagal tone
• Medications such as beta-blockers, calcium channel blockers, and digoxin
• Electrolyte imbalances, particularly hyperkalemia
• Myocardial ischemia or infarction
• Degenerative changes in the conduction system due to aging

Clinical Significance

First-degree AV block is often benign and does not require treatment. However, it can be an indicator of underlying heart disease or a precursor to more advanced forms of heart block. In some cases, it may be associated with an increased risk of atrial fibrillation and other arrhythmias.

Diagnosis

Diagnosis of first-degree AV block is typically made using an ECG, which will show a prolonged PR interval. It is important to differentiate it from other types of AV block, such as second-degree and third-degree AV block, which have different clinical implications and management strategies.

Management

In most cases, no specific treatment is required for first-degree AV block. Management focuses on addressing any underlying causes, such as adjusting medications or correcting electrolyte imbalances. Regular monitoring may be recommended to ensure that the block does not progress to a more severe form.

Prognosis

The prognosis for individuals with first-degree AV block is generally excellent, especially if there is no underlying heart disease. Most individuals live normal, healthy lives without any significant complications.

Also see

• Second-degree atrioventricular block
• Third-degree atrioventricular block
• Electrocardiogram
• Atrioventricular node
• Heart conduction system

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