Atrioventricular block, first degree

A type of heart block where the electrical conduction between the atria and ventricles is delayed

First-degree atrioventricular block
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Synonyms	N/A
Pronounce	N/A
Specialty	N/A
Symptoms	Often asymptomatic
Complications	Rarely progresses to higher degree blocks
Onset
Duration
Types	N/A
Causes	Degenerative changes, medications, increased vagal tone
Risks
Diagnosis	Electrocardiogram (ECG)
Differential diagnosis	N/A
Prevention	N/A
Treatment	Usually none required
Medication	N/A
Prognosis	Excellent
Frequency
Deaths	N/A

First-degree atrioventricular block (also known as first-degree AV block) is a type of heart block where the electrical conduction between the atria and ventricles of the heart is delayed. This condition is characterized by a prolonged PR interval on an electrocardiogram (ECG).

Pathophysiology

In first-degree AV block, the electrical impulse generated by the sinoatrial node is delayed at the atrioventricular node before it reaches the ventricles. This delay results in a prolonged PR interval, which is greater than 200 milliseconds. Unlike higher degrees of AV block, first-degree AV block does not result in missed beats or dropped QRS complexes.

Causes

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

• Degenerative changes in the conduction system due to aging.
• Increased vagal tone, which can occur in athletes.
• Medications such as beta-blockers, calcium channel blockers, and digoxin.
• Myocarditis or other inflammatory conditions affecting the heart.
• Electrolyte imbalances, particularly hyperkalemia.

Symptoms

Most individuals with first-degree AV block are asymptomatic and the condition is often discovered incidentally during an ECG performed for another reason. Rarely, patients may experience symptoms such as fatigue or lightheadedness, but these are uncommon.

Diagnosis

The diagnosis of first-degree AV block is made using an electrocardiogram (ECG). The hallmark finding is a PR interval greater than 200 milliseconds. It is important to differentiate first-degree AV block from other types of heart block, such as second-degree atrioventricular block and third-degree atrioventricular block.

Treatment

In most cases, first-degree AV block does not require treatment. It is generally considered a benign condition with an excellent prognosis. However, if the block is caused by medication, adjusting the dosage or discontinuing the medication may be necessary. Regular follow-up with a healthcare provider is recommended to monitor for any progression to higher degrees of block.

Prognosis

The prognosis for individuals with first-degree AV block is excellent. It rarely progresses to more severe forms of heart block and does not typically affect life expectancy.

Also see

• Second-degree atrioventricular block
• Third-degree atrioventricular block
• Electrocardiogram
• Sinoatrial node
• Atrioventricular node

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