Atrioventricular block, second degree

A type of heart block where some atrial impulses fail to reach the ventricles

Second-degree atrioventricular block
ECG showing second-degree AV block
Synonyms	N/A
Pronounce	N/A
Specialty	N/A
Symptoms	Dizziness, syncope, fatigue
Complications	Progression to third-degree AV block
Onset	Any age
Duration	Variable
Types	N/A
Causes	Myocardial infarction, cardiomyopathy, Lyme disease, medications
Risks	Age, heart disease, electrolyte imbalances
Diagnosis	Electrocardiogram
Differential diagnosis	N/A
Prevention	N/A
Treatment	Observation, pacemaker
Medication	N/A
Prognosis	Variable
Frequency	N/A
Deaths	N/A

Second-degree atrioventricular block is a type of heart block where some of the electrical signals from the atria fail to reach the ventricles. This condition is classified into two types: Mobitz type I (Wenckebach) and Mobitz type II.

Pathophysiology

The heart's electrical system controls the rate and rhythm of the heartbeat. In second-degree AV block, there is an intermittent failure of conduction between the atria and ventricles. This can occur at the level of the atrioventricular node (AV node) or below it in the His-Purkinje system.

Mobitz Type I (Wenckebach)

In Mobitz type I, there is a progressive prolongation of the PR interval on the electrocardiogram (ECG) until a beat is dropped. This type of block is usually due to a delay in the AV node and is often benign.

Mobitz Type II

Mobitz type II is characterized by a constant PR interval with intermittent non-conducted P waves. This type of block is more likely to be associated with disease in the His-Purkinje system and can progress to complete heart block.

Causes

Second-degree AV block can be caused by a variety of conditions, including:

• Myocardial infarction
• Cardiomyopathy
• Lyme disease
• Medications such as beta-blockers, calcium channel blockers, and digoxin
• Electrolyte imbalances

Symptoms

Patients with second-degree AV block may experience symptoms such as:

• Dizziness
• Syncope (fainting)
• Fatigue
• Palpitations

Diagnosis

The diagnosis of second-degree AV block is made using an electrocardiogram (ECG). The ECG will show the characteristic patterns of Mobitz type I or type II block.

Treatment

Treatment depends on the type of block and the presence of symptoms. Mobitz type I often requires no treatment if the patient is asymptomatic. Mobitz type II may require the implantation of a pacemaker to prevent progression to complete heart block.

Prognosis

The prognosis of second-degree AV block varies. Mobitz type I generally has a good prognosis, while Mobitz type II can lead to more serious complications if not treated appropriately.

Also see

• First-degree atrioventricular block
• Third-degree atrioventricular block
• Electrocardiogram
• Pacemaker

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