Definition

Atrioventricular block (AV block) occurs when the electrical signal that flows from the atria to ventricle is blocked or slowed down. Can be classified in three categories according to severity: first-degree block, second-degree block and third-degree block. 

  • First-degree: mild symptoms or asymptomatic. Generally no treatment is required. 

  • Second-degree & third can cause symptoms such as syncope, shortness of breath (SOB) and dizziness.

Aetiology

  • Heart conditions such as myocardial infarction (MI), cardiomyopathy and coronary artery disease 

  • Certain medications: beta blockers, calcium channel blockers (CCBs) and digoxin 

  • Congenital heart defects 

  • Certain infections: commonly Lyme disease (not very common in the UK)

  • Others causes: electrolytes imbalance, autoimmune causes, increased age

Pathophysiology

There is a slowing and obstruction of the heart's normal electrical impulse. This prevents the normal flow of electrical activity from the sinoatrial (SA) node to the bundle of His and Purkinje fibres.

Risk factors

  • Increased age 

  • Medications that may affect the electrical impulses to the heart, medications such as beta blockers, calcium channel blockers (CCBs) and digoxin. 

  • Congenital heart defects 

  • Heart conditions such as coronary artery disease, myocardial infarction (MI), cardiomyopathies. 

  • Some infections such as lyme disease 

  • Electrolyte imbalance 

  • Lifestyle factors such as excessive alcohol consumption, smoking, sedentary lifestyle

Sign and symptoms

  • First-degree AV block: asymptomatic

  • Second-degree: dizziness, syncope (worse on exertion)

  • Third-degree: fatigue, dizziness, syncope, shortness of breath and if severe loss of consciousness or cardiac arrest.

Investigations

  • Physical examination: may have irregular pulse, bradycardia, hypotension (in third-degree block)

  • Electrocardiogram (ECG) see figure 1, 2, 3 and 4.

  • Holter monitor (24-hr ECG)

  • Echocardiogram 

  • Bloods 

  • Imaging: CXR, MRI and cardiac catheterisation

Figure 1; First-degree AV block

The Rythm is regular. The P wave is present. However, the PR interval is prolonged ( >200ms).

Figure 2; Second-degree AV block (type 1)

The Rythm is irregular. The P wave is present but not all QRS Complex are present and they are dropped.

Figure 3; Second-degree AV (type 2)

The Rythm is irregular (in this example it is a regularly irregular 3:1 block). The P wave is present but there are more P waves compared to QRS complexes. The PR interval is normal but some QRS complexes are dropped.

Figure 3;third-degree (complete) AV block

The Rythm is varibale. The P waves are present but not associated with the QRS complexes. There is no PR interval.

Management

  • First degree AV block: no treatment

  • Second-degree: if a medication is the cause, it should be stopped. However, if the patient is symptomatic a pacemaker should be considered. 

  • Third-degree: Permanent Pacemaker

 
 
 

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