Atrioventricular Block
Cardiology (12%) Core Clinical Conditions
1B: Able to identify the condition as a possible diagnosis: may not have the knowledge or resources to confirm the diagnosis or to manage the condition safely, but can take measures to avoid immediate deterioration and refer appropriately
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Definition Aetiology Pathophysiology Risk factor Sign and Symptoms Investigations Management
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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