Third degree AV block (patient information)
Overview
What are the symptoms of Third degree AV block?
People with third-degree AV block typically experience severe bradycardia (an abnormally low measured heart rate), hypotension, and at times, hemodynamic instability.
What causes Third degree AV block?
Third-degree atrioventricular block (AV block) is a medical condition in which the nerve impulse generated in the sinoatrial node (SA node) in the atrium of the heart can not propagate to the ventricles.
Many conditions can cause third-degree heart block, but the most common cause is coronary ischemia. Progressive degeneration of the electrical conduction system of the heart can lead to third-degree heart block. This may be preceded by first-degree AV block, second-degree AV block, bundle branch block, or bifascicular block. In addition, acute myocardial infarction may present with third-degree AV block.
An inferior wall myocardial infarction may cause damage to the AV node, causing third-degree heart block. In this case, the damage is usually transitory. Studies have shown that third-degree heart block in the setting of an inferior wall myocardial infarction typically resolves within 2 weeks. The escape rhythm typically originates in the AV junction, producing a narrow complex escape rhythm.
An anterior wall myocardial infarction may damage the distal conduction system of the heart, causing third-degree heart block. This is typically extensive, permanent damage to the conduction system, necessitating a permanent pacemaker to be placed. The escape rhythm typically originates in the ventricles, producing a wide complex escape rhythm.
Third-degree heart block may also be congenital and has been linked to the presence of lupus in the mother. It is thought that maternal antibodies may cross the placenta and attack the heart tissue during gestation. The cause of congenital third-degree heart block in many patients is unknown. Studies suggest that the prevalence of congenital third-degree heart block is between 1 in 15,000 and 1 in 22,000 live births.
Hyperkalemia in those with previous cardiac disease and Lyme disease can also result in third-degree heart block.
Who is at highest risk?
Elderly, particularly those with ischemic heart disease, and patients with certain disorders such as Lyme disease are at increased risk of developing complete heart block (CHB).
Diagnosis
An electrocardiogram ( ECG) is used to diagnose CHB.
When to seek urgent medical care?
Treatment options
Medications to avoid
Patients diagnosed with third degree AV block(except in patients with a functioning artificial pacemaker) should avoid using the following medications:
- Adenosine
- Atenolol
- Fingolimod
- Flecainide
- Labetalol
- Penbutolol
- Pindolol
- Procainamide
- Propranolol
- Sotalol
- Timolol
- Verapamil
If you have been diagnosed with third degree AV block(except in patients with a functioning artificial pacemaker), consult your physician before starting or stopping any of these medications.