Third degree AV block overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Overview
Third degree AV block, also known as complete heart block, is a defect of the electrical system of the heart, in which the impulse generated in the atria (typically the SA node on top of the right atrium) does not propagate to the ventricles.
Causes
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.
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.
Diagnosis
History and Symptoms
Patients with third degree AV block typically experience a lower overall measured heart rate (as low as 28 beats per minute during sleep), low blood pressure, and poor circulation. In some cases, exercising may be difficult, as the heart cannot react quickly enough to sudden changes in demand or sustain the higher heart rates required for sustained activity.