Third-degree atrioventricular block

Third-degree atrioventricular block
Other names	Complete heart block
12-lead ECG showing complete heart block
Specialty	Cardiology
Symptoms	Dizziness, Fainting, Shortness of breath, Sudden cardiac death
Causes	Fibrosis in cardiac conduction system, myocardial infarction, post-cardiac surgery, medication, vagal tone, electrolyte disturbances
Diagnostic method	Electrocardiogram
Treatment	Pacemaker

Third-degree atrioventricular block (AV block) is a medical condition in which the electrical impulse generated in the sinoatrial node (SA node) in the atrium of the heart can not propagate to the ventricles.^[1]

Because the impulse is blocked, an accessory pacemaker in the lower chambers will typically activate the ventricles. This is known as an escape rhythm. Since this accessory pacemaker also activates independently of the impulse generated at the SA node, two independent rhythms can be noted on the electrocardiogram (ECG).

• The P waves with a regular P-to-P interval (in other words, a sinus rhythm) represent the first rhythm.
• The QRS complexes with a regular R-to-R interval represent the second rhythm. The PR interval will be variable, as the hallmark of complete heart block is the lack of any apparent relationship between P waves and QRS complexes.