An atrioventricular block (AV block) is the impairment, or delay, of the electrical conduction between the atria and ventricles of the heart. Strong vagal stimulation may produce atrioventricular block. The cholinergic receptor types affected are the muscarinic receptors. Atrioventricular (AV) block occurs when the atrial depolarization fail to reach the ventricles or when atrial depolarization is conducted with a delay.
Atrioventricular block is partial or complete interruption of impulse transmission from the atria to the ventricles. The most common cause is idiopathic fibrosis and sclerosis of the conduction system. Diagnosis is by ECG; symptoms and treatment depend on degree of block, but treatment, when necessary, usually involves pacing.
There are three types of AV block: 1) first degree AV block - PR interval greater than 0.20 second; 2) second degree AV block, with rogressive prolongation of PR interval with dropped beats, or PR interval remains unchanged prior to the P wave which suddenly fails to conduct to the ventricles; third degree AV block - No association between P waves and QRS complexes.