Atrioventricular block: Heart's electrical signal transmission block

2021-06-01 03:07 PM

In the third-degree block, there is no association between the P waves and the QRS complex because the ventricle has "escaped" from atrial control and is beating in its own rhythm.

 

When conditions cause poor conduction of the AV node and the His bundle, complete blockade of the atrioventricular to ventricular impulse occurs. The ventricles then spontaneously pulse, often far from the location of the AV node or bundle. His is blocked. Therefore, the P wave will dissociate from the QRS complex.

Figure. Complete atrioventricular block (lead II).

Normal atrial rhythm on electrocardiogram is about 100 beats/min, the ventricular rate is less than 40 beats/min. In the third-degree block, there is no association between the P waves and the QRS complex because the ventricle has "escaped" from atrial control and is beating in its own rhythm.

Adams-Stokes syndrome / Ventricular hernia. Some patients have an atrioventricular block. Complete block appears and then disappears, impulses conduction from the atria to the ventricles for a while and then suddenly lose conduction. The duration of the block is a few seconds, minutes, hours, or weeks or more before conduction resumes. This occurs in the heart with asymptotic ischemic conduction of the conduction system.

Whenever AV (atrioventricular) conduction stops, the ventricles will not spontaneously beat until the pulse is delayed for 5-30 seconds. This delay is caused by the phenomenon of “over-compression”. “Over compression” means that the excitable ventricle is compressed for the first time. Usually, the atrium-driven ventricle beats faster than its natural rhythm. However, after a few seconds, several parts of the Purkinje system escape block, usually in the distal part of the AV node. This site beats about 15-40 beats/min and acts as a ventricular pacemaker. This phenomenon is called loss.

Since the brain cannot function for more than 4-7 seconds without a blood supply, many patients’ faint seconds after a complete block occurs because the heart does not pump for 5-30 seconds until it "falls out". After exiting, ventricular bradycardia pumps enough blood to the brain to recover from syncope and the patient gradually regains consciousness. This episode of syncope is known as Adams Stokes syndrome

Sometimes, the ventricular pause incomplete block is so long that it affects the patient's health, possibly leading to death. As a result, most patients are provided with an artificial pacemaker, a small battery-powered machine. implanted under the skin with a power supply connected to the right ventricle. The pacemaker continuously stimulates the ventricles.