AV in ECG most commonly refers to the atrioventricular node and the concept of atrioventricular (AV) conduction. It can also sometimes refer to atrioventricular block. These are crucial elements of heart function depicted on an electrocardiogram (ECG). Let's break down each concept.
Atrioventricular (AV) Node
The atrioventricular (AV) node is a specialized mass of conducting cells located in the heart between the atria and ventricles. It plays a critical role in the heart's electrical conduction system.
- Function: The AV node delays the electrical impulse from the atria before it is passed on to the ventricles. This delay allows the atria to contract and empty their contents into the ventricles before ventricular contraction begins. This contributes to optimal cardiac output.
Atrioventricular (AV) Conduction
Atrioventricular conduction refers to the transmission of electrical impulses from the atria to the ventricles. This process is essential for coordinated heart contraction. The ECG reflects the efficiency and integrity of this conduction pathway. Issues with AV conduction can manifest as various arrhythmias or heart blocks.
Atrioventricular (AV) Block
An atrioventricular (AV) block, also known as heart block, refers to a delay or blockage of the electrical signal as it travels from the atria to the ventricles. AV blocks are categorized into different degrees based on the severity of the conduction disturbance:
-
First-Degree AV Block: Defined by a prolonged PR interval (greater than 0.20 seconds) on the ECG. This indicates a slowing of conduction through the AV node. There is consistent 1:1 AV conduction.
-
Second-Degree AV Block: Some, but not all, atrial impulses are blocked from reaching the ventricles. There are two main types:
- Mobitz Type I (Wenckebach): Progressive prolongation of the PR interval until a QRS complex is dropped.
- Mobitz Type II: PR interval is constant, but there are intermittent dropped QRS complexes.
-
Third-Degree AV Block (Complete Heart Block): No atrial impulses reach the ventricles. The atria and ventricles beat independently of each other. This is a serious condition requiring prompt treatment.
In summary, "AV" in the context of an ECG most commonly relates to the atrioventricular node, AV conduction, or AV block, all of which are fundamental to understanding the electrical activity and health of the heart.
