Q. If there is a blockage between the AV node and the AV bundle, how will this affect the appearance of the ECG?
NTA AbhyasNTA Abhyas 2020
Solution:
In an ECG, the P wave is a small upward wave that represents electrical excitation or depolarization of the atria that leads to contraction of both the atria. This is due to the trigger or activation of the SA node.
The QRS complex represents the depolarization of both ventricles, which initiates the ventricular contraction (ventricular systole). The contraction of the ventricles start shortly after Q and marks the beginning of the systole. The ventricles have a large muscle mass compared to the atria, so consequently, the amplitude of the QRS complex is usually much larger than the P wave.
A block between the AV node and the AV bundle is referred to as a third-degree AV block (a type of heart block). During this condition, there is an impairment in the conduction of electrical signal from the atria to the ventricles. Thus, the atrial depolarization does not reach the ventricles or is delayed. This causes the number of P waves to increase compared to its respective QRS complexes.
ECG waves for third-degree AV block
The QRS complex represents the depolarization of both ventricles, which initiates the ventricular contraction (ventricular systole). The contraction of the ventricles start shortly after Q and marks the beginning of the systole. The ventricles have a large muscle mass compared to the atria, so consequently, the amplitude of the QRS complex is usually much larger than the P wave.
A block between the AV node and the AV bundle is referred to as a third-degree AV block (a type of heart block). During this condition, there is an impairment in the conduction of electrical signal from the atria to the ventricles. Thus, the atrial depolarization does not reach the ventricles or is delayed. This causes the number of P waves to increase compared to its respective QRS complexes.
ECG waves for third-degree AV block