Question

If there is a blockage between the SA and the AV node, and each fires independetly, how will this affect the appearance of the electrocardiogram?

Group of answer choices
A. The T wave will disappear.
B. There will be more QRS complexes than P waves.
C. There will be more P waves than QRS complexes.
D. The QRS will be longer.

Answer 1

In a complete AV block, where the SA and AV nodes fire independently, there will be more P waves than QRS complexes on the ECG since atrial depolarization (P waves) and ventricular activity (QRS complexes) are not synchronized. The correct option is C.

Step-by-step explanation:

When there is a blockage between the SA (sinoatrial) node and the AV (atrioventricular) node, and each fires independently, this condition is referred to as a third-degree or complete AV block.

In this scenario, there will be more P waves than QRS complexes on the electrocardiogram (ECG) because the atria and ventricles are not synchronized. The SA node continues to initiate depolarization of the atria, which is seen as P waves on the ECG.

However, these impulses do not reach the AV node consistently to trigger the subsequent depolarization of the ventricles. The AV node, acting as a secondary pacemaker, initiates its independent rhythm resulting in fewer QRS complexes.

Therefore, the correct answer to the student's question is C. There will be more P waves than QRS complexes. This is because the P waves represent atrial activity, and the QRS complexes represent ventricular activity, with no correlation between the two in this complete block condition.