Question

_______________ occurs when some P waves are not conducted through the AV node; hence more P than QRS waves are seen. In this tracing, the ratio of P waves to QRS waves is mostly 2:1.

Answer 1

The condition in question is a second-degree AV block, where not all atrial impulses are conducted through the AV node, resulting in a 2:1 ratio of P waves to QRS complexes on the ECG and potentially a slower heart rate.

Step-by-step explanation:

The condition described is a second-degree AV block, specifically the type where there is a 2:1 ratio of P waves to QRS complexes. This indicates that only half of the atrial electrical impulses (represented by P waves on an electrocardiogram, or ECG) are being conducted through the AV node to stimulate ventricular contraction (represented by the QRS complex). In a typical ECG, one would expect to see a P wave followed by a QRS complex and then a T wave, indicating a normal cardiac cycle. In a second-degree AV block, some P waves are not followed by a QRS complex, leading to a scenario where the heart rate (pulse) might be slower than expected, as not all atrial contractions lead to ventricular contractions.

AV blocks can be categorized into degrees, with a first-degree AV block showing delayed conduction through the AV node, a second-degree AV block (as described in the question) revealing intermittent conduction, and a third-degree AV block showcasing a complete disassociation between atrial and ventricular activities. In the ECG tracing described, the 2:1 ratio of P waves to QRS waves is indicative of intermittent conduction failure in the AV node, characteristic of a second-degree AV block.