What does the P wave look like in first-degree AV block?

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Multiple Choice

What does the P wave look like in first-degree AV block?

In first-degree AV block the atrial depolarization looks normal, but conduction from the atria to the ventricles is slowed. On the ECG you still see normal P waves—upright and consistent in shape and duration—because the atria are depolarizing normally. The abnormality is the time it takes for the impulse to pass through the AV node, so the PR interval becomes longer than 0.20 seconds, while every P wave is still followed by a QRS complex. Therefore, the best description is a normal P wave with a prolonged PR interval. Inverted P waves would suggest atrial or junctional rhythms with retrograde activation, and absent P waves point to atrial fibrillation or other atrial nondepolarization. The key here is the combination of a normal-looking P wave with a lengthened PR interval.

In first-degree AV block the atrial depolarization looks normal, but conduction from the atria to the ventricles is slowed. On the ECG you still see normal P waves—upright and consistent in shape and duration—because the atria are depolarizing normally. The abnormality is the time it takes for the impulse to pass through the AV node, so the PR interval becomes longer than 0.20 seconds, while every P wave is still followed by a QRS complex. Therefore, the best description is a normal P wave with a prolonged PR interval.

Inverted P waves would suggest atrial or junctional rhythms with retrograde activation, and absent P waves point to atrial fibrillation or other atrial nondepolarization. The key here is the combination of a normal-looking P wave with a lengthened PR interval.

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