First degree AV block is characterized by

• A. Delayed conduction through AV node, sinus rhythm
• B. Complete dissociation of atria and ventricles
• C. Ventricular tachycardia
• D. Atrial flutter

Answer: (A)

First-degree AV block shows a delay in conduction from the atria to the ventricles at the AV node, but the atrial and ventricular activities stay in step. On the ECG this is a PR interval longer than about 200 ms, with a normal QRS and a consistent 1:1 relationship between P waves and QRS complexes. There’s no dropped beats or dissociation; every atrial impulse still reaches the ventricle, just more slowly.

This is different from complete dissociation, where atria and ventricles beat independently because the AV node no longer conducts any impulses. It’s also not ventricular tachycardia, which is a fast, ventricular-origin rhythm with wide QRS and no stable P-to-QRS relationship. And it isn’t atrial flutter, which shows a rapid atrial rate with flutter waves and typically an AV conduction pattern that isn’t simply a prolonged PR interval.

So the best description is delayed AV nodal conduction with a sustained sinus rhythm and a prolonged but regular PR interval.