What finding defines 1st Degree Heart Block?

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Multiple Choice

What finding defines 1st Degree Heart Block?

First-degree AV block is defined by slowed conduction through the AV node, which shows up on the ECG as a consistently prolonged PR interval—more than 200 milliseconds—while every atrial impulse still conducts to the ventricles. In other words, there is a P wave before each QRS, the rhythm stays regular, and the QRS complex is normal in width. This combination—PR prolongation without dropped beats—is what sets first-degree block apart. Normal sinus rhythm would have a normal PR interval, so it wouldn’t show this delay. A junctional rhythm often has absent or backwards-projected P waves and can have a different relationship between atrial and ventricular activity. A second-degree block Type I (Wenckebach) shows progressively lengthening PR intervals followed by a dropped QRS, not a constant prolonged PR with every beat conducted.

First-degree AV block is defined by slowed conduction through the AV node, which shows up on the ECG as a consistently prolonged PR interval—more than 200 milliseconds—while every atrial impulse still conducts to the ventricles. In other words, there is a P wave before each QRS, the rhythm stays regular, and the QRS complex is normal in width. This combination—PR prolongation without dropped beats—is what sets first-degree block apart.

Normal sinus rhythm would have a normal PR interval, so it wouldn’t show this delay. A junctional rhythm often has absent or backwards-projected P waves and can have a different relationship between atrial and ventricular activity. A second-degree block Type I (Wenckebach) shows progressively lengthening PR intervals followed by a dropped QRS, not a constant prolonged PR with every beat conducted.

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