What is first-degree AV block on ECG?

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Multiple Choice

What is first-degree AV block on ECG?

First-degree AV block occurs when the signal from the atria to the ventricles is slowed but still conducts every time. The key feature is a PR interval longer than 200 milliseconds, while every P wave is followed by a QRS complex and the QRS is otherwise normal in width. This means there is a consistent 1:1 relationship between P waves and QRS complexes, just with a prolonged conduction time through the AV node. If you see a pattern with PR intervals that progressively lengthen until a beat is dropped, that’s a second-degree block (Wenckebach). If there are intermittent dropped P waves with no preceding PR prolongation, that’s another form of second-degree block (Mobitz II). Complete AV dissociation, where atrial and ventricular activities run independently, is third-degree block.

First-degree AV block occurs when the signal from the atria to the ventricles is slowed but still conducts every time. The key feature is a PR interval longer than 200 milliseconds, while every P wave is followed by a QRS complex and the QRS is otherwise normal in width. This means there is a consistent 1:1 relationship between P waves and QRS complexes, just with a prolonged conduction time through the AV node.

If you see a pattern with PR intervals that progressively lengthen until a beat is dropped, that’s a second-degree block (Wenckebach). If there are intermittent dropped P waves with no preceding PR prolongation, that’s another form of second-degree block (Mobitz II). Complete AV dissociation, where atrial and ventricular activities run independently, is third-degree block.

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