A regular narrow-complex rhythm at 40-60/min with no upright P waves: any P is inverted, just before, inside or just after the QRS.
The AV junction paces the heart because nothing faster is reaching it. You get a regular rhythm at 40-60/min with narrow QRS complexes (the ventricles still activate normally) and no relationship to any sinus P wave. The junction activates the atria backward, so any P wave you see is inverted in II, III and aVF. It sits just before the QRS with a PR under 0.12 s, hidden inside it, or just after it. You'll see this rhythm with severe sinus bradycardia, sinus arrest, sinoatrial exit block, high-grade AV block, hyperkalemia, and beta-blocker, calcium-channel blocker or digoxin poisoning. Under 40/min, it's junctional bradycardia.
Each strip is 6 seconds of lead II, drawn to scale (25 mm a second, 10 mm a millivolt), so you can count boxes the way you would on paper. Each one is a different example, measured below it.
Everything normal sinus rhythm has, but under 60/min.
P waves and QRS complexes each regular but unrelated: no P is conducted, so the PR is all over the place.
Regular wide complexes at 20-40/min, with no P waves.
Want a new strip every time? The ECG Drill in the app draws a fresh, measured example on every try and steers you toward the rhythms you miss. It's part of the Paramedic level, and you can try 5 strips a day free.
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