Regular sinus rhythm with one whole P-QRS-T missing, and the next P exactly on time: the pause is exactly two P-P intervals.
The sinus node keeps firing on schedule, but one impulse never makes it out into the atria. You lose a whole P-QRS-T, and the next P shows up exactly when it was due. March out the P waves with calipers: the pause is exactly two P-P intervals. That's the difference from sinus arrest, where the node stops and restarts on its own schedule, so the pause isn't a whole number of cycles. And unlike Mobitz II, the P wave is missing too, not just the QRS.
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.
Regular sinus rhythm, then a pause of over 3 seconds that is not a whole number of P-P cycles.
A constant PR, then a P wave that suddenly isn't conducted. The QRS is often wide.
An early P wave on the T wave with no QRS after it, then a pause.
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.
Try the ECG Drill
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