August 11, 2026
human · beginner · rhythm strip
A 58-year-old man is seen in clinic for occasional "skipped beat" sensations. His telemetry strip shows an underlying regular rhythm at about 78 beats per minute, interrupted three times by an early beat. Each early beat has a narrow QRS identical in shape to the others, and just in front of it is a small upright bump that sits differently from the P waves of the regular beats. The pause after each early beat is short, and the underlying timing resumes without a full missed cycle. What is the rhythm?
Simulated tracing for education
Why
An irritable focus in atrial tissue outside the sinus node fires before the sinus node reaches threshold. Because the impulse still travels down the normal AV node and His-Purkinje system, the QRS looks exactly like the sinus beats. The ectopic focus sits away from the sinus node, so its P wave has a different shape or axis and often a different PR interval. It also resets the sinus node, giving a short, non-compensatory pause. A ventricular ectopic would arise below the AV node, producing a wide, bizarre QRS with no preceding P wave and typically a fully compensatory pause. A junctional beat would show no P wave in front, or a retrograde inverted one. Only isolated early beats are present, not three or more in a row, so this is not a run of atrial tachycardia.
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