August 13, 2026
human · beginner · rhythm strip
A 68-year-old comes to urgent care with two days of palpitations, mild shortness of breath, and fatigue. Blood pressure is 128/76 and the patient is alert. A lead II rhythm strip recorded at 25 mm/s is shown; the average ventricular rate is about 110 bpm and the QRS complexes are narrow. Based on the tracing, what is the rhythm?
Simulated tracing for education
Why
Instead of one sinus impulse organizing the atria, many chaotic wavelets circulate continuously in atrial tissue at 400 to 600 per minute. No single wavefront depolarizes enough myocardium at once to build a discrete P wave, so the baseline looks wavy or flat, and the AV node is bombarded randomly, letting only unpredictable impulses through. That produces narrow QRS complexes with R-R intervals that never settle into a pattern. Atrial flutter would show a regular sawtooth atrial rate near 300 with mathematically related R-R intervals, and both multifocal atrial tachycardia and sinus tachycardia with premature atrial beats still show visible P waves before each QRS.
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