August 12, 2026
human · beginner · rhythm strip
A 58-year-old presents to the clinic reporting occasional "skipped beats." The 12-lead tracing shows an underlying regular rhythm at about 78 beats per minute with upright P waves before most QRS complexes. Three times on the strip, an early, wide (>140 ms), bizarre-looking QRS appears with no P wave in front of it and with the T wave pointing opposite the QRS; each is followed by a brief pause before the next normal beat. No two early beats occur in a row. What is the rhythm?
Simulated tracing for education
Why
The sinus node is still driving the baseline rhythm, so most beats have a P wave and a narrow QRS. The early beats arise from an irritable focus in ventricular muscle below the His bundle. Because the impulse spreads cell to cell through myocardium rather than down the fast His-Purkinje system, depolarization is slow and asymmetric, giving a wide, odd-shaped QRS with repolarization pushed in the opposite direction (discordant T wave). No atrial activity precedes it, which separates it from a premature atrial complex, where an early ectopic P wave (often hidden in the prior T wave) comes first, even when conducted aberrantly. Ventricular tachycardia requires three or more consecutive ventricular beats; here they stay isolated.
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