A patient is undergoing a treadmill stress test. The appearance of abnormally wide, irregularly spaced QRS complexes on the ECG represents

A patient is undergoing a treadmill stress test. The appearance of abnormally wide, irregularly spaced QRS complexes on the ECG represents

• A. Ventricular depolarization
• B. Premature ventricular contractions
• C. Atrial fibrillation
• D. Atrial repolarization

Answer: (B)

The key idea is ventricular ectopy, specifically a premature ventricular contraction. When a beat originates in the ventricular myocardium rather than the normal conduction system, depolarization travels through the ventricles in a cell-to-cell fashion, producing a broad, bizarre QRS complex that lasts longer than 0.12 seconds. Because the beat comes early, the QRS occurs sooner than expected, and the rhythm becomes irregular as these premature beats interrupt the regular cadence. On a treadmill test, exercise can provoke PVCs due to increased irritability of the ventricles or ischemia, so you’d see these abnormally wide QRS complexes appearing irregularly. This pattern is distinct from atrial fibrillation, which involves chaotic atrial activity with an irregularly irregular rhythm and typically normal-width QRS unless conduction blocks are present, and from simple atrial repolarization concepts, which don’t explain the wide, premature-wide complexes you’re seeing.

The key idea is ventricular ectopy, specifically a premature ventricular contraction. When a beat originates in the ventricular myocardium rather than the normal conduction system, depolarization travels through the ventricles in a cell-to-cell fashion, producing a broad, bizarre QRS complex that lasts longer than 0.12 seconds. Because the beat comes early, the QRS occurs sooner than expected, and the rhythm becomes irregular as these premature beats interrupt the regular cadence. On a treadmill test, exercise can provoke PVCs due to increased irritability of the ventricles or ischemia, so you’d see these abnormally wide QRS complexes appearing irregularly. This pattern is distinct from atrial fibrillation, which involves chaotic atrial activity with an irregularly irregular rhythm and typically normal-width QRS unless conduction blocks are present, and from simple atrial repolarization concepts, which don’t explain the wide, premature-wide complexes you’re seeing.