Which feature identifies a paced rhythm on an ECG?

• A. Absence of QRS complexes
• B. Inverted T waves in all leads
• C. Evidence of pacing spikes before the QRS complexes and a paced rhythm pattern
• D. Prolonged PR interval without QRS

Answer: (C)

Recognizing a paced rhythm comes from noticing pacing spikes—tiny vertical deflections—before the QRS complexes. Those spikes are the pacemaker’s impulses delivering capture. When the ventricle is paced, the subsequent QRS is the paced complex, and the rhythm repeats with the same pattern, creating a recognizable paced rhythm. This pacing spike-before-QRS pattern is what identifies a paced rhythm.

Other features don’t fit: absence of all QRS complexes would mean no ventricular activation, not pacing; inverted T waves in all leads are nonspecific and don’t indicate pacing; a prolonged PR interval without QRS suggests first-degree AV block, not pacing.