Which feature is most characteristic of paroxysmal supraventricular tachycardia?

• A. Narrow QRS complex
• B. Wide QRS complex
• C. Absent P waves
• D. Prolonged QT interval

Answer: (A)

Paroxysmal supraventricular tachycardia comes from above the ventricles, so the impulse travels through the normal His-Purkinje system to activate the ventricles. That results in a very fast but relatively normal-appearing ventricular activation, producing narrow QRS complexes (usually under 120 ms). The rapid rhythm is often so brisk that P waves are hidden within the QRS or immediately after it, so you may not see distinct P waves, but the key clue on the ECG is the regular, fast rhythm with narrow QRS complexes. A wide QRS would point toward a ventricular origin or aberrant conduction rather than a typical SVT, and a prolonged QT interval is not a defining feature of PSVT.