In sinus tachycardia, which statement is true?

• A. Rhythm is irregular
• B. There is no P wave
• C. Rhythm is normal with a P wave and QRS complex, but the heart rate is fast
• D. QRS duration is wide

Answer: (C)

Sinus tachycardia means the heart’s natural pacemaker is firing faster than normal, but the impulse still follows the usual path through the atrioventricular conduction system. The hallmark is a regular rhythm with each heartbeat preceded by a P wave and followed by a QRS complex, and the QRS is narrow because conduction is intact. The rate is fast, typically over 100 beats per minute, while the overall rhythm and waves resemble normal sinus rhythm. That’s why the statement describing a normal-appearing rhythm with a P wave and QRS complex, but a fast heart rate, is correct. The other patterns don’t fit sinus tachycardia: irregular rhythm suggests atrial fibrillation or similar; no P wave points to a junctional or ventricular rhythm; a wide QRS points to ventricular conduction issues or ventricular origin, not sinus tachycardia.