Which feature defines Supraventricular Tachycardia?

• A. Narrow QRS complex, rate >150 bpm, P waves often lost
• B. Wide QRS complex tachycardia with visible P waves
• C. Slow rate with wide QRS
• D. P waves before each QRS with normal rate

Answer: (A)

Supraventricular tachycardia is a rapid rhythm that starts above the ventricles. Because the impulse travels through the normal ventricular conduction system, the QRS complexes stay narrow even though the rate is very fast. In adults, the rate usually exceeds 150 beats per minute. At such a high speed, atrial depolarization and ventricular depolarization collide so closely that the P waves are often hidden within the preceding T wave or buried in the QRS, making them hard to see. This combination—narrow QRS, rate over 150 bpm, and P waves not clearly visible—is the hallmark of SVT.

The other patterns don’t fit as well: a wide QRS tachycardia points toward ventricular origin or aberrant conduction; a slow rate with wide QRS isn’t tachycardia of this type; P waves before each QRS with a normal rate describes normal sinus rhythm rather than SVT.