A patient presents with abrupt onset of palpitations and a tachycardia around 150-250 beats per minute. What is the most likely diagnosis?

• A. Atrial fibrillation
• B. Sinus tachycardia
• C. Paroxysmal supraventricular tachycardia
• D. Ventricular tachycardia

Answer: (C)

A very fast, regular tachycardia that starts abruptly and reaches roughly 150–250 bpm is most consistent with paroxysmal supraventricular tachycardia due to an AV nodal reentry circuit. This pattern is typical: the rhythm is usually narrow-complex because the impulse travels through the normal His-Purkinje system, and the onset and termination occur suddenly, producing sudden palpitations. On ECG, you may not clearly see distinct P waves because they’re buried in the preceding T wave or occur right after, but the overall picture is a rapid, regular, narrow tachycardia.

This fits less with atrial fibrillation, which is an irregularly irregular rhythm with variable R-R intervals and often lacks that abrupt, sustained start. Sinus tachycardia tends to rise gradually in response to triggers (fever, anxiety, dehydration) and rarely locks in at such a fast, regular rate. Ventricular tachycardia usually presents as a wide-complex tachycardia and is more common in patients with structural heart disease.