A 22-year-old woman is evaluated in the emergency department because of symptoms of prolonged palpitations. She complains of no associated chest discomfort, shortness of breath, or lightheadedness. The palpitations have occurred twice before, but they always stopped spontaneously after 5 minutes, and she cannot associate them with any triggers. The past health history is negative and she is not on any medications.On physical examination, the blood pressure is 110/70 mm Hg, heart rate is 160/min and regular. The heart and lung examinations are normal, and the ECG is shown in Figure below. The heart rate abruptly changes to 72/min after applying carotid sinus pressure. Which of the following is the most likely diagnosis?
Correct Answer: paroxysmal supraventricular tachycardia (PSVT)
Description: The patient most likely has PSVT, since the tachycardia terminates after carotid sinus massage (CSM). CSM increases vagal tone (parasympathetic) which decreases AV nodal conduction and terminates AV node re-entry arrhythmias. Sinus tachycardia differs from PSVT tachycardia in that it does not start or stop abruptly; it will slow down with CSM but will resume the previous rate once the maneuver is stopped. In PSVT, the QRS is usually narrow without clearly discernible P waves. The ECG does not support the other answers, since ventricular tachycardia is a regular wide complex rhythm, atrial flutter can be a regular narrow complex tachycardia but usually atrial flutter waves are seen, and finally atrial fibrillation is an irregular rhythm with no atrial activity. A wide QRS in PSVT can result from a preexisting bundle branch block, or a functional bundle branch block secondary to the tachycardia. This can make the distinction from a ventricular arrhythmia quite difficult.
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