This 29-year-old woman presents to the Emergency Department complaining of palpitations, presyncope, and dyspnea. She reports experiencing palpitations for the past 14 years, that have a sudden-onset, are rapid and regular, and occur twice a year. She also states that they are accompanied by chest pounding, but no neck pulsation, and occasionally will terminate when she bends down:

• Supraventricular tachycardia, rate 157/min
• Non-specific ST abnormality

The possible presence of P waves at the end of the QRS in II, III and aVF was questioned, however, a definite diagnosis of the mechanism of the arrhythmia could not be made. On the basis of the ECG and the history, the differential diagnosis was between AVNRT and AVRT.

Vagal stimulation was unsuccessful. The arrhythmia terminated after the injection of IV adenosine. When sinus rhythm was restored, the ECG was normal. There were no delta waves. 

One month later, EP studies were carried out. With atrial pacing, a tachycardia was easily induced that was consistent with AVNRT. The slow pathway was ablated with a single RF application, and thereafter, tachycardia could no longer be induced.