This 59-year-old woman with a history of hypertension had been complaining for the past two years of episodes of rapid regular palpitation, starting and end suddenly, associated with dyspnea and weakness. They occurred 2-3 times a year. She presents to the Emergency Department one hour after onset of palpitation:

• Supraventricular tachycardia – AV Nodal Re-entrant Tachycardia (AVNRT)
• Non-specific ST abnormality

After unsuccessful vagal stimulation, the patient received an intravenous bolus injection of Adenosine and her palpitation subsided:

Compared with the previous tracing, sinus rhythm has been restored. This tracing is within normal limits:

Notice that the retrograde P waves that closely followed the QRS during AVNRT (pseudo S wave in II, III and aVF and pseudo r’ in V1) were no longer present after sinus rhythm was restored.

ECG 1-AVNRT

ECG 2-Sinus rhythm