A 61-year-old man has developed rapid palpitation with dyspnea and weakness while in the recovery room after GU surgery:

• Supraventricular tachycardia, rate 152/min
• Negative P waves in the inferior leads, positive P waves in aVR and V1 (pseudo-r’)
• The P waves follow immediately the QRS  (there is no gap between QRS and P)
• Findings typical of AV Nodal Re-entrant Tachycardia (AVNRT)

The arrhythmia subsided following vagal stimulation. There is now sinus rhythm, 92/min.
        

• In ECG 1 there is a supraventricular tachycardia (AVNRT) with P waves following the QRS complexes very closely (negative P in II, III and aVF, pseudo-R’ in V1)
• In  ECG 2 the P waves precede the QRS and are positive in I and aVF (sinus rhythm, 92/min)