A 44-year-old man is in the emergency department with rapid palpitation of 2 hours duration. He has had 3 similar episodes in the past 5 years, that had started and subsided spontaneously within 20-30 minutes:

• Supraventricular tachycardia, probably AVRT (Atrioventricular Re-entrant Tachycardia) or AVNRT (AV Nodal Re-entrant Tachycardia).
• Ventricular rate 210/min
• ST and T wave abnormality, consider inferior-lateral ischemia

Negative P waves, best seen in the limb leads, following closely the QRS complex (40-60 msec) suggest AVRT or AVNRT. However, the P waves appear separate from the QRS complex, which favours AVRT.

In AVRT the activation goes from the ventricle up to the atrium through the bypass tract so that the QRS and P appear separate in the majority of cases. In AVNRT the activation from the AV node travels simultaneously up to the atrium and down to the ventricle, so there is partial or total overlap of the QRS and P in the majority of case. (Notice: in the majority of the cases, not all cases!) In some patients, particularly in older subjects, the P waves may be separate from the QRS during AVNRT, That’s why both AVRT and AVNRT should be considered in the differential diagnosis.  

There was no response to vagal stimulation. The arrhythmia subsided after IV injection of Adenosine:  

• Sinus rhythm, 75/min
• Wolff-Parkinson-White
• The ST segment and T waves are normal  

The ECG pattern is typical of WPW. This confirms the diagnosis of AVRT. The advantages and risks of ablation of the bypass tract were discussed with the patient. He will be followed in the Electro-Physiology (EP) clinic.