There is a very short PR here and delta waves are visible in leads V3, II, III, and aVF. Most cases of “SVT” are AV nodal re-entrant tachycardia (AVNRT). This turned out to be orthodromic SVT in the setting of undiagnosed WPW. The distinction is not important in the moment. But had the QRS complex been wide, we would have had to assume it was VT.

The post conversion EKG shows WPW (short PR and delta wave)

This was a 21 year old lady, whom we now know has WPW. The post conversion EKG shows a short PR and a delta wave visible in V3 the inferior leads (II, III, and aVF).

20 month old