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Question 83#

The following tachycardia was induced during EP testing of a 36-year-old woman with recurrent palpitations (Fig. below).

Which of the following is the most likely diagnosis?

A. AVNRT
B. Orthodromic reentrant tachycardia
C. Antidromic reentrant tachycardia
D. VT
E. Idiopathic left VT

Correct Answer is A

Comment:

AVNRT. This tracing shows AVNRT. It is a narrow complex tachycardia using the slow pathway of the AV node in the antegrade direction (long AH) and the fast pathway of the AV node in the retrograde direction (short HA). It is unlikely to be orthodromic reentrant tachycardia in which the retrograde limb of the circuit is an accessory pathway, because the QRS-A time is very short (atrium and ventricle are activated almost spontaneously), not long enough to involve ventricular activation as part of the circuit. Because the QRS is narrow, VT is not a likely diagnosis. Idiopathic LV-VT can sometimes be narrow but has an RBBB morphology on the surface ECG.