SVT and AVNRT

Figure 1. (A) In typical atrioventricular nodal reentrant tachycardia (antegrade conduction down the slow atrioventricular nodal pathway and retrograde conduction up the fast pathway), the retrograde P wave may not be seen or may be visible early after the QRS complex. When visible, it often appears as a pseudo R wave in lead V1. Am Fam Physician. 2010;82(8):942-952 http://www.aafp.org/afp/2010/1015/p942.pdf

(B) In atrioventricular reciprocating tachycardia, there is typically a short RP interval, with the timing and morphology of the P wave dependent on the site and conduction velocity of the accessory pathway. Am Fam Physician. 2010;82(8):942-952 http://www.aafp.org/afp/2010/1015/p942.pdf

(C) Atrial tachycardia typically produces variable RP and PR intervals because atrioventricular conduction depends on atrioventricular nodal prop- erties and the tachycardia rate. In atrial tachycardia, the morphology and axis of the P wave are influenced by atrial site of origin and tachycardia mechanism. Am Fam Physician. 2010;82(8):942-952 http://www.aafp.org/afp/2010/1015/p942.pdf

(D) Normal sinus rhythm. Am Fam Physician. 2010;82(8):942-952 http://www.aafp.org/afp/2010/1015/p942.pdf

N Engl J Med 2012;367:1438-48

In reviewing the Narrow Complex tachycardia,

Look for PR and RP relationship

Short RP Tachycardia is seen in this case. (V2 or V5: P wave is seen at the end of QRS)
DDx of Short RP: Typical AVNRT, Orthodromic AVRT, Less Commonly AT

Short RP tachycardias — If the RP interval is less than one-half of the RR interval, the tachycardia is considered a short RP tachycardia. The differential diagnosis of a short RP tachycardia is generated by considering the P wave morphology.
●Abnormal P wave – The combination of abnormal P waves and a short RP interval is most often seen in the setting of an atrial tachycardia with AV nodal conduction delay.
●Retrograde P wave – The combination of retrograde P waves and a short RP interval is typical of the "common" form of AVNRT and of AVRT utilizing an accessory pathway.
In the "common" form of AVNRT (which accounts for 90 percent of AVNRT), reentry occurs in the AV node and perinodal tissues. Antegrade conduction occurs down the slow pathway and retrograde conduction up the fast pathway. This slow-fast pattern gives rise to retrograde P waves that may be inapparent if obscured by the QRS complex
AVRT utilizing an accessory pathway can be either orthodromic or antidromic. Orthodromic AVRT is more common, and in this form of the arrhythmia, antegrade conduction occurs through the AV node, producing a narrow QRS complex, and retrograde conduction to the atrium occurs over an AV bypass tract
In contrast, during antidromic AVRT, antegrade conduction occurs through the AV bypass tract and retrograde conduction occurs through the AV node or a second accessory pathway. This pattern of activation results in a wide QRS complex (thus, antidromic AVRT is not a narrow QRS complex tachycardia)

Clinical Question

34 yo F is seen in ER for palpitation. Follow is the EKG finding before and after adenosine. What kind of SVT is it?