Which SVT? The need to capture the beginning of an SVT

An adult with complex medical hx.

Image 1 -  (tachycardia cropped)

Image 2 (beginning)

This is the initiation/beginning of the narrow complex tachycardia (NCT). 

The blue asterisk is most likely a PAC that travelled the slow pathway. It hard to measure the PRI in this limited strip. The red arrows are (inverted P waves). Here the impulse went up/back/reentered using the fast pathway. So, this is a short-RP narrow complex tachycardia.

For seasoned ecg lovers, all heard of dual AV node physiology. For beginners, this might be the first. It means in the AV node the supraventirular impulse has to 2 ways to reach the His-Purkinje. One pathway, the impulse travels fast (fast pathway or FP) and other the impulse travels slow (slow pathway or SP). The FP recovers slow and the SP recovers fast. 

Image 3 (PAC diagram)

When there is a PAC, the impulse will travel the SP (creating a long PRI) because the FP did not recover yet. As the impulse go down, the FP has recovered and the impulse go reenter/go up using the FP (creating a short RP). 

Image 4 (mid cycle)

This is middle of the tachycardia cycle. It is hard to see the inverted P' in this strip. If you only see this, it is hard to say w/c SVT is it (sinus tachycardia, atrial tachycardia. atrial flutter, AF, VNRT or AVRT).

Image 5 - Termination

This is the termination. The last few complexes had a longer R to R meaning it kind of slowed down before the spontaneous termination.Hard to say if this terminated in a P wave.

From its behavior, this is most likely typical (slow-fast) AV nodal reetry tachycardia (AVNRT) using slow AV nodal pathway for antegrade conduction and the fast pathway for retrograde conduction. Typical AVNRT are initiated by a PAC and rates vary from 118-264 (181 +/- 35).

Image 6 - Diagram


Kumar UN et al. 2006. The 12L Electrocardiogram in Supraventricular Tachycardia. Cardiology Clinics ;24: 427-437

Bonnow et al. 2014. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 10Ed. PA Saunder



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