A Narrow Complex Tachycardia

Vignette: 70 yo with history of HTN and COPD c/o SOB.

Image 1

This is often labeled as a supraventricular tachycardia (SVT). Supraventricular tachycardia means that the focus originates, or in part, above (supra – Latin meaning above) the level of the ventricle which could be the sinus node, atria, AV node or the His-Bundle. It can be sinus tachycardia, atrial fibrillation, atrial flutter, , atrial tachycardia, AV nodal reentry, etc. 

Image 2

The 12L shows a regular narrow complex tachycardia (NCT) at rate of about 150 bpm. P waves (red arrowhead) are inverted in II, III and aVF (pseudo S) and upright in V1 (pseudo R). In relation to the PR interval, the RP interval is shorter than the RP interval. Thus, this is called a short RP tachycardia.

SVT Classification

Image 3 (SVT classification)

SVT can be classified based on 3 questions:

1. Is the tachycardia regular or irregular?
2. Narrow (<0.12 sec) QRS complex or wide (>/= 0.12 sec) QRS complex?
3. Is the RP interval shorter or longer than the PR interval?

In the table above, this tachycardia can be anything inside the red box. In humans, the most common form of regular supraventricular tachycardia is AV nodal reentry tachycardia (AVNRT).

Reentry Tachycardia

Image 4

Certain individuals have 2 conducting pathways in the AV node. One conducts fast (FAST PATHWAY or FP) but a has a long refractory period and one conducts slow (SLOW PATHWAY or SP) but has a short refractory period or recovers fast to allow the next incoming impulse to pass. This AV node pathways can allow retrograde flow (going to the direction of the atria). In the diagram above, the impulse is conducted via the SLOW PATHWAY, creating a LONG RP INTERVAL. It then reenters the FAST PATHWAY because the FP already recovered. This created the SHORT RP interval. This impulse will then depolarize the atria creating the INVERTED P WAVES in the inferior leads (II, III and aVF).

Image 5 (ladder diagram)

Another way of looking at this arrhythmia is using a ladder diagram.

One of the prime consideration in this SVT is AVNRT. The only way to definitely identify which SVT is through an electrophysiology (EP) study.

For this case, adenosine was given terminating the SVT. Patient was offered EP study.

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