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Supraventricular Tachycardia

Thu, 12/04/2014 - 23:47 -- Dawn

This ECG shows AV nodal reentrant tachycardia in an elderly man.  Clinical information is not available.  AVNRT is the rhythm most often associated with the term, "supraventricular tachycardia".

Although we can't see the beginning of this rhythm, one of the identifying features of SVT is an abrupt (paroxysmal) onset.  In patients with AVNRT, there are two pathways in the AV node, a pathway with fast conduction and a long refractory period, and a pathway with slow conduction and a short refractory period.  Normal sinus impulses travel down the fast pathway and into the ventricles, but also start up the slow pathway in a retrograde direction. The retrograde impulse and the normal impulse traveling down the slow pathway collide, cancelling each other out.  If a PAC occurs, it will travel down the slow pathway while the fast pathway is still refractory.  By the time the impulse reaches the end of the slow pathway, it finds the fast pathway no longer refractory, and travels back up to the atria.  This forms a circular movement (circus movement) of the impulse, and it repeats itself rapidly until interrupted.  When each impulse reaches the ventricles, it travels into the interventricular conduction system and causes ventricular depolarization and contraction, usually at a rate of 140 - 250+.  Unlike sinus tachycardia, AVNRT does not adjust its rate according to the needs or activity of the patient.

There are many forms of supraventricular tachycardia, and they are not always easy to differentiate based on ECG criteria alone.  AVNRT of the type described above is the most common PSVT in structurally normal hearts.  For more information on supraventricular tachycardia, go to Life in the Fast Lane.  For a discussion on clinical management, we recommend Dr. Grauer's ECG Video 6 - Rhythm Mgmt-Part 3.

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Comments

ekgpress@mac.com's picture

Dawn nicely summarized the key features for recognition of PSVT. I'll limit my comments to a few additional points.
  • The rhythm here is a regular SVT at ~ 200/minute in which normal P waves are not seen. The description of a regular SVT with uncertain atrial activity should bring to mind 3 possibilities: i) Sinus Tachycardia; ii) AFlutter; or iii) PSVT ( = AVNRT). The rate here is KEY! That's because 200/minute is too fast for sinus tach in a nonexercising adult - and 200/minute is "wrong" for AFlutter (since the usual 2:1 AV conduction with flutter would require the atrial to be going 200 X 2 = 400/minute if this was flutter - which is above the 350-360/min usual upper flutter range). Therefore - we can be fairly certain that the etiology of this regular SVT = AVNRT.
  • There IS atrial activity! It is present as a subtle-but-real notching at the very end of the QRS in leads I and aVL. The finding of such retrograde atrial activity virtually proves reentry as the mechanism.
  •  Dawn already mentioned that Part 3 of my Arrhythmia Video series addresses the SVT rhythms. You can fast forward to 7:40 in this 40-minute video if you want to go right to the section on AVNRT recognition and management.
  • If you prefer a PDF summarizing the basics of AVNRT - CLICK HERE -
P.S. For those interested - More on arrhythmias including Parts I and 2 videos can be found at - www.fafpecg.com -

 

Ken Grauer, MD  www.kg-ekgpress.com   [email protected] 

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