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Supraventricular Tachycardia

Dawn's picture
Thu, 01/02/2014 - 13:36 -- Dawn

This example of supraventricular tachycardia is from a 51-year-old woman who presented to the Emergency Dept. with a complaint of palpitations.  We do not have any more clinical information for her.  We know this tachycardia is supraventricular because the QRS complexes are narrow.  The term, "supraventricular tachycardia", or "SVT" actually describes many different rhythms with many different mechanisms and causes.  It would help a great deal to see the beginning (or end) of this rhythm to determine if the onset was sudden (paroxysmal) - or gradual.  Sinus rhythms tend to speed up gradually - picture a patient on a treadmill getting a faster and faster heartrate.  Take the patient off the treadmill, and the rate gradually decreases.  This reflects normal function of the sinus node.

SVT with paroxysmal onset indicates a re-entry mechanism, where the impulse travels from the atria to the ventricles by one pathway, but is able to return in a retrograde fashion, following a second pathway in the atria or AV node, and reenter the ventricles, depolarizing them antegradely, causing another QRS.  The atria are usually depolarized retrogradely as well.   Reentry can occur in the sinus node, in the AV node, or around the AV node via accessory pathways in the atria.  For a very clear and concise discussion of AV nodal reentry tachycardia (AVNRT), go to this Life in the Fast Lane link.  There is also a great discussion of AVNT and pre-excitation syndromes, including Wolff-Parkinson-White syndrome, at LITFL.

In this ECG, we do not know the patient's clinical situation,  and we haven't seen the onset of this rhythm.  The rate is 166 / min.  In order for her sinus node to naturally reach this rate, we can assume she would have some visible reason for tachycardia:  extreme anxiety, blood loss, hypoxia, exercise, etc.  An "inappropriate" sinus tachycardia is a possibility, but not the most common thing.  If she describes this rhythm as having a sudden onset, the most common and most likely diagnosis is AVNRT, also called SVT or PSVT.  

The presence of retrograde P waves can aid in the diagnosis of AVNRT.  Retrograde P waves are negative in Leads II, III, and aVF.  They can occur before, during, or after the QRS.   In this ECG, we cannot see P waves, either before or after the QRS.  Some of the QRS complexes (limb leads) have a small notch at the end, but it does not look like a typical retrograde P wave in II or aVF.

If sinus tachycardia can be ruled out, it is safe to treat this rhythm with Valsalva maneuvers and adenosine, and then investigate the cause.

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Comments

ekgpress@mac.com's picture
     This week’s tracing is a great teaching example of a regular SVT rhythm for which atrial activity is uncertain. I’ll add the following points to Dawn’s discussion:
  • We will often NOT know for sure what the rhythm is at the time we are called on to treat the patient. This is “par for the course” and NOT a problem - since many of the diagnostic/therapeutic interventions will be similar for many of the SVT rhythms.
  • The 1st KEY action on our part is to ENSURE that the patient is stable. Most of the time with SVT rhythms - the patient WILL be stable, but on occasion they may not be. In such cases - it NO LONGER MATTER what the rhythm is - since treatment becomes immediate need for cardioversion. The “fastest way out of a fast rhythm is with electricity”. We are not given specific hemodynamic information in this case - but let’s assume that this 51yo woman is stable.
  • Since she is stable - we therefore have the luxury of at least some time to contemplate the diagnosis prior to initiating therapy. To do this - think of what we have. This patient is in a Regular SVT at ~165/minute without definite sign of Atrial Activity. This should prompt consideration of my List for this problem. Over 90-95% of patients in a regular SVT rhythm without clear sinus P waves will have one of 3 entities: i) Sinus tachycardia (in which the sinus P wave is hidden within the preceding T wave due to the fast rate); ii) PSVT (or AVNRT); or iii) AFlutter. Being aware of this list is TREMENDOUSLY helpful - because it greatly narrows your differential diagnosis. This rhythm is not AFib - because it is regular. So we are left (in 90-95% of cases among both in-patients, emergency patients, and out-patients) with sinus tach vs PSVT vs AFlutter.
  • In the event that we have no idea which of the 3 is operative - one can try: i) a Vagal maneuver; ii) Adenosine (if working in a facility that has this drug available); or iii) some other AV nodal blocking drug. I review evaluation and management of Regular SVT Rhythms in FULL Detail at this LINKhttps://www.kg-ekgpress.com/acls_comments-_issue_09/ -
In this particular case - I’ll speculate on the following:
  1. I doubt this is sinus tachycardia. A rate of 165/minute is a little fast for sinus tachycardia (not impossible! - but a bit faster than you usually see for sinus tach in an adult). The ONLY thing I could construe as a possible “hidden P wave” in lead II would have a long PR interval - and most of the time if the PR interval looks long for a tachycardic rhythm, it is NOT sinus tachycardia.
  2. I don’t think this is PSVT. Although you will not always see the retrograde P wave with PSVT/AVNRT - sometimes you will (generally a positive pseudo-r’ in aVR or V1 - or a notch in the end of the QRS in inferior leads). I don’t see this here.
  3. I DO think this is AFlutter - though I cannot be certain. First - AFlutter is what is left given that I don’t think it is sinus tach or PSVT. So - We should “look” for P waves. I printed the download of this tracing out so as to magnify as much as possible. Calipers are essential! Setting my calipers to precisely HALF the R-R interval and starting on the point of the T wave in lead I and the slight notch at the end of the T in aVL - allows me to walk out 2:1 AV conduction for what I think is an extra P (flutter) wave in these leads I and aVL. Again - NOT something I’d be certain of - and clinically I’d still proceed with vagal maneuver followed by Adenosine. The results of these maneuvers should tell the tale. FULL DETAILS on my approach to SVT at THIS LINK. GREAT Teaching Case!

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

Dawn's picture
Submitted by Dawn on

Thanks, Dr. Ken, for your great lesson. I was troubled by the little notches at the terminal portion of the QRS, but they weren't retrograde- looking to me. I AGREE they look like hidden flutter waves!  I'm usually good at catching atrial flutter, but when the rate is this fast, I sometimes miss it. (The rate is a little slow for AVNRT, but fast for atrial flutter with 2:1 conduction. Thanks for the reminder to march those flutter waves out. I wasn't there for treatment, unfortunately. Often, the true nature of the beast is uncovered during Valsalva maneuvers, carotid sinus massage, or administration of AV blocking drugs. 

Dawn Altman, Admin

Dave Richley's picture

I too wondered if this mightbe atrial flutter but I just couldn't convince myself, even after studying it closely. I'm sure the the notch on the T wave of aVL does represent atrial activity, so I wondered if the rhythm might be an atrial tachycardia with 1:1 conduction. This ECG is a great example of a SV tachyarrhythmia that is very difficult to elucidate. Sometimes, despite all the diagnostic algorithms, guidelines, tips etc that are available, it is just not possible to be sure exactly what is going on.

 

Dave R

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