Dawn's picture

This series of ECG rhythm strips shows a paroxysmal supraventricular tachycardia successfully treated with adenosine.  The patient was complaining of a rapid heart rate and palpitations, but was hemodynamically stable.  It is not known whether any parasympathetic stimulation, such as a Valsalva maneuver or carotid sinus massage, was used initially.   

The first rhythm strip shows a PSVT, presumably AV nodal reentrant tachycardia, at a rate of about 215 per minute.  (We originally indicated a rate of 240 per minute, but this was a typo). Using the simplist method of determining rate, the six-second method, we see 21, but almost 22, QRS complexes in six seconds. Differential diagnosis would include sinus tachycardia, but this rate is too fast for sinus tach, especially in a resting patient.  Also, sinus tach would slow down as the patient is rested or made more comfortable, and this rate did not vary.  Also, when confronted with a supraventricular tachycardia, one should also consider atrial flutter and atrial fibrillation.  This is somewhat slow for atrial flutter with 1:1 conduction, and that rhythm is much more rare than AVNRT. It is too regular for atrial fibrillation.  So, we are left with the probable diagnosis of paroxysmal supraventricular tachycardia.  The “paroxysmal” part is presumed since AVNRT has an abrupt onset, and the patient’s symptoms started suddenly. 

The second rhythm strip shows what happened after adenosine was administered.  The patient received first a 6 mg dose, rapid IV push.  When that was not effective, he received 12 mg rapid IV push.  The rhythm strip is typical of the first minute or so after adenosine administration.  Adenosine can cause transient AV blocks, escape rhythms, and ectopic irritability.  The half-life of adenosine is only 6 seconds, so the dysrhythmias and uncomfortable symptoms are short-lived.  In this strip, we see frequent PVCs and runs of V tach.  

An interesting feature of this strip is FUSION BEATS.  In ventricular rhythms, the wave of depolarization travels backwards (retrograde conduction).  If the ventricular beat is timed just right, it might meet a sinus beat on its way down the conduction system.  The two impulses will fuse and the QRS complex will look like a hybrid of the two.  Beats 1 & 2 show the PSVT, beats 3, 4, 5, and 6 show a run of V tach.  Beat 7 has a sinus P wave, but the morphology closely resembles the PVCs.  It is a fusion beat.  Beat 8 is a fusion, and 9 and 10 are PVCs.  Beat 11 is a sinus capture beat.  The P wave is lost in the preceding T wave, but the morphology of the QRS matches the PSVT, indicating normal conduction through the ventricles.  After two more PVCs, the patient has sinus beats and a PAC (Beat 20), then settles into sinus rhythm at a rate of about 100/min. Fusion beats prove the existence of a ventricular rhythm, as two sinus or atrial impulses cannot fuse.  

The third strip shows normal sinus rhythm at a rate of about 95 / min with two PACs (arrows).  The patient had had quite an exciting time in the emergency department, and his adrenalin caused a fast rate.  It appropriately slowed down over the next 15 minutes.




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ekgpress@mac.com's picture

     Nice sequential case of AVNRT converted by Adenosine with "a little excitement" along the way. Excellent description by Dawn to which I'll just add a few points:
  • It is important to be as precise as possible in determination of the rate of rapid regular tachycardias - as rate is an important supportive feature of differential diagnosis. With rates in the 200s - the thickness of the QRS (or the thickness of your calipers) can easily make a substantial differential in your final calculation. As a result - I favor the Every-Other-Beat (or Every-Third-Beat) Method. NOTE - the 1st QRS complex in the TOP tracing shows the peak of the R wave to appear JUST BEFORE the first heavy line. If I count over 3 beats (ie, 3 QRS complexes) - the 4th QRS complex (counting over 3 beats) occurs RIGHT ON the 5th heavy line. Therefore - the amount of time that it takes for 3 beats to occur = just over 4 large boxes. This means that 1/3 of the rate ~ 300/4+ - or about 70/minute X 3 = 210/minute - being to me a closer estimate of the actual heart rate.
  • This is relevant - as a regular SVT rate of 240/minute is close to the lower range for 2:1 AFlutter - whereas 210/minute is clearly below the expected range for 2:1 AV conduction in untreated AFlutter. This makes me virtually certain that AVNRT is the diagnosis for the TOP rhythm strip.
  • It is good to describe in words the phenomena occurring in the MIDDLE rhythm strip. The definition of "VTach" = 3 or more PVCs in a row. In the Middle strip - we see that Adenosine has induced several runs of NSVT ( = Non-Sustained Ventricular Tachycardia). Specifically (counting fusion beats #8 and #12) - the runs of NSVT are from 3-4 beats (with a ventricular couplet accounting for beats #16,17). Distinction between NSVT vs "sustained" VT is subject to a variety of definitions - but I simplistically like using the thought that "If the run is long enough to give ME palpitations - it is sustained VT ... ".
  • The BOTTOM rhythm strip shows the PACs - as described by Dawn. This is important to note - since duration of action of Adenosine is short-lived - and PACs are often the precipitating event heralding AVNRT recurrence - so IF conditions causing the initial TOP tracing have not been corrected - then consideration of starting a longer-acting AV nodal blocking agent (ie, beta-blocker, verapamil/diltiazem) is in order. 
For those interested - Click HERE to download Section 06.0 (from ACLS-2013-ePub) on Using Adenosine. I added a brief copy of an article by Mallet highlighting that Adenosine not only may cause bradyarrhythmias - but ventricular tachyarrhythmias, as seen in this case.

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

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