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Paroxysmal Supraventricular Tachycardia

Sun, 04/12/2015 - 13:59 -- Dawn

This ECG is from a man in his 60's who is experiencing chest discomfort and palpitations.  The onset of the rapid heart rate and the symptoms was sudden, while he was at rest.  The rate did not slow when he was placed on oxygen, given IV fluids, and rested further. The rate is 177 / min.  

The rhythm is AV nodal reentry tachycardia (AVNRT), which is one of the rhythms that falls into the category of paroxysmal supraventricular tachycardia (PSVT).We can see signs of retrograde P waves in some leads (II, III, aVF, V1).  AVNRT is caused by a reentry circuit in the AV node.


Some instructors teach students that sinus tach is approximately 100-150 per minute, and atrial tach is usually 150-250 per minute.  If students only learn about differentiating these two rhythms by the rate difference, it will cause later problems.  Of course, there is actually an overlap in rates between the two rhythms.  For example, a febrile, dehydrated infant could easily reach this rate and be in sinus rhythm.  A young, healthy person on a treadmill could, too.  Clues to the ectopic origin of this rhythm are:  sudden onset (unfortunately, not witnessed here), regular rhythm with unwaivering rate, and the patient's situation (symptoms while at rest, no obvious reason for sinus tach).  Of course, we need to teach to the level of our students' abilities.  Consider whether they just memorizing rhythms criteria now, or are they learning about re-entry?

Ventricular Tachycardia

Thu, 03/19/2015 - 14:42 -- Dawn

This wide-complex tachycardia is ventricular tachycardia.  Along with the wide QRS and the fast rate, features which favor a diagnosis of VT over BBB include:  backwards (extreme right) QRS axis, negative QRS in V6, and an apparently monophasic QRS in V1, as opposed to the rSR' pattern of right bundle branch block. 
Remember, ALL wide-QRS tachycardias should be treated as V Tach until proven otherwise, as it is a life-threatening arrhythmia.  Factors which lower cardiac output during V Tach include:  Fast rate, wide QRS, and lack of P wave preceding the QRS.  The sudden severe lowering of perfusion that usually accompanies V Tach can lead to rapid deterioraton and ventricular fibrillation.

For discussions by Jason Roediger (ECG GURU extroidonairre) on recognizing ventricular tachycardia, go to this LINK, and this LINK.

Anti-tachycardia Function of ICD

Tue, 01/06/2015 - 02:53 -- Dawn

This ECG was donated to the ECG Guru by Brent Dubois, and was originally published on the FaceBook page, Paramedic Tips & Tricks.  We published it to this site three years ago, but believe it should be shown again, as it is somewhat rare to catch a good-quality 12-Lead ECG of an implanted cardioverter-defibrillator pacemaer using overdrive pacing to terminate a ventricular tachycardia.  Most of our examples have been rhythm strips.

In this strip, we see the patient in ventricular tachycardia (V tach) at a rate of about 190 / minute.  The ICD, in response to the fast rate, delivers a short burst of even faster paced beats.  The physological rule in the heart is, "the fastest pacemaker controls the heart".  Once the pacemaker has terminated the V tach, it paces at a much slower rate.  It is pacing the atria, and the conduction system is intact, allowing the impulse to travel normally through the ventricles.  If the sinus node is able to "outpace" the slower paced rhythm, the heart will resume a sinus rhythm.

This is called "overdrive pacing" and is done automatically by an ICD that is programmed to do so.  Overdrive pacing can also be accomplished by a temporary transvenous pacer or transcutaneous pacemaker.  

Right Ventricular Outflow Tract Tachycardia (RVOT)

Tue, 12/16/2014 - 00:00 -- Dawn

This ECG was taken from a patient who was complaining of palpitations and tachycardia, but who was hemodynamically stable, with no history of heart disease.  It is an example of RIGHT VENTRICULAR OUTFLOW TRACT TACHYCARDIA, a type of idiopathic ventricular tachycardia.  The ECG signs of RVOT are:  wide QRS complex, left bundle branch block pattern (QRS negative in V1 and positive in Leads I and V6), heart rate over 100 bpm, rightward or inferior axis (LBBB usually has a normal to leftward axis), AV dissociation.

RVOT accounts for about 10% of all ventricular tachycardias, and 70% of idiopathic VT.  It is most often found in structurally normal hearts, but it may occur in patients with arrhythmogenic right ventricular dysplasia.  For more on RVOT, read Life In the Fast Lane.

RVOT tachycardia sometimes converts with adenosine.  The patient in this example converted after being administered amiodarone.

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.

ECG Basics: Paroxysmal Supraventricular Tachycardia

Fri, 11/21/2014 - 21:07 -- Dawn

This two-lead rhythm strip clearly shows the transition from normal sinus rhythm to a paroxysmal supraventricular rhythm.  In this case, the arrhythmia is AV nodal reentrant tachycardia, AVNRT.  The rate of the first rhythm, NSR, is around 75 per minute.  The fourth beat on the strip is a PAC which initiates the paroxysm of tachycardia lasting 12 beats.  The arrhythmia terminates spontaneously at that point.  The tachycardia rate is about 150/min.

The topic of supraventricular tachycardias can be a very complex one to teach.  For an excellent example of a concise lesson geared toward Primary Practice physicians, go to Dr. Grauer's VIDEO - Part III of his Arrhythmia series.

To cover the important points for the beginner-level student:

  *  It can be difficult to determine a rhythm is SVT if the rhythm is near 150 bpm and you DON'T see the beginning or end of the arrhythmia.  If the onset (or offset) is sudden, then this is not a sinus rhythm.  The sinus node speeds and slows more gradually - it doesn't change rates in one heartbeat.  This strip has an excellent view of BOTH the onset and the offset.

  *  The faster the rate, the more likely we are looking at a PSVT rather than sinus rhythm.  If a sinus tachycardia exists, we can almost ALWAYS see the reason for it in the patient's clinical situation.  We may see fever, dehydration, bleeding, fear, pain, exercise.  Therefore, a patient at rest with a rate of 150 would be suspect for PSVT.  A patient on a treadmill for 5 minutes would be considered to have a sinus rhythm.

  *  Any patient with a rate around 150 per minute should be evaluated for ATRIAL FLUTTER with 2:1 conduction.  Atrial flutter often conducts at that ratio, because a rate of 150 is fairly easy for the AV node to conduct, whereas the instrinsic rate of atrial flutter (250-350) is not.  A 12-lead ECG makes it easier to search for tell-tale flutter waves.

Atrial Flutter With Variable Conduction

Tue, 11/04/2014 - 00:24 -- Dawn

This ECG provides an example of atrial flutter with variable conduction.  There are two distinct R - R intervals, making this a somewhat regularly-irregular  rhythm, as opposed to the irregular irregularity of atrial fibrillation.  The flutter waves (P waves) are very easy to see in most leads, but not in all.  If you are teaching students who are making the transition from reading monitors and rhythm strips to 12-lead ECGs, this is a great ECG to illustrate for them how the more leads you have, the more you will see.  The flutter waves are invisible in Lead I and, to the untrained eye, they may be hard to see in the precordial leads.  The four channels on this ECG are run simultaneously, so if  P waves or flutter waves are visible in one lead, they are also present in all leads that line up vertically with that one.  In other words, the Lead II rhythm strip at the bottom confirms that flutter waves exist across the entire ECG.

The R - R intervals in this ECG reflect alternating 2:1 and 4:1 conduction.  There are a couple of times when the 4:1 ratio repeats itself without alternating.  Often, the length of these varying R - R intervals will be multiples of each other, or have a common denominator.  These do not appear to, and may reflect the fact that, when R to P intervals lengthen, R to R intervals sometimes shorten.  In other words, the PR intervals, which are difficult to measure in atrial flutter, may be changing.  I would invite my colleagues with more expertise in this area to comment below.

There are no blatant ST segment abnormalities here, but ST segments can be very difficult to assess in atrial flutter because of the flutter waves.  We do not have clinical data, other than this is a 62-year-old man.

Atrial Flutter With 2:1 Conduction

Fri, 10/04/2013 - 23:07 -- Dawn

Unfortunately, we have no clinical information on this patient, not even age or gender, as the ECG machine defaults to "Age 60".  The rhythm is a supraventricular tachycardia at a rate of about 260/min. with 2:1 conduction, resulting in a heart rate of about 130 / minute.  Some would call this atrial tachycardia, and some atrial flutter.  Since the reentrant pathways involved in the two rhythms are different, it is probable that an electrophysiologist could determine the exact location of the pathway in the EP lab.  Without benefit of this test, we use our best guess.  We will leave it to our more advanced Gurus to debate the origins of this rhythm.

The fast P waves are best observed in the limb leads, with one P wave occuring in the QRS complex.  If you ignore the QRS complexes for a moment, you can draw an unbroken line through them, uncovering the flutter waves.  SVTs with 2:1 conduction can easily be mistaken for sinus tachycardia.  Always suspect and look for atrial flutter when the heart rate is around 150 / minute.  A 12-lead is a big help, as flutter waves show up better in some leads than in others.  Another way to uncover atrial flutter is to slow the rate with vagal maneuvers or medication to decrease the conduction ratio, and observe several flutter waves in a row without QRS complexes.

Of even more concern to this patient may be the ST elevations - slight but noticeable - in Leads V2 - V4, and possibly I and aVL.  The J points (the beginning point of the ST segment) can be obscurred by the P wave lying beneath the QRS, and it may be difficult to judge ST elevations.

We expect this ECG to elicit many opinions - possibly different from ours.  Please add your comments below.  We will enjoy the discussion.

Spontaneously Changing Conduction In Wide Complex Tachycardia

Wed, 04/10/2013 - 22:23 -- Dawn

This ECG was donated to the ECG Guru by Dr. Arnel Carmona, one of our favorite Gurus.  You will not often see such a great example of this.  We are very grateful to Dr. Carmona for his contribution to learning. Dr. Carmona's new blog is EZG - ECG for beginners and enthusiasts.    

An adult patient was admitted due to palpitations.  What is this rhythm?This is a tachyarrhythmia that initially is regular wide complex (RBB morphology) and later became regular narrow complex at a rate of about 187 bpm. There is normalization of the QRS without a change in heart rate. In the latter part of the tracing (narrow complex), pseudo-r can be seen in V1. So, this is SVT with aberrancy with spontaneous normalization.

What is the cause of the intraventricular aberration during acceleration of heart rate? It could be due to failure of the refractory period to shorten or possible lengthening in response to acceleration. 

What is the cause of the normalization of the of the QRS? The normalization of intraventricular conduction could be due to the gradual shortening of bundle branch refractory period in response to the tachycardia. 

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