This series of three ECGs is from a 60-year-old man who was brought to the Emergency Department after being involved in a motor vehicle accident.  No injuries were found, but the patient was severely intoxicated by alcohol consumption.  He was conscious but agitated. 

ECG NO. 1     15:07:23

The first ECG was taken by fire-rescue personnel at the scene of the accident. His hemodynamic status was stable, and the rate was not addressed in the field. ECG No. 1 shows a supraventricular rhythm at 161 bpm, with a narrow QRS and P waves visible before each QRS. 

A notable feature of this ECG are the left axis deviation, by default diagnosed at left anterior hemiblock (left anterior fascicular block).  The .10 second QRS width is typical of LAHB, as is the rS pattern in Lead III.

Also  noted is the unusual R wave progression in the precordial leads.  The R waves are prominent in V2, and then fail to progress across the precordium, and the S waves persist. This is probably due to the hemiblock.  We do not know this patient’s medical history, except that he self-described as an “alcoholic”.  LAFB can be associated with coronary artery disease. 

ECG NO. 2      15:20:38

Now being evaluated in the Emergency Dept., we see the patient's heart rate is 163 bpm.  Some variability in the rate was noted with patient agitation and activity, so it was determined that the rhythm was probably sinus tachycardia.  There were no other significant changes in the ECG from the first one.  Unfortunately, we no longer have access to lab results, so we do not know his electrolyte or hydration status.  Labs confirmed ETOH intoxication. 

ECG NO. 3   15:43:26

This ECG was obtained from a 13-year-old boy who had previously been in NSR.  At that time, he was diagnosed with Wolff-Parkinson-White syndrome, and he had delta waves.  He now presents with a supraventricular tachycardia.  People with W-P-W have one or more accessory pathways which allow atrial impulses to bypass the AV node and “pre-excite” the ventricles.  An accessory pathway, along with the normal pathway through the AV node, can form a functional circuit, allowing conduction to proceed down one pathway and return up the other, in a rapidly repeating circular motion.  This causes paroxysmal supraventricular tachycardia. 

In W-P-W, the most common type of SVT is AV reciprocating tachycardia (AVRT), also called AV reentry tachycardia.  Conduction through the accessory pathway can be forward (anterograde) or backward (retrograde).  The most common type of reentrant conduction in W-P-W is ORTHODROMIC, which we see here.  The impulse conducts forward through the AV node, and backward over the accessory pathway.  There is no delta wave, as there is no pre-excitation of the ventricles. 

Features of orthodromic AVRT are:

Fast rate (usually approximately 140-250 beats per minute)    

Narrow QRS complexes (unless BBB or IVCD present)   

P waves retrograde, if seen (negative in II, positive in aVR and V1)  

ST depression and T wave inversion common. 

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.

This strip is from a patient who experienced a sudden onset of palpitations and rapid pulse while at rest.  It shows a narrow-complex tachycardia, specifically a paroxysmal supraventricular tachycardia.  The subject of supraventricular tachycardias is a fascinating one, and is covered extensively throughout this website.  The mechanisms of SVT are many, and can be complex for the beginning student to understand.  Search the search terms on the left side of the page for entries from ASK the EXPERT and JASON's BLOG for more advanced information about SVT.

For the beginner, it is important to teach the difference between sinus tachycardia and "supraventricular tachycardia".  Of course, sinus tachycardia IS supraventricular - but current convention has us using the term "SVT" for atrial or junctional tachycardias, and especially for reentrant tachycardias.  Beginner students should understand the function of the sinus node, and it's ability to control the heart rate, based on direction given by the nervous system.  The sinus node increases and decreases the rate incrementally, or more gradually than the onset and offset of a reentrant tachycardia.  The appearance of a sudden onset of regular tachycardia following a PAC, producing a rhythm with a distinctly faster rate than the original sinus rhythm, is a sure sign of SVT.  When the onset or offset are caught on the rhythm strip, our job is SO much easier!

The heart rate helps with the diagnosis.  SVTs tend to be faster than sinus tachycardias.  SVTs tend to be faster than 150/min, while sinus rhythms TEND to be slower than 150.  And patients with sinus tachycardia usually have a readily determined reason for the tachycardia, such as fever, pain, fear, hypovolemia, hypoxia, or exertion.  So, a patient on a treadmill for an exercise stress test might very well have a heart rate over 150 / min.

When your students master the understanding of the different behaviors of the sinus node and the reentrant rhythms, and how important patient presentation is to the diagnosis, you will want to add atrial flutter and atrial fibrillation.  When these are mastered, be sure to remind your students that atrial flutter can conduct 2:1, and will mimic sinus tach.  A good rule of thumb is: Under 150/min.:  look for sinus tach first.  Around 150 / min.: look for atrial flutter with 2:1 conduction.  Over 150/min.: suspect PSVT.