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.

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.

This nice example of atrial flutter offers many teaching opportunities. "Sawtooth" flutter waves are readily visible in Leads II, III, avF, and V1, typically good "P wave" leads.  Other leads show small, discreet P waves that the beginning student might not recognize as flutter waves because they don't produce the sawtooth pattern.  The P waves' rate, approximately 360/min., gives them away as atrial flutter.  This is also a good example of a constant 4:1 conduction, resulting in a regular QRS rhythm and regular pulse, at a rate of about 90/min.  This demonstrates that not all narrow-complex rhythms between 60 and 100 bpm are "NSR".  The low voltage in the limb leads makes this a good ECG to demonstrate that the flutter waves are regular and do not pause when the QRS happens, illustrating the separate actions of the atria and the ventricles.  For students just learning 12-lead interpretation, this ECG serves to show that acute ST elevation M.I. is not the only valuable information that can be obtained from a 12-Lead, and that some leads are better than others for showing dysrhythmias.

This ECG shows a nice, clear atrial flutter with 4:1 conduction.  Also, there are frequent PVCs. Good for students who have mastered the criteria for the basic arrythmias and who need to see combinations.  That is, PVCs are not only seen with NSR, and it is important to state the underlying rhythm.  For your more advanced students who understand how to plot frontal plane axis, the axis of the PVCs is nearly straight up - a very strong argument for the ventricular origin of the beats.