This strip was taken from a patient at rest.  It shows a regular tachycardia with a slightly-widened QRS complex at about .10 seconds duration.  It is somewhat difficult to evaluate the baseline for P waves or flutter waves.  We ALWAYS recommend multi-lead assessment for such evaluation.  The P waves (or flutter waves) here have a sharp point, and can be easily "marched out", with a rate of about 300 per minute.

Whenever the ventricular rate is near 150/min., we should always consider the possibility of atrial flutter with 2:1 conduction.  Since atrial flutter results in atrial depolarization at around 250 - 350 per minute, conducting every other P wave results in a rate of about 150.  It can masquerade as sinus tach, but a patient with sinus tach at such a fast rate would probably have an obvious cause for a rapid heart rate, such as hypovolemia, drug overdose, or exertion.  This rhythm could also be mistaken for atrial tachycardia or other forms of supraventricular tachycardia (SVT, PSVT, AVNRT, etc.).   Multiple leads can more easily uncover the flutter waves running continuously "behind" and "through" the QRS complexes.

There is one beat that is obviously different from the others.  This beat is about the same width as the other QRS complexes, but is opposite in direction.  This probably represents aberrant conduction, possibly a hemiblock that occurs only in this beat.  Careful measurement will show that this QRS is very slightly early, while the others are all very regular. The slight width of all the QRS complexes suggests that there is a conduction delay, which cannot be diagnosed on one strip with no patient history available.

There are other differential diagnoses, such as ventricular tachycardia with a captured sinus beat.  We welcome discussion of this interesting strip. 

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.

One of the most frequently misdiagnosed rhythms, atrial flutter with 2:1 conduction often masquerades as sinus tach.  Sinus tach usually has an obvious cause, such as exercise, severe hypovolemia, or age less than 6 months.  Atrial flutter usually produces flutter waves (P waves) at a rate of 250 - 350 per minute.  Therefore, a 2:1 conduction ratio would result in a heart rate of about 125 - 175 bpm).  Often, students are taught about atrial flutter using an electronic rhythm generator or a book with limited illustrations, and they become acustomed to seeing atrial flutter with 3:1 or 4:1 conduction.  The flutter waves are very easy to see in such a situation.  However, the AV node, if not affected by medication, is usually well able to conduct at a rate of 150 or more.  Therefore, the physiological block that protects us from extreme rates will keep the heart rate around 150 bpm in atrial flutter.

This ECG shows two instances where the conduction ratio slows to 3:1 momentarily, at beats no. 3 and 20.  This makes the atrial flutter more apparent.  Students should be taught to check multiple leads in any patient with a heart rate of between 125 bpm and 175 bpm, and look for flutter waves.  Flutter waves are continuous - they do not "pause" for the QRS.  For a rhythm strip with the flutter waves highlighted, see this patient's rhythm strip.