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Instructors' Collection ECG of the Week: Hyperkalemia

Sun, 08/23/2015 - 16:06 -- Dawn

This ECG was obtained from a patient who had a serum potassium level of 7.4 mEq/L.  It shows some of the earliest ECG signs of hyperkalemia.  There are tall, sharply-peaked T waves in many leads.  The P waves have not yet widened and lost amplitude, but they will soon flatten out and disappear.  At this level of hyperkalemia, we can expect to see conduction disturbances (first-degree AV block in this case) and bradycardia (not yet). It is a bit surprising that the QRS complexes have not yet widened at this serum K level.    Caution:  hyperkalemia can progress and become life-threatening very quickly.

Potassium is primarily an intracellular electrolyte.  It is necessary for proper electrical functioning of the heart.  Extracellular  serum potassium can rise due to renal failure, or taking potassium supplements, potassium-sparing diuretics, or ACE inhibitors.  Occasionally, serum K levels may be artificially elevated by drawing the blood with too much syringe pressure, or using too small a needle, as the red blood cells can be damaged and release intracellular K into the serum.

ECG signs may vary among people with hyperkalemia, but in general:

Serum K levels of 5.5 mEq/L or greater can cause repolarization abnormalities like tall, peaked T waves.

Serum K levels of 6.5 mEq/L or greater cause progressive paralysis of the atria.  The P waves will lose amplitude, widen and flatten.   The PR segment will lengthen. Eventually, the P waves will disappear.

Serum K levels of 7.0 mEq/L or greater can cause conduction abnormalities.  The QRS will widen and the rate will slow.  There may be bundle branch blocks or fascicular blocks.  The QRS morphology will be bizarre - not necessarily showing a typical bundle branch block pattern.  AV blocks may occur, with either ventricular or junctional escape rhythms.

As the patient's condition worsens and the serum potassium rises, the QRS and T waves lose amplitude, widen, and may seem to blend together.  

At levels above 8.0 mEq/L, we may see what looks like a bizarre idioventricular rhythm, or a sine wave pattern.  This sine wave pattern signals cardiac arrest is imminent.

For a comprehensive discussion of hyperkalemia on the ECG with many examples of the different phases, go to Life In The Fast Lane.  Ed Burns has compiled a very instructive collection of ECGs that illustrate the progression of this deadly condition.

Dr. Steve Smith's blog has several very good discussions on the subject.  For a comparison of tall T waves caused by several factors, including hyperkalemia, go to Dr. Smith's Blog.

ECG Basics: Atrial Flutter With 2:1 Conduction And An Aberrantly-conducted Beat

Sun, 08/23/2015 - 14:20 -- Dawn

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. 

Ask the Expert

Tue, 08/18/2015 - 17:24 -- Dawn
Dr. Jerry W. Jones, MD, FACEP, FAAEM

QUESTION:

Dr. Jones, what advice do you have for teaching ECG beginners? 


Today’s expert is Dr. Jerry W. Jones, MD, FACEP, FAAEM
 

Jerry W. Jones, MD FACEP FAAEM is a diplomate of the American Board of Emergency Medicine who has practiced internal medicine and emergency medicine for 35 years. Dr. Jones has been on the teaching faculties of the University of Oklahoma and The University of Texas Medical Branch in Galveston. He is a published author who has also been featured in the New York Times and the Annals of Emergency Medicine for his work in the developing field of telemedicine. He is also a Fellow of the American College of Emergency Physicians and a Fellow of the American Academy of Emergency Medicine and, in addition, a member of the European Society of Emergency Medicine. 

Dr. Jones is the CEO of Medicus of Houston and the principal instructor for the Advanced ECG Interpretation Boot Camp and the Advanced Dysrhythmia Boot Camp. 

ANSWER: 

Even in my advanced classes I begin with "normal" ECGs. Throughout my residency in internal medicine, I was never up at 3 am wondering if an ECG was ABNORMAL ... I was always trying to decide if a finding was really NORMAL instead.

Here are a few of my thoughts...

A biphasic P wave in V1 is basically the norm. Even when there is only a monophasic deflection, it's usually because the other half of the biphasic deflection is isoelectric.

In my advanced courses we always begin with a normal tracing and I have all the participants measure the R-R intervals with ECG calipers to demonstrate that there is often considerable variation in the rhythm and that there is very rarely a perfectly regular sinus rhythm (and when there is - it's only for a few moments!). This comes in handy occasionally in deciding whether a tachycardia is sinus or not.

I often find that beginners have the impression that the R waves in the precordial leads increase in size from V1 through V6 - and that should never be the case in a "normal" ECG. Typically the tallest R wave peaks at V4 or V5. Because the V6 electrode is the furthest of all the regular precordial leads from the surface of the heart, it actually diminishes in amplitude. When the R wave in V6 is the tallest across the precordium, it means that the heart has enlarged enough to extend its surface a lot closer to the V6 electrode. That alone is a very good indication of cardiac enlargement.

One other thing I would really emphasize to a newbie is that the ST segment should rise gently into the upslope of the T wave and that there should never be a perceptible angle indicating where the ST ends and the T wave begins - it should be smooth and without a discernible margin. And the T wave should always be asymmetrical - NOT symmetrical. However, when the downslope of the T wave returns to the baseline it CAN create a noticeable angle. 

I hope some of these comments help you teach those who are just beginning to read ECGs.

Waves and Intervals Illustration

Click to open: 
Waves and Intervals, Measuring ECG Waves and Intervals

All illustrations on the ECG Guru website are FREE for you to use in a teaching application and are COPYRIGHT FREE for such use.  If you need an illustration for your packets or presentations, and don't find it here, contact the ECG Guru staff at Dawn.ECGGuru@gmail.com.  For commercial use, contact us at the same email address.  Click on illustration to open. 

Are You New to Laddergrams?

Fri, 02/20/2015 - 22:34 -- Dawn

A laddergram is a diagram of conduction through the heart, presented in a minimum of three tiers, one for the atria, one for the AV junction, and one for the ventricles.  Laddergrams are very useful for presenting and testing your theory of a dysrhythmia.  Instructors often use them to illustrate complex dysrhythmia mechanisms.  

If you don't yet have experience in using laddergrams, go to this LINK to find a short PowerPoint presentation that will give you the basics to get started.  Be careful - it can be a bit addicting to construct laddergrams, like working a puzzle.  If you want to use laddergrams to teach your students, this PowerPoint presentation can help you introduce them to the concept.  

Our thanks to Jason Roediger, ECG Guru and dysrhythmia expert, for the laddergram depicted here, and the many LADDERGRAMS featured in his blog posts on this site  to see the discussion accompanying this ECG, go to this LINK  (Warning: this is an ECG Challenge, which is advanced material)  

 “For another step-by-step review from Dr. Ken Grauer on How to Draw a Laddergram - Please check out Dr. Ken Grauer’s ECG Blog #69 - GO TO - http://tinyurl.com/KG-Blog-69

 

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