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Dawn's picture

Electrolyte Effects

This ECG is from a 46-year-old woman with diabetes mellitus.  She presented to the Emergency Dept. with a complaint of weakness.  Her BP was elevated at 186/102.  Her blood glucose was 936 mg/dL (normal 70-105). 

So, what does her ECG show?

1) Sinus bradycardia at 55 bpm.  The rhythm is regular, with no extrasystoles.

2) A slightly prolonged PR interval at 218 ms (.218 seconds). Normal is 120-200 ms. 

3) A “wide side of normal” QRS duration at 109 ms. Normal is 70-100, but can be a little longer in normal individuals.

4) A prolonged QTc interval at 520 ms.  Normal QTc is 460 ms or less in women. A helpful rule of thumb is that the QT should be less than half the preceding RR. 

5) Normal P waves.

6) Normal axes of P, QRS, and T waves.

7) A large Q wave in Lead III which is not repeated in aVL.  This can be inconsequential when confined to Lead III, or can be a pathological Q wave, especially if also seen in aVF. 

8) Flat ST segments.  Normal ST segments are convex upward, like a smile.

9) Tall, peaked T waves in precordial leads V2 through V6, and in Lead II. 

What does it mean?

Unfortunately, we do not have complete labs for this patient, or any information about her outcome.

We know that patients who have uncontrolled diabetes are at risk for renal failure, so we should consider electrolyte imbalances when we see abnormalities in the ECG. 

Dawn's picture

ECG Basics: Sinus Tachycardia, Peaked T Waves, and Baseline Artifact

This strip offers several good teaching opportunities.  If it were a 12-lead ECG, no doubt it would be a bonanza!  First, there is sinus tachycardia at a rate of about 138 per minute.  The P waves are all alike and regular.  The T waves are tall and narrow, with a sharp peak.  This is often a transient sign of hyperkalemia, and should be investigated with serum electrolyte tests and with a 12-lead ECG.  In addition, the baseline shows a wandering type of artifact.  This is due to the patient's deep breathing, and the fact that the arm electrodes were placed on the chest.  This patient was a diabetic in ketoacidosis with hyperkalemia. 

Dawn's picture


This ECG was obtained from a patient who was suffering from renal failure and had a serum potassium level of 6.8 mEq/L.  It shows some of the earliest ECG signs of hyperkalemia.  There are tall, sharply-peaked T waves in many leads.  There is an irregular, bradycardic rhythm.  We can just barely see P waves, but they will soon flatten out and disappear.  At this level of hyperkalemia, we can expect to see conduction disturbances and bradycardia.  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.

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 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.

It is important the patient with hyperkalemia is treated rapidly, as it can be rapidly fatal.

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