Below follows a discussion which aims to clarify some of the common misunderstandings. T-wave changes are notoriously misinterpreted, particularly inverted T-waves. Discordance and concordance between QRS and ST-T. A negative T-wave is also called an inverted T-wave. Otherwise there is discordance (opposite directions of QRS and T) which might be due to pathology. The T-wave should be concordant with the QRS complex, meaning that a net positive QRS complex should be followed by a positive T-wave, and vice versa ( Figure 17). Women have a more symmetrical T-wave, a more distinct transition from ST segment to T-wave and lower T-wave amplitude. The T-wave is normally slightly asymmetric since its downslope (second half) is steeper than its upslope (first half). As noted above, the transition from the ST segment to the T-wave should be smooth. The amplitude diminishes with increasing age. The T-wave amplitude is highest in V2–V3. The normal T-wave in adults is positive in most precordial and limb leads. It is important the patient with hyperkalemia is treated rapidly, as it can be rapidly fatal.Assessment of the T-wave represents a difficult but fundamental part of ECG interpretation. For a comparison of tall T waves caused by several factors, including hyperkalemia, go to Dr. Steve Smith's blog has several very good discussions on the subject. Ed Burns has compiled a very instructive collection of ECGs that illustrate the progression of this deadly condition.ĭr. This sine wave pattern signals cardiac arrest is imminent.įor a comprehensive discussion of hyperkalemia on the ECG with many examples of the different phases, go to Life In The Fast Lane. AV blocks may occur, with either ventricular or junctional escape rhythms.Īs the patient's condition worsens and the serum potassium rises, the QRS and T waves lose amplitude, widen, and may seem to blend together.Īt levels above 8.0 mEq/L, we may see what looks like a bizarre idioventricular rhythm, or a sine wave pattern. The QRS morphology will be bizarre - not necessarily showing a typical bundle branch block pattern. There may be bundle branch blocks or fascicular blocks.
The QRS will widen and the rate will slow. Serum K levels of 7.0 mEq/L or greater cause conduction abnormalities. The P waves will lose amplitude, widen and flatten. Serum K levels of 6.5 mEq/L or greater cause progressive paralysis of the atria. Serum K levels of 5.5 mEq/L or greater can cause repolarization abnormalities like tall, peaked T waves. Extracellular serum potassium can rise due to renal failure, or taking potassium supplements, potassium-sparing diuretics, or ACE inhibitors.ĮCG signs may vary among people with hyperkalemia, but in general: It is necessary for proper electrical functioning of the heart. Potassium is primarily an intracellular electrolyte. Caution: hyperkalemia can progress and become life-threatening very quickly. At this level of hyperkalemia, we can expect to see conduction disturbances and bradycardia. We can just barely see P waves, but they will soon flatten out and disappear. There is an irregular, bradycardic rhythm. There are tall, sharply-peaked T waves in many leads. It shows some of the earliest ECG signs of hyperkalemia. This ECG was obtained from a patient who was suffering from renal failure and had a serum potassium level of 6.8 mEq/L. 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. Unfortunately, we do not have complete labs for this patient, or any information about her outcome. Normal ST segments are convex upward, like a smile.ĩ) Tall, peaked T waves in precordial leads V 2 through V 6, and in Lead II. This can be inconsequential when confined to Lead III, or can be a pathological Q wave, especially if also seen in aVF.Ĩ) Flat ST segments. A helpful rule of thumb i s that the QT should be less than half the preceding RR.ħ) A large Q wave in Lead III which is not repeated in aVL. Normal is 70-100, but can be a little longer in normal i ndividuals.Ĥ) A prolonged QTc interval at 520 ms. Normal is 120-200 ms.ģ) A “wide side of normal” QRS duration at 109 ms. The rhythm is regular, with no extrasystoles.Ģ) A slightly prolonged PR interval at 218 ms (.218 seconds). Her blood glucose was 936 mg/dL (normal 70-105).ġ) Sinus bradycardia at 55 bpm. This ECG is from a 46-year-old woman with diabetes mellitus.
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