Electrolyte Abnormalities
Hyperkalemia and Hypokalemia Serum potassium is the major intracellular ion that participates in the depolarization and repolarization of myocardial cells. Hence its serum concentration has a profound effect on the QRS and ST-T complex. |
| Narrow and tall peaked T wave (A) is an early sign of hyperkalemia. It is unusual for T waves to be taller than 5 mm in limb leads and taller than 10 mm in chest leads. Hyperkalemia should be suspect if these limits are exceeded in more than one lead. | |
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As serum potassium concentration continues to rise, the PR interval becomes longer, the P wave loses its amplitude and may disappear, and the QRS complex widens (B). When hyperkalemia is very severe, the widened QRS complexes merge with their corresponding T waves and the resultant ECG looks like a series of sine waves (C). |
| If the rise in serum potassium continues unabated, the heart arrests in asystole. (NB: The narrow and tall peaked T wave of hyperkalemia may be confused with the hyper-acute T wave occasionally seen in transmural myocardial infarction. The patient’s presenting history and physical findings would help to differentiate the two.) |
| With hypokalemia, the T wave becomes flattened together with appearance of a prominent U wave. The ST segment may become depressed and the T wave inverted. Unlike hyperkalemia, these additional changes are not related to the degree of hypokalemia. |  |
Hypercalcemia and Hypocalcemia
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