Question

Discussion

The answer is A: hypokalemia. Although subtle, this electrocardiogram (ECG) demonstrates a flattening of the T waves with development of U waves (see arrows) associated with hypokalemia. The ECG patterns seen in patients with hypokalemia range from slight T-wave flattening alone to the appearance of prominent U waves, occasionally with ST depressions or T-wave inversions. This is usually a progressive pattern. When the U wave is greater than the T wave, the potassium level is usually less than 2.7 mEq per L (2.7 mmol per L). The most common causes of hypokalemia are medications (especially diuretics) or renal loss related to metabolic alkalosis or potassium loss in the stool secondary to diarrhea.¹ Hypokalemia, although tolerated well in most patients, can be life-threatening in those with underlying cardiac disease. The potassium level in this patient was 2.3 mEq per L (2.3 mmol per L). Treatment includes potassium replacement and correction of the underlying cause when possible. Some patients require daily potassium supplementation. Interestingly, the hypokalemia occurring in this patient was a result of Bartter's syndrome, a rare hereditary disorder of renal potassium wasting secondary to impaired electrolyte transport in the ascending loop of Henle.² It is treated mainly by liberal potassium supplementation. The use of spironolactone (Aldactone) can also help prevent potassium wasting.

As for the remaining multiple-choice answers, hypocalcemia manifests itself on ECG as a prolonged QT interval, which is not present in this tracing. There are no ST elevations or other changes suggestive of acute myocardial infarction in this tracing. First-degree atrioventricular block should also be ruled out because the PR interval on the ECG shown here is less than 0.20 mm. Finally, Wollf-Parkinson-White syndrome is a preexcitation syndrome characterized on ECG by wide QRS complexes, short PR intervals and delta waves, none of which are present on the ECG shown here.