A Subtle ECG
Am Fam Physician. 1999 May 1;59(9):2581-2582.
The electrocardiogram shown above is most diagnostic of which one of the following conditions?
C. Acute myocardial infarction.
D. First-degree atrioventricular block.
E. Wolff-Parkinson-White syndrome.
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.
The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Navy Medical Department or the Naval Service at large.
1. Gennari FJ. Hypokalemia. N Engl J Med. 1998;339:451–8.
2. Simon DB, Lifton RP. The molecular basis of inherited hypokalemic alkalosis: Bartter's and Gitelman's syndromes. Am J Physiol. 1996;271(5 pt 2):F961–6.
Contributing editor is MARC S. BERGER, M.D., C.M.
The editors of AFP welcome submissions for Photo Quiz. Guidelines for preparing and submitting a Photo Quiz manuscript can be found in the Authors' Guide at http://www.aafp.org/afp/photoquizinfo. To be considered for publication, submissions must meet these guidelines. E-mail submissions to firstname.lastname@example.org.
Copyright © 1999 by the American Academy of Family Physicians.
This content is owned by the AAFP. A person viewing it online may make one printout of the material and may use that printout only for his or her personal, non-commercial reference. This material may not otherwise be downloaded, copied, printed, stored, transmitted or reproduced in any medium, whether now known or later invented, except as authorized in writing by the AAFP. Contact email@example.com for copyright questions and/or permission requests.
Want to use this article elsewhere? Get Permissions