Case. A 54-year-old woman presents with weakness, poor appetite, and weight loss for several days. She also reports profuse non-bloody diarrhea. Vital signs are unremarkable, and an ECG is obtained and shown at right.
What are you concerned about?
ANSWER
This ECG demonstrates a prolonged QT interval and the presence of U waves. Given the patient’s symptoms, the most likely diagnosis is hypokalemia. A variety of arrhythmias may be seen in patients with hypokalemia, including sinus bradycardia, premature atrial and ventricular contractions, atrioventricular block, and even ventricular fibrillation. Other less common changes include QT prolongation, ST segment depression, and the presence of a
U wave. A U wave is a deflection after the T wave which is usually in the same direction, and is more pronounced in the presence of bradycardia.
When potassium levels are depleted, it is also prudent to check a magnesium and phosphorus level and replete accordingly, especially since hypokalemia and hypomagnesemia are associated with an increased risk of torsade de pointes. Hypomagnesemia can also worsen hypokalemia by furthering urinary potassium loss.
Finally, If the patient is hemodynamically unstable, potassium should be replaced through a central line for more rapid administration. This patient was indeed profoundly hypokalemic, with a level of 1.6. IV potassium was ordered in the ED and the patient was started on a potassium drip: 40mEq KCL in 1 liter of LR at a rate of 125mL/hr.
Learning Points
- Hypokalemia can present with a variety of ECG findings, ranging from sinus bradycardia to ventricular fibrillation. Presence of a U wave is usually associated with profound hypokalemia.
- In the presence of hypokalemia, it is important to aggressively treat other electrolyte abnormalities, specifically magnesium and phosphorus.
- If the patient is hemodynamically unstable, potassium should be replaced through a central line for more rapid administration.