VA ICU Report 7.8.15-U waves!

Hey all, last Friday Sahil, our intrepid and courageous ICU senior, presented a great case of a gentleman with severe electrolyte disturbances in the setting of diarrhea and excessive loop diuretic prescriptions.

U waves

EKG finding, a second deflection following the T wave but prior to the subsequent P wave, typically in the same direction as the T wave.

Normal-U-wave

Courtesy: http://lifeinthefastlane.com/ecg-library/basics/u-wave/

Normal U waves can be seen in bradycardia, may just be seeing delayed re-polarization of the Purkinje fibers. According to the inimitable Thomas Evans (ECG Cribsheets), A low amplitude positive U wave <1.5mm in height and between 160-200 msec in duration, typically seen in leads V2 and V3, can be termed “normal.”

The precise definition of abnormal is controversial, however any U wave that is larger or longer than above, or fuses with a T wave is considered abnormal. Classically seen in severe hypokalemia, digitalis toxicity, but also  can be seen in hypothermia, hypomagnesemia, increased ICP, or in LVH.

Other pearl: Chlorthalidone and hydrochlorothiazide are both thiazide diuretics, but chlorthalidone has a much longer half life, which may owe to its superior efficacy in early trials (see ALLHAT), but also remember it causes worse hypokalemia than typical thiazides, and when added to loop diuretics, monitor that K closely! (and magnesium).

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