Sunday, July 3, 2011

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Hypokalemia - ECG changes

The ECG changes in hypokalemia is mainly due to a delayed ventricular repolarisation. The changes normally do not correlate well with the plasma concentration.Early changes include flattening or inversion of the T wave, a prominent U wave, ST-segment depression k/a thumbprint-like ST depression, and a prolonged QU interval but the QT interval will be normal.

Severe K+ depletion may result in a prolonged PR interval, decreased voltage and widening of the QRS complex, and an increased risk of ventricular arrhythmias, especially in patients with myocardial ischemia or left ventricular hypertrophy. The QT interval may be normal or lengthened.


  1. Hi, In the Med challenger, there was a 32 years old post-surgical release of intestinal obstruction in Levin tube (gastrointestinal) low pressure suction with wt loss of 12.5 pound developed hypomagnesemia and hypokalemia (did not elaborate on the lab level of either), and had severe leg cramps. Amoung the answeres it quoted the prolong qt interval as an wrong answer. Why? My concern is with severe hypokalemia such as this patient with weight loss of 12.5 pounds, the qt can also be prolonged (and also can be normal). I wonder if there is a criteria to say when and at what level the hypokalemia that the qt interval would stay normal or be prolonged?
    Much appreciated
    Hoo Joon Cheung, M.D., Surgeon,FACM,ABEM,ABDA,AAPM

    ps, I am a trained surgeon by ABS, not a cardiologist, would you please instruct me on this. Much thanks

    1. Dear Dr Cheung, there is actually no cut-off value of hypokalemia whereby there is QT prolongation. QT interval remains more or less constant and it is the QU interval that increases. QT interval prolongation in hypokalemia is seen more commonly if associated with hypomagnesemia also.

      As for regarding Med Challenger, it is right to say prolonged QT interval as incorrect if there was hypokalemia only. I guess there was a more appropriate answer to that question.

      If in future researchers, there is a cut-off value for QT prolongation, i will definitely let you know...

    2. However, a study about the use of an antipsychotic drug and QTc prolongation,showed that the patients developed QT interval prolongation when the serum potassium levels was less that 2.4 mEq/L.


  2. Hoo Joon Cheung, M.D.
    Thanks. I recalled a patient I performed the Mitral valve surgery did have the history of hypomagnesemia and hypokalemia when he had the ekg changes with septicemia.