Does hyperkalemia prolong ventricular repolarization?

Potassium efflux is the major mechanism of repolarization of ventricular myocytes.  This current is sensitive to extracellular potassium level, and in hyperkalemia, potassium conductance is increased so that more potassium leaves the myocyte in any given time period.  This leads to an increase in the slope of phases 2 and 3 of the action potential and a shortening of the repolarization time.  This is thought to be the mechanism responsible for some of the early electrocardiographic manifestations of hyperkalemia, such as ST-T segment depression, peaked T waves, and Q-T interval shortening.

See http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1413606/

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