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Figure 3 The mean corrected QT interval (QTc) shortens in response to an elevation in serum K+. Graphic demonstration of the mean QTc intervals measured in ECG leads II, V2, and V4 at baseline and after increasing the serum K+ level with oral KCl and spironolactone. The treatment protocol was associated with a statistically significant decrease in QTc (p value = 0.002, 0.003, and 0.003 for leads II, V2, and V4, respectively, using the paired t test).