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Figure 2 The individual response of the corrected QT interval (QTc) to increased serum K⁺ in long QT syndrome type 2 (LQT2) subjects. Scatter plot of QTc intervals measured in lead V₂ at baseline and after a four-week course of oral KCl and spironolactone. An increase in serum K⁺ from 4.0 ± 0.3 at baseline to 5.2 ± 0.3 mEq/l resulted in a decrease in QTc in all subjects.