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A new oral therapy for long QT syndrome

Long-term oral potassium improves repolarization in patients with HERG mutations

Susan P. Etheridge, MD, FACC^*,*, Steven J. Compton, MD, FACC, Martin Tristani-Firouzi, MD^* and Jay W. Mason, MD, FACC

^* Primary Children's Medical Center and the Division of Pediatric Cardiology, University of Utah School of Medicine, Salt Lake City, Utah, USA
Alaska Heart Institute, Anchorage, Alaska, USA
Division of Cardiology, University of Kentucky, Lexington, Kentucky, USA

View larger version (30K): [in a new window]   Figure 1 Topology of the HERG channel subunit and location of HERG mutations. Six membrane-spanning domains are depicted, with the pore helix located between the fifth and sixth transmembrane domains.

View larger version (19K): [in a new window]   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.

View larger version (24K): [in a new window]   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).

View larger version (23K): [in a new window]   Figure 4 Relationship between individual serum K+ measurement and corrected QT interval (QTc). Scatter plot demonstrating a negative correlation between the QTc interval and serum K+ level from eight study patients (total of 81 determinations). Individual symbols represent a single study patient (Fig. 2). (r = –0.52, p < 0.0001 by linear mixed model analysis). The ECGs and serum electrolytes were obtained on the same day.

View larger version (86K): [in a new window]   Figure 5 The effect of elevated serum K+ on T-wave morphology. Representative ECG tracings from study Patients 2, 4, 5, and 6, showing the improvements in repolarization and T-wave morphology after increasing serum K+. Values represent serum K+ levels at baseline and after four weeks of KCl and spironolactone therapy.