CMAJ • November 22, 2005; 173 (11). doi:10.1503/cmaj.050596.
© 2005 CMA Media Inc. or its licensors
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Short QT syndrome

Ramon Brugada, Kui Hong, Jonathan M. Cordeiro and Robert Dumaine

From the Montreal Heart Institute (Brugada), Montréal, Qué.; Baylor College of Medicine (Hong), Houston, Texas; Masonic Medical Research Laboratory (Cordeiro), Utica, New York; and the University of Sherbrooke (Dumaine), Sherbrooke, Qué.



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  		Fig. 1: A. Ion channels are embedded in the membrane and allow the flux of ions in and out of the cells following voltage gradients. The Na+/Ca2+ exchanger (red) is electrogenic, as it transports 3 sodium ions for each calcium ion across the surface membrane. B. Ionic currents and their corresponding genes; the generation of electrical activity by the different ionic currents will generate the cardiac action potential. Top: 3 depolarizing currents; centre: a ventricular action potential; bottom: repolarizing currents. Mutations in KCNJ2, which affects the IK1 current, result in the third form of short QT syndrome; mutations in KCNH2/KCNE2, affecting the IKr current, result in the syndrome's first form; mutations in KCNQ1/KCNE1, affecting the IKs current, result in the second form. Reprinted, with permission, from ref. 5.

 


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  		Fig. 2: A. Schematic representation of the normal action potential and the flux of ions. B. With gain-of-function mutations in any of 3 different potassium channels, the cardiac action potential shortens and the QT interval decreases.

 


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  		Fig. 3: Current–voltage relationship for steady state current measured at the end of the activating pulse. Steady state current amplitudes were measured at the end of the 800-ms test pulses. Mutation N588K removes rapid inactivation and significantly increases the amplitude of the rapid delayed rectifier current IKr in a physiologic range of membrane potentials. In wild type, or normal, currents, the current amplitude increased up to a test potential of –10 mV and then gradually decreased past –10 mV as the channels inactivated. In contrast, the N588K current increased linearly and did not rectify. N588K currents were much larger than wild type past 0 mV in the range of the ventricular action potential plateau. Reprinted, with permission, from ref. 8.

 


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  		Fig. 4: Electrocardiogram of a patient with short QT syndrome. Observe the tall peaked T waves. Reprinted, with permission, from ref. 3.