Short QT syndrome types 1-3 are due to increased activity of outward potassium currents in phases 2 and 3 of the cardiac action potential.  This causes a shortening of the plateau phase of the action potential (phase 2), causing a shortening of the overall action potential, leading to an overall shortening of refractory periods and the QT interval. In the families afflicted by short QT syndrome, two different missense mutations have been described in the human ether-a-go-go gene (HERG).  These mutations result in the expression of the same amino acid change in the cardiac IKr ion channel.  This mutated IKr has increased activity compared to the normal ion channel, and would theoretically explain the above hypothesis.  Short QT syndrome types 4 and 5 are due to abnormalities in the calcium channel.
Short QT syndrome pathophysiology
Long QT Syndrome pathophysiology
Sick sinus syndrome pathophysiology
Brugada syndrome pathophysiology
Pacemaker syndrome pathophysiology
Dextrocardia pathophysiology
Sinoatrial arrest pathophysiology
Short QT syndrome risk factors