Fig. 5.

Alternative mechanisms of sodium channel gain-of-function in long QT syndrome type 3. a Increased window current due to delayed inactivation of cardiac sodium channels (green circles). Increased windows current is carried at potentials corresponding to phases 2 and 3 of the ventricular action potential (green area), remote from the peak sodium current during phase 0 (blue area). b Slower inactivation creates a late sodium current (green area). c Increased peak sodium current