QT interval

In cardiology and the electrocardiogram, the QT interval is the time from the start of the Q wave and the end of the T wave.

To correct the QT interval for heart rate:

${\mbox{QTc}}={\frac {\mbox{measured QT interval}}{\sqrt {RR\ interval\ (in\ sec)}}}$

Normal values for the corrected QT interval are between 0.36 and 0.44 seconds.

A prolonged QT internal may lead to Torsades de pointes. Drugs may prolong the QT interval. A list of these drugs is available at the Arizona Center for Education & Research on Therapeutics.

Congenital Long QT Syndrome

Andersen Syndrome

Andersen Syndrome is a "form of inherited long QT syndrome (or LQT7) that is characterized by a triad of potassium-sensitive periodic paralysis, ventricular ectopic beats, and abnormal features such as short stature, low-set ears, and scoliosis. It results from mutations of KCNJ2 gene which encodes a channel protein (inward rectifier potassium channels) that regulates resting membrane potential."

Jervell-Lange Nielsen Syndrome

Jervell-Lange Nielsen Syndrome is a "form of long QT syndrome that is associated with congenital deafness. It is characterized by abnormal cardioelectrophysiology involving the voltage-gated potassium channel. It results from mutation of KCNQ1 gene (Subtype 1 or JLN1) or the KCNE1 gene (Subtype 2 or JLN2).."

Romano-Ward Syndrome

Romano-Ward Syndrome (LQT1) is a "form of long QT syndrome that is without congenital deafness. It is caused by mutation of the KCNQ1 gene which encodes a protein in the voltage-gated potassium channel."