How to measure a QT interval.

n abnormally prolongedQT interval is associated with an increased risk of sudden cardiac death. ASome professional bodies recommend national population-based screening programs to detect QT prolongation. Familial long QT syndrome (LQTS) may remain undetected because of misdiagnosis (eg, as a seizure disorder) or through failure to measure the QT interval correctly. Psychiatrists fear the QT prolongation caused by many psychotropic medications, and it may also be seen during periods of hypothermia; electrolyte imbalance (such as hypokalaemia, hypomagnesaemia and hypocalcaemia); in the setting of raised intracranial pressure or postcardiac arrest; with other medications, such as type 1A, 1C and III antiarrhythmic agents; and with antihistamines and macrolide antibiotics.