Long QT Interval Syndromes By L Brent Mitchell, MD, Libin Cardiovascular Institute of Alberta, University of Calgary Reviewed / Revised Jan 2023 View Patient Education Pathophysiology Etiology Symptoms and Signs Diagnosis Treatment Key Points Topic Resources Schwartz Score for Long QT.. Overview of Long QT Syndrome The long QT interval syndromes (LQTS) result from any congenital or acquired disorder of cardiac ion channel function or regulation (channelopathy) that prolongs ventricular myocyte action potential duration as reflected by prolongation of the rate-corrected QT interval on the ECG.