Prolonged QT interval

An ECG finding in which the ventricular repolarization period (QT or rate-corrected QTc) exceeds normal limits (≥470 ms), reflecting delayed ventricular action potential duration and predisposing to polymorphic ventricular tachycardia (torsades de pointes). Possible causes are medications (antibiotics, antidepressants, antihistamines, antipsychotics), electrolyte imbalance (hypokalemia, hypomagnesemia, hypocalcemia), hypothermia, hypothyroidism, strokes, myocardial infarction, and congenital genetic conditions (Romano-Ward syndrome).