In the electrocardiogram, the QT interval represents the time it takes the ventricular myocardium to repolarize. Prolongation of the QT interval indicates congenital or acquired abnormality of cardiac membrane channels. In the critical care setting, acquired long QT interval most commonly results from administration of common pharmacologic agents, including some antiarrhythmics and antibiotics. Patients with prolonged QT interval may be at risk for developing torsades de pointes and cardiac arrest. Furthermore, new-onset bradyarrhythmias and electrolyte disorders may increase this risk. Warning signs of impending sustained torsades de pointes include occurrence of polymorphic ventricular ectopic complexes, T-wave alternans, and nonsustained polymorphic ventricular tachycardia. Measurement and documentation of the QT interval, corrected for heart rate (QTc), is an important component of cardiac monitoring in the critical care setting. When prolonged QTc occurs in patients at risk, specific clinical interventions must be implemented to prevent the occurrence of torsades de pointes.

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