Pain medicine : the official journal of the American Academy of Pain Medicine
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The most feared drug-induced complication is fatal cardiac arrest. Torsades de pointes (TdP) is a polymorphic ventricular tachycardia occurring in the setting of a QT interval prolongation and is the most frequent type of drug-induced pro-arrhythmia. The most common mechanism of QT prolongation and TdP is blockade of the rapid component of the delayed rectifier repolarizing potassium conductance IKr. ⋯ Due to factors such as inhibition of the parasympathetic nervous system, prevention of hypoxia and hypercarbia, and attention to serum electrolytes, TdP is a very rare occurrence in the perioperative environment. Methadone, however, is typically given to outpatients, over long periods, and in combination with agents that inhibit its metabolism or are QT prolonging in their own right. Thus, pre- and post-drug electrocardiograms may be appropriate when prescribing methadone for outpatients, while the much lower risk for TdP (and the difficulties inherent in QT measurement in the perioperative period) render this approach unfruitful and worthy of reevaluation.