The PMHNP is treating a 69-year-old man with ziprasidone (Geodon) for schizophrenia and orders an electrocardiogram. Which QTc interval places the patient at greatest risk for torsades de pointes?

Choice A reason: A QTc interval of 100–200 milliseconds is abnormally short and not typically associated with torsades de pointes. While short QT syndrome is a separate arrhythmogenic condition, torsades is linked to prolonged QTc intervals. Choice B reason: A QTc interval of 300–400 milliseconds is within the normal range for most adults. This range does not pose a significant risk for torsades de pointes unless accompanied by other risk factors or medications. Choice C reason: A QTc interval of 500–700 milliseconds is markedly prolonged and significantly increases the risk for torsades de pointes, a potentially life-threatening polymorphic ventricular tachycardia. Ziprasidone is known to prolong the QT interval, and monitoring is essential to prevent arrhythmias. Choice D reason: A QTc interval of 260–460 milliseconds includes both low-normal and upper-normal values. While the upper end may warrant caution, especially in patients on QT-prolonging drugs, it does not represent the highest risk range for torsades.