Also an electrocardiogram might have changes such as a prolonged QT, prolonged ST segment, and arrhythmias, like torsade de pointes and atrial fibrillation.
Harrison's PodClass: Internal Medicine Cases and Board Prep
Ibutilide should be avoided in patients with baseline prolonged QT interval or severe left ventricular dysfunction given the risk of torsades de points.
However these drugs may also cause arrhythmias, because slowly polarizations are associated with longer QT intervals and increased risk of torsades de pointes.