The arrhythmia known as "Torsade de pointes" is a potential lethal complication of some drugs, particulary the class Ia and III antiarrhythmic drugs. These molecules, acting directly on the action potential of the cardiac cells, can induce marked lenghtening of the QT interval, and increase the risk of developing lethal arrhythmias. A knowledge of the pharmacological properties and the possible interactions of these medications is mandatory prior to treatement initiation.
Badot, D., Brohet, C., & Scavée, C. (2007). Torsades de pointes et fibrillation ventriculaire liées à la prise de médicaments. Louvain médical, 126(7), 249-258. https://hdl.handle.net/2078.5/190984 (Original work published 2007)