[Extension of QT interval as a consequence of risk factor accumulation--case study]

Many non-cardiovascular drugs have a potential for QT interval prolongation. This phenomenon can be related to occurence of ventricular tachycardia torsades de pointes, syncopi and even sudden death.

A female patient treated with antracycline cytostatics developed a depression of left ventricle ejection fraction. At the same time she was administered 2 common drugs with proarrhythmic potential--terfenadine and itraconazole. In this patient hypokalemia also occured. Combination of the above mentioned risk factors led to QT interval prolongation and frequent ventricular tachycardias torsades de pointes degenerating in ventricular fibrillations with need of repeated defibrillations. Both drugs were withdrawn and dysiontaemia corrected. Then arrhythmias disappeared and QT interval completely normalized. In this patient the congenital long QT syndrome was not proved.

In proarrhythmic effect of non-cardiovascular drugs the following factors play role: predisposition of a particular individual, "repolarization reserve", interindividual differences in drug metabolism. The risk factors are age, sex, dysiontaemia, heart disease and drug interactions. By different choice of medication and attention to risk factors teh life threat to the described patient could have been avoided.