Thorough QT/QTc (TQT) study

With a number of drugs entering the market, cardiac safety remains a cause of major concern for the regulatory authorities, before approval. The incidence of drug induced arrhythmia with non-cardiovascular drugs is low, however the result is fatal, hence much focus is being given to assess the pro-arrhythmic potential of a drug. The arrhythmogenic risk of the drug is higher if the patient is on polypharmacy or has other risk factors such as an electrolyte imbalance or an underlying structural heart disease. QT prolongation can be either due to congenital causes such as Long QT syndromes (LQTS) which include Romano-Ward syndrome, Jervell and Lange-Nielson syndrome or can be acquired, which is mainly due to drugs. Several drugs such as terfenadine, astemizole, cisapride and grepafloxacin have been withdrawn from the market due to QT prolongation and development of a fatal ventricular arrythmia - torsades de pointes (TdP). This has led to implementation of guidelines to assess cardiac safety. The pro-arrhythmic risk can be assessed using thorough QT/QTc studies or exposure response modelling of intensive ECGs. This article will give an overall view of the use of QT/QTc interval as a biomarker for cardiac safety and the current guidelines for thorough QT/QTc studies which are mainly done to assess the pro-arrhythmic potential of a non-anti-arrhythmic drug.