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Some prominent examples of drugs recently withdrawn because of their potential to increase cardiac risk have lately led to a broad discussion about the need to have an early and thorough cardiac evaluation in clinical development for all drugs. So far, the most efficient and effective method of evaluating the cardiac effects of drugs is to analyse drug-induced changes in the surface electrocardiogram (ECG), although the ECG is certainly not a perfect biomarker.
The Food and Drug Administration (FDA) and the European Medicines Agency have recently published their recommendations for ECG QT/QTc studies to evaluate the proarrhythmic potential of non-anti-arrhythmic drugs (1). The QT interval represents the ventricular depolarisation and following repolarisation of the heart-cycle. The QT interval is commonly measured from the beginning of the QRS complex (Q-Point) to the end of the T-wave. Some drugs have the ability to delay cardiac repolarisation, which can be measured as prolongation of the QT (QTc) interval in the electrocardiogram (ECG). A delay in cardiac repolarisation favours the development of arrhythmias, such as Torsade de Pointes (TdP). A main feature of TdP is a significantly prolonged QT interval – unfortunately, TdP may degenerate into ventricular fibrillation, leading to sudden cardiac death. But the threshold level of regulatory concern is around 5ms, as evidenced by an upper bound of the 95 per cent confidence interval around the mean effect on QTc of 10ms – this requires very accurate acquisition and analysis of the 12 lead surface ECG (1).
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