Comparison of Two Highly Automated ECG Algorithms for Detection of Drug-Induced Cardiac Ion Channel Block

Translational Models and Tools to Reduce Clinical Trials and Improve Regulatory Decision Making for QTc and Proarrhythmia Risk (ICH E14/S7B Updates)

After multiple drugs were removed from the market secondary to drug-induced torsade de pointes (TdP) risk, the International Council for Harmonisation (ICH) released guidelines in 2005 that focused on the nonclinical (S7B) and clinical (E14) assessment of surrogate biomarkers for TdP. Recently, Vargas et al. published a pharmaceutical-industry perspective making the case that "double-negative" nonclinical data (negative in vitro hERG and in vivo heart-rate corrected QT (QTc) assays) are associated with such low probability of clinical QTc prolongation and TdP that potentially all double-negative drugs would not need detailed clinical QTc evaluation. Subsequently, the ICH released a new E14/S7B Draft Guideline containing Questions and Answers (Q&As) that defined ways that double-negative nonclinical data could be used to reduce the number of "Thorough QT" (TQT) studies and reach a low-risk determination when a TQT or equivalent could not be performed. We review the Vargas et al. proposal in the context of what was contained in the ICH E14/S7B Draft Guideline and what was proposed by the ICH E14/S7B working group for a "stage 2" of updates (potential expanded roles for nonclinical data and details for assessing TdP risk of QTc-prolonging drugs). Although we do not agree with the exact probability statistics in the Vargas et al. paper because of limitations in the underlying datasets, we show how more modest predictive value of individual assays could still result in low probability for TdP with double-negative findings. Furthermore, we expect that the predictive value of the nonclinical assays will improve with implementation of the new ICH E14/S7B Draft Guideline.

Comparison of Electrocardiographic Biomarkers for Differentiating Drug-Induced Single vs. Multiple Cardiac Ion Channel Block

Since introduction of the International Conference on Harmonization proarrhythmia guidelines in 2005, no new marketed drugs have been associated with unacceptable risk of Torsade de Pointes. Although cardiac safety improved, these guidelines had the unintended consequence of eliminating potentially beneficial drugs from pipelines early in development. More recently, it has been shown that a corrected QT (QTc) prolonging drug may be safe if it impacts multiple ion channels vs. only human ether‐a‐go‐go related gene (hERG) and that this effect can be discriminated using QT subintervals. We compared the predictive power of four electrocardiogram (ECG) repolarization metrics to discriminate single vs. multichannel block: (i) traditional 10‐second signal averaged triplicates, and (ii) three metrics that used increasing density of automatically measured beat‐to‐beat (btb) intervals. Predictive power was evaluated using logistic regression and quantified with receiver operating characteristic (ROC) area under the curve (AUC). Compared with the traditional 10‐second signal averaged triplicates, the reduction in classification error ranged from 2−6 with increasing density of btb measurements.

Update on the ECG component of the CiPA initiative

The Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative is validating a new paradigm for assessing proarrhythmic potential of drugs that goes beyond hERG block and QT prolongation. Based on in vitro data of the drug's effects on multiple cardiac ion channel currents, CiPA's in silico model of the human cardiomyocyte will classify drugs as low, intermediate or high risk for torsade de pointes. Under CiPA, early phase 1 ECG data will be used to determine if there are unexpected ion channel effects in humans compared to the in vitro ion channel data. CiPA's ECG biomarker working group identified the heart rate corrected J-Tpeak interval (J-Tpeakc, from the end of the QRS to the peak of the T-wave) as the best of 12 ECG biomarkers to detect late sodium current block in presence of hERG block. While predominant hERG blockers prolonged QTc and J-Tpeakc, "balanced" ion channel blocking drugs (hERG + late sodium and/or calcium block) prolonged QTc without prolonging J-Tpeakc. This manuscript reviews the ECG component of CiPA and provides a description of the ECG methods used in the CiPA ECG validation clinical study.