A new functional data‐based biomarker for monitoring cardiovascular behavior

Cardiac safety assessment in drug development concerns the ventricular repolarization (represented by electrocardiogram (ECG) T‐wave) abnormalities of a cardiac cycle, which are widely believed to be linked with torsades de pointes, a potentially life‐threatening arrhythmia. The most often used biomarker for such abnormalities is the prolongation of the QT interval, which relies on the correct annotation of onset of QRS complex and offset of T‐wave on ECG. A new biomarker generated from a functional data‐based methodology is developed to quantify the T‐wave morphology changes from placebo to drug interventions. Comparisons of T‐wave‐form characters through a multivariate linear mixed model are made to assess cardiovascular risk of drugs. Data from a study with 60 subjects participating in a two‐period placebo‐controlled crossover trial with repeat ECGs obtained at baseline and 12 time points after interventions are used to illustrate this methodology; different types of wave form changes were characterized and motivated further investigation. Copyright © 2012 John Wiley & Sons, Ltd.     

ECG abnormalities and stroke incidence

In this review, the authors discuss the role of ECG in prediction of stroke. ECG plays an important role in detection of several stroke risk factors/predictors including atrial fibrillation and left ventricular hypertrophy; both are components of the Framingham Stroke Risk Score. Multiple other ECG traits have also emerged as potential predictors of stroke, namely cardiac electrical/structural remodeling – Q wave, QRS/QT duration, bundle blocks, P wave duration/amplitude/dispersion, other waveform angles and slopes; higher automaticity – ectopic beats; and re-entry – atrial tachyarrhythmia; and higher vulnerability to arrhythmia – heart rate and its variability. Most of these predictors are not ready for prime time yet; however, further research focusing on their role in risk stratification and prevention of stroke may be useful. In this article, the authors discuss the prevalence, mechanisms and clinical applications of traditional and novel ECG markers in the prevention and treatment of stroke.     

Sildenafil Citrate Does Not Alter Ventricular Repolarization Properties: Novel Evidence from Dynamic QT Analysis

Background: Sildenafil citrate may have direct cardiac electrophysiological effects, and is possibly responsible for some cardiac events. The aim of our study was to investigate the effects of sildenafil citrate on QT dynamicity properties with a new QT analysis program showing even small changes in ventricular repolarization. Methods: Twenty‐four‐hour Holter electrocardiographic recordings were used to obtain the data in the predrug phase (1‐hour rest position before drug administration), and in the postdrug phase (1‐hour rest position, which began 60 minutes after 50 mg oral sildenafil citrate administration). With the special QT analysis program (Verda, Reynolds Medical Ltd., UK); mean values of RR, QT, QT_o (corrected QT), J (the exponent of correction formula) and S (QT/RR plots slope) parameters together with QT variability indexes (QTVI) were calculated for study phases. Results: Mean ± SEM values for RR and QT were higher in postdrug phase than in predrug phase (RR: 845 ± 42 ms vs 816 ± 46 ms, P < 0.05; QT: 371 ± 8 ms vs 361 ± 9 ms, P < 0.05). However, sildenafil did not induce any significant change in mean ± SEM values for QT_o, J, and S in postdrug phase compared with predrug phase (408 ± 10 ms vs 406 ± 8 ms, 0.474 ± 0.030 vs 0.433 ± 0.025, 0221 ± 0.020 vs 0.198 ± 0.017, respectively; P > 0.05). QTVIs were also not different in each phase (predrug: ?0.874 ± 0.071 vs postdrug: ?0.997 ± 0.067, P = 0.109). Conclusions: Fifty milligrams sildenafil does not affect QT dynamicity properties. The cardiac events associated with sildenafil could not be explained with ventricular arrhythmias.     

The Antiarrhythmic Drug BRL‐32872

BRL‐32872 is a new antiarrhythmic drug with balanced class‐III and class‐IV actions as categorized by the Vaughan‐Williams classification. BRL‐32872 blocks the rapid component of the cardiac delayed rectifier potassium channel IK_r (IC₅₀= 28 nM) and its molecular correlate HERG (“Human‐ether‐a‐go‐go related gene,” IC₅₀ of 19.8 nM in cell lines) at low concentrations. It also inhibits the L‐type calcium current (ICa) at higher concentrations (IC₅₀= 2.8 μM). This dual concentration‐dependent profile of action at higher concentrations may possibly prevent “torsades de pointes” ventricular arrhythmias, which is a dangerous side effect of many other class‐III antiarrhythmic drugs. With BRL‐32872, an excessive prolongation of the action potential duration and consecutive QTc prolongation is prevented by a concentration‐dependent increase of calcium channel block, resulting in the so‐called “bell‐shaped” profile of antiarrhythmic drug action. BRL‐32872 is very effective in the treatment of ventricular arrhythmias in animal models of cardiac ischemia. In the ischemic hearts of animals the drug significantly reduced early afterdepolarization and ventricular tachycardia. The antiarrhythmic effect of BRL‐32872 has not yet been demonstrated in humans.     

Impact of dosing regimen of custirsen,an antisense oligonucleotide,on safety,tolerability and cardiac repolarization in healthy subjects

Aims

Custirsen (OGX-011/TV-1011), a second-generation antisense oligonucleotide (ASO) that reduces clusterin production, is under investigation with chemotherapy in patients with solid tumours. Custirsen is associated with constitutional symptoms (CS) that may interfere with clinical pharmacology investigations, such as QT interval studies. Experience with other ASOs suggests NSAID premedication may ameliorate CS, but we observed suboptimal outcomes in healthy subjects given custirsen and NSAIDs. We sought to establish a custirsen regimen for future clinical pharmacology studies in healthy subjects.

Methods

Subjects received custirsen (640 mg intravenously over 120 min) with dexamethasone premedication or increasing doses (320, 480, 640 mg over 6 days) of custirsen with dexamethasone premedication, then one full custirsen dose without premedication on day 8. Incidence/severity of adverse events (AEs) and extensive electrocardiogram readings were evaluated. Pharmacokinetic parameters were estimated.

Results

AEs included CS, elevated transaminases and prolonged activated partial thromboplastin time (aPTT) that were predominantly grade 1/2. Administration of increasing custirsen doses and dexamethasone premedication reduced the incidence of CS associated with full dose custirsen. Transaminase elevation showed a dose-dependent effect (0% at days 2, 4, 27% at day 6) with the highest custirsen doses. Increasing doses of custirsen may have mitigated the severity but not incidence of aPTT prolongation. Neither regimen was associated with cardiac repolarization changes in QT values or concentration–effect analyses. The custirsen pharmacokinetic profile was consistent with previous experience.

Conclusion

Escalation of custirsen dose combined with dexamethasone premedication reduced CS associated with full dose custirsen and should be considered in future clinical pharmacology studies of custirsen.     

Small doses of droperidol do not present relevant torsadogenic actions: a double-blind,ondansetron-controlled study

AIM

Drugs used for postoperative nausea and vomiting prophylaxis are believed to provoke torsadogenic changes in cardiac repolarization. The aim of this study was to assess the effect of small doses of droperidol on the parameters of cardiac repolarization, including the QT_c interval and transmural dispersion of repolarization.

METHODS

A total of 75 patients were randomly allocated to receive 0.625 or 1.25 mg droperidol or 8 mg ondansetron. The QT_c interval was calculated using Bazett''s formula and the Framingham correction. The transmural dispersion of repolarization was determined as T_peak–T_end time.

RESULTS

Transient QT prolongation, corrected with both formulae, followed 1.25 mg of droperidol 10 min after administration. No change in the QT_c value was observed in the other groups. When corrected with Bazett''s formula, QT_c was prolonged above 480 ms in two patients receiving 1.25 mg droperidol (at the 10^th and 20^th minute of the study) and in one receiving ondansetron. No patients developed a QT_cB prolongation over 500 ms. No increase above 480 ms was observed relative to the Framingham correction method. There were no significant differences in the T_peak–T_end time either between or within the groups.

CONCLUSION

In men without cardiovascular disorders small doses (1.25 mg) of droperidol prophylaxis induced transient QT_c prolongation without changes in transmural dispersion of repolarization. The apparently low risk of the drug applies only in low risk male patients with a low pro-QT_c score.