The JT-area indicates dispersion of repolarization in dogs with atrioventricular block

Utility of the JT Peak Interval and the JT Area in Determining the Proarrhythmic Potential of QT-Shortening Agents

Drug-induced long QT increases the risk of ventricular tachyarrhythmia known as torsades de pointes (TdP). Many biomarkers have been used to predict TdP. At present, however, there are few biomarkers for arrhythmias induced by QT-shortening drugs. The objective of the present study was to identify the best biomarkers for predicting arrhythmias caused by the 4 potassium channel openers ICA-105574, NS-1643, R-L3, and pinacidil. Our results showed that, at higher concentrations, all 4 potassium channel openers induced ventricular tachycardia (VT) and ventricular fibrillation (VF) in Langendorff-perfused guinea pig hearts, but not in rabbit hearts. The electrocardiography parameters were measured including QT/QTc, JT peak, Tp-e interval, JT area, short-term beat-to-beat QT interval variability (STV), and index of cardiac electrophysiological balance (iCEB). We found that the potassium channel openers at test concentrations shortened the QT/QTc and the JT peak interval and increased the JT area. Nevertheless, even at proarrhythmic concentrations, they did not always change STV, Tp-e, or iCEB. Receiver operating characteristic curve analysis showed that the JT peak interval representing the early repolarization phase and the JT area reflecting the dispersion of ventricular repolarization were the best predictors of VT/VF. Action potential recordings in guinea pig papillary muscle revealed that except for pinacidil, the potassium channel openers shortened APD₃₀ in a concentration-dependent manner. They also evoked early or delayed afterdepolarizations at fast pacing rates. Patch-clamp recordings in guinea pig ventricular cardiomyocytes showed that the potassium channel openers enhanced the total outward currents during the early phase of action potential repolarization, especially at proarrhythmic concentrations. We concluded that the JT peak interval and the JT area are surrogate biomarkers identifying the risk of proarrhythmia associated with the administration of QT-shortening agents. The acceleration of early-phase repolarization and the increased dispersion of ventricular repolarization may contribute to the occurrence of arrhythmias.

Effect of action potential duration on Tpeak-Tend interval, T-wave area and T-wave amplitude as indices of dispersion of repolarization: Theoretical and simulation study in the rabbit heart

BACKGROUND

The aim of the study was to differentiate the effect of dispersion of repolarization (DOR) and action potential duration (APD) on T-wave parameters being considered as indices of DOR, namely, Tpeak-Tend interval, T-wave amplitude and T-wave area.

METHODS

T-wave was simulated in a wide physiological range of DOR and APD using a realistic rabbit model based on experimental data. A simplified mathematical formulation of T-wave formation was conducted.

RESULTS

Both the simulations and the mathematical formulation showed that Tpeak-Tend interval and T-wave area are linearly proportional to DOR irrespectively of APD range, while T-wave amplitude is non-linearly proportional to DOR and inversely proportional to the minimal repolarization time, or minimal APD value.

CONCLUSION

Tpeak-Tend interval and T-wave area are the most accurate DOR indices independent of APD. T-wave amplitude can be considered as an index of DOR when the level of APD is taken into account.

Effect of heart rate on ventricular repolarization in healthy individuals applying vectorcardiographic T vector and T vector loop analysis

BACKGROUND

Ventricular repolarization (VR) is strongly influenced by heart rate (HR) and autonomic nervous activity, both of which also are important for arrhythmogenesis. Their relative influence on VR is difficult to separate, but might be crucial for understanding while some but not other individuals are at risk for life-threatening arrhythmias at a certain HR. This study was therefore designed to assess the "pure" effect of HR increase by atrial pacing on the ventricular gradient (VG) and other vectorcardiographically (VCG) derived VR parameters during an otherwise unchanged condition.

METHODS

In 19 patients with structurally normal hearts, a protocol with stepwise increased atrial pacing was performed after successful arrhythmia ablation. Conduction intervals were measured on averaged three-dimensional (3D) QRST complexes. In addition, various VCG parameters were measured from the QRS and T vectors as well as from the T loop. All measurements were performed after at least 3 minutes of rate adaptation of VR.

RESULTS

VR changes at HR from 80 to 120 bpm were assessed. The QRS and QT intervals, VG, QRSarea, Tarea, and Tamplitude were markedly rate dependent. In contrast, the Tp-e/QT ratio was rate independent as well as the T-loop morphology parameters Tavplan and Teigenvalue describing the bulginess and circularity of the loop.

CONCLUSIONS

In healthy individuals, the response to increased HR within the specified range suggests a decreased heterogeneity of depolarization instants, action potential morphology, and consequently of the global VR.

A new ECG biomarker for drug toxicity: a combined signal processing and computational modeling study

QT prolongation is the only clinically proven, yet insufficient, electrocardiogram (ECG) biomarker for drug-induced cardiac toxicity. The goal of this study is to evaluate whether JT area, i.e., total area of the T-wave, can serve as an ECG biomarker for drug-induced cardiac toxicity using both signal processing and computational modeling approaches. An ECG dataset that contained recordings from patients under control and sotalol condition was analyzed. In order to relate sotalol-induced ECG changes to its effect on ion channel level, i.e., blockade of the rapid component of the delayed rectifier potassium channel (I(Kr)), varied degrees of I(Kr) blockade were simulated in a slab of ventricular tissue. The mean JT area increased by 36.5% following the administration of sotalol in patients. Simulations in the slab tissue showed that sotalol increased action potential duration preferentially in the midmyocardium, which led to increased transmural dispersion of repolarization and JT area. In conclusion, JT area reflects the transmural dispersion of repolarization and may be a potentially useful surrogate/supplemental ECG biomarker to assess drug safety.

Arrhythmic risk biomarkers for the assessment of drug cardiotoxicity: from experiments to computer simulations

In this paper, we illustrate how advanced computational modelling and simulation can be used to investigate drug-induced effects on cardiac electrophysiology and on specific biomarkers of pro-arrhythmic risk. To do so, we first perform a thorough literature review of proposed arrhythmic risk biomarkers from the ionic to the electrocardiogram levels. The review highlights the variety of proposed biomarkers, the complexity of the mechanisms of drug-induced pro-arrhythmia and the existence of significant animal species differences in drug-induced effects on cardiac electrophysiology. Predicting drug-induced pro-arrhythmic risk solely using experiments is challenging both preclinically and clinically, as attested by the rise in the cost of releasing new compounds to the market. Computational modelling and simulation has significantly contributed to the understanding of cardiac electrophysiology and arrhythmias over the last 40 years. In the second part of this paper, we illustrate how state-of-the-art open source computational modelling and simulation tools can be used to simulate multi-scale effects of drug-induced ion channel block in ventricular electrophysiology at the cellular, tissue and whole ventricular levels for different animal species. We believe that the use of computational modelling and simulation in combination with experimental techniques could be a powerful tool for the assessment of drug safety pharmacology.

Pulmonary valve replacement in tetralogy of Fallot improves the repolarization

OBJECTIVE

To assess the effect of pulmonary valve replacement (PVR) on the repolarization of patients with tetralogy of Fallot.

BACKGROUND

Pulmonary valve regurgitation may cause right ventricular failure in adult patients with Fallot's tetralogy. In these patients, prolonged depolarization and disturbed repolarization are associated with ventricular arrhythmias and sudden cardiac death.

METHODS

Thirty Fallot patients (age 32+/-9 years, 19 male) eligible for PVR were studied with cardiac magnetic resonance imaging (CMR) before and 6 months after PVR. Electrocardiograms obtained during initial and follow-up CMR were analyzed and occurrence of ventricular arrhythmias was studied.

RESULTS

Right ventricular end-diastolic volume (RV EDV) decreased from 322+/-87 to 215+/-57 ml after PVR (P<0.0001). The spatial QRS-T angle normalized from 117+/-34 to 100+/-35 degrees , P=0.0004 (normal angle <105 degrees). QT dispersion and T-wave complexity did not change significantly. T-wave amplitude decreased from 376+/-121 to 329+/-100 microV (P=0.01). T-wave area decreased from 43+/-15 to 38+/-13 microV s (P=0.02). Decreases in T-wave amplitude and area were most prominent in the right precordial leads overlying the RV. Three patients had sustained ventricular arrhythmias and one patient died suddenly. These patients had a QRS duration >160 ms. No severe ventricular arrhythmias were found in patients with a RV EDV <220 ml, QRS-T angle <100 degrees , QT dispersion <60 ms or T-wave complexity <0.30.

CONCLUSION

Normal repolarization indices may be associated with the absence of severe ventricular arrhythmias. PVR in Fallot patients with dilated right ventricles has a beneficial effect on electrocardiographic indices of repolarization heterogeneity.

Beat-to-Beat variability of repolarization determines proarrhythmic outcome in dogs susceptible to drug-induced torsades de pointes

OBJECTIVES

We investigated whether increasing or decreasing beat-to-beat variability of repolarization (BVR) would change drug-induced proarrhythmic outcome accordingly.

BACKGROUND

Increased variability of repolarization has been suggested as a prelude to proarrhythmic circumstances in experimental and clinical situations.

METHODS

The non-cardiovascular, I(Kr)-blocking drug sertindole was administered to anesthetized dogs with chronic atrioventricular block. Three interventions were used to prevent or suppress sertindole-induced torsades de pointes (TdP).

RESULTS

Supratherapeutic doses of sertindole (1.0 mg/kg intravenously) induced TdP in 10 of 13 dogs whereas 0.2 mg/kg induced no TdP, despite increases in QT intervals by both doses. The BVR, quantified as short-term variability (STV) from Poincaré plots, was the only parameter that predicted TdP outcome (1.0 mg/kg sertindole: 2.3 +/- 0.7 ms to 5.1 +/- 2.1 ms, p < 0.05; 0.2 mg/kg sertindole: 2.3 +/- 0.8 ms to 3.2 +/- 1.1 ms, p= NS).

INTERVENTIONS

1) KCl, intravenous, reduced the incidence of sertindole-induced TdP from 6 of 7 to 1 of 7 dogs (p<0.05) and prevented sertindole-related increase of STV: 3.0 +/- 1.1 ms vs. 4.5 +/- 1.3 ms (p < 0.05); 2) levcromakalim (I(K,ATP) activator) reduced sertindole-induced TdP and decreased STV from 4.9 +/- 2.1 ms to 2.6 +/- 0.9 ms (p < 0.05); 3) steady-state ventricular pacing (60 beats/min) abolished sertindole-induced TdP and decreased STV from 4.9 +/- 1.5 to 3.2 +/- 1.0 (p < 0.05). Torsades de pointes reappeared upon return to non-paced idioventricular rhythm. None of the 3 interventions reduced the sertindole-induced prolonged QT interval.

CONCLUSIONS

Proarrhythmic intervention is related to an increase in BVR, whereas antiarrhythmic treatment is associated with a decrease in BVR. The BVR is superior to QT interval prolongation in the prediction and prevention of drug-induced TdP in this experimental model.

Assessing the proarrhythmic potential of drugs: current status of models and surrogate parameters of torsades de pointes arrhythmias

Torsades de pointes (TdP) is a potentially lethal cardiac arrhythmia that can occur as an unwanted adverse effect of various pharmacological therapies. Before a drug is approved for marketing, its effects on cardiac repolarisation are examined clinically and experimentally. This paper expresses the opinion that effects on repolarisation duration cannot directly be translated to risk of proarrhythmia. Current safety assessments of drugs only involve repolarisation assays, however the proarrhythmic profile can only be determined in the predisposed model. The availability of these proarrhythmic animal models is emphasised in the present paper. It is feasible for the pharmaceutical industry to establish one or more of these proarrhythmic animal models and large benefits are potentially available if pharmaceutical industries and patient-care authorities embraced these models. Furthermore, suggested surrogate parameters possessing predictive power of TdP arrhythmia are reviewed. As these parameters are not developed to finalisation, any meaningful study of the proarrhythmic potential of a new drug will include evaluation in an integrated model of TdP arrhythmia.

Dispersion of repolarization in cardiac resynchronization therapy

BACKGROUND

Proarrhythmic effects of cardiac resynchronization therapy (CRT) as a result of increased transmural dispersion of repolarization (TDR) induced by left ventricular (LV) epicardial pacing in a subset of vulnerable patients have been reported. The possibility of identifying these patients by ECG repolarization indices has been suggested.

OBJECTIVES

The purpose of this study was to test whether repolarization indices on the ECG can be used to measure dispersion of repolarization during pacing.

METHODS

CRT devices of 28 heart failure patients were switched among biventricular, LV, and right ventricular (RV) pacing. ECG indices proposed to measure dispersion of repolarization were calculated. The effects of CRT on repolarization were simulated in ECGSIM, a mathematical model of electrocardiogram genesis. TDR was calculated as the difference in repolarization time between the epicardial and endocardial nodes of the heart model.

RESULTS

PATIENTS

The interval from the apex to the end of the T wave was shorter during biventricular pacing (102 +/- 18 ms) and LV pacing (106 +/- 21 ms) than during RV pacing (117 +/- 22 ms, P < or =.005). T-wave amplitude and area were low during biventricular pacing (287 +/- 125 microV and 56 +/- 22 microV.s, respectively, P = .0006 vs RV pacing). T-wave complexity was high during biventricular pacing (0.42 +/- 0.26, P = .004 vs RV pacing). Simulations: Repolarization patterns were highly similar to the preceding depolarization patterns. The repolarization patterns of different pacing modes explained the observed magnitudes of the ECG repolarization indices. Average and local TDR were not different between pacing modes.

CONCLUSION

In patients treated with CRT, ECG repolarization indices are related to pacing-induced activation sequences rather than transmural dispersion. TDR during biventricular and LV pacing is not larger than TDR during conventional RV endocardial pacing.

Validation of ECG Indices of Ventricular Repolarization Heterogeneity: A Computer Simulation Study

INTRODUCTION

Repolarization heterogeneity (RH) is functionally linked to dispersion in refractoriness and to arrhythmogenicity. In the current study, we validate several proposed electrocardiogram (ECG) indices for RH: T-wave amplitude, -area, -complexity, and -symmetry ratio, QT dispersion, and the Tapex-end interval (the latter being an index of transmural dispersion of the repolarization (TDR)).

METHODS AND RESULTS

We used ECGSIM, a mathematical simulation model of ECG genesis in a human thorax, and varied global RH by increasing the standard deviation (SD) of the repolarization instants from 20 (default) to 70 msec in steps of 10 msec. T-wave amplitude, -area, -symmetry, and Tapex-end depended linearly on SD. T-wave amplitude increased from 275 +/- 173 to 881 +/- 456 muV, T-wave area from 34 x 10(3)+/- 21 x 10(3) to 141 x 10(3)+/- 58 x 10(3)muV msec, T-wave symmetry decreased from 1.55 +/- 0.11 to 1.06 +/- 0.23, and Tapex-end increased from 84 +/- 17 to 171 +/- 52 msec. T-wave complexity increased initially but saturated at SD = 50 msec. QT dispersion increased modestly until SD = 40 msec and more rapidly for higher values of SD. TDR increased linearly with SD. Tapex-end increased linearly with TDR, but overestimated it.

CONCLUSION

T-wave complexity did not discriminate between differences in larger RH values. QT dispersion had low sensitivity in the transitional zone between normal and abnormal RH. In conclusion, T-wave amplitude, -area, -symmetry, and, with some limitations, Tapex-end and T-wave complexity reliably reflect changes in RH.

Increased Short-Term Variability of Repolarization Predicts d -Sotalol–Induced Torsades de Pointes in Dogs

Background— Identification of patients at risk for drug-induced torsades de pointes arrhythmia (TdP) is difficult. Increased temporal lability of repolarization has been suggested as being valuable to predict proarrhythmia. The predictive value of different repolarization parameters, including beat-to-beat variability of repolarization (BVR), was compared in this serial investigation in dogs with chronic AV block.

Methods and Results— In anesthetized dogs with electrically remodeled hearts, the dose-dependent difference in drug-induced TdP ( d -sotalol, 2 and 4 mg/kg IV over 5 minutes, 25% and 75% TdP, respectively) could not be accounted for by prolongation of QT c (410±37 to 475±60 versus 415±47 to 484±52 ms, respectively). BVR was quantified by Poincaré plots at baseline and immediately before onset of d -sotalol–induced extrasystolic activity. TdP occurrence was associated with an increase in short-term variability (STV) of the left ventricular monophasic action potential duration (3.5±1.5 to 5.5±1.6 versus 3.0±0.7 to 8.6±3.8 ms, respectively), which was reversible when TdP was abolished by I K,ATP activation. The absence of TdP despite QT c prolongation after chronic amiodarone treatment could also be explained by an unchanged STV. In experiments with isolated ventricular myocytes, STV increased after I Kr block and was highest in cells that subsequently showed early afterdepolarizations.

Conclusions— Proarrhythmia is not related to differences in prolongation of repolarization but corresponds to BVR, here quantified as STV of the left ventricle. STV could be a new parameter to predict drug-induced TdP in patients.