Variability Of Repolarization Duration Research Articles

Repolarization instability and arrhythmia by IKr block in single human-induced pluripotent stem cell-derived cardiomyocytes and 2D monolayers.

AimsHuman-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have proven valuable for studies in drug discovery and safety, although limitations regarding their structural and electrophysiological characteristics persist. In this study, we investigated the electrophysiological properties of Pluricyte® CMs, a commercially available hiPSC-CMs line with a ventricular phenotype, and assessed arrhythmia incidence by IKr block at the single-cell and 2D monolayer level.Methods and resultsAction potentials were measured at different pacing frequencies, using dynamic clamp. Through voltage-clamp experiments, we determined the properties of INa, IKr, and ICaL. Intracellular Ca2+ measurements included Ca2+-transients at baseline and during caffeine perfusion. Effects of IKr block were assessed in single hiPSC-CMs and 2D monolayers (multi-electrode arrays). Action-potential duration (APD) and its rate dependence in Pluricyte® CMs were comparable to those reported for native human CMs. INa, IKr, and ICaL revealed amplitudes, kinetics, and voltage dependence of activation/inactivation similar to other hiPSC-CM lines and, to some extent, to native CMs. Near-physiological Ca2+-induced Ca2+ release, response to caffeine and excitation–contraction coupling gain characterized the cellular Ca2+-handling. Dofetilide prolonged the APD and field-potential duration, and induced early afterdepolarizations. Beat-to-beat variability of repolarization duration increased significantly before the first arrhythmic events in single Pluricyte® CMs and 2D monolayers, and predicted pending arrhythmias better than action-potential prolongation.ConclusionTaking their ion-current characteristics and Ca2+ handling into account, Pluricyte® CMs are suitable for in vitro studies on action potentials and field potentials. Beat-to-beat variability of repolarization duration proved useful to evaluate the dynamics of repolarization instability and demonstrated its significance as proarrhythmic marker in hiPSC-CMs during IKr block.

Determinants of Beat-to-Beat Variability of Repolarization Duration in the Canine Ventricular Myocyte: A Computational Analysis

Beat-to-beat variability of repolarization duration (BVR) is an intrinsic characteristic of cardiac function and a better marker of proarrhythmia than repolarization prolongation alone. The ionic mechanisms underlying baseline BVR in physiological conditions, its rate dependence, and the factors contributing to increased BVR in pathologies remain incompletely understood. Here, we employed computer modeling to provide novel insights into the subcellular mechanisms of BVR under physiological conditions and during simulated drug-induced repolarization prolongation, mimicking long-QT syndromes type 1, 2, and 3. We developed stochastic implementations of 13 major ionic currents and fluxes in a model of canine ventricular-myocyte electrophysiology. Combined stochastic gating of these components resulted in short- and long-term variability, consistent with experimental data from isolated canine ventricular myocytes. The model indicated that the magnitude of stochastic fluctuations is rate dependent due to the rate dependence of action-potential (AP) duration (APD). This process (the “active” component) and the intrinsic nonlinear relationship between membrane current and APD (“intrinsic component”) contribute to the rate dependence of BVR. We identified a major role in physiological BVR for stochastic gating of the persistent Na+ current (INa) and rapidly activating delayed-rectifier K+ current (IKr). Inhibition of IKr or augmentation of INa significantly increased BVR, whereas subsequent β-adrenergic receptor stimulation reduced it, similar to experimental findings in isolated myocytes. In contrast, β-adrenergic stimulation increased BVR in simulated long-QT syndrome type 1. In addition to stochastic channel gating, AP morphology, APD, and beat-to-beat variations in Ca2+ were found to modulate single-cell BVR. Cell-to-cell coupling decreased BVR and this was more pronounced when a model cell with increased BVR was coupled to a model cell with normal BVR. In conclusion, our results provide new insights into the ionic mechanisms underlying BVR and suggest that BVR reflects multiple potentially proarrhythmic parameters, including increased ion-channel stochasticity, prolonged APD, and abnormal Ca2+ handling.

Diastolic Spontaneous Calcium Release From the Sarcoplasmic Reticulum Increases Beat-to-Beat Variability of Repolarization in Canine Ventricular Myocytes After β-Adrenergic Stimulation

Spontaneous Ca(2+) release (SCR) from the sarcoplasmic reticulum can cause delayed afterdepolarizations and triggered activity, contributing to arrhythmogenesis during β-adrenergic stimulation. Excessive beat-to-beat variability of repolarization duration (BVR) is a proarrhythmic marker. Previous research has shown that BVR is increased during intense β-adrenergic stimulation, leading to SCR. We aimed to determine ionic mechanisms controlling BVR under these conditions. Membrane potentials and cell shortening or Ca(2+) transients were recorded from isolated canine left ventricular myocytes in the presence of isoproterenol. Action-potential (AP) durations after delayed afterdepolarizations were significantly prolonged. Addition of slowly activating delayed rectifier K(+) current (I(Ks)) blockade led to further AP prolongation after SCR, and this strongly correlated with exaggerated BVR. Suppressing SCR via inhibition of ryanodine receptors, Ca(2+)/calmodulin-dependent protein kinase II inhibition, or by using Mg(2+) or flecainide eliminated delayed afterdepolarizations and decreased BVR independent of effects on AP duration. Computational analyses and voltage-clamp experiments measuring L-type Ca(2+) current (I(CaL)) with and without previous SCR indicated that I(CaL) was increased during Ca(2+)-induced Ca(2+) release after SCR, and this contributes to AP prolongation. Prolongation of QT, T(peak)-T(end) intervals, and left ventricular monophasic AP duration of beats after aftercontractions occurred before torsades de pointes in an in vivo dog model of drug-induced long-QT1 syndrome. SCR contributes to increased BVR by interspersed prolongation of AP duration, which is exacerbated during I(Ks) blockade. Attenuation of Ca(2+)-induced Ca(2+) release by SCR underlies AP prolongation via increased I(CaL.) These data provide novel insights into arrhythmogenic mechanisms during β-adrenergic stimulation besides triggered activity and illustrate the importance of I(Ks) function in preventing excessive BVR.

Increased ICaL Underlies Ventricular Action-Potential Prolongation After Spontaneous Ca2+ Release From The Sarcoplasmic Reticulum

Background: Spontaneous Ca2+ release from the sarcoplasmic reticulum (SCR) can cause delayed afterdepolarizations (DADs) and triggered activity, contributing to arrhythmogenesis during Ca2+ overload. Excessive beat-to-beat variability of repolarization duration (BVR) is a proarrhythmic marker. Previous research has shown that BVR is increased during Ca2+ overload in isolated myocytes. We aimed at determining ionic mechanisms controlling BVR during abnormal Ca2+ handling.

The Relationship between Ventricular Repolarization Duration and RR Interval in Normal Subjects and Patients with Myocardial Infarction

Objectives: When either ventricular myocardium becomes ischemic or autonomic nervous system activity changes with age, the relationship between ventricular repolarization duration and RR interval will change as well. We studied the relationship between ventricular repolarization duration and RR interval among normal subjects in different age groups and between patients with myocardial infarction (MI) and age-matched healthy subjects. Methods: Ventricular repolarization duration variability (RDV) spectra were separated into RR-dependent and RR-independent components. We compared spectral measures among normal subjects in different age groups and between patients with MI and age-matched healthy subjects. Results: The RR-dependent component of RDV spectra, which is correlated with autonomic nervous system activity, significantly decreased with age for healthy subjects. The RR-independent component significantly increased in MI patients compared to age-matched healthy subjects. Conclusions: We demonstrated the increase in RDV upon decreasing age and in the presence of MI. Our results support the idea that the RR-dependent part corresponds to the physiology-related part of the RDV spectra and the RR-independent part corresponds to the pathology-related part of the RDV spectra. Our study suggests that these spectral measures are likely to be helpful in the evaluation of a patient with MI and merit further investigation.

Beat-to-beat variability of QT intervals is increased in patients with drug-induced long-QT syndrome: a case control pilot study

Torsades de pointes arrhythmias (TdP) occur by definition in the setting of prolonged QT intervals. Animal models of drug induced Long-QT syndrome (dLQTS) have shown higher predictive value for proarrhythmia with beat-to-beat variability of repolarization duration (BVR) when compared with QT intervals. Here, we evaluate variability of QT intervals in patients with a history of drug-induced long QT syndrome (dLQTS) and TdP in absence of a mutation in any of the major LQTS genes. Twenty patients with documented TdP under drugs with QT-prolonging potential were compared with 20 matched control individuals. An observer blinded to diagnosis manually measured lead-II, RR, and QT intervals from 30 consecutive beats. BVR was determined from Poincaré plots of QT intervals as short-term variability (STV(QT) = Sigma|QT(n)(+1) - QT(n)|/[30 x radical2]). QRS interval and cycle length was comparable between study groups and controls. No difference was found in QTc between dLQTS and controls (428 +/- 25 vs. 421 +/- 34 ms, P = 0.26), whereas STV(QT) was significantly higher in dLQTS when compared with controls (8.1 +/- 3.7 vs. 3.6 +/- 1.3 ms, P = 0.001). Proarrhythmic predictive power of STV(QT) was superior to that of the QTc interval (AUC: 0.89 vs. 0.57, 95% CI: 0.79-0.99 vs. 0.39-0.75). In the absence of QTc prolongation, baseline STV(QT) characterized patients with documented drug-induced proarrhythmia. STV(QT) could prove to be a useful non-invasive, easily obtainable parameter aiding the identification of the patient at risk for potentially life threatening arrhythmia in the context of drugs with QT prolonging potential.

Projective filtering of time-aligned ECG beats for repolarization duration measurement

Automatic measurement of ventricular repolarization duration is difficult and highly prone to errors. We propose to mitigate this problem by applying projective filtering to enhance the ECG signal prior to measurements. Our method performs time-alignment of ECG beats and then employs the rules of principal component analysis to the desired ECG reconstruction. As a result, significant noise reduction is obtained while distortions of the desired ECG components remain negligible. The proposed method is presented under white noise conditions; the influence on the precision of repolarization duration measurement is then investigated. Finally, the method's influence on evaluation of repolarization duration variability when the analyzed signals are contaminated with real electromyographic noise is discussed.

Ventricular repolarization duration variability in patients with coronary artery disease.

Ventricular repolarization duration variability in patients with coronary artery disease.