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Beat-to-Beat QT Interval Variability and Autonomic Activity
Published in Herbert F. Jelinek, David J. Cornforth, Ahsan H. Khandoker, ECG Time Series Variability Analysis, 2017
The QT interval of a body surface electrocardiogram (ECG), illustrated in Figure 20.1 [1], reflects the depolarization and repolarization processes across the ventricular myocardium 20.2 [2]. Since the depolarization process reflected by the QRS complex is relatively stable, the QT interval is clinically used to measure prolongation or shortening of the ventricular repolarization process. QT interval prolongation can be either congenital or acquired. The former is caused by a range of potassium or sodium ion channel mutations, while the latter is associated with a reduction in repolarization reserve that can be induced by pharmaceutical agents, hypokalemia, or hypomagnesemia. Both conditions have been associated with increased cardiac mortality [3]. Since the QT interval is dependent on heart rate, it is typically reported after correcting for it (QTc), by using one of the many available correction formulas. QTc has gained wide acceptance as a steady-state measure of ventricular repolarization.
Usefulness of insertable cardiac monitors for risk stratification: current indications and clinical evidence
Published in Expert Review of Medical Devices, 2023
Amira Assaf, Dominic AMJ Theuns, Michelle Michels, Jolien Roos-Hesselink, Tamas Szili-Torok, Sing-Chien Yap
Congenital long QT syndrome (LQTS) is an inherited disease characterized by a prolonged heart-rate corrected QT interval and is associated with an increased risk of malignant ventricular arrhythmias triggered by early afterdepolarizations [47]. The diagnosis is based on a high Schwartz score (≥3.5) and/or the presence of a pathogenic mutation. Pathogenic mutations are found in up to 75% of patients and mainly comprise loss-of-function variants in KCNQ1 and KCNH2, or gain-of-function variants in SCN5A [48,49]. The cornerstone of treatment are beta blockers, preferably non-selective agents (i.e. nadolol and propranolol), and lifestyle measures (i.e. avoidance of QT prolonging drugs, correction of electrolyte abnormalities, avoidance of genotype-specific triggers) [18]. The antiarrhythmic effect of beta blockers is due to the prevention of early afterdepolarizations. In addition, LQT3 patients may benefit from blockers of the late sodium inward current (mexiletine, flecainide or ranolazine) [50]. In patients in whom beta blockers are not effective, not tolerated, not accepted, or contraindicated, left cardiac sympathetic denervation is recommended [17,18].
Pharmacokinetic and toxicological prediction of the chemical constituents of the essential oil of the leaves of Croton heliotropiifolius Kunth
Published in Journal of Toxicology and Environmental Health, Part A, 2023
Rosemarie Brandim Marques, Maria Das Dores Barreto Sousa, Wesley de Sousa Santos, Neirigelson Ferreira de Barros Leite, Esdras Morais Sobreiro Lima, Angélica Lima Soares, Charllyton Luís Sena da Costa, Francisco Artur e Silva Filho, Antônio Luiz Martins Maia Filho, Evandro Paulo Soares Martins, Ricardo Martins Ramos, Antonio de Macedo Filho
Voltage-gated potassium channels of the human ether-a-go-gorelated (hERG) type are essential for normal electrical activity in the heart. Dysfunction of the hERG channel results in long QT syndrome (LQTS), characterized by delayed repolarization and prolongation of the QT interval of the cardiac cell action potential, which enhances the risk of ventricular arrhythmias and sudden death. Thus, compounds that act on this channel and that possibly initiate long QT syndrome have been eliminated early in the non-clinical development process in safety assessment (Sanguinetti and Tistani-Firouzi 2006; Yu, Ijzerman, and Heitman 2015).
Spectral feature and optimization- based actor-critic neural network for arrhythmia classification using ECG signal
Published in Journal of Experimental & Theoretical Artificial Intelligence, 2020
Anoop Vylala, Bipin Plakkottu Radhakrishnan
The QT interval refers to the time interval between the Q wave and the T wave of the ECG signal of the patient. Finally, all the QT intervals present in the ECG signal of the patient is averaged to present the QT feature of the ECG signal.