Human and rabbit inter-species comparison of ionic mechanisms of arrhythmic risk: A simulation study

Renal artery denervation prevents ventricular arrhythmias in long QT rabbit models

Long QT syndrome (LQTS) is commonly presented with life-threatening ventricular arrhythmias (VA). Renal artery denervation (RDN) is an alternative antiadrenergic treatment that attenuates sympathetic activity. We aimed to evaluate the efficacy of RDN on preventing VAs in LQTS rabbits induced by drugs. The subtypes of LQTS were induced by infusion of HMR-1556 for LQTS type 1 (LQT1), erythromycin for LQTS type 2 (LQT2), and veratridine for LQTS type 3 (LQT3). Forty-four rabbits were randomized into the LQT1, LQT2, LQT3, LQT1-RDN, LQT2-RDN, and LQT3-RDN groups. All rabbits underwent cardiac electrophysiology studies. The QTc interval of the LQT2-RDN group was significantly shorter than those in the LQT2 group (650.08 ± 472.67 vs. 401.78 ± 42.91 ms, p = 0.011). The QTc interval of the LQT3-RDN group was significantly shorter than those in the LQT3 group (372.00 ± 22.41 vs. 335.70 ± 28.21 ms, p = 0.035). The VA inducibility in all subtypes of the LQT-RDN groups was significantly lower than those in the LQT-RDN groups, respectively (LQT1: 9.00 ± 3.30 vs. 47.44 ± 4.21%, p < 0.001; LQT2: 11.43 ± 6.37 vs. 45.38 ± 5.29%, p = 0.026; LQT3: 10.00 ± 6.32 vs. 32.40 ± 7.19%, p = 0.006). This study demonstrated the neuromodulation of RDN leading to electrical remodeling and reduced VA inducibility of the ventricular substrate in LQT models.

Characteristics of electromechanical window in anesthetized rabbit models of short QT and long QT syndromes

The current regulatory guidelines recommend the use of QT interval to assess the risk of arrhythmogenic potential of new chemical entities. Recently, the electromechanical window (EMW), the difference in duration between electrical and mechanical systole, has been proposed as markers for drug-induced torsades de pointes (TdP); however, data of EMW in short QT model are not available. This study aimed to characterize the EMW as a marker for drug-induced ventricular arrhythmias in anesthetized rabbit model of long QT syndrome type 2 (LQT2) and short QT syndrome (SQTS) infused with reference compounds known to lengthen or shorten QT intervals. After rabbits were anesthetized with isoflurane, body surface electrocardiograms and left ventricular pressure were recorded. The LQT2 was produced by intravenous infusion with dofetilide (n = 6), quinidine (n = 6) and sotalol (n = 6) whereas the SQTS was induced by intravenous escalating concentrations of nicorandil (n = 7), pinacidil (n = 5) and cromakalim (n = 5). The EMW in anesthetized rabbits ranged from 1.3 to 53.3 msec. All three drugs known to lengthen QT intervals prolonged QT and QTcF interval while the EMW was markedly decreased to negative values. Pinacidil significantly produced QT and QTcF shortening and significantly abbreviated the EMW (p < 0.05). This study demonstrated that the EMW is associated with QT intervals (p < 0.001). It is negative in the presence of QT-prolonging drugs while it is more positive in the presence of QT-shortening drugs. The results suggest that the EMW in anesthetized rabbits can be used in drug safety evaluation in addition to the QT interval.

Potassium currents in the heart: functional roles in repolarization, arrhythmia and therapeutics

This is the second of the two White Papers from the fourth UC Davis Cardiovascular Symposium Systems Approach to Understanding Cardiac Excitation-Contraction Coupling and Arrhythmias (3-4 March 2016), a biennial event that brings together leading experts in different fields of cardiovascular research. The theme of the 2016 symposium was 'K⁺ channels and regulation', and the objectives of the conference were severalfold: (1) to identify current knowledge gaps; (2) to understand what may go wrong in the diseased heart and why; (3) to identify possible novel therapeutic targets; and (4) to further the development of systems biology approaches to decipher the molecular mechanisms and treatment of cardiac arrhythmias. The sessions of the Symposium focusing on the functional roles of the cardiac K⁺ channel in health and disease, as well as K⁺ channels as therapeutic targets, were contributed by Ye Chen-Izu, Gideon Koren, James Weiss, David Paterson, David Christini, Dobromir Dobrev, Jordi Heijman, Thomas O'Hara, Crystal Ripplinger, Zhilin Qu, Jamie Vandenberg, Colleen Clancy, Isabelle Deschenes, Leighton Izu, Tamas Banyasz, Andras Varro, Heike Wulff, Eleonora Grandi, Michael Sanguinetti, Donald Bers, Jeanne Nerbonne and Nipavan Chiamvimonvat as speakers and panel discussants. This article summarizes state-of-the-art knowledge and controversies on the functional roles of cardiac K⁺ channels in normal and diseased heart. We endeavour to integrate current knowledge at multiple scales, from the single cell to the whole organ levels, and from both experimental and computational studies.