Guidelines for assessment of cardiac electrophysiology and arrhythmias in small animals.

Cardiac arrhythmias are a major cause of morbidity and mortality worldwide. Although recent advances in cell-based models, including human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM), are contributing to our understanding of electrophysiology and arrhythmia mechanisms, preclinical animal studies of cardiovascular disease remain a mainstay. Over the past several decades, animal models of cardiovascular disease have advanced our understanding of pathological remodeling, arrhythmia mechanisms, and drug effects and have led to major improvements in pacing and defibrillation therapies. There exist a variety of methodological approaches for the assessment of cardiac electrophysiology and a plethora of parameters may be assessed with each approach. This guidelines article will provide an overview of the strengths and limitations of several common techniques used to assess electrophysiology and arrhythmia mechanisms at the whole animal, whole heart, and tissue level with a focus on small animal models. We also define key electrophysiological parameters that should be assessed, along with their physiological underpinnings, and the best methods with which to assess these parameters.

High resolution optical mapping of cardiac electrophysiology in pre-clinical models.

Optical mapping of animal models is a widely used technique in pre-clinical cardiac research. It has several advantages over other methods, including higher spatial resolution, contactless recording and direct visualisation of action potentials and calcium transients. Optical mapping enables simultaneous study of action potential and calcium transient morphology, conduction dynamics, regional heterogeneity, restitution and arrhythmogenesis. In this dataset, we have optically mapped Langendorff perfused isolated whole hearts (mouse and guinea pig) and superfused isolated atria (mouse). Raw datasets (consisting of over 400 files) can be combined with open-source software for processing and analysis. We have generated a comprehensive post-processed dataset characterising the baseline cardiac electrophysiology in these widely used pre-clinical models. This dataset also provides reference information detailing the effect of heart rate, clinically used anti-arrhythmic drugs, ischaemia-reperfusion and sympathetic nervous stimulation on cardiac electrophysiology. The effects of these interventions can be studied in a global or regional manner, enabling new insights into the prevention and initiation of arrhythmia.

ESC working group on cardiac cellular electrophysiology position paper: relevance, opportunities, and limitations of experimental models for cardiac electrophysiology research.

Cardiac arrhythmias are a major cause of death and disability. A large number of experimental cell and animal models have been developed to study arrhythmogenic diseases. These models have provided important insights into the underlying arrhythmia mechanisms and translational options for their therapeutic management. This position paper from the ESC Working Group on Cardiac Cellular Electrophysiology provides an overview of (i) currently available in vitro, ex vivo, and in vivo electrophysiological research methodologies, (ii) the most commonly used experimental (cellular and animal) models for cardiac arrhythmias including relevant species differences, (iii) the use of human cardiac tissue, induced pluripotent stem cell (hiPSC)-derived and in silico models to study cardiac arrhythmias, and (iv) the availability, relevance, limitations, and opportunities of these cellular and animal models to recapitulate specific acquired and inherited arrhythmogenic diseases, including atrial fibrillation, heart failure, cardiomyopathy, myocarditis, sinus node, and conduction disorders and channelopathies. By promoting a better understanding of these models and their limitations, this position paper aims to improve the quality of basic research in cardiac electrophysiology, with the ultimate goal to facilitate the clinical translation and application of basic electrophysiological research findings on arrhythmia mechanisms and therapies.

Integrating new approaches to atrial fibrillation management: the 6th AFNET/EHRA Consensus Conference.

There are major challenges ahead for clinicians treating patients with atrial fibrillation (AF). The population with AF is expected to expand considerably and yet, apart from anticoagulation, therapies used in AF have not been shown to consistently impact on mortality or reduce adverse cardiovascular events. New approaches to AF management, including the use of novel technologies and structured, integrated care, have the potential to enhance clinical phenotyping or result in better treatment selection and stratified therapy. Here, we report the outcomes of the 6th Consensus Conference of the Atrial Fibrillation Network (AFNET) and the European Heart Rhythm Association (EHRA), held at the European Society of Cardiology Heart House in Sophia Antipolis, France, 17-19 January 2017. Sixty-two global specialists in AF and 13 industry partners met to develop innovative solutions based on new approaches to screening and diagnosis, enhancing integration of AF care, developing clinical pathways for treating complex patients, improving stroke prevention strategies, and better patient selection for heart rate and rhythm control. Ultimately, these approaches can lead to better outcomes for patients with AF.

European Society of Cardiology smartphone and tablet applications for patients with atrial fibrillation and their health care providers.

We are in the midst of a digital revolution in health care, although the application of new and useful technology in routine clinical practice is variable. The Characterizing Atrial fibrillation by Translating its Causes into Health Modifiers in the Elderly (CATCH ME) Consortium, in collaboration with the European Society of Cardiology (ESC), has funded the creation of two applications (apps) in atrial fibrillation (AF) for use in smartphones and tablets. The patient app aims to enhance patient education, improve communication between patients and health care professionals, and encourage active patient involvement in the management of their condition. The health care professional app is designed as an interactive management tool incorporating the new ESC Practice Guidelines on AF and supported by the European Heart Rhythm Association (EHRA), with the aim of improving best practice approaches for the care of patients with AF. Both stand-alone apps are now freely available for Android and iOS devices though the Google Play, Amazon, and Apple stores. In this article, we outline the rationale for the design and implementation of these apps. Our objective is to demonstrate the value of integrating novel digital technology into clinical practice, with the potential for patient engagement, optimization of pharmacological and interventional therapy in AF, and ultimately to improve patient outcomes.

Knock-in gain-of-function sodium channel mutation prolongs atrial action potentials and alters atrial vulnerability.

BACKGROUND: Patients with long QT syndrome (LQTS) are at increased risk not only for ventricular arrhythmias but also for atrial pathology including atrial fibrillation (AF). Some patients with "lone" AF carry Na(+)-channel mutations. OBJECTIVE: The purpose of this study was to determine the mechanisms underlying atrial pathology in LQTS. METHODS: In mice with a heterozygous knock-in long QT syndrome type 3 (LQT3) mutant of the cardiac Na(+) channel (ΔKPQ-SCN5A) and wild-type (WT) littermates, atrial size, function, and electrophysiologic parameters were measured in intact Langendorff-perfused hearts, and histologic analysis was performed. RESULTS: Atrial action potential duration, effective refractory period, cycle length, and PQ interval were prolonged in ΔKPQ-SCN5A hearts (all P < .05). Flecainide (1 µM) reversed atrial action potential duration prolongation and induced postrepolarization refractoriness (P < .05). Arrhythmias were infrequent during regular rapid atrial rate in both WT and ΔKPQ-SCN5A but were inducible in 15 (38%) of 40 ΔKPQ-SCN5A and 8 (29%) of 28 WT mice upon extrastimulation. Pacing protocols generating rapid alterations in rate provoked atrial extrasystoles and arrhythmias in 6 (66%) of 9 ΔKPQ-SCN5A but in 0 (0%) of 6 WT mice (P < .05). Atrial diameter was increased by nearly 10% in ΔKPQ-SCN5A mice > 5 months old without increase in fibrotic tissue. CONCLUSION: Murine hearts bearing an LQT3 mutation show abnormalities in atrial electrophysiology and subtle changes in atrial dimension, including an atrial arrhythmogenic phenotype on provocation. These results support clinical data suggesting that LQTS mutations can cause atrial pathology and arrhythmogenesis and indicate that murine sodium channel LQTS models may be useful for exploring underlying mechanisms.

Phytanic acid accumulation is associated with conduction delay and sudden cardiac death in sterol carrier protein-2/sterol carrier protein-x deficient mice.

INTRODUCTION: The sterol carrier protein-2 gene encodes two functionally distinct proteins: sterol carrier protein-2 (SCP2, a peroxisomal lipid carrier) and sterol carrier protein-x (SCPx, a peroxisomal thiolase known as peroxisomal thiolase-2), which is involved in peroxisomal metabolism of bile acids and branched-chain fatty acids. We show in this study that mice deficient in SCP2 and SCPx (SCP2null) develop a cardiac phenotype leading to a high sudden cardiac death rate if mice are maintained on diets enriched for phytol (a metabolic precursor of branched-chain fatty acids). METHODS AND RESULTS: In 210 surface and 305 telemetric ECGs recorded in wild-type (C57BL/6; wt; n = 40) and SCP2 null mice (n = 40), no difference was observed at baseline. However, on diet, cycle lengths were prolonged in SCP2 null mice (262.9 +/- 190 vs 146.3 +/- 43 msec), AV conduction was prolonged (58.3 +/- 17 vs 42.6 +/- 4 ms), and QRS complexes were wider (19.1 +/- 5 vs 14.0 +/- 4 ms). In 11 gene-targeted Langendorff-perfused hearts isolated from SCP2 null mice after dietary challenge, complete AV blocks (n = 5/11) or impaired AV conduction (Wenckebach point 132 +/- 27 vs 92 +/- 10 msec; P < 0.05) could be confirmed. Monophasic action potentials were not different between the two genotypes. Left ventricular function studied by echocardiography was similar in both strains. Phytanic acid but not pristanic acid accumulated in the phospholipid fraction of myocardial membranes isolated from SCP2 null mice. CONCLUSION: Accumulation of phytanic acid in myocardial phospholipid membranes is associated with bradycardia and impaired AV nodal and intraventricular impulse conduction, which could provide an explanation for sudden cardiac death in this model.

Overexpression of the catalytic subunit of protein phosphatase 2A impairs cardiac function.

Reversible protein phosphorylation is an essential regulatory mechanism in many cellular functions. In contrast to protein kinases, the role and regulation of protein phosphatases has remained ambiguous. To address this issue, we generated transgenic mice that overexpress the catalytic subunit alpha of protein phosphatase 2A (PP2A) (PP2Acalpha) in the heart driven by the alpha-myosin heavy chain promoter. Overexpression of the PP2Acalpha gene in the heart led to increased levels of the transgene both at RNA and protein levels. This was accompanied by a significant increase of PP2A enzyme activity in the myocardium. Morphological analysis revealed isles of necrosis and fibrosis. The phosphorylation state of phospholamban, troponin inhibitor, and eukaryotic elongation factor 2 was reduced significantly. The expression of junctional (calsequestrin) and free SR proteins (SERCA and phospholamban) was not altered. Whereas no increase in morbidity or mortality was noted, transgenic mice developed cardiac hypertrophy and reduced contractility of the heart, as well as cardiac dilatation as shown by biplane echocardiography. Taken together, these findings are indicative of the fundamental role of PP2A in cardiac function and imply that disturbances in protein phosphatases expression and activity may cause or aggravate the course of cardiac diseases.

Prolonged action potential durations, increased dispersion of repolarization, and polymorphic ventricular tachycardia in a mouse model of proarrhythmia.

INTRODUCTION: In the congenital long QT syndrome, inhomogeneously prolonged action potentials, bradycardia, and hypokalemia can cause afterdepolarizations and torsade de pointes. Other genetic factors may contribute to similar forms of ventricular tachycardias in hypertrophied or failing hearts, especially if the outward current I(Kr) is blocked pharmacologically. We sought to develop a mouse heart model for such arrhythmias in order to identify the proarrhythmic potential in transgenic animals. METHODS AND RESULTS: Hearts of adult wild-type (CD1) mice were isolated and the aorta was retrogradely perfused. Three monophasic action potentials and a volume-conducted ECG were simultaneously recorded. Sotalol (10(-5)M and 2 x 10(-5)M) prolonged action potential duration (APD) in a concentration-dependent and reverse frequency-dependent fashion (from 34 +/- 1 to 48 +/- 2 ms at 100 ms basic cycle length (BCL), from 38 +/- 2 to 54 +/- 3 ms at 180 ms BCL for APD90, p < 0.05). Sotalol did not alter the relation between refractoriness and APD (ERP/APD ratio = 0.76 - 0.93). AV nodal block caused ventricular bradycardia and doubled dispersion of APD (APD70max-min: 11 +/- 1 vs. 4 +/- 1 ms, APD90max-min: 12 +/- 1 vs. 5 +/- 1 ms, p < 0.05). If combined with hypokalemia, afterdepolarizations induced polymorphic ventricular tachycardias in 1 of 8 hearts at K(+) =3.0 mM and in 10 of 12 hearts at K(+) = 2.0 mM. Prior to polymorphic ventricular tachycardia, dispersion of APD further increased (APD70max-min: 17 +/- 3 ms; APD90max-min: 25 +/- 3 ms; p < 0.05). CONCLUSIONS: This isolated beating mouse heart model can be used to study drug-induced action potential prolongation and repolarization-related ventricular arrhythmias provoked by bradycardia and hypokalemia. It may be suitable to identify a genetic predisposition to ventricular arrhythmias that may only become apparent under such proarrhythmic conditions.