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.

[Update atrial fibrillation: the 2020 ESC guidelines and recent data on early rhythm control]. / Update Vorhofflimmern: Die ESC-Leitlinien 2020 sowie aktuelle Daten zur frühen antiarrhythmischen Therapie.

Atrial fibrillation (AF) can be a significant burden for patients as well as the health care system. Every third 55-year-old will develop AF. Despite improvements of disease management, a significant risk for cardiovascular events remains. The current AF guidelines of the European Society of Cardiology focus on an integrative therapy approach. The new algorithm "CC to ABC" comprises recommendations for diagnosis ("confirm" and "characterise") and treatment ("avoid stroke", "better symptom control", "comorbidities") of AF. Direct oral anticoagulants administered according to the CHA2DS2-VASc score remain the corner stones of stroke prevention. Besides the concept of heart rate control, rhythm control therapy like antiarrhythmic drugs or catheter ablation is recommended to relieve symptoms and in certain patient groups for the improvement of prognosis. Therapy of comorbidities and reduction of risk factors like hypertension, diabetes mellitus, obesity and obstructive sleep apnoea should be part of any comprehensive treatment approach. The results of the randomized, prospective EAST-AFNET 4 trial were published in August 2020. The trial shows that an early rhythm control therapy can lead to a reduction of cardiovascular mortality and incidence of stroke additionally to guideline-based AF management. Given the safety profile and potential positive effects of antiarrhythmic drugs and catheter ablation, early initiation of rhythm control therapy should be considered in every patient during the first months after diagnosis of AF.

[Careers in cardiac electrophysiology]. / Karrierewege in der Rhythmologie.

Cardiac electrophysiology has developed into a broad, exciting, and challenging subdiscipline of modern cardiology. The professional opportunities available to electrophysiologists are diverse and offer a wide variety of career goals. The aim of this article is to show young cardiologists what different career paths can look like if they opt for electrophysiology today. Personal testimonials from five experienced electrophysiologists on their own career paths show decisions, support, obstacles, and destinations of these paths to practice or university professorship. This article aims to support young cardiologists who are considering specialization in electrophysiology during their career planning.

Real-world vs. randomized trial outcomes in similar populations of rivaroxaban-treated patients with non-valvular atrial fibrillation in ROCKET AF and XANTUS.

AIMS: Based on Phase III data, non-vitamin K antagonist oral anticoagulants are recommended for stroke prevention in patients with atrial fibrillation. To determine whether trial outcomes translate into similar event rates in unselected patients, this analysis compared outcomes from the real-world XANTUS study with those from the Phase III ROCKET AF study. METHODS AND RESULTS: Individual patient data from 4020 XANTUS patients were re-weighted to match the proportion of selected baseline characteristics in 7061 rivaroxaban-treated patients from ROCKET AF, using the matching-adjusted indirect comparison (MAIC) method. For the primary analysis, CHADS2 scores and gender were selected as relevant variables. Adjusted annualized incidence rates for XANTUS were calculated and compared with incidence rates from ROCKET AF-the ratio of these rates ('MAIC ratio') was used as a relative effect estimate. Rates of major bleeding [3.10%/year vs. 3.60%/year; MAIC ratio 0.86; 95% confidence interval (CI) 0.67-1.12] and stroke/non-central nervous system systemic embolism (1.54%/year vs. 1.70%/year; MAIC ratio 0.91; 95% CI 0.62-1.32) were similar between XANTUS and ROCKET AF. The rate of all-cause death was higher in XANTUS (3.22%/year vs. 1.87%/year; MAIC ratio 1.72; 95% CI 1.31-2.27), but the rates of vascular death were similar (1.83%/year vs. 1.53%/year; MAIC ratio 1.19; 95% CI 0.84-1.70). Sensitivity analyses weighted by different baseline characteristics supported these results. CONCLUSION: The low rates of major bleeding and stroke in XANTUS were consistent with results from ROCKET AF. All-cause death, but not vascular death, was higher in XANTUS, as expected in an unselected real-world population.

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.

The future of atrial fibrillation management: integrated care and stratified therapy.

Atrial fibrillation is one of the major cardiovascular health problems: it is a common, chronic condition, affecting 2-3% of the population in Europe and the USA and requiring 1-3% of health-care expenditure as a result of stroke, sudden death, heart failure, unplanned hospital admissions, and other complications. Early diagnosis of atrial fibrillation, ideally before the first complication occurs, remains a challenge, as shown by patients who are only diagnosed with the condition when admitted to hospital for acute cardiac decompensation or stroke. Once diagnosed, atrial fibrillation requires chronic, multidimensional management in five domains (acute management, treatment of underlying and concomitant cardiovascular conditions, stroke prevention therapy, rate control, and rhythm control). The consistent provision of these treatment options to all patients with atrial fibrillation is difficult, despite recent improvements in organisation of care, knowledge about atrial fibrillation, and treatment options. Integrated care models that provide patient-centred care in, or close to, the patient's community while maintaining access to all specialist treatment options, emerge as the best approach to achieve consistent delivery of these chronic treatments to all patients with atrial fibrillation. Ongoing research efforts will establish when to initiate oral anticoagulation in patients with device-detected atrial high-rate episodes, quantify the prognostic effect of early and comprehensive rhythm control therapy, including atrial fibrillation ablation, and delineate optimum methods to reduce bleeding complications in patients treated with anticoagulation. Additionally, research efforts are needed to define different types of atrial fibrillation on the basis of the main causes of atrial fibrillation to pave the way for the clinical development of stratified atrial fibrillation therapy.

Impact of Switching From a Vitamin K Antagonist to Rivaroxaban on Satisfaction With Anticoagulation Therapy: The XANTUS-ACTS Substudy.

BACKGROUND: The efficacy, safety, and ease of use of rivaroxaban may reduce anticoagulation-treatment burden and improve nonvalvular atrial fibrillation (NVAF) patient satisfaction compared with vitamin K antagonists (VKAs). HYPOTHESIS: Transitioning from a VKA to rivaroxaban improves treatment satisfaction in routine practice. METHODS: Xarelto for Prevention of Stroke in Patients With Atrial Fibrillation (XANTUS) is a prospective, noninterventional study in patients with NVAF prescribed rivaroxaban for prevention of stroke in routine practice. Patients receiving a VKA 4 weeks prior to the initial XANTUS study visit and switched to rivaroxaban were asked to complete the Anti-Clot Treatment Scale (ACTS). Changes from the initial visit to the first follow-up visit at ∼ 3 months (corresponding to a comparison of rivaroxaban vs prior VKA) for ACTS burden and benefit scores were calculated using and reported as least squared mean differences (LSMDs) with 95% confidence intervals (CIs). RESULTS: The study included 1291 NVAF patients with prior VKA treatment. The mean baseline ACTS burden and benefit scores were 50.51 ± 8.42 and 10.30 ± 2.70, respectively. After ∼ 3 months of rivaroxaban treatment, LSMDs were 4.38 points (95% CI: 2.53-6.22, P < 0.0001) for the burden and 1.01 points (95% CI: 0.27-1.75, P = 0.0075) for the benefit score. Fifty-four percent and 48% of patients reported experiencing at least a minimally important clinical difference in burden and benefit scores, respectively. CONCLUSIONS: Within this XANTUS cohort, switching from a VKA to rivaroxaban yielded statistically and clinically significant improvements in ACT burden and benefit scores.

XANTUS: a real-world, prospective, observational study of patients treated with rivaroxaban for stroke prevention in atrial fibrillation.

AIMS: Although non-vitamin K antagonist oral anticoagulants are recommended for stroke prevention in patients with non-valvular atrial fibrillation (NVAF) based on clinical trial results, there is a need for safety and efficacy data from unselected patients in everyday clinical practice. XANTUS investigated the safety and efficacy of the Factor Xa inhibitor rivaroxaban in routine clinical use in the NVAF setting. METHODS AND RESULTS: Consecutive consenting patients with NVAF newly started on rivaroxaban were eligible and were followed up at ∼3-month intervals for 1 year, or for at least 30 days after permanent discontinuation. All adverse events (AEs) were recorded as AEs or serious AEs; major outcomes (including major bleeding, symptomatic thromboembolic events [stroke, systemic embolism, transient ischaemic attack, and myocardial infarction], and all-cause death) were centrally adjudicated. There were 6784 patients treated with rivaroxaban at 311 centres in Europe, Israel, and Canada. Mean patient age was 71.5 years (range 19-99), 41% were female, and 9.4% had documented severe or moderate renal impairment (creatinine clearance <50 mL/min). The mean CHADS2 and CHA2DS2-VASc scores were 2.0 and 3.4, respectively; 859 (12.7%) patients had a CHA2DS2-VASc score of 0 or 1. The mean treatment duration was 329 days. Treatment-emergent major bleeding occurred in 128 patients (2.1 events per 100 patient-years), 118 (1.9 events per 100 patient-years) died, and 43 (0.7 events per 100 patient-years) suffered a stroke. CONCLUSION: XANTUS is the first international, prospective, observational study to describe the use of rivaroxaban in a broad NVAF patient population. Rates of stroke and major bleeding were low in patients receiving rivaroxaban in routine clinical practice. TRIAL REGISTRATION NUMBER: Clinicaltrials.gov: NCT01606995.

Patient-reported treatment satisfaction and budget impact with rivaroxaban vs. standard therapy in elective cardioversion of atrial fibrillation: a post hoc analysis of the X-VeRT trial.

AIMS: We compared patient-reported treatment satisfaction and the economic impact of anticoagulation therapy with rivaroxaban vs. vitamin K antagonists (VKAs) in patients with non-valvular atrial fibrillation undergoing elective cardioversion procedures. METHODS AND RESULTS: The current study is a post hoc analysis of the prospective, multicentre X-VeRT (EXplore the efficacy and safety of once-daily oral riVaroxaban for the prevention of caRdiovascular events in subjects with non-valvular aTrial fibrillation scheduled for cardioversion) trial. Patient-reported treatment satisfaction with anticoagulation therapy was assessed using the Treatment Satisfaction Questionnaire for Medication version II in seven countries (US, UK, Canada, Germany, France, Italy, and the Netherlands). An economic model was also developed to estimate the impact of postponed cardioversions for two countries (UK and Italy). This model estimated the total costs of cardioversion, taking into consideration the costs for drug therapy (including extended treatment duration due to cardioversion postponement), international normalized ratio monitoring of VKAs, the cardioversion procedure, and rescheduling the procedure. These costs were linked to the respective X-VeRT study data to estimate the total costs. Patients receiving rivaroxaban in the delayed cardioversion group had significantly higher scores for Convenience, Effectiveness, and Global satisfaction (81.74 vs. 65.78; 39.41 vs. 32.95; and 82.07 vs. 66.74, respectively; P < 0.0001). Based on the total patient population included in the treatment satisfaction substudy (n = 632) in the delayed cardioversion group in X-VeRT, the use of rivaroxaban was estimated to result in a saving of £421 and €360 per patient in UK and Italian settings, respectively. CONCLUSION: The use of rivaroxaban in the setting of cardioversion resulted in greater patient satisfaction and cost savings, compared with that of VKA.

XANTUS: rationale and design of a noninterventional study of rivaroxaban for the prevention of stroke in patients with atrial fibrillation.

Atrial fibrillation (AF) is associated with a fivefold increase in the risk of stroke. The Phase III ROCKET AF (Rivaroxaban Once-Daily Oral Direct Factor Xa Inhibition Compared with Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation) trial showed that rivaroxaban, an oral, direct Factor Xa inhibitor, was noninferior to warfarin for the reduction of stroke or systemic embolism in patients with AF. Compared with warfarin, rivaroxaban significantly reduced rates of intracranial and fatal hemorrhages, although not rates of bleeding overall. XANTUS (Xarelto(®) for Prevention of Stroke in Patients with Atrial Fibrillation) is a prospective, international, observational, postauthorization, noninterventional study designed to collect safety and efficacy data on the use of rivaroxaban for stroke prevention in AF in routine clinical practice. The key goal is to determine whether the safety profile of rivaroxaban established in ROCKET AF is also observed in routine clinical practice. XANTUS is designed as a single-arm cohort study to minimize selection bias, and will enroll approximately 6,000 patients (mostly from Europe) with nonvalvular AF prescribed rivaroxaban, irrespective of their level of stroke risk. Overall duration of follow-up will be 1 year; the first patient was enrolled in June 2012. Similar studies (XANTUS-EL [Xarelto(®) for Prevention of Stroke in Patients with Nonvalvular Atrial Fibrillation, Eastern Europe, Middle East, Africa and Latin America] and XANAP [Xarelto(®) for Prevention of Stroke in Patients with Atrial Fibrillation in Asia-Pacific]) are ongoing in Latin America and Asia-Pacific. Data from these studies will supplement those from ROCKET AF and provide practical information concerning the use of rivaroxaban for stroke prevention in AF.

The importance of patient-reported outcomes: a call for their comprehensive integration in cardiovascular clinical trials.

Patient-reported outcomes (PROs), such as symptoms, health-related quality of life (HRQOL), or patient perceived health status, are reported directly by the patient and are powerful tools to inform patients, clinicians, and policy-makers about morbidity and 'patient suffering', especially in chronic diseases. Patient-reported outcomes provide information on the patient experience and can be the target of therapeutic intervention. Patient-reported outcomes can improve the quality of patient care by creating a holistic approach to clinical decision-making; however, PROs are not routinely used as key outcome measures in major cardiovascular clinical trials. Thus, limited information is available on the impact of cardiovascular therapeutics on PROs to guide patient-level clinical decision-making or policy-level decision-making. Cardiovascular clinical research should shift its focus to include PROs when evaluating the efficacy of therapeutic interventions, and PRO assessments should be scientifically rigorous. The European Society of Cardiology and other professional societies can take action to influence the uptake of PRO data in the research and clinical communities. This process of integrating PRO data into comprehensive efficacy evaluations will ultimately improve the quality of care for patients across the spectrum of cardiovascular disease.

Primary prevention of ischaemic stroke in atrial fibrillation: new oral anticoagulant drugs for all?

Atrial fibrillation (AF) confers a 4.5% risk of stroke per year. The risk of stroke increases with various risk factors and until recently, warfarin has been the gold standard of thromboembolism prophylaxis in AF for many years. The dosage of warfarin requires regular adjustment dependent on the INR, to keep within a narrow therapeutic range of 2.0- 3.0. The INR can be altered by concomitant drugs, foods and alcohol and requires inconvenient blood monitoring. Underanticoagulation places patients at risk of stroke, whilst over-anticoagulation confers significant bleeding risk. Consequently approximately half who would benefit from oral anticoagulation do not have it prescribed. Novel oral anticoagulants with predictable pharmacokinetics and improved efficacy and safety profiles are currently being developed for stroke prevention in AF. Three novel oral anticoagulants have just completed Phase III trials for stroke prevention, all with impressive results; the direct thrombin inhibitor, dabigatran and the oral factor Xa inhibitors, rivaroxaban and apixaban.

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.

T wave alternans does not assess arrhythmic risk in patients with Brugada syndrome.

BACKGROUND: Brugada syndrome is associated with a risk for sudden death, but the arrhythmic risk in an individual Brugada syndrome patient is difficult to predict. Pathologic changes in the early repolarization phase of the ventricular action potential probably constitute part of the arrhythmogenic substrate in Brugada syndrome. Microvolt T wave alternans (TWA) assesses dynamic beat-to-beat changes in repolarization and has been suggested as a marker for repolarization-related sudden death. We therefore tested whether TWA is an indicator for arrhythmias in Brugada syndrome with a focus on right precordial ECG leads. METHODS: We assessed TWA in nine symptomatic, inducible patients with established Brugada syndrome and in seven healthy controls. TWA was assessed at rest and during exercise using both standard methods and an algorithm that assesses TWA in the early ST segment and the right precordial leads. RESULTS: None of the Brugada patients developed TWA in this study irrespective of analysis at rest or during exercise, neither using standard methods nor when the early ST segment was included in the analysis. When the early ST segment was included in the analysis, nonsustained TWA was found in three out of seven, and sustained TWA in one control. CONCLUSION: T wave alternans is not an appropriate test to detect arrhythmic risk in patients with Brugada syndrome.

Pauses after burst pacing provoke afterdepolarizations and torsades de pointes in a patient with long QT syndrome.

A patient with long QT syndrome and syncope underwent electrophysiological testing and recording of monophasic action potentials (MAP). Programmed ventricular stimulation using up to three premature stimuli did not provoke arrhythmias. Transient action potential prolongation and afterdepolarizations were observed during pauses directly after high-rate fix frequent right ventricular burst pacing at 120-160 bpm. During the pause after burst pacing at 180 bpm, afterdepolarizations at 16-19% amplitude of the MAP plateau persisted for several beats and preceded a short episode of torsades de pointes. High-rate burst pacing provoked afterdepolarizations and triggered torsades de pointes in this patient with long QT syndrome.

Endocardial mapping of right ventricular outflow tract tachycardia using noncontact activation mapping.

INTRODUCTION: Activation mapping and pace mapping identify successful ablation sites for catheter ablation of right ventricular outflow tract (RVOT) tachycardia. These methods are limited in patients with nonsustained tachycardia or isolated ventricular ectopic beats. We investigated the feasibility of using noncontact mapping to guide the ablation of RVOT arrhythmias. METHODS AND RESULTS: Nine patients with RVOT tachycardia and three patients with ectopic beats were studied using noncontact mapping. A multielectrode array catheter was introduced into the RVOT and tachycardia was analyzed using a virtual geometry. The earliest endocardial activation estimated by virtual electrograms was displayed on an isopotential color map and measured 33 +/- 13 msec before onset of QRS. Virtual unipolar electrograms at this site demonstrated QS morphology. Guided by a locator signal, ablation was performed with a mean of 6.9 +/- 2.2 radiofrequency deliveries. Acute success was achieved in all patients. During follow-up, one patient had a recurrence of RVOT tachycardia. Compared with patients (n = 21) who underwent catheter ablation using a conventional approach, a higher success rate was achieved by noncontact mapping. Procedure time was significantly longer in the noncontact mapping group. Fluoroscopy time was not significantly different in the two groups. CONCLUSION: Noncontact mapping can be used as a reliable tool to identify the site of earliest endocardial activation and to guide the ablation procedure in patients with RVOT tachycardia and in patients with ectopic beats originating from the RVOT.

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.