Tamoxifen may contribute to preserve cardiac function in Duchenne muscular dystrophy.

Duchenne muscular dystrophy is life-limiting. Cardiomyopathy, which mostly ensues in the second decade of life, is the main cause of death. Treatment options are still limited. The TAMDMD (NCT03354039) trial assessed motor function, muscle strength and structure, laboratory biomarkers, and safety in 79 ambulant boys with genetically confirmed Duchenne muscular dystrophy, 6.5-12 years of age, receiving either daily tamoxifen 20 mg or placebo for 48 weeks. In this post-hoc analysis, available echocardiographic data of ambulant patients recruited at one study centre were retrieved and compared before and after treatment. Data from 14 patients, median 11 (interquartile range, IQR, 11-12) years of age was available. Baseline demographic characteristics were similar in participants assigned to placebo (n = 7) or tamoxifen (n = 7). Left ventricular end-diastolic diameter in the placebo group (median and IQR) was 39 (38-41) mm at baseline and 43 (38-44) mm at study end, while it was 44 (41-46) mm at baseline and 41 (37-46) mm after treatment in the tamoxifen group. Left ventricular fractional shortening in the placebo group was 35% (32-38%) before and 33% (32-36%) after treatment, while in the tamoxifen group it was 34% (33-34%) at baseline and 35% (33-35%) at study end. No safety signals were detected. CONCLUSION: This hypothesis-generating post-hoc analysis suggests that tamoxifen over 48 weeks is well tolerated and may help preserving cardiac structure and function in Duchenne muscular dystrophy. Further studies are justified. CLINICALTRIALS: gov Identifier: EudraCT 2017-004554-42, NCT03354039 What is known: • Duchenne muscular dystrophy (DMD) is life-limiting. Cardiomyopathy ensues in the second decade of life and is the main cause of death. Treatment options are still limited. • Tamoxifen reduced cardiac fibrosis in mice and improved cardiomyocyte function in human-induced pluripotent stem cell-derived cardiomyocytes. WHAT IS NEW: • In this post-hoc analysis of the TAMDMD trial among 14 boys, median 11 years of age, treated with either tamoxifen or placebo for 48 weeks, treatment was well-tolerated. • A visual trend of improved left-ventricular dimensions and better systolic function preservation generates the hypothesis of a potential beneficial effect of tamoxifen in DMD cardiomyopathy.

Clinical presentation of calmodulin mutations: the International Calmodulinopathy Registry.

AIMS: Calmodulinopathy due to mutations in any of the three CALM genes (CALM1-3) causes life-threatening arrhythmia syndromes, especially in young individuals. The International Calmodulinopathy Registry (ICalmR) aims to define and link the increasing complexity of the clinical presentation to the underlying molecular mechanisms. METHODS AND RESULTS: The ICalmR is an international, collaborative, observational study, assembling and analysing clinical and genetic data on CALM-positive patients. The ICalmR has enrolled 140 subjects (median age 10.8 years [interquartile range 5-19]), 97 index cases and 43 family members. CALM-LQTS and CALM-CPVT are the prevalent phenotypes. Primary neurological manifestations, unrelated to post-anoxic sequelae, manifested in 20 patients. Calmodulinopathy remains associated with a high arrhythmic event rate (symptomatic patients, n = 103, 74%). However, compared with the original 2019 cohort, there was a reduced frequency and severity of all cardiac events (61% vs. 85%; P = .001) and sudden death (9% vs. 27%; P = .008). Data on therapy do not allow definitive recommendations. Cardiac structural abnormalities, either cardiomyopathy or congenital heart defects, are present in 30% of patients, mainly CALM-LQTS, and lethal cases of heart failure have occurred. The number of familial cases and of families with strikingly different phenotypes is increasing. CONCLUSION: Calmodulinopathy has pleiotropic presentations, from channelopathy to syndromic forms. Clinical severity ranges from the early onset of life-threatening arrhythmias to the absence of symptoms, and the percentage of milder and familial forms is increasing. There are no hard data to guide therapy, and current management includes pharmacological and surgical antiadrenergic interventions with sodium channel blockers often accompanied by an implantable cardioverter-defibrillator.

Characterizing Associations of QTc Interval with Nocturnal Glycemic Control in Children with Type 1 Diabetes.

An association between QT prolongation (Bazett's corrected QT interval, QTcB) of 7 milliseconds and nocturnal hypoglycemia, compared with euglycemia, has been observed in children with type 1 diabetes (T1D). The objective of this pharmacometric analysis was to understand this association and other sources of QTc variability quantitatively. Data originate from a prospective observational study (25 cardiac healthy children with T1D, aged 8.1-17.6 years) with continuous subcutaneous glucose and electrocardiogram measurements for 5 consecutive nights. Mixed-effect modeling was used to compare QTcB with individual heart-rate correction (QTcI). Covariate models accounting for circadian variation, age, and sex were evaluated, followed by an investigation of glucose-QTc relationships (with univariable and combined adjusted analysis). Factors potentially modifying sensitivity to QTc lengthening were explored. Random inter-individual variability was reduced in the QTcI versus QTcB model (±12.6 vs 14.1 milliseconds), and was further reduced in the adjusted covariate model (±9.7 milliseconds), accounting for the significantly (P < .01) shortened QTc in adolescent boys (-14.6 milliseconds), circadian variation (amplitude, 19.2 milliseconds; shift, 2.9 hours), and linear glucose-QTc relationship (delay rate, 0.56-h ; slope, 0.76 milliseconds [95%CI 0.67- 0.85 milliseconds] per 1 mmol/L decrease in glucose). Differing sensitivity was suggested to depend upon hemoglobin A1c (HbA1c), T1D duration, and time spent in nocturnal hypoglycemia. In conclusion, a clinically mild association of QTc prolongation with nocturnal hypoglycemia was confirmed and quantified in this pharmacometric analysis, and the longest QTc interval was around 03:00 a.m. The characterized delayed association with glucose highlights the relevance of both the extent and the duration of hypoglycemia. Further clinical studies are warranted to investigate whether these factors contribute to increased risk of hypoglycemia-associated cardiac arrhythmia in children with T1D.

Apparent life-threatening events and brief resolved unexplained events: management of children at a Swiss tertiary care center.

AIMS OF THE STUDY: Apparent life threatening events (ALTEs) are highly stressful situations for the caregiver and commonly result in presentation of the child to an emergency department. As the events are usually brief and resolve in a short period of time, the entity is now called a brief resolved unexplained event (BRUE). Updated recommendations have been published in recent years on the management of BRUE, including a risk stratification to identify those at lower risk for subsequent events or severe underlying disorders. The aim of this study was to describe the epidemiology of ALTE and BRUE at our hospital and detail clinical practice of management in this population in a tertiary care children's hospital in Switzerland. METHODS: We retrospectively analysed all cases of children with an ALTE or BRUE admitted to the University Children's Hospital Basel between September 2009 and April 2018, identified using ICD-10GM coding. Electronic health records were used to extract data on diagnostic procedures, duration of admission and outcome. Infants with a lower-risk BRUE (defined as age >60 days and <1year, born at ≥32 weeks gestational age and postconceptional age ≥45 weeks, first BRUE episode with a duration of <1 minute and no cardiopulmonary resuscitation by trained medical provider required) were compared with those with a higher-risk BRUE/ALTE (not fulfilling all the criteria for lower-risk BRUE). RESULTS: A total of 65 patients with a median age of 42 days (interquartile range 20-67) were identified, of whom 15% were classified as having a lower-risk BRUE. A blood sample was analysed in 97% of patients, cranial ultrasound was performed in 63%, an electrocardiogram in 78% and polysomnography in 26%. The results remained normal in almost all patients and none had a further event recorded during admission. In one patient only QTc prolongation was detected as a potential serious underlying disease. CONCLUSIONS: Our data show that admission for more than 24 hours and extensive investigations for infants admitted for an ALTE/BRUE rarely led to identification of specific underlying causes. According to current recommendations, 15% of the admitted patients could be categorised as having a lower-risk BRUE and therefore hospital admissions and investigations can safely be reduced. We propose an adaptation of the current Swiss recommendations for ALTE/BRUE to optimise clinical management of children presenting with a BRUE.

The very low risk of myocarditis and pericarditis after mRNA COVID-19 vaccination should not discourage vaccination.

The benefits of vaccination - regarding COVID-19 infection and transmission, as well as COVID-associated complications - clearly outweigh the potential risk of vaccine-associated inflammation of the heart and other adverse events. Given the current state of knowledge, the outcome of myocarditis and pericarditis following vaccination is generally good. This review aims to guide physicians in the early diagnosis and management of suspected myocarditis following mRNA COVID vaccination. The initial work-up should include detailed history, a 12-lead electrocardiogram and serological biomarkers (high-sensitivity cardiac troponin T/I, natriuretic peptides and markers of inflammation) in accordance with the assessments recommended in current clinical practice guidelines for patients presenting with acute chest pain. In patients with suspected myocarditis, further assessment with transthoracic echocardiography and cardiovascular magnetic resonance imaging should be undertaken to confirm peri-/myocarditis and to distinguish the findings from other diseases with similar presentation. Patients with mRNA vaccine-associated myocarditis should be followed-up at least once to exclude chronic myocardial inflammation and deterioration of left ventricular ejection fraction. Consultation with an expert such as an immunologist with experience in vaccination regarding further mRNA vaccinations is advised in all patients with mRNA vaccine-associated perimyocarditis. Reporting of mRNA vaccine-associated myocarditis to Swissmedic is mandatory. Cohort studies prospectively follow-up on young adult and paediatric populations following immunisation with an mRNA COVID vaccine to monitor cardiac and immune parameters would generate valuable knowledge to better understand pathogenesis and risk factors for vaccine-associated perimyocarditis.

Autonomic cardiac regulation during spontaneous nocturnal hypoglycemia in children with type 1 diabetes.

BACKGROUND: Hypoglycemia is the most common complication in insulin treated diabetes. Though mostly mild, it can be fatal in rare cases: It is hypothesized that hypoglycemia related QTc prolongation contributes to cardiac arrhythmia. OBJECTIVE: To evaluate influence of nocturnal hypoglycemia on QTc and heart rate variability (HRV) in children with T1D. METHODS: Children and adolescents with T1D for at least 6 months participated in an observational study using continuous glucose monitoring (CGM) and Holter electrocardiogram for five consecutive nights. Mean QTc was calculated for episodes of nocturnal hypoglycemia (<3.7 mmol/L) and compared to periods of the same duration preceding hypoglycemia. HRV (RMSSD, low and high frequency power LF and HF) was analyzed for different 15 min intervals: before hypoglycemia, onset of hypoglycemia, before/after nadir, end of hypoglycemia and after hypoglycemia. RESULTS: Mean QTc during hypoglycemia was significantly longer compared to euglycemia (412 ± 15 vs. 405 ± 18 ms, p = 0.005). HRV changed significantly: RMSSD (from 88 ± 57 to 73 ± 43 ms) and HF (from 54 ± 17 to 47 ± 17nu) decreased from before hypoglycemia to after nadir, while heart rate (from 69 ± 9 to 72 ± 12 bpm) and LF (from 44 ± 17 to 52 ± 21 nu) increased (p = 0.04). CONCLUSION: A QTc lengthening effect of nocturnal hypoglycemia in children with T1D was documented. HRV changes occurred even before detection of nocturnal hypoglycemia by CGM, which may be useful for hypoglycemia prediction.

Intrauterine Growth Retardation in Pregnant Women with Long QT Syndrome Treated with Beta-Receptor Blockers.

Pregnant women with inherited long QT syndrome (iLQTS) are at an increased risk for preterm delivery and intrauterine growth retardation (IUGR) due to their underlying disease. Additionally, they are at a risk of arrhythmogenic events, particularly during the postpartum period because of physiological changes and increased emotional/physical stress. ß-receptor blockers can effectively prevent life-threatening Torsades de Pointes ventricular tachycardia and they are the treatment of choice in iLQTS. Use of ß-receptor blockers in pregnancy is recommended, although IUGR is commonly reported for prenatally exposed infants. IUGR, particularly in preterm infants, can result in adverse neonatal outcomes. This review was performed to support clinicians in their selection of ß-receptor blocker treatment for their pregnant iLQTS women by (i) summarizing the available literature addressing the impact of different ß-receptor blockers on IUGR and (ii) reporting additional aspects which might influence the ß-receptor blocker selection. In general, experts recommend to use nonselective ß-receptor blockers, such as nadolol and propranolol, for iLQTS management as these drugs seem to be superior in effectiveness. However, ß-1-selective receptor blockers, such as bisoprolol or metoprolol, seem to affect less likely uterine contraction, peripheral vasodilation, and are associated with lower IUGR rates and fetal hypoglycemia. They are therefore recommended, except atenolol, as first-line therapy for pregnant women. Additionally, maternal factors such as iLQTS genotype, other underlying comorbidities (e.g., diabetes mellitus type 1, asthma bronchiale), and uteroplacental dysfunction or fetal factors have to be taken into account. Therefore, each woman with iLQTS who wants to become pregnant should be well-advised for a personalized ß-receptor blocker therapy according to the individual risk-benefit evaluation by a multidisciplinary team of cardiologists, gynecologists, pediatric cardiologists, neonatologists, and clinical pharmacologists. During pregnancy, a close monitoring of IUGR and, after birth, monitoring of bradycardia, hypoglycemia, and respiratory depression in the neonate is mandatory. This review summarizes available data on ß-receptor blocker-related risk for IUGR in prenatally exposed infants and illustrates which factors might influence ß-receptor blocker selection with the aim to support clinicians in their pharmacological management of their pregnant iLQTS patients.

Mechanosensitive TREK-1 two-pore-domain potassium (K2P) channels in the cardiovascular system.

TWIK-related K+ channel (TREK-1) two-pore-domain potassium (K2P) channels mediate background potassium currents and regulate cellular excitability in many different types of cells. Their functional activity is controlled by a broad variety of different physiological stimuli, such as temperature, extracellular or intracellular pH, lipids and mechanical stress. By linking cellular excitability to mechanical stress, TREK-1 currents might be important to mediate parts of the mechanoelectrical feedback described in the heart. Furthermore, TREK-1 currents might contribute to the dysregulation of excitability in the heart in pathophysiological situations, such as those caused by abnormal stretch or ischaemia-associated cell swelling, thereby contributing to arrhythmogenesis. In this review, we focus on the functional role of TREK-1 in the heart and its putative contribution to cardiac mechanoelectrical coupling. Its cardiac expression among different species is discussed, alongside with functional evidence for TREK-1 currents in cardiomyocytes. In addition, evidence for the involvement of TREK-1 currents in different cardiac arrhythmias, such as atrial fibrillation or ventricular tachycardia, is summarized. Furthermore, the role of TREK-1 and its interaction partners in the regulation of the cardiac heart rate is reviewed. Finally, we focus on the significance of TREK-1 in the development of cardiac hypertrophy, cardiac fibrosis and heart failure.

"Chaotic Arrhythmia" During Successful Resuscitation After Ingestion of Yew (Taxus baccata) Needles.

OBJECTIVE: The study aims to describe the management of a case of life-threatening yew (Taxus baccata) intoxication. BACKGROUND: The needles of the yew tree contain highly cardiotoxic taxines. Intoxication with taxines, typically as part of suicide attempts, may lead to potentially lethal arrhythmias which often require prolonged cardiopulmonary resuscitation and other supportive measures. No specific therapy has been described. In some cases, extracorporeal life support has been used. CASE: After an attempted suicide with yew needles and out-of-hospital cardiac arrest, a female adolescent was resuscitated for 6 hours according to Advanced Cardiovascular Life Support guidelines. Complex ventricular tachycardias were treated by repeated direct current shocks and broad complex bradycardia managed with transvenous cardiac pacing. Antiarrhythmic drugs (amiodarone, lidocaine), magnesium sulfate, and supportive measures (intravenous lipids, sodium bicarbonate) were provided. The arrhythmias finally resolved, and the patient did not show any significant neurological or cardiac short-term sequelae after 24 hours. RESULTS: The authors describe the successful management of a case of severe taxine intoxication by prolonged conventional advanced cardiac life support lasting for more than 6 hours. CONCLUSIONS: In life-threatening yew intoxication, prolonged cardiopulmonary resuscitation is absolutely essential owing to the long duration of the cardiotoxic action of taxines and can lead to an outcome without cardiac or neurological sequelae.

A variant in MRPS14 (uS14m) causes perinatal hypertrophic cardiomyopathy with neonatal lactic acidosis, growth retardation, dysmorphic features and neurological involvement.

Dysfunction of mitochondrial translation is an increasingly important molecular cause of human disease, but structural defects of mitochondrial ribosomal subunits are rare. We used next-generation sequencing to identify a homozygous variant in the mitochondrial small ribosomal protein 14 (MRPS14, uS14m) in a patient manifesting with perinatal hypertrophic cardiomyopathy, growth retardation, muscle hypotonia, elevated lactate, dysmorphy and mental retardation. In skeletal muscle and fibroblasts from the patient, there was biochemical deficiency in complex IV of the respiratory chain. In fibroblasts, mitochondrial translation was impaired, and ectopic expression of a wild-type MRPS14 cDNA functionally complemented this defect. Surprisingly, the mutant uS14m was stable and did not affect assembly of the small ribosomal subunit. Instead, structural modeling of the uS14m mutation predicted a disruption to the ribosomal mRNA channel.Collectively, our data demonstrate pathogenic mutations in MRPS14 can manifest as a perinatal-onset mitochondrial hypertrophic cardiomyopathy with a novel molecular pathogenic mechanism that impairs the function of mitochondrial ribosomes during translation elongation or mitochondrial mRNA recruitment rather than assembly.

A modified approach for programmed electrical stimulation in mice: Inducibility of ventricular arrhythmias.

BACKGROUND: Electrophysiological studies in mice, the prevailing model organism in the field of basic cardiovascular research, are impeded by the low yield of programmed electrical stimulation (PES). OBJECTIVE: To investigate a modified approach for ventricular arrhythmia (VA) induction and a novel scoring system in mice. METHOD: A systematic review of literature on current methods for PES in mice searching the PubMed database revealed that VA inducibility was low and ranged widely (4.6 ± 10.7%). Based on this literature review, a modified PES protocol with 3 to 10 extrastimuli was developed and tested in comparison to the conventional PES protocol using up to 3 extrastimuli in anesthetized wildtype mice (C57BL/6J, n = 12). Induced VA, classified according to the Lambeth Convention, were assessed by established arrhythmia scores as well as a novel arrhythmia score based on VA duration. RESULTS: PES with the modified approach raised both the occurrence and the duration of VA compared to conventional PES (0% vs 50%; novel VA score p = 0.0002). Particularly, coupling of >6 extrastimuli raised the induction of VA. Predominantly, premature ventricular complexes (n = 6) and ventricular tachycardia <1s (n = 4) were observed. Repeated PES after adrenergic stimulation using isoprenaline resulted in enhanced induction of ventricular tachycardia <1s in both protocols. CONCLUSION: Our findings suggest that the presented approach of modified PES enables effective induction and quantification of VA in wildtype mice and may well be suited to document and evaluate detailed VA characteristics in mice.

Management of anaphylaxis and allergies in patients with long QT syndrome: A review of the current evidence.

OBJECTIVE: To develop a treatment algorithm for patients with long QT syndrome (LQTS) in case they need antiallergic medications for allergic reactions, including asthma and anaphylaxis. DATA SOURCES: A literature review was performed to assess safety and to develop antiallergic treatment strategies for patients with LQTS. STUDY SELECTIONS: LQTS is a heterogeneous group of myocardial repolarization disorders characterized by prolongation of the QT interval that potentially results in life-threatening torsades de pointes tachycardia. Data on pharmacologic treatment in case of anaphylaxis in LQTS are sparse. For this narrative review, all currently available articles on the use of antiallergic drugs for allergic reactions, anaphylaxis, and asthma in patients with LQTS were used. RESULTS: Local allergic symptoms can be safely treated primarily with fexofenadine, levocetirizine, desloratadine, or cetirizine and, if needed, a short course of corticosteroids. In case of systemic symptoms, epinephrine should be administered. It may be less effective in patients with LQTS treated with ß-blockers, necessitating the use of glucagon as add-on treatment. In case of lower airway obstruction, ipratropium bromide should be used, but if not effective, inhaled ß2-adrenergic agents may be used. Continuous cardiac monitoring is indicated with the use of epinephrine and inhaled ß2-adrenergic agents. The use of the latter also warrants intense monitoring of serum potassium levels. Clemastine and dimetindene should be avoided in patients with LQTS. CONCLUSION: Patients with LQTS have a higher risk of life-threatening complications during the treatment of their allergic reactions because of the underlying disease and concomitant treatment with ß-blockers. Treatment algorithms will certainly decrease these complications.

Complicated Postoperative Course after Pulmonary Artery Sling Repair and Slide Tracheoplasty.

Pulmonary artery sling (PAS) is a rare congenital condition in which the left pulmonary artery (LPA) arises from the right pulmonary artery, and then passes between the trachea and the esophagus to reach the left lung, thereby forming a sling around the airway. It is often associated with intrinsic tracheal stenosis due to complete cartilaginous rings. Therapeutic management nowadays consists of one-stage reimplantation of the LPA and tracheoplasty with cardiopulmonary bypass support. Here, we present a 7-week-old boy with PAS and long-segment tracheal stenosis (LSTS) who underwent surgical intervention consisting of reimplantation of the LPA and slide tracheoplasty. Multiple respiratory and cardiovascular complications marked the postoperative course. They consisted of recurrent failed attempts in weaning off mechanical ventilation due to bronchomalacia, left vocal cord paralysis, development of granulation tissue at the anastomosis and restenosis of the trachea, and the main stem bronchi requiring balloon dilatation. The patient also developed bilateral pulmonary artery thrombosis and stenosis of the LPA. After a prolonged hospitalization, the patient is doing well without any respiratory symptoms and has a good result on follow-up bronchoscopy 1 year after the initial surgery. The stenosis of the LPA responded well to percutaneous balloon dilatation 12 months after the primary surgery. The case illustrates that even though surgical techniques are improving and are in general associated with a low morbidity and mortality, management of PAS and tracheal stenosis can still be challenging. However, good long-term outcome can be achieved if the initial postoperative phase is overcome.

Pannexin-1 Deficient Mice Have an Increased Susceptibility for Atrial Fibrillation and Show a QT-Prolongation Phenotype.

BACKGROUND/AIMS: Pannexin-1 (Panx1) is an ATP release channel that is ubiquitously expressed and coupled to several ligand-gated receptors. In isolated cardiac myocytes, Panx1 forms large conductance channels that can be activated by Ca2+ release from the sarcoplasmic reticulum. Here we characterized the electrophysiological function of these channels in the heart in vivo, taking recourse to mice with Panx1 ablation. METHODS: Cardiac phenotyping of Panx1 knock-out mice (Panx1(-/-)) was performed by employing a molecular, cellular and functional approach, including echocardiography, surface and telemetric ECG recordings with QT analysis, physical stress testing and quantification of heart rate variability. In addition, an in vivo electrophysiological study entailed programmed electrical stimulation using an intracardiac octapolar catheter. RESULTS: Panx1 deficiency results in a higher incidence of AV-block, delayed ventricular depolarisation, significant prolongation of QT- and rate corrected QT-interval and a higher incidence of atrial fibrillation after intraatrial burst stimulation. CONCLUSION: Panx1 seems to play an important role in murine cardiac electrophysiology and warrants further consideration in the context of hereditary forms of atrial fibrillation.

Upregulation of K(2P)3.1 K+ Current Causes Action Potential Shortening in Patients With Chronic Atrial Fibrillation.

BACKGROUND: Antiarrhythmic management of atrial fibrillation (AF) remains a major clinical challenge. Mechanism-based approaches to AF therapy are sought to increase effectiveness and to provide individualized patient care. K(2P)3.1 (TASK-1 [tandem of P domains in a weak inward-rectifying K+ channel-related acid-sensitive K+ channel-1]) 2-pore-domain K+ (K(2P)) channels have been implicated in action potential regulation in animal models. However, their role in the pathophysiology and treatment of paroxysmal and chronic patients with AF is unknown. METHODS AND RESULTS: Right and left atrial tissue was obtained from patients with paroxysmal or chronic AF and from control subjects in sinus rhythm. Ion channel expression was analyzed by quantitative real-time polymerase chain reaction and Western blot. Membrane currents and action potentials were recorded using voltage- and current-clamp techniques. K(2P)3.1 subunits exhibited predominantly atrial expression, and atrial K(2P)3.1 transcript levels were highest among functional K(2P) channels. K(2P)3.1 mRNA and protein levels were increased in chronic AF. Enhancement of corresponding currents in the right atrium resulted in shortened action potential duration at 90% of repolarization (APD90) compared with patients in sinus rhythm. In contrast, K(2P)3.1 expression was not significantly affected in subjects with paroxysmal AF. Pharmacological K(2P)3.1 inhibition prolonged APD90 in atrial myocytes from patients with chronic AF to values observed among control subjects in sinus rhythm. CONCLUSIONS: Enhancement of atrium-selective K(2P)3.1 currents contributes to APD shortening in patients with chronic AF, and K(2P)3.1 channel inhibition reverses AF-related APD shortening. These results highlight the potential of K(2P)3.1 as a novel drug target for mechanism-based AF therapy.

In vivo electrophysiological characterization of TASK-1 deficient mice.

BACKGROUND/AIMS: TASK-1 is a potassium channel predominantly expressed in heart and brain. We have previously shown that anesthetized TASK-1(-/-)mice have prolonged QT intervals in surface electrocardiograms (ECGs). In addition, heart rate variability quantified by time and frequency domain parameters was significantly altered in TASK-1(-/-) mice with a sympathetic preponderance. Aims of the present study were the analysis of QT intervals by telemetric ECGs, to determine potential influences of anesthesia and ß-adrenergic stimulation on repolarization in surface ECGs, to investigate in vivo electrophysiological parameters by intracardiac electrical stimulation and to quantify heart rate turbulence after ischemia/reperfusion or ventricular pacing in TASK-1(+/+) and TASK-1(-/-) mice. METHODS: Rate corrected QT intervals (QTc) were recorded in conscious mice by telemetry and in surface ECGs following administration of various anesthetics (tribromoethanol (Avertin(®)), pentobarbital and isoflurane). TASK-1(+/+) and TASK-1(-/-) mice were characterized by programmed electrical stimulation using an intracardiac octapolar catheter. The baroreceptor reflex was analyzed by heart rate turbulence (turbulence onset and slope) after ischemia/reperfusion and by stimulated premature ventricular contractions. RESULTS: Telemetric and surface ECGs in mice sedated with Avertin(®) and pentobarbital, showed a significantly lengthened rate corrected QT interval in TASK-1(-/-) mice (telemetry: TASK-1(+/+) 43±3ms vs. TASK-1(-/-) 49±5ms, n=6, p<0.05; Avertin(®): TASK-1(+/+) 36±8ms vs. TASK-1(-/-) 48±4ms, n=13/16, p<0.0001). The prolongation of the QT interval was most pronounced at lower heart rates. Isoflurane, known for its stimulatory effects on the TASK channel family, attenuated the rate corrected QT interval prolongation in TASK-1(-/-)mice. Intracardiac electrical stimulation revealed normal values for electrical conduction and refractoriness. No significant arrhythmias after atrial and ventricular burst stimulation were induced before and after adrenergic challenge in both genotypes. Turbulence onset after premature ventricular contraction was significantly altered in TASK-1(-/-) mice. CONCLUSION: TASK-1(-/-) mice exhibit a phenotype of QT prolongation, which distinct relation to heart rate. TASK-1 deficiency does neither alter key electrophysiological parameters nor increases atrial/ventricular vulnerability after electrical stimulation. The heart rate response after premature ventricular contractions is significantly abolished indicating a diminished baroreceptor reflex in TASK-1(-/-) mice.

A presumably benign human ether-a-go-go-related gene mutation (R176W) with a malignant primary manifestation of long QT syndrome.

A 12-year-old girl presented with a first prolonged syncope. She was successfully resuscitated by external defibrillation after recording torsade de pointes tachycardia. Repeated electrocardiograms and a 12-channel Holter monitoring showed an intermittent prolongation of the QT interval. Genetic analysis identified a heterozygous point mutation in the KCNH2 gene, which is thought to be associated with a rather mild clinical phenotype of the long QT syndrome.

Functional role of TASK-1 in the heart: studies in TASK-1-deficient mice show prolonged cardiac repolarization and reduced heart rate variability.

TASK-1, a member of the recently identified K2P channel family, is mainly expressed in the heart and the nervous system. TASK-1 is regulated by several physiological and pathological conditions and functions as a background potassium channel. However, there are limited data concerning the significance of TASK-1 in cardiac physiology. We studied the functional role of TASK-1 in the heart by cardiac phenotyping the TASK-1-deficient mouse (TASK-1(-/-)). TASK-1 was predominantly expressed in the ventricles of control animals. Real-time PCR and immunoblot demonstrated that the expression of seven other K2P channels was unchanged in TASK-1(-/-) mice. No structural or functional abnormalities were found by histology and echocardiography. Electrophysiological studies recording monophasic action potentials (MAPs) showed a significant prolongation of action potential duration in spontaneously beating and atrially paced hearts, respectively. Surface ECGs of TASK-1(-/-) mice revealed a significant prolongation of the rate corrected QT interval. Telemetric ECG recordings for 24 h, during physical and pharmacological stress testing and after ischemia/reperfusion injury did not result in a higher incidence of arrhythmias. Infarct size was comparable in both genotypes. However, TASK-1(-/-) mice had a higher mean heart rate and significantly reduced heart rate variability (HRV). Time and frequency domain measurements as well as baroreceptor reflex testing revealed a sympathovagal imbalance with a shift to an increase in sympathetic influence in TASK-1(-/-) mice. In conclusion, TASK-1 plays a functional role in the repolarization of the cardiac action potential in vivo and contributes to the maintenance of HRV.