Correlations Between Endocardial Voltage Mapping, Diagnosis, and Genetics in Patients With Arrhythmogenic Right Ventricular Cardiomyopathy.

The relations between endocardial voltage mapping and the genetic background of patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) have not been investigated so far. A total of 97 patients with proved or suspected ARVC who underwent 3-dimensional endocardial mapping and genetic testing have been retrospectively included. Presence, localization, and size of scar areas were correlated to ARVC diagnosis and the presence of a pathogenic variant. A total of 78 patients (80%) presented with some bipolar or unipolar scar on endocardial voltage mapping, whereas 43 carried pathogenic variants (44%). Significant associations were observed between presence of endocardial scars on voltage mapping and previous or inducible ventricular tachycardia, right ventricular function and dimensions, or electrocardiogram features of ARVC. A total of 60 of the 78 patients (77%) with an endocardial scar fulfilled the criteria for a definitive arrhythmogenic right ventricular dysplasia diagnosis versus 8 of 19 patients (42%) without scar (p = 0.003). Patients with a definitive diagnosis of ARVC had more scars from any location and the scars were larger in patients with ARVC. In the 68 patients with a definitive diagnosis of ARVC, the presence of any endocardial scar was similar whether an ARVC-causal mutation was present or not. Only scar extent was significantly greater in patients with pathogenic variants. There was no difference in the presence and characteristics of scars in PKP2 mutated versus other mutated patients. The 3-dimensional endocardial mapping could have an important role for refining ARVC diagnosis and may be able to detect minor forms with otherwise insufficient criteria for diagnosis. The trend for larger scar extent were observed in mutated patients, without any difference according to the mutated genes.

Kickboxing a cardiomyopathy: mitochondrial sequencing provides answer for young athlete and her family.

Mitochondrial diseases are rare, often go undiagnosed and can lead to devastating cascades of multisystem organ dysfunction. This report of a young woman with hearing loss and gestational diabetes illustrates a novel presentation of a cardiomyopathy caused by a previously described mutation in a mitochondrial gene, MT-TL1. She initially had biventricular heart dysfunction and ventricular arrhythmia that ultimately recovered with beta blockade and time. She continues to participate in sport without decline. It is important to keep mitochondrial diseases in the differential diagnosis and understand the testing and management strategies in order to provide the best patient care.

Ventricular arrhythmias involving the His-Purkinje system in the structurally abnormal heart.

His-Purkinje-related ventricular arrhythmias are a subset of ventricular tachycardias that use the specialized cardiac conduction system. These arrhythmias can occur in various different forms of structural heart disease. Here, we review the basic science discoveries and their analogous clinical observations that implicate the His-Purkinje system as a crucial component of the arrhythmia circuit. While mutations serve the molecular basis for arrhythmias in the heritable cardiomyopathies, transcriptional and posttranslational changes constitute the adverse remodeling leading to arrhythmias in acquired structural heart disease. Additional studies on the electrical properties of the His-Purkinje network and its interactions with the surrounding myocardium will improve the clinical diagnosis and treatment of these arrhythmias.

EL20, a potent antiarrhythmic compound, selectively inhibits calmodulin-deficient ryanodine receptor type 2.

BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an arrhythmogenic disorder caused by mutations in the cardiac ryanodine receptor RyR2 that increase diastolic calcium cation (Ca2+) leak from the sarcoplasmic reticulum (SR). Calmodulin (CaM) dissociation from RyR2 has been associated with diastolic Ca2+ leak in heart failure. OBJECTIVE: Determine whether the tetracaine-derivative compound EL20 inhibits abnormal Ca2+ release from RyR2 in a CPVT model and investigate the underlying mechanism of inhibition. METHODS: Spontaneous Ca2+ sparks in cardiomyocytes and inducible ventricular tachycardia were assessed in a CPVT mouse model, which is heterozygous for the R176Q mutation in RyR2 (R176Q/+ mice) in the presence of EL20 or vehicle. Single-channel studies using sheep cardiac SR or purified RyR2 reconstituted into proteoliposomes with and without exogenous CaM were used to assess mechanisms of inhibition. RESULTS: EL20 potently inhibits abnormal Ca2+ release in R176Q/+ myocytes (half-maximal inhibitory concentration = 35.4 nM) and diminishes arrhythmia in R176Q/+ mice. EL20 inhibition of single-channel activity of purified RyR2 occurs in a similar range as seen in R176Q/+ myocytes (half-maximal inhibitory concentration = 8.2 nM). Inhibition of single-channel activity for cardiac SR or purified RyR2 supplemented with 100-nM or 1-µM CaM shows a 200- to 1000-fold reduction in potency. CONCLUSION: This work provides a potential therapeutic mechanism for the development of antiarrhythmic compounds that inhibit leaky RyR2 resulting from CaM dissociation, which is often associated with failing hearts. Our data also suggest that CaM dissociation may contribute to the pathogenesis of arrhythmias with the CPVT-linked R176Q mutation.

Ventricular tachycardia ablation in arrhythmogenic right ventricular cardiomyopathy patients with TMEM43 gene mutations.

INTRODUCTION: Catheter ablation of VT in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) is often challenging, frequently requiring multiple or epicardial ablation procedures; TMEM43 gene mutations typically cause aggressive disease. We sought to compare VT ablation outcomes for ARVC patients with and without TMEM43 mutations. METHODS: Patients with prior ablation for ARVC-related VT were reviewed. Demographic, procedural, and follow-up data were reviewed retrospectively. Patients with confirmed TMEM43 gene mutations were compared to those with other known mutations or who had no known mutations. RESULTS: Thirteen patients (10 male, mean age 49 ± 14 years) underwent 29 ablation procedures (median 2 procedures/patient, range 1-6) with a median of 4 targeted VTs/patient (range 1-9). They were followed for a mean duration of 7.3 ± 4.2 years. Gene mutations included TMEM43 (n = 5), PKP2 (n = 2), DSG2 (n = 2), unidentifiable (n = 4). TMEM patients showed more biventricular involvement compared to non-TMEM patients (80% vs. 12.5%, P = 0.032), more inducible VTs during their ablation procedures (mean VTs/patient: 5.8 ± 3 vs. 2.6 ± 1, P = 0.021). Acute and long-term procedural outcomes did not show a significant difference between the two groups, however TMEM patients had worse composite endpoint of death or transplantation (60% vs. 0, P = 0.035; log-rank P = 0.013). CONCLUSIONS: TMEM43 mutation patients were more likely to have biventricular arrhythmogenic substrate and more inducible VTs at EP study. Despite comparable acute VT ablation outcomes, long-term prognosis is unfavorable.

[Recurrent syncope related to catecholaminergic polymorphic ventricular tachycardia due to de novo RyR2-R2401H mutation].

Objective: To explore the clinical and molecular genetic features of a Chinese patient with catecholaminergic polymorphic ventricular tachycardia (CPVT). Methods: Clinical data including resting electrocardiography, echocardiography and treadmill exercise testing of a patient with CPVT admitted to our department in March 2013 were analyzed, and the peripheral venous blood samples of the patient and his family members and 400 ethnicity-matched healthy controls were obtained. All exons and exon-intron boundaries of the six CPVT-related genes including RYR2, CASQ2, TRDN, CALM1, KCNJ2 and ANKB were sequenced to detect the variants related to CPVT. The relationship between the genotypes and phenotypes was analyzed to direct the target therapy. Results: Recurrent syncope induced either by exercise or extreme frightened fear was observed in this patient. There was no positive family history of syncope or sudden death. The resting electrocardiography and echocardiography of the patient were normal, while the exercise testing revealed bidirectional and polymorphic ventricular tachycardia. A cardiac ryanodine receptor gene mutation (R2401H) was identified in this patient, while this mutation was absent in his parents and sister and 400 controls. No variant was detected in the remaining five candidate genes. Treatment with high dose of metoprolol succinate (118.75 mg/d) was effective and patient was free of syncopal attack during the 2 years follow-up. Conclusion: This is the first report on RyR2-R2401H mutation in Chinese patient with CPVT, and high dose of metoptolol is the effective therapy option for CPVT related to RyR2 mutation.

Treatment of catecholaminergic polymorphic ventricular tachycardia in mice using novel RyR2-modifying drugs.

RATIONALE: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal arrhythmic disorder caused by mutations in the type-2 ryanodine receptor (RyR2). Mutant RyR2 cause abnormal Ca2+ leak from the sarcoplasmic reticulum (SR), which is associated with the development of arrhythmias. OBJECTIVE: To determine whether derivatives of tetracaine, a local anesthetic drug with known RyR2 inhibiting action, could prevent CPVT induction by suppression of RyR2-mediated SR Ca2+ leak. METHODS AND RESULTS: Confocal microscopy was used to assess the effects of tetracaine and 9 derivatives (EL1-EL9) on spontaneous Ca2+ sparks in ventricular myocytes isolated from RyR2-R176Q/+ mice with CPVT. Whereas each derivative suppressed the Ca2+ spark frequency, derivative EL9 was most effective at the screening dose of 500nmol/L. At this high dose, the Ca2+ transient amplitude was not affected in myocytes from WT or R176Q/+ mice. The IC50 of EL9 was determined to be 13nmol/L, which is about 400× time lower than known RyR2 stabilizer K201. EL9 prevented the induction of ventricular tachycardia observed in placebo-treated R176Q/+ mice, without affecting heart rate or cardiac contractility. CONCLUSIONS: Tetracaine derivatives represent a novel class of RyR2 stabilizing drugs that could be used for the treatment of the potentially fatal disorder catecholaminergic polymorphic ventricular tachycardia.

Exercise-induced syncope in a 22-year-old man.

CLINICAL INTRODUCTION: A 22-year-old man was referred to us for syncope during a game of Captain's ball. There was no prodrome. His friends did not notice any ictal movements. He was otherwise well prior to passing out. He was not taking any medications or supplements. He was not usually physically active, but was otherwise well with no significant medical history. This is his first episode of syncope. There was no history of cardiac arrest or seizures. There is no family history of premature sudden cardiac death.Physical examination was normal. ECG at rest demonstrated sinus rhythm with corrected QT interval of 400 ms. Echocardiography revealed a structurally normal heart. Holter monitoring was normal. Treadmill exercise stress test demonstrated the following rhythm on figure 1 during stage 4 Bruce protocol. Stress test was terminated in view of sustained arrhythmia as illustrated. He felt light-headed during the period, but otherwise felt that he could carry on with the exercise. ECG during recovery was unremarkable.

Bundle Branch Re-Entrant Ventricular Tachycardia: Novel Genetic Mechanisms in a Life-Threatening Arrhythmia.

OBJECTIVES: This study sought to investigate for an underlying genetic etiology in cases of apparent idiopathic bundle branch re-entrant ventricular tachycardia (BBRVT). BACKGROUND: BBRVT is a life-threatening arrhythmia occurring secondary to macro-re-entry within the His-Purkinje system. Although classically associated with dilated cardiomyopathy, BBRVT may also occur in the setting of isolated, unexplained conduction system disease. METHODS: Cases of BBRVT with normal biventricular size and function were recruited from 6 North American centers. Enrollment required a clinically documented wide complex tachycardia and BBRVT proven during invasive electrophysiology study. Study participants were screened for mutations within genes associated with cardiac conduction system disease. Pathogenicity of identified mutations was evaluated using in silico phylogenetic and physicochemical analyses and in vitro biophysical studies. RESULTS: Among 6 cases of idiopathic BBRVT, each presented with hemodynamic compromise and 2 suffered cardiac arrests requiring resuscitation. Putative culprit mutations were identified in 3 of 6 cases, including 2 in SCN5A (Ala1905Gly [novel] and c.4719C>T [splice site mutation]) and 1 in LMNA (Leu327Val [novel]). Biophysical analysis of mutant Ala1905Gly Nav1.5 channels in tsA201 cells revealed significantly reduced peak current density and positive shifts in the voltage-dependence of activation, consistent with a loss-of-function. The SCN5A c.4719C>T splice site mutation has previously been reported as disease-causing in 3 cases of Brugada syndrome, whereas the novel LMNA Leu327Val mutation was associated with a classic laminopathy phenotype. Following catheter ablation, BBRVT was noninducible in all cases and none experienced a clinical recurrence during follow-up. CONCLUSIONS: Our investigation into apparent idiopathic BBRVT has identified the first genetic culprits for this life-threatening arrhythmia, providing further insight into its underlying pathophysiology and emphasizing a potential role for genetic testing in this condition. Our findings also highlight BBRVT as a novel genetic etiology of unexplained sudden cardiac death that can be cured with catheter ablation.

Finding the rhythm of sudden cardiac death: new opportunities using induced pluripotent stem cell-derived cardiomyocytes.

Sudden cardiac death is a common cause of death in patients with structural heart disease, genetic mutations, or acquired disorders affecting cardiac ion channels. A wide range of platforms exist to model and study disorders associated with sudden cardiac death. Human clinical studies are cumbersome and are thwarted by the extent of investigation that can be performed on human subjects. Animal models are limited by their degree of homology to human cardiac electrophysiology, including ion channel expression. Most commonly used cellular models are cellular transfection models, which are able to mimic the expression of a single-ion channel offering incomplete insight into changes of the action potential profile. Induced pluripotent stem cell-derived cardiomyocytes resemble, but are not identical, adult human cardiomyocytes and provide a new platform for studying arrhythmic disorders leading to sudden cardiac death. A variety of platforms exist to phenotype cellular models, including conventional and automated patch clamp, multielectrode array, and computational modeling. Induced pluripotent stem cell-derived cardiomyocytes have been used to study long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, hypertrophic cardiomyopathy, and other hereditary cardiac disorders. Although induced pluripotent stem cell-derived cardiomyocytes are distinct from adult cardiomyocytes, they provide a robust platform to advance the science and clinical care of sudden cardiac death.

Dantrolene rescues aberrant N-terminus intersubunit interactions in mutant pro-arrhythmic cardiac ryanodine receptors.

AIMS: The ryanodine receptor (RyR2) is an intracellular Ca(2+) release channel essential for cardiac excitation-contraction coupling. Abnormal RyR2 channel function results in the generation of arrhythmias and sudden cardiac death. The present study was undertaken to investigate the mechanistic basis of RyR2 dysfunction in inherited arrhythmogenic cardiac disease. METHODS AND RESULTS: We present several lines of complementary evidence, indicating that the arrhythmia-associated L433P mutation disrupts RyR2 N-terminus self-association. A combination of yeast two-hybrid, co-immunoprecipitation, and chemical cross-linking assays collectively demonstrate that a RyR2 N-terminal fragment carrying the L433P mutation displays substantially reduced self-interaction compared with wild type. Moreover, sucrose density gradient centrifugation reveals that the L433P mutation impairs tetramerization of the full-length channel. [(3)H]Ryanodine-binding assays demonstrate that disrupted N-terminal intersubunit interactions within RyR2(L433P) confer an altered sensitivity to Ca(2+) activation. Calcium imaging of RyR2(L433P)-expressing cells reveals substantially prolonged Ca(2+) transients and reduced Ca(2+) store content indicating defective channel closure. Importantly, dantrolene treatment reverses the L433P mutation-induced impairment and restores channel function. CONCLUSION: The N-terminus domain constitutes an important structural determinant for the functional oligomerization of RyR2. Our findings are consistent with defective N-terminus self-association as a molecular mechanism underlying RyR2 channel deregulation in inherited arrhythmogenic cardiac disease. Significantly, the therapeutic action of dantrolene may occur via the restoration of normal RyR2 N-terminal intersubunit interactions.

Flecainide therapy suppresses exercise-induced ventricular arrhythmias in patients with CASQ2-associated catecholaminergic polymorphic ventricular tachycardia.

BACKGROUND: Calsequestrin-associated catecholaminergic polymorphic ventricular tachycardia (CPVT2) can cause sudden death in young individuals in response to stress. Beta-blockers are the mainstay medical treatment for patients with CPVT2. However, they do not prevent syncope and sudden death in all patients. Flecainide was reported to reduce exercise-induced ventricular arrhythmias (EIVA) in patients with ryanodine receptor-associated CPVT. The role of flecainide in CPVT2 is not known. OBJECTIVE: To summarize our experience in combining flecainide and beta-blockers in high-risk patients with CPVT2. METHODS: All patients with CPVT2 (10 patients) who have high-risk features (syncope, EIVA, or appropriate implantable cardioverter-defibrillator [ICD] shocks) despite beta-blockers with or without calcium channel blockers were treated with a combination of flecainide and beta-blockers. Exercise test was done before and after beginning treatment with flecainide. RESULTS: All patients had EIVA and 4 had appropriate ICD shocks before flecainide treatment. EIVA-included frequent ventricular premature beats and or ventricular tachycardia during the exercise test while on high dose of beta-blockers with or without calcium channel blockers before treatment with flecainide. After combination therapy with flecainide and beta-blockers, EIVA were suppressed completely in all patients. During follow-up of 15.5 ± 10.4 months (range 2-29 months), 8 patients were free of symptoms and free of arrhythmias. Two patients had 1 VT storm episode with recurrent ICD shocks despite repeated normal stress test. CONCLUSIONS: Flecainide can completely prevent ventricular arrhythmia during exercise and partially prevent recurrent ICD shocks in high-risk patients with CPVT2.

Mutation-positive arrhythmogenic right ventricular dysplasia/cardiomyopathy: the triangle of dysplasia displaced.

INTRODUCTION: The traditional description of the Triangle of Dysplasia in Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy (ARVD/C) predates genetic testing and excludes biventricular phenotypes. METHODS AND RESULTS: We analyzed Cardiac Magnetic Resonance (CMR) studies of 74 mutation-positive ARVD/C patients for regional abnormalities on a 5-segment RV and 17-segment LV model. The location of electroanatomic endo- and epicardial scar and site of successful VT ablation was recorded in 11 ARVD/C subjects. Among 54/74 (73%) subjects with abnormal CMR, the RV was abnormal in almost all (96%), and 52% had biventricular involvement. Isolated LV abnormalities were uncommon (4%). Dyskinetic basal inferior wall (94%) was the most prevalent RV abnormality, followed by basal anterior wall (87%) dyskinesis. Subepicardial fat infiltration in the posterolateral LV (80%) was the most frequent LV abnormality. Similar to CMR data, voltage maps revealed scar (<0.5 mV) in the RV basal inferior wall (100%), followed by the RV basal anterior wall (64%) and LV posterolateral wall (45%). All 16 RV VTs originated from the basal inferior wall (50%) or basal anterior wall (50%). Of 3 LV VTs, 2 localized to the posterolateral wall. In both modalities, RV apical involvement never occurred in isolation. CONCLUSION: Mutation-positive ARVD/C exhibits a previously unrecognized characteristic pattern of disease involving the basal inferior and anterior RV, and the posterolateral LV. The RV apex is only involved in advanced ARVD/C, typically as a part of global RV involvement. These results displace the RV apex from the Triangle of Dysplasia, and provide insights into the pathophysiology of ARVD/C.

Modeling of catecholaminergic polymorphic ventricular tachycardia with patient-specific human-induced pluripotent stem cells.

OBJECTIVES: The goal of this study was to establish a patient-specific human-induced pluripotent stem cells (hiPSCs) model of catecholaminergic polymorphic ventricular tachycardia (CPVT). BACKGROUND: CPVT is a familial arrhythmogenic syndrome characterized by abnormal calcium (Ca(2+)) handling, ventricular arrhythmias, and sudden cardiac death. METHODS: Dermal fibroblasts were obtained from a CPVT patient due to the M4109R heterozygous point RYR2 mutation and reprogrammed to generate the CPVT-hiPSCs. The patient-specific hiPSCs were coaxed to differentiate into the cardiac lineage and compared with healthy control hiPSCs-derived cardiomyocytes (hiPSCs-CMs). RESULTS: Intracellular electrophysiological recordings demonstrated the development of delayed afterdepolarizations in 69% of the CPVT-hiPSCs-CMs compared with 11% in healthy control cardiomyocytes. Adrenergic stimulation by isoproterenol (1 µM) or forskolin (5 µM) increased the frequency and magnitude of afterdepolarizations and also led to development of triggered activity in the CPVT-hiPSCs-CMs. In contrast, flecainide (10 µM) and thapsigargin (10 µM) eliminated all afterdepolarizations in these cells. The latter finding suggests an important role for internal Ca(2+) stores in the pathogenesis of delayed afterdepolarizations. Laser-confocal Ca(2+) imaging revealed significant whole-cell [Ca(2+)] transient irregularities (frequent local and large-storage Ca(2+)-release events, broad and double-humped transients, and triggered activity) in the CPVT cardiomyocytes that worsened with adrenergic stimulation and Ca(2+) overload and improved with beta-blockers. Store-overload-induced Ca(2+) release was also identified in the hiPSCs-CMs and the threshold for such events was significantly reduced in the CPVT cells. CONCLUSIONS: This study highlights the potential of hiPSCs for studying inherited arrhythmogenic syndromes, in general, and CPVT specifically. As such, it represents a promising paradigm to study disease mechanisms, optimize patient care, and aid in the development of new therapies.

Effect of skeletal muscle Na(+) channel delivered via a cell platform on cardiac conduction and arrhythmia induction.

BACKGROUND: In depolarized myocardial infarct epicardial border zones, the cardiac sodium channel is largely inactivated, contributing to slow conduction and reentry. We have demonstrated that adenoviral delivery of the skeletal muscle Na(+) channel (SkM1) to epicardial border zones normalizes conduction and reduces induction of ventricular tachycardia/ventricular fibrillation. We now studied the impact of canine mesenchymal stem cells (cMSCs) in delivering SkM1. METHODS AND RESULTS: cMSCs were isolated and transfected with SkM1. Coculture experiments showed cMSC/SkM1 but not cMSC alone and maintained fast conduction at depolarized potentials. We studied 3 groups in the canine 7d infarct: sham, cMSC, and cMSC/SkM1. In vivo epicardial border zones electrograms were broad and fragmented in sham, narrower in cMSCs, and narrow and unfragmented in cMSC/SkM1 (P<0.05). During programmed electrical stimulation of epicardial border zones, QRS duration in cMSC/SkM1 was shorter than in cMSC and sham (P<0.05). Programmed electrical stimulation-induced ventricular tachycardia/ventricular fibrillation was equivalent in all groups (P>0.05). CONCLUSION: cMSCs provide efficient delivery of SkM1 current. The interventions performed (cMSCs or cMSC/SkM1) were neither antiarrhythmic nor proarrhythmic. Comparing outcomes with cMSC/SkM1 and viral gene delivery highlights the criticality of the delivery platform to SkM1 antiarrhythmic efficacy.

Diminished cardiac fibrosis in heart failure is associated with altered ventricular arrhythmia phenotype.

OBJECTIVES: We sought to define the role of interstitial fibrosis in the proarrhythmic phenotype of failing ventricular myocardium. BACKGROUND: Multiple cellular events that occur during pathological remodeling of the failing ventricle are implicated in the genesis of ventricular tachycardia (VT), including interstitial fibrosis. Recent studies suggest that ventricular fibrosis is reversible, and current anti-remodeling therapies attenuate ventricular fibrosis. However, the role of interstitial fibrosis in the proarrhythmic phenotype of failing ventricular myocardium is currently not well defined. METHODS: Class II histone deacetylases (HDACs) have been implicated in promoting collagen biosynthesis. As these enzymes are inhibited by protein kinase D1 (PKD1), we studied mice with cardiomyocyte-specific transgenic over-expression of a constitutively active mutant of PKD1 (caPKD). caPKD mice were compared with animals in which cardiomyopathy was induced by severe thoracic aortic banding (sTAB). Hearts were analyzed by echocardiographic and electrocardiographic means. Interstitial fibrosis was assessed by histology and quantified biochemically. Ventricular arrhythmias were induced by closed-chest, intracardiac pacing. RESULTS: Similar degrees of hypertrophic growth, systolic dysfunction and mortality were observed in the two models. In sTAB mice, robust ventricular fibrosis was readily detected, but myocardial collagen content was significantly reduced in caPKD mice. As expected, VT was readily inducible by programmed stimulation in sTAB mice and VT was less inducible in caPKD mice. Surprisingly, episodes of VT manifested longer cycle lengths and longer duration in caPKD mice. CONCLUSION: Attenuated ventricular fibrosis is associated with reduced VT inducibility, increased VT duration, and significantly longer arrhythmia cycle length.

Developing new anti-arrhythmics: clues from the molecular basis of cardiac ryanodine receptor (RyR2) Ca2+-release channel dysfunction.

Sudden cardiac death (SCD) remains a major cause of mortality, and despite our knowledge of the causative genetic, molecular and biochemical cellular mechanisms involved, effective therapeutic strategies are lacking. Perturbations in cardiac Ca2+ handling promote arrhythmias and there is enormous interest in developing new anti-arrhythmics aimed at correcting Ca2+ release dysfunction. In particular, abnormal Ca2+ release arising as a result of acquired or genetic defects in cardiac ryanodine receptors (RyR2) has emerged as an important arrhythmogenic trigger in heart failure, and in a devastating genetic arrhythmia syndrome termed catecholaminergic polymorphic ventricular tachycardia (CPVT). Here, we evaluate how experimental insights into RyR2 structure-function are unravelling the precise molecular basis of channel dysfunction and are advancing the development of new therapeutic strategies. We also discuss the functional role of RyR2 in the context of the exquisite synergism existing between numerous cellular components involved in cardiac Ca2+ signalling, and how these complex interactions may be used to design new anti-arrhythmic approaches that target multiple facets of RyR2 regulation.

Novel mutation in the SCN5A gene associated with arrhythmic storm development during acute myocardial infarction.

BACKGROUND: Ventricular tachycardia (VT) and ventricular fibrillation (VF) complicating Brugada syndrome, a genetic disorder linked to SCN5A mutations, and VF complicating acute myocardial infarction (AMI) both have been linked to phase 2 reentry. OBJECTIVE: Given the mechanistic similarities in arrhythmogenesis, the purpose of this study was to examine the contribution of SCN5A mutations to VT/VF complicating AMI. METHODS: Nineteen consecutive patients developing VF during AMI were enrolled in the study. Wild-type (WT) and mutant SCN5A genes were coexpressed with SCN1B in TSA201 cells and studied using whole-cell patch clamp techniques. RESULTS: Among the cohort of 19 patients, one missense mutation (G400A) in SCN5A was detected in a conserved region. An H558R polymorphism was detected on the same allele. Unlike the other 18 patients, who each developed 1-2 VF episodes during AMI, the mutation carrier developed six episodes of VT/VF within the first 12 hours. All VT/VF episodes were associated with ST-segment changes and were initiated by short-coupled extrasystoles. Flecainide and adenosine challenge performed to unmask Brugada and long QT syndromes both were negative. Peak G400A and G400A+H558R current were 70.7% and 88.4% less than WT current at -35 mV (P

Molecular and electrophysiological bases of catecholaminergic polymorphic ventricular tachycardia.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disorder characterized by adrenergically mediated polymorphic ventricular tachyarrhythmias. Genetic investigations have identified two variants of the disease: an autosomal dominant form associated with mutations in the gene encoding the cardiac ryanodine receptor (RyR2) and a recessive form associated with homozygous mutations in the gene encoding the cardiac isoform of calsequestrin (CASQ2). Functional characterization of mutations identified in the RyR2 and CASQ2 genes has demonstrated that CPVT are caused by derangements of the control of intracellular calcium. Investigations in a knock-in mouse model have shown that CPVT arrhythmias are initiated by delayed afterdepolarizations and triggered activity. In the present article, we review clinical and molecular understanding of CPVT and discuss the most recent approaches to develop novel therapeutic strategies for the disease.