Identification of large families in early repolarization syndrome

The proarrhythmogenic role of autonomics and emerging neuromodulation approaches to prevent sudden death in cardiac ion channelopathies

Ventricular arrhythmias in cardiac channelopathies are linked to autonomic triggers, which are sub-optimally targeted in current management strategies. Improved molecular understanding of cardiac channelopathies and cellular autonomic signalling could refine autonomic therapies to target the specific signalling pathways relevant to the specific aetiologies as well as the central nervous system centres involved in the cardiac autonomic regulation. This review summarizes key anatomical and physiological aspects of the cardiac autonomic nervous system and its impact on ventricular arrhythmias in primary inherited arrhythmia syndromes. Proarrhythmogenic autonomic effects and potential therapeutic targets in defined conditions including the Brugada syndrome, early repolarization syndrome, long QT syndrome, and catecholaminergic polymorphic ventricular tachycardia will be examined. Pharmacological and interventional neuromodulation options for these cardiac channelopathies are discussed. Promising new targets for cardiac neuromodulation include inhibitory and excitatory G-protein coupled receptors, neuropeptides, chemorepellents/attractants as well as the vagal and sympathetic nuclei in the central nervous system. Novel therapeutic strategies utilizing invasive and non-invasive deep brain/brain stem stimulation as well as the rapidly growing field of chemo-, opto-, or sonogenetics allowing cell-specific targeting to reduce ventricular arrhythmias are presented.

Early repolarization is independently associated with African-American race, younger age, higher BMI and lower heart rate

Background: Early repolarization (ER) is commonly seen in young adults. The goal of this study was to evaluate predictors of ER. Method: The authors used ECGs, available from 636 subjects, performed on healthy students for screening purposes. Results: The prevalence of ER was 13.5%. The prevalence of ER was higher in African-American subjects (48.0% vs 10.8%; odds ratio: 5.9; CI: 3.5-9.7; p < 0.0001), those with a BMI >25 (18.6% vs 11.7%; p = 0.02), those age <30 (16.4% vs 2.0%; p < 0.0001), male subjects (17.1% vs 8.3%; p = 0.001) and those with heart rate <70 (18.2% vs 9.2%; p = 0.001). With multivariate analysis, except gender, all other parameters remained significantly correlating with ER. Conclusion: The authors found younger age, African-American race, higher BMI and lower heart rate to be predictors of ER.

Genome-wide association studies of cardiac electrical phenotypes

The genetic basis of cardiac electrical phenotypes has in the last 25 years been the subject of intense investigation. While in the first years, such efforts were dominated by the study of familial arrhythmia syndromes, in recent years, large consortia of investigators have successfully pursued genome-wide association studies (GWAS) for the identification of single-nucleotide polymorphisms that govern inter-individual variability in electrocardiographic parameters in the general population. We here provide a review of GWAS conducted on cardiac electrical phenotypes in the last 14 years and discuss the implications of these discoveries for our understanding of the genetic basis of disease susceptibility and variability in disease severity. Furthermore, we review functional follow-up studies that have been conducted on GWAS loci associated with cardiac electrical phenotypes and highlight the challenges and opportunities offered by such studies.

Two siblings with early repolarization syndrome: clinical and genetic characterization by whole-exome sequencing

Aims 

The early repolarization syndrome (ERS) can cause ventricular fibrillation (VF) and sudden death in young, otherwise healthy individuals. There are limited data suggesting that ERS might be heritable. The aim of this study was to characterize the clinical phenotype and to identify a causal variant in an affected family using an exome-sequencing approach.

Methods and results 

Early repolarization syndrome was diagnosed according to the recently proposed Shanghai ERS Score. After sequencing of known ERS candidate genes, whole-exome sequencing (WES) was performed. The index patient (23 years, female) showed a dynamic inferolateral early repolarization (ER) pattern and electrical storm with intractable VF. Isoproterenol enabled successful termination of electrical storm with no recurrence on hydroquinidine therapy during 33 months of follow-up. The index patient’s brother (25 years) had a persistent inferior ER pattern with malignant features and a history of syncope. Both parents were asymptomatic and showed no ER pattern. While there was no pathogenic variant in candidate genes, WES detected a novel missense variant affecting a highly conserved residue (p. H2245R) in the ANK3 gene encoding Ankyrin-G in the two siblings and the father.

Conclusion 

We identified two siblings with a malignant ERS phenotype sharing a novel ANK3 variant. A potentially pathogenic role of the novel ANK3 variant is suggested by the direct interaction of Ankyrin-G with the cardiac sodium channel, however, more patients with ANK3 variants and ERS would be required to establish ANK3 as novel ERS susceptibility gene. Our study provides additional evidence that ERS might be a heritable condition.

Role of fragmented QRS and Shanghai score system in recurrence of ventricular fibrillation in patients with early repolarization syndrome

Background

The Shanghai Score System, which weighs electrocardiogram (ECG) findings reflecting repolarization abnormalities, has been proposed for diagnosis of early repolarization syndrome (ERS). However, recent studies have suggested the involvement of depolarization abnormalities in some ERS patients. The aim of this study was to validate the Shanghai Score System in predicting the recurrence of ventricular fibrillation (VF) in ERS patients. The predictive value of fragmented QRS (fQRS) was also investigated.

Methods

Fifteen consecutive ERS patients (14 males, median age of 47 years) with a history of VF were retrospectively reviewed. The Shanghai Score System points were calculated, and the presence of fQRS was evaluated.

Results

During the median follow‐up period of 79.2 months, five patients experienced VF recurrence. In the VF recurrence group, two patients showed augmented amplitude of J waves with horizontal ST‐segment, while the other three patients had dynamic changes in J‐wave amplitude. The Shanghai Score System points in the VF recurrence group were higher than those in the VF non‐recurrence group (6.5 [range: 5.8–6.8] vs. 4.5 [range: 4.0–4.5], p = 0.002). The presence of fQRS on standard 12‐lead ECG was more frequently observed in the VF recurrence group compared with the non‐recurrence group (100% vs. 10%, p = 0.002).

Conclusions

The present study demonstrated that the Shanghai Score System could effectively identify ERS patients at high risk for VF recurrence. The results also suggested that the presence of fQRS, a marker of depolarization abnormalities, may be useful for predicting VF recurrence in ERS patients.

Is Exercise Helpful or Harmful in Dealing With Specific Arrhythmia

Exercise is universally known to benefit health by lowering risk for cardiovascular disease and mortality. However, in patients with pre-existing cardiac conditions, including channelopathies, cardiomyopathies and coronary artery disease, exercise can cause sudden cardiac death (SCD). In this review, we explore exercise related risks and current recommendations for specific conditions. The risk of myocardial infarction (MI) during strenuous exercise in asymptomatic individuals with coronary artery disease is decreased with habitual exercise, especially if they have a normal ejection fraction and no ischemia. Furthermore, cardiac rehabilitation has been shown to be beneficial in heart failure. On the other hand, surgery is recommended for certain anomalous coronaries prior to engaging in vigorous activity. In addition, both exercise-induced disease progression and SCD in arrhythmogenic cardiomyopathy restrict ability to engage in competitive sports, as is the case in hypertrophic cardiomyopathy. Other diseases, like myocarditis only cause temporary risk for SCD. Previously considered benign, common conditions like early repolarization do increase SCD risk. Finally, certain gear including thicker chest protectors for athletes engaging in sports with hard, small spherical objects decrease risk of commotio cordis. While significant advances have been achieved in diagnosing and treating previously unrecognized conditions that predispose to sudden cardiac death, more research is needed to further tailor recommendations to allow beneficial exercise in those with rarer conditions that are under-represented in large systemic studies.

Heart Disease and Stroke Statistics-2020 Update: A Report From the American Heart Association

BACKGROUND

The American Heart Association, in conjunction with the National Institutes of Health, annually reports on the most up-to-date statistics related to heart disease, stroke, and cardiovascular risk factors, including core health behaviors (smoking, physical activity, diet, and weight) and health factors (cholesterol, blood pressure, and glucose control) that contribute to cardiovascular health. The Statistical Update presents the latest data on a range of major clinical heart and circulatory disease conditions (including stroke, congenital heart disease, rhythm disorders, subclinical atherosclerosis, coronary heart disease, heart failure, valvular disease, venous disease, and peripheral artery disease) and the associated outcomes (including quality of care, procedures, and economic costs).

METHODS

The American Heart Association, through its Statistics Committee, continuously monitors and evaluates sources of data on heart disease and stroke in the United States to provide the most current information available in the annual Statistical Update. The 2020 Statistical Update is the product of a full year's worth of effort by dedicated volunteer clinicians and scientists, committed government professionals, and American Heart Association staff members. This year's edition includes data on the monitoring and benefits of cardiovascular health in the population, metrics to assess and monitor healthy diets, an enhanced focus on social determinants of health, a focus on the global burden of cardiovascular disease, and further evidence-based approaches to changing behaviors, implementation strategies, and implications of the American Heart Association's 2020 Impact Goals.

RESULTS

Each of the 26 chapters in the Statistical Update focuses on a different topic related to heart disease and stroke statistics.

CONCLUSIONS

The Statistical Update represents a critical resource for the lay public, policy makers, media professionals, clinicians, healthcare administrators, researchers, health advocates, and others seeking the best available data on these factors and conditions.

A novel mutation in GPD1‑L associated with early repolarization syndrome via modulation of cardiomyocyte fast sodium currents

Early repolarization syndrome (ERS) is associated with genetic mutations, but the role of the glycerol‑3‑phosphate dehydrogenase 1‑like (GPD1‑L) mutation remains unclear. The aim of the present study was to investigate the role and potential underlying mechanism of GPD1‑L mutation P112L in the pathogenesis of ERS. Whole‑genome sequencing was performed on samples from a family with ERS, and the gene sequencing results were analyzed using bioinformatics. 293 cells were transfected with wild‑type (WT) or mutant‑type (MT) GPD1‑L and SCN5A plasmids. Successful transfection of GPD1‑L in 293 cells was verified by western blotting. Whole‑cell patch‑clamp recording, confocal microscopic observation and western blotting were used to uncover the potential mechanism of GPD1‑L P112L in ERS. The results of western blotting indicated that the expression of the GPD1‑L protein was lower in the MT group compared with that in the WT group, but the mock group did not express the GPD1‑L protein. The whole‑cell patch‑clamp recording results indicated that the activation current density of INa (at ‑30 mV) was ~60% lower in the MT group compared with the WT group (P<0.01). The mutation caused the inactivation voltage to move in a negative direction by ~3 mV compared with that of the WT group. However, there were no significant between‑group differences in the steady activation, steady inactivation, and steady recovery of INa. Confocal microscopy demonstrated that MT GPD1‑L was less expressed near the cell membrane and more expressed in the cytoplasm compared with WT GPD1‑L. Both WT and MT GPD1‑L were highly expressed in the cytoplasm and in small amounts in the nucleus. In conclusion, the GPD1‑L P112L mutation decreased INa activation and GPD1‑L cell expression, including in the region near the cell membrane. These results suggest that GPD1‑L P112L may be a pathogenic genetic mutation associated with ERS.

Epidemiology of inherited arrhythmias

The primary electrical disorders are a group of inherited cardiac ventricular arrhythmias that are a major cause of sudden cardiac death in young individuals. Inherited ventricular arrhythmias result from mutations in genes encoding cardiac ion channels or their modulatory subunits. Advances in genetic screening in the past three decades have led to the assembly of large patient cohorts with these disorders. Studies in these patients, as well as in the general population, have striven to define the prevalence of these inherited arrhythmias and the characteristics of patients with different genetic subtypes of the disease. In this Review, we provide a comprehensive update on the epidemiology of inherited ventricular arrhythmias, focusing on natural history, prevalence and patient demographics. In addition, we summarize the various founder populations (groups of individuals with a disease that is caused by a genetic defect inherited from a common ancestor) that have been identified for some of these disorders and which lead to increased prevalence in some geographical regions. To date, although numerous studies have markedly increased our understanding of the epidemiology of these disorders, demographic data, especially from non-Western countries, remain scarce. Furthermore, defining the true prevalence of these disorders remains challenging. International collaboration will undoubtedly accelerate the collection of demographic information and improve the accuracy of prevalence data.

Caring for the pregnant woman with an inherited arrhythmia syndrome

Pregnancy is a period of increased cardiovascular risk in a woman's life. In the setting of an inherited arrhythmia syndrome (IAS), cardiologists and obstetricians may be unfamiliar with cardiovascular optimization and risk stratification in pregnancy. Historically, there were little data addressing the safety of pregnancy in these rare disorders. Recent advances suggest that no type of IAS represents an absolute contraindication to pregnancy. However, it is imperative that obstetric and cardiovascular clinicians understand the major forms of IAS and how they affect the risks and course of pregnancy. This includes any disease-specific proarrhythmic triggers unique to pregnancy, such as the postpartum period in long QT syndrome (especially type 2), which poses the greatest risk of arrhythmias, and the adrenergic nature of labor and delivery, which is relevant to catecholaminergic polymorphic ventricular tachycardia. Fortunately, several effective antiarrhythmic options exist that pose little fetal risk. IAS-specific optimization of implantable cardioverter-defibrillator algorithms, drug therapy, and a maternal cardiac plan addressing the antepartum, labor, and delivery and postpartum periods reduces the risk. Where evidence does not exist, there are plausible mechanistic considerations to guide clinicians. To achieve optimal outcomes, early involvement of an expert pregnancy heart team comprising obstetrics, genetics, cardiology, and anesthesiology team members and a shared decision-making approach to IAS issues in pregnancy are needed.

A de novo gain-of-function KCND3 mutation in early repolarization syndrome

BACKGROUND

Early repolarization syndrome (ERS) is characterized by J-point elevation on electrocardiograms and ventricular fibrillation (VF). Early repolarization arises from augmentation of the transmural electrical gradient in the cardiac action potential; therefore, the transient outward potassium current (I_to) has been regarded as a key candidate current for elucidating the mechanism of ERS. KCND3 encoding Kv4.3, an α-subunit of the I_to channel, is considered as one of target genes.

OBJECTIVE

The purpose of this study was to search for novel KCND3 mutations associated with ERS and to clarify the pathogenesis.

METHODS

We performed genetic screening for 11 unrelated probands with ERS and analyzed the electrophysiological properties of detected mutations by patch-clamp methods.

RESULTS

A novel de novo KCND3 heterozygous mutation, Gly306Ala (c.917g>c), was found in 1 proband. The proband was a 12-year-old boy, who suffered VF storm and showed significant J-point elevation in multiple leads. Intravenous isoproterenol and subsequent administration of quinidine were effective in preventing VF recurrence and restored the J-point elevation. In electrophysiological analysis, cultured cells expressing mutant Kv4.3 showed significantly increased current densities, slow inactivation, and slow recovery from inactivation compared to wild type. Extracellular application of quinidine significantly restored the inactivation time course in mutant Kv4.3. A simulation study confirmed the relationship between the novel KCND3 mutation and early repolarization on electrocardiograms.

CONCLUSION

A novel KCND3 heterozygous mutation was found to be associated with ERS. The pathogenesis can be explained by the increased I_to. Genetic screening for KCND3 could be useful for understanding the pathogenesis and selecting effective treatment.

Role of ion channels in heart failure and channelopathies

Heart failure (HF) is a complication of multiple cardiac diseases and is characterized by impaired contractile and electric function. Patients with HF are not only limited by reduced contractile function but are also prone to life-threatening ventricular arrhythmias. HF itself leads to remodeling of ion channels, gap junctions, and intracellular calcium handling abnormalities that in combination with structural remodeling, e.g., fibrosis, produce a substrate for an arrhythmogenic disorders. Not only ventricular life-threatening arrhythmias contribute to increased morbidity and mortality but also atrial arrhythmias, especially atrial fibrillation (AF), are common in HF patients and contribute to morbidity and mortality. The distinct ion channel remodeling processes in HF and in channelopathies associated with HF will be discussed. Further basic research and clinical studies are needed to identify underlying molecular pathways of HF pathophysiology to provide the basis for improved patient care and individualized therapy based on individualized ion channel composition and remodeling.

J-Wave Syndromes: Electrocardiographic and Clinical Aspects

Early repolarization, Brugada syndrome, and pathologic J waves have been described for decades, but only recently experimental and clinical data have allowed reconciliation of Brugada and Early Repolarization under the common definition of J-wave syndromes. The concept was derived from studies showing, in both conditions, the presence of transmural dispersion of repolarization, localized conduction abnormalities, and abnormal transition between QRS and ST segment on electrocardiogram. Although several clinical studies have addressed the clinical presentation and epidemiology of J-wave syndromes, relevant knowledge gaps exist. Incomplete pathophysiologic understanding and uncertain electrocardiographic definitions limit effective risk stratification. Here, we review the current knowledge and recommendations for diagnosis and clinical management of these arrhythmogenic disorders.

The new kids on the block of arrhythmogenic disorders: Short QT syndrome and early repolarization

Short QT syndrome (SQTS) is one of the rarest inheritable cardiac channelopathies, characterized by an accelerated cardiac repolarization, which is also the substrate for the development of life-threatening ventricular arrhythmias. Up to this date, fewer than 200 SQTS cases have been reported in the literature worldwide. Patients with SQTS may experience a cardiac arrest as early as in the neonatal period or as late as 80 years old. The cumulative probability of experiencing a cardiac arrest by the fifth decade of life approaches 40%, highlighting the importance of early recognition and management. SQTS is an autosomal dominant disease with five identified causative genes, including three that encode for potassium channels (KCNH2, KCNQ1, and KCNJ2) and two that encode for subunits of the L-type calcium channels (CACNA1C and CACNB2). The term "early repolarization" (ER) has long been used to refer to a heterogeneous group of specific QRS-T junction patterns that are commonly found on the electrocardiograms of young healthy subjects. In the last decade, it has been suggested that in some individuals, the presence of ER may be associated with an increased risk of sudden cardiac death, and thus the term "early repolarization syndrome" (ERS) has progressively entered into use. Up to this point, however, whether ER constitutes a true primary arrhythmic disorder or whether it is simply a predisposing substrate that facilitates arrhythmias in the presence of other triggers remains an unresolved issue. In this review paper, we aim to integrate the current literature on SQTS and ERS. For each, we will describe the key steps that first led to the identification of the syndrome before moving into a discussion of our current understanding of each entity, including the epidemiology, genetics, diagnosis, clinical manifestations, and management.

Brugada Syndrome and Early Repolarisation: Distinct Clinical Entities or Different Phenotypes of the Same Genetic Disease?

Brugada and early repolarisation (ER) syndromes are currently considered two distinct inherited electrical disorders with overlapping clinical and electrocardiographic features. A considerable number of patients diagnosed with ER syndrome have a genetic mutation related to Brugada syndrome (BrS). Due to the high variable phenotypic manifestation, patients with BrS may present with inferolateral repolarisation abnormalities only, resembling the ER pattern. Moreover, the complex genotype-phenotype interaction in BrS can lead to the occurrence of mixed phenotypes with ER syndrome. The first part of this review focuses on specific clinical and electrocardiographic features of BrS and ER syndrome, highlighting the similarity shared by the two primary electrical disorders. The genetic background, with emphasis on the complexity of genotype-phenotype interaction, is explored in the second part of this review.

Electrocardiographic Abnormalities in Disease-Free Black South Africans and Correlations With Echocardiographic Indexes and Early Repolarization

Electrocardiographic abnormalities, and specifically early repolarization (ER) patterns, are increasingly found to be common variants in healthy populations free of heart disease or risk factors. Data are sparse in subjects of African descent, for which no increase in adverse cardiovascular outcomes have been demonstrated. A database of healthy disease-free adult volunteers of sub-Saharan African descent had 12 lead electrocardiograms (ECGs) and transthoracic echocardiograms performed. Statistical tests were then performed on the data to elicit associations; 396 volunteers (63.1% women) with a mean age of 37.4 years met the inclusion and exclusion criteria. An abnormal ECG was identified in 50.5% of volunteers, largely because of underlying ST elevation at the J point (ER), left ventricular hypertrophy (LVH) by voltage criteria, and T-wave inversion. Men were more likely to have abnormal ECGs (odds ratio [OR] 1.75; p <0.001), axes (OR 2.05; p = 0.023), display LVH by Sokolow-Lyon voltage criteria (OR 5.45; p <0.001), and have ER patterns (OR 11.61; p <0.001). Additionally, younger adults were also more likely to display LVH by voltage criteria and ER patterns. Volunteers with LVH by ECG had 5.7% higher LV mass indexes (p = 0.047). An abnormal ECG was not associated with a reduced left ventricular ejection fraction or diastolic dysfunction. ECG abnormalities, especially ER patterns, in black adults of Sub-Saharan descent are common, occurring in half of the normal adults.

12-lead electrocardiogram features of arrhythmic risk: A focus on early repolarization

The 12-lead electrocardiogram (ECG) is still the most used tool in cardiology clinical practice. Considering its easy accessibility, low cost and the information that it provides, it remains the starting point for diagnosis and prognosis. More specifically, its ability to detect prognostic markers for sudden cardiac death due to arrhythmias by identifying specific patterns that express electrical disturbances of the heart muscle, which may predispose to malignant arrhythmias, is universally recognized. Alterations in the ventricular repolarization process, identifiable on a 12-lead ECG, play a role in the genesis of ventricular arrhythmias in different cardiac diseases. The aim of this paper is to focus the attention on a new marker of arrhythmic risk, the early repolarization pattern in order to highlight the prognostic role of the 12-lead ECG.

Clinical Features of Genetic Cardiac Diseases Related to Potassium Channelopathies

Genetic cardiac diseases related to potassium channelopathies are a group of relatively rare syndromes that includes long QT syndrome, short QT syndrome, Brugada syndrome, and early repolarization syndrome. Patients with these syndromes share a propensity for the development of life-threatening ventricular arrhythmias in the absence of significant cardiac structural abnormalities. Familial atrial fibrillation has also been associated with potassium channel dysfunction but differs from the other syndromes by being a rare cause of a common condition. This article focuses on the clinical features, diagnosis, and management of these syndromes.

Sudden Cardiac Death Risk Stratification - An Update

Sudden cardiac death (SCD) remains a major public health problem worldwide, yet current methods to identify those at greatest risk are inadequate. High-risk individuals may benefit from potentially life-saving treatment, such as insertion of an implantable-cardioverter defibrillator (ICD). However, such treatments are expensive and have their own associated risks. Furthermore, most cases of SCD occur in the general adult population who may be relatively asymptomatic but yet have an underlying predisposition to SCD. Hence, there is great interest and clinical need in improving methods for risk stratification of SCD to identify those at greatest risk and implement the most appropriate treatment. This review provides an update on current risk-stratification methods for SCD in high-risk groups, in particular patients with reduced left ventricular function following acute myocardial infarction and those with non-ischaemic dilated cardiomyopathy, and highlights some novel methods that may have a role to play in future risk-stratification schemes. Approaches and challenges for SCD risk stratification among the general public are also discussed.

Genetics of sudden cardiac death

Sudden cardiac death occurs in a broad spectrum of cardiac pathologies and is an important cause of mortality in the general population. Genetic studies conducted during the past 20 years have markedly illuminated the genetic basis of the inherited cardiac disorders associated with sudden cardiac death. Here, we review the genetic basis of sudden cardiac death with a focus on the current knowledge on the genetics of the primary electric disorders caused primarily by mutations in genes encoding ion channels, and the cardiomyopathies, which have been attributed to mutations in genes encoding a broader category of proteins, including those of the sarcomere, the cytoskeleton, and desmosomes. We discuss the challenges currently faced in unraveling genetic factors that predispose to sudden cardiac death in the setting of sequela of coronary artery disease and present the genome-wide association studies conducted in recent years on electrocardiographic parameters, highlighting their potential in uncovering new biological insights into cardiac electric function.

Syncope in Hereditary Arrhythmogenic Syndromes

Since the discovery of the first mutation causing long QT syndrome (LQTS) in 1995, the field of hereditary arrhythmogenic syndromes has expanded greatly. Today, these syndromes include LQTS, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and short QT syndrome. There is also evidence suggesting that the newly described malignant early repolarization syndrome also has a genetic cause.

Early repolarization patterns associated with increased arrhythmic risk are common in young non-Caucasian Australian males and not influenced by athletic status

BACKGROUND

Early repolarization (ER) with a horizontal ST segment (ST-h) and high-amplitude J waves in the inferior leads is associated with an increased risk of cardiac arrhythmic death. The effect of ethnicity and athletic status on this increased-risk ER pattern has not been established. Aboriginal Australian/Torres Strait Islander and Pacific Islander/Maori (non-Caucasian [non-C]) subjects are well represented in Australian sport; however, the patterns and prevalence of ER in these populations are unknown.

OBJECTIVE

The purpose of this study was to assess the prevalence and effect of athletic activity on ER patterns in young non-C and Caucasian (C) subjects.

METHODS

Twelve-lead ECGs of 726 male athletes (23.8% non-C) and 170 male controls (45.9% non-C) aged 16-40 years were analyzed for the presence of ER, defined as J-point elevation (J wave, QRS slur, or discrete ST elevation) ≥0.1 mV in ≥2 inferior (II, III, aVF) or lateral (I, aVL,V4-V6) leads. ST morphology was coded as horizontal (ST-h) or ascending (ST-a). "Increased-risk ER" was defined as inferior ER with ST-h and J waves >2 mV.

RESULTS

Regardless of athletic status, ER and increased-risk ER were more prevalent in non-C than in C subjects (53.8% vs 32% and 7.6% vs 1.2%, respectively, P <.0001). Whereas lower heart rate, larger QRS voltage, and shorter QRS duration were predictors of ER, non-C ethnicity was the only independent predictor of increased-risk ER (odds ratio 17.621, 95% confidence interval 4.98-62.346, P < .0001).

CONCLUSION

ER patterns associated with increased arrhythmic risk are more common in young non-C than C subjects and were not influenced by athletic status. The long-term clinical significance of ER in these populations is yet to be determined.

Evaluation Of Patients With Early Repolarization Syndrome

In recent years, the early repolarization pattern has emerged as a risk factor for malignant ventricular arrhythmias and sudden cardiac death. The identification of the subset of patients who are at high risk of sudden death represents a significant challenge to the clinician. Multiple clinical and ECG features have been associated with an increased risk of sudden deathin however the majority of risk factors confer a small increase in absolute risk. The present article reviews current evidence and potential management strategies in patients with early repolarization.

Clinical aspects of inherited J-wave syndromes

Presence of J-point elevation with rapidly ascending ST segment in the anterior leads of the 12-lead electrocardiogram has been generally considered a benign phenomenon. The concept of benign nature of J-waves has changed as data emerged on variants of J-waves that were associated with the increased risk of sudden cardiac death. Two specific inherited arrhythmia syndromes, such as Brugada syndrome and early repolarization syndrome, have been recognized that carry an increased risk for ventricular fibrillation. The current review is aimed at discussing the clinical aspects of these syndromes and the implications of incidental recognition of the J-waves in a randomly recorded electrocardiogram of asymptomatic subjects.

Early repolarization pattern: its ECG characteristics, arrhythmogeneity and heritability

Early repolarization (ER) has been accepted as a benign ECG variant for decades. Two seminal studies challenged this notion and have demonstrated that ER pattern is associated with an increased risk of arrhythmic and cardiac mortality in patients with idiopathic ventricular fibrillation (IVF) and in the general population. Recent clinical studies demonstrate its varying impact as an arrhythmogenic substrate on different diseases. For example, in ER syndrome, a primary electrical disease, ER appears as a major arrhythmogenic substrate for development of VF whereas in patients with coronary artery disease, an ER pattern may exist as a silent substrate, increasing the risk of VF during episodes of cardiac ischaemia. Due to the high prevalence of an ER pattern in the general population and a low VF event rate, it remains challenging to differentiate a malignant ER pattern from a benign form. Recent research suggests that a J-wave amplitude of more than 0.1 mV combined with a descending/horizontal ST segment may constitute a malignant ER pattern. Further studies are however necessary to evaluate its prognostic value for cardiac and arrhythmic death in the general population as well as in cases with a malignant ER pattern. While genetic testing has revealed putative causal DNA variants in sporadic cases, the lack of co-segregation with the disease in affected families suggests that ER syndrome is not monogenic but is likely a complex disorder influenced by multiple genetic as well as environmental factors.

Cellular mechanism underlying hypothermia-induced ventricular tachycardia/ventricular fibrillation in the setting of early repolarization and the protective effect of quinidine, cilostazol, and milrinone

BACKGROUND

Hypothermia has been reported to induce ventricular tachycardia and fibrillation (VT/VF) in patients with early repolarization (ER) pattern. This study examines the cellular mechanisms underlying VT/VF associated with hypothermia in an experimental model of ER syndrome and examines the effectiveness of quinidine, cilostazol, and milrinone to prevent hypothermia-induced arrhythmias.

METHODS AND RESULTS

Transmembrane action potentials were simultaneously recorded from 2 epicardial and 1 endocardial site of coronary-perfused canine left ventricular wedge preparations, together with a pseudo-ECG. A combination of NS5806 (3-10 μmol/L) and verapamil (1 μmol/L) was used to pharmacologically model the genetic mutations responsible for ER syndrome. Acetylcholine (3 μmol/L) was used to simulate increased parasympathetic tone, which is known to promote ER. In controls, lowering the temperature of the coronary perfusate to induce mild hypothermia (32°C-34°C) resulted in increased J-wave area on the ECG and accentuated epicardial action potential notch but no arrhythmic activity. In the setting of ER, hypothermia caused further accentuation of the epicardial action potential notch, leading to loss of the action potential dome at some sites but not others, thus creating the substrate for development of phase 2 reentry and VT/VF. Addition of the transient outward current antagonist quinidine (5 μmol/L) or the phosphodiesterase III inhibitors cilostazol (10 μmol/L) or milrinone (5 μmol/L) diminished the ER manifestations and prevented the hypothermia-induced phase 2 reentry and VT/VF.

CONCLUSIONS

Hypothermia leads to VT/VF in the setting of ER by exaggerating repolarization abnormalities, leading to development of phase 2 reentry. Quinidine, cilostazol, and milrinone suppress the hypothermia-induced VT/VF by reversing the repolarization abnormalities.

Early repolarization syndrome: electrocardiographic signs and clinical implications

Early repolarization syndrome (ERS) was previously considered as a benign variant, but it has recently emerged as a risk marker for idiopathic ventricular fibrillation (VF) and sudden death. As measured by electrocardiogram (ECG), early repolarization is characterized by an elevation of the J point and/or ST segment from the baseline by at least 0.1 mV in at least two adjoining leads. In particular, early repolarization detected by inferior ECG leads was found to be associated with idiopathic VF and has been termed as ERS. This condition is mainly observed in young men, athletes, and blacks. Also, it has become evident that electrocardiographic territory, degree of J-point elevation, and ST-segment morphology are associated with different levels of risk for subsequent ventricular arrhythmia. However, it is unclear whether J waves are more strongly associated with a depolarization abnormality rather than a repolarization abnormality. Several clinical entities can cause ST-segment elevation. Therefore, clinical and ECG data are essential for differential diagnosis. At present, the data set is insufficient to allow risk stratification in asymptomatic individuals. ERS, idiopathic VF, and Brugada syndrome (known as J-wave syndromes) are three clinical conditions that share many common ECG features; however, their clinical consequences are remarkably different. This review summarizes the current electrocardiographic data concerning ERS with clinical implications.