Reversibility of PRKAG2 glycogen-storage cardiomyopathy and electrophysiological manifestations

Rare Variant in MRC2 Associated With Familial Supraventricular Tachycardia and Wolff-Parkinson-White Syndrome

BACKGROUND

Accessory pathways are a common cause of supraventricular tachycardia (SVT) and can lead to sudden cardiac death in otherwise healthy children and adults when associated with Wolff-Parkinson-White syndrome. The goal of this study was to identify genetic variants within a large family with structurally normal hearts affected by SVT and Wolff-Parkinson-White syndrome and determine causality of the gene deficit in a corresponding mouse model.

METHODS

Whole exome sequencing performed on 2 distant members of a 3-generation family in which multiple members were affected by SVT or Wolff-Parkinson-White pattern (preexcitation) on ECG identified MRC2 as a candidate gene. Serial electrocardiograms, intracardiac electrophysiology studies, echocardiography, optical mapping studies, and histology were performed on both Mrc2 mutant and WT (wild-type) mice.

RESULTS

A rare HET (heterozygous) missense variant c.2969A>G;p.Glu990Gly (E990G) in MRC2 was identified as the leading candidate gene variant segregating with the cardiac phenotype following an autosomal-dominant Mendelian trait segregation pattern with variable expressivity. In vivo electrophysiology studies revealed reentrant SVT in E990G mice. Optical mapping studies in E990G mice demonstrated abnormal retrograde conduction, suggesting the presence of an accessory pathway. Histological analysis of E990G mouse hearts showed a disordered ECM (extracellular matrix) in the annulus fibrosus. Finally, Mrc2 knockdown in human cardiac fibroblasts enhanced accelerated cell migration.

CONCLUSIONS

This study identified a rare nonsynonymous variant in the MRC2 gene in individuals with familial reentrant SVT, Wolff-Parkinson-White ECG pattern, and structurally normal hearts. Furthermore, Mrc2 knock-in mice revealed an increased incidence of reentrant SVT and bypass tract formation in the setting of preserved cardiac structure and function.

Revisiting Diagnosis and Treatment of Hypertrophic Cardiomyopathy: Current Practice and Novel Perspectives

Sarcomeric hypertrophic cardiomyopathy (HCM) is a prevalent genetic disorder characterised by left ventricular hypertrophy, myocardial disarray, and an increased risk of heart failure and sudden cardiac death. Despite advances in understanding its pathophysiology, treatment options for HCM remain limited. This narrative review aims to provide a comprehensive overview of current clinical practice and explore emerging therapeutic strategies for sarcomeric HCM, with a focus on cardiac myosin inhibitors. We first discuss the conventional management of HCM, including lifestyle modifications, pharmacological therapies, and invasive interventions, emphasizing their limitations and challenges. Next, we highlight recent advances in molecular genetics and their potential applications in refining HCM diagnosis, risk stratification, and treatment. We delve into emerging therapies, such as gene editing, RNA-based therapies, targeted small molecules, and cardiac myosin modulators like mavacamten and aficamten, which hold promise in modulating the underlying molecular mechanisms of HCM. Mavacamten and aficamten, selective modulators of cardiac myosin, have demonstrated encouraging results in clinical trials by reducing left ventricular outflow tract obstruction and improving symptoms in patients with obstructive HCM. We discuss their mechanisms of action, clinical trial outcomes, and potential implications for the future of HCM management. Furthermore, we examine the role of precision medicine in HCM management, exploring how individualised treatment strategies, including exercise prescription as part of the management plan, may optimise patient outcomes. Finally, we underscore the importance of multidisciplinary care and patient-centred approaches to address the complex needs of HCM patients. This review also aims to encourage further research and collaboration in the field of HCM, promoting the development of novel and more effective therapeutic strategies, such as cardiac myosin modulators, to hopefully improve the quality of life and outcome of patients with sarcomeric HCM.

Genome Editing and Cardiac Arrhythmias

This article reviews progress in the field of cardiac genome editing, in particular, its potential utility in treating cardiac arrhythmias. First, we discuss genome editing methods by which DNA can be disrupted, inserted, deleted, or corrected in cardiomyocytes. Second, we provide an overview of in vivo genome editing in preclinical models of heritable and acquired arrhythmias. Third, we discuss recent advancements in cardiac gene transfer, including delivery methods, gene expression optimization, and potential adverse effects associated with therapeutic somatic genome editing. While genome editing for cardiac arrhythmias is still in its infancy, this approach holds great promise, especially for inherited arrhythmia syndromes with a defined genetic defect.

Accessory pathways in monozygotic twins with different clinical phenotypes: a case report

Background

The atrioventricular reentrant tachycardia (AVRT) is the most common tachycardia associated with accessory pathways (APs). Although sporadic Wolff-Parkinson-White (WPW) syndrome has been well-described, AP occurrence in identical twins with WPW syndrome remains rarely reported.

Case presentation

We report a case of 14-year-old monozygotic twin brothers referred for an electrophysiology (EP) study. Twin A presented with recurrent symptomatic narrow complex tachycardia after exercise, noted for 3 years. His 12-lead surface electrocardiogram (ECG) did not show ventricular pre-excitation. However, an orthodromic AVRT utilizing a concealed right posteroseptal AP was found and successfully ablated. AVRT did not recur 12 months after the procedure. Twin B was asymptomatic. During his medical examination for firefighter volunteerism, his 12-lead ECG showed a spontaneous ventricular pre-excitation. EP study revealed a short anterograde right midseptal AP, which was then successfully eliminated by catheter ablation. His 12-lead ECG showed no ventricular pre-excitation recurrence 12 months after the procedure.

Conclusions

These identical twin brothers had a right-side AP in almost the same place but showed completely different phenotypes. This case clearly illustrates the difficulty in understanding genetic contribution in the origin of atrioventricular APs. Environmental exposure could play a role in their clinical presentations and AP electrophysiological properties.

Value of Electrocardiography to Distinguish Fabry Disease from Sarcomeric Hypertrophic Cardiomyopathy

Fabry disease (FD) is a rare genetic disorder that leads to left ventricular hypertrophy (LVH), frequently misdiagnosed as hypertrophic cardiomyopathy (HCM). We sought to assess the value of electrocardiography for distinguishing FD from HCM. We retrospectively reviewed and compared standard electrocardiograms and echocardiograms from 26 patients with FD and LVH and 33 sarcomeric patients with HCM, matched for gender, age, and degree of LVH. The mean age of patients with FD was 46 years (interquartile range) (28 to 53) and of HCM 50 (30 to 61) years (p = 0.27). Of them, 16 (61%) and 25 (76%) were male, respectively (p = 0.26). Indexed left ventricular mass was 166 g/m² in FD versus 181 g/m² in HCM (p = 0.88). All patients with FD and 30 (91%) with HCM were in sinus rhythm (p = 0.25). A higher prevalence of right bundle branch block (RBBB) was observed in FD (27%) versus HCM (6%) (p = 0.03). The PR interval was shorter in FD, 140 ms (120-160) versus 160 ms (140 to 180) (p = 0.004). P-wave duration was longer in patients with FD, 100 ms (80 to 120) versus 80 ms (80 to 100) (p = 0.01). The PQ interval (PR interval minus P-wave duration) was shorter in patients with FD, 40 ms (20 to 45) versus 80 ms (40 to 80) (p = 0.001). There were no differences regarding P-wave amplitude, QRS complex duration, corrected QT length, conduction or repolarization abnormalities, Sokolow-Lyon index, and Cornell index. After multivariate adjustments for RBBB, PR interval, P-wave duration, and PQ interval, a PQ interval ≤40 ms and RBBB were significantly associated with FD. In conclusion, there are electrocardiogram characteristics, such as the presence of RBBB or a PQ interval ≤40 ms, that may be helpful for screening and reducing the delay in FD diagnosis.

Identification of the pathogenic effects of missense variants causing PRKAG2 cardiomyopathy

BACKGROUND

Pathogenic missense variants in PRKAG2, the gene for the gamma 2 regulatory subunit of adenosine monophosphate-activated protein kinase (AMPK), cause severe progressive cardiac disease and sudden cardiac death, named PRKAG2 cardiomyopathy. In our previous study, we reported a E506K variant in the PRKAG2 gene that was associated with this disease. This study aimed to functionally characterize the three missense variants (E506K, E506Q, and R531G) of PRKAG2 and determine the possible effects on AMPK activity.

METHODS

The proband was clinically monitored for eight years. To investigate the functional effects of three missense variants of PRKAG2, in vitro mutagenesis experiments using HEK293 cells with wild and mutant transcripts and proteins were comparatively analyzed using quantitative RT-PCR, immunofluorescence staining, and enzyme-linked immunosorbent assay.

RESULTS

In the long-term follow-up, the proband was deceased due to progressive heart failure. In the in vitro experimental studies, PRKAG2 was overexpressed after 48 h of transfection in three mutated cells, after which the expression levels of PRKAG2 were regressed to the level of wild-type cells in 3-weeks stably transformed cells, except for the cells with E506K variant. E506K, E506Q, and R531G variants had caused a reduction in the AMPK activity and resulted in the formation of cytoplasmic glycogen deposits.

CONCLUSION

Three missense variants that alter AMPK activity affect a residue in the CBS4 domain associated with ATP/AMP-binding. Detailed information on the influence of PRKAG2 pathogenic variants on AMPK activity would be helpful to improve the treatment and management of patients with metabolic cardiomyopathy.

A New Perspective on the Quality of Life of Children with Glycogen Storage Diseases

PURPOSE

This study aimed to assess the quality of life (QoL) of children with glycogen storage disease (GSD) and their parents and to determine the impact of myopathies.

METHODS

A prospective case-control study was conducted at the Cairo University Children's Hospital and National Liver Institute, Menoufia University. A promising new style of questionnaire called the Stark Quality of Life Questionnaire was used to assess the quality of life.

RESULTS

Fifty-two children diagnosed with GSD (cases) and 55 age- and sex-matched healthy children (controls) were included. A statistically significant difference was found between cases and controls regarding food intake; mental behavior parameters such as mood, energy, and social contact; and physical behavior parameters such as running and tying shoelaces. Children with myopathies had significantly lower QoL scores in most of the parameters.

CONCLUSION

GSDs alter children and their parents' mental and physical abilities. Lower QoL scores were detected in children with both skeletal myopathy and cardiomyopathy, but the difference was not statistically significant when compared with the children without myopathies.

Echocardiographic characteristics of PRKAG2 syndrome: a research using three-dimensional speckle tracking echocardiography compared with sarcomeric hypertrophic cardiomyopathy

Background

PRKAG2 syndrome is a rare disease characterized as left ventricular hypertrophy (LVH), ventricular preexcitation syndrome, and sudden cardiac death. Its natural course, treatment, and prognosis were significantly different from sarcomeric hypertrophic cardiomyopathy (HCM). However, it is often clinically misdiagnosed as sarcomeric HCM. PRKAG2 patients tend to experience delayed treatment. The delay may lead to adverse outcomes. This study aimed to identify the echocardiographic parameters which can differentiate PRKAG2 syndrome from sarcomeric HCM.

Methods

Nine PRKAG2 patients with LVH, 41 HCM patients with sarcomere gene mutations, and 202 healthy volunteers were enrolled. Clinical characteristics, conventional echocardiography, and three-dimensional images were recorded, and reviewed by an attending cardiologist. We evaluated the parameters of left ventricular strains from three-dimensional speckle tracking echocardiography (3D STE) by TomTec software. Receiver operating characteristic (ROC) curves analysis was used to assess clinical and echocardiographic parameters’ differential diagnosis potential.

Results

The heart rate (HR) of the PRKAG2 group was significantly lower than both the healthy group (53.11 ± 10.14 vs. 69.22 ± 10.48 bpm, P < 0.001) and the sarcomeric HCM group (53.11 ± 10.14 vs. 67.23 ± 10.32 bpm, P = 0.001). The PRKAG2 group had similar interventricular septal thickness (IVS), posterior wall thickness (PWT), and maximum wall thickness (MWT) to the HCM group (P > 0.05). The absolute value of GLS in the PRKAG2 group was significantly higher than HCM patients (-18.92 ± 4.98 vs. -13.43 ± 4.30%, P = 0.004). SV calculated from EDV and ESV in PRKAG2 syndrome showed a higher value than sarcomeric HCM (61.83 ± 13.52 vs. 44.96 ± 17.53%, P = 0.020). The area under the ROC curve (AUC) for HR + GLS was 0.911 (0.803 -1). For HR + GLS, the sensitivity and specificity of the best cut-off value (0.114) were 69.0% and 100%, respectively.

Conclusions

PRKAG2 patients present deteriorated LV diastolic function and preserved LV systolic function. Bradycardia and preserved GLS are useful to identify PRKAG2 syndrome from sarcomeric HCM, which may be beneficial for clinical decision-making.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12947-022-00284-3.

Miniseries 1-Part IV: How frequent are fasciculo-ventricular connections in the normal heart?

AIMS

Seeking to account for accessory atrioventricular conduction potentially leading to ventricular pre-excitation, Mahaim in the mid-20th century had described pathways between the atrioventricular conduction axis and the muscular ventricular septum. We aimed to look for such 'paraspecific' connections in adult human hearts.

METHODS AND RESULTS

We serially sectioned 21 hearts, covering the triangle of Koch and the aortic root, and assessing the atrioventricular node, the penetration of the conduction axis, and the bundle branches in our search for fasciculo-ventricular connections. We also calculated the length of the non-branching bundle, and if present the origin of the fasciculo-ventricular connections. The non-branching bundle was 3.6 ± 1.7 mmin length, varying from 1.7 mm to 7.2 mm. Fasciculo-ventricular connections were found in more than half of the hearts, making direct contact with the muscular septum at an average of 3.5 ± 1.7 mm from the origin of the left bundle branch, with the site of origin varying from 1.1 mm to 5.5 mm from the first fascicle of the left bundle branch. In three hearts, additional fasciculo-fascicular connections were observed in the left bundle branch. Two loops were small, but one loop extended over 9.5 mm.

CONCLUSION

We endorse the finding of Mahaim that fasciculo-ventricular pathways exist in most human hearts. We presume the identified connections had the capability of producing ventricular pre-excitation. More studies are needed to determine the potential clinical manifestations.

Electrocardiographic Characteristics and Their Correlation with Echocardiographic Alterations in Fabry Disease

Fabry disease (FD) is an X-linked disorder with α-galactosidase A deficiency. Males (>30 years) and females (>40 years) often present with cardiac manifestations, predominantly left ventricular hypertrophy (LVH). The aim of this study was to evaluate electrocardiographic (ECG) characteristics within FD patients to identify gender related differences, and to additionally explore the association of ECG parameters with structural and functional alterations on transthoracic echocardiography (TTE). Retrospective cross-sectional analysis of 45 FD patients with contemporaneous ECG and TTE was performed and compared to age and gender matched healthy controls. FD patients demonstrated alterations in several ECG parameters particularly in males, including prolonged P-wave duration (91 vs. 81 ms, p = 0.022), prolonged QRS duration (96 vs. 84 ms, p < 0.001), increased R-wave amplitude in lead I (8.1 vs. 5.7 mV, p = 0.047), increased Sokolow–Lyon index (25 vs. 19 mV, p = 0.002) and were more likely to meet LVH criteria (31% vs. 7%, p = 0.006). FD patients with impaired basal longitudinal strain (LS) on TTE were more likely to meet LVH criteria (41% vs. 0%, p = 0.018). Those with more advanced FD (increased LV wall thickness on TTE) were more likely to meet LVH criteria but additionally demonstrated prolonged ventricular depolarization (QRS duration 101 vs. 88 ms, p = 0.044). Therefore, alterations on ECG demonstrating delayed atrial activation, delayed ventricular depolarization and evidence of LVH were more often seen in male FD patients. Impaired basal LS, a TTE marker of early cardiac involvement, correlated with ECG abnormalities. Increased LV wall thickness on TTE, a marker of more advanced FD, was associated with more severe ECG abnormalities.

LAMP2 Cardiomyopathy: Consequences of Impaired Autophagy in the Heart

Background

Human mutations in the X‐linked lysosome‐associated membrane protein‐2 (LAMP2) gene can cause a multisystem Danon disease or a primary cardiomyopathy characterized by massive hypertrophy, conduction system abnormalities, and malignant ventricular arrhythmias. We introduced an in‐frame LAMP2 gene exon 6 deletion mutation (denoted L2^Δ6) causing human cardiomyopathy, into mouse LAMP2 gene, to elucidate its consequences on cardiomyocyte biology. This mutation results in in‐frame deletion of 41 amino acids, compatible with presence of some defective LAMP2 protein.

Methods and Results

Left ventricular tissues from L2^Δ6 and wild‐type mice had equivalent amounts of LAMP2 RNA, but a significantly lower level of LAMP2 protein. By 20 weeks of age male mutant mice developed left ventricular hypertrophy which was followed by left ventricular dilatation and reduced systolic function. Cardiac electrophysiology and isolated cardiomyocyte studies demonstrated ventricular arrhythmia, conduction disturbances, abnormal calcium transients and increased sensitivity to catecholamines. Myocardial fibrosis was strikingly increased in 40‐week‐old L2^Δ6 mice, recapitulating findings of human LAMP2 cardiomyopathy. Immunofluorescence and transmission electron microscopy identified mislocalization of lysosomes and accumulation of autophagosomes between sarcomeres, causing profound morphological changes disrupting the cellular ultrastructure. Transcription profile and protein expression analyses of L2^Δ6 hearts showed significantly increased expression of genes encoding activators and protein components of autophagy, hypertrophy, and apoptosis.

Conclusions

We suggest that impaired autophagy results in cardiac hypertrophy and profound transcriptional reactions that impacted metabolism, calcium homeostasis, and cell survival. These responses define the molecular pathways that underlie the pathology and aberrant electrophysiology in cardiomyopathy of Danon disease.

Fabry Disease and the Heart: A Comprehensive Review

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by mutations of the GLA gene that result in a deficiency of the enzymatic activity of α-galactosidase A and consequent accumulation of glycosphingolipids in body fluids and lysosomes of the cells throughout the body. GB3 accumulation occurs in virtually all cardiac cells (cardiomyocytes, conduction system cells, fibroblasts, and endothelial and smooth muscle vascular cells), ultimately leading to ventricular hypertrophy and fibrosis, heart failure, valve disease, angina, dysrhythmias, cardiac conduction abnormalities, and sudden death. Despite available therapies and supportive treatment, cardiac involvement carries a major prognostic impact, representing the main cause of death in FD. In the last years, knowledge has substantially evolved on the pathophysiological mechanisms leading to cardiac damage, the natural history of cardiac manifestations, the late-onset phenotypes with predominant cardiac involvement, the early markers of cardiac damage, the role of multimodality cardiac imaging on the diagnosis, management and follow-up of Fabry patients, and the cardiac efficacy of available therapies. Herein, we provide a comprehensive and integrated review on the cardiac involvement of FD, at the pathophysiological, anatomopathological, laboratory, imaging, and clinical levels, as well as on the diagnosis and management of cardiac manifestations, their supportive treatment, and the cardiac efficacy of specific therapies, such as enzyme replacement therapy and migalastat.

Cardiometabolism as an Interlocking Puzzle between the Healthy and Diseased Heart: New Frontiers in Therapeutic Applications

Cardiac metabolism represents a crucial and essential connecting bridge between the healthy and diseased heart. The cardiac muscle, which may be considered an omnivore organ with regard to the energy substrate utilization, under physiological conditions mainly draws energy by fatty acids oxidation. Within cardiomyocytes and their mitochondria, through well-concerted enzymatic reactions, substrates converge on the production of ATP, the basic chemical energy that cardiac muscle converts into mechanical energy, i.e., contraction. When a perturbation of homeostasis occurs, such as an ischemic event, the heart is forced to switch its fatty acid-based metabolism to the carbohydrate utilization as a protective mechanism that allows the maintenance of its key role within the whole organism. Consequently, the flexibility of the cardiac metabolic networks deeply influences the ability of the heart to respond, by adapting to pathophysiological changes. The aim of the present review is to summarize the main metabolic changes detectable in the heart under acute and chronic cardiac pathologies, analyzing possible therapeutic targets to be used. On this basis, cardiometabolism can be described as a crucial mechanism in keeping the physiological structure and function of the heart; furthermore, it can be considered a promising goal for future pharmacological agents able to appropriately modulate the rate-limiting steps of heart metabolic pathways.

Hypertrophic Cardiomyopathy in Children: Pathophysiology, Diagnosis, and Treatment of Non-sarcomeric Causes

Hypertrophic cardiomyopathy (HCM) is a myocardial disease characterized by left ventricular hypertrophy not solely explained by abnormal loading conditions. Despite its rare prevalence in pediatric age, HCM carries a relevant risk of mortality and morbidity in both infants and children. Pediatric HCM is a large heterogeneous group of disorders. Other than mutations in sarcomeric genes, which represent the most important cause of HCM in adults, childhood HCM includes a high prevalence of non-sarcomeric causes, including inherited errors of metabolism (i.e., glycogen storage diseases, lysosomal storage diseases, and fatty acid oxidation disorders), malformation syndromes, neuromuscular diseases, and mitochondrial disease, which globally represent up to 35% of children with HCM. The age of presentation and the underlying etiology significantly impact the prognosis of children with HCM. Moreover, in recent years, different targeted approaches for non-sarcomeric etiologies of HCM have emerged. Therefore, the etiological diagnosis is a fundamental step in designing specific management and therapy in these subjects. The present review aims to provide an overview of the non-sarcomeric causes of HCM in children, focusing on the pathophysiology, clinical features, diagnosis, and treatment of these rare disorders.

Familial Atrial Enlargement, Conduction Disorder and Symmetric Cardiac Hypertrophy Are Early Signs of PRKAG2 R302Q

PRKAG2 cardiac syndrome (PS) is a rare inherited disease due to PRKAG2 gene mutation and characterized by Wolff-Parkinson-White syndrome (WPWs), conduction system lesions and myocardial hypertrophy. It can also lead to serious consequences, such as sudden death. But the genetic and clinical heterogeneity makes the early diagnosis of PS difficult. Here we studied a family with familial hypertrophic cardiomyopathy and other diverse manifestations. Gene analysis identified a missense mutation (Arg302Gln) in the five affected subjects of the family. The electrocardiograph performance of the five was composed of sinus bradycardia (SB), WPWs, right bundle branch block (RBBB), atrioventricular block (AVB), left bundle branch block (LBBB), supraventricular tachycardia (SVT) and atrial premature beat (APB). Among them, the youngest one began to show paroxysmal palpitation at the age of nine and was confirmed to have WPWs at 17 years old; two members progressed over time to serious conduction damage, and the proband received a pacemaker at the age of 27 due to AVB. Besides, according to cardiac magnetic resonance and echocardiography, the youngest one showed symmetric hypertrophy; three older members showed asymmetric myocardial hypertrophy characterized with a diffuse pattern of middle-anterior-lateral-inferior wall hypertrophy and especially interventricular septal hypertrophy; all five affected patients showed atrial enlargement regardless of myocardial hypertrophy at an earlier stage. In conclusion, the conduction system disorder, familial atrial enlargement and symmetric cardiac hypertrophy may occur in the early stage of PRKAG2 R302Q mutation.

Cardiac sodium-dependent glucose cotransporter 1 is a novel mediator of ischaemia/reperfusion injury

AIMS

We previously reported that sodium-dependent glucose cotransporter 1 (SGLT1) is highly expressed in cardiomyocytes and is further up-regulated in ischaemia. This study aimed to determine the mechanisms by which SGLT1 contributes to ischaemia/reperfusion (I/R) injury.

METHODS AND RESULTS

Mice with cardiomyocyte-specific knockdown of SGLT1 (TGSGLT1-DOWN) and wild-type controls were studied. In vivo, the left anterior descending coronary artery was ligated for 30 min and reperfused for 48 h. Ex vivo, isolated perfused hearts were exposed to 20 min no-flow and up to 2 h reperfusion. In vitro, HL-1 cells and isolated adult murine ventricular cardiomyocytes were exposed to 1 h hypoxia and 24 h reoxygenation (H/R). We found that TGSGLT1-DOWN hearts were protected from I/R injury in vivo and ex vivo, with decreased infarct size, necrosis, dysfunction, and oxidative stress. 5'-AMP-activated protein kinase (AMPK) activation increased SGLT1 expression, which was abolished by extracellular signal-related kinase (ERK) inhibition. Co-immunoprecipitation studies showed that ERK, but not AMPK, interacts directly with SGLT1. AMPK activation increased binding of the hepatocyte nuclear factor 1 and specificity protein 1 transcription factors to the SGLT1 gene, and HuR to SGLT1 mRNA. In cells, up-regulation of SGLT1 during H/R was abrogated by AMPK inhibition. Co-immunoprecipitation studies showed that SGLT1 interacts with epidermal growth factor receptor (EGFR), and EGFR interacts with protein kinase C (PKC). SGLT1 overexpression activated PKC and NADPH oxidase 2 (Nox2), which was attenuated by PKC inhibition, EGFR inhibition, and/or disruption of the interaction between EGFR and SGLT1.

CONCLUSION

During ischaemia, AMPK up-regulates SGLT1 through ERK, and SGLT1 interacts with EGFR, which in turn increases PKC and Nox2 activity and oxidative stress. SGLT1 may represent a novel therapeutic target for mitigating I/R injury.

Wolff-Parkinson-White syndrome: De novo variants and evidence for mutational burden in genes associated with atrial fibrillation

BACKGROUND

Wolff-Parkinson-White (WPW) syndrome is a relatively common arrhythmia affecting ~1-3/1,000 individuals. Mutations in PRKAG2 have been described in rare patients in association with cardiomyopathy. However, the genetic basis of WPW in individuals with a structurally normal heart remains poorly understood. Sudden death due to atrial fibrillation (AF) can also occur in these individuals. Several studies have indicated that despite ablation of an accessory pathway, the risk of AF remains high in patients compared to general population.

METHODS

We applied exome sequencing in 305 subjects, including 65 trios, 80 singletons, and 6 multiple affected families. We used de novo analysis, candidate gene approach, and burden testing to explore the genetic contributions to WPW.

RESULTS

A heterozygous deleterious variant in PRKAG2 was identified in one subject, accounting for 0.6% (1/151) of the genetic basis of WPW in this study. Another individual with WPW and left ventricular hypertrophy carried a known pathogenic variant in MYH7. We found rare de novo variants in genes associated with arrhythmia and cardiomyopathy (ANK2, NEBL, PITX2, and PRDM16) in this cohort. There was an increased burden of rare deleterious variants (MAF ≤ 0.005) with CADD score ≥ 25 in genes linked to AF in cases compared to controls (P = .0023).

CONCLUSIONS

Our findings show an increased burden of rare deleterious variants in genes linked to AF in WPW syndrome, suggesting that genetic factors that determine the development of accessory pathways may be linked to an increased susceptibility of atrial muscle to AF in a subset of patients.

Metabolic Alterations in Inherited Cardiomyopathies

The normal function of the heart relies on a series of complex metabolic processes orchestrating the proper generation and use of energy. In this context, mitochondria serve a crucial role as a platform for energy transduction by supplying ATP to the varying demand of cardiomyocytes, involving an intricate network of pathways regulating the metabolic flux of substrates. The failure of these processes results in structural and functional deficiencies of the cardiac muscle, including inherited cardiomyopathies. These genetic diseases are characterized by cardiac structural and functional anomalies in the absence of abnormal conditions that can explain the observed myocardial abnormality, and are frequently associated with heart failure. Since their original description, major advances have been achieved in the genetic and phenotype knowledge, highlighting the involvement of metabolic abnormalities in their pathogenesis. This review provides a brief overview of the role of mitochondria in the energy metabolism in the heart and focuses on metabolic abnormalities, mitochondrial dysfunction, and storage diseases associated with inherited cardiomyopathies.

Molecular and genetic insights into progressive cardiac conduction disease

Progressive cardiac conduction disease (PCCD) is often a primarily genetic disorder, with clinical and genetic overlaps with other inherited cardiac and metabolic diseases. A number of genes have been implicated in PCCD pathogenesis with or without structural heart disease or systemic manifestations. Precise genetic diagnosis contributes to risk stratification, better selection of specific therapy and allows familiar cascade screening. Cardiologists should be aware of the different phenotypes emerging from different gene-mutations and the potential risk of sudden cardiac death. Genetic forms of PCCD often overlap or coexist with other inherited heart diseases or manifest in the context of multisystem syndromes. Despite the significant advances in the knowledge of the genetic architecture of PCCD and overlapping diseases, in a measurable fraction of PCCD cases, including in familial clustering of disease, investigations of known cardiac disease-associated genes fail to reveal the underlying substrate, suggesting that new causal genes are yet to be discovered. Here, we provide insight into genetics and molecular mechanisms of PCCD and related diseases. We also highlight the phenotypic overlaps of PCCD with other inherited cardiac and metabolic diseases, present unmet challenges in clinical practice, and summarize the available therapeutic options for affected patients.

Single cell transcriptomics based-MacSpectrum reveals novel macrophage activation signatures in diseases

Adipose tissue macrophages (ATM) are crucial for maintaining adipose tissue homeostasis and mediating obesity-induced metabolic abnormalities, including prediabetic conditions and type 2 diabetes mellitus. Despite their key functions in regulating adipose tissue metabolic and immunologic homeostasis under normal and obese conditions, a high-resolution transcriptome annotation system that can capture ATM multifaceted activation profiles has not yet been developed. This is primarily attributed to the complexity of their differentiation/activation process in adipose tissue and their diverse activation profiles in response to microenvironmental cues. Although the concept of multifaceted macrophage action is well-accepted, no current model precisely depicts their dynamically regulated in vivo features. To address this knowledge gap, we generated single-cell transcriptome data from primary bone marrow-derived macrophages under polarizing and non-polarizing conditions to develop new high-resolution algorithms. The outcome was creation of a two-index platform, MacSpectrum (https://macspectrum.uconn.edu), that enables comprehensive high-resolution mapping of macrophage activation states from diverse mixed cell populations. MacSpectrum captured dynamic transitions of macrophage subpopulations under both in vitro and in vivo conditions. Importantly, MacSpectrum revealed unique "signature" gene sets in ATMs and circulating monocytes that displayed significant correlation with BMI and homeostasis model assessment of insulin resistance (HOMA-IR) in obese human patients. Thus, MacSpectrum provides unprecedented resolution to decode macrophage heterogeneity and will open new areas of clinical translation.

Cardiac manifestations of PRKAG2 mutation

Background

The Protein Kinase AMP-Activated Non-Catalytic Subunit Gamma 2 (PRKAG2) cardiac syndrome is characterized by glycogen accumulation in the cardiac tissue. The disease presents clinically with hypertrophic cardiomyopathy (HCM), and it is often associated with conduction abnormalities.

Case presentation

A 23 year-old female with history of Wolff-Parkinson-White (WPW) and HCM presented for evaluation after an episode of Non-ST Elevation Myocardial Infarction (NSTEMI). The patient was found to have severe coronary bridging on angiography and underwent an unroofing of the left anterior descending artery (LAD). Due to the constellation of symptoms, the patient underwent genetic testing and a cardiac muscle biopsy. Genetic testing was significant for an Arg302Gln mutation in the PRKAG2 gene. Cardiac tissue biopsy revealed significant myocyte hypertrophy and large vacuoles with glycogen stores.

Conclusion

The pathologic and genetics findings of our patient are consistent with PRKAG2 syndrome. Patients presenting with conduction abnormalities and suspected HCM should be considered for genetic testing to identify possible underlying genetic etiologies.

Human γ2-AMPK Mutations

In humans, dominant mutations in the gene encoding the regulatory γ2-subunit of AMP-activated protein kinase (PRKAG2) result in a highly penetrant phenotype dominated by cardiac features: left ventricular hypertrophy, ventricular pre-excitation, atrial tachyarrhythmia, cardiac conduction disease, and myocardial glycogen storage. The discovery of a link between the cell's fundamental energy sensor, AMPK, and inherited cardiac disease catalyzed intense interest into the biological role of AMPK in the heart. In this chapter, we provide an introduction to the spectrum of human disease resulting from pathogenic variants in PRKAG2, outlining its discovery, clinical genetics, and current perspectives on its pathogenesis and highlighting mechanistic insights derived through the evaluation of disease models. We also present a clinical perspective on the major components of the cardiomyopathy associated with mutations in PRKAG2, together with less commonly described extracardiac features, its prognosis, and principles of management.

Systemic pan-AMPK activator MK-8722 improves glucose homeostasis but induces cardiac hypertrophy

5'-Adenosine monophosphate-activated protein kinase (AMPK) is a master regulator of energy homeostasis in eukaryotes. Despite three decades of investigation, the biological roles of AMPK and its potential as a drug target remain incompletely understood, largely because of a lack of optimized pharmacological tools. We developed MK-8722, a potent, direct, allosteric activator of all 12 mammalian AMPK complexes. In rodents and rhesus monkeys, MK-8722-mediated AMPK activation in skeletal muscle induced robust, durable, insulin-independent glucose uptake and glycogen synthesis, with resultant improvements in glycemia and no evidence of hypoglycemia. These effects translated across species, including diabetic rhesus monkeys, but manifested with concomitant cardiac hypertrophy and increased cardiac glycogen without apparent functional sequelae.

Genetic Determinants of Hereditary Bradyarrhythmias: A Contemporary Review of a Diverse Group of Disorders

Bradyarrhythmia is a common clinical presentation. Although the majority of cases are acquired, genetic screening of families with bradyarrhythmia has led to the discovery of a growing number of causative hereditary mutations. These mutations can interfere with any of the steps required for the occurrence of each cardiac cycle, including generation of an action potential in the sinoatrial node, successful exit of the action potential from the node, propagation of the action potential throughout the atria until the depolarization waves reach the atrioventricular node, and finally transmission of the action potential to the ventricles through the His-Purkinje system. As expected, channelopathies are the predominant culprit for hereditary bradyarrhythmias, because they play a crucial role in action potential generation and propagation. Interestingly, there are an increasing number of genes that encode for various regulatory or structural cellular components that have been linked to hereditary bradyarrhythmias. Furthermore, population-based genetic screening has revealed that age-related conduction defects may in fact be caused by genetic predispositions rather than the simple process of aging. With recent advances in genetic testing and the creation of animal models, not only have we discovered new culprit genes but it has also has become evident that there are still significant gaps in our knowledge of cardiac pathophysiology. In this review, we discuss the clinical presentations of known hereditary bradyarrhythmias and their associated conditions in addition to detailing our current molecular understanding of the mechanisms by which they are manifested.

Reversible transition from a hypertrophic to a dilated cardiomyopathy

We report the case of a 17‐year‐old female patient with known hypertrophic cardiomyopathy and a Wolff‐Parkinson‐White syndrome. She came to our department for further evaluation of a new diagnosed dilated cardiomyopathy characterized by an enlargement of the left ventricle and a fall in ejection fraction. Clinically, she complained about atypical chest pain, arrhythmic episodes with presyncopal events, and dyspnea (NYHA III) during the last 6 months. Non‐invasive and invasive examinations including magnetic resonance imaging, electrophysiological examinations, and angiography did not lead to a conclusive diagnosis. Therefore, endomyocardial biopsies (EMBs) were taken to investigate whether a specific myocardial disease caused the impairment of the left ventricular function. EMB analysis resulted in the diagnosis of a virus‐negative, active myocarditis. Based on this diagnosis, an immunosuppressive treatment with prednisolone and azathioprine was started, which led to an improvement of cardiac function and symptoms within 3 months after initiating therapy. In conclusion, we show that external stress triggered by myocarditis can induce a reversible transition from a hypertrophic cardiomyopathy to a dilated cardiomyopathy phenotype. This case strongly underlines the need for a thorough and invasive examination of heart failure of unknown causes, including EMB investigations as recommend by the actual ESC position statement.

Genome editing with CRISPR/Cas9 in postnatal mice corrects PRKAG2 cardiac syndrome

PRKAG2 cardiac syndrome is an autosomal dominant inherited disease resulted from mutations in the PRKAG2 gene that encodes γ2 regulatory subunit of AMP-activated protein kinase. Affected patients usually develop ventricular tachyarrhythmia and experience progressive heart failure that is refractory to medical treatment and requires cardiac transplantation. In this study, we identify a H530R mutation in PRKAG2 from patients with familial Wolff-Parkinson-White syndrome. By generating H530R PRKAG2 transgenic and knock-in mice, we show that both models recapitulate human symptoms including cardiac hypertrophy and glycogen storage, confirming that the H530R mutation is causally related to PRKAG2 cardiac syndrome. We further combine adeno-associated virus-9 (AAV9) and the CRISPR/Cas9 gene-editing system to disrupt the mutant PRKAG2 allele encoding H530R while leaving the wild-type allele intact. A single systemic injection of AAV9-Cas9/sgRNA at postnatal day 4 or day 42 substantially restores the morphology and function of the heart in H530R PRKAG2 transgenic and knock-in mice. Together, our work suggests that in vivo CRISPR/Cas9 genome editing is an effective tool in the treatment of PRKAG2 cardiac syndrome and other dominant inherited cardiac diseases by selectively disrupting disease-causing mutations.

Electrocardiographic Changes and Arrhythmia in Fabry Disease

Fabry disease is an X-chromosome-linked lysosomal storage disease characterized by a deficient activity or, in most males, absence of the enzyme α-galactosidase A (a-Gal A) leading to systemic, primary lysosomal accumulation of globotriaosylceramide (Gb3) (1). Recent literature refers to an overall birth prevalence of 1:40,000–170,000; however, such data do not allow an estimation on an actual patient number suffering from Fabry disease (2). Multisystem morbidity commonly develops in childhood and, with progression of the disease, life-threatening complications often occur in adulthood, including renal failure, cardiovascular dysfunction, neuropathy, and stroke (3–6). Life expectancy is reduced by an average of 15 years in female patients and 20 years in male patients (7, 8). The pathognomonic Gb3 accumulation has been repeatedly observed over the past decades by many groups in vascular endothelial and smooth muscle cells, cardiomyocytes, cardiac conduction tissue, and valvular fibroblasts (3). Although incompletely described, it is likely that inflammatory and neurohormonal mechanisms are involved in subsequent cellular and vascular dysfunction, leading to tissue ischemia, hypertrophy, and fibrosis (9). Furthermore, recently published works on cardiomyocyte dysfunction and conduction tissue involvement have suggested that cardiac dysfunction may reflect increased myocardial nitric oxide production with oxidative damage of cardiomyocyte myofilaments and DNA, causing cell dysfunction and death, and accelerated conduction with prolonged refractoriness and electric instability (10, 11).

Mimics of Hypertrophic Cardiomyopathy - Diagnostic Clues to Aid Early Identification of Phenocopies

Hypertrophic cardiomyopathy (HCM) is the most common genetic cause of cardiomyopathy worldwide. Significant advances and widespread availability of genetic testing have improved detection of the sarcomeric mutations that cause HCM, but have also highlighted the significance of inborn errors of metabolism (IEM) or metabolic storage disorders that can mimic HCM ('HCM phenocopies'). These conditions cannot always be reliably differentiated on the basis of imaging alone. Whilst HCM phenocopies are relatively rare, it is crucial to distinguish these conditions at an early stage as their natural history, management and prognosis vary significantly from that of HCM with sarcomeric mutations. This review illustrates the salient features of HCM phenocopies and stresses the need for a high level of suspicion for these conditions in the assessment of cardiac hypertrophy.

Animal Models to Study AMPK

AMPK is an evolutionary conserved energy sensor involved in the regulation of energy metabolism. Based on biochemical studies, AMPK has brought much of interest in recent years due to its potential impact on metabolic disorders. Suitable animal models are therefore essential to promote our understanding of the molecular and functional roles of AMPK but also to bring novel information for the development of novel therapeutic strategies. The organism systems include pig (Sus scrofa), mouse (Mus musculus), fly (Drosophila melanogaster), worm (Caenorhabditis elegans), and fish (Danio rerio) models. These animal models have provided reliable experimental evidence demonstrating the crucial role of AMPK in the regulation of metabolism but also of cell polarity, autophagy, and oxidative stress. In this chapter, we update the new development in the generation and application of animal models for the study of AMPK biology. We also discuss recent breakthroughs from studies in mice, flies, and worms showing how AMPK has a primary role in initiating or promoting pathological or beneficial impact on health.

The Genetic Challenges and Opportunities in Advanced Heart Failure

The causes of heart failure are diverse. Inherited causes represent an important clinical entity and can be divided into 2 major categories: familial and metabolic cardiomyopathies. The distinct features that might be present in early disease states can become broadly overlapping with other diseases, such as in the case of inherited cardiomyopathies (ie, familial hypertrophic cardiomyopathy or mitochondrial diseases). In this review article, we focus on genetic issues related to advanced heart failure. Because of the emerging importance of this topic and its breadth, we sought to focus our discussion on the known genetic forms of heart failure syndromes, genetic testing, and newer data on pharmacogenetics and therapeutics in the treatment of heart failure, to primarily encourage clinicians to place a priority on the diagnosis and treatment of these potentially treatable conditions.

PRKAG2 mutation: An easily missed cardiac specific non-lysosomal glycogenosis

Mutations in PRKAG2 gene that regulates the γ2 subunit of the adenosine monophosphate (AMP) dependent protein kinase have been associated with the development of atrioventricular (AV) accessory pathways, cardiac hypertrophy, and conduction system abnormalities. These patients can potentially be misdiagnosed as hypertrophic cardiomyopathy (HOCM) and/or Wolf-Parkinson White (WPW) syndrome due to similar clinical phenotype. Early recognition of this disease entity is very important as ablation of suspected accessory pathways is not effective and the natural history of the disease is very different from HOCM and WPW syndrome.

AMP-activated protein kinase: a key regulator of energy balance with many roles in human disease

The AMP-activated protein kinase (AMPK) is a sensor of cellular energy status that regulates cellular and whole-body energy balance. A recently reported crystal structure has illuminated the complex regulatory mechanisms by which AMP and ADP cause activation of AMPK, involving phosphorylation by the upstream kinase LKB1. Once activated by falling cellular energy status, AMPK activates catabolic pathways that generate ATP whilst inhibiting anabolic pathways and other cellular processes that consume ATP. A role of AMPK is implicated in many human diseases. Mutations in the γ2 subunit cause heart disease due to excessive glycogen storage in cardiac myocytes, leading to ventricular pre-excitation. AMPK-activating drugs reverse many of the metabolic defects associated with insulin resistance, and recent findings suggest that the insulin-sensitizing effects of the widely used antidiabetic drug metformin are mediated by AMPK. The upstream kinase LKB1 is a tumour suppressor, and AMPK may exert many of its antitumour effects. AMPK activation promotes the oxidative metabolism typical of quiescent cells, rather than the aerobic glycolysis observed in tumour cells and cells involved in inflammation, explaining in part why AMPK activators have both antitumour and anti-inflammatory effects. Salicylate (the major in vivo metabolite of aspirin) activates AMPK, and this could be responsible for at least some of the anticancer and anti-inflammatory effects of aspirin. In addition to metformin and salicylates, novel drugs that modulate AMPK are likely to enter clinical trials soon. Finally, AMPK may be involved in viral infection: downregulation of AMPK during hepatitis C virus infection appears to be essential for efficient viral replication.

Misinterpretation of the mouse ECG: 'musing the waves of Mus musculus'

The ECG is a primary diagnostic tool in patients suffering from heart disease, underscoring the importance of understanding factors contributing to normal and abnormal electrical patterns. Over the past few decades, transgenic mouse models have been increasingly used to study pathophysiological mechanisms of human heart diseases. In order to allow extrapolation of insights gained from murine models to the human condition, knowledge of the similarities and differences between the mouse and human ECG is of crucial importance. In this review, we briefly discuss the physiological mechanisms underlying differences between the baseline ECG of humans and mice, and provide a framework for understanding how these inherent differences are relevant to the interpretation of the mouse ECG during pathology and to the translation of the results from the mouse to man.

AMP-activated protein kinase regulation and biological actions in the heart

AMP-activated protein kinase (AMPK) is a stress-activated kinase that functions as a cellular fuel gauge and master metabolic regulator. Recent investigation has elucidated novel molecular mechanisms of AMPK regulation and important biological actions of the AMPK pathway that are highly relevant to cardiovascular disease. Activation of the intrinsic AMPK pathway plays an important role in the myocardial response to ischemia, pressure overload, and heart failure. Pharmacological activation of AMPK shows promise as a therapeutic strategy in the treatment of heart disease. The purpose of this review is to assess how recent discoveries have extended and in some cases challenged existing paradigms, providing new insights into the regulation of AMPK, its diverse biological actions, and therapeutic potential in the heart.

Enzyme replacement therapy improves cardiac features and severity of Fabry disease

BACKGROUND

Although left ventricular hypertrophy (LVH) in Fabry disease (FD) can improve with enzyme-replacement therapy (ERT), the response is difficult to predict. Furthermore, the response of other cardiac features such as aortic dilatation and ECG changes are poorly understood.

METHODS

A local registry of 66 patients with FD was studied. ECG, echocardiogram and Fabry Outcome Survey-Mainz Severity Score Index (FOS-MSSI) data were compared between baseline and after long-term ERT (median 36 months).

RESULTS

In patients with LVH (n=42), left ventricular mass index (LVMI), maximal wall thickness (MWT), left ventricular end-diastolic diameter (LVEDD) and ejection fraction (EF) were all seen to improve after ERT (LVMI: 135±13 vs. 133±13 g/m(2), MWT: 17±6 vs. 16±5 mm, LVEDD: 55±6 vs. 54±6 mm; EF: 62±5 vs. 64±3%; p<0.05). In the entire patient group, PQ interval and P wave duration significantly increased with ERT (PQ: 131±13 vs. 144±13 ms, P: 76±5 vs. 90±6 ms; p values<0.001); QT(c) interval significantly decreased (418±18 vs. 410±15 ms; p<0.001); and median FOS-MSSI score fell from 16 to 14 (p<0.001). On logistic-regression analysis, none of the recorded baseline features (age, gender, LVMI, MWT, LVEDD, aortic diameter, EF, PQ interval, P wave duration, QRS duration, QT interval, Romhilt-Estes score or FOS-MSSI) predicted improvements in LVH or FOS-MSSI with ERT (p>0.05).

CONCLUSIONS

ERT improved LV morphology and function in patients with LVH - but there was no relationship between age, gender, FOS-MSSI or baseline ECG/TTE features and the response. ERT also normalised long QTc intervals, short PQ intervals and short P waves; and reduced disease burden (FOS-MSSI).

The history of the wolff-Parkinson-white syndrome

While Drs Wolff, Parkinson, and White fully described the syndrome in 1930, prior case reports had described the essentials. Over the ensuing century this syndrome has captivated the interest of anatomists, clinical cardiologists, and cardiac surgeons. Stanley Kent described lateral muscular connections over the atrioventricular (AV) groove which he felt were the normal AV connections. The normal AV connections were, however, clearly described by His and Tawara. True right-sided AV connections were initially described by Wood et al., while Öhnell first described left free wall pathways. David Scherf is thought to be the first to describe our current understanding of the pathogenesis of the WPW syndrome in terms of a re-entrant circuit involving both the AV node-His axis as well as the accessory pathway. This hypothesis was not universally accepted, and many theories were applied to explain the clinical findings. The basics of our understanding were established by the brilliant work of Pick, Langendorf, and Katz who by using careful deductive analysis of ECGs were able to define the basic pathophysiological processes. Subsequently, Wellens and Durrer applied invasive electrical stimulation to the heart in order to confirm the pathophysiological processes. Sealy and his colleagues at Duke University Medical Center were the first to successfully surgically divide an accessory pathway and ushered in the modern era of therapy for these patients. Morady and Scheinman were the first to successfully ablate an accessory pathway (posteroseptal) using high-energy direct-current shocks. Subsequently Jackman, Kuck, Morady, and a number of groups proved the remarkable safety and efficiency of catheter ablation for pathways in all locations using radiofrequency energy. More recently, Gollob et al. first described the gene responsible for a familial form of WPW. The current ability to cure patients with WPW is due to the splendid contributions of individuals from diverse disciplines throughout the world.

Value of electrocardiogram in the differentiation of hypertensive heart disease, hypertrophic cardiomyopathy, aortic stenosis, amyloidosis, and Fabry disease

Left ventricular hypertrophy is 1 of the most frequent cardiac manifestations associated with an unfavorable prognosis. However, many different causes of left ventricular hypertrophy exist. The aim of the present study was to assess the diagnostic value of common electrocardiographic (ECG) parameters to differentiate Fabry disease (FD), amyloidosis, and nonobstructive hypertrophic cardiomyopathy (HC) from hypertensive heart disease (HHD) and aortic stenosis (AS). In 94 patients with newly diagnosed FD (n = 17), HHD (n = 20), amyloidosis (n = 17), AS (n = 20), and HC (n = 20), common ECG parameters were analyzed and tested for their diagnostic value. A stepwise approach including the Sokolow-Lyon index, corrected QT duration, and PQ interval minus P-wave duration in lead II to overcome P-wave abnormalities was applied. A corrected QT duration <440 ms in combination with a PQ interval minus P-wave duration in lead II <40 ms was 100% sensitive and 99% specific for the diagnosis of FD, whereas a corrected QT duration >440 ms and a Sokolow-Lyon index ≤1.5 mV were found to have a sensitivity and specificity of 85% and 100%, respectively, for the diagnosis of amyloidosis and differentiation from HC, AS, and HHD. Moreover, a novel index ([PQ interval minus P-wave duration in lead II multiplied by corrected QT duration]/Sokolow-Lyon index) proved to be highly diagnostic for the differentiation of amyloidosis (area under the curve 0.92) and FD (area under the curve 0.91) by receiver operator characteristic analysis. In conclusion, a combined analysis of PQ interval minus P-wave duration in lead II, corrected QT duration, and Sokolow-Lyon index proved highly sensitive and specific in the differentiation of FD, amyloidosis, and HC compared to HHD and AS. Analysis of these easy-to-assess ECG parameters may be of substantial help in the diagnostic workup of these 5 conditions.

Origin and development of the atrioventricular myocardial lineage: insight into the development of accessory pathways

Defects originating from the atrioventricular canal region are part of a wide spectrum of congenital cardiovascular malformations that frequently affect newborns. These defects include partial or complete atrioventricular septal defects, atrioventricular valve defects, and arrhythmias, such as atrioventricular re-entry tachycardia, atrioventricular nodal block, and ventricular preexcitation. Insight into the cellular origin of the atrioventricular canal myocardium and the molecular mechanisms that control its development will aid in the understanding of the etiology of the atrioventricular defects. This review discusses current knowledge concerning the origin and fate of the atrioventricular canal myocardium, the molecular mechanisms that determine its specification and differentiation, and its role in the development of certain malformations such as those that underlie ventricular preexcitation.

Defective Tbx2-dependent patterning of the atrioventricular canal myocardium causes accessory pathway formation in mice

Ventricular preexcitation, a feature of Wolff-Parkinson-White syndrome, is caused by accessory myocardial pathways that bypass the annulus fibrosus. This condition increases the risk of atrioventricular tachycardia and, in the presence of atrial fibrillation, sudden death. The developmental mechanisms underlying accessory pathway formation are poorly understood but are thought to primarily involve malformation of the annulus fibrosus. Before birth, slowly conducting atrioventricular myocardium causes a functional atrioventricular activation delay in the absence of the annulus fibrosus. This myocardium remains present after birth, suggesting that the disturbed development of the atrioventricular canal myocardium may mediate the formation of rapidly conducting accessory pathways. Here we show that myocardium-specific inactivation of T-box 2 (Tbx2), a transcription factor essential for atrioventricular canal patterning, leads to the formation of fast-conducting accessory pathways, malformation of the annulus fibrosus, and ventricular preexcitation in mice. The accessory pathways ectopically express proteins required for fast conduction (connexin-40 [Cx40], Cx43, and sodium channel, voltage-gated, type V, α [Scn5a]). Additional inactivation of Cx30.2, a subunit for gap junctions with low conductance expressed in the atrioventricular canal and unaffected by the loss of Tbx2, did not affect the functionality of the accessory pathways. Our results suggest that malformation of the annulus fibrosus and preexcitation arise from the disturbed development of the atrioventricular myocardium.