Arrhythmogenic Phenotype in Dilated Cardiomyopathy: Natural History and Predictors of Life-Threatening Arrhythmias

BACKGROUND-\u2014Patients with dilated cardiomyopathy (DCM) may present with ventricular arrhythmias early in the disease course, unrelated to the severity of left ventricular dysfunction. These patients may be classified as having an arrhythmogenic DCM (ARDCM). We investigated the phenotype and natural history of patients with AR-DCM. METHODS AND RESULTS-\u2014Two hundred eighty-five patients with a recent diagnosis of DCM (median duration of the disease 1 month, range 0 to 7 months) and who had Holter monitoring at baseline were comprehensively evaluated and followed for 107 months (range 29 to 170 months). AR-DCM was defined by the presence of 651 of the following: unexplained syncope, rapid nonsustained ventricular tachycardia ( 655 beats, 65150 bpm), 651000 premature ventricular contractions/24 hours, and 6550 ventricular couplets/ 24 hours, in the absence of overt heart failure. The primary end points were sudden cardiac death (SCD), sustained ventricular tachycardia (SVT), or ventricular fibrillation (VF). The secondary end points were death from congestive heart failure or heart transplantation. Of the 285 patients, 109 (38.2%) met criteria for AR-DCM phenotype. AR-DCM subjects had a higher incidence of SCD/SVT/VF compared with non\u2013AR-DCM patients (30.3% vs 17.6%, P=0.022), with no difference in the secondary end points. A family history of SCD/SVT/VF and the AR-DCM phenotype were statistically significant and cumulative predictors of SCD/SVT/VF. CONCLUSIONS-\u2014One-third of DCM patients may have an arrhythmogenic phenotype associated with increased risk of arrhythmias during follow-up. A family history of ventricular arrhythmias in DCM predicts a poor prognosis and increased risk of SCD

Innate immune signaling in hearts and buccal mucosa cells of patients with arrhythmogenic cardiomyopathy

Background: Nuclear factor κB (NF-κB) signaling in cardiac myocytes causes disease in a mouse model of arrhythmogenic cardiomyopathy (ACM) by mobilizing CCR2-expressing macrophages that promote myocardial injury and arrhythmias. Buccal mucosa cells exhibit pathologic features similar to those seen in cardiac myocytes in patients with ACM. Objectives: We sought to determine if persistent innate immune signaling via NF-κB occurs in cardiac myocytes in patients with ACM and if this is associated with myocardial infiltration of proinflammatory cells expressing CCR2. We also determined if buccal mucosa cells from young subjects with inherited disease alleles exhibit NF-κB signaling. Methods: We analyzed myocardium from ACM patients who died suddenly or required cardiac transplantation. We also analyzed buccal mucosa cells from young subjects with inherited disease alleles. The presence of immunoreactive signal for RelA/p65 in nuclei of cardiac myocytes and buccal cells was used as a reliable indicator of active NF-κB signaling. We also counted myocardial CCR2-expressing cells. Results: RelA/p65 signal was seen in numerous cardiac myocyte nuclei in 34 of 36 cases of ACM but not in 19 age-matched control individuals. Cells expressing CCR2 were increased in patient hearts in numbers directly correlated with the number of cardiac myocytes showing NF-κB signaling. NF-κB signaling was observed in buccal cells in young subjects with active disease. Conclusions: Patients with clinically active ACM exhibit persistent innate immune responses in cardiac myocytes and buccal mucosa cells, reflecting a local and systemic inflammatory process. Such individuals may benefit from anti-inflammatory therapy

Mechanisms of Impaired Exercise Capacity in Short Duration Experimental Hyperthyroidism

Abstract To investigate the mechanism of reduced exercise tolerance in hyperthyroidism, we characterized cardiovascular function and determinants of skeletal muscle metabolism in 18 healthy subjects aged 26±1 yr (mean±SE) before and after 2 wk of daily ingestion of 100 pg of triiodothyronine (T3). Resting oxygen uptake, heart rate, and cardiac output increased and heart rate and cardiac output at the same submaximal exercise intensity were higher in the hyperthyroid state (P < 0.05). However, maximal oxygen uptake decreased after T3 administration (3.08±0.17 vs. 2.94±0.19 l/min; P < 0.001) despite increased heart rate and cardiac output at maximal exercise (P < 0.05). Plasma lactic acid concentration at an equivalent submaximal exercise intensity was elevated 25% (P < 0.01) and the arteriovenous oxygen difference at maximal effort was reduced (P < 0.05) in the hyperthyroid state. These effects were associated with a 21-37% decline in activities of oxidative (P < 0.001) and glycolytic (P < 0.05) enzymes in skeletal muscle and a 15% decrease in type 11A muscle fiber cross-sectional area (P < 0.05). Lean body mass was reduced (P < 0.001) and the rates of whole body leucine oxidation and protein breakdown were enhanced (P < 0.05). Thus, exercise tolerance is impaired in short duration hyperthyroidism because of decreased skeletal muscle mass and oxidative capacity related to accelerated protein catabolism but cardiac pump function is not reduced. (J. Clin

Remodelling of gap junctions and connexin expression in diseased myocardium

Gap junctions form the cell-to-cell pathways for propagation of the precisely orchestrated patterns of current flow that govern the regular rhythm of the healthy heart. As in most tissues and organs, multiple connexin types are expressed in the heart: connexin43 (Cx43), Cx40 and Cx45 are found in distinctive combinations and relative quantities in different, functionally-specialized subsets of cardiac myocyte. Mutations in genes that encode connexins have only rarely been identified as being a cause of human cardiac disease, but remodelling of connexin expression and gap junction organization are well documented in acquired adult heart disease, notably ischaemic heart disease and heart failure. Remodelling may take the form of alterations in (i) the distribution of gap junctions and (ii) the amount and type of connexins expressed. Heterogeneous reduction in Cx43 expression and disordering in gap junction distribution feature in human ventricular disease and correlate with electrophysiologically identified arrhythmic changes and contractile dysfunction in animal models. Disease-related alterations in Cx45 and Cx40 expression have also been reported, and some of the functional implications of these are beginning to emerge. Apart from ventricular disease, various features of gap junction organization and connexin expression have been implicated in the initiation and persistence of the most common form of atrial arrhythmia, atrial fibrillation, though the disparate findings in this area remain to be clarified. Other major tasks ahead focus on the Purkinje/working ventricular myocyte interface and its role in normal and abnormal impulse propagation, connexin-interacting proteins and their regulatory functions, and on defining the precise functional properties conferred by the distinctive connexin co-expression patterns of different myocyte types in health and disease

Mechanistic insights into arrhythmogenic right ventricular cardiomyopathy caused by desmocollin-2 mutations

Aims: Recent immunohistochemical studies observed the loss of plakoglobin (PG) from the intercalated disc (ID) as a hallmark of arrhythmogenic right ventricular cardiomyopathy (ARVC), suggesting a final common pathway for this disease. However, the underlying molecular processes are poorly understood. Methods and results: We have identified novel mutations in the desmosomal cadherin desmocollin 2 (DSC2 R203C, L229X, T275M, and G371fsX378). The two missense mutations (DSC2 R203C and T275M) have been functionally characterized, together with a previously reported frameshift variant (DSC2 A897fsX900), to examine their pathogenic potential towards PG's functions at the ID. The three mutant proteins were transiently expressed in various cellular systems and assayed for expression, processing, localization, and binding to other desmosomal components in comparison to wild-type DSC2a protein. The two missense mutations showed defects in proteolytic cleavage, a process which is required for the functional activation of mature cadherins. In both cases, this is thought to cause a reduction of functional DSC2 at the desmosomes in cardiac cells. In contrast, the frameshift variant was incorporated into cardiac desmosomes; however, it showed reduced binding to PG. Conclusion: Despite different modes of action, for all three variants, the reduced ability to provide a ligand for PG at the desmosomes was observed. This is in agreement with the reduced intensity of PG at these structures observed in ARVC patients

Innate immune signaling in hearts and buccal mucosa cells of patients with arrhythmogenic cardiomyopathy.

BACKGROUND: Nuclear factor κB (NF-κB) signaling in cardiac myocytes causes disease in a mouse model of arrhythmogenic cardiomyopathy (ACM) by mobilizing CCR2-expressing macrophages that promote myocardial injury and arrhythmias. Buccal mucosa cells exhibit pathologic features similar to those seen in cardiac myocytes in patients with ACM. OBJECTIVES: We sought to determine if persistent innate immune signaling via NF-κB occurs in cardiac myocytes in patients with ACM and if this is associated with myocardial infiltration of proinflammatory cells expressing CCR2. We also determined if buccal mucosa cells from young subjects with inherited disease alleles exhibit NF-κB signaling. METHODS: We analyzed myocardium from ACM patients who died suddenly or required cardiac transplantation. We also analyzed buccal mucosa cells from young subjects with inherited disease alleles. The presence of immunoreactive signal for RelA/p65 in nuclei of cardiac myocytes and buccal cells was used as a reliable indicator of active NF-κB signaling. We also counted myocardial CCR2-expressing cells. RESULTS: RelA/p65 signal was seen in numerous cardiac myocyte nuclei in 34 of 36 cases of ACM but not in 19 age-matched control individuals. Cells expressing CCR2 were increased in patient hearts in numbers directly correlated with the number of cardiac myocytes showing NF-κB signaling. NF-κB signaling was observed in buccal cells in young subjects with active disease. CONCLUSIONS: Patients with clinically active ACM exhibit persistent innate immune responses in cardiac myocytes and buccal mucosa cells, reflecting a local and systemic inflammatory process. Such individuals may benefit from anti-inflammatory therapy

Early markers for myocardial ischemia and sudden cardiac death.

The post-mortem diagnosis of acute myocardial ischemia remains a challenge for both clinical and forensic pathologists. We performed an experimental study (ligation of left anterior descending coronary artery in rats) in order to identify early markers of myocardial ischemia, to further apply to forensic and clinical pathology in cases of sudden cardiac death. Using immunohistochemistry, Western blots, and gene expression analyses, we investigated a number of markers, selected among those which are currently used in emergency departments to diagnose myocardial infarction and those which are under investigation in basic research and autopsy pathology studies on cardiovascular diseases. The study was performed on 44 adult male Lewis rats, assigned to three experimental groups: control, sham-operated, and operated. The durations of ischemia ranged between 5 min and 24 h. The investigated markers were troponins I and T, myoglobin, fibronectin, C5b-9, connexin 43 (dephosphorylated), JunB, cytochrome c, and TUNEL staining. The earliest expressions (≤30 min) were observed for connexin 43, JunB, and cytochrome c, followed by fibronectin (≤1 h), myoglobin (≤1 h), troponins I and T (≤1 h), TUNEL (≤1 h), and C5b-9 (≤2 h). By this investigation, we identified a panel of true early markers of myocardial ischemia and delineated their temporal evolution in expression by employing new technologies for gene expression analysis, in addition to traditional and routine methods (such as histology and immunohistochemistry). Moreover, for the first time in the autopsy pathology field, we identified, by immunohistochemistry, two very early markers of myocardial ischemia: dephosphorylated connexin 43 and JunB

Mutations with pathogenic potential in proteins located in or at the composite junctions of the intercalated disk connecting mammalian cardiomyocytes: a reference thesaurus for arrhythmogenic cardiomyopathies and for Naxos and Carvajal diseases

In the past decade, an avalanche of findings and reports has correlated arrhythmogenic ventricular cardiomyopathies (ARVC) and Naxos and Carvajal diseases with certain mutations in protein constituents of the special junctions connecting the polar regions (intercalated disks) of mature mammalian cardiomyocytes. These molecules, apparently together with some specific cytoskeletal proteins, are components of (or interact with) composite junctions. Composite junctions contain the amalgamated fusion products of the molecules that, in other cell types and tissues, occur in distinct separate junctions, i.e. desmosomes and adherens junctions. As the pertinent literature is still in an expanding phase and is obviously becoming important for various groups of researchers in basic cell and molecular biology, developmental biology, histology, physiology, cardiology, pathology and genetics, the relevant references so far recognized have been collected and are presented here in the following order: desmocollin-2 (Dsc2, DSC2), desmoglein-2 (Dsg2, DSG2), desmoplakin (DP, DSP), plakoglobin (PG, JUP), plakophilin-2 (Pkp2, PKP2) and some non-desmosomal proteins such as transmembrane protein 43 (TMEM43), ryanodine receptor 2 (RYR2), desmin, lamins A and C, striatin, titin and transforming growth factor-β3 (TGFβ3), followed by a collection of animal models and of reviews, commentaries, collections and comparative studies

Detailed Anatomical and Electrophysiological Models of Human Atria and Torso for the Simulation of Atrial Activation

Atrial arrhythmias, and specifically atrial fibrillation (AF), induce rapid and irregular activation patterns that appear on the torso surface as abnormal P-waves in electrocardiograms and body surface potential maps (BSPM). In recent years both P-waves and the BSPM have been used to identify the mechanisms underlying AF, such as localizing ectopic foci or high-frequency rotors. However, the relationship between the activation of the different areas of the atria and the characteristics of the BSPM and P-wave signals are still far from being completely understood. In this work we developed a multi-scale framework, which combines a highly-detailed 3D atrial model and a torso model to study the relationship between atrial activation and surface signals in sinus rhythm. Using this multi scale model, it was revealed that the best places for recording P-waves are the frontal upper right and the frontal and rear left quadrants of the torso. Our results also suggest that only nine regions (of the twenty-one structures in which the atrial surface was divided) make a significant contribution to the BSPM and determine the main P-wave characteristics.This work was partially supported by the "VI Plan Nacional de Investigacion Cientifica, Desarrollo e Innovacion Tecnologica" from the Ministerio de Economia y Competitividad of Spain and the European Commission (European Regional Development Funds - ERDF - FEDER), Award Number: TIN2012-37546-C03-01 (Recipient: Ana Ferrer); the "Programa Estatal de Investigacion, Desarrollo e Innovacion Orientado a los Retos de la Sociedad" from the Ministerio de Economia y Competitividad and the European Commission (European Regional Development Funds - ERDF - FEDER), Award Number: TIN2014-59932-JIN (Recipient: Rafael Sebastion); and the "Programa Prometeo" from the Generalitat Valenciana, Award Number: 2012/030 (Recipient: Laura Martinez).Ferrer Albero, A.; Sebastián Aguilar, R.; Sánchez Quintana, D.; Rodriguez, JF.; Godoy, EJ.; Martinez, L.; Saiz Rodríguez, FJ. (2015). Detailed Anatomical and Electrophysiological Models of Human Atria and Torso for the Simulation of Atrial Activation. PLoS ONE. 10(11):1-29. https://doi.org/10.1371/journal.pone.0141573S129101