Increased Cardiac Arrhythmogenesis Associated With Gap Junction Remodeling With Upregulation of RNA-Binding Protein FXR1

BACKGROUND

Gap junction remodeling is well established as a consistent feature of human heart disease involving spontaneous ventricular arrhythmia. The mechanisms responsible for gap junction remodeling that include alterations in the distribution of, and protein expression within, gap junctions are still debated. Studies reveal that multiple transcriptional and posttranscriptional regulatory pathways are triggered in response to cardiac disease, such as those involving RNA-binding proteins. The expression levels of FXR1 (fragile X mental retardation autosomal homolog 1), an RNA-binding protein, are critical to maintain proper cardiac muscle function; however, the connection between FXR1 and disease is not clear.

METHODS

To identify the mechanisms regulating gap junction remodeling in cardiac disease, we sought to identify the functional properties of FXR1 expression, direct targets of FXR1 in human left ventricle dilated cardiomyopathy (DCM) biopsy samples and mouse models of DCM through BioID proximity assay and RNA immunoprecipitation, how FXR1 regulates its targets through RNA stability and luciferase assays, and functional consequences of altering the levels of this important RNA-binding protein through the analysis of cardiac-specific FXR1 knockout mice and mice injected with 3xMyc-FXR1 adeno-associated virus.

RESULTS

FXR1 expression is significantly increased in tissue samples from human and mouse models of DCM via Western blot analysis. FXR1 associates with intercalated discs, and integral gap junction proteins Cx43 (connexin 43), Cx45 (connexin 45), and ZO-1 (zonula occludens-1) were identified as novel mRNA targets of FXR1 by using a BioID proximity assay and RNA immunoprecipitation. Our findings show that FXR1 is a multifunctional protein involved in translational regulation and stabilization of its mRNA targets in heart muscle. In addition, introduction of 3xMyc-FXR1 via adeno-associated virus into mice leads to the redistribution of gap junctions and promotes ventricular tachycardia, showing the functional significance of FXR1 upregulation observed in DCM.

CONCLUSIONS

In DCM, increased FXR1 expression appears to play an important role in disease progression by regulating gap junction remodeling. Together this study provides a novel function of FXR1, namely, that it directly regulates major gap junction components, contributing to proper cell-cell communication in the heart.

Dilated Cardiomyopathy: Genetic Determinants and Mechanisms

Nonischemic dilated cardiomyopathy (DCM) often has a genetic pathogenesis. Because of the large number of genes and alleles attributed to DCM, comprehensive genetic testing encompasses ever-increasing gene panels. Genetic diagnosis can help predict prognosis, especially with regard to arrhythmia risk for certain subtypes. Moreover, cascade genetic testing in family members can identify those who are at risk or with early stage disease, offering the opportunity for early intervention. This review will address diagnosis and management of DCM, including the role of genetic evaluation. We will also overview distinct genetic pathways linked to DCM and their pathogenetic mechanisms. Historically, cardiac morphology has been used to classify cardiomyopathy subtypes. Determining genetic variants is emerging as an additional adjunct to help further refine subtypes of DCM, especially where arrhythmia risk is increased, and ultimately contribute to clinical management.

Personalizing Risk Stratification for Sudden Death in Dilated Cardiomyopathy: The Past, Present, and Future

Results from the DANISH Study (Danish Study to Assess the Efficacy of ICDs in Patients With Non-Ischemic Systolic Heat Failure on Mortality) suggest that for many patients with dilated cardiomyopathy (DCM), implantable cardioverter-defibrillators do not increase longevity. Accurate identification of patients who are more likely to die of an arrhythmia and less likely to die of other causes is required to ensure improvement in outcomes and wise use of resources. Until now, left ventricular ejection fraction has been used as a key criterion for selecting patients with DCM for an implantable cardioverter-defibrillator for primary prevention purposes. However, registry data suggest that many patients with DCM and an out-of-hospital cardiac arrest do not have a markedly reduced left ventricular ejection fraction. In addition, many patients with reduced left ventricular ejection fraction die of nonsudden causes of death. Methods to predict a higher or lower risk of sudden death include the detection of myocardial fibrosis (a substrate for ventricular arrhythmia), microvolt T-wave alternans (a marker of electrophysiological vulnerability), and genetic testing. Midwall fibrosis is identified by late gadolinium enhancement cardiovascular magnetic resonance imaging in ≈30% of patients and provides incremental value in addition to left ventricular ejection fraction for the prediction of sudden cardiac death events. Microvolt T-wave alternans represents another promising predictor, supported by large meta-analyses that have highlighted the negative predictive value of this test. However, neither of these strategies have been routinely adopted for risk stratification in clinical practice. More convincing data from randomized trials are required to inform the management of patients with these features. Understanding of the genetics of DCM and how specific mutations affect arrhythmic risk is also rapidly increasing. The finding of a mutation in lamin A/C, the cause of ≈6% of idiopathic DCM, commonly underpins more aggressive management because of the malignant nature of the associated phenotype. With the expansion of genetic sequencing, the identification of further high-risk mutations appears likely, leading to better-informed clinical decision making and providing insight into disease mechanisms. Over the next 5 to 10 years, we expect these techniques to be integrated into the existing algorithm to form a more sensitive, specific, and cost-effective approach to the selection of patients with DCM for implantable cardioverter-defibrillator implantation.

Abnormal Global Longitudinal Strain Predicts Future Deterioration of Left Ventricular Function in Heart Failure Patients With a Recovered Left Ventricular Ejection Fraction

BACKGROUND

Patients with recovery of left ventricular ejection fraction (LVEF) remain at risk for future deterioration of LVEF. However, there are no tools to risk stratify these patients. We hypothesized that global longitudinal strain (GLS) could predict sustained recovery within this population.

METHODS AND RESULTS

We retrospectively identified 96 patients with a reduced LVEF <50% (screening echocardiogram), whose LVEF had increased by at least 10% and normalized (>50%) on evidence-based medical therapies (baseline echocardiogram). We examined absolute GLS on the baseline echocardiogram in relation to changes in LVEF on a follow-up echocardiogram. Patients with recovered LVEF had a wide range of GLS. The GLS on the baseline study correlated with the LVEF at the time of follow-up (r=0.33; P<0.001). The likelihood of having an LVEF >50% on follow-up increased by 24% for each point increase in absolute GLS on the baseline study (odds ratio, 1.24; P=0.001). An abnormal GLS (≤16%) at baseline had a sensitivity of 88%, a specificity of 46%, and an accuracy of 0.67 (P<0.001) as a predictor of a decrease in LVEF >5% during follow-up. A normal GLS (>16%) on the baseline study had a sensitivity of 47%, a specificity of 83%, and an accuracy of 0.65 (P=0.002) for predicting a stable LVEF (-5% to 5%) on follow-up.

CONCLUSIONS

In patients with a recovered LVEF, an abnormal GLS predicts the likelihood of having a decreased LVEF during follow-up, whereas a normal GLS predicts the likelihood of stable LVEF during recovery.

Prostaglandin E2 Reduces Cardiac Contractility via EP3 Receptor

BACKGROUND

Prostaglandin E2 (PGE2) EP receptors EP3 and EP4 signal via decreased and increased cAMP production, respectively. Previously, we reported that cardiomyocyte-specific EP4 knockout mice develop dilated cardiomyopathy with reduced ejection fraction. Thus, we hypothesized that PGE2 increases contractility via EP4 but decreases contractility via EP3.

METHODS AND RESULTS

The effects of PGE2 and the EP1/EP3 agonist sulprostone on contractility were examined in the mouse Langendorff preparation and in adult mouse cardiomyocytes. Isolated hearts of adult male C57Bl/6 mice were perfused with PGE2 (10(-6) M) or sulprostone (10(-6) M) and compared with vehicle. Both PGE2 and sulprostone decreased +dp/dt (P<0.01) and left ventricular developed pressure (P<0.001) with reversal by an EP3 antagonist. In contrast, the EP4 agonist had the opposite effect. Adult mouse cardiomyocytes contractility was also reduced after treatment with either PGE2 or sulprostone for 10 minutes. We then examined the acute effects of PGE2, sulprostone, and the EP4 agonist on expression of phosphorylated phospholamban and sarcoendoplasmic reticulum Ca(2+)-ATPase 2a in adult mouse cardiomyocytes using Western blot. Treatment with either PGE2 or sulprostone decreased expression of phosphorylated phospholamban corrected to total phospholamban, whereas treatment with the EP4 agonist had the opposite effect. Sarcoendoplasmic reticulum Ca(2+)-ATPase 2a expression was unaffected. Finally, we examined the effect of these compounds in vivo using pressure-volume loops. Both PGE2 and sulprostone decreased +dp/dt, whereas the EP4 agonist increased +dp/dt.

CONCLUSIONS

Contractility is reduced via the EP3 receptor but increased via EP4. These effects may be mediated through changes in phospholamban phosphorylation and has relevance to detrimental effects of inflammation.

A current approach to heart failure in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a genetic, progressive neuromuscular condition that is marked by the long-term muscle deterioration with significant implications of pulmonary and cardiac dysfunction. As such, end-stage heart failure (HF) in DMD is increasingly becoming the main cause of death in this population. The early detection of cardiomyopathy is often challenging, due to a long subclinical phase of ventricular dysfunction and difficulties in assessment of cardiovascular symptomatology in these patients who usually loose ambulation during the early adolescence. However, an early diagnosis of cardiovascular disease in patients with DMD is decisive since it allows a timely initiation of cardioprotective therapies that can mitigate HF symptoms and delay detrimental heart muscle remodelling. Echocardiography and ECG are standardly used for screening and detection of cardiovascular abnormalities in these patients, although these tools are not always adequate to detect an early, clinically asymptomatic phases of disease progression. In this regard, cardiovascular magnetic resonance (CMR) with late gadolinium enhancement is emerging as a promising method for the detection of early cardiac involvement in patients with DMD. The early detection of cardiac dysfunction allows the therapeutic institution of various classes of drugs such as corticosteroids, beta-blockers, ACE inhibitors, antimineralocorticoid diuretics and novel pharmacological and surgical solutions in the multimodal and multidisciplinary care for this group of patients. This review will focus on these challenges and available options for HF in patients with DMD.

Endothelial Restoration of Receptor Activity-Modifying Protein 2 Is Sufficient to Rescue Lethality, but Survivors Develop Dilated Cardiomyopathy

RAMPs (receptor activity-modifying proteins) serve as oligomeric modulators for numerous G-protein-coupled receptors, yet elucidating the physiological relevance of these interactions remains complex. Ramp2 null mice are embryonic lethal, with cardiovascular developmental defects similar to those observed in mice null for canonical adrenomedullin/calcitonin receptor-like receptor signaling. We aimed to genetically rescue the Ramp2(-/-) lethality in order to further delineate the spatiotemporal requirements for RAMP2 function during development and thereby enable the elucidation of an expanded repertoire of RAMP2 functions with family B G-protein-coupled receptors in adult homeostasis. Endothelial-specific expression of Ramp2 under the VE-cadherin promoter resulted in the partial rescue of Ramp2(-/-) mice, demonstrating that endothelial expression of Ramp2 is necessary and sufficient for survival. The surviving Ramp2(-/-) Tg animals lived to adulthood and developed spontaneous hypotension and dilated cardiomyopathy, which was not observed in adult mice lacking calcitonin receptor-like receptor. Yet, the hearts of Ramp2(-/-) Tg animals displayed dysregulation of family B G-protein-coupled receptors, including parathyroid hormone and glucagon receptors, as well as their downstream signaling pathways. These data suggest a functional requirement for RAMP2 in the modulation of additional G-protein-coupled receptor pathways in vivo, which is critical for sustained cardiovascular homeostasis. The cardiovascular importance of RAMP2 extends beyond the endothelium and canonical adrenomedullin/calcitonin receptor-like receptor signaling, in which future studies could elucidate novel and pharmacologically tractable pathways for treating cardiovascular diseases.

Short QT Interval Prevalence and Clinical Outcomes in a Pediatric Population

BACKGROUND

Risk associated with short QT interval has recently received recognition. European studies suggest a prevalence of 0.02% to 0.1% in the adult population, but similar studies in pediatric patients are limited. We sought to determine the prevalence of short QT interval in a pediatric population and associated clinical characteristics and outcomes.

METHODS AND RESULTS

Retrospective review of an ECG database at a single pediatric institution. The database was queried for ECGs on patients ≤21 years with electronically measured QTc of 140 to 340 ms. Patients with QTc of 140 to 340 ms confirmed by a pediatric electrophysiologist were identified for chart review for associated clinical characteristics, symptoms, and outcome. Patients with and without symptoms were compared in an attempt to identify variables associated with outcome. The query included 272 504 ECGs on 99 380 unique patients. Forty-five patients (35 men, 76%) had QTc ≤340 ms, for a prevalence of 0.05%. Median age was 15 years (interquartile range, 2-17), median QT 330 ms (interquartile range, 280-360), and median QTc 323 ms (IQR, 313-332). Women had significantly shorter QTc compared with men (312 versus 323 ms; P=0.03). Two deaths were noted in chart review--one from respiratory failure and the second of unknown pathogenesis in a patient with dilated cardiomyopathy.

CONCLUSIONS

Short QT interval was a rare finding in this pediatric population, with a prevalence of 0.05%. Male predominance was identified, although the median QT interval was significantly shorter in women. There seem to be no unifying clinical characteristics for this pediatric patient cohort with short QT interval.

Loss of secreted frizzled-related protein-1 leads to deterioration of cardiac function in mice and plays a role in human cardiomyopathy

BACKGROUND

The Wnt/β-catenin signaling pathway plays a central role during cardiac development and has been implicated in cardiac remodeling and aging. However, the role of Wnt modulators in this process is unknown. In this study, we examined the role of the Wnt signaling inhibitor secreted frizzled-related protein-1 (sFRP-1) in aged wild-type and sFRP-1-deficient mice.

METHODS AND RESULTS

sFRP-1 gene deletion mice were grossly normal with no difference in mortality but developed abnormal cardiac structure and dysfunction with progressive age. Ventricular dilation and hypertrophy in addition to deterioration of cardiac function and massive cardiac fibrosis, all features present in dilated cardiomyopathy, were observed in the aged sFRP-1 knockout mice. Loss of sFRP-1 led to increased expression of Wnt ligands (Wnt1, 3, 7b, and 16) and Wnt target genes (Wisp1 and Lef1) in aged hearts, which correlated with increased protein levels of β-catenin. Cardiac fibroblasts lacking endogenous sFRP-1 showed increased α-smooth muscle actin expression, higher cell proliferation rates, and increased collagen production consistent with the cardiac phenotype exhibited in aged sFRP-1 knockout mice. The clinical relevance of these findings was supported by the demonstration of decreased sFRP-1 gene expression and increased Wisp-1 levels in the left ventricles of patients with ischemic dilated cardiomyopathy and dilated cardiomyopathy.

CONCLUSIONS

This study identifies a novel role of sFRP-1 in age-related cardiac deterioration and fibrosis. Further exploration of this pathway will identify downstream molecules important in these processes and also suggest the potential use of Wnt signaling agents as therapeutic targets for age-related cardiovascular disorders in humans.

Therapeutic Molecular Phenotype of β-Blocker-Associated Reverse-Remodeling in Nonischemic Dilated Cardiomyopathy

BACKGROUND

When β-blockers produce reverse-remodeling in idiopathic dilated cardiomyopathy, they partially reverse changes in fetal-adult/contractile protein, natriuretic peptide, SR-Ca(2+)-ATPase gene program constituents. The objective of the current study was to further test the hypothesis that reverse-remodeling is associated with favorable changes in myocardial gene expression by measuring additional contractile, signaling, and metabolic genes that exhibit a fetal/adult expression predominance, are thyroid hormone-responsive, and are regulated by β1-adrenergic receptor signaling. A secondary objective was to identify which of these putative regulatory networks is most closely associated with observed changes.

METHODS AND RESULTS

Forty-seven patients with idiopathic dilated cardiomyopathy (left ventricular ejection fraction, 0.24±0.09) were randomized to the adrenergic-receptor blockers metoprolol (β1-selective), metoprolol+doxazosin (β1/α1), or carvedilol (β1/β2/α1). Serial radionuclide ventriculography and endomyocardial biopsies were performed at baseline, 3, and 12 months. Expression of 50 mRNA gene products was measured by quantitative polymerase chain reaction. Thirty-one patients achieved left ventricular ejection fraction reverse-remodeling response defined as improvement by ≥0.08 at 12 months or by ≥0.05 at 3 months (Δ left ventricular ejection fraction, 0.21±0.10). Changes in gene expression in responders versus nonresponders were decreases in NPPA and NPPB and increases in MYH6, ATP2A2, PLN, RYR2, ADRA1A, ADRB1, MYL3, PDFKM, PDHX, and CPT1B. All except PDHX involved increase in adult or decrease in fetal cardiac genes, but 100% were concordant with changes predicted by inhibition of β1-adrenergic signaling.

CONCLUSIONS

In addition to known gene expression changes, additional calcium-handling, sarcomeric, adrenergic signaling, and metabolic genes were associated with reverse-remodeling. The pattern suggests a fetal-adult paradigm but may be because of reversal of gene expression controlled by a β1-adrenergic receptor gene network.

CLINICAL TRIAL REGISTRATION

URL: www.clinicaltrials.gov. Unique Identifier: NCT01798992.

Thioredoxin-2 inhibits mitochondrial reactive oxygen species generation and apoptosis stress kinase-1 activity to maintain cardiac function

BACKGROUND

Thioredoxin 2 (Trx2) is a key mitochondrial protein that regulates cellular redox and survival by suppressing mitochondrial reactive oxygen species generation and by inhibiting apoptosis stress kinase-1 (ASK1)-dependent apoptotic signaling. To date, the role of the mitochondrial Trx2 system in heart failure pathogenesis has not been investigated.

METHODS AND RESULTS

Western blot and histological analysis revealed that Trx2 protein expression levels were reduced in hearts from patients with dilated cardiomyopathy, with a concomitant increase in ASK1 phosphorylation/activity. Cardiac-specific Trx2 knockout mice develop spontaneous dilated cardiomyopathy at 1 month of age with increased heart size, reduced ventricular wall thickness, and a progressive decline in left ventricular contractile function, resulting in mortality due to heart failure by ≈4 months of age. The progressive decline in cardiac function observed in cardiac-specific Trx2 knockout mice was accompanied by the disruption of mitochondrial ultrastructure, mitochondrial membrane depolarization, increased mitochondrial reactive oxygen species generation, and reduced ATP production, correlating with increased ASK1 signaling and increased cardiomyocyte apoptosis. Chronic administration of a highly selective ASK1 inhibitor improved cardiac phenotype and reduced maladaptive left ventricular remodeling with significant reductions in oxidative stress, apoptosis, fibrosis, and cardiac failure. Cellular data from Trx2-deficient cardiomyocytes demonstrated that ASK1 inhibition reduced apoptosis and reduced mitochondrial reactive oxygen species generation.

CONCLUSIONS

Our data support an essential role for mitochondrial Trx2 in preserving cardiac function by suppressing mitochondrial reactive oxygen species production and ASK1-dependent apoptosis. Inhibition of ASK1 represents a promising therapeutic strategy for the treatment of dilated cardiomyopathy and heart failure.

Cardiac transcriptome and dilated cardiomyopathy genes in zebrafish

BACKGROUND

Genetic studies of cardiomyopathy and heart failure have limited throughput in mammalian models. Adult zebrafish have been recently pursued as a vertebrate model with higher throughput, but genetic conservation must be tested.

METHODS AND RESULTS

We conducted transcriptome analysis of zebrafish heart and searched for fish homologues of 51 known human dilated cardiomyopathy-associated genes. We also identified genes with high cardiac expression and genes with differential expression between embryonic and adult stages. Among tested genes, 30 had a single zebrafish orthologue, 14 had 2 homologues, and 5 had ≥3 homologues. By analyzing the expression data on the basis of cardiac abundance and enrichment hypotheses, we identified a single zebrafish gene for 14 of 19 multiple-homologue genes and 2 zebrafish homologues of high priority for ACTC1. Of note, our data suggested vmhc and vmhcl as functional zebrafish orthologues for human genes MYH6 and MYH7, respectively, which are established molecular markers for cardiac remodeling.

CONCLUSIONS

Most known genes for human dilated cardiomyopathy have a corresponding zebrafish orthologue, which supports the use of zebrafish as a conserved vertebrate model. Definition of the cardiac transcriptome and fetal gene program will facilitate systems biology studies of dilated cardiomyopathy in zebrafish.

Phenotype and physiological significance of the endocardial smooth muscle cells in human failing hearts

BACKGROUND

Extravascular smooth muscle cells are often observed in the endocardium of human failing hearts. Here, we characterized the phenotype of those cells and investigated their physiological significance.

METHODS AND RESULTS

We examined left ventricular biopsy specimens obtained from 44 patients with dilated cardiomyopathy and 6 nonfailing hearts. In Masson trichrome-stained histological preparations, bundles of smooth muscle cells were seen localized in the endocardium in 23 of the 44 specimens (none of the 6 controls). These cells were immunopositive for α-smooth muscle actin, type 2 smooth muscle myosin, desmin, and calponin, but were negative for embryonic smooth muscle myosin, vimentin, fibronectin, and periostin. This profile is indicative of a late differentiation (contractile) smooth muscle phenotype. Electron microscopy confirmed that phenotype, revealing the cells to contain abundant myofilaments with dense bodies but little rough endoplasmic reticulum or Golgi apparatus. In the endocardial smooth muscle-positive group, the left ventricular end-systolic volume index (73±34 versus 105±50 mL/m(2); P=0.021), left ventricular peak wall stress (164±47 versus 196±43 dynes 10(3)/cm(2); P=0.023), and left ventricular end-systolic meridional wall stress (97±38 versus 121±37 dynes 10(3)/cm(2); P=0.036) were all significantly smaller, and the ejection fraction was larger (41±8.8 versus 33±9.3%; P=0.005) than in the endocardial smooth muscle-negative group. However, no histological parameters differed between the 2 groups.

CONCLUSIONS

Endocardial smooth muscle cell bundles in hearts with dilated cardiomyopathy exhibit a mature contractile phenotype and may play a compensatory role mitigating heart failure by reducing left ventricular wall stress and systolic dysfunction.

Age-related differences in phosphodiesterase activity and effects of chronic phosphodiesterase inhibition in idiopathic dilated cardiomyopathy

BACKGROUND

Despite the application of proven adult heart failure therapies to children with idiopathic dilated cardiomyopathy (IDC), prognosis remains poor. Clinical experience with phosphodiesterase 3 inhibitors (PDE3i) in pediatric patients with IDC, however, demonstrates improved heart failure symptoms without the increased incidence of sudden death seen in adults treated with PDE3i. We sought to determine age-related differences in PDE activity and associated intracellular signaling responsible for the efficacy and relative safety of chronic PDE3i in pediatric heart failure.

METHODS AND RESULTS

cAMP levels, PDE activity, and phospholamban phosphorylation (pPLB) were determined in explanted human left ventricular myocardium (pediatric n=41; adult n=88). Adults and children with IDC (not treated with PDE3i) had lower cAMP and pPLB compared with nonfailing controls. In contrast to their adult counterparts, pediatric IDC patients chronically treated with PDE3i had elevated cAMP (P=0.0403) and pPLB (P=0.0119). In addition, total PDE- and PDE3-specific activities were not altered in pediatric IDC patients on PDE3i, whereas adult IDC patients on PDE3i demonstrated higher total PDE-specific (74.6±13.8 pmol/mg per minute) and PDE3-specific (48.2±15.9 pmol/mg per minute) activities in comparison with those of nonfailing controls (59.5±14.4 and 35.5±12.8 pmol/mg per minute, respectively).

CONCLUSIONS

Elevated cAMP and higher pPLB may contribute to sustained hemodynamic benefits in pediatric IDC patients treated with PDE3i. In contrast, higher total PDE and PDE3 activities in adult IDC patients treated with PDE3i may perpetuate lower myocardial cAMP and pPLB levels, limiting the potential benefits of PDE3i therapy.

Usefulness of sugammadex in a patient with Becker muscular dystrophy and dilated cardiomyopathy

A 54-year-old patient with Becker muscular dystrophy and dilated cardiomyopathy underwent laparoscopic cholecystectomy under total intravenous anesthesia. Muscle relaxation was induced by rocuronium (0.4 mg/kg body weight) under train-of-four (TOF) ratio monitoring. The TOF ratio was 0 at intubation, and 0.2 at the end of surgery. Residual muscle relaxant activity was successfully reversed by sugammadex (2 mg/kg body weight) without any hemodynamic adverse effects (TOF ratio 1.0 at extubation). The clinical and hemodynamic findings suggest that sugammadex can be safely used in patients with Becker muscular dystrophy and dilated cardiomyopathy.

Aortic stiffness and interstitial myocardial fibrosis by native T1 are independently associated with left ventricular remodeling in patients with dilated cardiomyopathy

Increased aortic stiffness is related to increased ventricular stiffness and remodeling. Myocardial fibrosis is the pathophysiological hallmark of failing heart. We investigated the relationship between noninvasive imaging markers of myocardial fibrosis, native T1, and late gadolinium enhancement, respectively, and aortic stiffness in ventricular remodeling. Consecutive patients with known dilated cardiomyopathy (n=173) underwent assessment of cardiac volumes and function, T1 mapping, scar imaging, and pulse wave velocity, a measure of aortic stiffness. Asymptomatic healthy volunteers served as controls (n=47). Controls and patients showed an increase in pulse wave velocity with age, which was accelerated in the presence of cardiovascular disease. On the contrary, native T1 increased with age in patients, but not in controls. Pulse wave velocity was associated with native T1 in the presence of disease, but not in health. Native T1 showed a strong relationship with markers of structural and functional left ventricular remodeling and diastolic impairment. Ischemic and nonischemic pathophysiology of ventricular remodeling showed a similar slope of relationship between pulse wave velocity and native T1. However, in nonischemic patients, increase in pulse wave velocity was associated with greater increase in native T1. Aortic stiffness is related to age, and this process is accelerated in the presence of disease. On the contrary, increase in interstitial myocardial fibrosis is associated with age in the presence of disease. Patients with ischemic and nonischemic dilated cardiomyopathy have a similar relationship between native T1 and pulse wave velocity, which is stronger in the latter group.

Outcome in phospholamban R14del carriers: results of a large multicentre cohort study

BACKGROUND

The pathogenic phospholamban R14del mutation causes dilated and arrhythmogenic right ventricular cardiomyopathies and is associated with an increased risk of malignant ventricular arrhythmias and end-stage heart failure. We performed a multicentre study to evaluate mortality, cardiac disease outcome, and risk factors for malignant ventricular arrhythmias in a cohort of phospholamban R14del mutation carriers.

METHODS AND RESULTS

Using the family tree mortality ratio method in a cohort of 403 phospholamban R14del mutation carriers, we found a standardized mortality ratio of 1.7 (95% confidence interval, 1.4-2.0) with significant excess mortality starting from the age of 25 years. Cardiological data were available for 295 carriers. In a median follow-up period of 42 months, 55 (19%) individuals had a first episode of malignant ventricular arrhythmias and 33 (11%) had an end-stage heart failure event. The youngest age at which a malignant ventricular arrhythmia occurred was 20 years, whereas for an end-stage heart failure event this was 31 years. Independent risk factors for malignant ventricular arrhythmias were left ventricular ejection fraction <45% and sustained or nonsustained ventricular tachycardia with hazard ratios of 4.0 (95% confidence interval, 1.9-8.1) and 2.6 (95% confidence interval, 1.5-4.5), respectively.

CONCLUSIONS

Phospholamban R14del mutation carriers are at high risk for malignant ventricular arrhythmias and end-stage heart failure, with left ventricular ejection fraction <45% and sustained or nonsustained ventricular tachycardia as independent risk factors. High mortality and a poor prognosis are present from late adolescence. Genetic and cardiac screening is, therefore, advised from adolescence onwards.

Atrial natriuretic peptide affects cardiac remodeling, function, heart failure, and survival in a mouse model of dilated cardiomyopathy

Dilated cardiomyopathy is a frequent cause of heart failure and death. Atrial natriuretic peptide (ANP) is a biomarker of dilated cardiomyopathy, but there is controversy whether ANP modulates the development of heart failure. Therefore, we examined whether ANP affects heart failure, cardiac remodeling, function, and survival in a well-characterized, transgenic model of dilated cardiomyopathy. Mice with dilated cardiomyopathy with normal ANP levels survived longer than mice with partial ANP (P<0.01) or full ANP deficiency (P<0.001). In dilated cardiomyopathy mice, ANP protected against the development of heart failure as indicated by reduced lung water, alveolar congestion, pleural effusions, etc. ANP improved systolic function and reduced cardiomegaly. Pathological cardiac remodeling was diminished in mice with normal ANP as indicated by decreased ventricular interstitial and perivascular fibrosis. Mice with dilated cardiomyopathy and normal ANP levels had better systolic function (P<0.001) than mice with dilated cardiomyopathy and ANP deficiency. Dilated cardiomyopathy was associated with diminished cardiac transcripts for NP receptors A and B in mice with normal ANP and ANP deficiency, but transcripts for NP receptor C and C-type natriuretic peptide were selectively altered in mice with dilated cardiomyopathy and ANP deficiency. Taken together, these data indicate that ANP has potent effects in experimental dilated cardiomyopathy that reduce the development of heart failure, prevent pathological remodeling, preserve systolic function, and reduce mortality. Despite the apparent overlap in physiological function between the NPs, these data suggest that the role of ANP in dilated cardiomyopathy and heart failure is not compensated physiologically by other NPs.

Deep sequence analysis of gene expression identifies osteopontin as a downstream effector of integrin-linked kinase (ILK) in cardiac-specific ILK knockout mice

BACKGROUND

Integrin-linked kinase (ILK) is a serine/threonine kinase that has been linked to human and experimental heart failure, but its role in the heart is not fully understood.

METHODS AND RESULTS

To define the role of cardiomyocyte ILK, we generated cardiac-specific ILK knockout mice using α-myosin heavy chain-driven Cre expression. Cardiac-specific ILK knockout mice spontaneously developed lethal dilated cardiomyopathy and heart failure with an early increase in apoptosis, fibrosis, and cardiac inflammation. To identify downstream effectors, we used deep sequence analysis of gene expression to compare comprehensive transcriptional profiles of cardiac-specific ILK knockout and wild-type hearts from 10-day-old mice before the development of cardiac dysfunction. Approximately 2×10(6) cDNA clones from each genotype were sequenced, corresponding to 33 274 independent transcripts. A total of 93 genes were altered, using nominal thresholds of >1.4-fold change and P<0.001. The most highly upregulated gene was osteopontin (47-fold increase; P=9.6×10(-45)), an inflammatory chemokine implicated in heart failure pathophysiology. ILK also regulated osteopontin expression in cardiomyocytes in vitro. Importantly, blocking antibodies to osteopontin mitigated but did not fully rescue the functional decline in cardiac-specific ILK knockout mice.

CONCLUSIONS

Cardiomyocyte-specific ILK deletion leads to a lethal cardiomyopathy characterized by cardiomyocyte death, fibrosis, and inflammation. Comprehensive profiling identifies ILK-dependent transcriptional effects and implicates osteopontin as a contributor to these phenotypes.

Comparison of transendocardial and intracoronary CD34+ cell transplantation in patients with nonischemic dilated cardiomyopathy

BACKGROUND

In an open-label blinded study, we compared intracoronary and transendocardial CD34(+) cell transplantation in patients with nonischemic dilated cardiomyopathy.

METHODS AND RESULTS

Of the 40 patients with dilated cardiomyopathy, 20 were randomized to receive intracoronary injection and 20 received transendocardial CD34(+) cell delivery. In both groups, CD34(+) cells were mobilized by filgrastim, collected via apheresis, and labeled with technetium-99m radioisotope for single-photon emission computed tomographic imaging. In the intracoronary group, cells were injected intracoronarily in the artery supplying segments of greater perfusion defect on myocardial perfusion scintigraphy. In the transendocardial group, electroanatomic mapping was used to identify viable but dysfunctional myocardium, and transendocardial cell injections were performed. Nuclear single-photon emission computed tomographic imaging for quantification of myocardial retention was performed 18 hours thereafter. At baseline, groups did not differ in age, sex, left ventricular ejection fraction, or N-terminal pro-brain natriuretic peptide levels. The number of CD34(+) cells was also comparable (105 ± 31 × 10(6) in the transendocardial group versus 103 ± 27 × 10(6) in the intracoronary group, P=0.62). At 18 hours after procedure, myocardial retention was higher in the transendocardial group (19.2 ± 4.8%) than in the intracoronary group (4.4 ± 1.2%, P<0.01). At 6 months, left ventricular ejection fraction improved more in the transendocardial group (+8.1 ± 4.3%) than in the intracoronary group (+4.2 ± 2.3%, P=0.03). The same pattern was observed for the 6-minute walk test distance (+125 ± 33 m in the transendocardial group versus +86 ± 13 m in the intracoronary group, P=0.03) and N-terminal pro-brain natriuretic peptide (-628 ± 211 versus -315 ± 133 pg/mL, P=0.04).

CONCLUSIONS

In patients with dilated cardiomyopathy, transendocardial CD34(+) cell transplantation is associated with higher myocardial retention rates and greater improvement in ventricular function, N-terminal pro-brain natriuretic peptide, and exercise capacity compared with intracoronary route.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT01350310.

Comparison of transendocardial and intracoronary CD34+ cell transplantation in patients with nonischemic dilated cardiomyopathy. Circulation. 2013;128:S42-S49. [PMID: 24030420 DOI: 10.1161/circulati onaha.112.000230]

BACKGROUND

In an open-label blinded study, we compared intracoronary and transendocardial CD34(+) cell transplantation in patients with nonischemic dilated cardiomyopathy.

METHODS AND RESULTS

Of the 40 patients with dilated cardiomyopathy, 20 were randomized to receive intracoronary injection and 20 received transendocardial CD34(+) cell delivery. In both groups, CD34(+) cells were mobilized by filgrastim, collected via apheresis, and labeled with technetium-99m radioisotope for single-photon emission computed tomographic imaging. In the intracoronary group, cells were injected intracoronarily in the artery supplying segments of greater perfusion defect on myocardial perfusion scintigraphy. In the transendocardial group, electroanatomic mapping was used to identify viable but dysfunctional myocardium, and transendocardial cell injections were performed. Nuclear single-photon emission computed tomographic imaging for quantification of myocardial retention was performed 18 hours thereafter. At baseline, groups did not differ in age, sex, left ventricular ejection fraction, or N-terminal pro-brain natriuretic peptide levels. The number of CD34(+) cells was also comparable (105 ± 31 × 10(6) in the transendocardial group versus 103 ± 27 × 10(6) in the intracoronary group, P=0.62). At 18 hours after procedure, myocardial retention was higher in the transendocardial group (19.2 ± 4.8%) than in the intracoronary group (4.4 ± 1.2%, P<0.01). At 6 months, left ventricular ejection fraction improved more in the transendocardial group (+8.1 ± 4.3%) than in the intracoronary group (+4.2 ± 2.3%, P=0.03). The same pattern was observed for the 6-minute walk test distance (+125 ± 33 m in the transendocardial group versus +86 ± 13 m in the intracoronary group, P=0.03) and N-terminal pro-brain natriuretic peptide (-628 ± 211 versus -315 ± 133 pg/mL, P=0.04).

CONCLUSIONS

In patients with dilated cardiomyopathy, transendocardial CD34(+) cell transplantation is associated with higher myocardial retention rates and greater improvement in ventricular function, N-terminal pro-brain natriuretic peptide, and exercise capacity compared with intracoronary route.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT01350310.

Myocardial fibrosis as a key determinant of left ventricular remodeling in idiopathic dilated cardiomyopathy: a contrast-enhanced cardiovascular magnetic study

BACKGROUND

In idiopathic dilated cardiomyopathy, there are scarce data on the influence of late gadolinium enhancement (LGE) assessed by cardiovascular magnetic resonance on left ventricular (LV) remodeling.

METHODS AND RESULTS

Fifty-eight consecutive patients with idiopathic dilated cardiomyopathy underwent baseline clinical, biohumoral, and instrumental workup. Medical therapy was optimized after study enrollment. Cardiovascular magnetic resonance was used to assess ventricular volumes, function, and LGE extent at baseline and 24-month follow-up. LV reverse remodeling (RR) was defined as an increase in LV ejection fraction ≥10 U, combined with a decrease in LV end-diastolic volume ≥10% at follow-up. ΔLGE extent was the difference in LGE extent between follow-up and baseline. LV-RR was observed in 22 patients (38%). Multivariate regression analysis showed that the absence of LGE at baseline cardiovascular magnetic resonance was a strong predictor of LV-RR (odds ratio, 10.857 [95% confidence interval, 1.844-63.911]; P=0.008) after correction for age, heart rate, New York Heart Association class, LV volumes, and LV and right ventricular ejection fractions. All patients with baseline LGE (n=26; 45%) demonstrated LGE at follow-up, and no patient without baseline LGE developed LGE at follow-up. In LGE-positive patients, there was an increase in LGE extent over time (P=0.034), which was inversely related to LV ejection fraction variation (Spearman ρ, -0.440; P=0.041). Five patients showed an increase in LGE extent >75th percentile of ΔLGE extent, and among these none experienced LV-RR and 4 had a decrease in LV ejection fraction ≥10 U at follow-up.

CONCLUSIONS

In patients with idiopathic dilated cardiomyopathy, the absence of LGE at baseline is a strong independent predictor of LV-RR at 2-year follow-up, irrespective of the initial clinical status and the severity of ventricular dilatation and dysfunction. The increase in LGE extent during follow-up was associated with progressive LV dysfunction.

Divergent mitochondrial biogenesis responses in human cardiomyopathy

BACKGROUND

Mitochondria are key players in the development and progression of heart failure (HF). Mitochondrial (mt) dysfunction leads to diminished energy production and increased cell death contributing to the progression of left ventricular failure. The fundamental mechanisms that underlie mt dysfunction in HF have not been fully elucidated.

METHODS AND RESULTS

To characterize mt morphology, biogenesis, and genomic integrity in human HF, we investigated left ventricular tissue from nonfailing hearts and end-stage ischemic (ICM) or dilated (DCM) cardiomyopathic hearts. Although mt dysfunction was present in both types of cardiomyopathy, mt were smaller and increased in number in DCM compared with ICM or nonfailing hearts. mt volume density and mtDNA copy number was increased by ≈2-fold (P<0.001) in DCM hearts in comparison with ICM hearts. These changes were accompanied by an increase in the expression of mtDNA-encoded genes in DCM versus no change in ICM. mtDNA repair and antioxidant genes were reduced in failing hearts, suggestive of a defective repair and protection system, which may account for the 4.1-fold increase in mtDNA deletion mutations in DCM (P<0.05 versus nonfailing hearts, P<0.05 versus ICM).

CONCLUSIONS

In DCM, mt dysfunction is associated with mtDNA damage and deletions, which could be a consequence of mutating stress coupled with a peroxisome proliferator-activated receptor γ coactivator 1α-dependent stimulus for mt biogenesis. However, this maladaptive compensatory response contributes to additional oxidative damage. Thus, our findings support further investigations into novel mechanisms and therapeutic strategies for mt dysfunction in DCM.

Effects of carvedilol on plasma levels of pro-inflammatory cytokines in patients with ischemic and nonischemic dilated cardiomyopathy

We prospectively investigated the effects of adding carvedilol to the standard treatment of ischemic and nonischemic dilated cardiomyopathy (DCM), by measuring the plasma levels of pro-inflammatory cytokines. Sixty patients with DCM (35 ischemic and 25 nonischemic) were divided into 2 subgroups: patients on standard therapy alone (digoxin, angiotensin-converting enzyme inhibitors, and diuretics) and patients on standard therapy plus carvedilol. Study participants' serum levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-2 (IL-2), and interleukin-6 (IL-6) were measured at the beginning and again at the end of the study. Left ventricular ejection fraction and left ventricular diastolic function were evaluated by means of radionuclide ventriculography. In ischemic patients on carvedilol, levels of IL-6 and TNF-alpha dropped significantly (P= 0.028 and P=0.034, respectively). In ischemic patients on standard treatment, plasma IL-2 levels were elevated after treatment (P=0.047). No significant differences occurred in IL-6 levels, while TNF-alpha levels were elevated (P=0.008). In nonischemic patients on carvedilol, IL-6 and TNF-alpha levels dropped significantly (P=0.018 and P=0.004, respectively). The left ventricular ejection fraction increased significantly (P=0.006). In nonischemic patients on standard treatment, no significant change occurred in any value. Carvedilol suppressed the plasma levels of TNF-alpha and IL-6 in both ischemic and nonischemic patients. The carvedilol effect was more pronounced in patients with nonischemic dilated cardiomyopathy than in those with ischemic disease.

Peripartum cardiomyopathy: the value of endomyocardial biopsy in diagnosis, prognostication, and therapy

We describe the case of a 21-year-old black female who was readmitted postpartum because of increasing exertional dyspnea, orthopnea, pleuritic chest pain, and pedal edema. The patient underwent a successful course of clinical treatment for peripartum cardiomyopathy consisting of a regimen of digoxin, diuretics, captopril, and heparin. The results of an endomyocardial biopsy done at readmission were normal: there was no evidence of inflammation, necrosis, or fibrosis; the endocardium, intramural arterioles, mitochondria, and ultrastructure were normal, as was the amount of glycogen; nuclear chromatin were evenly dispersed; and no antibodies were found. Previous studies have shown that approximately half of patients who suffer from peripartum cardiomyopathy recover, while half develop a more severe form of dilated cardiomyopathy. We venture to speculate that normal endomyocardial biopsy findings during the acute stage of the disease may be predictive of recovery. With more certainty, we propose that histologic findings from material taken during an acute episode can and should guide the course of therapy.