Abnormalities in Alternative Splicing of Apoptotic Genes and Cardiovascular Diseases

Apoptosis is required for normal heart development in the embryo, but has also been shown to be an important factor in the occurrence of heart disease. Alternative splicing of apoptotic genes is currently emerging as a diagnostic and therapeutic target for heart disease. This review addresses the involvement of abnormalities in alternative splicing of apoptotic genes in cardiac disorders including cardiomyopathy, myocardial ischemia and heart failure. Many pro-apoptotic members of the Bcl-2 family have alternatively spliced isoforms that lack important active domains. These isoforms can play a negative regulatory role by binding to and inhibiting the pro-apoptotic forms. Alternative splicing is observed to be increased in various cardiovascular diseases with the level of alternate transcripts increasing elevated in diseased hearts compared to healthy subjects. In many cases these isoforms appear to be the underlying cause of the disease, while in others they may be induced in response to cardiovascular pathologies. Regardless of this, the detection of alternate splicing events in the heart can serve as useful diagnostic or prognostic tools, while those splicing events that seem to play a causative role in cardiovascular disease make attractive future drug targets.

Decrement Evoked Potential Mapping: Basis of a Mechanistic Strategy for Ventricular Tachycardia Ablation

BACKGROUND

Substrate-based mapping for ventricular tachycardia (VT) ablation is hampered by its inability to determine critical sites of the VT circuit. We hypothesized that those potentials, which delay with a decremental extrastimulus (decrement evoked potentials or DEEPs), are more likely to colocalize with the diastolic pathways of VT circuits.

METHODS AND RESULTS

DEEPs were identified in intraoperative left ventricular maps from 6 patients with ischemic cardiomyopathy (total 9 VTs) and were compared with late potential (LP) and activation maps of the diastolic pathway for each VT. Mathematical modeling was also used to further validate and elucidate the mechanisms of DEEP mapping. All patients demonstrated regions of DEEPs and LPs. The mean endocardial surface area of these potentials was 18±4% and 21±6%, respectively (P=0.13). The mean sensitivity for identifying the diastolic pathway in VT was 50±23% for DEEPs and 36±32% for LPs (P=0.31). The mean specificity was 43±23% versus 20±8% for DEEP and LP mapping, respectively (P=0.031). The electrograms that displayed the greatest decrement in each case had a sensitivity and specificity for the VT isthmus of 29±10% and 95±1%, respectively. Mathematical modeling studies recapitulated DEEPs at the VT isthmus and demonstrated their role in VT initiation with a critical degree of decrement.

CONCLUSIONS

In this preliminary study, DEEP mapping was more specific than LP mapping for identifying the critical targets of VT ablation. The mechanism of DEEPs relates to conduction velocity restitution magnified by zigzag conduction within scar channels.

Electrocardiographic Left Atrial Abnormality and Risk of Stroke: Northern Manhattan Study

BACKGROUND AND PURPOSE

Electrocardiographic left atrial abnormality has been associated with stroke independently of atrial fibrillation (AF), suggesting that atrial thromboembolism may occur in the absence of AF. If true, we would expect an association with cryptogenic or cardioembolic stroke rather than noncardioembolic stroke.

METHODS

We conducted a case-cohort analysis in the Northern Manhattan Study, a prospective cohort study of stroke risk factors. P-wave terminal force in lead V1 was manually measured from baseline ECGs of participants in sinus rhythm who subsequently had ischemic stroke (n=241) and a randomly selected subcohort without stroke (n=798). Weighted Cox proportional hazard models were used to examine the association between P-wave terminal force in lead V1 and stroke etiologic subtypes while adjusting for baseline demographic characteristics, history of AF, heart failure, diabetes mellitus, hypertension, tobacco use, and lipid levels.

RESULTS

Mean P-wave terminal force in lead V1 was 4452 (±3368) μV*ms among stroke cases and 3934 (±2541) μV*ms in the subcohort. P-wave terminal force in lead V1 was associated with ischemic stroke (adjusted hazard ratio per SD, 1.20; 95% confidence interval, 1.03-1.39) and the composite of cryptogenic or cardioembolic stroke (adjusted hazard ratio per SD, 1.31; 95% confidence interval, 1.08-1.58). There was no definite association with noncardioembolic stroke subtypes (adjusted hazard ratio per SD, 1.14; 95% confidence interval, 0.92-1.40). Results were similar after excluding participants with a history of AF at baseline or new AF during follow-up.

CONCLUSIONS

ECG-defined left atrial abnormality was associated with incident cryptogenic or cardioembolic stroke independently of the presence of AF, suggesting atrial thromboembolism may occur without recognized AF.

Abnormal Left Ventricular Mechanics of Ventricular Ectopic Beats: Insights Into Origin and Coupling Interval in Premature Ventricular Contraction-Induced Cardiomyopathy

BACKGROUND

Left ventricular (LV) dyssynchrony caused by premature ventricular contractions (PVCs) has been proposed as a mechanism of PVC-induced cardiomyopathy. We sought to understand the impact of different PVC locations and coupling intervals (prematurity) on LV regional mechanics and global function of the PVC beat itself.

METHODS AND RESULTS

Using our premature pacing algorithm, pentageminal PVCs at coupling intervals of 200 to 375 ms were delivered from the epicardial right ventricular apex, RV outflow tract, and LV free wall, as well as premature atrial contractions, from the left atrial appendage at a coupling interval of 200 ms in 7 healthy canines. LV short-axis echocardiographic images, LV stroke volume, and dP/dtmax were obtained during all ectopic beats and ventricular pacing. LV dyssynchrony was assessed by dispersion of QRS-to-peak strain (earliest-last QRS-to-peak strain) between 6 different LV segments during each of the aforementioned beats (GE, EchoPac). LV dyssynchrony was greater during long-coupled rather than short-coupled PVCs and PVCs at 375 ms compared with rapid ventricular pacing at 400 ms (P<0.0001), whereas no difference was found between PVC locations. Longer PVC coupling intervals were associated with greater stroke volume and dP/dtmax despite more pronounced dyssynchrony (P<0.001).

CONCLUSIONS

PVCs with longer coupling intervals demonstrate more pronounced LV dyssynchrony, whereas PVC location has minimal impact. LV dyssynchrony cannot be attributed to prematurity or abnormal ventricular activation alone, but rather to a combination of both. This study suggests that late-coupled PVCs may cause a more severe cardiomyopathy if dyssynchrony is the leading mechanism responsible for PVC-induced cardiomyopathy.

Genetics of sudden cardiac death

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

The spectrum of epidemiology underlying sudden cardiac death

Sudden cardiac death (SCD) from cardiac arrest is a major international public health problem accounting for an estimated 15%-20% of all deaths. Although resuscitation rates are generally improving throughout the world, the majority of individuals who experience a sudden cardiac arrest will not survive. SCD most often develops in older adults with acquired structural heart disease, but it also rarely occurs in the young, where it is more commonly because of inherited disorders. Coronary heart disease is known to be the most common pathology underlying SCD, followed by cardiomyopathies, inherited arrhythmia syndromes, and valvular heart disease. During the past 3 decades, declines in SCD rates have not been as steep as for other causes of coronary heart disease deaths, and there is a growing fraction of SCDs not due to coronary heart disease and ventricular arrhythmias, particularly among certain subsets of the population. The growing heterogeneity of the pathologies and mechanisms underlying SCD present major challenges for SCD prevention, which are magnified further by a frequent lack of recognition of the underlying cardiac condition before death. Multifaceted preventative approaches, which address risk factors in seemingly low-risk and known high-risk populations, will be required to decrease the burden of SCD. In this Compendium, we review the wide-ranging spectrum of epidemiology underlying SCD within both the general population and in high-risk subsets with established cardiac disease placing an emphasis on recent global trends, remaining uncertainties, and potential targeted preventive strategies.

Clinical management and prevention of sudden cardiac death

Despite the revolutionary advancements in the past 3 decades in the treatment of ventricular tachyarrhythmias with device-based therapy, sudden cardiac death (SCD) remains an enormous public health burden. Survivors of SCD are generally at high risk for recurrent events. The clinical management of such patients requires a multidisciplinary approach from postresuscitative care to a thorough cardiovascular investigation in an attempt to identify the underlying substrate, with potential to eliminate or modify the triggers through catheter ablation and ultimately an implantable cardioverter-defibrillator (ICD) for prompt treatment of recurrences in those at risk. Early recognition of low left ventricular ejection fraction as a strong predictor of death and association of ventricular arrhythmias with sudden death led to significant investigation with antiarrhythmic drugs. The lack of efficacy and the proarrhythmic effects of drugs catalyzed the development and investigation of the ICD through several major clinical trials that proved the efficacy of ICD as a bedrock tool to detect and promptly treat life-threatening arrhythmias. The ICD therapy is routinely used for primary prevention of SCD in patients with cardiomyopathy and high risk inherited arrhythmic conditions and secondary prevention in survivors of sudden cardiac arrest. This compendium will review the clinical management of those surviving SCD and discuss landmark studies of antiarrhythmic drugs, ICD, and cardiac resynchronization therapy in the primary and secondary prevention of SCD.

A Rapid, High-Quality, Cost-Effective, Comprehensive and Expandable Targeted Next-Generation Sequencing Assay for Inherited Heart Diseases

RATIONALE

Thousands of mutations across >50 genes have been implicated in inherited cardiomyopathies. However, options for sequencing this rapidly evolving gene set are limited because many sequencing services and off-the-shelf kits suffer from slow turnaround, inefficient capture of genomic DNA, and high cost. Furthermore, customization of these assays to cover emerging targets that suit individual needs is often expensive and time consuming.

OBJECTIVE

We sought to develop a custom high throughput, clinical-grade next-generation sequencing assay for detecting cardiac disease gene mutations with improved accuracy, flexibility, turnaround, and cost.

METHODS AND RESULTS

We used double-stranded probes (complementary long padlock probes), an inexpensive and customizable capture technology, to efficiently capture and amplify the entire coding region and flanking intronic and regulatory sequences of 88 genes and 40 microRNAs associated with inherited cardiomyopathies, congenital heart disease, and cardiac development. Multiplexing 11 samples per sequencing run resulted in a mean base pair coverage of 420, of which 97% had >20× coverage and >99% were concordant with known heterozygous single nucleotide polymorphisms. The assay correctly detected germline variants in 24 individuals and revealed several polymorphic regions in miR-499. Total run time was 3 days at an approximate cost of $100 per sample.

CONCLUSIONS

Accurate, high-throughput detection of mutations across numerous cardiac genes is achievable with complementary long padlock probe technology. Moreover, this format allows facile insertion of additional probes as more cardiomyopathy and congenital heart disease genes are discovered, giving researchers a powerful new tool for DNA mutation detection and discovery.

Relationship between alcohol consumption and cardiac structure and function in the elderly: the Atherosclerosis Risk In Communities Study

BACKGROUND

Excessive alcohol consumption is associated with cardiomyopathy, but the influence of moderate alcohol use on cardiac structure and function is largely unknown.

METHODS AND RESULTS

We studied 4466 participants from visit 5 of the Atherosclerosis Risk in Communities (ARIC) study (76±5 years and 60% women) who underwent transthoracic echocardiography, excluding former drinkers and those with significant valvular disease. Participants were classified into 4 categories based on self-reported alcohol intake: nondrinkers, drinkers of ≤7, ≥7 to 14, and ≥14 drinks per week. We related alcohol intake to measures of cardiac structure and function, stratified by sex, and fully adjusted for covariates. In both genders, increasing alcohol intake was associated with larger left ventricular diastolic and systolic diameters and larger left atrial diameter (P<0.05). In men, increasing alcohol intake was associated with greater left ventricular mass (8.2±3.8 g per consumption category; P=0.029) and higher E/E' ratio (0.82±0.33 per consumption category; P=0.014). In women, increasing alcohol intake was associated with lower left ventricular ejection fraction (-1.9±0.6% per consumption category; P=0.002) and a tendency for worse left ventricular global longitudinal strain (0.45±0.25% per consumption category; P=0.07).

CONCLUSIONS

In an elderly community-based population, increasing alcohol intake is associated with subtle alterations in cardiac structure and function, with women appearing more susceptible than men to the cardiotoxic effects of alcohol.

ZBTB17 (MIZ1) Is Important for the Cardiac Stress Response and a Novel Candidate Gene for Cardiomyopathy and Heart Failure

BACKGROUND

Mutations in sarcomeric and cytoskeletal proteins are a major cause of hereditary cardiomyopathies, but our knowledge remains incomplete as to how the genetic defects execute their effects.

METHODS AND RESULTS

We used cysteine and glycine-rich protein 3, a known cardiomyopathy gene, in a yeast 2-hybrid screen and identified zinc-finger and BTB domain-containing protein 17 (ZBTB17) as a novel interacting partner. ZBTB17 is a transcription factor that contains the peak association signal (rs10927875) at the replicated 1p36 cardiomyopathy locus. ZBTB17 expression protected cardiac myocytes from apoptosis in vitro and in a mouse model with cardiac myocyte-specific deletion of Zbtb17, which develops cardiomyopathy and fibrosis after biomechanical stress. ZBTB17 also regulated cardiac myocyte hypertrophy in vitro and in vivo in a calcineurin-dependent manner.

CONCLUSIONS

We revealed new functions for ZBTB17 in the heart, a transcription factor that may play a role as a novel cardiomyopathy gene.

Loss of cardiomyocyte integrin-linked kinase produces an arrhythmogenic cardiomyopathy in mice

BACKGROUND

Integrin-linked kinase (ILK), a serine/threonine protein kinase, has roles in cell signaling and molecular scaffolding. ILK mutation/deletion causes cardiomyopathic phenotypes, but the functional and electrophysiological features have not been characterized. This study investigated the structural, functional, ion channel, and electrophysiological changes associated with cardiomyocyte-directed ILK deletion in mice.

METHODS AND RESULTS

Adult mice with cardiomyocyte-directed ILK knockout were compared with littermate controls. Knockout mice showed markedly increased mortality, with sudden death beginning after 5 weeks and 100% mortality at 18 weeks. In 10-week-old knockout mice, spontaneous and inducible ventricular tachyarrhythmias were common, occurring in 60% and 86%, respectively, and absent in controls (P<0.001, P<0.05 versus knockout mice). Ventricular refractoriness was prolonged, along with both QRS and QT interval. Action potentials were prolonged and displayed triggered activity. A wide range of ion currents were downregulated, including total, fast and slow components of transient outward K(+) current and inward rectifier K(+) current, along with corresponding ion channel subunit genes, providing a plausible explanation of action potential prolongation. At 5 weeks, only voltage-dependent K(+) currents were reduced, possibly related to direct ILK-Kv4.2 subunit interactions. Action potentials were prolonged, but no arrhythmias or cardiac dysfunction were noted. Structural remodeling was prominent at 10 weeks: connexin-43 was downregulated and redistributed to lateral cell margins, and left ventricular fibrosis occurred, with a strong regional distribution (predominating in the basal left ventricle). Conduction was slowed. High-throughput quantitative polymerase reaction gene-expression studies in 10-week-old ILK knockout showed upregulation of structural, remodeling and fibrosis-related genes, and downregulation of a wide range of ion channel and transporter subunits.

CONCLUSIONS

Cardiomyocyte ILK deletion produces a lethal arrhythmogenic cardiomyopathy associated with important ion channel and structural remodeling.

Interdependence of Parkin-Mediated Mitophagy and Mitochondrial Fission in Adult Mouse Hearts

RATIONALE

The role of Parkin in hearts is unclear. Germ-line Parkin knockout mice have normal hearts, but Parkin is protective in cardiac ischemia. Parkin-mediated mitophagy is reportedly either irrelevant, or a major factor, in the lethal cardiomyopathy evoked by cardiac myocyte-specific interruption of dynamin-related protein 1 (Drp1)-mediated mitochondrial fission.

OBJECTIVE

To understand the role of Parkin-mediated mitophagy in normal and mitochondrial fission-defective adult mouse hearts.

METHODS AND RESULTS

Parkin mRNA and protein were present at low levels in normal mouse hearts, but were upregulated after cardiac myocyte-directed Drp1 gene deletion in adult mice. Alone, forced cardiac myocyte Parkin overexpression activated mitophagy without adverse effects. Likewise, cardiac myocyte-specific Parkin deletion evoked no adult cardiac phenotype, revealing no essential function for, and tolerance of, Parkin-mediated mitophagy in normal hearts. Concomitant conditional Parkin deletion with Drp1 ablation in adult mouse hearts prevented Parkin upregulation in mitochondria of fission-defective hearts, also increasing 6-week survival, improving ventricular ejection performance, mitigating adverse cardiac remodeling, and decreasing cardiac myocyte necrosis and replacement fibrosis. Underlying the Parkin knockout rescue was suppression of Drp1-induced hyper-mitophagy, assessed as ubiquitination of mitochondrial proteins and mitochondrial association of autophagosomal p62/sequestosome 1 (SQSTM1) and processed microtubule-associated protein 1 light chain 3 (LC3-II). Consequently, mitochondrial content of Drp1-deficient hearts was preserved. Parkin deletion did not alter characteristic mitochondrial enlargement of Drp1-deficient cardiac myocytes.

CONCLUSIONS

Parkin is rare in normal hearts and dispensable for constitutive mitophagic quality control. Ablating Drp1 in adult mouse cardiac myocytes not only interrupts mitochondrial fission, but also markedly upregulates Parkin, thus provoking mitophagic mitochondrial depletion that contributes to the lethal cardiomyopathy.

Early detection of anthracycline cardiotoxicity and improvement with heart failure therapy

BACKGROUND

Three types of anthracycline-induced cardiotoxicities are currently recognized: acute, early-onset chronic, and late-onset chronic. However, data supporting this classification are lacking. We prospectively evaluated incidence, time of occurrence, clinical correlates, and response to heart failure therapy of cardiotoxicity.

METHODS AND RESULTS

We assessed left ventricular ejection fraction (LVEF), at baseline, every 3 months during chemotherapy and for the following year, every 6 months over the following 4 years, and yearly afterward in a heterogeneous cohort of 2625 patients receiving anthracycline-containing therapy. In case of cardiotoxicity (LVEF decrease >10 absolute points, and <50%), heart failure therapy was initiated. Recovery from cardiotoxicity was defined as partial (LVEF increase >5 absolute points and >50%) or full (LVEF increase to the baseline value). The median follow-up was 5.2 (quartile 1 to quartile 3, 2.6-8.0) years. The overall incidence of cardiotoxicity was 9% (n=226). The median time elapsed between the end of chemotherapy and cardiotoxicity development was 3.5 (quartile 1 to quartile 3, 3-6) months. In 98% of cases (n=221), cardiotoxicity occurred within the first year. Twenty-five (11%) patients had full recovery, and 160 (71%) patients had partial recovery. At multivariable analysis, end-chemotherapy LVEF (hazard ratio, 1.37; 95% confidence interval, 1.33-1.42 for each percent unit decrement) and cumulative doxorubicin dose (hazard ratio, 1.09; 95% confidence interval, 1.04-1.15 for each 50 mg/m(2) increment) were independent correlates of cardiotoxicity.

CONCLUSIONS

Most cardiotoxicity after anthracycline-containing therapy occurs within the first year and is associated with anthracycline dose and LVEF at the end of treatment. Early detection and prompt therapy of cardiotoxicity appear crucial for substantial recovery of cardiac function.

Cardiomyopathy and Worsened Ischemic Heart Failure in SM22-α Cre-Mediated Neuropilin-1 Null Mice: Dysregulation of PGC1α and Mitochondrial Homeostasis

OBJECTIVE

Neuropilin-1 (NRP-1) is a multidomain membrane receptor involved in angiogenesis and development of neuronal circuits, however, the role of NRP-1 in cardiovascular pathophysiology remains elusive.

APPROACH AND RESULTS

In this study, we first observed that deletion of NRP-1 induced peroxisome proliferator-activated receptor γ coactivator 1α in cardiomyocytes and vascular smooth muscle cells, which was accompanied by dysregulated cardiac mitochondrial accumulation and induction of cardiac hypertrophy- and stress-related markers. To investigate the role of NRP-1 in vivo, we generated mice lacking Nrp-1 in cardiomyocytes and vascular smooth muscle cells (SM22-α-Nrp-1 KO), which exhibited decreased survival rates, developed cardiomyopathy, and aggravated ischemia-induced heart failure. Mechanistically, we found that NRP-1 specifically controls peroxisome proliferator-activated receptor γ coactivator 1 α and peroxisome proliferator-activated receptor γ in cardiomyocytes through crosstalk with Notch1 and Smad2 signaling pathways, respectively. Moreover, SM22-α-Nrp-1 KO mice exhibited impaired physical activities and altered metabolite levels in serum, liver, and adipose tissues, as demonstrated by global metabolic profiling analysis.

CONCLUSIONS

Our findings provide new insights into the cardioprotective role of NRP-1 and its influence on global metabolism.

Differential Cardiac MicroRNA Expression Predicts the Clinical Course in Human Enterovirus Cardiomyopathy

BACKGROUND

Investigation of disease pathogenesis confined to protein-coding regions of the genome may be incomplete because many noncoding variants are associated with disease. We aimed to identify novel predictive markers for the course of enterovirus (CVB3) cardiomyopathy by screening for noncoding elements influencing the grossly different antiviral capacity of individual patients.

METHODS AND RESULTS

Transcriptome mapping of CVB3 cardiomyopathy patients revealed distinctive cardiac microRNA (miR) patterns associated with spontaneous virus clearance and recovery (CVB3-ELIM) versus virus persistence and progressive clinical deterioration (CVB3-PERS). Profiling of protein-coding genes and 754 miRs in endomyocardial biopsies of test cohorts was performed at their initial presentation, and those spontaneously eliminating the virus were compared with those with virus persistence on follow-up. miR profiling revealed highly significant differences in cardiac levels of 16 miRs, but not of protein-coding genes. Evaluation of this primary distinctive miR pattern in validation cohorts, and multivariate receiver operating characteristic curve analysis, confirmed this pattern as highly predictive for disease course (area under the curve, 0.897±0.071; 95% confidence interval, 0.758-1.000). Eight miRs were strongly induced in CVB3-PERS (miRs 135b, 155, 190, 422a, 489, 590, 601, 1290), but undetectable in CVB3-ELIM or controls. They are predicted to target multiple immune response genes, and 2 of these were confirmed by antisense-mediated ablation of miRs 135b, 190, and 422a in the monocytic THP-1 cell line.

CONCLUSIONS

An immediate clinical application of the data is cardiac miR profiling to assess the risk of virus persistence and progressive clinical deterioration in CVB3 cardiomyopathy. Patients at risk are eligible for immediate antiviral therapy to minimize irreversible cardiac damage.

Cardiac structure and function across the glycemic spectrum in elderly men and women free of prevalent heart disease: the Atherosclerosis Risk In the Community study

BACKGROUND

Individuals with diabetes mellitus and pre-diabetes mellitus are at particularly high risk of incident heart failure or death, even after accounting for known confounders. Nevertheless, the extent of impairments in cardiac structure and function in elderly individuals with diabetes mellitus and pre-diabetes mellitus is not well known. We aimed to assess the relationship between echocardiographic measures of cardiac structure and function and dysglycemia.

METHODS AND RESULTS

We assessed measures of cardiac structure and function in 4419 participants without prevalent coronary heart disease or heart failure who attended the Atherosclerosis Risk In the Community (ARIC) visit 5 examination (2011-2013) and underwent transthoracic echocardiography (age, 75±6 years; 61% women, 23% black). Subjects were grouped across the dysglycemia spectrum as normal (39%), pre-diabetes mellitus (31%), or diabetes mellitus (30%) based on medical history, antidiabetic medication use, and glycated hemoglobin levels. Glycemic status was related to measures of cardiac structure and function. Worsening dysglycemia was associated with increased left ventricular mass, worse diastolic function, and subtle reduction in left ventricular systolic function (P≤0.01 for all). For every 1% higher glycated hemoglobin, left ventricular mass was higher by 3.0 g (95% confidence interval, 1.5-4.6 g), E/E' by 0.5 (95% confidence interval, 0.4-0.7), and global longitudinal strain by 0.3% (95% confidence interval, 0.2-0.4) in multivariable analyses.

CONCLUSIONS

In a large contemporary biracial cohort of elderly subjects without prevalent cardiovascular disease or heart failure, dysglycemia was associated with subtle and subclinical alterations of cardiac structure, and left ventricular systolic and diastolic function. It remains unclear whether these are sufficient to explain the heightened risk of heart failure in individuals with diabetes mellitus.

Chronic administration of the nitroxyl donor 1-nitrosocyclo hexyl acetate limits left ventricular diastolic dysfunction in a mouse model of diabetes mellitus in vivo

BACKGROUND

Nitroxyl (HNO), a redox congener of nitric oxide (NO·), is a novel regulator of cardiovascular function, combining concomitant positive inotropic, lusitropic, and vasodilator properties. Moreover, HNO exhibits myocardial antihypertrophic and superoxide-suppressing actions. Despite these favorable actions, the impact of chronic HNO administration has yet to be reported in the context of cardiomyopathy. Diabetic cardiomyopathy is characterized by early diastolic dysfunction and adverse left ventricular (LV) structural remodeling, with LV superoxide generation playing a major causal role. We tested the hypothesis that the HNO donor 1-nitrosocyclohexylacetate (1-NCA) limits cardiomyocyte hypertrophy and LV diastolic dysfunction in a mouse model of diabetes mellitus in vivo.

METHODS AND RESULTS

Diabetes mellitus was induced in male FVB/N mice using streptozotocin. After 4 weeks, diabetic and nondiabetic mice were allocated to 1-NCA therapy (83 mg/kg per day IP) or vehicle and followed up for a further 4 weeks. Diabetes mellitus-induced LV diastolic dysfunction was evident on echocardiography-derived E and A wave velocities, E:A ratio, deceleration, and isovolumic relaxation times; LV systolic function was preserved. Increased LV cardiomyocyte size, hypertrophic and profibrotic gene expression, and upregulation of LV superoxide were also evident. These characteristics of diabetic cardiomyopathy were largely prevented by 1-NCA treatment. Selectivity of 1-NCA as an HNO donor was demonstrated by sensitivity of acute 1-NCA to l-cysteine but not to hydroxocobalamin in the normal rat heart ex vivo.

CONCLUSIONS

Our studies provide the first evidence that HNO donors may represent a promising strategy for treatment of diabetic cardiomyopathy and implies therapeutic efficacy in settings of chronic heart failure.

Application of Next Generation Sequencing for personalized medicine for sudden cardiac death

Sudden cardiac death (SCD) is a serious public health problem. In the United States, more than 300,000 people are affected by SCD every year. Significantly, sudden deaths represent 20% of the total mortality and 50% of cardiovascular mortality in Western countries. In addition, SCD constitutes one of the most important unsolved challenges in the practice of forensic pathology because of the failure to determine the exact cause of sudden death. In young individuals, SCD is frequently caused by cardiomyopathies and channelopathies, that have generally an autosomal dominant pattern of inheritance. The impact of genetics and genetic testing on the clinical management of these diseases is unquestioned. In particular, genetic tests are an important tool for identifying pre-symptomatic individuals carrying genetic variant that predisposes them to SCD. High-throughput sequencing technologies offer novel opportunities to deeper investigate the genetic background underlying these fatal diseases and to early identify individuals at risk for SCD. In this review, we provide an overview of the development of Next-Generation Sequencing (NGS) technologies and of guidelines useful to design an efficient sequencing protocol and to perform an accurate data analysis. We suggest a flow chart to follow for the set up of a genetic screening protocol for the prevention of cardiac pathologies, in particular SCD events, in young athletes.

Extracellular volume fraction is more closely associated with altered regional left ventricular velocities than left ventricular ejection fraction in nonischemic cardiomyopathy

BACKGROUND

Nonischemic cardiomyopathy is a common cause of left ventricular (LV) dysfunction and myocardial fibrosis. The purpose of this study was to noninvasively evaluate changes in segmental LV extracellular volume (ECV) fraction, LV velocities, myocardial scar, and wall motion in nonischemic cardiomyopathy patients.

METHODS AND RESULTS

Cardiac MRI including pre- and postcontrast myocardial T1 mapping and velocity quantification (tissue phase mapping) of the LV (basal, midventricular, and apical short axis) was applied in 31 patients with nonischemic cardiomyopathy (50±18 years). Analysis based on the 16-segment American Heart Association model was used to evaluate the segmental distribution of ECV, peak systolic and diastolic myocardial velocities, scar determined by late gadolinium enhancement, and wall motion abnormalities. LV segments with scar or impaired wall motion were significantly associated with elevated ECV (rs =0.26; P<0.001) and reduced peak systolic radial velocities (r=-0.43; P<0.001). Regional myocardial velocities and ECV were similar for patients with reduced (n=12; ECV=0.28±0.06) and preserved left ventricular ejection fraction (n=19; ECV=0.30±0.09). Patients with preserved left ventricular ejection fraction showed significant relationships between increasing ECV and reduced systolic (r=-0.19; r=-0.30) and diastolic (r=0.34; r=0.26) radial and long-axis peak velocities (P<0.001). Even after excluding myocardial segments with late gadolinium enhancement, significant relationships between ECV and segmental LV velocities were maintained indicating the potential of elevated ECV to identify regional diffuse fibrosis not visible by late gadolinium enhancement, which was associated with impaired regional LV function.

CONCLUSIONS

Regionally elevated ECV negatively affected myocardial velocities. The association of elevated regional ECV with reduced myocardial velocities independent of left ventricular ejection fraction suggests a structure-function relationship between altered ECV and segmental myocardial function in nonischemic cardiomyopathy.

The Validity of Adding ECG to the Preparticipation Screening of Athletes An Evidence Based Literature Review

OBJECTIVE

To review the available evidence establishing the validity of adding electrocardiogram to the preparticipation cardiac screening in athletes.

DATA SOURCES

MEDLINE and CINAHL databases were searched. Additional references from the bibliographies of retrieved articles were also reviewed and experts in the area were contacted.

SELECTION CRITERIA

Only original research articles seeking to establish the use of electrocardiography followed by second line investigations in athletes under 36 years of age were reviewed.

SEARCH RESULT AND QUALITY ASSESSMENT

The initial literature search identified 226 papers. Of these, 16 original articles (all type II evidence-population-based clinical studies) met the selection criteria and directly related to the use of electrocardiography in athletes cardiac screening. The methodological qualities of included studies were assessed using the Downs and Black checklist.

CONCLUSION

Screening with electrocardiography represents best clinical practice to prevent or reduce the risk of sudden cardiac death in athletes. It significantly improves the sensitivity of history and physical examination alone; it has reasonable specificity and excellent negative predictive value; and it is cost-effective. Future studies must be large, multicentre, multination, prospective trials powered to determine how different screening options affect the incidence of sudden cardiac death. Efforts should also be targeted toward secondary prevention of sudden cardiac death with pitch side cardiac resuscitation and the immediate use of defibrillator.

Calcium/calmodulin-dependent protein kinase II couples Wnt signaling with histone deacetylase 4 and mediates dishevelled-induced cardiomyopathy

Activation of Wnt signaling results in maladaptive cardiac remodeling and cardiomyopathy. Recently, calcium/calmodulin-dependent protein kinase II (CaMKII) was reported to be a pivotal participant in myocardial remodeling. Because CaMKII was suggested as a downstream target of noncanonical Wnt signaling, we aimed to elucidate the role of CaMKII in dishevelled-1-induced cardiomyopathy and the mechanisms underlying its function. Dishevelled-1-induced cardiomyopathy was reversed by deletion of neither CaMKIIδ nor CaMKIIγ. Therefore, dishevelled-1-transgenic mice were crossed with CaMKIIδγ double-knockout mice. These mice displayed a normal cardiac phenotype without cardiac hypertrophy, fibrosis, apoptosis, or left ventricular dysfunction. Further mechanistic analyses unveiled that CaMKIIδγ couples noncanonical Wnt signaling to histone deacetylase 4 and myosin enhancer factor 2. Therefore, our findings indicate that the axis, consisting of dishevelled-1, CaMKII, histone deacetylase 4, and myosin enhancer factor 2, is an attractive therapeutic target for prevention of cardiac remodeling and its progression to left ventricular dysfunction.

Prognostic value of quantitative contrast-enhanced cardiovascular magnetic resonance for the evaluation of sudden death risk in patients with hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most common cause of sudden death in the young, although not all patients eligible for sudden death prevention with an implantable cardioverter-defibrillator are identified. Contrast-enhanced cardiovascular magnetic resonance with late gadolinium enhancement (LGE) has emerged as an in vivo marker of myocardial fibrosis, although its role in stratifying sudden death risk in subgroups of HCM patients remains incompletely understood.

METHODS AND RESULTS

We assessed the relation between LGE and cardiovascular outcomes in 1293 HCM patients referred for cardiovascular magnetic resonance and followed up for a median of 3.3 years. Sudden cardiac death (SCD) events (including appropriate defibrillator interventions) occurred in 37 patients (3%). A continuous relationship was evident between LGE by percent left ventricular mass and SCD event risk in HCM patients (P=0.001). Extent of LGE was associated with an increased risk of SCD events (adjusted hazard ratio, 1.46/10% increase in LGE; P=0.002), even after adjustment for other relevant disease variables. LGE of ≥15% of LV mass demonstrated a 2-fold increase in SCD event risk in those patients otherwise considered to be at lower risk, with an estimated likelihood for SCD events of 6% at 5 years. Performance of the SCD event risk model was enhanced by LGE (net reclassification index, 12.9%; 95% confidence interval, 0.3-38.3). Absence of LGE was associated with lower risk for SCD events (adjusted hazard ratio, 0.39; P=0.02). Extent of LGE also predicted the development of end-stage HCM with systolic dysfunction (adjusted hazard ratio, 1.80/10% increase in LGE; P<0.03).

CONCLUSIONS

Extensive LGE measured by quantitative contrast enhanced CMR provides additional information for assessing SCD event risk among HCM patients, particularly patients otherwise judged to be at low risk.

Actin binding GFP allows 4D in vivo imaging of myofilament dynamics in the zebrafish heart and the identification of Erbb2 signaling as a remodeling factor of myofibril architecture

RATIONALE

Dilated cardiomyopathy is a leading cause of congestive heart failure and a debilitating complication of antineoplastic therapies. Despite disparate causes for dilated cardiomyopathy, maladaptive cardiac remodeling and decreased systolic function are common clinical consequences, begging an investigation of in vivo contractile dynamics in development and disease, one that has been impossible to date.

OBJECTIVE

To image myocardial contractile filament dynamics in vivo and to assess potential causes of dilated cardiomyopathy in antineoplastic therapies targeting the epidermal growth factor receptor Erbb2.

METHODS AND RESULTS

We generated a transgenic zebrafish line expressing an actin-binding green fluorescent protein in cardiomyocytes, allowing an in vivo imaging of myofilaments. Analysis of this line revealed architectural differences in myofibrils of the distinct cardiomyocyte subtypes. We used this model to investigate the effects of Erbb2 signaling on myofibrillar organization because drugs targeting ERBB2 (HER2/NEU) signaling, a mainstay of breast cancer chemotherapy, cause dilated cardiomyopathy in many patients. High-resolution in vivo imaging revealed that Erbb2 signaling regulates a switch between a dense apical network of filamentous myofibrils and the assembly of basally localized myofibrils in ventricular cardiomyocytes.

CONCLUSIONS

Using this novel line, we compiled a reference for myofibrillar microarchitecture among myocardial subtypes in vivo and at different developmental stages, establishing this model as a tool to analyze in vivo cardiomyocyte contractility and remodeling for a broad range of cardiovascular questions. Furthermore, we applied this model to study Erbb2 signaling in cardiomyopathy. We show a direct link between Erbb2 activity and remodeling of myofibrils, revealing an unexpected mechanism with potentially important implications for prevention and treatment of cardiomyopathy.

β-adrenergic receptor-mediated cardiac contractility is inhibited via vasopressin type 1A-receptor-dependent signaling

BACKGROUND

Enhanced arginine vasopressin levels are associated with increased mortality during end-stage human heart failure, and cardiac arginine vasopressin type 1A receptor (V1AR) expression becomes increased. Additionally, mice with cardiac-restricted V1AR overexpression develop cardiomyopathy and decreased β-adrenergic receptor (βAR) responsiveness. This led us to hypothesize that V1AR signaling regulates βAR responsiveness and in doing so contributes to development of heart failure.

METHODS AND RESULTS

Transaortic constriction resulted in decreased cardiac function and βAR density and increased cardiac V1AR expression, effects reversed by a V1AR-selective antagonist. Molecularly, V1AR stimulation led to decreased βAR ligand affinity, as well as βAR-induced Ca(2+) mobilization and cAMP generation in isolated adult cardiomyocytes, effects recapitulated via ex vivo Langendorff analysis. V1AR-mediated regulation of βAR responsiveness was demonstrated to occur in a previously unrecognized Gq protein-independent/G protein receptor kinase-dependent manner.

CONCLUSIONS

This newly discovered relationship between cardiac V1AR and βAR may be informative for the treatment of patients with acute decompensated heart failure and elevated arginine vasopressin.

Targeted analysis of whole genome sequence data to diagnose genetic cardiomyopathy

BACKGROUND

Cardiomyopathy is highly heritable but genetically diverse. At present, genetic testing for cardiomyopathy uses targeted sequencing to simultaneously assess the coding regions of >50 genes. New genes are routinely added to panels to improve the diagnostic yield. With the anticipated $1000 genome, it is expected that genetic testing will shift toward comprehensive genome sequencing accompanied by targeted gene analysis. Therefore, we assessed the reliability of whole genome sequencing and targeted analysis to identify cardiomyopathy variants in 11 subjects with cardiomyopathy.

METHODS AND RESULTS

Whole genome sequencing with an average of 37× coverage was combined with targeted analysis focused on 204 genes linked to cardiomyopathy. Genetic variants were scored using multiple prediction algorithms combined with frequency data from public databases. This pipeline yielded 1 to 14 potentially pathogenic variants per individual. Variants were further analyzed using clinical criteria and segregation analysis, where available. Three of 3 previously identified primary mutations were detected by this analysis. In 6 subjects for whom the primary mutation was previously unknown, we identified mutations that segregated with disease, had clinical correlates, and had additional pathological correlation to provide evidence for causality. For 2 subjects with previously known primary mutations, we identified additional variants that may act as modifiers of disease severity. In total, we identified the likely pathological mutation in 9 of 11 (82%) subjects.

CONCLUSIONS

These pilot data demonstrate that ≈30 to 40× coverage whole genome sequencing combined with targeted analysis is feasible and sensitive to identify rare variants in cardiomyopathy-associated genes.

Investigating the role of uncoupling of troponin I phosphorylation from changes in myofibrillar Ca(2+)-sensitivity in the pathogenesis of cardiomyopathy

Contraction in the mammalian heart is controlled by the intracellular Ca(2+) concentration as it is in all striated muscle, but the heart has an additional signaling system that comes into play to increase heart rate and cardiac output during exercise or stress. β-adrenergic stimulation of heart muscle cells leads to release of cyclic-AMP and the activation of protein kinase A which phosphorylates key proteins in the sarcolemma, sarcoplasmic reticulum and contractile apparatus. Troponin I (TnI) and Myosin Binding Protein C (MyBP-C) are the prime targets in the myofilaments. TnI phosphorylation lowers myofibrillar Ca(2+)-sensitivity and increases the speed of Ca(2+)-dissociation and relaxation (lusitropic effect). Recent studies have shown that this relationship between Ca(2+)-sensitivity and TnI phosphorylation may be unstable. In familial cardiomyopathies, both dilated and hypertrophic (DCM and HCM), a mutation in one of the proteins of the thin filament often results in the loss of the relationship (uncoupling) and blunting of the lusitropic response. For familial dilated cardiomyopathy in thin filament proteins it has been proposed that this uncoupling is causative of the phenotype. Uncoupling has also been found in human heart tissue from patients with hypertrophic obstructive cardiomyopathy as a secondary effect. Recently, it has been found that Ca(2+)-sensitizing drugs can promote uncoupling, whilst one Ca(2+)-desensitizing drug Epigallocatechin 3-Gallate (EGCG) can reverse uncoupling. We will discuss recent findings about the role of uncoupling in the development of cardiomyopathies and the molecular mechanism of the process.

Reversible de novo left ventricular trabeculations in pregnant women: implications for the diagnosis of left ventricular noncompaction in low-risk populations

BACKGROUND

Patients with heart failure and chronic anemia frequently demonstrate left ventricular (LV) trabeculations, which may be compatible with the diagnosis of LV noncompaction. We used the pregnancy model, which is characterized by a reversible increase in cardiac preload and other changes in cardiac function, to assess the development of de novo LV trabeculations in women with morphologically normal hearts.

METHODS AND RESULTS

One hundred two primigravida pregnant women were evaluated longitudinally with a series of echocardiograms in the first trimester, in the third trimester, and postpartum. Echocardiograms were analyzed according to established guidelines. Increased LV trabeculations and the presence of LV noncompaction were based on established criteria. Pregnancy was associated with an increased heart rate, stroke volume, and cardiac output, as well as increased LV volume and mass. During pregnancy, 26 women (25.4%) developed increased trabeculations. Eight women showed sufficient trabeculations to fulfill criteria for LV noncompaction. During the postpartum follow-up period of 24±3 months, 19 women (73%) demonstrated complete resolution of trabeculations, and 5 showed a marked reduction in the trabeculated layer.

CONCLUSIONS

Pregnancy induces de novo LV trabeculations in a significant proportion of women. The results suggest that LV trabeculations occur in response to increased LV loading conditions or other physiological responses to pregnancy and are not specific for LV noncompaction. These factors should be considered in the assessment of individuals with LV trabeculations outside the context of symptoms of heart failure or familial cardiomyopathy.

Sumo E2 enzyme UBC9 is required for efficient protein quality control in cardiomyocytes

RATIONALE

Impairment of proteasomal function is pathogenic in several cardiac proteinopathies and can eventually lead to heart failure. Loss of proteasomal activity often results in the accumulation of large protein aggregates. The ubiquitin proteasome system (UPS) is primarily responsible for cellular protein degradation, and although the role of ubiquitination in this process is well studied, the function of an ancillary post-translational modification, SUMOylation, in protein quality control is not fully understood.

OBJECTIVE

To determine the role of ubiquitin-conjugating enzyme 9 (UBC9), a small ubiquitin-like modifier-conjugating enzyme, in cardiomyocyte protein quality control.

METHODS AND RESULTS

Gain- and loss-of-function approaches were used to determine the importance of UBC9. Overexpression of UBC9 enhanced UPS function in cardiomyocytes, whereas knockdown of UBC9 by small interfering RNA caused significant accumulations of aggregated protein. UPS function and relative activity was analyzed using a UPS reporter protein consisting of a short degron, CL1, fused to the COOH-terminus of green fluorescent protein (GFPu). Subsequently, the effects of UBC9 on UPS function were tested in a proteotoxic model of desmin-related cardiomyopathy, caused by cardiomyocyte-specific expression of a mutated αB crystallin, CryAB(R120G). CryAB(R120G) expression leads to aggregate formation and decreased proteasomal function. Coinfection of UBC9-adenovirus with CryAB(R120G) virus reduced the proteotoxic sequelae, decreasing overall aggregate concentrations. Conversely, knockdown of UBC9 significantly decreased UPS function in the model and resulted in increased aggregate levels.

CONCLUSIONS

UBC9 plays a significant role in cardiomyocyte protein quality control, and its activity can be exploited to reduce toxic levels of misfolded or aggregated proteins in cardiomyopathy.

Nationwide study on hypertrophic cardiomyopathy in Iceland: evidence of a MYBPC3 founder mutation

BACKGROUND

The geographic isolation and homogeneous population of Iceland are ideally suited to ascertain clinical and genetic characteristics of hypertrophic cardiomyopathy (HCM) at the population level.

METHODS AND RESULTS

Medical records and cardiac imaging studies obtained between 1997 and 2010 were reviewed to identify Icelandic patients with HCM. Surviving patients were recruited for clinical and genetic studies. A previously identified Icelandic mutation, MYBPC3 c.927-2A>G, was genotyped, and mutation-negative samples were sequenced for HCM genes and other hypertrophic genes. Record review identified 180 patients with HCM. Genetic analyses of 151 patients defined pathogenic mutations in 101 (67%), including MYBPC3 c.927-2A>G (88 patients, 58%), 4 other MYBPC3 or MYH7 mutations (5 patients, 3.3%), and 2 GLA mutations (8 patients, 5.3%). Haplotype and genetic genealogical data defined MYBPC3 c.927-2A>G as a founder mutation, introduced into the Icelandic population in the 15th century, with a current population prevalence of 0.36%. MYBPC3 c.927-2A>G mutation carriers exhibited phenotypic diversity but were younger at diagnosis (42 versus 49 years; P=0.001) and sustained more adverse events (15% versus 2%; P=0.02) than mutation-negative patients. All-cause mortality for patients with HCM was similar to that of an age-matched Icelandic population (hazard ratio, 0.98; P=0.9). HCM-related mortality (0.78%/y) occurred at a mean age of 68 compared with 81 years for non-HCM-related mortality (P=0.02).

CONCLUSIONS

A founder MYBPC3 mutation that arose >550 years ago is the predominant cause of HCM in Iceland. The MYBPC3 c.927-2A>G mutation is associated with low adverse event rates but earlier cardiovascular mortality, illustrating the impact of genotype on outcomes in HCM.

Super-suppression of mitochondrial reactive oxygen species signaling impairs compensatory autophagy in primary mitophagic cardiomyopathy

RATIONALE

Mitochondrial reactive oxygen species (ROS) are implicated in aging, chronic degenerative neurological syndromes, and myopathies. On the basis of free radical hypothesis, dietary, pharmacological, and genetic ROS suppression has been tested to minimize tissue damage, with remarkable therapeutic efficacy. The effects of mitochondrial-specific ROS suppression in primary mitophagic dysfunction are unknown.

OBJECTIVE

An in vivo dose-ranging analysis of ROS suppression in an experimental cardiomyopathy provoked by defective mitochondrial clearance.

METHODS AND RESULTS

Mice lacking mitofusin 2 (Mfn2) in hearts have impaired parkin-mediated mitophagy leading to accumulation of damaged ROS-producing organelles and progressive heart failure. As expected, cardiomyocyte-directed expression of mitochondrial-targeted catalase at modest levels normalized mitochondrial ROS production and prevented mitochondrial depolarization, respiratory impairment, and structural degeneration in Mfn2 null hearts. In contrast, catalase expression at higher levels that supersuppressed mitochondrial ROS failed to improve either mitochondrial fitness or cardiomyopathy, revealing that ROS toxicity is not the primary mechanism for cardiac degeneration. Lack of benefit from supersuppressing ROS was associated with failure to invoke secondary autophagic pathways of mitochondrial quality control, revealing a role for ROS signaling in mitochondrial clearance. Mitochondrial permeability transition pore function was normal, and genetic inhibition of mitochondrial permeability transition pore function did not alter mitochondrial or cardiac degeneration, in Mfn2 null hearts.

CONCLUSIONS

Local mitochondrial ROS (1) contribute to mitochondrial degeneration and (2) activate mitochondrial quality control mechanisms. A therapeutic window for mitochondrial ROS suppression should minimize the former while retaining the latter, which we achieved by expressing lower levels of catalase.

A bailout approach: Transaxillary Impella implantation in toxic cardiomyopathy

The femoral artery has been the traditional approach for implantation of the Impella left ventricular assist device. We describe the case of a young man with toxic (cocaine-related) cardiomyopathy, severe left ventricular dysfunction, and moderate mitral insufficiency who received a transfemoral Impella left ventricular assist device that was relocated to the right axillary artery due to uncontrolled femoral access bleeding. The patient immediately stabilized post-implantation and was successfully bridged to a full recovery 6 days later.

β-Myosin heavy chain variant Val606Met causes very mild hypertrophic cardiomyopathy in mice, but exacerbates HCM phenotypes in mice carrying other HCM mutations

RATIONALE

Approximately 40% of hypertrophic cardiomyopathy (HCM) is caused by heterozygous missense mutations in β-cardiac myosin heavy chain (β-MHC). Associating disease phenotype with mutation is confounded by extensive background genetic and lifestyle/environmental differences between subjects even from the same family.

OBJECTIVE

To characterize disease caused by β-cardiac myosin heavy chain Val606Met substitution (VM) that has been identified in several HCM families with wide variation of clinical outcomes, in mice.

METHODS AND RESULTS

Unlike 2 mouse lines bearing the malignant myosin mutations Arg453Cys (RC/+) or Arg719Trp (RW/+), VM/+ mice with an identical inbred genetic background lacked hallmarks of HCM such as left ventricular hypertrophy, disarray of myofibers, and interstitial fibrosis. Even homozygous VM/VM mice were indistinguishable from wild-type animals, whereas RC/RC- and RW/RW-mutant mice died within 9 days after birth. However, hypertrophic effects of the VM mutation were observed both in mice treated with cyclosporine, a known stimulator of the HCM response, and compound VM/RC heterozygous mice, which developed a severe HCM phenotype. In contrast to all heterozygous mutants, both systolic and diastolic function of VM/RC hearts was severely impaired already before the onset of cardiac remodeling.

CONCLUSIONS

The VM mutation per se causes mild HCM-related phenotypes; however, in combination with other HCM activators it exacerbates the HCM phenotype. Double-mutant mice are suitable for assessing the severity of benign mutations.

Pre-participation musculoskeletal and cardiac screening of male athletes in the United arab emirates

This study presents the results of pre-participation musculoskeletal and cardiac screening using the Lausanne recommendations, which include a personal and family history, physical examination and electrocardiography. Cross sectional study using the Lausanne screenings and the European Society of Cardiology (ESC) recommendations carried out at Al-Ahli club in Dubai, United Arab Emirates. 230 male athletes participating in organised sports were included. Exclusion criteria were those under 14 or over 35 years old, females and athletes with established cardiovascular disease. Primary outcome are the results of Lausanne screening with outline of the negative, positive and false positive results and number needed to screen. Secondary outcomes include the results of musculoskeletal and neurological screening. A total of 174 (76%) athletes had a negative screening result. Fifty-four athletes (23%) underwent additional testing. Forty-seven athletes (20.4%) had false positive screening results. Seven athletes (3%) had a positive screening result and four athletes (2%) were restricted from sport. The number of athletes needed to screen to detect one lethal cardiovascular condition was 33 athletes. The Lausanne recommendations are well suited for the United Arab Emirates. The number needed to screen to detect one athlete with serious cardiovascular disease is acceptable at 33.

Somatic Cell Reprogramming into Cardiovascular Lineages

Ischemic cardiac disease is the leading cause of death in the developed world. The inability of the adult mammalian heart to adequately repair itself has motivated stem cell researchers to explore various strategies to regenerate cardiomyocytes after myocardial infarction. Over the past century, progressive gains in our knowledge about the cellular mechanisms governing fate determination have led to recent advances in cellular reprogramming. The identification of specific factors capable of inducing pluripotent phenotype in somatic cells as well as factors that can directly reprogram somatic cells into cardiomyocytes suggests the potential for these approaches to translate into clinical therapies in the future. Although conceptually appealing, the field of cell lineage reprogramming is in its infancy, and further research will be needed to improve the efficiency of the reprogramming process and the fidelity of the reprogrammed cells to their in vivo counterpart.

Linker of nucleoskeleton and cytoskeleton complex proteins in cardiac structure, function, and disease

The linker of nucleoskeleton and cytoskeleton (LINC) complex, composed of proteins within the inner and the outer nuclear membranes, connects the nuclear lamina to the cytoskeleton. The importance of this complex has been highlighted by the discovery of mutations in genes encoding LINC complex proteins, which cause skeletal or cardiac myopathies. Herein, this review summarizes structure, function, and interactions of major components of the LINC complex, highlights how mutations in these proteins may lead to cardiac disease, and outlines future challenges in the field.

Mechanistic insights and characterization of sickle cell disease-associated cardiomyopathy

BACKGROUND

Cardiovascular disease is an important cause of morbidity and mortality in sickle cell disease (SCD). We sought to characterize sickle cell cardiomyopathy using multimodality noninvasive cardiovascular testing and identify potential causative mechanisms.

METHODS AND RESULTS

Stable adults with SCD (n=38) and healthy controls (n=13) prospectively underwent same day multiparametric cardiovascular magnetic resonance (cine, T2* iron, vasodilator first pass myocardial perfusion, and late gadolinium enhancement imaging), transthoracic echocardiography, and applanation tonometry. Compared with controls, patients with SCD had severe dilation of the left ventricle (124±27 vs 79±12 mL/m(2)), right ventricle (127±28 vs 83±14 mL/m(2)), left atrium (65±16 vs 41±9 mL/m(2)), and right atrium (78±17 vs 56±17 mL/m(2); P<0.01 for all). Patients with SCD also had a 21% lower myocardial perfusion reserve index than control subjects (1.47±0.34 vs 1.87±0.37; P=0.034). A significant subset of patients with SCD (25%) had evidence of late gadolinium enhancement, whereas only 1 patient had evidence of myocardial iron overload. Diastolic dysfunction was present in 26% of patients with SCD compared with 8% in controls. Estimated filling pressures (E/e', 9.3±2.7 vs 7.3±2.0; P=0.0288) were higher in patients with SCD. Left ventricular dilation and the presence of late gadolinium enhancement were inversely correlated to hepatic T2* times (ie, hepatic iron overload because of frequent blood transfusions; P<0.05 for both), whereas diastolic dysfunction and increased filling pressures were correlated to aortic stiffness (augmentation pressure and index, P<0.05 for all).

CONCLUSIONS

Sickle cell cardiomyopathy is characterized by 4-chamber dilation and in some patients myocardial fibrosis, abnormal perfusion reserve, diastolic dysfunction, and only rarely myocardial iron overload. Left ventricular dilation and myocardial fibrosis are associated with increased blood transfusion requirements, whereas left ventricular diastolic dysfunction is predominantly correlated with increased aortic stiffness.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT01044901.

Determination of the longest intrapatient left ventricular electrical delay may predict acute hemodynamic improvement in patients after cardiac resynchronization therapy

BACKGROUND

One of the reasons for patient nonresponse to cardiac resynchronization therapy is a suboptimal left ventricular (LV) pacing site. LV electric delay (Q-LV interval) has been indicated as a prognostic parameter of cardiac resynchronization therapy response. This study evaluates the LV delay for the optimization of the LV pacing site.

METHODS AND RESULTS

Thirty-two consecutive patients (23 men; mean age, 71±11 years; LV ejection fraction, 30±6%; 18 with ischemic cardiomyopathy; QRS, 181±25 ms; all mean±SD) underwent cardiac resynchronization therapy device implantation. All available tributary veins of the coronary sinus were tested, and the Q-LV interval was measured at each pacing site. The hemodynamic effects of pacing at different sites were evaluated by invasive measurement of LV dP/dtmax at baseline and during pacing. Overall, 2.9±0.8 different veins and 6.4±2.3 pacing sites were tested. In 31 of 32 (96.8%) patients, the highest LV dP/dtmax coincided with the maximum Q-LV interval. Q-LV interval correlated with the increase in LV dP/dtmax in all patients at each site (AR1 ρ=0.98; P<0.001). A Q-LV value >95 ms corresponded to a >10% in LV dP/dtmax. An inverse correlation between paced QRS duration and improvement in LV dP/dtmax was seen in 24 patients (75%).

CONCLUSIONS

Pacing the LV at the latest activated site is highly predictive of the maximum increase in contractility, expressed as LV dP/dtmax. A positive correlation between Q-LV interval and hemodynamic improvement was found in all patients at every pacing site, a value of 95 ms corresponding to an increase in LV dP/dtmax of ≥10%.

Incremental prognostic value of myocardial fibrosis in patients with non-ischemic cardiomyopathy without congestive heart failure

BACKGROUND

We conducted a prospective longitudinal study to investigate the yet unknown clinical significance of myocardial fibrosis in patients with non-ischemic cardiomyopathy without history of congestive heart failure (CHF).

METHODS AND RESULTS

At 3 tertiary referral centers, 228 patients with non-ischemic cardiomyopathy without history of CHF were studied with cardiovascular magnetic resonance for late gadolinium enhancement (LGE) detection and quantification and prospectively followed up for a median of 23 months. The end point was a composite of cardiac death, onset of CHF, and aborted sudden cardiac death. LGE was detected in 61 (27%) patients. Thirty-one of 61 (51%) patients with LGE reached combined end point when compared with 18 of 167 (11%) patients without LGE (hazard ratio, 5.10 [2.78-9.36]; P<0.001). Patients with LGE had greater risk of developing CHF than patients without LGE (hazard ratio, 5.23 [2.61-10.50]; P<0.001) and higher rate of aborted sudden cardiac death (hazard ratio, 8.31 [1.66-41.55]; P=0.010). Multivariate analysis showed that LGE was associated with high likelihood of composite end point independent of other prognostic determinants, including age; duration of cardiomyopathy; and left ventricular volumes, mass, and ejection fraction (hazard ratio, 4.02 [2.08-7.76]; P<0.001). Improvement χ(2) analysis disclosed that LGE addition to models, including clinical data alone or in combination with parameters of left ventricular remodeling and function, yielded an improvement in outcome prediction (P<0.001). Addition of LGE to age and left ventricular ejection fraction improved risk stratification for composite end point (net reclassification improvement, 29.6%) and onset of CHF (net reclassification improvement, 25.4%; both P<0.001).

CONCLUSIONS

In patients with non-ischemic cardiomyopathy without history of CHF, myocardial fibrosis is a strong and independent predictor of outcome, providing incremental prognostic information and improvement in risk stratification beyond clinical data and degree of left ventricular dysfunction.

Desensitization of myofilaments to Ca2+ as a therapeutic target for hypertrophic cardiomyopathy with mutations in thin filament proteins

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a common genetic disorder caused mainly by mutations in sarcomeric proteins and is characterized by maladaptive myocardial hypertrophy, diastolic heart failure, increased myofilament Ca(2+) sensitivity, and high susceptibility to sudden death. We tested the following hypothesis: correction of the increased myofilament sensitivity can delay or prevent the development of the HCM phenotype.

METHODS AND RESULTS

We used an HCM mouse model with an E180G mutation in α-tropomyosin (Tm180) that demonstrates increased myofilament Ca(2+) sensitivity, severe hypertrophy, and diastolic dysfunction. To test our hypothesis, we reduced myofilament Ca(2+) sensitivity in Tm180 mice by generating a double transgenic mouse line. We crossed Tm180 mice with mice expressing a pseudophosphorylated cardiac troponin I (S23D and S24D; TnI-PP). TnI-PP mice demonstrated a reduced myofilament Ca(2+) sensitivity compared with wild-type mice. The development of pathological hypertrophy did not occur in mice expressing both Tm180 and TnI-PP. Left ventricle performance was improved in double transgenic compared with their Tm180 littermates, which express wild-type cardiac troponin I. Hearts of double transgenic mice demonstrated no changes in expression of phospholamban and sarcoplasmic reticulum Ca(2+) ATPase, increased levels of phospholamban and troponin T phosphorylation, and reduced phosphorylation of TnI compared with Tm180 mice. Moreover, expression of TnI-PP in Tm180 hearts inhibited modifications in the activity of extracellular signal-regulated kinase and zinc finger-containing transcription factor GATA in Tm180 hearts.

CONCLUSIONS

Our data strongly indicate that reduction of myofilament sensitivity to Ca(2+) and associated correction of abnormal relaxation can delay or prevent development of HCM and should be considered as a therapeutic target for HCM.