Lethal Heart Failure Research Articles

Lethal Right Heart Failure due to Ruptured Aortic Arch Aneurysm into the Main Pulmonary Artery.

Lethal Right Heart Failure due to Ruptured Aortic Arch Aneurysm into the Main Pulmonary Artery.

Progression of myocardial ischemia leads to unique changes in immediate-early gene expression in the spinal cord dorsal horn.

The pathological consequences of ischemic heart disease involve signaling through the autonomic nervous system. Although early activation may serve to maintain hemodynamic stability, persistent aberrant sympathoexcitation contributes to the development of lethal arrhythmias and heart failure. We hypothesized that as the myocardium reacts and remodels to ischemic injury over time, there is an analogous sequence of gene expression changes in the thoracic spinal cord dorsal horn, the processing center for incoming afferent fibers from the heart to the central nervous system. Acute and chronic myocardial ischemia (MI) was induced in a large animal model of Yorkshire pigs, and the thoracic dorsal horn of treated pigs, along with control nonischemic pigs, was harvested for transcriptome analysis. We identified 32 differentially expressed genes between healthy and acute ischemia cohorts and 46 differentially expressed genes between healthy and chronic ischemia cohorts. The canonical immediate-early gene c-fos was upregulated after acute MI, along with fosB, dual specificity phosphatase 1 and 2 ( dusp1 and dusp2), and early growth response 2 (egr2). After chronic MI, there was a persistent yet unique activation of immediate-early genes, including fosB, nuclear receptor subfamily 4 group A members 1-3 ( nr4a1, nr4a2, and nr4a3), egr3, and TNF-α-induced protein 3 ( tnfaip3). In addition, differentially expressed genes from the chronic MI signature were enriched in pathways linked to apoptosis, immune regulation, and the stress response. These findings support a dynamic progression of gene expression changes in the dorsal horn with maturation of myocardial injury, and they may explain how early adaptive autonomic nervous system responses can maintain hemodynamic stability, whereas prolonged maladaptive signals can predispose patients to arrhythmias and heart failure. NEW & NOTEWORTHY Activation of the autonomic nervous system after myocardial injury can provide early cardiovascular support or prolonged aberrant sympathoexcitation. The later response can lead to lethal arrhythmias and heart failure. This study provides evidence of ongoing changes in the gene expression signature of the spinal cord dorsal horn as myocardial injury progresses over time. These changes could help explain how an adaptive nervous system response can become maladaptive over time.

Abstract P185: Periostin Increases Inducible Nitric Oxide Synthase Expression in Right Ventricular Fibroblasts From Pulmonary Arterial Hypertension Rats

Background: Pulmonary arterial hypertension (PAH) leads to a lethal right heart failure (RHF), effective treatment for which has not been established. Inducible nitric oxide synthase (iNOS) is thought to be associated with the pathogenesis of heart failure. Inflammatory cytokines, which are increased in RHF, are known to induce iNOS expression in cardiac fibroblasts. We previously demonstrated that the mRNA expression of periostin, a matricellular protein, was upregulated in right ventricles (RVs) of monocrotaline (MCT)-induced PAH model rats. In the present study, we investigated the effects of periostin on iNOS expression in right ventricular fibroblasts isolated from PAH model rats. Methods: MCT (60 mg/kg) was injected intraperitoneally to 4-week-old male Wistar rats. Two weeks after the MCT-injection, cardiac fibroblasts were enzymatically isolated from RVs using a modified Langendorff apparatus. A soluble form of recombinant rat periostin protein was produced by Escherichia coli . The right ventricular fibroblasts (RVFs) were stimulated with a recombinant rat periostin (10-1000 ng/ml, 30 min-24 h). The expression of iNOS and activation of extracellular signal-regulated kinase (ERK) 1/2 and c-jun N-terminal kinase (JNK) were investigated by Western blotting. Results: Periostin (1000 ng/ml, 24 h) significantly increased iNOS (3.9 ± 0.6-fold, P <0.01, n=4) but not eNOS in RVFs. Periostin (1000 ng/ml, 30 min) increased phosphorylation of ERK1/2 (4.0 ± 2.3-fold, n=3) and JNK (13.2 ± 2.7-fold, P <0.05, n=3) in RVFs. An ERK pathway inhibitor, PD98059 (10 μM) or JNK inhibitor, SP600125 (30 μM) almost completely suppressed the periostin-induced iNOS expression (PD98059, P <0.01; SP600125, P <0.05, n=3). Conclusion: We for the first time demonstrated that periostin increases iNOS expression via the activation of ERK and JNK in RVFs isolated from PAH model rats. It is suggested that inflammatory reaction mediated by periostin might be a novel target for treatment of PAH-induced RHF.

A novel LMNA nonsense mutation causes two distinct phenotypes of cardiomyopathy with high risk of sudden cardiac death in a large five-generation family.

Characterization of the cardiac phenotype associated with the novel LMNA nonsense mutation c.544C>T, p.Q182*, which we have identified in a large five-generation family. A family tree was constructed. Clinical data [arrhythmia, syncope, sudden cardiac death (SCD), New York Heart Association (NYHA) class] were collected from living and deceased family members. DNA of 23 living family members was analysed for mutations in LMNA. Additionally, dilated cardiomyopathy multi-gene-panel testing and whole exome sequencing were performed in some family members to identify potential phenotype-modifiers. In this five-generation family (n = 65), 17 SCDs occurred at 49.3 ± 10.0 years. Furthermore, we identified eight additional mutation-carriers, seven symptomatic (44 ± 13 years), and one asymptomatic (44 years). First signs of disease [sinus bradycardia with atrioventricular (AV)-block I°] occurred at 36.5 ± 8.1 years. Paroxysmal atrial fibrillation (AF) (onset at 41.8 ± 5.7 years) rapidly progressed to permanent AF (46.2 ± 9.8 years). Subsequently, AV-conduction worsened, syncope, pacemaker-dependence, and non-sustained ventricular tachycardia (43.3 ± 8.2 years) followed. Ventricular arrhythmia caused SCD in patients without implantable cardioverter-defibrillator (ICD). Patients protected by ICD developed rapidly progressive heart failure (45.2 ± 10.6 years). A different phenotype was seen in a sub-family in three patients with early onset of rapidly decompensating heart failure and only minor prior arrhythmia-related symptoms. One patient received high-urgency heart transplantation (HTX) at 32 years, while two died prior to HTX. One of them developed lethal peripartum-associated heart failure. Possible disease-modifiers were identified in this 'heart failure sub-family'. The novel LMNA nonsense mutation c.544C>T causes a severe arrhythmogenic phenotype manifesting with high incidence of SCD in most patients; and in one sub-family, a distinct phenotype with fast progressing heart failure, indicating the need for early consideration of ICD-implantation and listing for heart-transplantation.

Characterization of fibroblasts from hypertrophied right ventricle of pulmonary hypertensive rats.

Pulmonary arterial hypertension (PAH), which is characterized by an elevation of pulmonary arterial resistance, leads to a lethal right heart failure. It is an urgent issue to clarify the pathogenesis of PAH-induced right heart failure. The present study aimed to elucidate the characteristics of cardiac fibroblasts (CFs) isolated from hypertrophied right ventricles of monocrotaline (MCT)-induced PAH model rats. CFs were isolated from the right ventricles of MCT-injected rats (MCT-CFs) and saline-injected control rats (CONT-CFs). Expression of α-smooth muscle actin and collagen type I in MCT-CFs was lower than that in CONT-CFs. On the other hand, proliferation, migration, and matrix metalloproteinase (MMP)-9 production were significantly enhanced in MCT-CFs. In MCT-CFs, phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, c-Jun N-terminal kinase (JNK), and Ca2+/calmodulin-dependent protein kinase (CaMK) II was significantly enhanced. In addition to mRNA expression of Orai1, a Ca2+ release-activated Ca2+ channel, and stromal interaction molecules (STIM) 1, an endoplasmic reticulum Ca2+ sensor, the associated store-operated Ca2+ entry (SOCE) was significantly higher in MCT-CFs than CONT-CFs. Pharmacological inhibition of ERK1/2 pathway prevented the enhanced proliferation of MCT-CFs. The enhanced migration of MCT-CFs was prevented by a pharmacological inhibition of ERK1/2, JNK, CaMKII, or SOCE pathway. The enhanced MMP-9 production in MCT-CFs was prevented by a pharmacological inhibition of ERK1/2, CaMKII, or SOCE pathway but not JNK. The present results suggested that MCT-CFs exhibit proliferative and migratory phenotypes perhaps through multiple signaling pathways. This study for the first time determined the characteristics of CFs isolated from hypertrophied right ventricles of MCT-induced PAH model rats.

Analysis of Cardiac Myocyte Maturation Using CASAAV, a Platform for Rapid Dissection of Cardiac Myocyte Gene Function In Vivo.

Loss-of-function studies in cardiac myocytes (CMs) are currently limited by the need for appropriate conditional knockout alleles. The factors that regulate CM maturation are poorly understood. Previous studies on CM maturation have been confounded by heart dysfunction caused by whole organ gene inactivation. To develop a new technical platform to rapidly characterize cell-autonomous gene function in postnatal murine CMs and apply it to identify genes that regulate transverse tubules (T-tubules), a hallmark of mature CMs. We developed CRISPR/Cas9/AAV9-based somatic mutagenesis, a platform in which AAV9 delivers tandem guide RNAs targeting a gene of interest and cardiac troponin-T promoter-driven Cre to RosaCas9GFP/Cas9GFP neonatal mice. When directed against junctophilin-2 (Jph2), a gene previously implicated in T-tubule maturation, we achieved efficient, rapid, and CM-specific JPH2 depletion. High-dose AAV9 ablated JPH2 in 64% CMs and caused lethal heart failure, whereas low-dose AAV9 ablated JPH2 in 22% CMs and preserved normal heart function. In the context of preserved heart function, CMs lacking JPH2 developed T-tubules that were nearly morphologically normal, indicating that JPH2 does not have a major, cell-autonomous role in T-tubule maturation. However, in hearts with severe dysfunction, both adeno-associated virus-transduced and nontransduced CMs exhibited T-tubule disruption, which was more severe in the transduced subset. These data indicate that cardiac dysfunction disrupts T-tubule structure and that JPH2 protects T-tubules in this context. We then used CRISPR/Cas9/AAV9-based somatic mutagenesis to screen 8 additional genes for required, cell-autonomous roles in T-tubule formation. We identified RYR2 (Ryanodine Receptor-2) as a novel, cell-autonomously required T-tubule maturation factor. CRISPR/Cas9/AAV9-based somatic mutagenesis is a powerful tool to study cell-autonomous gene functions. Genetic mosaics are invaluable to accurately define cell-autonomous gene function. JPH2 has a minor role in normal T-tubule maturation but is required to stabilize T-tubules in the failing heart. RYR2 is a novel T-tubule maturation factor.

Effects of Adrenomedullin on Doxorubicin-Induced Cardiac Damage in Mice.

Doxorubicin (DOX) is one of the best known anticancer drugs, and is used in the treatment of lymphoma, lung cancer, stomach cancer, and a number of other cancers. However, DOX has some serious side effects, the worst being lethal heart failure. Occasionally, its side effects result in the cessation of the anticancer treatment, thus having a serious adverse influence on prognosis. Agents that can be administered as alternative prophylactics or to ameliorate the side effects of DOX will be useful in increasing the safety and efficacy of anticancer therapy. Adrenomedullin (AM) is a peptide hormone secreted by many organs, including the heart; it has an organ-protective effect, including antiapoptotic, anti-inflammatory, and antioxidative stress. Blood AM levels increase with heart failure; endogenic AM has been suggested in order to protect the heart. Furthermore, exogenous AM administration has shown therapeutic effects for heart failure in patients. However, it is unclear whether AM can protect the heart against drug-induced cardiac injury in vivo. The present study was performed in order to investigate the effects of AM on DOX-induced cardiac damage. Male BALB/c mice were treated with DOX and/or AM. Exogenous AM improved the survival ratio of DOX-treated mice. In addition, AM reduced serum lactate dehydrogenase (LDH) levels following DOX treatment. On pathological examination, AM was shown to inhibit DOX-induced cardiac tissue damage, mitochondrial abnormality, and cell death. These findings suggest that AM has a protective effect against DOX-induced cardiac damage.

X-Linked Dilated Cardiomyopathy: A Cardiospecific Phenotype of Dystrophinopathy.

X-linked dilated cardiomyopathy (XLDCM) is a distinct phenotype of dystrophinopathy characterized by preferential cardiac involvement without any overt skeletal myopathy. XLDCM is caused by mutations of the Duchenne muscular dystrophy (DMD) gene and results in lethal heart failure in individuals between 10 and 20 years. Patients with Becker muscular dystrophy, an allelic disorder, have a milder phenotype of skeletal muscle involvement compared to Duchenne muscular dystrophy (DMD) and sometimes present with dilated cardiomyopathy. The precise relationship between mutations in the DMD gene and cardiomyopathy remain unclear. However, some hypothetical mechanisms are being considered to be associated with the presence of some several dystrophin isoforms, certain reported mutations, and an unknown dystrophin-related pathophysiological mechanism. Recent therapy for Duchenne muscular dystrophy, the severe dystrophinopathy phenotype, appears promising, but the presence of XLDCM highlights the importance of focusing on cardiomyopathy while elucidating the pathomechanism and developing treatment.

Trbp regulates heart function through microRNA-mediated Sox6 repression.

Cardiomyopathy is associated with altered expression of genes encoding contractile proteins. Here we show that Trbp (Tarbp2), an RNA binding protein, is required for normal heart function. Cardiac-specific inactivation of Trbp (TrbpcKO) caused progressive cardiomyopathy and lethal heart failure. Trbp loss of function resulted in upregulation of Sox6, repression of genes encoding normal cardiac slow-twitch myofiber proteins, and pathologically increased expression of skeletal fast-twitch myofiber genes. Remarkably, knockdown of Sox6 fully rescued the Trbp mutant phenotype, whereas Sox6 overexpression phenocopied the TrbpcKO phenotype. Trbp inactivation was mechanistically linked to Sox6 upregulation through altered processing of miR-208a, which is a direct inhibitor of Sox6. Transgenic overexpression of miR-208a sufficiently repressed Sox6, restored the balance of fast- and slow- twitch myofiber gene expression, and rescued cardiac function in TrbpcKO mice. Together, our studies reveal a novel Trbp-mediated microRNA processing mechanism in regulating a linear genetic cascade essential for normal heart function.

Novel Roles of GATA4/6 in the Postnatal Heart Identified through Temporally Controlled, Cardiomyocyte-Specific Gene Inactivation by Adeno-Associated Virus Delivery of Cre Recombinase.

GATA4 and GATA6 are central cardiac transcriptional regulators. The postnatal, stage-specific function of the cardiac transcription factors GATA4 and GATA6 have not been evaluated. In part, this is because current Cre-loxP approaches to cardiac gene inactivation require time consuming and costly breeding of Cre-expressing and “floxed” mouse lines, often with limited control of the extent or timing of gene inactivation. We investigated the stage-specific functions of GATA4 and GATA6 in the postnatal heart by using adeno-associated virus serotype 9 to control the timing and extent of gene inactivation by Cre. Systemic delivery of recombinant, adeno-associated virus 9 (AAV9) expressing Cre from the cardiac specific Tnnt2 promoter was well tolerated and selectively and efficiently recombined floxed target genes in cardiomyocytes. AAV9:Tnnt2-Cre efficiently inactivated Gata4 and Gata6. Neonatal Gata4/6 inactivation caused severe, rapidly lethal systolic heart failure. In contrast, Gata4/6 inactivation in adult heart caused only mild systolic dysfunction but severe diastolic dysfunction. Reducing the dose of AAV9:Tnnt2-Cre generated mosaics in which scattered cardiomyocytes lacked Gata4/6. This mosaic knockout revealed that Gata4/6 are required cell autonomously for physiological cardiomyocyte growth. Our results define novel roles of GATA4 and GATA6 in the neonatal and adult heart. Furthermore, our data demonstrate that evaluation of gene function hinges on controlling the timing and extent of gene inactivation. AAV9:Tnnt2-Cre is a powerful tool for controlling these parameters.

Immobilization Stress With α2-Adrenergic Stimulation Induces Regional and Transient Reduction of Cardiac Contraction Through Gi Coupling in Rats.

Stress cardiomyopathy is characterized by transient apical hypokinesia related to catecholamine overflow. Recently, excessive epinephrine administration was shown to recapitulate stress cardiomyopathy through β2-adrenoceptor (AR)-inhibitory G protein (Gi) coupling in rats. We aimed to study whether α2-AR and Gi affect cardiac contraction in rats in which emotional stress was evoked using immobilization (IMO). Echocardiography results showed that when male rats were exposed to IMO for 30 minutes and then injected with the α2-AR agonist xylazine (Xy), ejection fraction and the movement of the anterior wall (AW) were suppressed, maximally at 5 minutes post-injection, whereas posterior wall (PW) movement was preserved. At the same time points, the phosphorylation of Ser282 in myosin-binding protein-C (MyBP-C-Ser282) was higher in the PW than in the AW. Pretreatment with the Gi inhibitor pertussis toxin (PTX) reversed the low contractility and MyBP-C-Ser282 phosphorylation in the AW, but induced lethal heart failure in 3 out of 11 rats. Moreover, at 5 minutes after Xy injection following 30 minutes of IMO, serum epinephrine levels were increased. Thus, in rats exposed to psychological stress, α2-AR stimulation triggered transient hypo-contractility and MyBP-C-Ser282 hypo-phosphorylation in the AW, in association with an epinephrine surge. PTX treatment reversed the AW hypo-contractility and MyBP-C hypo-phosphorylation, but induced acute heart failure. These findings suggest α2AR/Gi-dependent signaling attenuates MyBP-C phosphorylation and contractility in the AW through an epinephrine surge in rats subjected to IMO and α2-AR stimulation. This model can recapitulate stress cardiomyopathy and thereby deepen our understanding of regional cardiac hypo-contractility and prosurvival mechanisms.

Deep Sequence Analysis of Gene Expression Identifies Osteopontin as a Downstream Effector of Integrin-Linked Kinase (ILK) in Cardiac-Specific ILK Knockout Mice

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. 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. 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.

A microRNA links prolactin to peripartum cardiomyopathy

For decades, peripartum cardiomyopathy has remained an enigma. Despite extensive research, our understanding of how a previously healthy woman can develop lethal heart failure in the context of pregnancy remains vague. Recent work suggests that inadequacy of the cardiac microvasculature may be the primary abnormality and has implicated an antiangiogenic fragment of the nursing hormone prolactin as playing an important role. In this issue of the JCI, Halkein et al. explore signaling downstream of this prolactin fragment and demonstrate that miR-146a is a critical mediator of the antiangiogenic effects in endothelial cells. In addition, the study uncovers unexpected exosomal transfer of this microRNA to cardiomyocytes that may affect myocardial metabolism.

175: Association between silent Atrial Fibrillation and heart failure after Acute Myocardial infarction

Atrial Fibrillation (AF) complicating an acute myocardial infarction (AMI) is frequent and associated with a worse prognosis after MI, particularly because of lethal heart failure (HF) episodes and cardiogenic shock. Although silent AF has also been suggested to be common in AMI, its association with development of heart failure during the first days after AMI remains unknown. In this study we aimed to assess a potential association between silent AF and episodes of heart failure after AMI. For AF screening, 581 consecutive AMI were prospectively analyzed by Continuous ECG Scope Monitoring (CSM) for 48H after hospital admission. Left Ventricular Ejection Fraction (LVEF) was determined on admission by echocardiography. We analyzed the study population into 3 groups: No AF, silent AF (asymptomatic episodes of AF lasting at least >30 sec) and symptomatic AF (symptomatic episodes of AF that lasted ≥12 hours). Diagnosis of heart failure episode was based on plasmatic level of Nt-ProBNP. Ninety-five (16.4%) patients had AF on CSM after MI, of whom 76 (80%) developed silent AF. Compared with No AF group, patients with silent AF were markedly older (80 (69-85) vs 62 (53-74);p<0.001), more frequently women (45 vs 27%;p=0.006), hypertensive (76vs52%;p<0.001) but less smoker (18vs38%;p<0.001). On admission, patients with silent AF had animpaired LVEF (46%(13) vs 54%(11);p<0.001), with higher Nt-ProBNP (1817 (556-7078) vs435 (111-1512);p<0.001) and more frequent episode of heart failure (42 vs21%;p<0.001). Comparing the three groups, heart failure episodes during the acute phase after myocardial infarction were more frequent in silent AF group (42%) and in symptomatic AF group (53%)than in noAF group (21%), with p<0.001. This studyshows that silent AF is very common after MI (16.4%), and highlights for the first time that itis significantly associated with episodes of heart failure. This outcome suggests the potential impact of silent AF on the prognosis of patients after AMI.

Cardiomyocyte-specific deletion of leptin receptors causes lethal heart failure in Cre-recombinase-mediated cardiotoxicity

Although disruption of leptin signaling is associated with obesity as well as cardiac lipid accumulation and dysfunction, it has been difficult to separate the direct effects of leptin on the heart from those associated with the effects of leptin on body weight and fat mass. Using Cre-loxP recombinase technology, we developed tamoxifen-inducible, cardiomyocyte-specific leptin receptor-deficient mice to assess the role of leptin in regulating cardiac function. Cre recombinase activation in the heart resulted in transient reduction in left ventricular systolic function which recovered to normal levels by day 10. However, when cardiomyocyte leptin receptors were deleted in the setting of Cre recombinase-induced left ventricular dysfunction, irreversible lethal heart failure was observed in less than 10 days in all mice. Heart failure after leptin receptor deletion was associated with marked decreases of cardiac mitochondrial ATP, phosphorylated mammalian target of rapamycin (mTOR), and AMP-activated kinase (pAMPK). Our results demonstrate that specific deletion of cardiomyocyte leptin receptors, in the presence of increased Cre recombinase expression, causes lethal heart failure associated with decreased cardiac energy production. These observations indicate that leptin plays an important role in regulating cardiac function in the setting of cardiac stress caused by Cre-recombinase expression, likely through actions on cardiomyocyte energy metabolism.

Role of ER Stress in Ventricular Contractile Dysfunction in Type 2 Diabetes

BackgroundDiabetes mellitus (DM) is associated with an increased risk of ischemic heart disease and of adverse outcomes following myocardial infarction (MI). Here we assessed the role of endoplasmic reticulum (ER) stress in ventricular dysfunction and outcomes after MI in type 2 DM (T2DM).Methodology and Principal FindingsIn hearts of OLETF, a rat model of T2DM, at 25∼30 weeks of age, GRP78 and GRP94, markers of ER stress, were increased and sarcoplasmic reticulum calcium ATPase (SERCA)2a protein was reduced by 35% compared with those in LETO, a non-diabetic control. SERCA2a mRNA levels were similar, but SERCA2a protein was more ubiquitinated in OLETF than in LETO. Left ventricular (LV) end-diastolic elastance (Eed) was higher in OLETF than in LETO (53.9±5.2 vs. 20.2±5.6 mmHg/µl), whereas LV end-systolic elastance and positive inotropic responses to β-adrenergic stimulation were similar in OLETF and LETO. 4-Phenylbutyric acid (4-PBA), an ER stress modulator, suppressed both GRP up-regulation and SERCA2a ubiquitination and normalized SERCA2a protein level and Eed in OLETF. Sodium tauroursodeoxycholic acid, a structurally different ER stress modulator, also restored SERCA2a protein level in OLETF. Though LV dysfunction was modest, mortality within 48 h after coronary occlusion was markedly higher in OLETF than in LETO (61.3% vs. 7.7%). Telemetric recording showed that rapid progression of heart failure was responsible for the high mortality rate in OLETF. ER stress modulators failed to reduce the mortality rate after MI in OLETF.ConclusionsER stress reduces SERCA2a protein via its augmented ubiquitination and degradation, leading to LV diastolic dysfunction in T2DM. Even at a stage without systolic LV dysfunction, susceptibility to lethal heart failure after infarction is markedly increased, which cannot be explained by ER stress or change in myocardial response to sympathetic nerve activation.

Abstract P144: ER Stress-Mediated Reduction of SERCA2a Protein Is Not Involved in Increase in Lethal Heart Failure After Myocardial Infarction in Obese Type 2 Diabetes

Rationale: Our previous studies showed that increased endoplasmic reticulum (ER) stress in the myocardium impairs cytoprotective signaling in obese type 2 diabetes mellitus (T2DM). Objective: We examined roles of ER stress in alterations of ventricular function and mortality after myocardial infarction by T2DM. Methods and Results: SERCA2a protein level was significantly lower by 45% and Ser16- and Thr17-phosphorylated phospholamban levels tended to be lower in a rat model of T2DM (OLETF) than those in non-diabetic control rats (LETO). Treatment with an ER stress modulator, 4-phenylbutyric acid (4-PBA) or tauroursodeoxycholic acid (TUDCA), restored SERCA2a protein in OLETF to the level of that in LETO. Although left ventricular (LV) ejection fractions were comparable in OLETF and LETO, LV end-systolic elastance (1685±86 vs. 1953±68 mmHg/ml) and LVdP/dtmax (5886±337 vs. 7389±457 mmHg/s) were lower and tau was larger (12.1±0.9 vs. 8.9±0.8 msec) in OLETF. These impairments of LV function in OLETF were restored by treatment with 4-PBA (LV end-systolic elastance: 1813±58 mmHg/ml, LVdP/dtmax: 7053±546 mmHg/s and tau: 8.5±0.5 msec). Elevation of LV systolic pressure and dP/dtmax levels by dobutamine infusion was reduced, and inhibitory effects of verapamil on the dobutamine-induced positive inotropism were blunted in OLETF. In patch-clamp experiments using isolated cardiomyocytes, increase in L-type Ca 2+ channel current after isoproterenol treatment was markedly attenuated in OLETF as compared with the change in LETO. Mortality rate within 48 hrs after myocardial infarction was significantly higher in OLETF than in LETO (64.0% vs. 7.7%). Telemetric recording indicated that rapid progression of heart failure but not arrhythmia was responsible for the high mortality rate in OLETF. In contrast to the improvement of baseline ventricular dysfunction, neither 4-PBA nor TUDCA significantly reduced mortality rate after infarction in OLETF. Conclusions: ER stress plays a major role in reduction of SERCA2a by T2DM. Blunted response of cardiac L-type Ca 2+ channels to adrenoceptor activation, rather than reduced SERCA2a, may contribute to increase in lethal heart failure after myocardial infarction in T2DM.

Clinical significance of late high-degree atrioventricular block in patients with left ventricular dysfunction after an acute myocardial infarction—A Cardiac Arrhythmias and Risk Stratification After Acute Myocardial Infarction (CARISMA) substudy

High-degree atrioventricular block (HAVB) is a frequent complication in the acute stages of a myocardial infarction associated with an increased rate of mortality. However, the incidence and clinical significance of HAVB in late convalescent phases of an AMI is largely unknown. The aim of this study was to assess the incidence and prognostic value of late HAVB documented by continuous electrocardiogram (ECG) monitoring in post-AMI patients with reduced left ventricular function. The study included 286 patients from the CARISMA study with AMI and left ventricular ejection fraction of 40% or less. An insertable loop recorder was implanted 5 to 21 days after AMI for incessant arrhythmia surveillance. Furthermore, ECG documentation was supplemented by a 24-hour Holter monitoring conducted at week 6 post-AMI. The clinical significance of HAVB occurring more than 21 days after AMI was examined with respect to development of major heart failure events and major ventricular tachyarrhythmic events. During a median follow-up of 1.9 years (interquartile range 0.9-2.0), late HAVB was documented in 30 patients. The risk of major heart failure events (hazard ratio [HR] 4.08 [1.38-12.09], P = .01) and major ventricular tachyarrhythmic events (HR = 5.41 [1.88-15.58], P = .002) were significantly increased in patients who developed late HAVB. High-degree atrioventricular block documented by continuous ECG monitoring occurring more than 3 weeks after AMI is a frequent complication in post-AMI patients with left ventricular dysfunction. Furthermore, HAVB is associated with ominous prognostic implications of both potentially lethal arrhythmias and heart failure.

In Silico Investigation of Electrically Silent Acute Cardiac Ischemia in the Human Ventricles

Acute cardiac ischemia, which is caused by the occlusion of a coronary artery, often leads to lethal ventricular arrhythmias or heart failure. The early diagnosis of this pathology is based on changes of the electrocardiogram (ECG), i.e., mainly shifts of the ST segment. However, the underlying mechanisms responsible for these shifts are not completely understood. Furthermore, clinical observations indicate that some acute ischemia cases can hardly be detected using standard 12-lead ECG only. Therefore, multiscale computer simulations of cardiac ischemia using realistic models of human ventricles were carried out in this work. For this purpose, the transmembrane voltage distributions in the heart and the corresponding body surface potentials were computed with varying transmural extent of the ischemic region at different ischemia stages. Some of the simulated ischemia cases were " electrically silent," i.e., they could hardly be identified in the 12-lead ECG.

Investigation of platelet activating factor (PAF) in acute myocardial infarction

Objective To investigate the level of platelet activating factor (PAF) in acute myocardial infarction (AMI) in minipig model and patients, and to study the relationship between PAF and lethal arrhythmia referring to ventricular fibrillation and ventricular tachycardia. Method ( 1 ) The levels of PAF in minipig models ( n = 20) were measured by using ELISA before and 1h after occlusion of left anterior descending coronary artery with balloon at the junction of 1/3 middle and distal portion. The lethal arrythmia was recorded by using electrocardiography. (2) In patients with AMI (n = 72), the levels of PAF were measured on arrival, and 24 h,48 h and 72 h later. The lethal arrythmia, acute heart failure and cardiogenic shock were documented. Results ( 1 ) In minipigs with occlusion of coronary artery for one hour, the mean level of PAF increased from (4.66± 2.89)ng/mL to (6.00±2.82) ng/mL,and thus the increment in PAF was (1 .34± 1.40) ng/mL (P ＜ 0.05). In 13 minipigs with lethal anythmia after occlusion of coronary artery for one hour, the increment in mean level of PAF was ( 1.92 ± 1 .34) ng/mL, whereas the increment in mean level of PAF in other 7 minipigs without lethal arrythmia after occlusion of coronary artery for one hour was as low as (0.28 ± 0. 74 ) ng/mL ( P ＜ 0. 05 ). ( 2 ) In patients, the mean levels of PAF on arrival, 24 h,48 h,and 72 hous after admission were (0.47 ± 0.05) ng/mL,(2.38±0.12) ng/mL,(3.65±0.15) ng/mL and (3.02±0.10) ng/mL, respectively. Of 72 ACI patients, 40 (55%) had complication of lethal arrythnia, heart failure or cardiogenic shock and their mean level of PAF 48 h after admission was (4.72 ± 0.16) ng/mL, whereas mean level of PAF in other 32 (44.44%) without complications was (2.31 ±0.03) ng/mL ( P ＜0.05). Conclusions The level of PAF increased after acute myocardial infarction, and the minipigs and AMI patients complicated with lethal arrythmia had higher levels of PAF. Key words: Platelet activating factor (PAF); Acute myocardial infarction; Ischemic/repeffusion; Arrhythmia