Epicardial Fibrosis Research Articles

Abstract 12816: Epicardial Adipose Tissue Around the Left Atrium is Associated With Atrial Fibrosis in Patients With Atrial Fibrillation

Background: Obesity is a risk factor for atrial fibrillation (AF) and strongly influences the response to treatment. Atrial fibrosis shows similar associations. Left atrial epicardial fat (LAEF) may be a link to these associations. Objective: We sought to assess whether LAEF is associated with atrial fibrosis and BMI (Body Mass Index). Methods: Patients with atrial fibrillation undergoing catheter ablation were assessed with cardiac MRI for overall epicardial fat, LAEF, and fibrosis quantification. Epicardial fat was imaged using a 3-dimensional Dixon sequence and quantified by contouring regions of fat on axial images (Panel A; Blue regions represent LAEF). Atrial fibrosis was quantified from the Late Gadolinium Enhancement (LGE) MRI. Image registration was used to assess the relationship between left atrial epicardial fat and left atrial fibrosis. Results: 45 patients underwent the imaging protocol (64±10 years; 76% male). BMI was 29.3±6.1 kg/m 2 , LAEF was 248±155 cm 2 , and LA fibrosis was 17.4±8.4%. LAEF was significantly correlated with both LA fibrosis (Fig B; P=0.017; R 2 =0.125) and BMI (y[BMI] = 0.093x[LAEF] + 5.37; p=0.01, R 2 =0.155). Total epicardial fat was also correlated with BMI (y[BMI] = 0.014x[total epicardial fat] + 9.01; p<0.001, R 2 =0.33). The overlap of LAEF and fibrosis was moderate with a Dice coefficient ranging from 0.26 to 0.49. (Fig C). Conclusion: LAEF is associated with obesity (BMI) and LA fibrosis with a moderate degree of colocalization. These findings support a role for LAEF as a contributor to atrial fibrosis and a link between obesity and atrial fibrillation.

Abstract 11048: Serotonin Transporter Deficiency Leads to a Specific Fibrotic Pattern in Valvular and Myocardial Tissue

Introduction: Increased serotonin (5HT) levels can lead to heart valve disease. This mechanism is observed in patients with 5HT-secreting carcinoid tumors and after treatment with the diet drug Dexfenfluoramine, which acts as a 5HT receptor (HTR)-2B agonist and as an inhibitor of the 5HT transporter (SERT). SERT internalizes 5HT, limiting HTR signaling (Figure 1A). We showed that SERT reduction on human mitral valve (MV) contributes to the progression of MV regurgitation. We investigated the impact of SERT deficiency on cardiac substructures in a SERT-/- murine model. Methods: SERT-/- and wild type (WT) C57BL/6J mice (n≥8/group) were sacrificed at 16 weeks of age, after echocardiography (Fig. 1B). Cardiac substructures (left ventricle (LV) apex, MV leaflets, aortic valve (AV) leaflets and aortic-mitral (AM curtain) were isolated in three animals/group (Fig. 1E). Results: Ventricular dimensions were significantly larger in SERT-/- mice vs. WT at end-systole and end-diastole (Fig. 1C). Fractional shortening was significantly reduced in SERT-/- mice vs. WT. Pricosirius staining of collagen showed that SERT-/- mice had increased MV leaflet fibrosis, MV and AV sub-valvular fibrosis at leaflet attachment points (AM curtain, Fig. 1D), and epicardial fibrosis. PCR (Fig. 1F) showed significantly increased COL1A1 expression in the LV myocardium, MV, AV and AM curtain in SERT-/- mice vs. WT. Fibrosis marker alpha smooth muscle actin (αSMA) was significantly increased in the myocardium and AM curtain of SERT-/- mice, but not in the valve leaflets. HTR2B expression was significantly increased in the MV and AM curtain of SERT-/- mice. Conclusions: SERT-/- mice have decreased cardiac function, and cardiac fibrosis that is associated with HTR2B upregulation in the MV leaflets and valve leaflet attachment points. Our results support the hypothesis that decreased 5HT clearance by SERT downregulation may increase HTR2B signaling in the MV leading to remodeling and regurgitation.

Correlation of Histopathological Changes in the Left Atrium and Left Atrial Appendage with the Degree of Dilation in Cats

Although atrial dilation is a common finding in feline cardiac disease, detailed investigations of atrial pathology are rare in cats. The aim of the study was to investigate the correlation between pathohistological findings, morphometric data and the degree of dilation of the left atrial appendage (LAA) in 53 cats. Based on the LAA volume, the samples were grouped into normal/control (group 0, ≤1ml [n=9]), mildly dilated (group 1, >1 to ≤2ml [n=16]), moderately dilated (group 2, >2 to ≤3ml [n=14]) and markedly dilated (group 3, >3ml [n=14]) groups, independent of the underlying disease. Samples from the LAA and the left atrium (LA) were histologically evaluated using haematoxylin and eosin- and Picrosirius red-stained sections, and morphometrically analysed using an image analysis system. The degree of endo-, myo- and epicardial fibrosis was directly correlated with increased LAA dilation. Due to cardiomyocyte hyperplasia and hypertrophy, the mean thickness of the atrial wall was significantly greater in groups 1 and 2 than in group 0. Conversely, group 3 had a lower mean atrial wall thickness than groups 1 and 2, which was attributed to increased transmural fibrosis and cardiomyocyte atrophy. These findings reflect intensive dynamic remodelling processes during LA and LAA dilation, indicating that reversibility appears to be limited in cases of severe left atrial dilation.

Radiofrequency ablation in Brugada syndrome.

Radiofrequency ablation in Brugada syndrome.

Abstract P329: Exosomes Derived From Podoplanin Positive Cells Alter The Cellular Composition Of Healthy Mouse Hearts

Fibrosis and blood hypoperfusion stimulated by paracrine signals enhances the ventricular dysfunctionafter myocardial infarction (MI). We have earlier reported that within 2 days post-MI a cohort ofpodoplanin (PDPN) positive cells populate injured heart and enhance inflammatory response by physicalinteractions with monocytes. Here we explored whether exosomes from these cells could independentlyalter healthy heart physiology and structure. PDPN+ cells were isolated 2 days after MI, culture expandedand activated with TNFα and Angiotensin II. Exosomes derived from activated PDPN+cells conditionedmedia (PDPN+exo) were used in vitro for the treatment of mouse cardiac endothelial cells (mCECs) andmouse fibroblast (3T3) and in vivo for the treatment of healthy mouse hearts. In vitro, PDPN+exoinfluenced the phenotype of mCECs, stimulating their lineage into lymphatic endothelial cells andfacilitated fibroblasts transition to myofibroblast. Characterization of the protein content of PDPN+exoshowed high concentration of Notch receptors and γ-Secretase, suggesting these cellular transitions maydepend on exosome-mediated Notch translocation and cleavage. In fact, after exosomes treatmentcleaved notch (NICD) translocated in the nuclei of mCECs and 3T3 as early as 1h of treatment and eitherHes-1 or Hey-1, major transcription factors activated by NICD were enhanced within 2d of treatment.Using DAPT, a γSecretase inhibitor, notch cleavage was inhibited, and no phenotype switching in responseto exosome treatment was observed. In vivo, PDPN+exo were injected into the left ventricle of healthymouse hearts followed by boosters delivered by retro-orbital vein injection. Treated mice developed anextended epicardial fibrosis with a subsequent impairment in the contractility and increase of the enddiastolic and systolic volumes. The fibrotic area was characterized by vessels double positive toendothelial and lymphatic endothelial markers, and infiltrating CD45+ cells. Podoplanin positive cellsrepresent 80% of the scar’s cells of a chronic infarcted myocardium and the specific exosomes cargo highlyinfluence the lineage of cardiac cells altering the biology of endothelial cells and fibroblasts which mayfacilitate adverse remodeling.

Ventricular tachycardia with epicardial and pericardial fibrosis 6 months after resolution of subclinical COVID-19: a case report\xa0

BackgroundCoronavirus disease 2019 (COVID-19) has been shown to have extensive effects on the cardiovascular system. Its long-term cardiac manifestations, however, remain unclear.Case presentationWe report the case of a Caucasian patient with a mild and self-limited presentation of COVID-19, with subsequent development, months later, of exertional dyspnea and non-sustained ventricular tachycardia, long after resolution of his illness and after returning to aerobic exercise. The patient had normal screening tests including electrocardiogram (ECG) and echocardiogram 4 months after his illness. Cardiac magnetic resonance imaging demonstrated epicardial and pericardial fibrosis of the right ventricle free wall and outflow tract and the pericardium over the anterior wall, 6 months following the initial infection. First abnormal ECG was recorded at month 7 following illness.ConclusionsThis case suggests an insidious and possible long-term cardiac involvement and reflects the challenges in traditional workups and screening modalities in identifying cardiac involvement in COVID-19.

Left Atrial Appendage Electrical Isolation Reduces Atrial Fibrillation Recurrences: A Simulation Study.

Left Atrial Appendage Electrical Isolation Reduces Atrial Fibrillation Recurrences: A Simulation Study.

Abstract 14839: High-resolution Spatiotemporal Changes in Dominant Frequency and Structural Organization During Persistent Atrial Fibrillation

Introduction: Spatiotemporal differences in atrial activity are thought to contribute to the maintenance of atrial fibrillation (AF). While recent evidence has identified changes in dominant frequency (DF) during the transition from paroxysmal to persistent AF, little is known about the frequency characteristics of the epicardium during this transition. The purpose of this study was to perform high-resolution mapping of the atrial epicardium and to characterize changes in frequency activity and structural organization during the transition from paroxysmal to persistent AF. Hypothesis: In a porcine model of persistent AF, we tested the hypothesis that the epicardium undergoes spatiotemporal changes in atrial activity and structural organization during persistent AF. Methods: Paroxysmal and persistent AF was induced in adult Yorkshire swine by atrial tachypacing. Atrial morphology was segmented from magnetic resonance imaging and high-resolution patient-specific flexible mapping arrays were 3D printed to match the epicardial contours of the atria. Epicardial activation and DF mapping was performed in four paroxysmal and four persistent AF animals using personalized mapping arrays. Histological analysis was performed to determine structural differences between paroxysmal and persistent AF. Results: The left atrial epicardium was associated with a significant increase in DF between paroxysmal and persistent AF (6.5 ± 0.2 vs. 7.4 ± 0.5 Hz, P = 0.03). High-resolution spatiotemporal mapping identified organized clusters of DF during paroxysmal AF which were lost during persistent AF. The development of persistent AF led to structural remodeling with increased atrial epicardial fibrosis. The organization index (OI) significantly decreased during persistent AF in both the left atria (0.3 ± 0.03 vs. 0.2 ± 0.03, P = 0.01) and right atria (0.33 ± 0.04 vs. 0.23 ± 0.02, P = 0.02). Conclusions: In the porcine model of persistent AF, the epicardium undergoes structural remodeling with increased epicardial fibrosis, reflected by changes in atrial organization index and dominant frequency.

Abstract 16950: Exosomes Derived From Podoplanin Positive Cells Induce Fibrosis and Inflammation in Healthy Mouse Heart

Superseding fibrosis through paracrine signals enhances the ventricular dysfunction aftermyocardial infarction (MI). We have earlier reported that within 2 days post-MI a cohort ofpodoplanin (PDPN), a platelet aggregation-inducing type I transmembrane glycoprotein,positive cells populate injured heart and enhance inflammatory response by physicalinteractions with monocytes. Here we explored whether exosomes from these cells couldindependently alter healthy heart physiology and structure. PDPN+ cells were isolated 2 daysafter MI, cultured expanded and activated with TNFα and AngiotensinII. Exosomes derived fromactivated PDPN+ cells conditioned media were used in vitro treatment of mouse cardiacendothelial cells (mCECs), mouse embryonic fibroblast (MEF) and monocytes and in vivo forthe treatment of healthy mouse hearts. PDPN+ cells derived exosomes (PDPN-exo)reprogramed mCECs to the lymphatic phenotype enhancing the expression of the majorlymphatic lineage markers and upregulated the expression of fibrotic markers suggesting anendothelial-mesenchymal transition. Furthermore, PDPN-exo drove the MEF to myo-fibroblastphenotype and monocytes toward pro-inflammatory phenotype. Proteomic analysis of PDPN-exo suggest these transitions may depend on NOTCH cleavage trough β-γSecretase. In vivo,PDPN-exo were initially injected into the left ventricle of healthy mouse hearts followed withexosomes boosters delivered by retro-orbital vein injection. Treated mice developed anextended epicardial fibrosis with a subsequent impairment in the contractility and increase ofthe end diastolic and systolic volumes. The fibrotic area was characterized by vessels doublepositive to endothelial and lymphatic endothelial markers, and infiltrating CD45+ cells. Inconclusion these data suggest that PDPN-exo alter the biology of mCECs, fibroblast andmonocytes and participate in adverse remodeling after MI; their specific cargo may representa cohort of targets for the treatment of cardiac fibrosis.

Abstract 15006: Serotonin Transporter (SERT) Knockout Leads to Increased Myocardial and Mitral Valvular Fibrosis in a Murine Model

Introduction: Heart valve disease attributed to serotonin (5HT) has been observed with 5HT-secreting carcinoid tumors and with the diet drug, Dexfenfluoramine, a 5HT transporter (SLC6A4, also known as SERT) inhibitor and 5HT receptor (HTR) 2B agonist. 5HT/SLC6A4 mechanisms had not been investigated in mitral valve (MV) regurgitation. SLC6A4 internalizes 5HT, limiting HTR signaling. Selective 5HT reuptake inhibitor (SSRI) antidepressants target SLC6A4 to increase 5HT. We showed that SLC6A4 reduction in human MV influences MV regurgitation through enhanced HTR signaling. We further investigate the cardiac impact of SLC6A4 deficiency in a SERT -/- mouse reported to have cardiac abnormalities. Hypothesis: Absence of SERT leads to increased myocardial and MV fibrosis. Methods: SERT -/- and wild type (WT) C57BL/6J mice underwent echocardiography at 8 and 16 weeks (w) of age (N=5 / group). Collagen staining was performed with Masson’s trichrome. Markers of myocardial fibrosis α-smooth muscle actin (αSMA) and collagen type1, alpha 1 (COL1A1) were measured by PCR. Results: 8w and 16w SERT -/- mice showed increased epicardial fibrosis and MV sub-valvular fibrosis, particularly at leaflet attachment points, and in 16w SERT -/- mice MV leaflet fibrosis was also present. At 8w, posterior ventricular wall thickness was greater in SERT -/- mice vs. WT, both in systole (1.30 ± 0.09mm vs. 1.61 ± 0.2mm, p=0.003) and diastole (0.78 ± 0.11mm vs. 1.22 ± 0.29mm, p=0.001). At 16 w, ventricular dimensions were larger in SERT -/- mice vs. WT at end-systole (2.29 ± 0.54mm vs. 3.0 ± 0.47mm, p=0.008) and end-diastole (3.48 ± 0.45mm vs. 4.07 ± 0.35, p=0.006). Fractional shortening was reduced in 16w SERT -/- mice vs. WT (35.20 ± 7.66 vs. 26.74 ± 6.14, p=0.017) and vs. 8w SERT -/- mice (38.85 ± 4.57 vs. 26.74 ± 6.14, p=0.002). PCR showed increased fibrosis markers αSMA and COL1A1 in SERT -/- mice (8w and 16w) vs. WT (all p<0.05). Conclusions: SERT -/- mice show pathologic structural changes and fibrosis in both myocardium and MV, corresponding to functional differences that worsen with age. As inhibition of SLC6A4, combined with active HTR2A/B signaling would hypothetically increase MV remodeling and regurgitation, these animals could be ideal to test 5HT pharmacology.

Abstract 16837: Exosomes Derived From Podoplanin Positive Cells Induce Serum Amyloid A3 Amyloidosis in Healthy Mouse Heart

The extra-cellular-matrix (ECM) composition of scar tissue after myocardial infarction (MI)has been largely investigated; although fibronectin and collagen are favorable for newmyocyte formation there is a missing component that increase the stiffness and reducethe remodeling of the ischemic area. We identified a primary Serum Amyloid A3 (Saa3)extracellular accumulation that contribute to the chronic alteration of the tissue. Serumamyloid amyloidosis (AA) are characterized by deposition of hepatic misfolded protein,Saa3 is the only amyloid protein that is released locally after inflammation, mostly bymesenchymal progenitor cells. We already described that two days after MI,mesenchymal and endothelial progenitor cells express Podoplanin (PDPN) a plateletaggregation-inducing type I transmembrane glycoprotein as a signal of activation. Exosomes derived from this cohort of cells actively release Saa3 in the ECM affecting thebiology of fibrosis beyond the inflammation. Specific histological staining such asthioflavin t and Congo red, showed amyloid deposition in mouse hearts 1 month after MI;furthermore, immunohistochemistry for Saa3 detected the deposition of the misfoldedprotein alongside fibronectin and collagen. PDPN+ cells were isolated 2 days after MI,cultured expanded and activated with TNFα and AngiotensinII. Activated PDPN positivecells highly expressed Saa3 and exosomes derived from activated PDPN+ cellsconditioned media were used in vivo for the treatment of healthy mouse hearts. Treatedmice developed an extended epicardial fibrosis and amyloidosis with a subsequentimpairment in the contractility and increase of the end diastolic and systolic volumes. Thefibrotic area was characterized by infiltrating CD45+ cells. Novel therapies aimed atpromoting clearance of existing amyloid deposits may be an effective approach in thenear future in the treatment of scar remodeling after MI.

Relationship between epicardial fat and left atrium fibrosis in patients with atrial fibrillation

Abstract Background Epicardial adipose tissue (EAT) has recently been shown to be associated with the presence, severity, and recurrence of atrial fibrillation (AF). Although the pathophysiological mechanisms underlying this association remain to be established, several hypotheses have been put forward, including direct adipocyte infiltration, oxidative stress, and the secretion of adipokines causing inflammation and fibrosis of atrial tissue. We hypothesized that the volume of EAT and the amount of left atrium (LA) fibrosis assessed by non-invasive imaging would be significantly correlated in patients with AF, and that both would predict time to relapse after pulmonary vein isolation (PVI). Methods Sixty-eight patients with AF being studied for a first PVI procedure underwent both cardiac computerized tomography (CT) and cardiac magnetic resonance (CMR) within less than 48h. EAT was quantified on contrast-enhanced CT images. LA fibrosis was quantified on isotropic 1.5mm 3D delayed enhancement CMR for image intensity ratio values >1.20. Radiofrequency PVI was performed using an irrigated contact force-sensing ablation catheter, guided by electroanatomical mapping. After PVI, patients were followed for AF recurrence, defined as symptomatic or documented AF after a 3-month blanking period. Pearson's correlation coefficient was used for gauging the correlation between EATLM volume and LA fibrosis. The relationship between these two variables and time to AF recurrence was assessed by Cox regression. Results Most of the 68 patients (46 men, mean age 61±12 years) had paroxysmal AF (71%, n=48). The mean body mass index (BMI) was 28.0±4.0 kg/m2. Patients had a median EATLM volume of 2.4 cm3/m2 [interquartile range (IQR) 1.6–3.2 cm3/m2], and a median estimated amount of LA fibrosis of 8.9 g (IQR 5–15 g), corresponding to 8% (IQR 5–11%) of the total LA wall mass. The correlation between EATLM and LA fibrosis was statistically significant but weak (Pearson's R = 0.38, P=0.001) – Figure 1. During a median follow-up of 22 months (IQR 12–31), 31 patients (46%) suffered AF recurrence. Four predictors of relapse were identified in univariate Cox regression: EATLM (HR 2.19, 95% CI 1.65–2.91, P<0.001), LA fibrosis (HR 1.05, 95% CI 1.01–1.09, P=0.033), non-paroxysmal AF (HR 3.36, 95% CI 1.64–6.87, P=0.001), and LA volume (HR 1.03, 95% CI 1.01–1.06, P=0.006). Multivariate analysis yielded two independent predictors of time to AF relapse: EATLM (HR 2.05, 95% CI 1.51–2.79, P<0.001), and non-paroxysmal AF (HR 2.36, 95% CI 1.08–5.16, P=0.031). Conclusion The weak correlation between EAT and LA suggests that LA fibrosis is not the main mechanism by which EAT and AF are linked. EAT was more strongly associated with AF recurrence than LA fibrosis, which supports the existence of other, more important mediators between EAT and this arrhythmia. Correlation between EAT and LA Funding Acknowledgement Type of funding source: None

Abstract 467: Exosomes Derived From Podoplanin Positive Cells Alter Physiology and Structure of Healthy Mouse Heart

Superseding fibrosis through paracrine signals enhances the ventricular dysfunction aftermyocardial infarction (MI). We have earlier reported that within 2 days post-MI a cohort ofpodoplanin (PDPN), a platelet aggregation-inducing type I transmembrane glycoprotein,positive cells populate injured heart and enhance inflammatory response by physicalinteractions with monocytes. Here we explored whether exosomes from these cells couldindependently alter healthy heart physiology and structure. PDPN+ cells were isolated 2 daysafter MI, cultured expanded and activated with TNFα and AngiotensinII. Exosomes derivedfrom activated PDPN+ cells conditioned media were used in vitro treatment of mouse cardiacendothelial cells (mCECs), mouse embryonic fibroblast (MEF) and monocytes and in vivo forthe treatment of healthy mouse hearts. PDPN+ cells derived exosomes (PDPN-exo)reprogramed mCECs to the lymphatic phenotype enhancing the expression of the majorlymphatic lineage markers and upregulated the expression of fibrotic markers suggesting anendothelial-mesenchymal transition. Furthermore, PDPN-exo drove the MEF to myo-fibroblastphenotype and monocytes toward pro-inflammatory phenotype. Proteomic analysis of PDPN-exo suggest these transitions may depend on NOTCH cleavage trough β-γSecretase andSerum Amyloid A3 protein accumulation/mis-folding. In vivo, PDPN-exo were initially injectedinto the left ventricle of healthy mouse hearts followed with exosomes boosters delivered byretro-orbital vein injection. Treated mice developed an extended epicardial fibrosis andamyloidosis with a subsequent impairment in the contractility and increase of the end diastolicand systolic volumes. The fibrotic area was characterized by vessels double positive toendothelial and lymphatic endothelial markers, and infiltrating CD45+ cells. In conclusionthese data suggest that PDPN-exo alter the biology of mCECs, fibroblast and monocytes andparticipate in adverse remodeling after MI; their specific cargo may represent a cohort oftargets for the treatment of cardiac fibrosis.

Arrhythmogenic Right Ventricular Cardiomyopathy: a case report

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a myocardial disease, often familial, characterized pathologically by fibrofatty replacement of the right ventricular myocardium, resulting in thinning of the ventricle. ARVC is an important cause of sudden death in individuals less than 30 years of age and has been found in up to 20% of sudden deaths in young people. A 21-year-old male collapsed to the ground while playing with his friends for about 10 minutes time. There was no history of trauma prior to the collapse. He had a mild upper respiratory tract infection three days prior, however he was not on any medication at the time of this incident. He was immediately taken to the nearby hospital where he was found to be in cardiac arrest. Post-mortem examination revealed an enlarged heart (heart weight 545 g). The right ventricular wall thickness was 6 mm. Coronary arteries were normal in configuration with a left dominant circulation. The right and left coronary ostiae were patent. Coronaries were free from atherosclerotic narrowing. Sections from the right ventricular myocardium showed variable, predominantly epicardial fibrosis throughout and transmural infiltration of adipocytes. The cardiomyocytes in these areas showed patchy vacuolation and nuclear hypertrophy. The remaining myocardium was mainly unremarkable. These findings were in keeping with arrythmogenic right ventricular cardiomyopathy. The importance of a thorough knowledge on specific cardiac conditions that can lead to sudden death and the importance in thorough sampling of cardiac muscle in such cases is highlighted here.

Epicardial Fibrosis Explains Increased Endo-Epicardial Dissociation and Epicardial Breakthroughs in Human Atrial Fibrillation.

BackgroundAtrial fibrillation (AF) is accompanied by progressive epicardial fibrosis, dissociation of electrical activity between the epicardial layer and the endocardial bundle network, and transmural conduction (breakthroughs). However, causal relationships between these phenomena have not been demonstrated yet. Our goal was to test the hypothesis that epicardial fibrosis suffices to increase endo–epicardial dissociation (EED) and breakthroughs (BT) during AF.MethodsWe simulated the effect of fibrosis in the epicardial layer on EED and BT in a detailed, high-resolution, three-dimensional model of the human atria with realistic electrophysiology. The model results were compared with simultaneous endo–epicardial mapping in human atria. The model geometry, specifically built for this study, was based on MR images and histo-anatomical studies. Clinical data were obtained in four patients with longstanding persistent AF (persAF) and three patients without a history of AF.ResultsThe AF cycle length (AFCL), conduction velocity (CV), and EED were comparable in the mapping studies and the simulations. EED increased from 24.1 ± 3.4 to 56.58 ± 6.2% (p < 0.05), and number of BTs per cycle from 0.89 ± 0.55 to 6.74 ± 2.11% (p < 0.05), in different degrees of fibrosis in the epicardial layer. In both mapping data and simulations, EED correlated with prevalence of BTs. Fibrosis also increased the number of fibrillation waves per cycle in the model.ConclusionA realistic 3D computer model of AF in which epicardial fibrosis was increased, in the absence of other pathological changes, showed increases in EED and epicardial BT comparable to those in longstanding persAF. Thus, epicardial fibrosis can explain both phenomena.

Abstract 513: Exosomes Derived From Podoplanin Positive Cells Induce Fibrosis and Inflammation in Healthy Mouse Heart

Superseding fibrosis is the leading cause of the adverse remodeling after myocardial infarction (MI); inflammation and paracrine signals enhance the fibrosis and ventricular dysfunction and inhibit the favorable repair. It has been reported that cells expressing Podoplanin (PDPN), a platelet aggregation- inducing type I transmembrane glycoprotein, appear around 2 days after MI as a signal of activation. We hypothesized that exosomes derived from these cells may actively affect the biology of fibrosis and inflammation. PDPN+ cells were isolated from hearts of mice 2 days after MI, expanded in a selective media and treated with TNFα, Angiotensin II or the combination of both. Exosomes derived from activated PDPN+ cells were isolated from the conditioned media and used in vitro for the treatment of mouse cardiac endothelial cells (mCECs), mouse embryonal fibroblast (MEF) and monocytes and in vivo for the treatment of healthy mouse hearts. Data from q-PCR showed that stimulated PDPN+ cells derived exosomes reprogramed mCECs to the endothelial lymphatic phenotype enhancing the expression of the major lymphatic lineage markers and upregulated the expression of fibrotic markers suggesting an endothelial-mesenchymal transition. Furthermore, stimulated PDPN+ cells derived exosomes drove the fibroblast to myo-fibroblast phenotype and activated monocytes toward pro-inflammatory lineage with an increased expression of TNFα and IL- 1β. In vivo, stimulated PDPN+ cells derived exosomes were initially injected in to the left ventricle of healthy mouse hearts followed with additional boosters delivered by retro-orbital vein injection. Treated mice developed an extended epicardial fibrosis with a subsequent impairment in the contractility and increase in the end diastolic and systolic volumes. In conclusion stimulated PDPN+ cells derived exosomes may impair the biology of mCECs, fibroblast and monocytes leading to adverse remodeling after MI.

Histopathological efficiency of amifostine in radiation‑induced heart disease in rats.

Amifositine is a phosphorylated thiol that holds its radioprotective actions by several indirect mechanisms. The purpose of this study was to evaluate histopathologically whether amifositine administration prior to irradiation would have a long‑term protective effect on heart tissue in an experimental rat model. Single dose of 18 Gy radiation and sham radiation exposure were used in related groups. A dose of 200 mg/kg of amifostine was injected intraperitoneally 30 min prior to radiation exposure. Analyses were performed 6 months after irradiation. Vascular damage and vasculitis were significantly decreased in amifositine treatment group. At the same time, significant thickening of the medial layer was accompanied by vascular damage in irradiated groups. The number and severity of myocyte necrosis were diminished with amifostine.Nevertheless, it could not prevent epicardial and myocardial fibrosis. Severe myocardial fibrosis was observed prominently in three regions, particularly on the apex, tips of papillary muscles and in sites adjacent to the atrioventricular valves. The anti-inflammatory effect of amifostine was not seen. The development of vascular damage and vasculitis were prevented by the use of amifostine. There was a correlation between vascular damage and fibrosis development. According to histopathological results, amifostine could be used as a protective agent against the side effects of radiotherapy (Tab. 4, Fig. 2, Ref. 22).

Mouse genome-wide association study identifies polymorphisms on chromosomes 4, 11, and 15 for age-related cardiac fibrosis.

Dystrophic cardiac calcinosis (DCC), also called epicardial and myocardial fibrosis and mineralization, has been detected in mice of a number of laboratory inbred strains, most commonly C3H/HeJ and DBA/2J. In previous mouse breeding studies between these DCC susceptible and the DCC-resistant strain C57BL/6J, 4 genetic loci harboring genes involved in DCC inheritance were identified and subsequently termed Dyscalc loci 1 through 4. Here, we report susceptibility to cardiac fibrosis, a sub-phenotype of DCC, at 12 and 20months of age and close to natural death in a survey of 28 inbred mouse strains. Eight strains showed cardiac fibrosis with highest frequency and severity in the moribund mice. Using genotype and phenotype information of the 28 investigated strains, we performed genome-wide association studies (GWAS) and identified the most significant associations on chromosome (Chr) 15 at 72 million base pairs (Mb) (P<10(-13)) and Chr 4 at 122Mb (P<10(-11)) and 134Mb (P<10(-7)). At the Chr 15 locus, Col22a1 and Kcnk9 were identified. Both have been reported to be morphologically and functionally important in the heart muscle. The strongest Chr 4 associations were located approximately 6Mb away from the Dyscalc 2 quantitative trait locus peak within the boundaries of the Extl1 gene and in close proximity to the Trim63 and Cap1 genes. In addition, a single-nucleotide polymorphism association was found on chromosome 11. This study provides evidence for more than the previously reported 4 genetic loci determining cardiac fibrosis and DCC. The study also highlights the power of GWAS in the mouse for dissecting complex genetic traits.

Abstract P261: Genome-wide Association Study of Susceptibility to Particulate Matter-associated Reduced Heart Rate Variability

Background: Heart rate variability (HRV) is a heritable electrocardiographic measure of cardiac autonnomic control that is consistently and inversely associated with ambient particulate matter (PM) air pollution and risk of both incident cardiovascular disease, and death. However, genetic susceptibility to PM-associated decreases in HRV has not been characterized. Methods: To characterize such susceptibility in a genome-wide context, we conducted cohort-, race/ethnicity-, and sex-stratified longitudinal analyses of ten Women’s Health Initiative clinical trials and Atherosclerosis Risk in Communities Study subpopulations (total n: 27,121; mean age: 64.6 yr; 81% female; 25% black; 7% Hispanic; mean visits/person: 2.5). In each subpopulation, we log-transformed three previously validated and reliable measures of HRV: RR interval duration (RR); root mean square of successive differences in normal-to-normal RR (RMSSD); and standard deviation of normal-to-normal RR (SDNN). We also estimated mean concentrations of PM &lt; 10 μm on the day of and before HRV measurement. We then used generalized estimating equations (GEE) methods adapted for low prevalence exposure to leverage the repeated measures of HRV and PM10. The GEE models estimated interactions between approximately 2.5 million single nucleotide polymorphisms (SNPs) and PM10 concentrations dichotomized at subpopulation-specific 90th percentiles, while adjusting for age, geographic region or center, season, calendar year, and ancestry. We combined the SNP x PM10 interaction estimates in a Bayesian meta-analysis accounting for ancestral heterogeneity to identify trans-ethnic interactions exceeding genome-wide thresholds: log10 Bayes Factor (BF) &gt; 6 and posterior probability of heterogeneity (PHet) &lt; 0.5. Results: Preliminary analyses of RMSSD provided suggestive evidence of a trans-ethnically important interaction at five SNPs on one locus. The lead SNP (rs17809071; T allele frequency range: 3-16%) is located on chromosome 4, 120 kilobases downstream from SPRY1 (log10BF = 5.31; PHet = 0.14). SPRY1 encodes sprouty receptor tyrosine kinase signaling antagonist 1 which is expressed in cardiac fibroblasts, antagonizes cytokine-induced epicardial fibrosis, and inhibits adipogenesis. Conclusions: Findings from this genome-wide association study of SNP x PM10 interactions suggest that genetic factors may affect susceptibility to PM10-associated decreases in HRV among racially/ethnically diverse populations of men and women protected by the U.S. Environmental Protection Agency under the Clean Air Act.

Epicardial adipose tissue, aortic stiffness and myocardial fibrosis in healthy individuals: a quantitative cardiac magnetic resonance study

Epicardial adipose tissue, aortic stiffness and myocardial fibrosis in healthy individuals: a quantitative cardiac magnetic resonance study