End-diastolic Pressure-volume Relationship Research Articles

CARDIAC EFFECTS OF COMBINED SGLT 1/2 INHIBITION FOLLOWING EXPERIMENTAL MYOCARDIAL INFARCTION IN THE RAT

Dual SGLT1/2 inhibition offers the potential to not only increase glucosuria beyond that seen with selective SGLT2 inhibition alone but to reduce glucose absorption from that gut as well and to stimulate glucagon-like peptide 1 (GLP-1) secretion. However, beyond the kidney and gut, SGLT1 is expressed in other organs including the heart where it potentially assists GLUT-mediated glucose transport. Since cardiac myocytes become more reliant on glucose as a fuel source in the setting of stress, this study sought to compare the effects of dual SGLT1/2 inhibition with selective SGLT2 inhibition in the diseased heart. Hyperglycaemic Fischer F344 rats were randomized to receive either vehicle, the dual SGLT1/2 inhibitor, T-1095, or the selective SGLT2 inhibitor, dapagliflozin. Animals were then further randomized to undergo sham surgery or ligation of the left anterior descending (LAD) coronary artery. Cardiac function was assessed prior to termination 4 weeks later that was followed by assessment of cardiac structure and expression of glucose transporters GLUT1, GLUT4 and SGLT1. Dapagliflozin and T-1095 induced glucosuria to a similar extent in both the control and myocardial infarction settings with similar effects on glycaemia. Neither dapagliflozin nor T-1095 had any demonstrable effect on cardiac function or structure in the control setting. Following myocardial infarction, however, significant (p < 0.05) differences were noted. When compared with vehicle or dapagliflozin-treated animals, rats that received T-1095 displayed worse cardiac function as evidenced by (i) lower EF, (ii) reduced dP/dt max, (iii) impaired isovolumic relaxation in diastole (dP/dt min), (iv) prolongation of Tau, and (v) increase in the end-diastolic pressure volume relationship (EDPVR). While vehicle and dapagliflozin-treated rats underwent hypertrophic changes following myocardial infarction this did not occur in animals that had received T-1095. Following myocardial infarction, lung weight was higher in T-1095 treated rats than in those animals that had received either vehicle of dapagliflozin. Notably, expression of GLUT 1 and GLUT4 were reduced in the hearts of all animals that had sustained myocardial infarction while that of SGLT1 was unchanged. T-1095 prevented the hypertrophic response following experimental myocardial infarction in the rat with adverse consequences on both systolic and diastolic function. The reduction in GLUT expression post-MI suggests that the heart may be more reliant on SGLT1-mediated glucose transport in the disease setting. These findings suggest the need for caution with dual SGLT1/2 inhibition in patients with diabetes at high cardiovascular risk.

Ischemia/reperfusion injury study in isolated mouse hearts using a pressure-volume curve

Objective: To establish and assess the feasibility and sensitivity of left ventricular elasticity, compliance and stiffness for study of ischemia/reperfusion injury in an isolated mouse heart model utilizing the pressure-volume curve framework. Methods: An isolated, balloon-in-ventricle, isovolumically contracting, crystalloid-perfused Langendorff heart preparation was set up from 15 male C57/6BL mice aged 12-14 weeks. End-systolic pressure-volume relationship (ESPVR) and end-diastolic pressure-volume relationship (EDPVR) were obtained by measuring left ventricular (LV) systolic pressure (LVSP) and diastolic pressure under different balloon volumes. End-systolic elasticity (E(es)), end-diastolic stiffness (S(ed)) and compliance (C(ed)) were calculated from the slope of ESPVR and EDPVR. Measurements of LVSP, developed pressure (LVDP), end of diastolic pressure (EDP), the rate of pressure development dp/dt(max) and dp/dt(min) were monitored during 30 min stabilization, 20 min global ischemia and 40 min reperfusion. The reliability and coefficient of variation (CV) of these parameters were compared with E(es) and C(ed). Results: During stabilization, the heart rate was (395±40) bpm, LVDP was (126±25) mmHg, + dp/dt(max) was (5 590±625) mmHg/s, -dp/dt(min) was (-4 128±625) mmHg/s, E(es) was 5.7±0.3, C(ed) was 0.7±0.2, S(ed) was 1.4±0.1. Ischemia/reperfusion injury resulted in significant decrease in contractile function parameters. The recovery level of LVSP, LVDP, dp/dt(max) and dp/dt(min) were (57±19)%, (23±6)%, (23±7)% and (21±5)% (all P<0.001), respectively. The EDP increased to (5.4±2.0) times than the baseline after ischemia/reperfusion injury. The E(es) and C(ed) was deceased to (42±2)% and (33±2)%, compared with baseline. The stiffness was increased up to (3.1±0.2) times higher than the baseline. The CV of E(es,)S(ed) and C(ed) were lower than LVSP, LVDP, EDP, dp/dt(max,)dp/dt(min,)while the reliability of E(es), S(ed) and C(ed) were higher than the classic contractile function parameters. Conclusion: Pressure-volume curves are feasible during ischemia/reperfusion injury in the isolated mouse heart model with acceptable reliability and sensitivity.

Cardiac and systemic rejuvenation after cardiosphere-derived cell therapy in senescent rats.

The aim is to assess the effects of CDCs on heart structure, function, gene expression, and systemic parameters in aged rats. Diastolic dysfunction is characteristic of aged hearts. Cardiosphere-derived cell (CDC) therapy has exhibited several favourable effects on heart structure and function in humans and in preclinical models; however, the effects of CDCs on aging have not been evaluated. We compared intra-cardiac injections of neonatal rat CDCs to vehicle (phosphate-buffered saline, PBS) in 21.8 ± 1.6 month-old rats (mean ± standard deviation; n = 23 total). Ten rats 4.1 ± 1.5 months of age comprised a young reference group. Blood, echocardiographic, haemodynamic and treadmill stress tests were performed at baseline in all animals, and 1 month after treatment in old animals. Histology and the transcriptome were assessed after terminal phenotyping. For in vitro studies, human heart progenitors from older donors, or cardiomyocytes from aged rats were exposed to human CDCs or exosomes secreted by CDCs (CDC-XO) from paediatric donors. Transcriptomic analysis revealed that CDCs, but not PBS, recapitulated a youthful pattern of gene expression in the hearts of old animals (85.5% of genes differentially expressed, P < 0.05). Telomeres in heart cells were longer in CDC-transplanted animals (P < 0.0001 vs. PBS). Cardiosphere-derived cells attenuated hypertrophy by echo (P < 0.01); histology confirmed decreases in cardiomyocyte area (P < 0.0001) and myocardial fibrosis (P < 0.05) vs. PBS. Cardiosphere-derived cell injection improved diastolic dysfunction [lower E/A (P < 0.01), E/E' (P = 0.05), end-diastolic pressure-volume relationship (P < 0.05) compared with baseline), and lowered serum brain natriuretic peptide (both P < 0.05 vs. PBS). In CDC-transplanted old rats, exercise capacity increased ∼20% (P < 0.05 vs. baseline), body weight decreased ∼30% less (P = 0.05 vs. PBS) and hair regrowth after shaving was more robust (P < 0.05 vs. PBS). Serum biomarkers of inflammation (IL-10, IL-1b, and IL-6) improved in the CDC group (P < 0.05 for each, all vs. PBS). Young CDCs secrete exosomes which increase telomerase activity, elongate telomere length, and reduce the number of senescent human heart cells in culture. Young CDCs rejuvenate old animals as gauged by cardiac gene expression, heart function, exercise capacity, and systemic biomarkers.

The link between exercise and titin passive stiffness

What is the topic of this review? This review focuses on how in vivo and molecular measurements of cardiac passive stiffness can predict exercise tolerance and how exercise training can reduce cardiac passive stiffness. What advances does it highlight? This review highlights advances in understanding the relationship between molecular (titin-based) and in vivo (left ventricular) passive stiffness, how passive stiffness modifies exercise tolerance, and how exercise training may be therapeutic for cardiac diseases with increased passive stiffness. Exercise can help alleviate the negative effects of cardiovascular disease and cardiovascular co-morbidities associated with sedentary behaviour; this may be especially true in diseases that are associated with increased left ventricular passive stiffness. In this review, we discuss the inverse relationship between exercise tolerance and cardiac passive stiffness. Passive stiffness is the physical property of cardiac muscle to produce a resistive force when stretched, which, in vivo, is measured using the left ventricular end diastolic pressure-volume relationship or is estimated using echocardiography. The giant elastic protein titin is the major contributor to passive stiffness at physiological muscle (sarcomere) lengths. Passive stiffness can be modified by altering titin isoform size or by post-translational modifications. In both human and animal models, increased left ventricular passive stiffness is associated with reduced exercise tolerance due to impaired diastolic filling, suggesting that increased passive stiffness predicts reduced exercise tolerance. At the same time, exercise training itself may induce both short- and long-term changes in titin-based passive stiffness, suggesting that exercise may be a treatment for diseases associated with increased passive stiffness. Direct modification of passive stiffness to improve exercise tolerance is a potential therapeutic approach. Titin passive stiffness itself may be a treatment target based on the recent discovery of RNA binding motif 20, which modifies titin isoform size and passive stiffness. Translating these discoveries that link exercise and left ventricular passive stiffness may provide new methods to enhance exercise tolerance and treat patients with cardiovascular disease.

Abstract 398: Growth Hormone Releasing Hormone Agonist (GHRH-A) Restores Cardiac Function in a Rodent Model of Heart FailureWith Preserved Ejection Fraction (HFpEF)

Background: Roughly half of patients with heart failure (HF) have preserved EF (HFpEF) and this rate is increasing. The pathophysiology of HFpEF is unclear and treatment of HFpEF remains a critical unmet need. Hypothesis: Growth hormone releasing hormone agonist (GHRH-A) restores cardiac function in a rodent model of HFpEF. Methods: C57BL/6N mice (n=4-5) received angiotensin-II (Ang-II: 0.8 mg/kg/day) via mini-osmotic pump for 4 weeks with concurrent daily administration of GHRH-A (MR-356: 200 μg/kg) or vehicle (DMSO+propylene-glycol). Echocardiography was assessed at baseline and 4 weeks after Alzet pump placement. Hemodynamic studies were performed and the titin N2BA/N2B ratio measured. Results: Ang-II administration increased end-diastolic pressure (EDP, p=0.0186) with no changes in EF (p=ns) or end-systolic pressure (ESP, p=ns) in comparison to control mice. Isovolumetric relaxation time (IVRT, p&lt;0.05) and end-diastolic pressure-volume relationship (EDPVR, p=0.0229) were significantly increased in the Ang-II/vehicle group, consistent with increased ventricular stiffness and impaired relaxation. Importantly, GHRH-A treatment reset these parameters to normal conditions (table). HFpEF mice exhibited higher HW/BW ratios and lung weight. The titin N2BA/N2B ratio, which was increased (p&lt;0.05) in the Ang-II group, was restored by GHRH-A treatment. Conclusion: Chronic administration of Ang-II mediates structural and functional changes that mimic HFpEF. GHRH-A treatment improves diastolic dysfunction and impaired relaxation. Therefore, GHRH-A therapy may be beneficial in the treatment of HFpEF.

Abstract 87: Alterations to Cardiac Mechanics Do Not Preserve Normal Cardiac Function in a Novel Ossabaw Swine Model of Heart Failure with Preserved Ejection Fraction

Introduction: Heart failure with preserved ejection fraction (HFpEF) is clinically characterized by an increased incidence in females and many comorbidities including type 2 diabetes (T2D) and obesity. Animal models accurately representing clinical HFpEF are lacking; thus, the purpose of this study was to examine left ventricular (LV) mechanics in a novel Ossabaw swine model of chronic pressure-overload (aortic-banding; AB) and T2D (Western diet; WD) using two dimensional speckle tracking echocardiography (2D-STE). We hypothesized that global LV strain would be decreased primarily in the longitudinal direction in WD-AB animals. Methods: Female Ossabaws were randomly divided into 2 groups: CON (n=5) and WD-AB (n=5). LV function and strain were measured at 1 year of age after 6 mo. of AB and 9 mo. of WD via pressure-volume relations and 2D-STE. Significance was set at P &lt; 0.05 using t-test vs. CON. Results: In the WD-AB group, ejection fraction (EF%) and end diastolic volume were normal (&gt;50%), and observed in parallel with increased LV weight, lung weight, and LV diastolic wall thickness (i.e. concentric hypertrophy). WD-AB group had increased HOMA-IR and body surface area, two common features in T2D. In WD-AB animals, although global longitudinal systolic strain rate and end systolic displacement were increased, stroke volume index was decreased. Early diastolic rotation rate was decreased, while global longitudinal late diastolic strain rate was increased in the WD-AB group. These changes, considered in parallel with an increased end diastolic pressure-volume relationship in WD-AB animals, are consistent with diastolic dysfunction. In contrast, longitudinal, radial, and circumferential early diastolic strain rates increased in the WD-AB group. Conclusion: Contrary to our hypothesis, LV longitudinal strain was increased during both systole and diastole, and observed in parallel with decreased early diastolic untwisting in WD-AB animals. Our results suggest alterations to LV mechanics do not preserve normal systolic and diastolic cardiac function, despite normal resting EF%, in this novel translational model of pressure-overload HF with potential relevance to human HFpEF including associated clinical comorbidities (sex, obesity, and T2D).

Synergistic effects of remote perconditioning with terminal blood cardioplegia in an in vivo piglet model.

This study tested the hypothesis that remote perconditioning offers effective and synergistic cardioprotection to terminal warm blood cardioplegia for prompt ventricular recovery after prolonged cardioplegic arrest in an in vivo piglet model. Twenty-four piglets were subjected to 120 min of single-dose cardioplegic arrest and were divided into 4 groups according to the mode of reperfusion: control (simple aortic unclamp), remote perconditioning, terminal warm blood cardioplegia or remote perconditioning + terminal warm blood cardioplegia; remote perconditioning (4 cycles of 5-min ischaemia-reperfusion of the lower limb) was applied prior to aortic unclamping. Left ventricular systolic and diastolic functions were assessed by pressure-volume loop analysis at baseline and after 60 min of reperfusion. Biochemical injury was evaluated by plasma troponin T level. The control group showed decreased end-systolic elastance, preload recruitable stroke work and inverse of end-diastolic pressure-volume relationship of 51.3 ± 14.0%, 46.1 ± 22.5% and 34.8 ± 14.9%, respectively. Percentage recovery of end-systolic elastance and preload recruitable stroke work were significantly better with terminal warm blood cardioplegia (with or without remote perconditioning) (end-systolic elastance: 95% confidence interval, 38.6-84.1; preload recruitable stroke work: 95% confidence interval, 0.4-54.3). Percentage recovery of inverse of end-diastolic pressure-volume relationship was significantly better in the remote perconditioning groups (with or without terminal warm blood cardioplegia) (95% confidence interval, 1.6-41.6). No synergistic effects of remote perconditioning and terminal warm blood cardioplegia on troponin T release were noted. Remote perconditioning offers promising synergistic cardioprotection to terminal warm blood cardioplegia, implicating potential clinical benefit by contributing to prompt left ventricular functional recovery during paediatric open-heart surgery.

Replication of pressure-volume loop with controllable ESPVR and EDPVR curves on a personalized mock circulatory loop based on elastance function.

In the development of a left ventricular assist device (LVAD), it is important to evaluate the LVAD's hemodynamic effect on the compromised left ventricle (LV) before surgical implantation. The mock circulatory loop (MCL) is widely accepted as an in vitro test platform to evaluate LVADs across a wide range of operational conditions as a way to examine how the device and the cardiovascular system interact. Unfortunately, most MCLs represent an oversimplified model of cardiac function, with disease states simulated through generalized changes in heart rate and stroke volume. Because heart failure (HF) severity varies substantially among patients, an MCL is needed that can mimic the pressure-volume loop of an individual patient. In this work, two numerical elastance models, derived from a specific pressure volume loop template, were used to control the LV simulator of the MCL to simulate different degrees of HF. The numerical elastance model was then scaled to change the slopes of the end-systolic (ESPVR) and end-diastolic (EDPVR) pressure volume relationship curves to simulate systolic and diastolic dysfunction. The resulting experimental pressure volume loops are consistent with theoretical loops, demonstrating the feasibility of creating an MCL that can be customized for the patient.

The Sphingosine‐1‐Phosphate Analog, FTY720, Reverses Diastolic Dysfunction and Hypertrophy in Familial Hypertrophic Cardiomyopathy

BackgroundHypertrophic cardiomyopathy (HCM) patients present with progressively worsening hypertrophy, diastolic dysfunction and fibrosis, ending in heart failure with preserved ejection fraction. At the molecular level, a common pathology found is an increase in myofilament‐calcium (Ca) sensitivity. Previously, we have shown that oxidative modification of myofilament proteins, as a result of increased oxidative stress in HCM, may be a direct mediator of this increase. FTY720 is an immunomodulating drug, clinically used in the treatment of multiple sclerosis, which we have previously identified to have anti‐fibrotic and anti‐hypertrophic effects in a model of pressure‐overload‐induced hypertrophy. We sought to understand whether agonism of the sphingosine‐1‐phosphate receptor by FTY720 would be of therapeutic benefit in HCM, and its effects on oxidative modification.MethodsWe treated an HCM mouse model linked to a mutation in tropomyosin (Tm‐E180G) and non‐transgenic (NTG) littermates with FTY720 or vehicle for six weeks. We assessed cardiac function and morphology using echocardiography and pressure‐volume (PV) relations and the myofilament‐Ca‐response using detergent‐treated (skinned) fibers. We also investigated if signaling pathways were altered.ResultsWe found that FTY720‐treated Tm‐E180G mice had a significant reduction in left atrial size, E/A and E/Em ratios compared to significantly increased baseline measurements as assessed by echocardiography. PV relations revealed significant improvements in the end‐diastolic pressure volume relationship, preload recruitable stroke work, and relaxation constant (Tau). FTY720‐treated NTG mice displayed a significant decrease in ejection fraction and rate of maximum pressure development in early systole compared to vehicle‐treated NTG mice assessed by PV relations. Skinned fiber bundles revealed a significant decrease in myofilament‐Ca‐responsiveness. We attributed these functional improvements to a down‐regulation of S‐glutathionylation of cardiac myosin binding protein‐C in FTY720‐treated Tm‐E180G mice. The increases in oxidative modification in vehicle treated Tm‐E180G mice were due to an up‐regulation of NADPH oxidase 2 enzyme expression (NOX2), and fibrosis and hypertrophy to increased periostin, TGF‐beta expression, and GATA4 phosphorylation. These maladaptive changes were reversed by FTY720 treatment.ConclusionsIn Tm‐E180G mice, FTY720 improves diastolic function and morphology by reversing oxidative modification of myofilament proteins, resulting in a decrease in myofilament‐Ca‐responsiveness, via down‐regulation of NOX2 and other maladaptive remodeling signals.Support or Funding InformationR01 HL128468 (BMW, RJS) and F31 HL127996 (DMR)

Cardiac sympathetic afferent reflex control of cardiac function in normal and chronic heart failure states.

Cardiac sympathetic afferents are considered to be essential pathways for transmission of cardiac nociception to the central nervous system during myocardial ischaemia. However, a potential contribution of the CSAR control of cardiac dysfunction in both normal and chronic heart failure (CHF) states remains unknown. We found that activation of the CSAR evokes little increase in cardiac contractility with an exaggerated peripheral vasoconstriction in the CHF state. CSAR inhibition by epicardial lidocaine decreased cardiac contractility to a greater extent in CHF rats than sham rats. Furthermore, we also found that epicardial lidocaine paradoxically decreased left ventricular end-diastolic pressure (LVEDP) and left ventricular end-diastolic volume (preload) in CHF rats, which was not observed in sham rats. Chronic ablation of the CSAR by epicardial application of the afferent neurotoxin, RTX, selectively lowered diastolic blood pressure CHF rats. The observation suggests that CSAR has a differential effect on cardiac function in normal and CHF states. CSAR activation in normal state causes significant increase in cardiac contractility and cardiac output. The enhanced 'cardiac sympathetic afferent reflex' (CSAR) critically contributes to the exaggerated global sympathetic tone in chronic heart failure (CHF). However, a potential contribution of the cardio-cardiac reflex control of cardiac function in both normal and CHF states remains unknown. In this study, we evaluated the effects of direct activation or inhibition of the CSAR on cardiac function by pressure-volume (P-V) loop analysis in ∼12-week sham-operated and myocardial infarcted (MI) rats. In sham rats, acute CSAR activation by epicardial application of bradykinin (BK) increased heart rate (HR), left ventricular systolic pressure (LVSP), the maximum first derivative of left ventricular pressure (dp/dtmax ), and the slope of the end-systolic P-V relationship (ESPVR), suggesting that acute CSAR activation in the normal state enhances myocardial contractility. CSAR activation also decreased left ventricular (LV) systolic and diastolic volumes with little effect on LV end-diastolic pressure (LVEDP) or the end-diastolic P-V relationship (EDPVR) in sham rats. Compared to sham, CHF rats exhibit a reduced increase in the slope of the ESPVR and dp/dtmax in response to BK, indicating a poor contractile response to CSAR activation. Interestingly, BK application in CHF rats increased cardiac systolic and diastolic volumes and further increased the elevated LVEDP, neither of which was seen in sham rats. Following CSAR inhibition by epicardial lidocaine, blood pressure, HR, LVSP, dp/dt, LVEDP and ESPVR decreased in CHF rats whereas lidocaine had little effect in sham rats, indicating that the CSAR is tonically active in CHF and contributes to cardiac dysfunction. Furthermore, we found that epicardial lidocaine paradoxically decreased LV end-diastolic volume (preload) in CHF rats, which was not observed in sham rats. The decreased preload by lidocaine in CHF rats may be due to a reduction in peripheral vascular resistance since epicardial lidocaine significantly lowered peripheral (renal) sympathetic nerve activity in CHF rats but not in sham rats. Furthermore, chronic ablation of CSAR by epicardial application of a selective afferent neurotoxin, resiniferatoxin, selectively lowered diastolic blood pressure both at daytime and night-time with less effect on systolic blood pressure in CHF rats. Our data suggest that there is an imbalance between cardiac and peripheral responses to CSAR in CHF animals compared to sham-operated controls.

Biodegradable vs Nonbiodegradable Cardiac Support Device for Treating Ischemic Cardiomyopathy in a Canine Heart

Clinical studies of the efficacy of the nonbiodegradable CorCap device have shown inconsistent findings, at least in part, because of device-related impairment of diastolic cardiac function. We hypothesized that use of biodegradable material for the cardiac support device could contribute to an improvement in the diastolic function of the failing heart. Polyglycolic acid and polyethylene terephthalate were used to prepare biodegradable and nonbiodegradable cardiac support devices, respectively. Twelve-month-old beagles underwent anterior coronary artery ligation. One week after, the beagles were randomly assigned for implantation of a biodegradable cardiac support device (n = 7), nonbiodegradable cardiac support device (n = 8), or sham operation (n = 8). Twelve weeks after coronary artery ligation, the biodegradable group showed a significantly greater recovery of echocardiographical ejection fraction than the nonbiodegradable and the sham groups (40% ± 3.3%, 32% ± 2.5%, and 29 ± 2.6%, respectively). Of note, diastolic function, as assessed by Tau, -dp/dt min, and end-diastolic pressure-volume relationship in the cardiac catheter, was significantly better in both left and right ventricles in the biodegradable group than in the nonbiodegradable group. Moreover, global end-systolic wall stress was significantly lower in the 2 device groups than in the sham group (P < 0.03). Furthermore, global end-diastolic wall stress was significantly less in the biodegradable device group than in the nonbiodegradable group (P < 0.02). The cardiac support devices made of biodegradable material were more effective in improving systolic function, with preservation of diastolic function in the canine infarct heart, than devices made of nonbiodegradable material.

Cardiac structural remodeling in hypertensive cardiomyopathy.

Heart failure with preserved ejection fraction (HFpEF), which is a primary driver of morbidity and mortality, accounts for approximately half of all heart failure cases. Therefore, it is essential to develop preclinical animal models for HFpEF pharmacological treatment strategies. We created a porcine model of severe hypertension and hyperlipidemia by using a combination of deoxycorticosterone acetate (DOCA, 100 mg kg-1), Western diet (WD) and angiotensin II infusion. Systolic blood pressure, echocardiography and invasive pressure-volume loop were assessed at baseline, 12 weeks and 18 weeks. A detailed histological assessment was also performed to determine the cardiac structural remodeling. Compared with controls (n=10), hypertensive animals (n=10) showed markedly higher systolic blood pressure (181 vs. 86 mm Hg) at 18 weeks. Concentric remodeling, characterized by a normal chamber size with a thicker wall, was observed in hypertensive animals. Left ventricle diastolic function showed a tendency toward decline, according to the echocardiographic data. Hemodynamic data showed that the end-diastolic pressure-volume relationship was elevated without changes in the end-systolic pressure-volume relationship. Histological results revealed that the fibrotic area in hypertensive animals (P<0.05 vs. controls) and the fibrotic area in the posterior wall of hypertensive animals' left atria were larger than other sites of the left atria (P<0.05 vs. other sites). This model can mimic clinical HFpEF to some degree. We found that the posterior wall of the left atrium is more susceptible to atrial remodeling associated with hypertension compared with other regions of the left atrium.

Gene Therapy With Angiotensin-(1-9) Preserves Left Ventricular Systolic Function After Myocardial Infarction

BackgroundAngiotensin-(1-9) [Ang-(1-9)] is a novel peptide of the counter-regulatory axis of the renin-angiotensin-aldosterone system previously demonstrated to have therapeutic potential in hypertensive cardiomyopathy when administered via osmotic mini-pump. Here, we investigate whether gene transfer of Ang-(1-9) is cardioprotective in a murine model of myocardial infarction (MI). ObjectivesThe authors evaluated effects of Ang-(1-9) gene therapy on myocardial structural and functional remodeling post-infarction. MethodsC57BL/6 mice underwent permanent left anterior descending coronary artery ligation and cardiac function was assessed using echocardiography for 8 weeks followed by a terminal measurement of left ventricular pressure volume loops. Ang-(1-9) was delivered by adeno-associated viral vector via single tail vein injection immediately following induction of MI. Direct effects of Ang-(1-9) on cardiomyocyte excitation/contraction coupling and cardiac contraction were evaluated in isolated mouse and human cardiomyocytes and in an ex vivo Langendorff-perfused whole-heart model. ResultsGene delivery of Ang-(1-9) reduced sudden cardiac death post-MI. Pressure volume measurements revealed complete restoration of end-systolic pressure, ejection fraction, end-systolic volume, and the end-diastolic pressure volume relationship by Ang-(1-9) treatment. Stroke volume and cardiac output were significantly increased versus sham. Histological analysis revealed only mild effects on cardiac hypertrophy and fibrosis, but a significant increase in scar thickness. Direct assessment of Ang-(1-9) on isolated cardiomyocytes demonstrated a positive inotropic effect via increasing calcium transient amplitude and contractility. Ang-(1-9) increased contraction in the Langendorff model through a protein kinase A–dependent mechanism. ConclusionsOur novel findings showed that Ang-(1-9) gene therapy preserved left ventricular systolic function post-MI, restoring cardiac function. Furthermore, Ang-(1-9) directly affected cardiomyocyte calcium handling through a protein kinase A–dependent mechanism. These data emphasized Ang-(1-9) gene therapy as a potential new strategy in the context of MI.

Abstract 12874: E/e’ SV is a Better Predictor of Outcome Than E/e’ in Patients With Heart Failure With Preserved Left Ventricular Ejection Fraction

Introduction: Predictors of outcome in patients with heart failure with preserved left ventricular ejection fraction (HFpEF) remain unclear. The ratio of early diastolic transmitral flow velocity to early diastolic myocardial velocity (E/e’) has been proposed as one of them, but the predictive accuracy remains insufficient. Hypothesis: We hypothesized E/e’ SV, E/e’ normalized by the stroke volume (SV), may be a better predictor of outcome in patients with HFpEF than E/e’, by reflecting the terminal slope of the end-diastolic pressure-volume relation, i.e., stiffness of the left ventricle. The aims of this study were to propose a novel echocardiographic index, E/e’ SV, and investigate the feasibility and accuracy of this method in HFpEF patients. Methods: Echocardiography including E/e’ SV measurement was performed in consecutive 43 patients with HFpEF at discharge in index hospitalization (female 22 patients (51%), age 78±9 years old). Patients were followed for a median of 6.5 months. The end points included the admission for heart failure and cardiovascular death. Results: During the follow-up, 9 patients (21%) encountered the end points. In ROC analysis, E/e’ SV was a better predictive factor than E/e’ (E/e’ SV: AUC=0.820; E/e’: AUC=0.768). Kaplan-Meier analysis showed patients with E/e’ SV&gt;0.420 had a poorer prognosis than those with E/e’ SV&lt;0.420 (P&lt;0.01). In Cox regression multivariate analysis, high E/e’ SV was an independent predictor of event-free survival (Adjusted Hazard ratio [95% CI] = 17.2 [3.1, 94.8] (p=0.001)). Conclusion: E/e’ SV is a better predictor of outcome in patients with HFpEF than E/e’.

Assessment of dexmedetomidine effects on left ventricular function using pressure-volume loops in rats.

The role of dexmedetomidine on left ventricular function is ambiguous. We analyzed pressure-volume loops to investigate whether dexmedetomidine has a myocardial depressive effect. Thirty-two Sprague-Dawley rats were anesthetized and a pressure-volume loop catheter was advanced into the left ventricle. Rats were divided into four groups (n=8 each). The control group received a 10-min infusion of 0.1ml of normal saline, and the other three groups received 1.0 (Dex1.0 group) , 2.5 (Dex2.5 group), and 5.0μg/kg (Dex5.0 group) dexmedetomidine in a similar fashion to the control group. Steady-state hemodynamic parameters were recorded. The inferior vena cava was occluded intermittently to assess preload-independent indices. Compared with the control group, changes in the Dex1.0 group were insignificant. In the Dex2.5 group, only the systolic blood pressure was higher (vs control, P=0.03), and other parameters were insignificant. The Dex5.0 group exhibited a lower heart rate, higher systolic blood pressure, higher arterial elastance (vs control, all P<0.001), and unaltered cardiac output. The Dex5.0 group showed steeper slopes of end-systolic pressure increment and end-systolic pressure-volume relationship than the control, Dex1.0, and Dex2.5 groups (all P<0.001). Slopes of end-diastolic pressure decrement and end-diastolic pressure-volume relationship did not differ among groups. Dexmedetomidine had no direct myocardial depressant effect in the rat heart in doses that are similar to those encountered under clinical conditions. Dexmedetomidine did not significantly alter the ability of the heart to cope with bradycardia and greatly increased afterload. Their potentially negative impact on cardiac output was effectively attenuated by improved myocardial contractility and preserved diastolic function in healthy subjects.

Sex-Specific Effects of Adrenergic-Induced Left Ventricular Remodeling in Spontaneously Hypertensive Rats

ObjectiveThe aim of this work was to determine whether adrenergic-induced left ventricular (LV) dilation and eccentric remodeling in pressure-overload hypertrophy is sex specific. Methods and ResultsChronic β-adrenoreceptor activation was produced in male and female spontaneously hypertensive rats (SHRs) by means of daily administration of isoproterenol (ISO; 0.04 mg/kg daily) from 9 to 15 months of age. LV chamber dimensions were determined in vivo by means of echocardiography and ex vivo in isolated perfused heart preparations. The acute hemodynamic response to ISO, the degree of myocardial necrosis and apoptosis, and collagen distribution were also assessed. Female SHRs demonstrated inotropic and chronotropic responses to ISO similarly to male SHRs. Compared with control subjects (saline solution vehicle), following chronic ISO administration, LV end-diastolic diameter (mm) was increased in male (ISO 7.8 ± 0.3 vs control 6.6 ± 0.2; P < .001) but not in female (ISO 6.3 ± 0.2 vs control 6.2 ± 0.2; P = .23) SHRs. Similarly, compared with control, ISO administration increased the volume intercept of the LV end-diastolic pressure-volume relation (mL) in male (ISO 0.31 ± 0.02 vs control 0.22 ± 0.01; P < .0001) but not in female (ISO 0.17 ± 0.01 vs control 0.17 ± 0.01; P = 1.00) SHRs. Relative wall thickness was also decreased in male SHRs receiving ISO but not in female SHRs receiving ISO. Chronic ISO administration increased the percentage of area covered by interstitial collagen in male but not in female SHRs. Finally, chronic adrenergic stimulation failed to influence LV chamber or myocardial systolic function in either male or female SHRs. ConclusionsMale SHRs are more susceptible to adrenergic-induced LV dilation and eccentric LV remodeling than female SHRs. These effects are associated with increased collagen deposition. In pressure-overload hypertrophy, LV dilation and eccentric LV remodeling occur before LV dysfunction in male rats.

O9-2 - (E/E')/Sv is a Better Predictor of Outcome Than E/E' in Patients with Heart Failure with Preserved Left Ventricular Ejection Fraction

Background and Objective: Predictors of outcome in patients with heart failure with preserved left ventricular ejection fraction (HFpEF) remain unclear. The ratio of early diastolic transmitral velocity to early diastolic tissue velocity (E/e') has been proposed as one of them, but the predictive accuracy remains insufficient. We hypothesized(E/e')/SV, E/e' normalized by the stroke volume (SV), may be a better predictor of outcome in patients with HFpEF than E/e', by reflecting the terminal slope of the end-diastolic pressure-volume relation, i.e., stiffness of the left ventricle. Methods: Echocardiography including (E/e')/SV measurement was performed in consecutive 43 patients of HFpEF before discharge (female 22 patients (51%), age 78 ± 9 years old). Patients were followed for a median of 6.5 months. The end points included the admission for heart failure and cardiovascular death. Results: During the follow-up, 9 patients (21%) encountered the end points. In ROC analysis, (E/e')/SV was a better predictive factor than E/e' ((E/e')/SV AUC = 0.820, E/e' AUC = 0.768). Kaplan-Meier analysis showed patients with high(E/e')/SV (>0.420) had poor prognosis (P < .01). Conclusion: (E/e')/SV is a better predictor of outcome than E/e'in patients with HFpEF.

Abstract 74: Cardioprotective Effect of Growth Hormone Releasing Hormone in Mouse Model of Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is characterized by impaired relaxation, ventricular stiffening and fibrosis. We previously showed that activation of GHRH receptor markedly reduces fibrosis in rat and swine models of ischemic myocardial injury. Therefore, we hypothesized that activation of GHRH receptor signaling can improve diastolic dysfunction in a mouse model of HFpEF. C57BL6N mice (n=4-5) were implanted with a mini-osmotic pump to deliver angiotensin-II (Ang-II: 0.8 mg/kg/day) for 4 weeks and randomly assigned to receive daily injections of GHRH-Agonist (GHRH-A [MR-409]: 100 μg/kg) or vehicle (DMSO+propylene-glycol). Cardiac performance was assessed by serial echocardiography and hemodynamic analysis. Chronic administration of Ang-II resulted in increased end-diastolic pressure (EDP, p=0.0186) with no changes in EF (p=ns) or end-systolic pressure (ESP, p=ns) in comparison to control mice. Isovolumetric relaxation time (IVRT, p&lt;0.05) and end-diastolic pressure-volume relationship (EDPVR, p=0.0229) were markedly increased in the Ang-II group consistent with increased ventricular stiffness and poor myocardial relaxation. MR-409 treatment reset these parameters to normal levels (table 1). Our findings demonstrate that chronic administration of Ang-II mediates structural and functional changes that mimic HFpEF. Importantly, MR-409 treatment reduces Ang-II-induced elevation of EDP, EDPVR and IVRT; thus preventing HFpEF–like effects, suggesting that activation of the GHRH receptor signaling pathways represents a potential new therapeutic approach for HFpEF.

Abstract 85: Interactions Between Cardiac Myosin Binding Protein C and Actin Contribute to the Regulation of Cardiac Contraction

Cardiac myosin binding protein C (cMyBP-C) is a regulatory muscle protein that is essential for proper cardiac contraction, and mutations in cMyBP-C are commonly associated with hypertrophic cardiomyopathy. cMyBP-C not only interacts with myosin, but with actin as well. In vitro studies have demonstrated that multiple functions of cMyBP-C could readily be explained by an interaction between cMyBP-C and actin, but the in vivo significance of cMyBP-C binding to either myosin or actin is not well understood. Here we created transgenic mice with a single point mutation (L348P) in a key binding domain of cMyBP-C that enhances the binding affinity of cMyBP-C for actin in vitro (Bezold et al , JBC 2013) to gain insights into the relevance of cMyBP-C binding to actin in working hearts. Echocardiograms from 3 month old male L348P-Tg mice (N=23) and non-transgenic (nTg, N=17) controls were used to assess systolic and diastolic function. Results showed significantly prolonged isovolumetric relaxation time (L348P-Tg: 18.5±0.6 vs nTg: 10.2±0.3 ms) and slower movement of the mitral valve annulus (E’: -17.2±1.5 vs -32.2±1.6 and A’: -9.1±1.7 vs -17.6±1.0 mm/s, p&lt;0.05), accompanied by slower inflow of blood into the left ventricle (reduced E and A, prolonged mitral valve deceleration time). Pressure-volume measurements showed significantly reduced rates of pressure decay in L348P-Tg mice (Tau Glantz: 39.1±2.6 vs 12.7±0.9 ms) and an increased end-diastolic pressure volume relationship (0.13±0.02 vs 0.07±0.01). We challenged mice with acute beta-adrenergic stimulation (isoprenaline injection) to determine whether the L348P mutation affected contractile reserve. Isoprenaline had little effect on diastolic parameters, but revealed systolic dysfunction in L348P-Tg mice as evident from a blunted increase in contraction (e.g. fractional shortening after isoprenaline: 38.5±1.3 vs 44.2±1.7%). Taken together our results show for the first time that interactions between cMyBP-C and actin are relevant for functioning of the whole heart. Increasing the cMyBP-C-actin interaction by the L348P mutation caused increased stiffness of the left ventricle, slowed relaxation and diastolic dysfunction. Results also suggested that the L348P mutation reduces contractile reserve.

Role of tissue transglutaminase in age-associated ventricular stiffness.

Aging is associated with increased cardiomyocyte loss, left-ventricular hypertrophy, and the accumulation of extracellular matrix, which results in declining cardiac function. The role of the matrix crosslinking enzyme, tissue transglutaminase (TG2), in age-related myocardial stiffness, and contractile function remains incompletely understood. In this study, we examined the role of TG2 in cardiac function, and determined whether TG2 inhibition can prevent age-associated changes in cardiac function. Male Fisher rats (18-month-old) were administered the transglutaminase inhibitor cystamine (study group) or saline (age-matched controls) for 12weeks via osmotic mini-pumps. Cardiac function was determined by echocardiography and invasive pressure-volume loops. Rat hearts were dissected out, and TG2 expression, activity, and S-nitrosation were determined. Young (6-month-old) males were used as controls. TG2 activity significantly increased in the saline-treated but not in the cystamine-treated aging rat hearts. TG2 expression also increased with age and was unaltered by cystamine treatment. Aged rats showed increased left ventricular (LV) end-systolic dimension and a decrease in fractional shortening compared with young, which was not affected by cystamine. However, cystamine treatment preserved the preload-independent index of LV filling pressure and restored end-diastolic pressure, end-diastolic pressure-volume relationships, and arterial elastance toward young. An increase in TG2 activity contributes to age-associated increase in diastolic stiffness, thereby contributing to age-associated diastolic dysfunction. TG2 may thus represent a novel target for age-associated diastolic heart failure.