Closed-chest Model Research Articles

A Novel Large Animal Model of Thrombogenic Coronary Microembolization.

Coronary microembolization is one of the main causes of the “no-reflow” phenomenon, which commonly occurs after reperfusion of an occluded coronary artery. Given its high incidence and the fact that it has been proven to be an independent predictor of cardiac morbidity and mortality, there is an imperative need to study its underlying mechanisms and pathophysiology. Large animal models are essential to perform translational studies. Currently there is no animal model that recapitulates a clinical scenario of thrombogenic microembolism with preceding myocardial ischemia. Therefore, the goal of this study was to develop and characterize a novel pig model of coronary microembolization using autologous thrombus injection (CMET). Twenty-three pigs underwent myocardial infarction through percutaneous balloon occlusion of the left anterior descending artery (LAD). Each animal was enrolled in one of two groups: (1) the CMET group, in which the LAD occlusion was followed by delivery of autologous clotted blood in the LAD (distal to the balloon occlusion) and reperfusion; (2) the ischemic reperfusion (I/R) group, in which the LAD ischemia was followed by reperfusion. Surviving animals underwent functional and morphological characterization at 1-week post-procedure. Three sham operated animals were used as a control. CMET resulted in impaired left ventricular function compared to I/R pigs at 1 week. Three-dimensional echocardiography demonstrated reduced ejection fraction in the CMET group (CMET vs. I/R: 35.6 ± 4.2% vs. 47.6 ± 2.4%, p = 0.028). Invasive hemodynamic measurements by Swan-Ganz and left ventricular pressure-volume catheters revealed that CMET impaired left ventricular contractility and diastolic function. This was confirmed by both load-dependent indices including cardiac output (CMET vs. I/R: 2.7 ± 0.2 l/min, vs. 4.0 ± 0.1 l/min, p = 0.002) and load independent indices including preload-recruitable stroke work (CMET vs. I/R: 25.8 ± 4.0 vs. 47.5 ± 6.5 mmHg, p = 0.05) and end-diastolic pressure-volume relationship (slope, 0.68 ± 0.07 vs. 0.40 ± 0.11 mmHg/ml, p = 0.01). Our unique closed-chest model of coronary microembolization using autologous thrombus injection resembles the clinical condition of thrombogenic coronary microembolization in I/R injury. This model offers opportunities to conduct translational studies for understanding and treating coronary microembolization in myocardial infarction.

2183Intravenous administration of IV-STATIN CARDIOSHIELD during myocardial infarction renders higher cardioprotection than oral atorvastatin given shortly after reperfusion: a translational CMR study

Abstract Background Statins are known to exert rapid cardioprotective effects irrespective of their lipid-lowering properties. Several trials have suggested that high-dose statin treatment may reduce cardiovascular complications in patients undergoing invasive management. However, the ideal timing and administration regime is not clear. Purpose We compared the cardioprotective effects derived from IV-STATIN CARDIOSHIELD® administered intravenously during myocardial infarction (MI) with those attained by oral atorvastatin administration shortly after reperfusion. This study was conducted in a preclinical pig model of MI by serial CMR imaging. Methods Diet-induced hypercholesterolemic pigs (N=21; cholesterol: 387±74mg/dL) were subjected to 90 minutes of complete coronary occlusion (closed-chest model of MI), then reperfusion was established and animals were kept for 42 days. Within this experimental design animals were distributed in 3 groups (G) (7animals/arm): G1) animals received an intravenous bolus (0.3mg/kg) of IV-STATIN during MI; G2) animals received an intravenous bolus of the vehicle during MI (placebo-control); and G3) animals were administered atorvastatin p.o. initiated within the first 2h post-MI (Atorva-post-MI). G1 and G3 animals remained on atorvastatin p.o. for the following 42 days whereas G2 controls received placebo-pills. We assessed cardiac damage and global and regional functional parameters by CMR at day3 and day42 post-MI. Myocardial samples were processed for molecular studies on cardiac remodeling-related parameters (collagen and AMPK). Results CMR analysis at day-3 revealed that G1 pigs showed a marked reduction in infarct size as compared to both G3 and G2 animals (19.1±2.8% LV vs. 29.0±1.8% and 29.3%±3.2%, respectively; p<0.05) with a resultant 50% increase in myocardial salvage (p<0.05 vs. both). At day-42 both G1 and G3 animals showed a significant decrease in the size of the scar vs. G2 animals; however, G1 animals showed a further 24% scar reduction as compared to G3 (14.4±1.1% vs. 18.8±1.0% LV; p<0.05). Functional analyses revealed higher LVESV in G1 animals as compared to G2 (p<0.05) and less wall motion abnormalities in the jeopardized myocardium (p<0.05) vs. both groups at day42 post-MI. Collagen expression and AMPK activation were found to be significantly enhanced in the scar of G1 (p<0.05 vs. both groups). No changes were detected in lipids levels or liver and renal parameters throughout the study in any pig group. Conclusions Intravenous IV-STATIN CARDIOSHIELD® treatment during MI limited cardiac damage and improved cardiac function and remodeling to a larger extent than when atorvastatin was administered orally shortly after reperfusion. Our results support this novel regime of intravenous administration of IV-STATIN CARDIOSHIELD® as a routine procedure during MI. Further investigation of the potential benefits of this new therapeutic approach in STEMI patients is warranted.

Targeting Mitochondrial Fission Using Mdivi-1 in A Clinically Relevant Large Animal Model of Acute Myocardial Infarction: A Pilot Study.

Background: New treatments are needed to reduce myocardial infarct size (MI) and prevent heart failure (HF) following acute myocardial infarction (AMI), which are the leading causes of death and disability worldwide. Studies in rodent AMI models showed that genetic and pharmacological inhibition of mitochondrial fission, induced by acute ischemia and reperfusion, reduced MI size. Whether targeting mitochondrial fission at the onset of reperfusion is also cardioprotective in a clinically-relevant large animal AMI model remains to be determined. Methods: Adult pigs (30–40 kg) were subjected to closed-chest 90-min left anterior descending artery ischemia followed by 72 h of reperfusion and were randomized to receive an intracoronary bolus of either mdivi-1 (1.2 mg/kg, a small molecule inhibitor of the mitochondrial fission protein, Drp1) or vehicle control, 10-min prior to reperfusion. The left ventricular (LV) size and function were both assessed by transthoracic echocardiography prior to AMI and after 72 h of reperfusion. MI size and the area-at-risk (AAR) were determined using dual staining with Tetrazolium and Evans blue. Heart samples were collected for histological determination of fibrosis and for electron microscopic analysis of mitochondrial morphology. Results: A total of 14 pigs underwent the treatment protocols (eight control and six mdivi-1). Administration of mdivi-1 immediately prior to the onset of reperfusion did not reduce MI size (MI size as % of AAR: Control 49.2 ± 8.6 vs. mdivi-1 50.5 ± 11.4; p = 0.815) or preserve LV systolic function (LV ejection fraction %: Control 67.5 ± 0.4 vs. mdivi-1 59.6 ± 0.6; p = 0.420), when compared to vehicle control. Similarly, there were no differences in mitochondrial morphology or myocardial fibrosis between mdivi-1 and vehicle control groups. Conclusion: Our pilot study has shown that treatment with mdivi-1 (1.2 mg/kg) at the onset of reperfusion did not reduce MI size or preserve LV function in the clinically-relevant closed-chest pig AMI model. A larger study, testing different doses of mdivi-1 or using a more specific Drp1 inhibitor are required to confirm these findings.

Abstract 793: Macrophage Transcription Factor EB Attenuates Left Ventricular Remodeling Via Lysosomal Lipolysis

Background: Autophagy, lipid metabolism, and inflammation are interrelated cellular processes that implicate lysosomes in human disease. After ischemia reperfusion (IR) injury, inflammasome activation and interleukin 1-beta (IL1-beta) secretion promote heart failure progression. Whether macrophage autophagy and lysosomal biogenesis can attenuate post-IR remodeling and inflammation is unknown. We hypothesized that macrophages exhibit lysosome dysfunction and autophagic impairment after IR injury, and that augmentation of macrophage lysosomal biogenesis via macrophage-specific overexpression of transcription factor EB (Mf-TFEB), a master regulator of autophagy and lysosomal biogenesis, would attenuate myocardial remodeling and inflammation in ischemic cardiomyopathy. Methods and Results: In mice subject to IR injury and humans with ischemic cardiomyopathy, we observed evidence of lysosomal and autophagic impairment. To ameliorate post-IR macrophage lysosomal injury, we expressed Mf-TFEB in a closed-chest IR murine model using a tamoxifen-inducible CX3CR1erCre and TFEB overexpression cassette bearing a Cre-excisable STOP codon. Compared to Cre-only controls, Mf-TFEB mice had significantly increased left ventricular (LV) ejection fraction 28-days post-IR (40% relative increase, p=0.002, n=15-17 per group), decreased abundance of pro-inflammatory macrophages, and reduced levels of IL1-beta in myocardial tissue. Surprisingly, neither inflammasome suppression nor TFEB-mediated attenuation of post-IR remodeling required intact macro-autophagy as evidenced by Mf-TFEB-mediated rescue of post-IR LV dysfunction in mice with concomitant inducible ATG5 ablation. RNA sequencing of flow-sorted macrophages from post-IR mice identified lysosomal acid lipase amongst other lipases regulated by TFEB. Mechanistically, pharmacologic inhibition of lysosomal acid lipase specifically abrogated the in vivo effects of TFEB on post-IR remodeling. Conclusions: Our findings suggest that macrophage TFEB regulates lysosomal lipolysis to attenuate inflammasome activity and protect against post-IR LV dysfunction, suggesting an alternative paradigm for how lysosome function may impact acute inflammation in vivo.

Tailoring optogenetic tools for AF treatment.

A novel bioelectronic system that combines automated arrhythmia detection with optogenetic engineering for arrhythmia termination is able to stop atrial fibrillation without the need of electrical shock in a closed-chest experimental model.

Infarct-Related Ventricular Tachycardia: Redefining the Electrophysiological Substrate oftheIsthmusDuring SinusRhythm.

In this study, the scientific objective was to characterize the electrophysiological substrate of the ventricular tachycardia (VT) isthmus during sinus rhythm. The authors have recently described the electrophysiological characteristics of the VT isthmus using a novel invivo high-resolution mapping technology. Sixteen swine with healed infarction were studied using high-resolution mapping technology (Rhythmia, Boston Scientific, Cambridge, Massachusetts) in a closed-chest model. The left ventricle was mapped during sinus rhythm and analyzed for activation, conduction velocity, electrogram shape, and amplitude. Twenty-four VTs allowed detailed mapping of the common-channel "isthmus," including the "critical zone." This was defined as the zone of maximal conduction velocity slowing in the circuit, often occurring at entrance and exit from the isthmus caused by rapid angular change in activation vectors. The VT isthmus corresponded to sites displaying steep activation gradient (SAG) during sinus rhythm with conduction velocity slowing of 58.5 ± 22.4% (positive predictive value [PPV] 60%). The VT critical zone displayed SAG with greater conduction velocity slowing of 68.6 ± 18.2% (PPV 70%). Critical-zone sites were consistently localized in areas with bipolar voltage≤0.55 mV, whereas isthmus sites were localized in areas with variable voltage amplitude (1.05± 0.80 mV [0.03 to 2.88 mV]). Importantly, critical zones served as common-site "anchors" for multiple VT configurations and cycle lengths. Isthmus and critical-zone sites occupied only 18.0 ± 7.0% of the low-voltage area (≤1.50 mV). Isolated late potentials were present in both isthmus and nonisthmus sites, including dead-end pathways (PPV 36%; 95% confidence interval: 34.2% to 39.6%). The VT critical zone corresponds to a location characterized by SAG and very low voltage amplitude during sinus rhythm. Thus, it allows identification of a re-entry anchor with high sensitivity and specificity. By contrast, voltage and electrogram characteristics during sinus rhythm have limited specificity for identifying the VT isthmus.

Abstract 423: Role of Autophagy in Macrophages During Acute Myocardial Infraction

Acute myocardial infarction (AMI) is associated with inflammation and proinflammatory cytokine release, including IL-1β, but the role of NLRP3 inflammasome in cardiac injury remains controversial and requires further investigation. Autophagy, important for stress responses in injury and diseases, is a self-digestion process for the recycling of cytosolic macromolecules and damaged organelles. While autophagy has been previously investigated in cardiac muscle cells in AMI, its role in inflammatory cells is unknown. We generated macrophage (Mφ)-specific Atg16L1 KO mice ( Atg16l1 fl/fl LysM-Cre) and performed permanent ligation of the left anterior descending artery (LAD) using closed-chest model. 24 hours post ligation, Mφ-specific Atg16L1 KO mice had significantly larger infarction area as measured by myoglobin staining, and more TUNEL staining compared with control groups. This suggested that autophagy in macrophages plays a cardioprotective role during AMI. Since autophagy negatively regulates NLRP3 inflammasome activation and IL-1β secretion, we investigated the role of NLRP3 inflammasome in AMI. NLRP3 KO mice were subjected to LAD ligation and KO mice had less infarction compared with control mice. We also observed reduced infarction in IL-1R1 deficient mice, suggesting that NLRP3 inflammasome and subsequent IL-1β secretion and signaling play a role in AMI pathology. Multiple reports indicate that autophagy associated proteins induction have reduced expression in aged tissues and that autophagy diminishes with aging. We therefore investigated IL-1 signaling blockade with Anakinra (IL-1 receptor antagonist) in aged C57BL/6 mice. Mice were injected with Anakinra daily 10 mg/kg starting 1 h after LAD ligation. While we observed 14% larger infarct size in aged mice (18 months) compared to young mice (12 weeks), Anakinra treatment displayed significantly reduced infarction compared with age matched controls and the reduction of infarction by anakinra treatment was significantly greater in aged mice (75% reduction) compared with young mice (50% reduction). Taken together, these data demonstrate that autophagy plays a protective role in macrophages and NLRP3 and IL-1β mediate pathology, with an increased effect on aged mice during AMI.

Synthetic CpG oligonucleotides induce a genetic profile ameliorating murine myocardial I/R injury.

We previously demonstrated that pre‐conditioning with CpG oligonucleotide (ODN) 1668 induces quick up‐regulation of gene expression 3 hours post‐murine myocardial ischaemia/reperfusion (I/R) injury, terminating inflammatory processes that sustain I/R injury. Now, performing comprehensive microarray and biocomputational analyses, we sought to further enlighten the “black box” beyond these first 3 hours. C57BL/6 mice were pretreated with either CpG 1668 or with control ODN 1612, respectively. Sixteen hours later, myocardial ischaemia was induced for 1 hour in a closed‐chest model, followed by reperfusion for 24 hours. RNA was extracted from hearts, and labelled cDNA was hybridized to gene microarrays. Data analysis was performed with BRB ArrayTools and Ingenuity Pathway Analysis. Functional groups mediating restoration of cellular integrity were among the top up‐regulated categories. Genes known to influence cardiomyocyte survival were strongly induced 24 hours post‐I/R. In contrast, proinflammatory pathways were down‐regulated. Interleukin‐10, an upstream regulator, suppressed specifically selected proinflammatory target genes at 24 hours compared to 3 hours post‐I/R. The IL1 complex is supposed to be one regulator of a network increasing cardiovascular angiogenesis. The up‐regulation of numerous protective pathways and the suppression of proinflammatory activity are supposed to be the genetic correlate of the cardioprotective effects of CpG 1668 pre‐conditioning.

A Closed-chest Model to Induce Transverse Aortic Constriction in Mice

A Closed-chest Model to Induce Transverse Aortic Constriction in Mice

A Closed-chest Model to Induce Transverse Aortic Constriction in Mice.

Research on cardiac hypertrophy and heart failure is frequently based on pressure overload mouse models induced by TAC. The standard procedure is to perform a partial thoracotomy to visualize the transverse aortic arch. However, the surgical trauma caused by the thoracotomy in open-chest models changes the respiratory physiology as the ribs are dissected and left unattached after chest closure. To prevent this, we established a minimally invasive, closed chest approach via lateral thoracotomy. Herein we approach the aortic arch via the 2nd intercostal space without entering the chest cavities, leaving the mouse with a less traumatic injury to recover from. We perform this operation using standard laboratory settings for open chest TAC procedures with equal survival rates. Apart from maintaining physiological breathing patterns due to the closed chest approach, the mice seem to benefit by showing rapid recovery, as the less invasive technique appears to facilitate a fast healing process and to reduce immune response after trauma.

A Pig Model of Myocardial Infarction: Catheter-Based Approaches.

Despite enormous efforts in treating myocardial infarction (MI) and subsequent heart failure, the recent statistics from the American Heart Association evidently show that there still remains room for improvements. To develop and translate new therapeutics toward clinics, large animal models that allow us to test new therapies in human-like conditions are of extraordinary importance. In this chapter, we describe detailed protocols for the creation of a closed-chest MI model in pigs. The advantages of this model include high survival rate (>90% after ischemia-reperfusion), adjustable MI size depending on coronary occlusion site, reproducible cardiac dysfunction, and relatively low invasive method. The temporary coronary occlusion method for ischemia-reperfusion injury as well as the permanent occlusion method, using clot injection or embolic coil implantation, are described. Furthermore, we describe the keysteps needed for understanding, performing, and analyzing cardiac angiography and echocardiography in pigs.

In vivo MRI and ex vivo histological assessment of the cardioprotection induced by ischemic preconditioning, postconditioning and remote conditioning in a closed-chest porcine model of reperfused acute myocardial infarction: importance of microvasculature

BackgroundCardioprotective value of ischemic post- (IPostC), remote (RIC) conditioning in acute myocardial infarction (AMI) is unclear in clinical trials. To evaluate cardioprotection, most translational animal studies and clinical trials utilize necrotic tissue referred to the area at risk (AAR) by magnetic resonance imaging (MRI). However, determination of AAR by MRI‚ may not be accurate, since MRI-indices of microvascular damage, i.e., myocardial edema and microvascular obstruction (MVO), may be affected by cardioprotection independently from myocardial necrosis. Therefore, we assessed the effect of IPostC, RIC conditioning and ischemic preconditioning (IPreC; positive control) on myocardial necrosis, edema and MVO in a clinically relevant, closed-chest pig model of AMI.Methods and resultsAcute myocardial infarction was induced by a 90-min balloon occlusion of the left anterior descending coronary artery (LAD) in domestic juvenile female pigs. IPostC (6 × 30 s ischemia/reperfusion after 90-min occlusion) and RIC (4 × 5 min hind limb ischemia/reperfusion during 90-min LAD occlusion) did not reduce myocardial necrosis as assessed by late gadolinium enhancement 3 days after reperfusion and by ex vivo triphenyltetrazolium chloride staining 3 h after reperfusion, however, the positive control, IPreC (3 × 5 min ischemia/reperfusion before 90-min LAD occlusion) did. IPostC and RIC attenuated myocardial edema as measured by cardiac T2-weighted MRI 3 days after reperfusion, however, AAR measured by Evans blue staining was not different among groups, which confirms that myocardial edema is not a measure of AAR, IPostC and IPreC but not RIC decreased MVO.ConclusionWe conclude that IPostC and RIC interventions may protect the coronary microvasculature even without reducing myocardial necrosis.

Multiparametric CMR imaging of infarct remodeling in a percutaneous reperfused Yucatan mini-pig model.

To further understanding of the temporal evolution and pathophysiology of adverse ventricular remodeling over the first 60 days following a myocardial infarction (MI) in both the infarcted and remote myocardium, we performed multi-parametric cardiac magnetic resonance (CMR) imaging in a closed-chest chronic Yucatan mini-pig model of reperfused MI. Ten animals underwent 90 min left anterior descending artery occlusion and reperfusion. Three animals served as controls. Multiparametric CMR (1.5T) was performed at baseline, Day 2, Day 30 and in four animals on Day 60 after MI. Left ventricular (LV) volumes and infarct size were measured. T1 and T2 mapping sequences were performed to measure values in the infarct and remote regions. Remote region collagen fractions were compared between infarcted animals and controls. Procedure success was 80%. The model created large infarcts (28 ± 5% of LV mass on Day 2), which led to significant adverse myocardial remodeling that stabilized beyond 30 days. Native T1 values did not reliably differentiate remote and infarct regions acutely. There was no evidence of remote fibrosis as indicated by partition coefficient and collagen fraction analyses. The infarct T2 values remained elevated up to 60 days after MI. Multiparametric CMR in this model showed significant adverse ventricular remodeling 30 days after MI similar to that seen in humans. In addition, this study demonstrated that remote fibrosis is absent and that infarct T2 signal remains chronically elevated in this model. These findings need to be considered when designing preclinical trials using CMR endpoints.

Reduced acute myocardial ischemia–reperfusion injury in IL-6-deficient mice employing a closed-chest model

Objective and designWe examined the role of IL-6 in the temporal development of cardiac ischemia–reperfusion injury employing a closed-chest I/R model.Materials/methodsInfarction, local and systemic inflammation, neutrophil infiltration, coagulation and ST elevation/resolution were compared between wild-type (WT) and IL-6-deficient (IL-6−/−) mice after 1 h ischemia and 0, ½, 3, and 24 h reperfusion.ResultsIL-6 deficiency reduced infarct size at 3 h reperfusion (28.8 ± 4.5 % WT vs 17.6 ± 2.5 % IL-6−/−), which reduction persisted and remained similar at 24 h reperfusion (25.1 ± 3.0 % WT vs 14.6 ± 4.4 % IL-6−/−). Serum Amyloid A was reduced at 24 h reperfusion only (57.5 ± 4.9 WT vs 24.8 ± 5.6 ug/ml IL-6−/− mice). Cardiac cytokines (IL-6, IL-1β and TNFα) peaked at 3 h reperfusion, but IL-1β and TNFα levels were unaffected by IL-6 deficiency. Significant neutrophil influx was only detected at 24 h reperfusion and was similar for WT and IL-6−/−. Tissue factor peaked at 24 h reperfusion, whereas fibrin/fibrinogen peaked at 3 h reperfusion and was completely resolved at 24 h reperfusion; both coagulation factors were unaltered by IL-6 deficiency. Prolonged ST elevation was observed during ischemia that completely resolved for both genotypes at early reperfusion.ConclusionsThe data suggest that, in the absence of major surgical intervention, IL-6 contributes to the development of infarct size in the early phase of reperfusion; this contribution did not depend on neutrophil influx, IL-1β and TNFα, tissue factor and fibrin.

Loss of the LIM-only protein Fhl2 impairs inflammatory reaction and scar formation after cardiac ischemia leading to better hemodynamic performance

AimsThe pathogenesis of myocardial ischemia-reperfusion injury (MI/R) involves an inflammatory response. Since the four-and-a-half LIM domain-containing protein 2 (Fhl2) has been observed to modulate immune cell migration, we aimed to study the consequences of Fhl2−/− under MI/R with respect to immune reaction, scar formation, and hemodynamic performance. Material and methodsIn a closed chest model of 1h MI/R, immune cell invasion of phagocytic monocytes was characterized by flow cytometry and immunohistochemistry. In addition, infarct size was assessed by triphenyltetrazolium chloride/Masson trichrome staining 24h/21days after reperfusion and a set of hemodynamic parameters was recorded by catheterisation in Fhl2−/− mice and controls. Key findingsWhile flow cytometry did not reveal differences in myocardial CD45high immune cell infiltrate, histological analysis showed that infiltrating immune cells in Fhl2−/− animals were preferentially located in the perivascular area, whereas in wild type, immune cells were well dispersed within the area at risk. After 24h and 21days of reperfusion, infarct size was significantly reduced in Fhl2−/− compared to WT animals. In addition, hemodynamic performance was better in Fhl2−/− mice, compared to WT mice up to day 21 of reperfusion.The loss of Fhl2 leads to an altered immune response to myocardial ischemia, which results in smaller infarcts and better hemodynamic performance up to 21days after myocardial ischemia reperfusion. SignificanceImmune cell invasion plays a pivotal role in the context of MI/R. Fhl2 significantly influences immune cell function and immune cell interaction with injured cardiac tissue leading to altered scar composition.

Metallothioneins 1 and 2 Modulate Inflammation and Support Remodeling in Ischemic Cardiomyopathy in Mice.

Aims. Repetitive brief ischemia and reperfusion (I/R) is associated with left ventricular dysfunction during development of ischemic cardiomyopathy. We investigated the role of zinc-donor proteins metallothionein MT1 and MT2 in a closed-chest murine model of I/R. Methods. Daily 15-minute LAD-occlusion was performed for 1, 3, and 7 days in SV129 (WT)- and MT1/2 knockout (MT−/−)-mice (n = 8–10/group). Hearts were examined with M-mode echocardiography and processed for histological and mRNA studies. Results. Expression of MT1/2 mRNA was transiently induced during repetitive I/R in WT-mice, accompanied by a transient inflammation, leading to interstitial fibrosis with left ventricular dysfunction without infarction. In contrast, MT−/−-hearts presented with enhanced apoptosis and small infarctions leading to impaired global and regional pump function. Molecular analysis revealed maladaptation of myosin heavy chain isoforms and antioxidative enzymes in MT1/2−/−-hearts. Despite their postponed chemokine induction we found a higher total neutrophil density and macrophage infiltration in small infarctions in MT−/−-hearts. Subsequently, higher expression of osteopontin 1 and tenascin C was associated with increased myofibroblast density resulting in predominately nonreversible fibrosis and adverse remodeling in MT1/2−/−-hearts. Conclusion. Cardioprotective effects of MT1/2 seem to be exerted via modulation of contractile elements, antioxidative enzymes, inflammatory response, and myocardial remodeling.

Hyperpolarized Metabolic MR Imaging of Acute Myocardial Changes and Recovery after Ischemia-Reperfusion in a Small-Animal Model.

To implement hyperpolarized magnetic resonance (MR) imaging in an animal model of ischemia-reperfusion and to assess in vivo the regional changes in pyruvate metabolism within the 1st hour and at 1 week after a brief episode of coronary occlusion and reperfusion. All animal experiments were performed with adherence to the Swiss Animal Protection law and were approved by the regional veterinary office. A closed-chest rat model was implemented by using an inflatable balloon secured around the left coronary artery. Animals were placed in an MR system 5-7 days after surgery. [1-(13)C]pyruvate was polarized by using a home-built multisample hyperpolarizer. Hyperpolarized pyruvate was injected at five stages: at baseline; at reperfusion after 15 minutes of coronary occlusion; and at 30 minutes, 60 minutes, and 1 week after ischemia reperfusion. The conversion of pyruvate into lactate and bicarbonate was imaged by using dedicated MR sequences alongside wall motion and delayed enhancement imaging. After imaging, the heart was removed and stained to delineate the area at risk (AAR). Differences between AAR and remote myocardium were assessed by using a repeated measures analysis of variance and a post hoc Bonferroni multiple comparison test. Data were collected in 12 animals. Occlusion led to hypokinesia of the anterior or anterolateral segments of the myocardium. At reperfusion, the average lactate-to-bicarbonate ratio increased in the AAR relative to that at baseline (from 1.93 ± 0.48 to 3.01 ± 0.74, P < .001) and was significantly higher when compared with that in the remote area (1.91 ± 0.38, P < .001). In the 60 minutes after occlusion, the lactate-to-bicarbonate ratio in the AAR recovered but was still elevated relative to that in the remote area. One week after ischemia-reperfusion, no difference between AAR and remote area could be detected. Hyperpolarized metabolic MR imaging can be used to successfully detect acute changes in [1-(13)C]pyruvate metabolism after ischemia-reperfusion, thereby enabling in vivo monitoring of the metabolic effects of reperfusion strategies.

Immunomodulation by splenectomy or by FTY720 protects the heart against ischemia reperfusion injury.

The pathogenesis of myocardial ischemia-reperfusion injury (MI/R) involves an inflammatory response in the myocardium undergoing reperfusion. Modulation of this response by splenectomy constitutes an option to protect the heart from MI/R. To mimic the effect of splenectomy in a pharmacological approach, the sphingosine-1-phosphate agonist FTY720 was applied at the onset of reperfusion. In a closed chest model of MI/R, infarct size was assessed by triphenyltetrazolium chloride staining after 1h of ischemia and 24h of reperfusion, and by Masson trichrome staining 21days after reperfusion in splenectomised mice, mice post-conditioned with FTY720 IP (1mg/kg), and controls. In addition, hemodynamic parameters were recorded after 24h and 21days by catheterization. Infarct size, and immune cell invasion of phagocytic monocytes investigated by FACS after 24h of reperfusion were significantly reduced by both splenectomy, and FTY720 treatment. Evaluation after 21days of reperfusion revealed that FTY720 treated animals had an improved hemodynamic outcome compared to placebo treated as well as splenectomised animals. FTY720 treatment reduced cell injury as effectively as splenectomy by lowering the number of phagocytic monocytes invading the myocardium and ameliorated hemodynamic outcome within the first 21days.

Influence of acute glycaemic level on measures of myocardial infarction in non-diabetic pigs

>Objective. Patients with diabetes are at increased risk of experiencing myocardial infarction. The influence of the prevailing plasma glucose level on infarction and mortality after acute ischaemia is however unknown. The aim was to study the effect of the acute plasma glucose level on the myocardial infarction size in a closed-chest pig model. Design. 38 non-diabetic pigs were randomised to hypoglycaemic (1.8–2.2 mmol/l; n = 15), normoglycaemic (5–7 mmol/l; n = 12) or hyperglycaemic glucose clamping (22–23 mmol/l; n = 11). After 30 min within glucose target myocardial infarction was induced for 30 min followed by reperfusion for 120 min. Hereafter the heart was double-stained to delineate infarction from viable tissue within the area at risk. Results. Mean infarction size was 201 ± 35 mm2 (mean ± SEM) in the hypoglycaemic group, 154 ± 40 mm2 in the normoglycaemic group and 134 ± 40 mm2 in the hyperglycaemic group, with no differences in infarction size, infarct/area at risk ratio or troponin T levels between the groups. There was no difference in incidence of ventricular fibrillation or mortality between the groups. Conclusion. No statistically significant associations were observed between the acute glycaemic level and measures of myocardial infarction, rates of ventricular fibrillation and subsequent premature death in the setting of acute ischaemia and reperfusion.

Continuous monitoring of cardiac function by 3-dimensional accelerometers in a closed-chest pig model.

Cardiac wall motions reflect systolic and diastolic function. We have previously demonstrated the ability of a miniaturized three-axis (3D) accelerometer to monitor left ventricular function in experimental models and in patients. The main aim of this study was to investigate the clinical utility of the method for monitoring the left and right ventricular function during changes in global and regional cardiac function in a postoperative closed-chest situation. In 13 closed-chest pigs, miniaturized 3D accelerometers were placed on the left ventricle in the apical and basal regions and in the basal region of the right ventricle. An epicardial 3D motion vector was calculated from the acceleration signals in each heart region. Peak systolic velocity along this 3D vector (3D V(sys)) was compared with the positive time derivative of the left and right ventricular pressure and with cardiac index during changes in global LV function (unloading, fluid loading, esmolol, dobutamine) and with ultrasound during regional left ventricular dysfunction (3-min occlusion of the left anterior descending coronary artery). Significant and typical changes in accelerometer 3D V(sys) were seen in all heart regions during changes in global cardiac function. 3D V(sys) reflected the left and right ventricular contractility via significant correlations with the positive time derivative of the left and right ventricular pressure, r = 0.86 and r = 0.72, and with cardiac index r = 0.82 and r = 0.73 (all P < 0.001), respectively. The miniaturized accelerometers also detected regional dysfunction, but showed reduced ability to localize ischaemia as the 3D V(sys) in all heart regions showed similar reductions during coronary artery occlusion. Miniaturized 3D accelerometers placed on the heart can assess global and regional function in a closed-chest model. The technique may be used for continuous postoperative monitoring after cardiac surgery.