Sheep Heart Research Articles

Isolation, Characterization, and Spatial Distribution of Cardiac Progenitor Cells in the Sheep Heart

Laboratory large animal models are important for establishing the efficacy of stem cell therapies that may be translated into clinical use. The similarity of ovine and human cardiovascular systems provides an opportunity to use the sheep as a large animal model in which to optimize cell-based treatments for the heart. Recent clinical trials in humans using endogenous cardiovascular progenitor cells report significant improvement in cardiac function following stem cell-based therapy. To date, however, endogenous cardiovascular progenitor cells have not been isolated from the sheep heart. Cardiovascular cells expressing SSEA-4, CD105 and c-kit were isolated by flow cytometry and cloned from the right atrium of neonatal sheep. The expression of GATA-4, c-kit, and Isl1 was identified by PCR in the cloned cells. Immunohistochemical staining was used to compare the number of SSEA-4 positive cells in the right auricle, right atrium, left ventricle and the apex of the heart of fetal, neonatal and adult sheep. The number of SSEA4+cells was also compared in fetal, pregnant and non-pregnant adult sheep. Four distinct cardiac progenitor cell sub-populations were identified in sheep, including CD105+SSEA-4+c-kit+Isl1+GATA-4+cells, CD105+SSEA-4+c-kit+Isl1+GATA-4-cells, CD105+SSEA-4-c-kit-Isl1+GATA-4-cells, and CD105+SSEA-4-c-kit+Isl1+GATA-4-cells. Immunohistochemical staining for SSEA-4 showed that labeled cells were most abundant in the right atrium of fetal hearts where niches of progenitor cells could be identified. We determined the phenotype and distribution of cardiac progenitor cells in the sheep heart. The availability of cloned endogenous cardiac progenitor cells from sheep will provide a valuable resource for optimizing the conditions for cardiac repair in the ovine model.

The Effect of a Sheep Heart on the Cognitive and Affective Area of the Elementary Students, Case Study: Canakkale, Science Camp

Learning referred to the changing and expansion of the schemes in the mind of the child through the addition of new knowledge. This determination is based on the cognitive area. The learning also happens in the affective area. The aim of this research is to study the effects of the usage of advanced organizer and haptic learning applications on the cognitive and affective learning area of the 5th grade students in Canakkale, Turkey. The activity has been applied on a sheep heart in a science camp. The data is collected within the mixed methodology, and evaluated within a case study. At the completion of the study, students were observed to acquire knowledge successfully and they had found the activity interesting and entertaining. As a result, it was concluded that the advanced organizer and haptic learning are effective on cognitive and affective learning area

Impaired Cross Bridge Formation Contributes to Reduced Cardiac Contraction in the Infarct Border Zone

After myocardial infarction, adjacent to the infarct there is a poorly contracting non-ischemic border zone. The mechanism of border zone dysfunction is unclear. We found that border zone dysfunction does not involve myocardial fibrosis, or a decreased content of either myofibrils or myosin, suggesting there is a defect in the contractile mechanism. Goal: Determine the mechanism for border zone dysfunction. Methods: We used sheep hearts 2 weeks after apical infarction. Cardiac muscle strips were dissected from the border zone adjacent to the infarct and from a zone remote from the infarct. Myofilament contraction was assessed using in-vitro isometric and isotonic contractions of demembranated cardiac muscle strips bathed in activating solutions. To assess strongly bound cross-bridge formation, we measured muscle stiffness using high frequency, low amplitude oscillations of muscle length in the absence of ATP (in this rigor state, cross bridge formation should be maximal). Results: In border zone myocardium, maximal force development (Fmax) was reduced by 31±2% (n=6, P<0.01) compared to Fmax of remote zone myocardium (85±1 mN/mm2). The stiffness in the rigor state was reduced by 34±6% (n=5, P<0.05) in border zone myocardium versus remote zone myocardium, suggesting impaired cross bridge formation in the border zone. There was no difference between border zone and remote zone myocardium in the maximum velocity of muscle shortening (∼0.35 muscle lengths/s), or in the rate constant of force redevelopment (Ktr, ∼2.5 s−1) after briefly mechanically disrupting cross bridges with a rapid perturbation of muscle length. Conclusions: Impaired contraction of border zone myocardium involves a reduction in cross bridge formation, without effects on cross bridge kinetics. Preliminary studies suggest proteolytic cleavage of contractile proteins may play a role.

Image-Based Model of Atrial Anatomy and Electrical Activation: A Computational Platform for Investigating Atrial Arrhythmia

Computer models provide a powerful platform for investigating mechanisms that underlie atrial rhythm disturbances. We have used novel techniques to build a structurally-detailed, image-based model of 3-D atrial anatomy. A volume image of the atria from a normal sheep heart was acquired using serial surface macroscopy, then smoothed and down-sampled to 50 μm(3) resolution. Atrial surface geometry was identified and myofiber orientations were estimated throughout by eigen-analysis of the 3-D image structure tensor. Sinus node, crista terminalis, pectinate muscle, Bachman's bundle, and pulmonary veins were segmented on the basis of anatomic characteristics. Heterogeneous electrical properties were assigned to this structure and electrical activation was simulated on it at 100 μm(3) resolution, using both biophysically-detailed and reduced-order cell activation models with spatially-varying membrane kinetics. We confirmed that the model reproduced key features of the normal spread of atrial activation. Furthermore, we demonstrate that vulnerability to rhythm disturbance caused by structural heterogeneity in the posterior left atrium is exacerbated by spatial variation of repolarization kinetics across this region. These results provide insight into mechanisms that may sustain paroxysmal atrial fibrillation. We conclude that image-based computer models that incorporate realistic descriptions of atrial myofiber architecture and electrophysiologic properties have the potential to analyse and identify complex substrates for atrial fibrillation.

Effects of Ranolazine on Paroxysmal and Persistent Atrial Fibrillation in Isolated Sheep Hearts

Background Ranolazine inhibits the peak Na+ current in the atria and has been shown to suppress paroxysmal atrial fibrillation (PxAF). However, the underlying mechanisms are not clear, and its antiarrhythmic efficacy in persistent AF (PsAF) is unknown. Methods We investigated the effects of ranolazine in Langendorff-perfused sheep hearts. PxAF was induced by burst pacing during acute stretch (12 mm H2O; N = 5). PsAF was induced in chronically implanted animals (single-chamber pacemaker, right atrial lead) by intermittent pacing (20 Hz) maintained for 6 months (N = 3). Epicardial and endocardial optical mapping of the left atrial appendage (LAA) and the posterior left atrium (PLA), respectively, was performed simultaneously. Following a control period of 50 minutes of AF, 10 μM ranolazine was perfused for 20 minutes. If sinus rhythm (SR) was not restored, the concentration of ranolazine was increased to 20 μM. LAA samples were taken for Western blot (WB) analysis to determine the expression of Na+ channel protein (NaV1.5) in PxAF vs PsAF. Results In PxAF, the baseline dominant frequency (DF) in the PLA was 10.1 ± 1.6 Hz. Ranolazine at 10 μM decreased DF to 7.2 ± 0.9 Hz (P = .008, N = 5) and terminated AF in all hearts after 15 ± 4 minutes. Ranolazine also significantly decreased the number of singularity points (SP) in PxAF (51.9 ± 11.9/cm2 to 29.5 ± 4.6/cm2, per 5 seconds, P = .005). AF could be reinduced in 4 5 hearts, but was nonsustained (median duration = 28 seconds). In PsAF, baseline DF in the PLA was 10.9 ± 2.9 Hz. Ranolazine 10 μM decreased DF to 7.2 ± 1.1 Hz (P = .05, N = 3) but did not terminate AF. Increasing concentration to 20 μM decreased DF to 5.8 ± 1.1 Hz (P = .019) but without reversal to SR. Ranolazine did not decrease the SP in PsAF, even at 20 μM (17.3 ± 3.6/cm2 to 10.7 ± 3.6/cm2, per 5 seconds, P = NS). WB analysis of LAA showed a 59.4% decrease in NaV1.5 in PsAF (N = 3) compared with PxAF (N = 3, P Conclusions Ranolazine exerts an antiarrhythmic effect in PxAF by reducing both DF and SP. In contrast, ranolazine did not terminate PsAF despite reducing DF. This is partly due to the lack of effect of ranolazine in altering the number of SP (representing wavebreaks), thus allowing AF to sustain, and may be related to electrical and/or structural remodeling of the atria occurring in PsAF.

Restraint to the left ventricle alone is superior to standard restraint

In standard ventricular restraint therapy, a single level of restraint is applied to the entire ventricular surface. We showed previously that at high restraint levels, cardiac tamponade develops because of the thin-walled right ventricle, even while the left ventricle remains unaffected. We now hypothesize that applying restraint exclusively to the left ventricle permits higher levels of restraint, resulting in increased benefit to the left ventricle. The acute effect of restraint applied to the left ventricle alone was analyzed in healthy and cardiomyopathic sheep hearts. Restraint therapy was applied by fluid-filled epicardial balloons placed solely around the left ventricle. Restraint level was defined by the measured balloon luminal pressure at end diastole. At incrementally higher restraint levels (0, 3, 5, 8, 10, 12, and 14 mm Hg), transmural myocardial left ventricular pressure (P(tm) = Left ventricle pressure - Balloon pressure) and indices of myocardial oxygen consumption were measured in healthy sheep (n = 5) and in sheep with heart failure (n = 6). Increasing restraint from 0 to 14 mm Hg decreased transmural myocardial pressure by 48.8% (P ≤ .02) and the left ventricle tension-time index by 39.1% (P ≤ .01), and the pressure-volume area decreased by 58.4% (P ≤ .01). Similarly, stroke work decreased by 57.9% (P ≤ .03). Systemic hemodynamics were unchanged. There was no difference in the trend for all indices between animals that were healthy and those with heart failure. We showed previously that, with standard restraint, right ventricle tamponade develops at high restraint levels, limiting restraint therapy. We now show that restraint applied to the left ventricle alone permits increased restraint levels, without causing right ventricle or left ventricle tamponade, for greater therapeutic benefit. We conclude that partial left ventricle restraint may be more effective than standard restraint.

Ectopic and reentrant activation patterns in the posterior left atrium during stretch-related atrial fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in humans and is predicted to dramatically increase its prevalence in the future. There is experimental evidence that increasing stretch increases the dominance of the pulmonary veins (PVs) during AF in isolated hearts and ectopic activity in the isolated PVs, but the ionic mechanisms underlying such effects are not clear and the ability of the PVs to favorably host functional reentry during stretch cannot be excluded. We used a combination of endocardial–epicardial optical mapping with phase and spectral analysis to study stretch-related AF (SRAF) in normal isolated sheep hearts. We have found rapid AF sources in the posterior left atrium (PLA) and PV region and their activation frequency and level of organization correlated with intra-atrial pressure. Analysis of the surfaces' optical mapping data in the phase domain reveals that activation of the PLA consisted of alternating patterns of breakthroughs, reentries and relatively simple waves swiping across the mapped field. The patterns on the endocardial and epicardial PLA surface at any given moment of time of the SRAF could be either identical or not identical, and the activity in the thickness of the PLA wall is hypothesized to conform to either ectopic discharge or scroll waves, but a definite evidence for the presence of such mechanisms is currently lacking. Thus the understanding of the manner by which the mechano-electric feedback effects in the PLA, including the PVs, become important in the initiation and maintenance of AF requires further detailed investigation.

Energy Harvesting from the Beating Heart by a Mass Imbalance Oscillation Generator

Energy-harvesting devices attract wide interest as power supplies of today's medical implants. Their long lifetime will spare patients from repeated surgical interventions. They also offer the opportunity to further miniaturize existing implants such as pacemakers, defibrillators or recorders of bio signals. A mass imbalance oscillation generator, which consists of a clockwork from a commercially available automatic wrist watch, was used as energy harvesting device to convert the kinetic energy from the cardiac wall motion to electrical energy. An MRI-based motion analysis of the left ventricle revealed basal regions to be energetically most favorable for the rotating unbalance of our harvester. A mathematical model was developed as a tool for optimizing the device's configuration. The model was validated by an in vitro experiment where an arm robot accelerated the harvesting device by reproducing the cardiac motion. Furthermore, in an in vivo experiment, the device was affixed onto a sheep heart for 1h. The generated power in both experiments-in vitro (30μW) and in vivo (16.7μW)-is sufficient to power modern pacemakers.

Echocardiographic-Based Assessment of Myocardial Fiber Structure in Individual, Excised Hearts

The objective of this study was to assess the feasibility of using echocardiographic imaging as an approach for determining the myocardial fiber structure of intact, individual hearts. Seven formalin-fixed, ex vivo sheep hearts were imaged using a commercially available echocardiographic imaging system, and the intrinsic fiber structure for the reconstructed short-axis cross section was determined for a specific distance from the apex of each heart. Diffusion tensor magnetic resonance (DT-MR) images of each heart were acquired and fiber maps were created for comparison with the fiber structure obtained from the corresponding reconstructed echocardiographic images. These two methods of obtaining the fiber structure showed relatively good agreement, suggesting that measurements of fiber orientation for individual hearts can be derived from echocardiographic images. Further development of this method may provide a clinically useful approach for mapping the fiber orientation in individual patients over the heart cycle.

IGF-2R-Mediated Signaling Results in Hypertrophy of Cultured Cardiomyocytes from Fetal Sheep1

Activation of the insulin-like growth factor-1 receptor (IGF-1R) is known to play a role in cardiomyocyte hypertrophy. While IGF-2R is understood to be a clearance receptor for IGF-2, there is also evidence that it may play a role in the induction of pathological cardiomyocyte hypertrophy. It is not known whether IGF-2R activates cardiomyocyte hypertrophy during growth of the fetal heart. Fetal sheep hearts (125 ± 0.4 days gestation) were dissected, and the cardiomyocytes isolated from the left and right ventricles for culturing. Cultured cardiomyocytes were treated with either LONG R(3)IGF-1, an IGF-1R agonist; picropodophyllin, an IGF-1R autophosphorylation inhibitor; U0126, an inhibitor of extracellular signal-regulated protein kinase (ERK); Leu(27)IGF-2, an IGF-2R agonist; Gö6976, a protein kinase C inhibitor; KN-93, an inhibitor of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII); or KN-92, an L-type calcium channel inhibitor and negative control for KN-93. The cross-sectional area of cultured cardiomyocytes was determined relative to control cardiomyocytes treated with serum-free culture medium. IGF-1R and IGF-2R activation each resulted in ERK signaling, but IGF-2R activation alone induced CaMKII signaling, resulting in hypertrophy of cardiomyocytes in the late gestation sheep fetus. These data suggest that changes in the intrauterine environment that result in increased cardiac IGF-2R may also lead to cardiomyocyte hypertrophy in the fetus and potentially an increased risk of cardiovascular disease in adult life.

A genome resource to address mechanisms of developmental programming: determination of the fetal sheep heart transcriptome

The pregnant sheep has provided seminal insights into reproduction related to animal and human development (ovarian function, fertility, implantation, fetal growth, parturition and lactation). Fetal sheep physiology has been extensively studied since 1950, contributing significantly to the basis for our understanding of many aspects of fetal development and behaviour that remain in use in clinical practice today. Understanding mechanisms requires the combination of systems approaches uniquely available in fetal sheep with the power of genomic studies. Absence of the full range of sheep genomic resources has limited the full realization of the power of this model, impeding progress in emerging areas of pregnancy biology such as developmental programming. We have examined the expressed fetal sheep heart transcriptome using high-throughput sequencing technologies. In so doing we identified 36,737 novel transcripts and describe genes, gene variants and pathways relevant to fundamental developmental mechanisms. Genes with the highest expression levels and with novel exons in the fetal heart transcriptome are known to play central roles in muscle development. We show that high-throughput sequencing methods can generate extensive transcriptome information in the absence of an assembled and annotated genome for that species. The gene sequence data obtained provide a unique genomic resource for sheep specific genetic technology development and, combined with the polymorphism data, augment annotation and assembly of the sheep genome. In addition, identification and pathway analysis of novel fetal sheep heart transcriptome splice variants is a first step towards revealing mechanisms of genetic variation and gene environment interactions during fetal heart development.

Junctophilin 2 is reduced in the border zone 3 hours after a myocardial infarction in sheep heart

Eccentric contraction‐induced injury of skeletal muscle is associated with weakness stemming in large part from impaired voltage‐gated sarcoplasmic reticulum Ca2+ release that appears to be mediated by the loss of the triadic protein junctophilin (JP). After a myocardial infarction (MI), the myocytes in the region around the MI (i.e., border zone) appear to be lengthened while activated (i.e., eccentric contraction). If injured by eccentric contractions, these myocytes may contribute to abnormal contractile mechanics, myocardial remodeling and failure. The purpose of this study was to test the hypothesis that JP2 content is reduced in the border zone after an MI in sheep heart. Sheep left anterior descending and second diagonal coronary arteries were ligated for 1 hr followed by 2 hr of reperfusion. Immunoblotting was used to measure JP2 and tubulin content in left ventricular wall samples taken from the infarct (n=5), border zone (n=5), and control remote (n=5) regions. Three hours after inducing the MI, JP2/tubulin ratio is significantly (P&lt;0.05) reduced in infarct (0.28±0.46) and border zone (0.58±0.56) myocardium compared to control remote region (1.52±0.29) of the heart. MI results in the preferential loss of JP2 in the border zone within 3 hours of the MI and may contribute to weakness and abnormal strain in the left ventricular myocardium. .

Chloroquine Terminates Stretch-Induced Atrial Fibrillation More Effectively Than Flecainide in the Sheep Heart

Blockade of inward-rectifier K+ channels by chloroquine terminates reentry in cholinergic atrial fibrillation (AF). However, it is unknown whether inward-rectifier K+ channels and reentry are also important in maintaining stretch-induced AF (SAF). We surmised that reentry underlies SAF, and that abolishing reentry with chloroquine terminates SAF more effectively than traditional Na+-channel blockade by flecainide. Thirty Langendorff-perfused sheep hearts were exposed to acute and continuous atrial stretch, and mapped optically and electrically. AF dynamics were studied under control and during perfusion of either chloroquine (4 µmol/L, n=7) or flecainide (2-4 µmol/L, n=5). Chloroquine increased rotor core size and decreased reentry frequency from 10.6±0.7 Hz in control to 6.3±0.7 Hz (P<0.005) just before restoring sinus rhythm (7/7). Flecainide had lesser effects on core size and reentry frequency than chloroquine and did not restore sinus rhythm (0/5). Specific IKr blockade by E-4031 (n=7) did not terminate AF when frequency values were >8 Hz. During pacing (n=11), flecainide reversibly reduced conduction velocity (≈30% at cycle length 300, 250, and 200 ms; P<0.05) to a larger extent than chloroquine (11% to 19%; cycle length, 300, 250, and 200 ms; P<0.05). Significant action potential duration prolongation was demonstrable only for chloroquine at cycle length 300 (12%) and cycle length 250 ms (9%) (P<0.05). Chloroquine is more effective than flecainide in terminating SAF in isolated sheep hearts by significantly increasing core size and decreasing reentry frequency. Chloroquine's effectiveness may be explained by its inward-rectifier K+ channel blockade profile and suggest that reentry is important to maintain acute SAF.

Heterogeneous atrial wall thickness and stretch promote scroll waves anchoring during atrial fibrillation

Atrial dilatation and myocardial stretch are strongly associated with atrial fibrillation (AF). However, the mechanisms by which the three-dimensional (3D) atrial architecture and heterogeneous stretch contribute to AF perpetuation are incompletely understood. We compared AF dynamics during stretch-related AF (pressure: 12 cmH(2)O) in normal sheep hearts (n = 5) and in persistent AF (PtAF, n = 8)-remodelled hearts subjected to prolonged atrial tachypacing. We hypothesized that, in the presence of stretch, meandering 3D atrial scroll waves (ASWs) anchor in regions of large spatial gradients in wall thickness. We implemented a high-resolution optical mapping set-up that enabled simultaneous epicardial- and endoscopy-guided endocardial recordings of the intact atria in Langendorff-perfused normal and PtAF (AF duration: 21.3 ± 11.9 days) hearts. The numbers and lifespan of long-lasting ASWs (>3 rotations) were greater in PtAF than normal (lifespan 0.9 ± 0.5 vs. 0.4 ± 0.2 s/(3 s of AF), P< 0.05). Than normal hearts, focal breakthroughs interacted with ASWs at the posterior left atrium and left atrial appendage to maintain AF. In PtAF hearts, ASW filaments seemed to span the atrial wall from endocardium to epicardium. Numerical simulations using 3D atrial geometries (Courtemanche-Ramirez-Nattel human atrial model) predicted that, similar to experiments, filaments of meandering ASWs stabilized at locations with large gradients in myocardial thickness. Moreover, simulations predicted that ionic remodelling and heterogeneous distribution of stretch-activated channel conductances contributed to filament stabilization. The heterogeneous atrial wall thickness and atrial stretch, together with ionic and anatomic remodelling caused by AF, are the main factors allowing ASW and AF maintenance.

Preliminary feasibility and hemodynamic performance of a newly-developed self-expanding bioprosthesis and 16-F delivery system in transcatheter aortic valve implantation in sheep

We sought to evaluate the feasibility and hemodynamic performance of a new self-expanding bioprosthesis and 16-F delivery system in sheep. A 23-mm new self-expanding aortic bioprosthesis was implanted in sheep (n = 10) with a 16-F catheter via the right common carotid artery. Each sheep underwent angiography and coronary angiography before intervention, immediately and 1 h after stent implantation. Electrocardiographic monitoring was carried out during and 2 h after the procedure. Transthoracic echocardiography was employed to detect he-modynamic performance before intervention, immediately and 1 and 2 h after stent implantation. All sheep were euthanized 2 h after successful implantation for macroscopic inspection. In all cases, the new self-expanding aortic bioprosthesis was successfully delivered to the aortic root and released with a 16-F catheter. Successful implantation was achieved in 8 of 10 sheep. Hemodynamic performance and device position of successful implantation were stable 2 h after device deployment. Atrioventricular block was not observed. We conclude that it is feasible to implant the new self-expanding aortic valve with a 16-F delivery system into sheep hearts via the retrograde route.

Fiber architecture in remodeled myocardium revealed with a quantitative diffusion CMR tractography framework and histological validation.

BackgroundThe study of myofiber reorganization in the remote zone after myocardial infarction has been performed in 2D. Microstructural reorganization in remodeled hearts, however, can only be fully appreciated by considering myofibers as continuous 3D entities. The aim of this study was therefore to develop a technique for quantitative 3D diffusion CMR tractography of the heart, and to apply this method to quantify fiber architecture in the remote zone of remodeled hearts.MethodsDiffusion Tensor CMR of normal human, sheep, and rat hearts, as well as infarcted sheep hearts was performed ex vivo. Fiber tracts were generated with a fourth-order Runge-Kutta integration technique and classified statistically by the median, mean, maximum, or minimum helix angle (HA) along the tract. An index of tract coherence was derived from the relationship between these HA statistics. Histological validation was performed using phase-contrast microscopy.ResultsIn normal hearts, the subendocardial and subepicardial myofibers had a positive and negative HA, respectively, forming a symmetric distribution around the midmyocardium. However, in the remote zone of the infarcted hearts, a significant positive shift in HA was observed. The ratio between negative and positive HA variance was reduced from 0.96 ± 0.16 in normal hearts to 0.22 ± 0.08 in the remote zone of the remodeled hearts (p<0.05). This was confirmed histologically by the reduction of HA in the subepicardium from −52.03° ± 2.94° in normal hearts to −37.48° ± 4.05° in the remote zone of the remodeled hearts (p < 0.05).ConclusionsA significant reorganization of the 3D fiber continuum is observed in the remote zone of remodeled hearts. The positive (rightward) shift in HA in the remote zone is greatest in the subepicardium, but involves all layers of the myocardium. Tractography-based quantification, performed here for the first time in remodeled hearts, may provide a framework for assessing regional changes in the left ventricle following infarction.

Myofilament Dysfunction in the Infarct Border Zone

Introduction: Soon after myocardial infarction, a poorly contracting border zone forms adjacent to the infarct. Myocardium in the infarct border zone remains normally perfused with blood, and the cause of border zone dysfunction is unclear. Goal: Investigate the role of myofilament dysfunction in the impaired contraction of the infarct border zone. Methods: We studied sheep hearts, 2 or 8 weeks after infarction of the apex of the heart and non-operated controls. Myofilament contraction was assessed using in-vitro contractions of skinned cardiac muscle fibers. Muscle fiber bundles were dissected from the infarct border zone and from multiple regions ranging up to 6 cm from the infarct. Skinned fiber force development was referenced to several measures of the content of contractile material within the samples. Results: In the border zone immediately adjacent to the infarct, maximal force development (Fmax) was reduced by 38 ± 2% (n=7, P<0.001) compared with Fmax of myocardium remote from the infarct. Fmax for remote zone myocardium was similar to that for uninjured myocardium (∼90 mN/mm2). The width of the border zone was defined by a decreased Fmax that extended up to 5-6 cm away from the infarct. Fmax rose in a linear gradient between the infarct and the remote zone. There were no differences between border zone and remote zone in: histological staining for collagen; the area fraction of myocardium occupied by myofilbrils (or mitochondria); or in the abundance of myosin. Therefore, depressed border zone Fmax was not explained by decreased content of contractile material. Moreover, treatment of skinned fibers with protein phosphatase 1 did not affect border zone Fmax, suggesting that myofilament protein phosphorylation was not involved in border zone dysfunction. Conclusions: Myofilament dysfunction contributes to impaired contraction in the infarct border zone.

Abstract 8437: Volumetric Studies of the Right Ventricle Using Anatomically Accurate Expandable Latex Models

Background: Right ventricular (RV) anatomy is far more complex than left ventricular anatomy due to its challenging three-dimensional shape. Recently, TomTec imaging has developed new software known as 4D RV-Function. It is the first software for 3D echo data. This program allows one to study and envisage RV function and RV anatomy. Methods: Clay molds were made from the RVs of 5 sheep hearts. Each mold was layered with liquid latex to form a sac of the right ventricle. A hole was cut at the top of each latex RV model and a tube placed within it for attaching to the pulsatile pump. 4D images were acquired using a GE Vivid I9 ultrasound system. The obtained 4D images were then entered into TomTec's 4D RV Function imaging program to execute the volumes. Results: At all steady states, there was a good correlation between the volumes from TomTec's 4D RV Function analysis program and the actual volumes that were emptied out of the heart at systole and diastole (R=0.93, p&lt;0.001). Conclusions: Volumes of different right ventricle models could be defined quite accurately using TomTec's 4D RV Function program. This will prove useful in the future because it will not only increase diagnostic confidence, but it will ultimately improve the management and treatment of patients with congenital heart disease, heart failure, and pulmonary hypertension.

Influence of Mild Metabolic Acidosis on Cardiac Contractility and Isoprenaline Response in Isolated Ovine Myocardium

The postoperative course after major surgical procedures such as cardiothoracic operations is often accompanied by acute metabolic abnormalities due to large volume and temperature shifts. In general, those intervention-induced trauma might cause the use of catecholamines to stabilize hemodynamics. Within the cardiac community, there are still controversial discussions about standardized medical therapy to treat postoperative acidosis, for example, buffering versus nonbuffering for improving catecholaminergic response of myocardial contractility. The aim of this study was to investigate the influence of mild (and thus clinically relevant) acidosis on myocardial contractility and catecholamine response in explanted trabeculae of ovine hearts. Intact trabeculae (n = 24) were isolated from the right ventricle of healthy sheep hearts. Two different groups (group 1: pH = 7.40, n = 9 and group 2: pH = 7.20, n = 13) were investigated, and force amplitudes were measured at frequencies between 30 and 180 beats per minute and increasing catecholamine concentrations (isoprenaline 0-3 × 10(-6) mM). Force-frequency relation experiments in the presence of a physiological and/or mild acidotic pH solution showed no significant differences. Mean force amplitudes normalized to the lowest frequency showing no significant differences in force development between 0.5 and 3 Hz (n = 9 vs. 13, P = n.s.) (0.5 Hz absolute values 3.1 ± 2.6 for pH = 7.40 vs. 3.8 ± 2.6 mN/mm(2) for pH = 7.20, P = n.s.). Moreover, there was no significant difference in relaxation kinetics between the two groups. Furthermore, the experiments showed similar catecholamine responses in both groups. Force amplitudes normalized to baseline and maximum force showed no significant differences in force development between baseline and maximum isoprenaline concentrations (n = 6 vs. 9, P = n.s.) (baseline absolute values 4.3 ± 4.0 for pH = 7.40 vs. 3.9 ± 1.2 mN/mm(2) for pH = 7.20, P = n.s.). Additionally, relaxation kinetics did not show differences after catecholamine stimulation. The presented experiments revealed no significant negative inotropic effects on isometrically contracting ovine trabeculae with mild metabolic acidosis (pH = 7.2) compared with physiological pH (7.4). Additionally, similar catecholamine responses were seen in both groups. Further investigations (e.g., in vivo and/or in failing hearts with reduced compensatory reserves) will be necessary to examine optimal medical treatment for metabolic abnormalities after cardiac surgery.

Three-Year Follow-up of Sirolimus-Eluting Stents vs. Bare Metal Stents for Acute Myocardial Infarction

The long-term safety and efficacy of drug-eluting stents for patients with acute myocardial infarction (AMI) remain controversial. A total of 143 consecutive patients who presented between August 2004 and July 2006 with AMI and who underwent primary percutaneous coronary intervention (PCI) using sirolimus-eluting stents (SES), were compared with a historical control cohort of 129 consecutive patients who presented between August 2002 and July 2004 and who underwent primary PCI using bare metal stents (BMS). The rate of major adverse cardiovascular events at 3 years was significantly lower in the SES group than in the BMS group (20.3% vs. 33.1%, respectively; P=0.01). This reduction was mainly driven by a decrease in the rate of target vessel revascularization (12.3% vs. 22.4%, respectively; P=0.02). There was no significant difference in the rate of cardiovascular death (4.5% vs. 5.7%, respectively; P=0.67), non-fatal myocardial infarction (4.5% vs. 9.2%, respectively; P=0.16), coronary artery bypass grafting (2.3% vs. 2.5%, respectively; P=0.93), stroke (2.4% vs. 0.8%, respectively; P=0.35), and stent thrombosis (2.9% vs. 2.3%, respectively; P=0.80) between the 2 groups. SES can be used safely and effectively in patients with AMI.