Left ventricular wall motion analysis using real-time three-dimensional ultrasound.

This study tested the ability of real-time 3-D (RT 3-D) echocardiography to detect and delineate regions of abnormal contraction (akinesia or dyskinesia) in a canine model of regional myocardial injury and to develop methods to simplify injury assessments. Closed chest RT 3-D scans were obtained and regional left ventricular (LV) contractile function was assessed in nine animals at baseline and after myocardial cryoinjury with a 1-cm cryoprobe. Evaluation of contractile function was based on radial shortening of LV chamber cross-sections at multiple levels. Radial length changes were analyzed using color-coded circumferential maps of the LV. Seven sets of motion maps demonstrated new areas of poorly contracting myocardium in the cryoinjured region relative to baseline. Two sets of data were excluded due to insufficient LV visualization. Motion maps derived from RT 3-D echo have the ability to detect and localize regions of abnormal LV wall motion.

Results of cellular therapy for ischemic myocardial dysfunction. A review.

BACKGROUND: Ischemic heart disease (IHD) terminally injures the heart with attendant myocardial dysfunction. Effective therapy for IHD is limited when the myocardium cannot be revascularized. Thus, alternative therapies for IHD are emerging, including immature cell transplantation to injured hearts. One experience with this technique and its effect upon indices of myocardial performance are reviewed. METHODS: Micromanometry and sonomicrometry determined in vivo left ventricular pressure (P) and segment length (SL) following irreversible myocardial injury and 3 weeks after cell transplantation with either autologous skeletal myoblasts or autologous dermal fibroblasts. Systolic performance was based on the linear regression of stroke work and end-diastolic (ED) SL. Diastolic properties were assessed using the curvilinear relationships between LVEDP and strain (e). Cellular engraftment was assessed histologically at study conclusion. RESULTS: Skeletal myoblasts formed dense, engrafted tissue within injured hearts but did not extend beyond the borders of the injury. Engrafted fibroblasts were more uniformly distributed throughout the injured region. Diastolic performance improved following cell transplantation with either myoblasts or fibroblasts. Cell transplantation with skeletal myoblasts also improved contractile performance, but fibroblast transfer was associated with a significant decrement in systolic performance. CONCLUSIONS: Cellular transplantation with either myoblasts or fibroblasts can successfully and reliably regenerate viable tissue within areas of terminally injured heart. Cellular engraftment favorably alters the regional geometry within the injured heart, conferring improved functional indices upon treated animals. Further investigation is needed to ensure the safety of these techniques, to ascertain the optimal cell type and delivery method for transplantation, and to improve the reproducibility of cellular engraftment.

Comparison of benefits on myocardial performance of cellular cardiomyoplasty with skeletal myoblasts and fibroblasts.

Cellular cardiomyoplasty (CCM), or introduction of immature cells into terminally injured heart, can mediate repair of chronically injured myocardium. Several different cell types, ranging from embryonic stem cells to autologous skeletal myoblasts, have been successfully propagated within damaged heart and shown to improve myocardial performance. However, it is unclear if the functional advantages associated with CCM depend upon the use of myogenic cells or if similar results can be seen with other cell types. Thus, we compared indices of regional contractile (systolic) and diastolic myocardial performance following transplantation of either autologous skeletal myoblasts (Mb) or dermal fibroblasts (Fb) into chronically injured rabbit heart. In vivo left ventricular (LV) pressure (P) and regional segment length (SL) were determined in 15 rabbits by micromanometry and sonomicrometry 1 week following LV cryoinjury (CRYO) and again 3 weeks after autologous skeletal Mb or dermal Fb transplantation. Quantification of systolic performance was based on the linear regression of regional stroke work and end-diastolic (ED) SL. Regional diastolic properties were assessed using the curvilinear relationships between LVEDP and strain (epsilon) as well as LVEDP and EDSL. At study termination, cellular engraftment was characterized histologically in a blinded fashion. Indices of diastolic performance were improved following CCM with either Mb or Fb. However, only Mb transplantation improved systolic performance; Fb transfer actually resulted in a significant decline in systolic performance. These data suggest that both contractile and noncontractile cells can improve regional material properties or structural integrity of terminally injured heart, as reflected by improvements in diastolic performance. However, only Mb improved systolic performance in the damaged region, supporting the role of myogenic cells in augmenting contraction. Further studies are needed to define the mechanism by which these effects occur and to evaluate the long-term safety and efficacy of CCM with any cell type.

Early effects of right ventricular volume overload on ventricular performance and beta-adrenergic signaling.

OBJECTIVE: Right ventricular dysfunction is a poorly understood but persistent clinical problem. This study was undertaken to evaluate ventricular performance and beta-adrenergic receptor signaling in a tricuspid regurgitation model of right ventricular overload. METHODS: Seventeen dogs were chronically instrumented with epicardial dimension transducers. By means of the shell-subtraction model, right ventricular pressure-volume relationships were evaluated in normal and right ventricular overload states. Right ventricular chamber performance was quantified by the stroke work at an end-diastolic volume relationship. RESULTS: Right ventricular volume overload caused a 28% +/- 11% and 31% +/- 9% decline in chamber performance acutely and at 1 week, respectively, whereas end-diastolic volume increased from 45 +/- 21 to 60 +/- 30 mL (P =. 019). beta-Adrenergic receptor signaling in myocardial samples was assessed, examining adenylyl cyclase and G-protein-coupled receptor kinase activity. Stimulated adenylyl cyclase activity significantly decreased, and G-protein-coupled receptor kinase activity significantly increased in both left and right ventricular samples caused by increased levels of beta-adrenergic receptor kinase 1. No change in beta-adrenergic receptor density was seen at 1 week. CONCLUSIONS: Early right ventricular overload is associated with impaired right ventricular chamber contractility, dilation, and, importantly, a biventricular alteration of beta-adrenergic receptor signaling.

Calcitonin gene-related peptide enhances the recovery of contractile function in stunned myocardium.

INTRODUCTION: Calcitonin gene-related peptide, a potent vasodilating inotropic agent, increases coronary artery perfusion when administered exogenously and reduces ischemic injury in nonmyocardial tissue. However, it is unclear whether this agent improves recovery of myocardial performance after reversible myocardial ischemia. METHODS: Nine dogs underwent complete occlusion of the left anterior descending coronary artery for 15 minutes and were monitored during 24 hours of reperfusion. Calcitonin gene-related peptide (0.07 microgram. kg(-1). min(-1)), nitroglycerin (65 microgram. kg(-1). min(-1)), or saline solution placebo was infused intravenously during initial reperfusion. Ischemia/reperfusion was repeated in concurrent 24-hour periods until all animals received infusions in random order. Micromanometry and sonomicrometry determined left ventricular pressure and myocardial segment length. Myocardial performance, based on the linear relationship between stroke work and end-diastolic segment length, was estimated with the preload recruitable work area. Results were analyzed as percent control and compared statistically with the use of repeated measures analysis of variance. RESULTS: Recovery of myocardial performance was augmented during reperfusion with calcitonin gene-related peptide infusion relative to placebo

Myogenic cell transplantation improves in vivo regional performance in infarcted rabbit myocardium.

BACKGROUND: Although cardiac transplantation is an ideal treatment for end-stage heart disease, inadequate donor availability has stimulated efforts to manage terminally injured myocardium by other innovative methods. Autologous skeletal myoblast transplantation, or cellular cardiomyoplasty, is one method to potentially mediate myocardial repair within chronically injured hearts. However, few investigators have documented the ability of myogenic cells to alter load-insensitive indices of systolic and diastolic performance in vivo. In this study, both systolic and diastolic regional myocardial function were evaluated following left ventricular cryoinjury and compared with function after myogenic cell transplantation. METHODS: Left ventricular pressure and segment length were determined in 9 rabbits by micromanometry and sonomicrometry 1 week following cryoinjury and 3 weeks after myoblast transplantation. At study termination, the extent of myoblast engraftment was determined by histologic analysis. Systolic performance was based on the linear regression of stroke work and end-diastolic segment length. Diastolic properties were evaluated by the curvilinear relationships between left ventricular pressure and strain, and left ventricular pressure and end-diastolic segment length. RESULTS: Although mean indices of systolic performance were unchanged after cell transplantation, systolic performance improved in 3 animals. In contrast, myoblast engraftment was associated with significantly improved diastolic properties (strain and dynamic stiffness) in all animals. CONCLUSIONS: These data quantify temporal changes in regional myocardial performance and suggest that cellular cardiomyoplasty improves diastolic compliance prior to affecting systolic performance. Cellular cardiomyoplasty, a potential therapeutic option for ischemic heart disease, appears to reverse diastolic creep and thus may represent a clinical alternative to transplantation in the near future.

Means for load variation during echocardiographic assessment of the Frank-Starling relationship.

Because minimally invasive methods of preload variation are not validated for load-insensitive indexes of cardiac performance, intravenous nitroglycerin (NTG), phenylephrine, and saline solution (VOL) boluses were used in blocked and intact autonomic states to alter load and were compared with vena caval occlusion in the assessment of preload recruitable stroke work relationships between stroke work and left ventricular end-diastolic volume in dogs. In both autonomic states NTG and VOL produced comparable linear relationships. NTG and saline solution were combined with noninvasive measurements of left ventricular pressure and volume to construct echocardiographic relationships between stroke work and left ventricular end-diastolic cross-sectional area; NTG produced linear relationships similar to vena caval occlusion. Therefore NTG and VOL reliably alter load in constructing preload recruitable stroke work relationships, and NTG may be used with noninvasive measurements to provide load-insensitive estimates of cardiac function in a minimally invasive manner.

Cellular cardiomyoplasty improves diastolic properties of injured heart.

BACKGROUND: Acute myocardial infarction leads to loss of functional myocytes and structural integrity that often decreases diastolic compliance and increases resting myocardial segment length (diastolic creep). Successfully engrafting autologous skeletal myoblasts could improve compliance and potentially reverse creep. Thus, we transplanted myoblasts into cryoinjured rabbit heart (n = 15, CRYO) and measured regional diastolic properties in the presence (n = 9, +ENG) or absence (n = 6, -ENG) of engraftment. MATERIALS AND METHODS: Left ventricular (LV) pressures (P) and myocardial segment lengths (SL) were measured in vivo by micromanometry and sonomicrometry after cryoinjury (CRYO) and again 3 weeks following transplantation of myoblasts. Performance was estimated from the relationships between end-diastolic (ED) P and strain (epsilon) or between EDP and EDSL. Compliance was characterized by strain (epsilon(8)) and dynamic stiffness (dP/dL(8)) at 8 mm Hg. Creep was characterized by resting myocardial segment length (EDSL(0)) and static stiffness at 8 mm Hg (m(stat8)). RESULTS: Successful myoblast engraftment was determined via histologic examination. In nine +ENG animals, diastolic properties improved. Regional strain (epsilon(8)) increased (0.06 +/- 0.02 CRYO vs 0.10 +/- 0.04 +ENG; P = 0.0009) while dynamic stiffness (dP/dL(8)) decreased (43 +/- 23 mm Hg/mm CRYO vs 23 +/- 14 mm Hg/mm +ENG; P = 0.009). Static stiffness (m(stat8)) was unaffected (0.78 +/- 0.2 mm Hg/mm CRYO vs 0.72 +/- 0. 1 mm Hg/mm +ENG; P = 0.08), and creep did not occur (EDSL(0) = 10.3 +/- 2.8 CRYO vs 10.4 +/- 2.3 +ENG; P = 0.74). In the absence of myoblast engraftment (n = 6, -ENG), strain decreased (epsilon(8) = 0. 06 +/- 0.02 CRYO vs 0.05 +/- 0.02 -ENG; P = 0.048), but dynamic stiffness (dP/dL(8)) did not (36 +/- 19 mm Hg/mm CRYO vs 28 +/- 12 mm Hg/mm -ENG; P = 0.20). Furthermore, static stiffness decreased (0. 78 +/- 0.3 mm Hg/mm CRYO vs 0.65 +/- 0.2 mm Hg/mm -ENG; P = 0.05) and creep was obvious (EDSL(0) = 10.8 +/- 3.6 mm CRYO vs 13.0 +/- 4. 4 mm -ENG, P = 0.04). CONCLUSIONS: Myoblast engraftment may partially overcome the loss of myocytes and structural integrity that often follow chronic myocardial ischemia. Improved compliance and reversal of diastolic creep suggest regeneration of viable muscle within once infarcted myocardium.

Intracardiac transplantation of skeletal myoblasts yields two populations of striated cells in situ.

BACKGROUND: Adult heart lacks stem cells and cannot effectively regenerate. In contrast, skeletal muscle is constantly undergoing repair. We proposed to transplant immature skeletal myoblasts into injured myocardium. METHODS: Approximately 7x10(6) soleus skeletal myoblasts were expanded in vitro from adult New Zealand White rabbits (n = 23) whose posterior left ventricle was cryoinjured to create a transmural lesion. Autologous myoblasts (n = 18) or saline (n = 5) was transplanted into the central cryolesion at the time of injury (n = 6) or 1 week later (n = 12). Hearts were harvested 2 weeks after injection. RESULTS: Myoblast transfer did not incur further morbidity. After cryolesion, grossly, a 1.6-cm epicardial hemorrhagic lesion could be seen. Histologically, the transmural lesion contained inflammatory cells and active scarring but no viable cardiomyocytes. Electron microscopy demonstrated a predominance of collagen and fibroblasts. Nine hearts contained multinucleated cells within the cryolesion that covered approximately 75% of the central cryolesion in 17% of animals. Immunohistochemical analysis confirmed their skeletal muscle origin. At the periphery of the lesion, isolated clusters of nonskeletal muscle cells could be visualized (n = 12) that resembled immature cardiocytes. CONCLUSIONS: Autologous skeletal myoblasts can regenerate viable striated tissue within damaged myocardium. Myoblast transfer warrants further investigation as a new method for improving myocardial performance within infarcted myocardium.

A load-independent in vivo model for evaluating therapeutic interventions in injured myocardium.

Although cardiomyocyte damage is normally irreversible, gene therapy and somatic cell transfer offer potential for improving function in damaged regions of the heart. However, in ischemic models of injury, variability in depth, size, and location of damage compromises statistical evaluation of in vivo function. We have adapted cryoablation to create a reproducible, posterior, transmural lesion within rabbit myocardium in which small changes in function are measurable in vivo. Before and at 2 and 6 wk postinjury, in vivo left ventricular intracavitary pressure and myocardial segment length were measured. Regional indexes of performance, segmental stroke work (SW), and percent systolic shortening (SS) were significantly decreased (P < 0.001) postcryoinjury as was the slope (Mw) of the linear preload recruitable SW relationship between SW and end-diastolic segment length (P = 0.0001). Decreased SW, SS, and Mw correlated with wall thinning, loss of myocytes, presence of fibroblasts, and transmural scar formation. Reproducible changes in regional myocardial performance in vivo postcryoinjury suggest that this is a reasonable model for evaluating novel therapies for cardiovascular disease.

Regenerating functional myocardium: improved performance after skeletal myoblast transplantation.

The adult heart lacks reserve cardiocytes and cannot regenerate. Therefore, a large acute myocardial infarction often develops into congestive heart failure. To attempt to prevent this progression, we transplanted skeletal myoblasts into cryoinfarcted myocardium of the same rabbits (autologous transfer), monitored cardiac function in vivo for two to six weeks and examined serial sections of the hearts by light and electron microscopy. Islands of different sizes comprising elongated, striated cells that retained characteristics of both skeletal and cardiac cells were found in the cryoinfarct. In rabbits in which myoblasts were incorporated, myocardial performance was improved. The ability to regenerate functioning muscle after autologous myoblast transplantation could have a important effect on patients after acute myocardial infarction.

Ventricular and myocardial efficiencies during acute aortic regurgitation in conscious dogs.

BACKGROUND: Alterations in cardiac efficiency may signal pathologic stresses and energetic adaptation during aortic regurgitation (AR). METHODS AND RESULTS: LV systolic function, left coronary blood flow, and AVO2 difference were measured in conscious dogs to assess LV and contractile efficiencies at baseline, 1 day (n=10), 1 week (n=10), and 3 weeks (n=8) of AR. LV systolic function was assessed by the preload recruitable stroke work relationship. Total LV Efficiency (TEFF=SWxHeart Rate/MVO2) and contractile efficiency (CEFF=1/the slope of the MVO2 -pressure-volume area relationship) and steady-state potential energy (PVA-SWxHR), mechanical coupling efficiency (MCE=SWxHR/PVA) were calculated. LV systolic function decreased by 17% at 1 day (P<.05) and by 24% at 3 weeks (P<.05). CEFF decreased from 58+/-8% to 38+/-10% (P<.05) at 1 day, normalized at 1 week, and decreased to 28+/-14% at 3 weeks (P<.05). TEFF was not altered at 1 day and 1 week but decreased by 3 weeks (P<.05). MCE trended downward from baseline of 47+/-5%, reaching significance at 3 weeks (34+/-6%, P<.05). CONCLUSIONS: CEFF decreases acutely, indicating diminished economy of myocardial contraction. CEFF normalizes at 1 week, suggesting adequate compensation. TEFF is not altered in early AR. By 3 weeks, LV systolic dysfunction is accompanied by depressed TEFF, mechanical coupling, and CEFF signaling the onset of decompensated AR. Thus, volume overload of acute AR resulted in early compensation at the expense of myocardial efficiency with subsequent global dysfunction characterized by depressed LV systolic mechanics, mechanical, coupling, and contractile efficiencies.

Results of valve replacement with mechanical and biological prostheses in chronic renal dialysis patients.

BACKGROUND: Whether biological or mechanical valves should be used in patients on chronic dialysis therapy remains to be clearly defined. METHODS: A retrospective review was performed on 19 consecutive patients from our institution with end-stage renal disease on chronic peritoneal or hemodialysis undergoing aortic (n = 12), mitral (n = 5), or aortic-mitral (n = 2) valve replacement. RESULTS: The 9 biological and 10 mechanical valve patients had similar ages (56.5 versus 56.6 years) and cardiovascular risk factors. The overall estimated Kaplan-Meier survival was 60% +/- 12% at 12 months and 42% +/- 14% at 60 months. Mechanical valve patients had a significantly higher rate of postoperative cerebrovascular accidents or bleeding complications (10/10 versus 0/9; chi 2 = 17.0; p < 0.001). No subsequent reoperations were required for biological valve failure at a mean follow-up of 32 +/- 53 months. CONCLUSIONS: These results demonstrate that in patients with end-stage renal disease, use of mechanical valves is associated with significant risk of complications, whereas biological valve failure from prosthetic dysfunction is unusual. Overall survival is poor in both groups of patients. Therefore, preference should be given to biological valve instead of mechanical valve prostheses in patients on chronic renal dialysis.

The in vivo quantification of myocardial performance in rabbits: a model for evaluation of cardiac gene therapy.

Evaluating cardiac gene therapy in the intact animal requires an index of cardiac function capable of detecting regional differences in contractility in a load-independent fashion. Potentially load-insensitive measures of ventricular performance were therefore evaluated in 10 open- and closed-chested, anesthetized rabbits. LV transmural pressure and myocardial segment length were measured using micromanometry and sonomicrometry during steady-state and transient inferior vena caval occlusion, over a range of inotropic and loading conditions. For each intervention, segmental stroke work was calculated as the area within the left ventricular transmural pressure-length loops at a given end-diastolic segment length during inferior vena caval occlusion; regression analysis was applied to obtain the linear Frank-Starling relationship. In both open- and closed-chested states, these relationships were highly linear (r = 0.97 +/- 0.1) and reproducible. The slope of the linear relationship between segmental stroke work and end-diastolic segment length increased significantly with calcium and epinephrine infusions (P < 0.05 v control) but was not significantly altered by decreased afterload or increased afterload (P > 0.4). The x-intercept was not significantly altered by changes in intropy or afterload (P > 0.4). These data validate the linear Frank-Starling relationship and the slope, MW, as a load-insensitive index of contractility in the intact rabbit. This study presents a novel approach to the quantification of regional cardiac function in smaller animals.