Background— Patients with diastolic heart failure (DHF) have significant abnormalities in left ventricular (LV) diastolic function, including slow and delayed relaxation and increased chamber stiffness. Whether and to what extent these abnormalities in diastolic function occur in association with abnormalities in LV systolic performance, function, and contractility has not been investigated thoroughly. Methods and Results— The systolic properties of the LV were examined in 75 patients with heart failure and a normal ejection fraction (ie, DHF) and 75 normal control subjects with no evidence of cardiovascular disease. LV systolic properties were assessed with echocardiographic and cardiac catheterization data. Stroke work (an index of LV systolic performance), preload recruitable stroke work and ejection fraction (indices of LV systolic function), systolic stress-shortening relationship, end-systolic pressure-volume relationship, and peak (+)dP/dt (indices of LV contractility) were examined. The systolic properties of the LV were normal in patients with DHF. Stroke work was 8.4±2.3 in DHF versus 8.8±2.5 kg · cm in controls ( P =0.26). Preload recruitable stroke work was 99±22 in DHF versus 109±18 g/cm 2 in controls ( P =0.13). The relationship between stroke work and end-diastolic volume was similar in DHF and controls. Peak (+) dP/dt was 1596±362 in DHF versus 1664±305 mm Hg/s in controls ( P =0.54). The end-systolic pressure-volume relationship was increased in DHF. The systolic stress versus endocardial fractional shortening relationship was similar in DHF and controls. Conclusions— Patients with DHF had normal LV systolic performance, function, and contractility. The pathophysiology of DHF does not appear to be related to significant abnormalities in these systolic properties of the LV.

Patients with chronic heart failure can be divided into 2 broad categories: systolic heart failure and diastolic heart failure. There are significant differences in demographics, prognosis, left ventricular structure, as well as systolic and diastolic function between these 2 groups of patients. The purpose of this presentation is to define the terminology used to describe these 2 broad categories of heart failure and to characterize the functional measurements that constitute their pathophysiological mechanisms.

Introduction: Both pressure overload hypertrophy (POH) and aging cause increased diastolic chamber stiffness. Whether and to what extent these changes are dependent on increased LV mass, increased myocardial viscoelastic stiffness, changes in the extracellular matrix (ECM) and/or changes in the constitutive properties of the cardiac muscle cells is not completely defined. Methods: Three groups of mice (C57Bl) were studied: young adults (controls; n = 7, age=16±5 wks), POH (n = 6, age = 16±1 wks) and senescent (n = 7, age = 96±10 wks). POH was created by transverse aortic constriction (TAC) for 4 weeks. Left ventricular (LV) structure and function were determined by echocardiography. LV papillary muscles were isolated and viscoelastic properties studied. Cardiomyocytes were isolated (collagenase), embedded in a gel matrix and viscoelastic properties studied. In both papillary muscles and cardiomyocytes a stress vs strain hysteresis loop was derived, which was fit by a constitutive equation to derive the elastic stiffness constant β. Additionally, normalized area of the hysteresis loop was used to derive the viscosity constant η. Results: In the POH mice echocardiography showed a significant increase in LV/Body Weight ratio (3.04±0.16 before vs 5.69±1.09∗ mg/gm after TAC) with no change in end diastolic volume or ejection fraction. Stiffness and viscosity were increased in papillary muscle and cardiomyocytes in both POH and senescent mice (Table). POH caused a 118% increase in myocardial stiffness and a 21% increase in cardiomyocyte stiffness. Aging caused a 29% increase in myocardial stiffness and a 31% increase in cardiomyocyte stiffness. Therefore, both the ECM and cardiomyocyte properties play a role in increased myocardial stiffness. Conclusion: Data suggest that the observed increase in myocardial stiffness may be more dependent on changes in the ECM in POH, but more dependent on changes in the cardiomyocyte in aging. Therefore, treatment developed to decrease myocardial stiffness may target either ECM or cardiomyocyte but must affect both to completely normalize the increased stiffness that occurs in POH and aging. ≠ Comparison of viscoelastic properties Control POH Senescent Papillary muscle Stiffness ß 0.028±0.005 0.061±0.014 ≠ p<0.001 0.036±0.004 ∗ p<0.05 vs control Viscosity η 33.5±1.5 43.4±5.0 ∗ p<0.05 vs control 37.2±2.9 Cardiomyocytes Stiffness ß 6.7±2.5 8.1±5.5 ∗ p<0.05 vs control 8.8±2.9 ∗ p<0.05 vs control Viscosity η 33.8±5.1 46.1±14.2 ∗ p<0.05 vs control 34.8±5.0 Mean±SD ≠ p<0.001 ∗ p<0.05 vs control Open table in a new tab Mean±SD

We have developed a counter rotating cone extrusion device to produce the next generation of three-dimensional collagen scaffold for tissue engineering. The device can produce a continuously varying fibril angle from the lumen to the outside of a 5-mm-diameter collagen tube, similar to the pattern of heart muscle cells in the intact heart. Our scaffold is a novel, oriented, type I collagen, tubular scaffold. We selected collagen because we believe there are important signals from the collagen both geometrically and biochemically that elicit the in vivo -like phenotypic response from the cardiomyocytes. We have shown that cardiomyocytes can be cultured in these tubes and resemble an in vivo phenotype. This new model system will provide important information leading to the design and construction of a functional, biologically based assist device.

BACKGROUNDPatients with signs and symptoms of heart failure and a normal left ventricular ejection fraction are said to have diastolic heart failure. It has traditionally been thought that the pathophysiological cause of heart failure in these patients is an abnormality in the diastolic properties of the left ventricle; however, this hypothesis remains largely unproven.METHODSWe prospectively identified 47 patients who met the diagnostic criteria for definite diastolic heart failure; all the patients had signs and symptoms of heart failure, a normal ejection fraction, and an increased left ventricular end-diastolic pressure. Ten patients who had no evidence of cardiovascular disease served as controls. Left ventricular diastolic function was assessed by means of cardiac catheterization and echocardiography.RESULTSThe patients with diastolic heart failure had abnormal left ventricular relaxation and increased left ventricular chamber stiffness. The mean ( +/- SD) time constant for the isovolumic-pressure decline (tau) was longer in the group with diastolic heart failure than in the control group ( 59 +/- 14 msec vs. 35 +/- 10 msec, P = 0.01). The diastolic pressure - volume relation was shifted up and to the left in the patients with diastolic heart failure as compared with the controls. The corrected left ventricular passive-stiffness constant was significantly higher in the group with diastolic heart failure than in the control group (0.03 +/- 0.01 vs. 0.01 +/- 0.01, P< 0.001).CONCLUSIONSPatients with heart failure and a normal ejection fraction have significant abnormalities in active relaxation and passive stiffness. In these patients, the pathophysiological cause of elevated diastolic pressures and heart failure is abnormal diastolic function.

To determine whether and to what extent one component of the extracellular matrix, fibrillar collagen, contributes causally to abnormalities in viscoelasticity, collagen was acutely degraded by activation of endogenous matrix metalloproteinases (MMPs) with the serine protease plasmin. Papillary muscles were isolated from normal cats and cats with right ventricular pressure overload hypertrophy (POH) induced by pulmonary artery banding. Plasmin treatment caused MMP activation, collagen degradation, decreased the elastic stiffness constant, and decreased the viscosity constant in both normal and POH muscles. Thus, whereas many mechanisms may contribute to the abnormalities in myocardial viscoelasticity in the POH myocardium, changes in fibrillar collagen appear to play a predominant role.

Recent studies have suggested that pressure overload hypertrophy (POH) alters the viscoelastic properties of individual cardiocytes when studied in isolation. However, whether these changes in cardiocyte properties contribute causally to changes in the material properties of the cardiac muscle as a whole is unknown. Accordingly, a selective, isolated, acute change in cardiocyte constitutive properties was imposed in an in vitro system capable of measuring the resultant effect on the material properties of the composite cardiac muscle. POH caused an increase in both myocardial elastic stiffness, from 20.5 +/- 1.3 to 28.4 +/- 1.8, and viscous damping, from 15.2 +/- 1.1 to 19.8 +/- 1.5 s (normal vs. POH, P < 0.05), respectively. Recent studies have shown that cardiocyte constitutive properties could be acutely altered by depolymerizing the microtubules with colchicine. Colchicine caused a significant decrease in the viscous damping in POH muscles (19.8 +/- 1.5 s at baseline vs. 14.7 +/- 1.3 s after colchicine, P < 0.05). Therefore, myocardial material properties can be altered by selectively changing the constitutive properties of one element within this muscle tissue, the cardiocyte. Changes in the constitutive properties of the cardiocytes themselves contribute to the abnormalities in myocardial stiffness and viscosity that develop during POH.

In large mammals there is a correlation between microtubule network densification and contractile dysfunction in severe pressure-overload hypertrophy. In small mammals there is a similar correlation for the shift to beta-myosin heavy chain (MHC), a MHC isoform having a slower ATPase Vmax. In this study, murine left ventricular (LV) pressure overload invoked both mechanisms: microtubule network densification and beta-MHC expression. Cardiac beta-MHC was also augmented without altering tubulin levels by two load-independent means, chemical thyroidectomy and transgenesis. In hypertrophy, contractile function of the LV and its cardiocytes decreased proportionally; microtubule depolymerization restored normal cellular contraction. In hypothyroid mice having a complete shift from alpha-MHC to beta-MHC, contractile function of the LV and its cardiocytes also decreased, but microtubule depolymerization had no effect on cellular contraction. In transgenic mice having a cardiac beta-MHC increase similar to that in hypertrophy, contractile function of the LV and its cardiocytes was normal, and microtubule depolymerization had no effect. Thus, although both mechanisms may cause contractile dysfunction, for the extent of MHC isoform switching seen even in severe murine LV pressure-overload hypertrophy, microtubule network densification appears to have the more important role.

In vivo studies show that β3-integrin–mediated focal adhesion formation (FAF) causes recruitment of nonreceptor tyrosine kinases to the cytoskeleton in pressure-overloaded myocardium. To define the mechanism of β3-integrin–mediated signaling, we developed a cell culture model (adult feline cardiocytes embedded in a 3-dimensional matrix of native type 1 collagen, fibronectin, and vitronectin) wherein β3-integrin–mediated focal adhesion kinase occurs. Focal adhesion kinase was analyzed immunocytochemically using confocal microscopy. Initial studies suggested that cardiocytes cultured in a 3-dimensional matrix formed focal adhesions consisting of both β3-integrin and the muscle-specific isoform, β1-integrin (β1D). The focal adhesions were associated with focal adhesion kinase on both costameres and intercalated disks. To determine the cause of β1D-integrin–mediated focal adhesion kinase in this model, time course studies were done. Beta3-integrin–mediated focal adhesion kinase occurred within 30 minutes after embedding cardiocytes and persisted for >24 hours, whereas β1D-integrin–mediated focal adhesion kinase was present from the outset. Because confocal microscopy showed that laminin was present on the surface of freshly isolated cardiocytes, we hypothesized that this was causative of β1D-integrin–mediated focal adhesion kinase. Freshly isolated cardiocytes washed with acidic medium (2 minutes, pH 3.0) to remove laminin and then embedded in a 3-dimensional matrix showed complete absence of β1D-integrin–mediated focal adhesion kinase, but β3-integrin–mediated focal adhesion kinase occurred with a time course similar to that seen in cultured, unwashed cardiocytes. Acid washing did not alter the binding ability of β1D-integrin, because acid-washed cardiocytes in the presence of laminin showed β1D-integrin–mediated focal adhesion kinase. Thus, cardiocytes embedded in a 3-dimensional matrix show β3-integrin–mediated focal adhesion kinase and provide an in vitro model to study β3-integrin–mediated signaling in response to hemodynamic cardiac loading.