The estimation of patient-specific cardiac diastolic functions from clinical measurements

An unresolved issue in patients with diastolic dysfunction is that the estimation of myocardial stiffness cannot be decoupled from diastolic residual active tension (AT) because of the impaired ventricular relaxation during diastole. To address this problem, this paper presents a method for estimating diastolic mechanical parameters of the left ventricle (LV) from cine and tagged MRI measurements and LV cavity pressure recordings, separating the passive myocardial constitutive properties and diastolic residual AT. Dynamic C₁-continuous meshes are automatically built from the anatomy and deformation captured from dynamic MRI sequences. Diastolic deformation is simulated using a mechanical model that combines passive and active material properties. The problem of non-uniqueness of constitutive parameter estimation using the well known Guccione law is characterized by reformulation of this law. Using this reformulated form, and by constraining the constitutive parameters to be constant across time points during diastole, we separate the effects of passive constitutive properties and the residual AT during diastolic relaxation. Finally, the method is applied to two clinical cases and one control, demonstrating that increased residual AT during diastole provides a potential novel index for delineating healthy and pathological cases.     

Myocardial material property determination in the in vivo heart using magnetic resonance imaging

Objectives: To determine nonlinear material properties of passive, diastolic myocardium using magnetic resonance imaging (MRI) tissue-tagging, finite element analysis (FEA) and nonlinear optimization.Background: Alterations in the diastolic material properties of myocardium may pre-date the onset of or exist exclusive of systolic ventricular dysfunction in disease states such as hypertrophy and heart failure. Accordingly, significant effort has been expended recently to characterize the material properties of myocardium in diastole. The present study defines a new technique for determining material properties of passive myocardium using finite element (FE) models of the heart, MRI tissue-tagging and nonlinear optimization. This material parameter estimation algorithm is employed to estimate nonlinear material parameters in thein vivo canine heart and provides the necessary framework to study the full complexities of myocardial material behavior in health and disease.Methods and results: Material parameters for a proposed exponential strain energy function were determined by minimizing the least squares difference between FE model-predicted and MRI-measured diastolic strains. Six mongrel dogs underwent MRI imaging with radiofrequency (RF) tissue-tagging. Two-dimensional diastolic strains were measured from the deformations of the MRI tag lines. Finite element models were constructed from early diastolic images and were loaded with the mean early to late left ventricular and right ventricular diastolic change in pressure measured at the time of imaging. A nonlinear optimization algorithm was employed to solve the least squares objective function for the material parameters. Average material parameters for the six dogs wereE=28,722 ± 15,984 dynes/cm² andc=0.00182 ± 0.00232 cm²/dyne.Conclusion: This parameter estimation algorithm provides the necessary framework for estimating the nonlinear, anisotropic and non-homogeneous material properties of passive myocardium in health and disease in thein vivo beating heart.     

Assessment of myocardial function: a review of quantification methods and results using tagged MRI.

Tagged MRI provides a noninvasive way to assess the regional function of the heart. Clinical use of myocardial strain measurements from tagged MRI requires identifying new normative values. As for cardiac motion estimation, a variety of methods for quantifying myocardial deformations have been proposed in the image analysis and medical literature, based on heart geometry and continuum mechanics. This article comparatively reviews existing quantification techniques, and synthesizes their results to establish confidence intervals for the standard deformation parameters.     

Characterization of Alterations in Diabetic Myocardial Tissue Using High Resolution MRI

Cardiovascular complications, including diabetic cardiomyopathy, are the major cause of fatalities in diabetes. Diabetic cardiomyopathy is expressed in part through fibrosis and left ventricular hypertrophy, increasing myocardial stiffness leading to heart failure. In order to search for curative interventions, precise evaluation of the diabetic heart pathology is extremely important. Magnetic resonance imaging (MRI) is ideally suited for the assessment of heart disorders due to its high resolution, three-dimensional properties and dimensional accuracy. In this study streptozotocin injected Sprague-Dawley rats were used as a model of type 1 diabetes to characterize abnormalities in the diabetic left ventricle (LV). High resolution MRI using a 9.4 T horizontal bore scanner was performed on control and 7 weeks diabetic rats. In the diabetic rats as compared to controls, we found increased LV wall volume to body weight ratio, suggestive of LV hypertrophy; increased LV wall mean pixel intensity, and decreased T2 relaxation time, both suggestive of changes in the diabetic tissue properties, perhaps due to presence of fibrosis which was detected through increase in the collagen fractional area. In addition, changes in the LV cavity area were observed and quantified in post-mortem diabetic hearts indicative of stiffer and less resilient LV myocardial tissue with diabetes. Together the data suggest that LV hypertrophy and fibrosis may be a major factor underlying structural and functional abnormalities in the diabetic heart, and MRI is a valuable tool to non-invasively monitor the pathological changes in diabetic cardiomyopathy.     

Characterization of the failing murine heart in a desmin knock-out model using a clinical 3 T MRI scanner

The purpose of this study was to establish an MRI protocol on a clinical scanner for assessment of left (LV) and right (RV) ventricular myocardial function of the murine heart, and to apply this protocol for the first in vivo assessment of myocardial function in a mouse model of cardiomyopathy (Desmin-/-). MRI was performed on a clinical 3?T whole body MRI system using a dedicated solenoid receive-only coil. Contiguous short axis slices were acquired covering the entire heart using a spoiled cine gradient echo sequence (TR 9-12 ms, TE 3-4?ms, α 25°, 1.0?×?0.23?×?0.23?mm3). Global LV- and RV-myocardial functional parameters such as end-diastolic ventricular volume, ejection fraction (EF), LV mass and cardiac output (CO) of Desmin-/- mice and age-matched controls were determined. Global myocardial functional data of healthy controls (n?=?4) were in very good agreement with previously reported data. The transgenic mice (n?=?8) revealed a significantly reduced LV- and RV-EF as well as CO. Body weight-normalized LV- and RV-end-diastolic volumes and LV mass were significantly increased. In addition desmin deficient mice exhibited segmental wall thinning and akinesia, suggesting myocardial necrosis. This study demonstrates that clinical 3?T MRI-systems may reliably be used for non-invasive assessment of LV- and RV-myocardial function in normal and in genetically engineered mice with cardiomyopathies. In addition, this proof of principle study presents first in vivo MRI data of the cardiac phenotype of desmin knock-out mice.     

A novel ultrasound technique to estimate right ventricular geometry during fibrillation

Finite element modelling of the heart for the purpose of studying the electric fields of defibrillation shocks requires knowledge of the geometry of the heart during fibrillation. However, the standard method of measuring this geometry, MRI. cannot be used during fibrillation because the heart geometry changes rapidly and perhaps unpredictably. We present a new ultrasound approach to measuring the right ventricular geometry during fibrillation and preliminary data using this technique. In six anaesthetized pigs, we find that a short axis cross-sectional area of the right ventricle increases by 38% during a 30 s episode of ventricular fibrillation. A long axis cross-sectional area increases by 19% during this same time. By fitting parameters of a simple geometric model to the experimental data, we estimate that the volume of blood in the right ventricular cavity increases by approximately 30% during the episode of ventricular fibrillation. We present the first study of the RV area during-fibrillation with the estimated volume. Our data suggest changes in defibrillation threshold may be linked to current shunting through the increased blood volume.     

Correlation of CT-based regional cardiac function (SQUEEZ) with myocardial strain calculated from tagged MRI: an experimental study

The objective of this study was to investigate the correlation between local myocardial function estimates from CT and myocardial strain from tagged MRI in the same heart. Accurate detection of regional myocardial dysfunction can be an important finding in the diagnosis of functionally significant coronary artery disease. Tagged MRI is currently a reference standard for noninvasive regional myocardial function analysis; however, it has practical drawbacks. We have developed a CT imaging protocol and automated image analysis algorithm for estimating regional cardiac function from a few heartbeats. This method tracks the motion of the left ventricular (LV) endocardial surface to produce local function maps: we call the method Stretch Quantification of Endocardial Engraved Zones (SQUEEZ). Myocardial infarction was created by ligation of the left anterior descending coronary artery for 2 h followed by reperfusion in canine models. Tagged and cine MRI scans were performed during the reperfusion phase and first-pass contrast enhanced CT scans were acquired. The average delay between the CT and MRI scans was <1 h. Circumferential myocardial strain (E_cc) was calculated from the tagged MRI data. The agreement between peak systolic E_cc and SQUEEZ was investigated in 162 segments in the 9 hearts. Linear regression and Bland–Altman analysis was used to assess the correlation between the two metrics of local LV function. The results show good agreement between SQUEEZ and E_cc: (r = 0.71, slope = 0.78, p < 0.001). Furthermore, Bland–Altman showed a small bias of ?0.02 with 95 % confidence interval of 0.1, and standard deviation of 0.05 representing ~6.5 % of the dynamic range of LV function. The good agreement between the estimates of local myocardial function obtained from CT SQUEEZ and tagged MRI provides encouragement to investigate the use of SQUEEZ for measuring regional cardiac function at a low clinical dose in humans.     

Left ventricular torsion and longitudinal shortening: two fundamental components of myocardial mechanics assessed by tagged cine-MRI in normal subjects

Cardiac magnetic resonance imaging (Cardiac MRI) has become a gold standard diagnostic technique for the assessment of cardiac mechanics, allowing the non-invasive calculation of left ventricular long axis longitudinal shortening (LVLS) and absolute myocardial torsion (AMT) between basal and apical left ventricular slices, a movement directly related to the helicoidal anatomic disposition of the myocardial fibers. The aim of this study is to determine AMT and LVLS behaviour and normal values from a group of healthy subjects. A group of 21 healthy volunteers (15 males) (age: 23–55 y.o., mean: 30.7 ± 7.5) were prospectively included in an observational study by Cardiac MRI. Left ventricular rotation (degrees) was calculated by custom-made software (Harmonic Phase Flow) in consecutive LV short axis planes tagged cine-MRI sequences. AMT was determined from the difference between basal and apical planes LV rotations. LVLS (%) was determined from the LV longitudinal and horizontal axis cine-MRI images. All the 21 cases studied were interpretable, although in three cases the value of the LV apical rotation could not be determined. The mean rotation of the basal and apical planes at end-systole were −3.71° ± 0.84° and 6.73° ± 1.69° (n:18) respectively, resulting in a LV mean AMT of 10.48° ± 1.63° (n:18). End-systolic mean LVLS was 19.07 ± 2.71%. Cardiac MRI allows for the calculation of AMT and LVLS, fundamental functional components of the ventricular twist mechanics conditioned, in turn, by the anatomical helical layout of the myocardial fibers. These values provide complementary information about systolic ventricular function in relation to the traditional parameters used in daily practice.     

Noninvasive measurement and clinical relevance of myocardial twist and torsion

Left ventricular (LV) torsion (twisting) and untwisting results in equalization of wall stress and augmentation of pressure generated for a given shortening of sarcomere during the systolic contraction and aids early diastolic relaxation. This is attributed to the dynamic interaction of epicardial and endocardial helical myocardial fibers. Recent advances in noninvasive imaging techniques have enabled us to quantify torsion accurately and reliably in health and disease. LV torsional mechanics are altered in range of clinical conditions from those that cause minimal cardiac architectural changes as seen in hypertension, diabetes mellitus or older age to advanced cardiac remodeling as seen dilated or hypertrophic cardiomyopathy. Therefore, assessment of LV rotational mechanics may be a potentially sensitive marker of cardiac dysfunction and may provide important insights into the pathophysiology of heart failure.     

Increased left ventricular stiffness impairs filling in dogs with pulmonary emphysema in respiratory failure.

In a chronic canine model of pulmonary emphysema, we studied the interaction between left ventricular (LV) mechanics and pulmonary disease during severe hypoxemia. The hypoxemia was similar to that which may occur during a severe exacerbation of chronic obstructive lung disease. In six dogs with papain-induced emphysema and in seven dogs without emphysema, LV mechanics were examined when a hypoxic gas mixture was inspired to reduce PO2 to about 35 mmHg (hypoxic study) and during nonhypoxic conditions (room air study). In both groups, LV diastolic compliance was reduced during the hypoxic study by a similar amount. This finding could not be explained in terms of ventricular interdependence. Our analysis suggested that hypoxia decreased diastolic compliance (i.e., increased LV diastolic stiffness) by impairing LV relaxation. The primary effect of hypoxia was to decrease the extent to which LV relaxation occurred for a given end-diastolic pressure, while the rate of LV relaxation was decreased just slightly. This study indicates that severe hypoxemia because of respiratory failure may impair myocardial relaxation leading to a decrease in LV filling.     

Gestational changes in left ventricular myocardial contractile function: new insights from two-dimensional speckle tracking echocardiography

The goal of this study was to evaluate the impact of pregnancy and labor on left ventricular (LV) myocardial mechanics using speckle tracking echocardiography (STE). Pregnancy is characterized by profound hormonal and hemodynamic alterations that directly or indirectly influence cardiac structure and function. However, the impact of these changes on left ventricular (LV) myocardial contractile function has not been fully elucidated. In this prospective, longitudinal study, 35 pregnant women underwent serial clinical and echocardiographic evaluation during each trimester and at labor. Two dimensional STE was performed to measure global LV longitudinal, circumferential and radial strain (GLS, GCS and GRS, respectively). Similar data obtained from 20 nulliparous, age-matched women were used as control. All strain values during pregnancy were adjusted for age and hemodynamic parameters. There was a progressive increase in heart rate, systolic and diastolic blood pressure, cardiac output and LV stroke-work during pregnancy. LV end-diastolic and end-systolic volumes also increased progressively but LV ejection fraction remained unaltered, except for slight reduction during the second trimester. Compared to the controls, GLS and GCS were reduced in the first trimester itself (GLS ?22.39?±?5.43?% vs. ?18.66?±?0.64?%, P 0.0002; GCS ?20.84?±?3.20 vs. ?17.88?±?0.09, P?<?0.001) and remained so throughout the pregnancy and labor. In contrast, GRS showed an increase during pregnancy which peaked during the second trimester (24.18?±?0.39?% vs. 18.06?±?8.14?% in controls, P?<?0.001). Alterations in loading conditions during pregnancy are associated with counterbalancing changes in the myocardial mechanics. LV longitudinal and circumferential strain are reduced whereas radial strain is increased. These counterbalancing changes serve to maintain overall LV ejection performance within a normal range and enable the maternal heart to meet the hemodynamic demands of pregnancy and labor.     

Myocardial cytokine IL-8 and nitric oxide synthase activity during and after resuscitation: preliminary observations in regards to post-resuscitation myocardial dysfunction

AIM: Increases in serum cytokines have been reported after successful resuscitation from prolonged ventricular fibrillation (VF). Pro-inflammatory cytokines can stimulate inducible nitric oxide synthase (iNOS) to produce excessive levels of nitric oxide (NO). High levels of both myocardial inflammatory cytokines and nitric oxide levels can depress myocardial contractile function. We hypothesized that myocardial pro-inflammatory cytokines and iNOS activity would increase following successful resuscitation from prolonged ventricular fibrillation cardiac arrest, and that such increases would parallel the development of post-resuscitation myocardial dysfunction. METHODS: Ventricular fibrillation cardiac arrest was induced in seven domestic swine (25+/-5kg). After 10min of untreated VF, the animals were defibrillated and resuscitated. Left ventricular (LV) systolic and diastolic function measurements, serum samples (arterial and coronary sinus) for IL-8 cytokine quantification, and LV myocardial biopsies were collected before, during, and after resuscitation. Quantification of myocardial endothelial (eNOS) and inducible (iNOS) nitric oxide synthase protein levels were determined using immunoblot analyses and protein localization was examined using immunohistochemistry. RESULTS: Post-resuscitation LV systolic and diastolic functions were depressed while increases in both coronary sinus IL-8 levels and myocardial iNOS activity were found. Compared to pre-arrest baseline, levels of iNOS protein increased during VF (p相似文献   

Three-dimensional motion reconstruction and analysis of the right ventricle using tagged MRI

Right ventricular (RV) dysfunction can serve as an indicator of heart and lung disease and can adversely affect the left ventricle. However, normal RV function must be characterized before abnormal states can be detected. We describe a method for reconstructing the 3D motion of the RV by fitting a deformable model to tag and contour data extracted from multiview tagged magnetic resonance images. The deformable model is a biventricular finite element mesh built directly from segmented contours. Our approach accommodates the geometrically complex RV by using the entire lengths of the tags, localized degrees of freedom, and finite elements for geometric modeling. Also, we outline methods for converting the 3D motion reconstruction results into potentially useful motion variables, such as strains and displacements. The technique was applied to synthetic data, two normal hearts, and two hearts with right ventricular hypertrophy (RVH). Noticeable differences were found between the motion variables calculated for normal volunteers and RVH patients.     

Left ventricular remodeling, mechanics, and tissue characterization in congenital aortic stenosis.

BACKGROUND: As the response of the myocardium to pressure overload is age-dependent, this study was designed to examine left ventricular (LV) remodeling, mechanics, and tissue characterization in children with moderate congenital aortic stenosis. METHODS: We studied by echocardiography Doppler 22 patients (mean age 12.4 +/- 5.6 years) with peak and mean transvalvular gradient of 63 +/- 6 and 32 +/- 4 mm Hg, respectively. In addition, 30 age- and body surface area-matched participants with structurally normal hearts were used as a control group. Sex- and age-specific cut-off levels for LV mass/height(2.7) and relative wall thickness were defined to assess LV geometry. As a load-independent index of myocardial contractility, the relation between the rate-corrected velocity of circumferential fiber shortening both at endocardium and midwall, and meridional end-systolic stress was assessed. In addition, LV diastolic function was also evaluated by the mitral flow indexes. Finally, ultrasonic tissue characterization of the LV myocardium was performed by calculating the magnitude of cyclic variation, which reflects the intramural contractile function, and the averaged myocardial intensity of integrated backscatter, which is directly related to the myocardium collagen content. RESULTS: The endocardial velocity of circumferential fiber shortening endocardium and meridional end-systolic stress relationship was within the normal range (mean +/- 2SD) in 18 of 22 patients (81.8%), and midwall velocity of circumferential fiber shortening at endocardium and meridional end-systolic stress was normal in all 22 patients. No mitral flow index of LV diastolic function was significantly different between aortic stenosis group and normal participants. In our study population, 16 of 22 patients (72.7%) showed normal LV geometry, 3 (13.6%) had a pattern of concentric remodeling, and 3 (13.6%) concentric hypertrophy. LV hypertrophy was not marked (left ventricular mass index [LVMI] < 51 g/m(2.7)) in any patient. Finally, compared with control participants our study population showed, both at interventricular septum and posterior wall, comparable values of cyclic variation integrated backscatter, but significantly higher values of averaged myocardial integrated backscatter intensity (P <.01). CONCLUSIONS: In children with moderate congenital aortic stenosis, the total amount of myocardial collagen was increased despite normal LV myocardial contractility and diastolic function. Furthermore, LV remodeling was abnormal in only about a quarter of our patients and none had more than mild hypertrophy. Although the majority of these patients do not have markers now recognized to predict higher risk of cardiovascular events, the long-term significance of myocardial fibrosis and its response to treatment remain to be investigated.     

Abnormal cardiac function in the streptozotocin-diabetic rat. Changes in active and passive properties of the left ventricle.

To provide an integrated assessment of changes in systolic and diastolic function in diabetic rats, we measured conscious hemodynamics and performed ex vivo analysis of left ventricular passive-elastic properties. Rats given streptozotocin (STZ) 65 mg/kg i.v. (n = 14) were compared with untreated age-matched controls (n = 15) and rats treated with insulin after administration of STZ (n = 11). After 7 d, diabetic rats exhibited decreases in heart rate and peak developed left ventricular (LV) pressure during aortic occlusion. After 26 d of diabetes there were significant decreases in resting LV systolic pressure, developed pressure, and maximal +dP/dt, whereas LV end-diastolic pressure increased and the time constant of LV relaxation was prolonged. The passive LV pressure-volume relationship was progressively shifted away from the pressure axis, and the overall chamber stiffness constant was decreased. However, "operating chamber stiffness" calculated at end-diastolic pressure was increased at 7 d, and unchanged at 26 d. LV cavity/wall volume and end-diastolic volume were increased after 26 d of diabetes. Myocardial stiffness was unchanged at both time intervals. All of the above abnormalities were reversed by the administration of insulin. We conclude that the hemodynamic and passive-elastic changes that occur in diabetic rats represent an early dilated cardiomyopathy which is reversible with insulin.     

In vivo strain and stress estimation of the heart left and right ventricles from MRI images

Mechanical properties of the myocardium have been investigated intensively in the last four decades. Many complex strain energy functions have been used to estimate the stress-strain relationship of myocardium because the heart muscle is an inhomogeneous, anisotropic, and nearly incompressible material, which undergoes large deformations. These functions can be effective for fitting in vitro experimental data from myocardial stretch testing. However, it is difficult to model in vivo myocardium using these strain energy functions. Moreover, such estimates have so far been carried out almost exclusively on the left ventricle, because of the relative thinness and complex geometry of the right ventricle. Previous work from our research group has successful estimated the motion and deformation of both the left and the right ventricles, using data from noninvasive tagged magnetic resonance imaging. In this paper, we present a novel statistical model to estimate the in vivo material properties and strain and stress distribution in both ventricles, using such data. Two normal hearts and two hearts with right-ventricular hypertrophy (RVH) were studied and noticeable differences were found between the strain and stress distributions for normal volunteers and RVH patients. Compared to the strain energy function approach, our model is more intuitively understandable.     

MRI of myocardial infarction with tissue tagging

Myocardial tagging with MRI has been available for three decades as a method for direct noninvasive quantification of regional myocardial motion for assessing the impact of ischemia, electrical asynchrony, and heart failure, among other conditions. In recent years, new developments in imaging sequences, hybrid techniques, and automated postprocessing have brought tagging closer to clinical application. Improvements in acquisition strategies have increased tag-tissue contrast and persistence, making automated tag detection easier and more robust. Imaging techniques such as harmonic phase MRI and displacement encoding with stimulated echoes that quantify pixel-by-pixel myocardial motion have simplified postprocessing. Parallel imaging and the increased signal-to-noise ratio available at the higher field strengths of new clinical scanners have moved the assessment of cardiac function into the real-time imaging domain. All of these developments have made myocardial motion mapping with tagged MRI a gold standard for the quantification of regional function within the research world, with potential to become an extremely valuable clinical technique.     

Cardiac involvement in Mulibrey nanism: characterization with magnetic resonance imaging.

Mulibrey nanism (MUL) is an autosomal recessive disorder that is enriched in the Finnish population. Variable degrees of pericardial and myocardial involvement can lead to heart failure and premature death. The purpose of this study was using magnetic resonance imaging (MRI) to assess structural and functional abnormalities of the MUL cardiopathy in all four cardiac chambers as well as in the pericardium. Thirty-one patients with MUL (mean age 27, range 15-50 years) and 16 controls (mean age 31, range 19-45 years) were examined with a Siemens Vision 1.5-T imager. Ten patients had undergone pericardiectomies to relieve symptoms of constrictive pericarditis. In surgery performed 0.5-25 years before MRI, the removed pericardium was found to be thickened and consisting of scarlike fibrosis. Turbo spin echo images were obtained for assessment of pericardial thickness, and breath hold left ventricular (LV) short axis and four-chamber cine images were obtained for the volumetric data. In MRI, pericardial thickness was normal (under 3.4 mm) in all patients with MUL. In the 10 pericardiectomized patients, the remnants of the pericardium were of normal thickness as well. The LV septum (p = 0.01) and posterior wall (p<0.001) were hypertrophied and end-diastolic volumes of both ventricles (p<0.05) were reduced in all patients. The LV systolic function was preserved. The volume chance during the first third of diastole (p = 0.030), the absolute peak filling rate (p = 0.047), and the time to peak rate of LV diastolic filling (p = 0.030) indicated restrictive LV diastolic filling. The right ventricular ejection fraction and contraction of both atria were reduced.     

The diastolic dysfunction of the left ventricle in patients with systemic lupus erythematosus and system scleroderma

The subjects of the study were 22 patients with systemic lupus erythematosus (SLE) and 18 patients with system scleroderma (SS). The mean age of the subjects was 36.3 +/- 2.4 years, the onset of the disease had taken place 5 to 10 years ago. The control group consisted of 20 practically healthy individuals with no complaints, clinical signs or instrumental data suggesting cardiovascular pathology. In order to evaluate the character of left ventricular (LV) diastolic filling, all the patients underwent transthoracal Doppler analysis with measurement of transmitral flow in four-chamber heart position using apical approach with the control volume at the level of the ends of mitral valvular cusps (computed sonography system ACUSON 128 XP/10). The study found no significant difference between SLE and SS patients in such parameters as LV myocardial mass and LV mass index. All the patients with rheumatic diseases, with or without arterial hypertension (AH), had diastolic dysfunction, which was manifested by increase of atrial systolic contribution into LV filling, prolongation of blood flow slowdown time in the stage of its early filling, and prolongation of LV isometric relaxation time; heart diastolic disorder was accompanied by significant increase of end diastolic pressure in LV cavity. It should be noted that the most prominent changes were found in rheumatic patients with AH, which must be caused by the hypertrophy and remodeling of the myocardium. Myocardial hypertrophy was associated with substantial changes in the ventricular septum, which consisted in its hypokinesia, associated with impairment of myocardial contractility (ejection fraction of 48.3 +/- 3.5%).     

Early Increase in Left Ventricular Compliance after Myocardial Infarction

The left ventricular (LV) pressure-volume (P-V) relationship is a resultant of several determinants, including initial ventricular volume, geometry, and wall stiffness. A quantitative index of one of these determinants, LV wall stiffness, was developed from a mathematical analysis of the isolated P-V relationship. Since this relationship was exponential, stiffness (dP/dV) could be expressed by the equation dP/dV = aP + b, where a and b are constants. The a constant, termed the passive elastic modulus, was independent of both pressure and volume, was modified only slightly by changes in geometry, and thus was primarily affected by changes in wall stiffness. LV wall stiffness was assessed by determination of the passive elastic modulus in eight normal canine hearts and in five hearts 1 hr after acute myocardial infarction. The value of the passive elastic modulus for the normal canine LV was found to be 0.099+/-0.006 cc(-1). In the five infarcted hearts there was a modest, but statistically insignificant, shift of the P-V curves from control, such that for the same pressure the infarcted hearts contained greater volume. However, the passive elastic modulus decreased 41% to 0.057+/-0.006 cc(-1) (P < 0.001). Thus, although LV wall stiffness may increase later in the course of myocardial infarction, it is concluded that it was significantly decreased 1 hr after infarction. Calculation of the passive elastic modulus provided a sensitive means of detecting such changes, whereas P-V curves alone were generally insensitive.