Diastolic function and myocardial structure in patients with myocardial hypertrophy. Special reference to normalized viscoelastic data

Strain-Dependent Stress Relaxation Behavior of Healthy Right Ventricular Free Wall

The increasing evidence of stress-strain hysteresis in large animal or human myocardium calls for extensive characterizations of the passive viscoelastic behavior of the myocardium. Several recent studies have investigated and modeled the viscoelasticity of the left ventricle while the right ventricle (RV) viscoelasticity remains poorly understood. Our goal was to characterize the biaxial viscoelastic behavior of RV free wall (RVFW) using two modeling approaches. We applied both quasi-linear viscoelastic (QLV) and nonlinear viscoelastic (NLV) theories to experimental stress relaxation data from healthy adult ovine. A three-term Prony series relaxation function combined with an Ogden strain energy density function were used in the QLV modeling, while a power-law formulation was adopted in the NLV approach. The ovine RVFW exhibited an anisotropic and strain-dependent viscoelastic behavior relative to anatomical coordinates, and the NLV model showed a higher capacity in predicting strain-dependent stress relaxation than the QLV model. From the QLV fitting, the relaxation term associated with the largest time constant played the dominant role in the overall relaxation behavior at all strains from early to late diastole, whereas the term associated with the smallest time constant was pronounced only at low strains at early diastole. From the NLV fitting, the parameters showed a nonlinear dependence on the strain. Overall, our study characterized the anisotropic, nonlinear viscoelasticity to capture the elastic and viscous resistances of the RVFW during diastole. These findings deepen our understanding of RV myocardium dynamic mechanical properties. STATEMENT OF SIGNIFICANCE: Although significant progress has been made to understand the passive elastic behavior of the right ventricle free wall (RVFW), its viscoelastic behavior remains poorly understood. In this study, we originally applied both quasi-linear viscoelastic (QLV) and nonlinear viscoelastic (NLV) models to published experimental data from healthy ovine RVFW. Our results revealed an anisotropic and strain-dependent viscoelastic behavior of the RVFW. The parameters from the NLV fitting showed nonlinear relationships with the strain, and the NLV model showed a higher capacity in predicting strain-dependent stress relaxation than the QLV model. These findings characterize the anisotropic, nonlinear viscoelasticity of RVFW to fully capture the total (elastic and viscous) resistance that is critical to diastolic function.

Computational modeling of cardiac growth and remodeling in pressure overloaded hearts-Linking microstructure to organ phenotype

Cardiac growth and remodeling (G&R) refers to structural changes in myocardial tissue in response to chronic alterations in loading conditions. One such condition is pressure overload where elevated wall stresses stimulate the growth in cardiomyocyte thickness, associated with a phenotype of concentric hypertrophy at the organ scale, and promote fibrosis. The initial hypertrophic response can be considered adaptive and beneficial by favoring myocyte survival, but over time if pressure overload conditions persist, maladaptive mechanisms favoring cell death and fibrosis start to dominate, ultimately mediating the transition towards an overt heart failure phenotype. The underlying mechanisms linking biological factors at the myocyte level to biomechanical factors at the systemic and organ level remain poorly understood. Computational models of G&R show high promise as a unique framework for providing a quantitative link between myocardial stresses and strains at the organ scale to biological regulatory processes at the cellular level which govern the hypertrophic response. However, microstructurally motivated, rigorously validated computational models of G&R are still in their infancy. This article provides an overview of the current state-of-the-art of computational models to study cardiac G&R. The microstructure and mechanosensing/mechanotransduction within cells of the myocardium is discussed and quantitative data from previous experimental and clinical studies is summarized. We conclude with a discussion of major challenges and possible directions of future research that can advance the current state of cardiac G&R computational modeling. STATEMENT OF SIGNIFICANCE: The mechanistic links between organ-scale biomechanics and biological factors at the cellular size scale remain poorly understood as these are largely elusive to investigations using experimental methodology alone. Computational G&R models show high promise to establish quantitative links which allow more mechanistic insight into adaptation mechanisms and may be used as a tool for stratifying the state and predict the progression of disease in the clinic. This review provides a comprehensive overview of research in this domain including a summary of experimental data. Thus, this study may serve as a basis for the further development of more advanced G&R models which are suitable for making clinical predictions on disease progression or for testing hypotheses on pathogenic mechanisms using in-silico models.

Biomechanics of infarcted left Ventricle-A review of experiments

Myocardial infarction (MI) is one of leading diseases to contribute to annual death rate of 5% in the world. In the past decades, significant work has been devoted to this subject. Biomechanics of infarcted left ventricle (LV) is associated with MI diagnosis, understanding of remodelling, MI micro-structure and biomechanical property characterizations as well as MI therapy design and optimization, but the subject has not been reviewed presently. In the article, biomechanics of infarcted LV was reviewed in terms of experiments achieved in the subject so far. The concerned content includes experimental remodelling, kinematics and kinetics of infarcted LVs. A few important issues were discussed and several essential topics that need to be investigated further were summarized. Microstructure of MI tissue should be observed even carefully and compared between different methods for producing MI scar in the same animal model, and eventually correlated to passive biomechanical property by establishing innovative constitutive laws. More uniaxial or biaxial tensile tests are desirable on MI, border and remote tissues, and viscoelastic property identification should be performed in various time scales. Active contraction experiments on LV wall with MI should be conducted to clarify impaired LV pumping function and supply necessary data to the function modelling. Pressure-volume curves of LV with MI during diastole and systole for the human are also desirable to propose and validate constitutive laws for LV walls with MI.

Current Understanding of the Biomechanics of Ventricular Tissues in Heart Failure

Heart failure is the leading cause of death worldwide, and the most common cause of heart failure is ventricular dysfunction. It is well known that the ventricles are anisotropic and viscoelastic tissues and their mechanical properties change in diseased states. The tissue mechanical behavior is an important determinant of the function of ventricles. The aim of this paper is to review the current understanding of the biomechanics of ventricular tissues as well as the clinical significance. We present the common methods of the mechanical measurement of ventricles, the known ventricular mechanical properties including the viscoelasticity of the tissue, the existing computational models, and the clinical relevance of the ventricular mechanical properties. Lastly, we suggest some future research directions to elucidate the roles of the ventricular biomechanics in the ventricular dysfunction to inspire new therapies for heart failure patients.

Epidemiologic observations guiding clinical application of a urinary peptidomic marker of diastolic left ventricular dysfunction

Hypertension, obesity, and old age are major risk factors for left ventricular (LV) diastolic dysfunction (LVDD), but easily applicable screening tools for people at risk are lacking. We investigated whether HF1, a urinary biomarker consisting of 85 peptides, can predict over a 5-year time span mildly impaired diastolic LV function as assessed by echocardiography. In 645 white Flemish (50.5% women; 50.9 years [mean]), we measured HF1 by capillary electrophoresis coupled with mass spectrometry in 2005-2010. We measured early (E) and late (A) peak velocities of the transmitral blood flow and early (e') and late (a') mitral annular peak velocities and their ratios in 2009-2013. In multivariable-adjusted analyses, per 1-standard deviation increment in HF1, e' was -0.193 cm/s lower (95% confidence interval: -0.352 to -0.033; P = .018) and E/e' 0.174 units higher (0.005-0.342; P = .043). Of 645 participants, 179 (27.8%) had LVDD at follow-up, based on impaired relaxation in 69 patients (38.5%) or an elevated filling pressure in the presence of a normal (74 [43.8%]) or low (36 [20.1%]) age-specific E/A ratio. For a 1-standard deviation increment in HF1, the adjusted odds ratio was 1.37 (confidence interval, 1.07-1.76; P = .013). The integrated discrimination (+1.14%) and net reclassification (+31.7%) improvement of the optimized HF1 threshold (-0.350) in discriminating normal from abnormal diastolic LV function at follow-up over and beyond other risk factors was significant (P ≤ .024). In conclusion, HF1 may allow screening for LVDD over a 5-year horizon in asymptomatic people.

Myocardial Architecture, Mechanics, and Fibrosis in Congenital Heart Disease

Congenital heart disease (CHD) is the most common category of birth defect, affecting 1% of the population and requiring cardiovascular surgery in the first months of life in many patients. Due to advances in congenital cardiovascular surgery and patient management, most children with CHD now survive into adulthood. However, residual and postoperative defects are common resulting in abnormal hemodynamics, which may interact further with scar formation related to surgical procedures. Cardiovascular magnetic resonance (CMR) has become an important diagnostic imaging modality in the long-term management of CHD patients. It is the gold standard technique to assess ventricular volumes and systolic function. Besides this, advanced CMR techniques allow the acquisition of more detailed information about myocardial architecture, ventricular mechanics, and fibrosis. The left ventricle (LV) and right ventricle have unique myocardial architecture that underpins their mechanics; however, this becomes disorganized under conditions of volume and pressure overload. CMR diffusion tensor imaging is able to interrogate non-invasively the principal alignments of microstructures in the left ventricular wall. Myocardial tissue tagging (displacement encoding using stimulated echoes) and feature tracking are CMR techniques that can be used to examine the deformation and strain of the myocardium in CHD, whereas 3D feature tracking can assess the twisting motion of the LV chamber. Late gadolinium enhancement imaging and more recently T1 mapping can help in detecting fibrotic myocardial changes and evolve our understanding of the pathophysiology of CHD patients. This review not only gives an overview about available or emerging CMR techniques for assessing myocardial mechanics and fibrosis but it also describes their clinical value and how they can be used to detect abnormalities in myocardial architecture and mechanics in CHD patients.

Diastolic Left Ventricular Function in Relation to Urinary and Serum Collagen Biomarkers in a General Population

Current knowledge on the pathogenesis of diastolic heart failure predominantly rests on case-control studies involving symptomatic patients with preserved ejection fraction and relying on invasive diagnostic procedures including endomyocardial biopsy. Our objective was to gain insight in serum and urinary biomarkers reflecting collagen turnover and associated with asymptomatic diastolic LV dysfunction. We randomly recruited 782 Flemish (51.3% women; 50.5 years). We assessed diastolic LV function from the early and late diastolic peak velocities of the transmitral blood flow and of the mitral annulus. By sequencing urinary peptides, we identified 70 urinary collagen fragments. In serum, we measured carboxyterminal propeptide of procollagen type 1 (PICP) as marker of collagen I synthesis and tissue inhibitor of matrix metalloproteinase type 1 (TIMP-1), an inhibitor of collagen-degrading enzymes. In multivariable-adjusted analyses with Bonferroni correction, we expressed effect sizes per 1-SD in urinary collagen I (uCI) or collagen III (uCIII) fragments. In relation to uCI fragments, e’ decreased by 0.183 cm/s (95% confidence interval, 0.017 to 0.350; p = 0.025), whereas E/e’ increased by 0.210 (0.067 to 0.353; p = 0.0012). E/e’ decreased with uCIII by 0.168 (0.021 to 0.316; p = 0.018). Based on age-specific echocardiographic criteria, 182 participants (23.3%) had subclinical diastolic LV dysfunction. Partial least squares discriminant analysis contrasting normal vs. diastolic LV dysfunction confirmed the aforementioned associations with the uCI and uCIII fragments. PICP and TIMP-1 increased in relation to uCI (p<0.0001), whereas these serum markers decreased with uCIII (p≤0.0006). Diastolic LV dysfunction was associated with higher levels of TIMP-1 (653 vs. 696 ng/mL; p = 0.013). In a general population, the non-invasively assessed diastolic LV function correlated inversely with uCI and serum markers of collagen I deposition, but positively with uCIII. These observations generalise previous studies in patients to randomly recruited people, in whom diastolic LV function ranged from normal to subclinical impairment, but did not encompass overt diastolic heart failure.

Transmural gradients of myocardial structure and mechanics: Implications for fiber stress and strain in pressure overload

Although a truly complete understanding of whole heart activation, contraction, and deformation is well beyond our current reach, a significant amount of effort has been devoted to discovering and understanding the mechanisms by which myocardial structure determines cardiac function to better treat patients with cardiac disease. Several experimental studies have shown that transmural fiber strain is relatively uniform in both diastole and systole, in contrast to predictions from traditional mechanical theory. Similarly, mathematical models have largely predicted uniform fiber stress across the wall. The development of this uniform pattern of fiber stress and strain during filling and ejection is due to heterogeneous transmural distributions of several myocardial structures. This review summarizes these transmural gradients, their contributions to fiber mechanics, and the potential functional effects of their remodeling during pressure overload hypertrophy.

Evaluating the Utility of Circulating Biomarkers of Collagen Synthesis in Hypertrophic Cardiomyopathy

Background—

In hypertrophic cardiomyopathy (HCM), accumulation of myocardial collagen may play a central role in the pathogenesis of diastolic dysfunction and arrhythmia. Previous studies have suggested that peripheral levels of byproducts of collagen synthesis are reflective of myocardial extracellular matrix metabolism, although this has not been validated in detail. Given the potential clinical utility of such biomarkers, we sought to validate the assumed relationship between peripheral markers and myocardial fibrosis in HCM.

Methods and Results—

Fifty patients with HCM and 25 healthy controls underwent peripheral venous sampling to determine plasma concentrations of key collagen precursors (procollagen I and III N-terminal propeptides [PINP, PIIINP]). Contrast-enhanced cardiac magnetic resonance imaging was performed to quantify regional (by late-gadolinium enhancement) and diffuse (by T 1 mapping) myocardial fibrosis. Nineteen subjects also underwent simultaneous arterial and coronary sinus blood sampling (to derive transcardiac concentration gradients of PINP, PIIINP, and C-terminal telopeptide of type I collagen) and right heart catheterization. Despite cardiac magnetic resonance evidence of regional (late-gadolinium enhancement quantity, 6.4±8.0%) and diffuse (T 1 time, 478±79 ms) myocardial fibrosis in patients with HCM, peripheral levels of collagen precursors were similar compared with control subjects (PINP, 45.9±22.9 versus 53.4±25.9 μg/L; P =0.21; PIIINP, 4.8±1.7 versus 4.4±1.1 μg/L; P =0.26). No significant net positive transcardiac concentration gradient was detected for either biomarker of collagen synthesis.

Conclusions—

The cardiac contribution to peripheral levels of byproducts of collagen synthesis in patients with HCM is insignificant. Furthermore, peripheral levels of these biomarkers do not accurately reflect myocardial collagen content in these patients.

Myocardial fibrosis and QTc are reduced following treatment with spironolactone or amiloride in stroke survivors: a randomised placebo-controlled cross-over trial

INTRODUCTION

Myocardial fibrosis is dysrhythmogenic and may contribute to the high incidence of cardiac death in stroke survivors, especially if they have long QTc. We tested the hypothesis that procollagen-1-carboxy terminal peptide (P1CP), a biomarker of myocardial fibrosis, might be improved following treatment with spironolactone or amiloride in stroke survivors. We also tested the hypothesis that both drugs would shorten QTc.

METHODS

STUDY DESIGN

randomised, double-blinded, placebo-controlled, cross-over trial (spironolactone vs. amiloride vs. placebo). Duration of Study: 3 months (1 month per drug). Primary endpoints: P1CP, QTc

RESULTS

11 stroke survivors (5 female), aged 71 ± 4, BP 139/81 mmHg ± 20/11 mmHg, completed the study. Both spironolactone and amiloride significantly reduced P1CP [Spironolactone-Placebo = -24 ug/L, 95% CI = -40 to -6.9; Amiloride-Placebo = -28 ug/L, 95% CI = -44 to -11]. Spironolactone and amiloride both shortened QTc [Spironolactone vs. Placebo=-18 ms(1/2), 95% CI = -36 to -0.55; Amiloride vs Placebo = -25 ms(1/2), 95% CI = -42 to -7.5].

CONCLUSIONS

Procollagen-1-carboxy terminal peptide was reduced following treatment with spironolactone within a month. Further, this is the first study demonstrating amiloride could also improve myocardial fibrosis. The beneficial effects of both drugs on myocardial fibrosis, coupled with their effects on raising potassium translated to a shortening of QTc. Future studies should test the hypothesis that these drugs might reduce the risk of sudden cardiac death in stroke survivors.

Chronic pressure-overload hypertrophy attenuates vortex formation time in patients with severe aortic stenosis and preserved left ventricular systolic function undergoing aortic valve replacement

OBJECTIVE

Transmitral blood flow produces a vortex ring that enhances the hydraulic efficiency of early left ventricular (LV) filling. The effect of pressure-overload hypertrophy on the duration of LV vortex ring formation (vortex formation time [VFT]) is unknown. The current investigation tested the hypothesis that chronic LV pressure-overload hypertrophy produced by severe aortic stenosis (AS) reduces VFT in patients with preserved LV systolic function undergoing aortic valve replacement.

DESIGN

Observational study.

SETTING

Veterans Affairs Medical Center.

PARTICIPANTS

After the Institutional Review Board's approval, 8 patients (7 men and 1 woman; age, 62±5 y; and ejection fraction, 59%±5%) with AS (peak pressure gradient, 81±22 mmHg; aortic valve area, 0.78±0.25 cm(2)) scheduled for aortic valve replacement were compared with 8 patients (all men; age, 63±3 y; and ejection fraction, 60%±7%) without AS undergoing coronary artery bypass graft surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Under general anesthesia, peak early LV filling (E) and atrial systole (A) blood flow velocities and their corresponding velocity-time integrals were obtained using pulse-wave Doppler echocardiography to determine E/A and atrial filling fraction (β). Mitral valve diameter (D) was calculated as the average of minor and major axis lengths obtained in the midesophageal bicommissural and long-axis transesophageal echocardiography imaging planes, respectively. Posterior wall thickness (PWT) was measured at end-diastole using M-mode echocardiography. VFT was calculated as 4×(1-β)×SV/πD(3), where SV = stroke volume measured using thermodilution. Systemic and pulmonary hemodynamics, LV diastolic function, PWT, and VFT were determined during steady-state conditions 30 minutes before cardiopulmonary bypass. Early LV filling was attenuated in patients with AS (eg, E/A, 0.77±0.11 compared with 1.23±0.13; β, 0.43±0.09 compared with 0.35±0.02; p<0.05 for each). LV hypertrophy was observed (PWT, 1.4±0.1 cm compared with 1.1±0.2 cm; p<0.05) and VFT was lower (3.0±0.9 v 4.3±0.5; p<0.05) in patients with versus without AS. Linear regression analysis showed a significant correlation between VFT and PWT (VFT = -2.57 ×PWT + 6.81; r(2) = 0.345; p = 0.017).

CONCLUSION

The results indicated that pressure-overload hypertrophy produced by AS reduced VFT in patients with normal LV systolic function undergoing aortic valve replacement.

The Association of Left Ventricular Hypertrophy with Intraventricular Dyssynchrony at Rest and during Exercise in Hypertensive Patients

Background

Impaired exercise tolerance with dyspnea is common in hypertensive patients and this may be due to the exaggeration of nonuniform ventricular activation during exercise. So we want to evaluate the effect of left ventricular hypertrophy (LVH) on systolic intraventricular dyssynchrony during exercise.

Methods

A total of 85 patients with hypertension who having exertional dyspnea and 30 control individuals were enrolled. Exercise stress echocardiography was performed using a symptom limited, multistage supine bicycle test. To evaluate the dyssynchrony of left ventricular (LV), we calculated the standard deviation (SD) of the averaged time-to-peak systolic velocity (TPs-SD, ms) of 12 middle and basal LV segments obtained from the three standard apical views at rest and peak exercise.

Results

There was no significant difference in systolic blood pressure (BP) and heart rate between the two groups. TPs-SD was significantly higher in patients with LVH at rest (31.5 ± 12.1 vs. 22.0 ± 12.6 ms, p = 0.002) with exaggeration of the degree at peak exercise (39.0 ± 11.9 vs. 24.6 ± 13.3 ms, p < 0.001). Multiple regression analysis showed LV mass index was independently associated with LV dyssynchrony at peak exercise (β = 0.515, p = 0.001) when controlled for age, sex, and systolic BP at peak exercise.

Conclusion

Intraventricular systolic dyssynchrony during exercise is significantly associated with the degree of LVH in hypertensive patients.

Muscle contraction and force: the importance of an ancillary network, nutrient supply and waste removal

Muscle contraction studies often focus solely on myofibres and the proteins known to be involved in the processes of sarcomere shortening and cross-bridge cycling, but skeletal muscle also comprises a very elaborate ancillary network of capillaries, which not only play a vital role in terms of nutrient delivery and waste product removal, but are also tethered to surrounding fibres by collagen ”wires”. This paper therefore addresses aspects of the ancillary network of skeletal muscle at both a microscopic and functional level in order to better understand its role holistically as a considerable contributor to force transfer within muscular tissue.

Clinical and echocardiographic correlates of plasma procollagen type III amino-terminal peptide levels in the community

BACKGROUND

Left ventricular remodeling is characterized by increased collagen deposition in the extracellular matrix. Levels of plasma procollagen type III amino-terminal peptide (PIIINP), a marker of collagen turnover, are elevated in the setting of recent myocardial infarction, heart failure, and cardiomyopathy. Whether plasma PIIINP levels are a useful indicator of subclinical left ventricular abnormalities in ambulatory individuals has not been studied.

METHODS

We examined 967 Framingham Heart Study participants (mean age, 56 years; 60% women) who underwent routine echocardiography and measurement of plasma PIIINP levels. All participants were free of prior myocardial infarction or heart failure. Multivariable regression analyses were performed to examine the clinical and echocardiographic correlates of PIIINP levels.

RESULTS

Plasma PIIINP levels increased with age and body mass index but did not significantly correlate with other cardiovascular risk factors including hypertension and diabetes. In multivariable models, there was no association between plasma PIIINP levels and left ventricular mass (P = .89), left ventricular fractional shortening (P = .15), left ventricular end-diastolic dimension (P = .51), or left atrial size (P = .68). Plasma PIIINP levels were positively correlated with tissue inhibitor of metalloproteinase-1 levels (multivariable-adjusted, P = .001).

CONCLUSIONS

The use of biomarkers of extracellular matrix turnover has generated recent interest, with plasma PIIINP being the most commonly studied biomarker in acute settings. However, our findings in a large, community-based cohort suggest that plasma PIIINP has limited use for the detection of structural heart disease in ambulatory individuals.

Blockade of the renin-angiotensin-aldosterone system: a key therapeutic strategy to reduce renal and cardiovascular events in patients with diabetes

Diabetes (particularly type 2 diabetes) represents a global health problem of epidemic proportions. Individuals with diabetes are not only more likely to develop hypertension, dyslipidemia, and obesity, but are also at a significantly higher risk for coronary heart disease, peripheral vascular disease, and stroke. Angiotensin II plays a key pathophysiological role in the progression of diabetic renal disease, and blockade of the renin-angiotensin system with angiotensin-converting enzyme inhibitors (ACEi) or angiotensin II antagonists has therefore become an important therapeutic strategy to reduce renal and cardiovascular events in patients with diabetes. Several studies have demonstrated the effects of angiotensin II antagonists on the reduction of albuminuria and the progression of renal disease from microalbuminuria to macroalbuminuria. More importantly, several endpoint trials have shown that the antiproteinuric effects of losartan and irbesartan translate into cardiovascular and renoprotective benefits beyond blood pressure lowering, thereby delaying the need for dialysis or kidney transplantation by several years. These and other studies indicate that angiotensin II antagonists not only improve survival and quality of life of patients with diabetic nephropathy, but also have the potential to reduce the substantial healthcare burden associated with managing these patients. ACEi also appear to exert similar beneficial effects in diabetic patients, but whether clinically significant differences in renoprotection or mortality exist between angiotensin II antagonists and ACEi in patients with type 2 diabetes remains to be fully investigated in appropriate head-to-head studies.

Soy diet worsens heart disease in mice

We report that dietary modification from a soy-based diet to a casein-based diet radically improves disease indicators and cardiac function in a transgenic mouse model of hypertrophic cardiomyopathy. On a soy diet, males with a mutation in the alpha-myosin heavy chain gene progress to dilation and heart failure. However, males fed a casein diet no longer deteriorate to severe, dilated cardiomyopathy. Remarkably, their LV size and contractile function are preserved. Further, this diet prevents a number of pathologic indicators in males, including fibrosis, induction of beta-myosin heavy chain, inactivation of glycogen synthase kinase 3beta (GSK3beta), and caspase-3 activation.

[Quantitative analysis of left ventricular wall motion with MRI tagging]

PURPOSE

The purpose of this study was to establish a quantification of different parameters of left ventricular wall motion from tagged MR images. This evaluation method was to be applied to characterize the physiological contraction cycle and to determine pathophysiological changes.

MATERIALS AND METHODS

Myocardial tagging was performed at a basal, a mid-ventricular and an apical level of the left ventricle. A suitable software was programmed for the automatic quantification of rotation, contraction and circumferential shortening. The evaluation method was used in 8 healthy volunteers, 13 patients suffering from aortic stenosis before and one year after surgery and in 10 patients with myocardial infarction before and after revascularization.

RESULTS

The software allows the quantification of left ventricular wall motion by assessment of rotation, contraction and circumferential shortening. In the healthy volunteers, there was a wringing motion with opposite rotation of base and apex of the heart. Before valve replacement, patients with aortic stenosis showed significantly increased apical rotation and torsion. One year after surgery, left-ventricular torsion had normalized. In patients with myocardial infarction, circumferential shortening increased after revascularization.

CONCLUSION

The quantification of left ventricular wall motion using tagged MR images allows to characterize and follow-up changes of left ventricular wall motion in various diseases of the heart.

The fibrous matrix of ventricular myocardium in hypoplastic left heart syndrome: a quantitative and qualitative analysis

BACKGROUND

Controversy exists as to whether the right ventricle will be able to cope as the sole pumping chamber following a univentricular repair of hypoplastic left heart syndrome. The significance of the collagenous matrix on ventricular function has been studied extensively yet there is little information available on its quantity and quality in hypoplastic left heart syndrome.

METHODS

We selected 23 specimens with hypoplastic left heart syndrome for anatomical study. Using a combination of morphometric analysis and scanning electron microscopy we analyzed the quantity and quality of the collagenous matrix. We compared the results with 16 age-matched controls.

RESULTS

Hearts with hypoplastic left heart syndrome have significantly less collagen matrix than normal. The right ventricle has more collagen than the left and there is significant transmural variation. There was no difference in the ratio of the two main collagen subtypes or in the quality of the matrix.

CONCLUSIONS

We believe this difference in fibrous matrix to be an inherent abnormality intrinsic to the malformation affecting not only the hypoplastic left but also the "normal" right ventricle. This in turn may have significant implications for the expected long-term outcome of reconstructive surgery.

Low-dose ACE with alpha- or beta-adrenergic receptor inhibitors have beneficial SHR cardiovascular effects

BACKGROUND

There are no data regarding the prolonged effect of alpha-1 adrenergic receptor antagonists on ventricular collagen content and coronary hemodynamics in spontaneously hypertensive rats (SHR). This study, therefore, was designed to determine the effects of chronic treatment with the alpha-1 adrenergic receptor inhibitor doxazosin on SHR systemic and regional (especially coronary) hemodynamics, cardiovascular mass, and ventricular collagen. The effects of the combination of doxazosin with low-dose angiotensin-converting enzyme inhibitor were studied versus the alpha-1 antagonist alone. These effects were compared with those of a beta-1 adrenergic receptor inhibitor.

METHODS AND RESULTS

Systemic and regional hemodynamics (radionuclide-labeled microspheres), left and right ventricular weight, hydroxyproline concentration, and aortic weight were measured at age 35 weeks. Doxazosin reduced arterial pressure and total peripheral resistance without changing left ventricular mass and collagen content, whereas monotherapies with the beta-1 antagonist metoprolol or a subdepressor dose of the ACE inhibitor enalapril were effective in reducing left ventricular mass and hydroxyproline without altering pressure. Doxazosin combined with the same low-dose ACE inhibitor reduced left ventricular mass and hydroxyproline without potentiating the hypotensive effect of doxazosin. By contrast, the combination of beta-1 antagonist with the low-dose ACE inhibitor reduced pressure, unlike either agent alone. Aortic weight index was significantly reduced only by doxazosin whether when used alone or with the ACE inhibitor. Low-dose ACE inhibitor with doxazosin or the beta-1 receptor antagonist as well as doxazosin alone decreased renal vascular resistance.

CONCLUSION

These data show that the low subdepressor dose ACE inhibitor with an alpha- or beta-adrenergic receptor antagonist provides beneficial cardiovascular effects in SHR.

Relaxation in hypertrophic cardiomyopathy and hypertensive heart disease: relations between hypertrophy and diastolic function

AIM

To determine the relation between the extent and distribution of left ventricular hypertrophy and the degree of disturbance of regional relaxation and global left ventricular filling.

METHODS

Regional wall thickness (rWT) was measured in eight myocardial regions in 17 patients with hypertrophic cardiomyopathy, 12 patients with hypertensive heart disease, and 10 age matched normal subjects, and an asymmetry index calculated. Regional relaxation was assessed in these eight regions using regional isovolumetric relaxation time (rIVRT) and early to late peak filling velocity ratio (rE/A) derived from Doppler tissue imaging. Asynchrony of rIVRT was calculated. Doppler left ventricular filling indices were assessed using the isovolumetric relaxation time, the deceleration time of early diastolic filling (E-DT), and the E/A ratio.

RESULTS

There was a correlation between rWT and both rIVRT and rE/A in the two types of heart disease (hypertrophic cardiomyopathy: r = 0.47, p < 0.0001 for rIVRT; r = -0.20, p < 0.05 for rE/A; hypertensive heart disease: r = 0.21, p < 0.05 for rIVRT; r = -0.30, p = 0.003 for rE/A). The degree of left ventricular asymmetry was related to prolonged E-DT (r = 0. 50, p = 0.001) and increased asynchrony (r = 0.42, p = 0.002) in all patients combined, but not within individual groups. Asynchrony itself was associated with decreased E/A (r = -0.39, p = 0.01) and protracted E-DT (r = 0.69, p < 0.0001) and isovolumetric relaxation time (r = 0.51, p = 0.001) in all patients. These correlations were still significant for E-DT in hypertrophic cardiomyopathy (r = 0.56, p = 0.02) and hypertensive heart disease (r = 0.59, p < 0.05) and for isovolumetric relaxation time in non-obstructive hypertrophic cardiomyopathy (n = 8, r = 0.87, p = 0.005).

CONCLUSIONS

Non-invasive ultrasonographic examination of the left ventricle shows that in both hypertrophic cardiomyopathy and hypertensive heart disease, the local extent of left ventricular hypertrophy is associated with regional left ventricular relaxation abnormalities. Asymmetrical distribution of left ventricular hypertrophy is indirectly related to global left ventricular early filling abnormalities through regional asynchrony of left ventricular relaxation.

Myocardial fibrosis in transforming growth factor beta(1)heterozygous mice

Aging is associated with an increase in myocardial extracellular matrix components and contractile dysfunction. Transforming growth factor- beta(1)(TGF- beta(1)) has been shown to regulate expression of collagen genes and extracellular matrix component synthesis in the heart, and may contribute to the increase in myocardial fibrosis with aging. Therefore, we examined whether TGF- beta(1)heterozygous mutant mice would exhibit less age-associated myocardial fibrosis than normal mice. Twelve heterozygous TGF- beta(1)(+/-) deficient mice and 26 wild-type controls were examined to determine if there was a difference in development of myocardial fibrosis or mortality at 24 months of age due to the loss of one TGF- beta(1)allele. Animals which survived to 24 months of age were killed, and morphometric and functional studies were performed in isolated perfused hearts and in hearts from 6 month old control mice. Pressure-volume relations of the LV were assessed in the isovolumic (balloon in LV) Langendorff preparation. Eleven of 12 (92%) TGF- beta(1)deficient mice survived to 24 months of age in comparison to 66% (12/18) age-matched controls (P<0.05). Hearts from the 24 month old TGF- beta(1)deficient mice exhibited a decrease in myocardial fibrosis (4+/-1 v. 10+/-1% average LV fibrosis in TGF- beta(1)(+/-) and age-matched controls, respectively (P<0.05) and greater compliance (i.e.,lower LV end-diastolic pressure at a given balloon volume), decreased myocardial stiffness, and shorter contractile duration in comparison to 24-month-old wild-type controls. This suggests that modulation of collagen production and/or degradation by TGF- beta(1)may contribute to changes in myocardial structure and function with age. Thus, loss of one TGF- beta(1)allele appears to ameliorate age associated myocardial fibrosis and improve LV compliance, which may contribute to increased survival over the life span of these mice.

Mechanisms of desensitization to a PDE inhibitor (milrinone) in conscious dogs with heart failure

The goal of this study was to determine the extent to which the effects of milrinone were desensitized in heart failure (HF) and to determine the mechanisms, i.e., whether these effects could be ascribed to changes in cAMP or phosphodiesterase (PDE) activity in HF. Accordingly, we examined the effects of milrinone in seven conscious dogs before and after HF was induced by rapid ventricular pacing at 240 beats/min. The dogs were chronically instrumented for measurements of left ventricular (LV) pressure and first derivative of LV pressure (dP/dt), arterial pressure, LV internal diameter, and wall thickness. Milrinone (10 micrograms . kg-1. min-1 iv) increased LV dP/dt by 1,854 +/- 157 from 2,701 +/- 105 mmHg/s (P < 0.05) before HF. After HF the increase in LV dP/dt in response to milrinone was attenuated significantly (P < 0.05); it increased by 615 +/- 67 from 1,550 +/- 107 mmHg/s, indicating marked desensitization. In the presence of ganglionic blockade the increases in LV dP/dt (+445 +/- 65 mmHg/s) in response to milrinone were markedly less (P < 0.01), and milrinone increased LV dP/dt even less in HF (+240 +/- 65 mmHg/s). cAMP and PDE activity were measured in endocardial and epicardial layers in normal and failing myocardium. cAMP was decreased significantly (P < 0.05) in LV endocardium (-26%) but not significantly in LV epicardium (-14%). PDE activity was also decreased significantly (P < 0.05) in LV endocardium (-18%) but not in LV epicardium (-4%). Thus significant desensitization to milrinone was observed in conscious dogs with HF. The major effect was autonomically mediated. The biochemical mechanism appears to be due in part to the modest reductions in PDE activity in failing myocardium, which, in turn, may be a compensatory mechanism to maintain cAMP levels in HF. Reductions in cAMP and PDE levels were restricted to the subendocardium, suggesting that the increased wall stress and reduced coronary reserve play a role in mediating these changes.

Collagenous skeleton of the human mitral papillary muscle

The papillary muscles (PM) of the heart have been the subject of numerous structural and functional studies. However, despite the importance of the collagenous compartment of the heart in the mechanical and electrical properties of the myocardium, little information is available on the structural organization of collagen within the PM. We study here the structural organization of collagen within the mitral papillary muscles (PM) of the human heart. Fragments of human mitral PM from normal and hypertensive subjects were macerated in NaOH to eliminate the cellular components. Macerated and nonmacerated samples were then studied with the scanning electron microscope (SEM). SEM shows that cardiac myocytes and endomysial capillaries are ensheathed in a layer of collagenous tissue. The myocyte sheath wall is formed by thin collagen fibers oriented at right angles to the main cell axis. These sheaths are open structures, collagen fibers continuing into adjacent sheaths at the points of lateral communications. Thick perimysial septa do not divide the PM tissue into separate compartments. Hypertensive hearts show perivascular and interstitial fibrosis. In addition, the lumen of the coronary vessels is reduced or obliterated, and large areas of the myocardium are substituted by densely packed collagen. Endomysial sheaths constitute a continuous collagenous layer that replicates the myocyte network. The endomysium should play a complex role in myocardial mechanics, assuring the equal distribution of force during the cardiac cycle. The absence of insulating boundaries should facilitate lateral propagation of excitation. Fibrosis in hypertensive hearts appears to be both reactive and reparative. The increase in the amount of collagen should greatly impair contractile capabilities and electrical conductance, severely compromise heart function, and contribute to development of heart failure.

Effect of myocardial hypertrophy on systolic and diastolic function in children: insights from the force-frequency and relaxation-frequency relationships

OBJECTIVE

The objective of this study was to evaluate the effect of myocardial hypertrophy on systolic and diastolic properties of the left ventricle in children.

BACKGROUND

In children with myocardial hypertrophy, ejection phase indices are invariably increased. However, indices of force-generation, e.g., end-systolic elastance and invasive indices of diastolic properties, have been studied infrequently in children with myocardial hypertrophy.

METHODS

We studied 10 children with congenital aortic stenosis or coarctation of aorta and nine control patients. Systolic properties were assessed from shortening fraction, end-systolic fiber elastance (Ef(es)) measured at resting heart rates, and force-frequency relationship measured at heart rates increasing from 110 to 160 beats per minute. Diastolic properties were assessed from time constant of relaxation (tau) at matched heart rates, chamber stiffness constant, myocardial stiffness constant, and relaxation-frequency relationship measured at gradually increasing heart rates.

RESULTS

Ef(es) remained unchanged by myocardial hypertrophy, however, tau was prolonged (tauL: 27.3+/-2.3 vs. 21.8+/-2.2 ms, p < 0.001; and tauD: 43.2+/-3.1 vs. 34.3+/-3.3 ms, p < 0.001). Both chamber and myocardial stiffness constants remained unchanged. Incremental increases in heart rate produced incremental improvement in both contraction and relaxation. Slopes of force-frequency and relaxation-frequency relationships remained unchanged in the experimental group. However, the relaxation-frequency relationship manifested a parallel shift upward.

CONCLUSIONS

In conscious, sedated children with myocardial hypertrophy, systolic function assessed by an index of force generation remains unchanged. However, relaxation is prolonged but passive diastolic properties remain unaffected. The combined effect of hypertrophy and heart rate does not alter the force-frequency and relaxation-frequency relationships.

Preserved Frank-Starling mechanism in human end stage heart failure

OBJECTIVE

The goal of the present study was to examine the ability of failing myocardium to respond to enhanced preload with an increase in force development.

METHODS

The effect of various preload conditions (2.5-15 mN) on force development was studied in right ventricular trabeculae carneae from explanted human failing hearts with ischemic cardiomyopathy (ICM, n = 5, 42 preparations) or idiopathic dilated cardiomyopathy (DCM, n = 9, 77 preparations). To determine the severity of cardiac impairment we measured the positive inotropic effect of beta-adrenoceptor stimulation and calcium (ISO/Ca2+ ratio) and the expression of atrial natriuretic peptide (ANP) mRNA in all hearts.

RESULTS

(1) Force of contraction increased with stepwise augmentation of preload (length at 2.5 mN preload to length of maximal force development) from 3.7 +/- 0.5 (ICM) and 2.7 +/- 0.4 (DCM) to 8.3 +/- 0.9 and 6.5 +/- 0.8 mN/mm2, respectively (p < 0.05). (2) The ISO/Ca2+ ratio was 0.40 +/- 0.04 (ICM) and 0.35 +/- 0.03 (DCM), respectively. (3) ANP mRNA was expressed in all preparations, albeit at greatly varying levels (ICM 22.5 +/- 6.1 and DCM 18.7 +/- 4.7 normalized arbitrary units). (4) Contraction experiments performed in left ventricular tissue (n = 3, 32 preparations) essentially confirmed the results.

CONCLUSION

The Frank-Starling mechanism is preserved in terminally failing human hearts irrespective of the underlying etiology. We found no relation between the severity of cardiac impairment as assessed by either ANP expression or the ISO/Ca2+ ratio and the ability of failing human myocardium to respond to enhanced preload with an increase in force development.

Assessment of myocardial fibrosis in cardiomyopathic hamsters with gadolinium-DTPA enhanced magnetic resonance imaging

RATIONALE AND OBJECTIVES

The authors investigated whether magnetic resonance (MR) imaging enhanced with gadolinium (Gd)-DTPA would be useful for assessment of myocardial fibrosis in cardiomyopathy.

METHODS

The authors compared MR images of the excised heart after Gd-DTPA injection with histopathologic findings in 33 hamsters with cardiomyopathy of the Bio 14.6 strain and 26 healthy hamsters of various age groups and assessed localization of Gd-14C-DTPA by autoradiography in the myocardium of three hamsters with cardiomyopathy.

RESULTS

The mean signal intensity ratios for the entire myocardium in hamsters with cardiomyopathy relative to that in healthy hamsters was significantly higher in a younger age group than in an older age group (1.30+/-0.09 versus 1.03+/-0.08, P < 0.001, respectively). This myocardial enhancement was more obvious in areas containing massive fibrosis in the early and mid stages than in the late stage. Autoradiograms of hamsters with cardiomyopathy showed patchy or linear increases in uptake, corresponding to the areas of myocardial fibrosis. Gadolinium-14C-DTPA radioactivity ratios of myocardial fibrosis to healthy myocardium were significantly higher in the early and mid stages than in the late stage (P < 0.01).

CONCLUSIONS

Myocardial fibrosis with high cellularity and proliferation of vessels was delineated as an area enhanced with Gd-DTPA on MR images, and its signal intensity decreased with the late stage of myocardial fibrosis.

Role of left ventricular hypertrophy in diastolic dysfunction in aged hypertensive patients

OBJECTIVE

To evaluate the influence of left ventricular hypertrophy (LVH) on the diastolic dysfunction in older hypertensive patients.

METHODS

In total 665 patients (58% men, 61% White, aged 55-80 years) with mild-to-moderate essential hypertension underwent Doppler echocardiography. Data included left ventricular dimensions, left ventricular mass index, body mass index, E- and A-wave mitral flow velocities, E:A ratio, deceleration time > 150 ms), impaired relaxation (E:A ratio < 1.0, prolonged deceleration time according to age), and restrictive physiology (E:A ratio > 2.1, deceleration time < 150 ms)]. Data were distributed according to age (50-59, 60-69, and 70-80 years).

RESULTS

The overall prevalence of sex-adjusted LVH in this study was 65%. When we compared hypertensive patients with and without LVH, the E- and A-wave velocities, E:A ratio, and deceleration time were similar. Moreover, the prevalences of normal, impaired relaxation, and restrictive physiology patterns among patients with and without LVH did not differ significantly (20, 79.5, and 0.5 versus 24, 75.5, and 0.5%). When the mitral flow patterns were adjusted according to age, the impaired relaxation pattern increased further with age (to 73% during the fifth decade, 83% during the sixth decade, and 88% during the seventh decade).

CONCLUSIONS

LVH is not an independent factor associated with abnormal flow patterns in hypertensive patients aged over 50 years with normal systolic contractility. The impaired relaxation is the predominant pattern of diastolic dysfunction in older hypertensive patients and increases further with aging.

Diastolic properties in canine hypertensive left ventricular hypertrophy: effects of angiotensin converting enzyme inhibition and angiotensin II type-1 receptor blockade

OBJECTIVE

Angiotensin II has been suggested to be involved in the pathogenesis of diastolic dysfunction in left ventricular hypertrophy (LVH). The purpose of this study was to asses the effects of enalaprilat and L-158,809, an angiotensin II type-1 receptor antagonist, on LV diastolic function in 16 normal control dogs and 20 LVH dogs with perinephritic hypertension.

METHODS

LV hemodynamics was studied before and after intravenous injection of enalaprilat (0.25 mg/kg) or L-158,809 (0.3 mg/kg). The hemodynamic data were analyzed in relation to the changes in myocardial blood flow (measured by radioactive microspheres) and in the circulating angiotensin II and norepinephrine levels.

RESULTS AND CONCLUSIONS

At baseline, significant increases were observed for LV/body weight ratio as well as LV systolic and end-diastolic pressure in the LVH dogs (all P < 0.01 vs. the control group). In addition, LV relaxation time constant was prolonged and the chamber and myocardial stiffness constants were increased (P < 0.01) in the LVH dogs, suggesting an impairment of LV diastolic function. Administration of enalaprilat or L-158,809 improved LV stiffness constants in the LVH dogs (P < 0.05). The diastolic LV pressure-diameter relation shifted downwards in the LVH dogs whereas diastolic distensibility was not altered in the control dogs. Although the circulating angiotensin II levels were significantly decreased by enalaprilat in the LVH dogs, they did not correlate with the changes in the stiffness constants. Furthermore, the alterations of LV diastolic properties in the LVH group could not be attributed to myocardial perfusion, which was rather decreased by administration of enalaprilat and L-158,809. These results suggest that angiotensin II, particularly at the local level, is involved in the pathogenesis of diastolic dysfunction in pressure-overload LVH. The data also support the concept that ACE inhibitors and angiotensin II receptor blockers are potentially beneficial in the treatment of the hypertrophied heart.

M-mode echocardiography in aortic stenosis. Clinical correlates and prognostic significance after valve replacement

To relate preoperative findings at M-mode echocardiography to preoperative clinical and haemodynamic status and to identify possible echocardiographic risk factors for mortality after aortic valve replacement (AVR), 250 patients with AVR for aortic stenosis (AS) were studied. In follow-up averaging 3.2 years there were 22 early (< 30 days) and 23 late deaths. Rising NYHA function class and cardiothoracic index, and left ventricular (LV) failure were related to rising LV end-diastolic and end-systolic diameter index (EDDI, ESDI), and to increasing LV muscle mass index and decreasing fractional shortening (FS). High peak-to-peak systolic aortic valve gradient and LV end-systolic pressure were related to small dimensions of LV with increased FS and posterior wall thickness (PWTh). EDDI < or = 20 mm/m2 and increasing PWTh were independent risk factors for early mortality. Patients with EDDI < or = 20 mm/m2 had normal or supranormal FS. PWTh was the only independent risk factor in long-term survival: 5-year rates being 81 +/- 6%, 94 +/- 3% and 85 +/- 7% for PWTh < or = 13, 14-17 and > or = 18 mm, respectively (p = 0.03). Prevalence of concomitant coronary artery disease (CAD) rose with decreasing PWTh. Angina pectoris in non-CAD patients was related to very high PWTh. Subnormal EDDI was associated with poor surgical outcome, and dilated, poorly contracting LV with congestive heart failure prior to AVR. The degree of LV hypertrophy seemed to be the dominant risk factor, but confounders included myocardial ischaemia due to CAD in low-grade hypertrophy or to hypertrophy per se. A hypothetically confounding factor is the reversibility potential of moderate or severe LV hypertrophy following AVR.

Collagen content in normal, pressure, and pressure-volume overloaded developing human hearts

Increased myocardial collagen accompanies pressure overload of the adult left ventricle. This phenomenon is poorly understood in infants. This study compares the myocardial volume fraction of collagen in infants who did not have primary heart disease with infants with isolated pressure overload of the right ventricle (tetralogy of Fallot [ToF]), and with infants with combined volume and pressure overload (aortic valve atresia [AVA]). The distribution of collagen in the neonatal myocardium was also determined. We measured the volume fraction of collagen from right ventricular biopsy specimens of cadaver hearts in normal infants (1 to 9 months old; n = 7), infants with ToF (1 day to 9 months old; n = 9), newborns with AVA (AVA-NB) (1 to 4 days old; n = 5), and older patients with AVA (AVA-I) (5 to 8 months old; n = 5). Myocardium from 3 patients undergoing repair of ToF (6 to 8 months old) was also analyzed. Specimens were stained with Masson's trichrome and myocardial volume fraction of collagen determined by point counting. Myocardial volume fraction of collagen was significantly higher (p = 0.02) in AVA-I patients (8.0 +/- 3.5%) versus normal (3.3 +/- 2.7%), ToF (3.2 +/- 1.8%), and AVA-NB (3.5 +/- 2.3%) patients. There was a tendency for increased collagen in the subendocardium, especially in AVA-I patients (p > 0.05). We conclude that patients with AVA-I have increased collagen relative to normal subjects, patients with ToF, and patients with AVA-NB, and that this increase is greatest in the subendocardium.

Toward the biochemical assessment of myocardial fibrosis in hypertensive patients

The serum concentrations of amino-terminal procollagen type III and carboxy-terminal procollagen type I-derived peptides, which have been proposed as useful markers of the tissue synthesis of collagen types III and type I, respectively, were abnormally increased in patients with essential hypertension and became normal after angiotensin-converting enzyme (ACE) inhibition. An association was found between baseline serum concentrations of these peptides and left ventricular hypertrophy, diastolic dysfunction, and ventricular arrhythmias in hypertensive patients. On the other hand, increased serum concentration of the carboxy-terminal procollagen type I-derived peptide was found in spontaneously hypertensive rats compared with normotensive Wistar-Kyoto control rats. An association was found between the serum concentration of this peptide and the extent of myocardial fibrosis and the hydroxyproline concentration in the left ventricle of spontaneously hypertensive rats. It is proposed that procollagen-derived peptides in serum may be markers of exaggerated collagen tissue synthesis involved in hypertensive myocardial fibrosis.

The cardiac structure-function relationship and the renin-angiotensin-aldosterone system in hypertension and heart failure

According to the Framingham Study, arterial hypertension and coronary artery disease are the major etiologic factors in the development of heart failure. Regulatory systems that may affect heart failure include the Frank-Starling mechanism, neurohormonal responses, cardiac growth and peripheral oxygen delivery. Recently, the interrelationship between the neuroendocrine system and cardiac growth has aroused much interest. In the pressure- or volume-overloaded heart, hypertrophic growth of the myocardium includes the enlargement of cardiac myocytes, an adaptation governed by ventricular loading. Nonmyocyte cell growth involving cardiac fibroblasts may also occur but is not primarily regulated by the hemodynamic load. Cardiac fibroblast activation is responsible for the accumulation of fibrillar type I and type III collagens within the interstitium and adventitia of intramyocardial coronary arteries, while vascular smooth muscle cell growth accounts for the medial thickening of these vessels. This remodeling of the cardiac interstitium is a major determinant of pathological hypertrophy in that it accounts for abnormal myocardial stiffness and impaired coronary vasodilator reserve, leading to ventricular diastolic and systolic dysfunction and, ultimately, symptomatic heart failure. Several lines of evidence suggest that the renin-angiotensin-aldosterone system is involved in regulating the structural remodeling of the nonmyocyte compartment; this accounts for the cardioprotective effects of angiotensin converting enzyme (ACE) inhibition, which prevents myocardial fibrosis in rats with renovascular hypertension. In rats with genetic hypertension, established left ventricular hypertrophy, abnormal diastolic stiffness due to interstitial fibrosis and reduced coronary vasodilator reserve associated with medial wall thickening of intramyocardial resistance vessels, the ACE inhibitor lisinopril restored myocardial structure and function towards normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Diastolic heart function--pathophysiology, characterization, and therapeutic approaches

In recent years diastolic cardiac function has attracted increasing attention since parameters of diastolic function were found to be altered earlier or more specifically than parameters of systolic function. Diastolic cardiac function is determined by both active (muscular relaxation, redistribution of calcium, synchronization, etc.) and passive (myocardial structure, fibrosis, etc.) factors. As a consequence, a comprehensive assessment of diastolic cardiac function cannot be based on one single parameter. For a complete analysis of diastolic function it is necessary to perform invasive diagnostic procedures involving the measurement of atrial and ventricular pressures, as well as the registration of volume changes with a high time resolution. In addition, it is necessary to measure wall thickness and ventricular configuration, so that apart from filling parameters the stress-strain relationship can be obtained. Noninvasive techniques (Doppler echocardiography, radionuclear ventriculography, apexcardiography) may suggest alterations in diastolic function as well. They ought to be complemented by additional diagnostic procedures (pulmonary pressure, stress testing, etc.). Therapy must consider potentially harmful effects on diastolic function parameters, particularly if changes in myocardial oxygen consumption may result (heart rate, parietal wall stress). Calcium antagonists (verapamil, diltiazem, nifedipine), phosphodiesterase inhibitors (milrinone), beta-adrenergic agonists and antagonists with vasodilating effects (e.g., celiprolol) all have beneficial effects on diastolic myocardial function. A range of diastolic function parameters is being reviewed in the following paper. Their role in the estimation of cardiac function and their responsiveness to therapy in hypertrophy, cardiomyopathy, and coronary heart disease is being discussed.

Diminished contractile response to increased heart rate in intact human left ventricular hypertrophy. Systolic versus diastolic determinants

BACKGROUND

Experimental studies indicate that in addition to diastolic dysfunction, hypertrophied myocardium can display depressed contractile responses, particularly at rapid heart rates, compounding reserve limitations. This study tests whether such abnormalities exist in intact human subjects at physiological paced rates and, if so, whether they are linked to simultaneous rate-dependent deterioration in diastolic function.

METHODS AND RESULTS

Ten subjects with left ventricular hypertrophy (LVH) and 8 normal control subjects were studied. Most LVH patients presented with dyspnea and/or pulmonary edema and had concentric hypertrophy. Since rapid pacing simultaneously alters cardiac filling volumes and pressures, pressure-volume relation analysis was used to better define changes in contractile response. Patients were instrumented with a conductance catheter and micromanometer for pressure-volume data recording and a balloon occluder at the right atrial-inferior vena caval junction to vary filling and thus generate function relations. Data were obtained at baseline and at three atrial pacing rates (100, 120, 150 min-1). In addition, single-beat force-interval data were used to indirectly examine calcium cycling kinetics. LVH subjects demonstrated baseline diastolic abnormalities, including prolonged relaxation, elevated end-diastolic pressure, and reduced chamber compliance. However, systolic function was similar to that in control subjects. With rapid pacing, normal subjects displayed a positive contractile response, whereas this was markedly diminished in LVH subjects. With abrupt termination of pacing and return to slower sinus rhythm, LVH subjects displayed greater initial potentiation followed by a more rapid decline than control subjects, suggesting abnormalities of calcium handling. Despite contractile abnormalities, diastolic function did not further deteriorate with rapid pacing and thus did not appear to be tightly linked to the systolic changes.

CONCLUSIONS

Pacing stress in intact human LVH can result in systolic impairment superimposed on preexisting but not worsened diastolic dysfunction. Abnormal calcium handling probably contributes prominently to this response.

Left ventricular diastolic dysfunction late after coarctation repair in childhood: influence of left ventricular hypertrophy

OBJECTIVES

Left ventricular systolic and diastolic function were evaluated late after successful operation for aortic coarctation in childhood.

BACKGROUND

Persistent arterial hypertension and left ventricular hypertrophy after coarctation repair might impair left ventricular function.

METHODS

Biplane angiography and simultaneous high fidelity pressure measurements were performed in 12 patients 3 to 12 years postoperatively (residual pressure gradient 4 mm Hg). Eight patients were normotensive and four had borderline hypertension. Data at rest and after nitroprusside infusion (1.7 micrograms/kg per min) were evaluated and compared with data from 12 control subjects.

RESULTS

Systolic left ventricular function (ejection fraction-end-systolic wall stress relation) was normal in all patients. However, left ventricular muscle mass (113 vs. 86 g/m2), right atrial pressure (5.2 vs. 1.9 mm Hg) and left ventricular end-diastolic pressure (16 vs. 11 mm Hg) were significantly higher in patients than in control subjects. There was a linear relation between muscle mass and left ventricular end-diastolic (r = 0.66, p < 0.001) or right atrial (r = 0.60, p < 0.01) pressure. Left ventricular relaxation and myocardial stiffness were normal. However, there was an upward shift of the diastolic pressure-volume curve when compared with control values, but this shift was reversed by the administration of nitroprusside.

CONCLUSIONS

Systolic function is normal late after coarctation repair. However, diastolic function can be abnormal with an upward shift of the diastolic pressure-volume curve that is reversed by nitroprusside administration and is probably due to residual left ventricular hypertrophy.

Changes in diastolic function during development and correction of chronic LV volume overload produced by mitral regurgitation

BACKGROUND

Mitral regurgitation (MR) causes an augmentation in left ventricular (LV) diastolic function, increasing early diastolic filling rate and decreasing LV stiffness. Whether these changes in diastolic function persist, return to normal, or become abnormal after mitral valve replacement (MVR) is unknown.

METHODS AND RESULTS

Simultaneous LV echocardiography and catheterization studies were performed in six dogs in the baseline state (baseline), 3 months after creation of MR (chronic MR), and 3 months after MVR. Chronic MR caused LV dilation (end-diastolic dimension increased from 4.5 +/- 0.1 cm in baseline to 5.8 +/- 0.1 cm in chronic MR, p < 0.05) and eccentric LV hypertrophy (LV-to-body weight ratio increased from 3.6 +/- 0.2 g/kg in baseline to 4.9 +/- 0.4 g/kg in chronic MR, p < 0.05). Chronic MR caused an increase in LV early diastolic filling rate (peak rate of increase in minor-axis dimension increased from 11 +/- 1 cm/sec in baseline to 18 +/- 1 cm/sec in chronic MR, p < 0.05), did not change the time constant of myocardial relaxation (tau was 31 +/- 4 msec in baseline and 30 +/- 2 msec in chronic MR), and caused a decrease in the modulus of regional chamber stiffness from 7.7 +/- 1.2 in baseline to 2.4 +/- 0.03 in chronic MR, p < 0.05. MVR caused the resolution of LV dilation (end-diastolic dimension returned to normal [4.8 +/- 0.2 cm]), but three months after MVR, regression of LV hypertrophy was incomplete (LV-to-body weight ratio remained elevated [4.4 +/- 0.5 g/kg]). After MVR, LV early diastolic filling rate (8 +/- 1 cm/sec), the relaxation time constant (31 +/- 2 msec), chamber stiffness (7.1 +/- 1.8), myocardial stiffness (11.2 +/- 3.1), and LV end-diastolic pressure (8 +/- 1 mm Hg) returned to normal.

CONCLUSIONS

The enhanced diastolic function seen in chronic MR returned to normal after correction of the chronic volume overload by MVR.

Effect of captopril on the prevention and regression of myocardial cell hypertrophy and interstitial fibrosis in pressure overload cardiac hypertrophy

This article reports on the effects of captopril on both the prevention and the regression of myocardial cell hypertrophy and interstitial fibrosis in experimental animals (rats) with pressure overloaded hearts. Constriction of the abdominal aorta just below the diaphragm during periods of 20 days (prevention experiment) and 40 days (regression experiment) resulted in hypertension and cardiac hypertrophy. In the prevention experiment, captopril was able to inhibit the development of high blood pressure levels and cardiac hypertrophy in aortic-constricted rats. Similarly, the treatment of sham-operated rats with captopril led to a reduction in the weight of the heart and in the myocyte diameter compared with controls. The myocyte volume fraction of the left ventricles of both aortic-constricted and sham-operated animals that were treated with captopril was significantly diminished compared with that of the control group. The interstitial collagen volume fraction of all experimental groups was elevated as compared with the control group. As a consequence, the ratios of myocytes to interstitial collagen in groups of aortic-constricted rats, aortic-constricted rats that were treated with captopril, and sham-operated rats that were treated with captopril were reduced compared with the control group; that is, although captopril was able to prevent myocardial cell hypertrophy after aortic constriction, it could not prevent the maintenance of a normal ratio of myocytes to interstitial collagen, which was due to increased collagen volume fraction. In the regression experiment, captopril lowered high blood pressure levels and augmented heart weights to control values. The mean myocyte transverse diameter in aortic-constricted rats that were treated with captopril was significantly smaller than that of controls.(ABSTRACT TRUNCATED AT 250 WORDS)

The hypertrophied myocardium and coronary disease. Structural changes in patients submitted to aortocoronary bypass surgery

Seventeen patients with coronary disease submitted to myocardial revascularization were studied. Ten patients had a hypertrophied ventricle, and 7 had normal ventricular mass. Myocardial biopsies were obtained before ischemia and at the time of reperfusion and were assessed for: volume fraction of fibrous tissue, myocyte diameter, morphometric mitochondrial studies and ultrastructural changes. The volume fraction of fibrous tissue in patients with hypertrophied ventricle was 1.9 +/- 0.04, and in patients with normal ventricular mass was 0.9 +/- 0.01 (p less than 0.05). The diameter of the myocyte was 23 +/- 0.3 microns and 18 +/- 1.2 microns for patients with hypertrophied and normal ventricular mass, respectively (p less than 0.01). The value of volumetric density for pre-ischemia samples in patients with a hypertrophied ventricle was 23 +/- 2.2 and in patients with normal ventricular mass was 35 +/- 2.7 (p less than 0.02). Grades 3 and 4 of damaged mitochondria were significantly increased in reperfusion samples from patients with a hypertrophied ventricle compared to pre-ischemia samples. Collagen growth was increased in hypertrophied hearts which were also more sensitive to the ischemia/reperfusion mechanism.

Alterations in left ventricular diastolic function in conscious dogs with pacing-induced heart failure

We investigated in conscious dogs (a) the effects of heart failure induced by chronic rapid ventricular pacing on the sequence of development of left ventricular (LV) diastolic versus systolic dysfunction and (b) whether the changes were load dependent or secondary to alterations in structure. LV systolic and diastolic dysfunction were evident within 24 h after initiation of pacing and occurred in parallel over 3 wk. LV systolic function was reduced at 3 wk, i.e., peak LV dP/dt fell by -1,327 +/- 105 mmHg/s and ejection fraction by -22 +/- 2%. LV diastolic dysfunction also progressed over 3 wk of pacing, i.e., tau increased by +14.0 +/- 2.8 ms and the myocardial stiffness constant by +6.5 +/- 1.4, whereas LV chamber stiffness did not change. These alterations were associated with increases in LV end-systolic (+28.6 +/- 5.7 g/cm2) and LV end-diastolic stresses (+40.4 +/- 5.3 g/cm2). When stresses and heart rate were matched at the same levels in the control and failure states, the increases in tau and myocardial stiffness were no longer observed, whereas LV systolic function remained depressed. There were no increases in connective tissue content in heart failure. Thus, pacing-induced heart failure in conscious dogs is characterized by major alterations in diastolic function which are reversible with normalization of increased loading condition.

Hemodynamic performance and myosin light chain-1 expression of the hypertrophied left ventricle in aortic valve disease before and after valve replacement

Previously, we have reported on the selective accumulation of an atrial-like myosin light chain-1 (ALC1) in different forms of human ventricular hypertrophy. The present study involves the determination of ALC1 content in a control group and in patients with aortic stenosis or insufficiency before and 56 +/- 23 months after valve replacement and compares the hemodynamic and angiographic parameters. ALC1 was quantified densitometrically after two-dimensional electrophoretic resolution of biopsy specimens from the left ventricle and was expressed in percent of total ventricular light chain-1. The mean ALC1 content was 11.2 +/- 9.2% in preoperative aortic stenosis and 4.5 +/- 1.4% in aortic insufficiency, both being significantly (p less than 0.001) higher than the control value of 0.3 +/- 0.3%. After valve replacement, mean ALC1 content was lower than before, 4.2 +/- 3.3% (p less than 0.05) in stenosis and 3.4 +/- 3.1% (p = NS) in insufficiency. Left ventricular systolic pressure yields a significant (p less than 0.01) linear correlation (r = 0.45) with the ALC1 content in all preoperative and postoperative patients. Patient group averages of ALC1 content correlate directly with left ventricular systolic and end-diastolic pressure and wall thickness (r = 0.94-0.98) and, in an exponential fashion, with peak systolic circumferential wall stress (r = 0.98) but not with muscle mass or any other parameter. The ventricular ALC1 binds to myosin in proportion to its occurrence in the myocardium. The content of the endogenous ventricular light chain-1 did not change under pathological hemodynamics. The response in expression of the ALC1 to pressure and volume overload suggests an adaptational process.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathological hypertrophy and cardiac interstitium. Fibrosis and renin-angiotensin-aldosterone system

Left ventricular hypertrophy (LVH) is the major risk factor associated with myocardial failure. An explanation for why a presumptive adaptation such as LVH would prove pathological has been elusive. Insights into the impairment in contractility of the hypertrophied myocardium have been sought in the biochemistry of cardiac myocyte contraction. Equally compelling is a consideration of abnormalities in myocardial structure that impair organ contractile function while preserving myocyte contractility. For example, in the LVH that accompanies hypertension, the extracellular space is frequently the site of an abnormal accumulation of fibrillar collagen. This reactive and progressive interstitial and perivascular fibrosis accounts for abnormal myocardial stiffness and ultimately ventricular dysfunction and is likely a result of cardiac fibroblast growth and enhanced collagen synthesis. The disproportionate involvement of this nonmyocyte cell, however, is not a uniform accompaniment to myocyte hypertrophy and LVH, suggesting that the growth of myocyte and nonmyocyte cells is independent of each other. This has now been demonstrated in in vivo studies of experimental hypertension in which the abnormal fibrous tissue response was found in the hypertensive, hypertrophied left ventricle as well as in the normotensive, nonhypertrophied right ventricle. These findings further suggest that a circulating substance that gained access to the common coronary circulation of the ventricles was involved. This hypothesis has been tested in various animal models in which plasma concentrations of angiotensin II and aldosterone were varied. Based on morphometric and morphological findings, it can be concluded that arterial hypertension (i.e., an elevation in coronary perfusion pressure) together with elevated circulating aldosterone are associated with cardiac fibroblast involvement and the resultant heterogeneity in tissue structure. Nonmyocyte cells of the cardiac interstitium represent an important determinant of pathological LVH. The mechanisms that invoke short- (e.g., collagen metabolism) and long-term (e.g., mitosis) responses of cardiac fibroblasts require further investigation and integration of in vitro with in vivo studies. The stage is set, however, to prevent pathological LVH resulting from myocardial fibrosis as well as to reverse it.

Doppler echocardiographic transmitral peak early velocity does not directly reflect hemodynamic changes in humans: importance of normalization to mitral stroke volume

Doppler echocardiographic transmitral peak early velocity normalized to the time-velocity integral during diastole is equivalent to volumetric peak filling rate normalized to stroke volume. To compare the pathophysiologic validity of normalized and nonnormalized peak early flow velocity, pulsed Doppler echocardiography with simultaneous high fidelity left ventricular pressure measurements was performed in 52 patients with coronary artery disease. Left ventricular loading conditions were changed by intravenous administration of norepinephrine in 15 patients and synthetic atrial natriuretic polypeptide in 15 others. Norepinephrine increased nonnormalized and normalized peak early flow velocities in association with significantly elevated end-diastolic, peak systolic and mitral valve opening pressures and decelerated the time constant of left ventricular isovolumetric pressure decline. Atrial natriuretic polypeptide did not change either nonnormalized or normalized peak early flow velocity, despite significant reductions in end-diastolic, peak systolic and mitral valve opening pressure and an accelerated time constant. Normalized peak early flow velocity showed the highest univariate correlation with long-term change in mitral valve opening pressure (n = 52, r = 0.67, p less than 0.0001). It provided a modest univariate correlation (n = 30, r = 0.74, p less than 0.0001) with immediate change in mitral valve opening pressure during norepinephrine infusion, whereas this correlation was lower (n = 30, r = 0.57, p less than 0.001) during polypeptide infusion. However, multivariate regression analysis relating normalized peak velocity with long- and short-term changes in end-diastolic, peak systolic and mitral valve opening pressures, time constant and constant of left ventricular chamber stiffness improved the correlation coefficients (r = 0.80 to 0.85, all p less than 0.0001). In contrast, neither univariate nor multivariate correlations of nonnormalized velocity with long- and short-term changes in these hemodynamic variables were satisfactory. Thus, nonnormalized peak early flow velocity does not directly reflect underlying hemodynamic changes in humans. Normalization to mitral stroke volume clarifies the dependence of peak early flow velocity on the determinants of early diastolic filling. When left ventricular early diastolic filling is evaluated by Doppler echocardiography, normalized peak early flow velocity should be taken into consideration.