Reduced volume fraction of myofibrils in myocardium of patients with decompensated pressure overload

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.

Alpha1-adrenergic receptors prevent a maladaptive cardiac response to pressure overload

An alpha1-adrenergic receptor (alpha1-AR) antagonist increased heart failure in the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), but it is unknown whether this adverse result was due to alpha1-AR inhibition or a nonspecific drug effect. We studied cardiac pressure overload in mice with double KO of the 2 main alpha1-AR subtypes in the heart, alpha 1A (Adra1a) and alpha 1B (Adra1b). At 2 weeks after transverse aortic constriction (TAC), KO mouse survival was only 60% of WT, and surviving KO mice had lower ejection fractions and larger end-diastolic volumes than WT mice. Mechanistically, final heart weight and myocyte cross-sectional area were the same after TAC in KO and WT mice. However, KO hearts after TAC had increased interstitial fibrosis, increased apoptosis, and failed induction of the fetal hypertrophic genes. Before TAC, isolated KO myocytes were more susceptible to apoptosis after oxidative and beta-AR stimulation, and beta-ARs were desensitized. Thus, alpha1-AR deletion worsens dilated cardiomyopathy after pressure overload, by multiple mechanisms, indicating that alpha1-signaling is required for cardiac adaptation. These results suggest that the adverse cardiac effects of alpha1-antagonists in clinical trials are due to loss of alpha1-signaling in myocytes, emphasizing concern about clinical use of alpha1-antagonists, and point to a revised perspective on sympathetic activation in heart failure.

Dilated cardiomyopathy in juvenile Portuguese Water Dogs

Dilated cardiomyopathy recently has been recognized in juvenile Portuguese Water Dogs. The purpose of this study was to evaluate unaffected and affected puppies by physical examination, electrocardiogram (ECG), echocardiogram, specific biochemical assays, and ultrastructure to document disease progression and to develop a method of early detection. Results of segregation analysis were consistent with autosomal recessive inheritance. Of 124 puppies evaluated clinically and echocardiographically, 10 were affected. No significant differences were found between unaffected and affected puppies for blood and myocardial carnitine or taurine concentrations, serum chemical variables, results of ophthalmological examinations, ECGs, or measurement of urine metabolites. Ultrastructural examination of myocardium from affected dogs revealed myofibrillar atrophy and small regions of myo‐fibrillar degeneration, most prominently at the region of the intercalated discs. Only echocardiography allowed detection of affected puppies before clinical signs became evident. Echocardiography revealed a significant difference in the shortening fraction, E point to septal separation, and the end systolic and diastolic left ventricular internal diameters. Affected puppies were detected 1–4 weeks before the development of acute congestive heart failure.

Dilated cardiomyopathy in juvenile Portuguese Water Dogs

Dilated cardiomyopathy recently has been recognized in juvenile Portuguese Water Dogs. The purpose of this study was to evaluate unaffected and affected puppies by physical examination, electrocardiogram (ECG), echocardiogram, specific biochemical assays, and ultrastructure to document disease progression and to develop a method of early detection. Results of segregation analysis were consistent with autosomal recessive inheritance. Of 124 puppies evaluated clinically and echocardiographically, 10 were affected. No significant differences were found between unaffected and affected puppies for blood and myocardial carnitine or taurine concentrations, serum chemical variables, results of ophthalmological examinations, ECGs, or measurement of urine metabolites. Ultrastructural examination of myocardium from affected dogs revealed myofibrillar atrophy and small regions of myofibrillar degeneration, most prominently at the region of the intercalated discs. Only echocardiography allowed detection of affected puppies before clinical signs became evident. Echocardiography revealed a significant difference in the shortening fraction, E point to septal separation, and the end systolic and diastolic left ventricular internal diameters. Affected puppies were detected 1-4 weeks before the development of acute congestive heart failure.

Myocardial fibrosis assessment by semiquantitative, point-counting and computer-based methods in patients with heart muscle disease: a comparative study

AIMS

No study has directly compared different histomorphometric methods of quantification of myocardial fibrosis. Therefore we compared the results of semiquantitative, point-counting and computer-based methods in the assessement of myocardial fibrosis in a consecutive series of endomyocardial biopsy samples from patients with heart muscle disease.

METHODS AND RESULTS

Histological samples (at least three per patient) were obtained by endomyocardial biopsy from 11 patients with focal myocarditis and from 24 ambulatory patients with idiopathic dilated cardiomyopathy, or during surgery in 10 patients who underwent partial left ventriculectomy. Samples were cut and stained with Masson-trichrome for better contrast. From each sample, a representative field was digitized, and the amount of fibrosis was assessed by semiquantitative scoring, by point-counting, and by computer-based software. Semiquantitative scoring correlated with both point-counting (Spearman's r = 0.69, P < 0.0001) and computer-based (Spearman's r = 0.83, P < 0.0001) methods. There was also a good correlation between point-counting and computer-based methods (r = 0.71, P < 0.0001). However, when compared with the point-counting method, the computer-based method overestimated percent fibrosis by 3.0 +/- 6.7% (P = 0.004). This overestimation correlated with the mean percent fibrosis (r = 0.38, P = 0.014).

CONCLUSIONS

Our data show good correlations between the three methods of myocardial fibrosis assessment. However, systematic differences between them emphasize that this should be taken into consideration when comparing results of the studies using different methods of fibrosis assessment.

ECG characteristics of dilated cardiomyopathy

To elucidate the electrocardiographic (ECG) characteristics of dilated cardiomyopathy (DCM), the authors analyzed the 12-lead ECGs and echocardiograms in 45 patients with DCM, 54 patients with left ventricular (LV) dilatation secondary to valvular heart disease (VHD), 101 hypertensive patients with LV hypertrophy, and 63 normal control subjects. In addition, serial ECG and echocardiographic changes in DCM during a mean follow-up period of 1.6 years were evaluated. Sokolow's criterion (S wave in lead V1 [SV1] + R wave in lead V5 or V6 [RV5 or RV6] > 35 mm) was met comparably in patients with DCM (69%), VHD (61%), and hypertension (74%) (P = NS). Notably, RV6 in DCM was the highest among the four groups and correlated with the degree of LV dilatation. In contrast, the R waves in leads I, II, and III (RI, RII, RIII) in DCM were the lowest and were not affected by the degree of LV dilatation, although RII and RIII in VHD and RI in hypertension correlated with the degree of LV dilatation and hypertrophy, respectively. As a result, all voltage ratios of RV6/RI, RII, RIII in DCM were not only the highest, but also increased linearly as the LV dilated progressively during the follow-up period. In particular, RV6 over the maximum R wave in leads I, II, and III (RV6/Rmax) in DCM correlated with the degree of LV dilatation and inversely correlated with ejection fraction. Subjects with DCM had a significantly higher RV6/Rmax than did patients with VHD, hypertension, and normal subjects (3.4 vs 1.7, 1.4, 1.2, respectively; P < .001), and this ratio of > or = 3 was seen in 67% of the DCM patients versus 4% of the VHD patients, 1% of the hypertensive patients, and 0% of the normal subjects. Thus, DCM commonly shows the ECG signs of LV hypertrophy, but characteristically has the high voltage ratios of RV6/RI, RII, RIII.

Pathologic changes in the long-term transplanted heart: a morphometric study of myocardial hypertrophy, vascularity, and fibrosis

Myocyte hypertrophy and myocardial fibrosis have been observed in transplanted human hearts, and both could potentially have an adverse effect on long-term cardiac function. There has been some concern that distant donor heart procurement and cyclosporine treatment increase the risk of these changes, but their incidence and severity have not been documented quantitatively in large numbers of cardiac transplant recipients. We used light microscopic morphometric methods to estimate myocardial collagen volume fraction and myocyte width in right ventricular endomyocardial biopsies from 95 recipients at 3 years posttransplantation, and electron microscopic stereology to estimate myocardial vascularity and myocyte myofibril content in 40 recipients, also at 3 years posttransplantation. We compared those with locally and distantly procured donor hearts (mean ischemic time 160 minutes) and cyclosporine versus noncyclosporine immunosuppression. Controls were pretransplant right ventricular biopsies from 20 donor hearts which were free of heart disease. We found no significant differences in myocardial collagen volume fractions. Myocyte hypertrophy was typical of all the transplant biopsies (mean myocyte width 20.2 microns, SD 3.0 in all transplants versus 11.8 microns, SD 2.2 in controls, P less than 0.001), but distant donor procurement and cyclosporine had no significant effect. There were significant reductions of myofibril volume fraction in the transplants, which raises the possibility of gradual decompensation in some patients. There were no significant differences in myocardial vascularity, although a few patients were well below the control range. We conclude that distant donor heart procurement, with ischemic times averaging less than 3 hours, and cyclosporine treatment are not responsible for significant hypertrophy or fibrosis in most transplants. Hypertrophy is typical of the transplanted heart, and it is possible that associated abnormalities might have an effect on cardiac function in some long-term survivors.

Estimation of left-ventricular systolic performance and its determinants in man from pressures and dimensions of one beat: effects of aortic valve stenosis and replacement

Within a thick heart-chamber wall, there is a midwall element or layer whose displacements best express systolic performance. The volume enclosed by that midwall element (Vm) and the average stress in that element (sigma m) can be calculated accurately by simple formulae. From simultaneous left-side pressure tracings and contrast cine-ventriculograms, Vm and sigma m were calculated at 20-ms intervals for an entire cardiac cycle in five normal subjects and in eight patients before and one year after replacement of stenotic aortic valves. Prior to surgery, the overloaded left ventricles were not hypertrophied enough to restore normal mid- and end-ejection stresses. Four had subnormal cavity ejection fractions, but all had subnormal midwall ejection fractions. All had subnormal fractional midwall ejection rates and prolonged active intervals (from the beginning of activation to the end of deactivation). Judging from pre-ejection pressure-development rates, the pressure-developing ability was not consistently elevated by concentric hypertrophy, because the stress-developing ability (contractility) was usually subnormal. The ability to shorten in the absence of afterload appeared to be subnormal in about half of the cases. The subnormal midwall ejection fractions appeared to be due to various combinations of increased mid- and late-ejection stresses, reduced contractility, and reduced shortening ability. On average and in several cases, reduced shortening ability appeared to be the main cause of the reduced performance. The effect of the slowed fractional midwall ejection rate to reduce the midwall ejection fraction was partially compensated by a prolonged active interval, by prolonged ejection time relative to the active interval, and by a more sustained ejection rate. Valve replacement partially restored all values except contractility towards normal, but the restorations of wall/cavity ratio and active interval were slight.

Functional and structural abnormalities in patients with dilated cardiomyopathy

Passive diastolic properties of the left ventricle were determined in 10 control subjects and 12 patients with dilated cardiomyopathy. Simultaneous left ventricular angiography and high fidelity pressure measurements were performed in all patients. Left ventricular chamber stiffness was calculated from left ventricular pressure-volume and myocardial stiffness from left ventricular stress-strain relations with use of a viscoelastic model. Patients with dilated cardiomyopathy were classified into two groups according to the diastolic constant of myocardial stiffness (beta). Group 1 consisted of seven patients with a normal constant of myocardial stiffness less than or equal to 9.6 (normal range 2.2 to 9.6) and group 2 of 5 patients with a beta greater than 9.6. Structural abnormalities (percent interstitial fibrosis, fibrous content) in patients with dilated cardiomyopathy were assessed by morphometry from right ventricular endomyocardial biopsies. Heart rate was similar in the three groups. Left ventricular end-diastolic pressure was significantly greater in patients with cardiomyopathy (18 mm Hg in group 1 and 22 mm Hg in group 2) than in the control patients (10 mm Hg). Left ventricular ejection fraction was significantly lower in groups 1 (37%) and 2 (36%) than in the control patients (66%). Left ventricular muscle mass index was significantly increased in both groups with cardiomyopathy. The constant of chamber stiffness (beta*) was slightly although not significantly greater in groups 1 and 2 (0.58 and 0.58, respectively) than in the control group (0.35). The constant of myocardial stiffness beta was normal in group 1 (7.0; control group 6.9, p = NS) but was significantly increased in group 2 (23.5). Interstitial fibrosis was 19% in group 1 and 43% (p less than 0.001) in group 2 (normal less than or equal to 10%). There was an exponential relation between both diastolic constant of myocardial stiffness (beta) and interstitial fibrosis (IF) (r = 0.95; p less than 0.001) and beta and fibrous content divided by end-diastolic volume index (r = 0.93; p less than 0.001). It is concluded that myocardial stiffness can be normal in patients with dilated cardiomyopathy despite severely depressed systolic function. Structural alterations of the myocardium with increased amounts of fibrous tissues are probably responsible for the observed changes in passive elastic properties of the myocardium in patients with dilated cardiomyopathy. The constant of myocardial stiffness (beta) helps to identify patients with severe structural alterations (group 2), representing possibly a more advanced stage of the disease.

Molecular cardiology: new avenues for the diagnosis and treatment of cardiovascular disease

This review summarizes some of the major advances in the investigation of molecular mechanisms underlying both normal and abnormal cardiovascular function. Four major areas are highlighted including cardiac muscle, the blood vessel, atherosclerosis and thrombosis/thrombolysis. The remarkable strides in understanding multifactorial diseases such as atherosclerosis, and the development of innovative new therapies such as the use of thrombolytic agents produced by recombinant deoxyribonucleic acid (DNA) technology, are noted. Moreover, it is concluded that the past decade of basic research has provided a solid framework for improvements in the diagnosis and therapy of other forms of cardiovascular disease as well. An evaluation of current trends in basic cardiovascular research suggests that diagnostic and therapeutic approaches to disease will increasingly target specific molecular processes underlying the pathophysiologic state.

Electrocardiographic markers of impaired left ventricular ejection performance in aortic stenosis

To determine whether the ECG would be useful in the prediction of impaired left ventricular ejection performance in aortic valve stenosis, the authors evaluated 121 patients according to (1) the time relationship of the R peak in V6 to the S peak in V2; and (2) the negative P wave terminal force in V1 (Morris index, n = 109). Left ventricular ejection fraction (LVEF) was significantly depressed in patients with the R peak in V6 later than the S peak in V2 (R peak delay in V6, n = 24), compared with those with the R peak in V6 preceding the S peak in V2 or with both peaks occurring simultaneously (n = 97) (LVEF 40.8 +/- 11.8% vs 69.9 +/- 13.3%, p = .000). LVEF less than 55% was present in 87.5% of patients with the R peak delay in V6 and in only 23.7% of those without this finding. The Morris Index was significantly greater in patients with LVEF less than 55% (n = 39) than in those with LVEF greater than or equal to 55% (n = 70) (Morris Index 0.063 +/- 0.035 msec vs 0.030 +/- 0.025 msec, p = .000). The R peak delay in V6 is a highly specific (96.1%), but less sensitive (47.7%), indicator of depressed LVEF, its positive predictive value and predictive accuracy being 87.5% and 78.5%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of proto-oncogenes in myocardial hypertrophy

A question of major clinical significance in cardiology is the nature of the signals that initiate and maintain the various types of myocardial hypertrophy, either in response to hemodynamic loading or in the absence of altered load. This review suggests that the proto-oncogene model, a concept derived from the study of cancer, can be very useful in identifying these signals. The proto-oncogene model conceives of cell growth regulation in terms of a limited number of classes of critical regulatory proteins: growth factors, growth factor receptors, intracellular transducing proteins and ribonucleic acid (RNA) transcription factors. Growth of all cells has dissociable components: hypertrophy (growth in size), deoxyribonucleic acid synthesis, mitosis and cytokinesis. Hypertrophy may be the end result of activation of RNA transcription. The various types of hypertrophy could reflect transcription of specific myocyte genes in response to different growth factors. At least 1 member of each functional class of proto-oncogenes has been detected in the myocardium or myocytes, or both. The alpha 1-adrenergic receptor has been shown to be a growth factor receptor and to regulate RNA transcription. Continued work on proto-oncogenes in myocytes may open the way to manipulate the growth of these cells.

Relationship of myocardial morphometry in aortic valve regurgitation to myocardial function and post-operative results

In 24 patients with aortic insufficiency undergoing aortic valve replacement, a clinical and hemodynamic study was performed pre-operatively. Left ventricular biopsies were obtained perioperatively for morphometric study. No significant relations were found when morphometric data were compared to functional class, cardiothoracic radio and ECG findings. The percentage of interstitial fibrosis was not correlated with any of the measured hemodynamic parameters. Myocardial cell diameter was weakly correlated with left ventricular systolic function parameters. A decrease in the percentage of contractile material was strongly correlated with an impaired left ventricular function, assessed pre-operatively. During clinical follow-up, patients were divided into two groups: Group A (17 patients) included patients who were in class I or II of NYHA after surgery. Group B (seven patients) included patients who died or were in functional class III or IV. As compared with Group A, Group B patients had a significantly lower ejection fraction; their myocardial cell diameter was larger and the percentage of myofibrils, and the content of contractile material were significantly lower. This suggests that, in aortic regurgitation, left ventricular dysfunction is correlated with contractile material loss and not with interstitial fibrosis, and that morphometric changes are good predictors of follow-up after surgery.

Diagnostic implications of figure-of-eight and clockwise QRS loop rotation on the horizontal vectorcardiogram in chronic aortic valve disease

In chronic aortic valve disease the left ventricular (LV) volumes, mass and ejection fraction (EF), as well as selected Frank ECG measurements of patients with a normal counterclockwise rotation (Type A) of the horizontal QRS vector loop are compared with those of patients showing an abnormal figure-of-eight or clockwise configuration (Type B) to investigate whether the different QRS patterns reflect ventriculographic alterations or depends on a conduction delay. In aortic stenosis (AS,n = 21) and combined AS and aortic insufficiency (AS + AI,n = 23) the Type B vectorcardiograms (VCGs) correlate with significantly increased LV end-diastolic volumes (p. .01, .01, respectively) and depressed EF (p .07, .009, respectively). In pure AI (n = 39) LV volumes, mass and EF do not differ between the Type A and Type B patterns. As compared to Type B VCGs of AS (n = 6), the LV end-diastolic volume index is clearly higher in Type A VCGs of pure AI (n = 21)(p .028). The only ECG change which is significant at the p .01 level in each group is the increase of the R peak time in lead X in the Type B VCGs. This can be related to greater volume and mass only in AS and AS+ AI, but is not substantiated by equivalent ventriculographic alterations in pure AI. The findings indicate that Type B VCGs are very likely caused by a left ventricular conduction delay since they cannot be strictly correlated with increases in LV volume and mass alone.

Quantitation of fibrosis of the heart in chronic obstructive pulmonary disease with and without cor pulmonale

This study examined the hearts of 55 patients dying of chronic obstructive pulmonary disease, with and without cor pulmonale, quantitated histologically the degree of myocardial fibrosis in the left and right ventricle, and determined the relationship to associated disease states. Comparison has been made to a control group of 17 patients free of cardiopulmonary disease. Patients with associated and advanced ischemic heart disease, as proved by marked atherosclerosis and myocardial infarction, have significantly increased myocardial fibrosis throughout all layers of the left ventricular wall in comparison to control patients or patients with chronic obstructive pulmonary disease free of associated cardiac disease. Right ventricular fibrosis was not significantly increased; however, one case showed a marked degree of fibrosis related to myocardial infarction. Subdivision of patients with chronic obstructive pulmonary disease into groups with definite anatomic right ventricular hypertrophy, a clinical diagnosis of cor pulmonale, or with chronic hypoxemia failed to show any difference in the percentage of myocardial fibrosis of the ventricles among these groups. Increased fibrosis of the right or left ventricle in patients with chronic obstructive pulmonary disease, therefore, is not related to the degree of myocardial hypertrophy pathologically, the hypoxemic state, or clinical heart failure, but to ischemic heart disease with myocardial infarction.

Morphology of the heart in hypertrophy

Cardiac hypertrophy involves not only an increase in heart size but progressive, initially subtle, structural changes in muscle cells. The ability to describe these changes in detail has contributed greatly to our understanding of their possible functional significance. Structural and functional correlations in the evolving progression of cardiac hypertrophy are examined.

An ultrastructural morphometric study of the papillary muscle of the right ventricle of the cat

The papillary muscle of the cat heart's right ventricle has not been studied previously with quantitative ultrastructural techniques despite its wide use for functional studies. This tissue was perfusion-fixed, processed for electron microscopy, and morphometric techniques were used to assess the ultrastructural characteristics of the papillary muscle as well as the working myocardial cells. The results of this study were that 73.5% of the papillary muscle was composed of muscle cells, 9.7% of blood vessels, and the remainder of interstitial connective tissue. In the muscle cell the volume fraction of mitochondria was 17.3%, that of myofibrils was 49.8%, and that of the nucleus was 2.0%. The mitochondria to myofibrils ratio was 0.36 and the surface to volume ratio was 0.309. In a quantitative ultrastructural comparison of perfusion and immersion fixed tissue it was found that significant differences in the volume density of the blood vessel lumen existed between the two groups. In addition, there were significant differences in the volume fraction of mitochondria and nucleus between perfusion-fixed and immersion-fixed muscle cells. A concurrent significant decrease between the two groups was also found for the ratio of mitochondria to myofibrils. The perfusion-fixed tissue can be considered to provide only normal baseline data for the papillary muscle of the right ventricle. These data are important as they can be used in future structure-function studies on normal and pathological heart tissue.

Quantitative morphologic findings of the myocardium in idiopathic dilated cardiomyopathy

This study assesses the relation between quantitative morphologic findings and left ventricular contractile function in patients with idiopathic dilated cardiomyopathy. Left ventricular endomyocardial catheter biopsy specimens were obtained from 73 patients during diagnostic heart catheterization. All patients had normal coronary arteriograms but abnormal electrocardiograms. Twenty-six patients had normal left ventricular function (ejection fraction greater than or equal to 55%), whereas 47 patients had contractile dysfunction (ejection fraction less than or equal to 54%). Myocardial fiber diameter, volume fraction of interstitial fibrosis, and intracellular volume fraction of myofibrils were determined by light microscopic morphometry. Results of light microscopic morphometry were confirmed by electron microscopic morphometry in 12 patients. The coefficient of variation (analysis of several biopsies from the same patient) was 6% for determination of fiber diameter, 43% for interstitial fibrosis, and 3% for volume fraction of myofibrils. Fiber diameter (r = -0.32, p less than 0.01) and fibrosis (r = -0.47, p less than 0.001) showed a negative correlation, the volume fraction of myofibrils (r = 0.55, p less than 0.001) and calculated myofibrillar mass per 100 g of myocardium (r = 0.64, p less than 0.001) a positive correlation with the ejection fraction. Thus, (1) sampling error is low for determination of fiber diameter and myofibrils but high for evaluation of fibrosis, and (2) a reduction in the volume fraction of myofibrils and an increase in fibrosis are morphologic correlates of left ventricular dysfunction in patients with idiopathic dilated cardiomyopathy.