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

The right ventricle in tetralogy of Fallot: adaptation to sequential loading

Right ventricular dysfunction is a major determinant of outcome in patients with complex congenital heart disease, as in tetralogy of Fallot. In these patients, right ventricular dysfunction emerges after initial pressure overload and hypoxemia, which is followed by chronic volume overload due to pulmonary regurgitation after corrective surgery. Myocardial adaptation and the transition to right ventricular failure remain poorly understood. Combining insights from clinical and experimental physiology and myocardial (tissue) data has identified a disease phenotype with important distinctions from other types of heart failure. This phenotype of the right ventricle in tetralogy of Fallot can be described as a syndrome of dysfunctional characteristics affecting both contraction and filling. These characteristics are the end result of several adaptation pathways of the cardiomyocytes, myocardial vasculature and extracellular matrix. As long as the long-term outcome of surgical correction of tetralogy of Fallot remains suboptimal, other treatment strategies need to be explored. Novel insights in failure of adaptation and the role of cardiomyocyte proliferation might provide targets for treatment of the (dysfunctional) right ventricle under stress.

Accelerated Growth, Differentiation, and Ploidy with Reduced Proliferation of Right Ventricular Cardiomyocytes in Children with Congenital Heart Defect Tetralogy of Fallot

The myocardium of children with tetralogy of Fallot (TF) undergoes hemodynamic overload and hypoxemia immediately after birth. Comparative analysis of changes in the ploidy and morphology of the right ventricular cardiomyocytes in children with TF in the first years of life demonstrated their significant increase compared with the control group. In children with TF, there was a predominantly diffuse distribution of Connexin43-containing gap junctions over the cardiomyocytes sarcolemma, which redistributed into the intercalated discs as cardiomyocytes differentiation increased. The number of Ki67-positive cardiomyocytes varied greatly and amounted to 7.0–1025.5/10⁶ cardiomyocytes and also were decreased with increased myocytes differentiation. Ultrastructural signs of immaturity and proliferative activity of cardiomyocytes in children with TF were demonstrated. The proportion of interstitial tissue did not differ significantly from the control group. The myocardium of children with TF under six months of age was most sensitive to hypoxemia, it was manifested by a delay in the intercalated discs and myofibril assembly and the appearance of ultrastructural signs of dystrophic changes in the cardiomyocytes. Thus, the acceleration of ontogenetic growth and differentiation of the cardiomyocytes, but not the reactivation of their proliferation, was an adaptation of the immature myocardium of children with TF to hemodynamic overload and hypoxemia.

SLIT3 deficiency attenuates pressure overload-induced cardiac fibrosis and remodeling

In pulmonary hypertension and certain forms of congenital heart disease, ventricular pressure overload manifests at birth and is an obligate hemodynamic abnormality that stimulates myocardial fibrosis, which leads to ventricular dysfunction and poor clinical outcomes. Thus, an attractive strategy is to attenuate the myocardial fibrosis to help preserve ventricular function. Here, by analyzing RNA-sequencing databases and comparing the transcript and protein levels of fibrillar collagen in WT and global-knockout mice, we found that slit guidance ligand 3 (SLIT3) was present predominantly in fibrillar collagen-producing cells and that SLIT3 deficiency attenuated collagen production in the heart and other nonneuronal tissues. We then performed transverse aortic constriction or pulmonary artery banding to induce left and right ventricular pressure overload, respectively, in WT and knockout mice. We discovered that SLIT3 deficiency abrogated fibrotic and hypertrophic changes and promoted long-term ventricular function and overall survival in both left and right ventricular pressure overload. Furthermore, we found that SLIT3 stimulated fibroblast activity and fibrillar collagen production, which coincided with the transcription and nuclear localization of the mechanotransducer yes-associated protein 1. These results indicate that SLIT3 is important for regulating fibroblast activity and fibrillar collagen synthesis in an autocrine manner, making it a potential therapeutic target for fibrotic diseases, especially myocardial fibrosis and adverse remodeling induced by persistent afterload elevation.

Balance of Active, Passive, and Anatomical Cardiac Properties in Doxorubicin-Induced Heart Failure

Late-onset heart failure (HF) is a known side effect of doxorubicin chemotherapy. Typically, patients are diagnosed when already at an irreversible stage of HF, which allows few or no treatment options. Identifying the causes of compromised cardiac function in this patient group may improve early patient diagnosis and support treatment selection. To link doxorubicin-induced changes in cardiac cellular and tissue mechanical properties to overall cardiac function, we apply a multiscale biophysical biomechanics model of the heart to measure the plausibility of changes in model parameters representing the passive, active, or anatomical properties of the left ventricle for reproducing measured patient phenotypes. We create representative models of healthy controls (N = 10) and patients with HF induced by (N = 22) or unrelated to (N = 25) doxorubicin therapy. The model predicts that HF in the absence of doxorubicin is characterized by a 2- to 3-fold stiffness increase, decreased tension (0–20%), and ventricular dilation (of order 10–30%). HF due to doxorubicin was similar but showed stronger bias toward reduced active contraction (10–30%) and less dilation (0–20%). We find that changes in active, passive, and anatomical properties all play a role in doxorubicin-induced cardiotoxicity phenotypes. Differences in parameter changes between patient groups are consistent with doxorubicin cardiotoxicity having a greater dependence on reduced cellular contraction and less anatomical remodeling than HF not caused by doxorubicin.

The effect of right ventricular myocardial remodeling on ventricular function as assessed by two-dimensional speckle tracking echocardiography in patients with tetralogy of Fallot: a single center experience from China

BACKGROUND

Published correlations between histological abnormalities and right ventricular (RV) function, as evaluated by speckle tracking echocardiography (STE), are scarce in patients with tetralogy of Fallot (TOF). The purpose of the study is to assess age-associated differences in the effect of RV myocardial remodeling on ventricular function in patients with TOF.

METHODS

Operatively resected crista supraventricularis muscle from 30 patients (median age 12months) undergoing intracardiac repair of TOF were studied by light microscopy. The patients were divided into younger (age at surgery ≤12months) and older (age at surgery >12months) subgroups. The RV global longitudinal peak systolic strain (GLS), strain rate (GLSRs) and early diastolic strain rate (GLSRe) were measured by two-dimensional STE before and 6months after repair.

RESULTS

The histopathological data revealed hypertrophy of the cardiomyocytes, a thickened endocardium, and increased interstitial and perivascular collagen in RV, which were associated with older age at the time of repair. The RV global systolic and diastolic functions in patients with repaired TOF were increased compared with the preoperative values. The RV cardiomyocyte diameter and collagen volume fraction (CVF) correlated with the preoperative GLS, GLSRs and GLSRe, respectively, in the younger patients (r1=-0.566, P1=0.018; r2=-0.493, P2=0.004; r3=-0.504, P3=0.039). The RV cardiomyocyte diameter and CVF correlated with preoperative GLS, GLSRs and GLSRe, respectively, in the older patients (r1=-737, P1=0.004; r2=-0.588, P2=0.035; r3=-0.812, P3=0.001). The correlation of the RV cardiomyocyte diameter with the postoperative GLS and GLSRe (r1=-665, P1=0.036; r2=-0.787, P2=0.007) and the CVF with the postoperative GLSRs and GLSRe (r1=-762, P1=0.002; r2=-0.713, P2=0.004) were identified only in the older patients. Multivariate analysis indicated that the age at repair was an independent predictor of postoperative GLSRs and GLSRe in all of the patients (β=-0.449, P=0.041; β=-0.607, P=0.004).

CONCLUSIONS

The effect of RV myocardial remodeling on preoperative RV function was more pronounced in the older patients with TOF than in the younger ones. Preoperative myocardial remodeling affected the postoperative RV function in the older but not in the younger patients. The age at the time of surgical repair was the independent determinant of the postoperative RV myocardial function.

Diffuse myocardial fibrosis following tetralogy of Fallot repair: a T1 mapping cardiac magnetic resonance study

BACKGROUND

Adverse ventricular remodeling after tetralogy of Fallot (TOF) repair is associated with diffuse myocardial fibrosis.

OBJECTIVE

The goal of this study was to measure post-contrast myocardial T1 in pediatric patients after TOF repair as surrogates of myocardial fibrosis.

MATERIALS AND METHODS

Children after TOF repair who underwent cardiac magnetic resonance imaging with T1 mapping using the modified look-locker inversion recovery (MOLLI) sequence were included. In addition to routine volumetric and flow data, we measured post-contrast T1 values of the basal interventricular septum, the left ventricular (LV) lateral wall, and the inferior and anterior walls of the right ventricle (RV). Results were compared to data from age-matched healthy controls.

RESULTS

The scans of 18 children who had undergone TOF repair and 12 healthy children were included. Post-contrast T1 values of the left ventricular lateral wall (443 ± 54 vs. 510 ± 77 ms, P = 0.0168) and of the right ventricular anterior wall (333 ± 62 vs. 392 ± 72 ms, P = 0.0423) were significantly shorter in children with TOF repair than in controls, suggesting a higher degree of fibrosis. In children with TOF repair, but not in controls, post-contrast T1 values were shorter in the right ventricle than the left ventricle and shorter in the anterior wall of the right ventricle than in the inferior segments. In the TOF group, post-contrast T1 values of the RV anterior wall correlated with the RV end-systolic volume indexed to body surface area (r = 0.54; r(2) = 0.30; P = 0.0238).

CONCLUSION

In children who underwent tetralogy of Fallot repair the myocardium of both ventricles appears to bear an abnormally high fibrosis burden.

Diabetes influences cardiac extracellular matrix remodelling after myocardial infarction and subsequent development of cardiac dysfunction

This study was conducted to examine the influence of acute streptozotocin-induced diabetes on cardiac remodelling and function in mice subjected to myocardial infarction (MI) by coronary artery ligation. Echocardiography analysis indicated that diabetes induced deleterious cardiac functional changes as demonstrated by the negative differences of ejection fraction, fractional shortening, stroke volume, cardiac output and left ventricular volume 24 hrs after MI. Temporal analysis for up to 2 weeks after MI showed higher mortality in diabetic animals because of cardiac wall rupture. To examine extracellular matrix remodelling, we used fluorescent molecular tomography to conduct temporal studies and observed that total matrix metalloproteinase (MMP) activity in hearts was higher in diabetic animals at 7 and 14 days after MI, which correlated well with the degree of collagen deposition in the infarct area visualized by scanning electron microscopy. Gene arrays indicated temporal changes in expression of distinct MMP isoforms after 1 or 2 weeks after MI, particularly in diabetic mice. Temporal changes in cardiac performance were observed, with a trend of exaggerated dysfunction in diabetic mice up to 14 days after MI. Decreased radial and longitudinal systolic and diastolic strain rates were observed over 14 days after MI, and there was a trend towards altered strain rates in diabetic mouse hearts with dyssynchronous wall motion clearly evident. This correlated with increased collagen deposition in remote areas of these infarcted hearts indicated by Masson's trichrome staining. In summary, temporal changes in extracellular matrix remodelling correlated with exaggerated cardiac dysfunction in diabetic mice after MI.

Left ventricle after palliation of hypoplastic left heart syndrome: friend, fiend, or innocent bystander?

Hypoplasia of the left side of the heart is the most common cause of death from congenital heart disease in the first weeks of life. Once considered a surgically fatal disease, hypoplasia has been successfully palliated for more than 30 years. Although the palliative route is staged by an early differential bypass of the systemic outflow and the venous inflow to the right ventricle, the left ventricle remains anatomically and biologically influential throughout. Given the variation of the left ventricle, contemporary outcomes for different hypoplastic left heart subsets can vary both early after palliation and long term. This review critically examines the contemporary understanding of the structure and function of the hypoplastic ventricle in this syndrome. It also provides insight into future research directions relevant to clinicians and surgeons.

Localization of matrix metalloproteinases and their inhibitors in experimental progressive kidney scarring

The extracellular matrix (ECM) is in a continual state of turnover with homeostasis maintained by balancing synthesis and degradation rates. During progressive kidney scarring an imbalance occurs leading to ECM accumulation. Reduced matrix metalloproteinase (MMP) activity is believed to central to this imbalance. However, most of the data relating to MMPs and their natural inhibitors (tissue inhibitors of matrix metalloproteinase (TIMP)) is based on homogenate studies where in situ compartmentalization is lost and thus changes in MMP activity may be artificial. To address this we have developed a sensitive, high-resolution in situ zymography technique and applied it, along with immunohistochemistry, to the 5/6th subtotal nephrectomy model of kidney scarring. ECM proteolytic activity in kidney homogenates progressively declined post-SNx against both gelatin (-82%) and collagen I (-78%) substrates. In situ zymography revealed higher activity with both substrates within the cytoplasm of normal tubular cells compared to the SNx. In contrast, there was 96% greater activity in the SNx glomeruli than normal. Immunohistochemistry confirmed a predominantly intracellular tubular location of all MMPs and TIMPs. Tubules showed reduced MMP-3 and elevated TIMP-2, whereas MMP-1 increased significantly in the glomeruli, especially in the mesangial matrix. TIMP-1 showed a fourfold increase in the remnant kidney by Western blot analysis, but could not be localized. Lowered MMP activity in homogenates results from reduced intracellular activity in the tubules, indicating that reduced MMP activity may not play a direct role in the expansion of the tubular ECM in scarring. However, elevated MMP-1 activity in the glomeruli may play a significant role in initiating glomerular remodelling.

Matching procedure to morphology improves outcomes in neonates with tricuspid atresia

OBJECTIVE

This study was undertaken to characterize morphologic substrate of tricuspid atresia with ventriculoarterial concordance and discriminate management strategies that lead to successful definitive repair.

METHODS

From 1999 to 2004, a total of 150 babies with type I tricuspid atresia were enrolled from first diagnosis at 26 institutions. Antegrade pulmonary blood flow was absent in 19%, restricted in 54%, and unrestricted in 28%. Competing-risk methodology determined the time-related prevalence and risk factors for death versus cavopulmonary anastomosis and subsequent death versus Fontan completion.

RESULTS

Overall 5-year survival was 86%. Initial palliation included systemic-pulmonary arterial shunt in 64%, pulmonary artery banding in 11%, and cavopulmonary anastomosis in 24%. Median age at cavopulmonary anastomosis was 6 months, with 83% undergoing bidirectional Glenn shunt and 17% undergoing hemi-Fontan procedure. By the age of 2 years, 89% had cavopulmonary anastomosis, 6% were dead, and 4% remained alive without cavopulmonary anastomosis. Risk factors for death without cavopulmonary anastomosis included presence of mitral regurgitation (P = .03) and palliation with systemic-pulmonary arterial shunts not originating from the innominate artery (P = .04). Factors associated with decreased transition rate to cavopulmonary connection included patient variables (younger admission age to a participating institution, noncardiac anomalies) and procedural variables (larger systemic-pulmonary arterial shunt diameter, previous palliation). Of patients undergoing cavopulmonary anastomosis, 75% had undergone a Fontan operation within 3 years.

CONCLUSION

Smaller shunt size and decreased pulmonary blood flow decrease mortality after initial palliation and increase the rate of successful transition to cavopulmonary anastomosis. Outcomes can be improved by placing smaller shunts from the innominate artery, especially in patients with any mitral regurgitation.

Neonatal physiology of the functionally univentricular heart

The neonate with functionally univentricular physiology presents unique challenges to the cardiac team. An integrated approach that applies working knowledge of cardiac anatomy, cardiopulmonary physiology, and basic principles of intensive care is essential to guide management of each individual patient. This requires cooperative and constructive involvement of a surgical, medical, nursing and respiratory care team experienced in the management of such patients. In the neonate with this physiology, systemic oxygen delivery is optimized by manipulating pulmonary and systemic resistances, augmenting total cardiac output, and utilizing strategies for ventilation that preserve optimal pulmonary recruitment.

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.

Single-ventricle physiology

The patient with single-ventricle physiology presents a significant challenge to the intensive care team at all stages of management. An integrated approach that applies a working knowledge of cardiac anatomy, cardiopulmonary physiology, and the basic principles of intensive care is essential to guide management for each individual patient. This management requires cooperative and constructive involvement of surgeons, cardiologists, and intensivists, as well as a nursing and respiratory care team experienced in the management of single-ventricle patients. The outcome of each stage of palliation for single-ventricle lesions should continue to improve as new ideas are developed and as older ideas are subjected to rigorous scientific analyses.

Structural immaturity of the heart in congenital diaphragmatic hernia in rats

PURPOSE

The form and function of the heart are the final result of an integration of cells, tissues, and extracellular material. The extracellular matrix (ECM) is a complex array of different molecular components, and it plays an important role for the transfer of mechanical force in both contraction and relaxation phases in the cardiac cycle. ECM plays also a significant role in the development of the heart. The aim of this study was to evaluate the expression of important ECM components in the heart of rats with induced CDH to test the hypothesis that an alteration of ECM may contribute to the cardiac maldevelopment, which recently has been identified as a contributive factor for the high mortality rate in babies with congenital diaphragmatic hernia (CDH).

METHODS

CDH model was induced in pregnant rats after administration of 100 mg of nitrofen on day 9.5 of gestation (term, 22 days). In control animals the same dose of olive oil was given without nitrofen. Cesarean section was performed on day 21 of gestation. The fetuses were divided into 2 groups: normal control (n = 10) and nitrofen-induced CDH (n = 10). Reverse transcription polymerase chain reaction (RT-PCR) was performed to evaluate the relative amount of tropoelastin and alpha1 (I) procollagen mRNA expression. Elastin protein content was measured using enzyme-linked immunosorbent assay (ELISA).

RESULTS

There was a reduction in tropoelastin mRNA (P <.05) and procollagen mRNA (P <.05) in CDH compared with controls. The cardiac alpha-elastin content also was reduced in CDH (P <.01).

CONCLUSIONS

The reduced cardiac tropoelastin and procollagen gene expression and the reduced alpha-elastin content indicate that the heart in CDH structurally is immature. The reduced production of cardiac ECM may contribute to a contractile dysfunction, which makes the heart unable to respond to the hemodynamic load accompanying persistent pulmonary hypertension (PPH).

Myocardial fibrosis in DOCA-salt hypertensive rats: effect of endothelin ET(A) receptor antagonism

BACKGROUND

To test the hypothesis that endothelin-1 contributes to cardiac fibrosis, cardiac collagen deposition was studied in deoxycorticosterone acetate-salt (DOCA-salt) hypertensive rats, in which the endothelin system is activated. The effects of the ET(A)-selective endothelin receptor antagonist A-127722 were evaluated.

METHODS AND RESULTS

A-127722 (30 mg/kg per day) was administered for 4 weeks. Myocardial fibrosis was evaluated after Sirius red F3BA staining. Systolic blood pressure was 103+/-1.6 mm Hg in unilaterally nephrectomized rats (Uni-Nx), 202+/-3.2 mm Hg in DOCA-salt rats (P:<0.01 versus Uni-Nx), and 182+/-3.1 mm Hg in ET(A) antagonist-treated DOCA-salt rats (P:<0.01 versus DOCA-salt or Uni-Nx). In DOCA-salt rats, interstitial and perivascular collagen density was increased in the subendocardial and midmyocardial regions of the left ventricle (3- to 4-fold, P:<0.05), whereas in subepicardial myocardium, the increase was predominantly perivascular. The ET(A) antagonist prevented cardiac fibrosis in DOCA-salt rats. Procollagen I and III mRNA, which were increased in hearts of DOCA-salt rats, were normalized by ET(A) antagonist treatment. TGF-beta(1) mRNA and TGF-beta(1) protein increased at 1 week in DOCA-salt rats and were lowered in ET(A) antagonist-treated rats.

CONCLUSIONS

ET(A) receptor-mediated collagen deposition in hearts of DOCA-salt rats results from increased procollagen synthesis associated with an initial increment in expression of TGF-beta(1). These results support the hypothesis of a role for endothelin-1 in cardiac collagen deposition in mineralocorticoid hypertension, which may have pathophysiological and pharmacological implications in hypertensive heart disease.

Progressive cardiac dysfunction and fibrosis in the cardiomyopathic hamster and effects of growth hormone and angiotensin-converting enzyme inhibition

BACKGROUND

Growth hormone (GH) improves cardiac function in the rat with myocardial infarction, but its effects in a model of primary dilated cardiomyopathy have not been reported. GH effects were examined at early (4 months) and late (10 months) phases of disease in the cardiomyopathic (CM) hamster, and the combination of GH with chronic ACE inhibition was assessed in late-phase heart failure.

METHODS AND RESULTS

CM hamsters (CHF 147 line) at 4 months showed severe systolic left ventricular (LV) dysfunction with normal LV filling pressure, and at 10 months there was more severe systolic as well as diastolic dysfunction with increasing myocardial fibrosis. Recombinant human GH alone for 3 weeks at age 4 months increased LV wall thickness and reduced systolic wall stress without altering diastolic wall stress, whereas at 10 months, wall stress and fractional shortening did not improve. The LV dP/dt(max) was enhanced at both ages by GH, which at 4 months reflected increased contractility, but at 10 months was most likely caused by elevation of the LV filling pressure. The increasing degree of fibrosis correlated inversely with LV function but was unaffected by GH. In other CM hamsters, high-dose ACE inhibition alone (quinapril), started at 8 months and continued for 11 weeks, improved LV function and inhibited unfavorable remodeling, but the addition of GH for 3 weeks at age 10 months produced increased wall thickness with little additional functional benefit and increased the LV filling pressure and diastolic wall stress.

CONCLUSIONS

GH treatment alone improved LV dysfunction at 4 months of age in CM hamsters by increasing contractility and reducing wall stress but had few beneficial effects at 10 months in severe LV failure. After chronic ACE inhibition, addition of GH at 10 months had no additional beneficial effects and further increased LV diastolic pressure. These differing effects of GH may relate to the progressive increase of LV fibrosis in the CM hamster.

Resting coronary flow and coronary flow reserve in human infants after repair or palliation of congenital heart defects as measured by positron emission tomography

OBJECTIVE

Coronary physiology in infants with congenital heart disease remains unclear. Our objective was to better understand coronary physiology in infants with congenital heart disease.

METHODS

We used positron emission tomography with nitrogen 13-labeled ammonia to measure myocardial perfusion at rest and with adenosine (142 micrograms/kg/min x 6 minutes) in five infants after anatomic repair of a congenital heart lesion (group I), and in five infants after Norwood palliation for hypoplastic left heart syndrome (group II). The groups were matched for age, weight, and time from the operation.

RESULTS

Resting coronary flow in the left ventricle in group I was 1.8 +/- 0.2 ml/min/gm; resting flow in the right ventricle in group II was 1.0 +/- 0.3 ml/min/gm (p = 0.003). Coronary flow with adenosine was 2.6 +/- 0.5 ml/min/gm in group I and 1.5 +/- 0.7 ml/min/gm in group II (p = 0.02). Absolute coronary flow reserve was the same in both groups (1.5 +/- 0.2 in group I vs 1.6 +/- 0.3 in group II, p = 0.45). Oxygen delivery was reduced in group II compared with group I at rest (16.1 +/- 4.2 ml/min/100 gm vs 28.9 +/- 4.42 ml/min/100 gm, p = 0.02) and with adenosine (25.5 +/- 8.1 ml/min/100 gm vs 42.3 +/- 5.8 ml/min/100 gm, p = 0.02).

CONCLUSIONS

Infants with repaired heart disease have higher resting flow and less coronary flow reserve than previously reported for adults. After Norwood palliation, infants have less perfusion and oxygen delivery to the systemic ventricle than do infants with a repaired lesion. This may in part explain why the outcome for patients with Norwood palliation is less favorable than for others.