Fiber architecture in remodeled myocardium revealed with a quantitative diffusion CMR tractography framework and histological validation

Background: The study of myofiber reorganization in the remote zone after myocardial infarction has been performed in 2D. Microstructural reorganization in remodeled hearts, however, can only be fully appreciated by considering myofibers as continuous 3D entities. The aim of this study was therefore to develop a technique for quantitative 3D diffusion CMR tractography of the heart, and to apply this method to quantify fiber architecture in the remote zone of remodeled hearts. Methods: Diffusion Tensor CMR of normal human, sheep, and rat hearts, as well as infarcted sheep hearts was performed ex vivo. Fiber tracts were generated with a fourth-order Runge-Kutta integration technique and classified statistically by the median, mean, maximum, or minimum helix angle (HA) along the tract. An index of tract coherence was derived from the relationship between these HA statistics. Histological validation was performed using phase-contrast microscopy. Results: In normal hearts, the subendocardial and subepicardial myofibers had a positive and negative HA, respectively, forming a symmetric distribution around the midmyocardium. However, in the remote zone of the infarcted hearts, a significant positive shift in HA was observed. The ratio between negative and positive HA variance was reduced from 0.96 +/- 0.16 in normal hearts to 0.22 +/- 0.08 in the remote zone of the remodeled hearts (p<0.05). This was confirmed histologically by the reduction of HA in the subepicardium from -52.03 degrees +/- 2.94 degrees in normal hearts to -37.48 degrees +/- 4.05 degrees in the remote zone of the remodeled hearts (p < 0.05). Conclusions: A significant reorganization of the 3D fiber continuum is observed in the remote zone of remodeled hearts. The positive (rightward) shift in HA in the remote zone is greatest in the subepicardium, but involves all layers of the myocardium. Tractography-based quantification, performed here for the first time in remodeled hearts, may provide a framework for assessing regional changes in the left ventricle following infarction.

Sanguineous normothermic, intermittent cardioplegia, effects on hypertrophic myocardium: morphometric, metabolic and ultrastructural studies in rabbits hearts

OBJECTIVES: The present investigation aimed to study the protective effect of intermittent normothermic cardioplegia in rabbit's hypertrophic hearts. METHODS: The parameters chosen were 1) the ratio heart weight / body weight, 2) the myocardial glycogen levels, 3) ultrastructural changes of light and electron microscopy, and 4) mitochondrial respiration. RESULTS: 1) The experimental model, coarctation of the aorta induced left ventricular hypertrophy; 2) the temporal evolution of the glycogen levels in hypertrophic myocardium demonstrates that there is a significant decrease; 3) It was observed a time-dependent trend of higher oxygen consumption values in the hypertrophic group; 4) there was a significant time-dependent decrease in the respiratory coefficient rate in the hypertrophic group; 5) the stoichiometries values of the ADP: O2 revealed the downward trend of the values of the hypertrophic group; 6) It was possible to observe damaged mitochondria from hypertrophic myocardium emphasizing the large heterogeneity of data. CONCLUSION: The acquisition of biochemical data, especially the increase in speed of glycogen breakdown, when anatomical changes are not detected, represents an important result even when considering all the difficulties inherent in the process of translating experimental results into clinical practice. With regard to the adopted methods, it is clear that morphometric methods are less specific. Otherwise, the biochemical data allow detecting alterations of glycogen concentrations and mitochondria respiration before the morphometric alterations should be detected

Cell therapy prevents structural, functional and molecular remodeling of remote non-infarcted myocardium

Background/objectives: Therapy using bone marrow (BM) cells has been tested experimentally and clinically due to the potential ability to restore cardiac function by regenerating lost myocytes or increasing the survival of tissues at risk after myocardial infarction (MI). In this study we aimed to evaluate whether BM-derived mononuclear cell (MNC) implantation can positively influence the post-MI structural remodeling, contractility and Ca(2 +)-handling proteins of the remote non-infarcted tissue in rats. Methods and results: After 48 h of MI induction, saline or BM-MNC were injected. Six weeks later, MI scars were slightly smaller and thicker, and cardiac dilatation was just partially prevented by cell therapy. However, the cardiac performance under hemodynamic stress was totally preserved in the BM-MNC treated group if compared to the untreated group, associated with normal contractility of remote myocardium as analyzed in vitro. The impaired post-rest potentiation of contractile force, associated with decreased protein expression of the sarcoplasmic reticulum Ca2 +-ATPase and phosphorylated-phospholamban and overexpression of Na(+)/Ca(2 +) exchanger, were prevented by BM-MNC, indicating preservation of the Ca(2 +) handling. Finally, pathological changes on remodeled remote tissue such as myocyte hypertrophy, interstitial fibrosis and capillary rarefaction were also mitigated by cell therapy. Conclusions: BM-MNC therapy was able to prevent cardiac structural and molecular remodeling after MI, avoiding pathological changes on Ca(2 +)-handling proteins and preserving contractile behavior of the viable myocardium, which could be the major contributor to the improvements of global cardiac performance after cell transplantation despite that scar tissue still exists.

Cancer therapy-associated cardiotoxicity and signaling in the myocardium

The cardiotoxic potential of cytotoxic cancer chemotherapy is well known. Prime examples are the anthracyclines, which are highly efficacious agents for hemopoietic malignancies and solid tumors, but their clinical use is limited primarily by cardiotoxicity. Besides the conventional chemotherapeutics, new cancer drugs were developed in the last decade with the goal to specifically inhibit selected molecular targets such as growth factor receptors or intracellular tyrosine kinases in cancer cells. However, the outcome of combining conventional and newer cancer therapies could have unexpected side effects not anticipated so far and the long-term outcome is not known. Sometimes, however, unexpected side effects also shed light on previously unknown physiological functions. For example, the anti-HER2 cancer therapeutic trastuzumab (Herceptin), which can induce cardiac dysfunction, has demonstrated the importance of the ErbB/neuregulin signaling system in the adult heart. Subsequently, the role of endothelial-myocardial communication in maintaining phenotype and survival of adult cardiomyocytes has increasingly been recognized.

Hypodense regions in unenhanced CT identify nonviable myocardium: validation versus 18F-FDG PET

The aim of the present study was to evaluate the accuracy of hypodense regions in non-contrast-enhanced cardiac computed tomography (unenhanced CT) to identify nonviable myocardial scar tissue.

Acute myocardial infarction in early pregnancy: definition of myocardium at risk with noncontrast T2-weighted cardiac magnetic resonance

We report a case of a 34-year-old woman who had a left anterior wall myocardial infarction develop in the first trimester of pregnancy. Despite urgent and successful revascularization, she demonstrated persistent segmental wall motion abnormalities by transthoracic echocardiography. To manage this patient safely through pregnancy with a better definition of myocardium at risk, a cardiac magnetic resonance examination was performed. This identified a large territory of acutely edematous myocardium in addition to providing accurate volumetric measurements of left ventricular size and function. Because of her gravid state, gadolinium was not administered nor was it required to delineate the region of myocardium at risk.

Gender modulates the expression of calcium-regulating proteins in pediatric atrial myocardium

A differential expression of sarcoplasmic reticulum calcium-ATPase (SERCA2a) and phospholamban (PLB) characterizes the remodeling process in heart failure and atrial arrhythmias in adult patients. Gender is known to modulate the course and prognosis of different forms of heart disease. We hypothesized that gender plays a role in molecular changes of myocardial calcium regulating components already in childhood. Moreover, we studied the influence of volume overloaded (VO) on SERCA2a and PLB in pediatric patients. Quantitative reverse transcription-polymerase chain reaction was used to measure mRNA expression of SERCA2a and PLB in atrial myocardium from 30 pediatric patients (12 girls, 18 boys). Eighteen patients had VO right atria, and 12 patients had not-overloaded atria (NO). Protein expression was studied by Western blot. In the entire population, SERCA2a and PLB expression was not different between girls and boys. If hemodynamic overload was taken into account, SERCA2a mRNA expression was significantly reduced in the VO group compared with the NO group (P = 0.021). The VO versus NO difference was restricted to boys, which corresponds to a highly significant interaction of gender versus VO status (P = 0.002). The PLB to SERCA2a protein ratio was significantly lower in girls (P = 0.028). The decrease in SERCA2a mRNA expression in VO atrial myocardium and the PLB to SERCA2a ratio of protein expression was modulated by gender in this pediatric population. To our knowledge, this study is the first to show the impact of gender on the differential expression of calcium-regulating components in pediatric cardiac patients.

Age-dependent suppression of SERCA2a mRNA in pediatric atrial myocardium

Differential expression of sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) and phospholamban (PLB) has been shown in heart failure and atrial arrhythmias. We investigated the influence of volume overload and age on their expression in pediatric atrial myocardium. Right atrial specimens from 18 children with volume overloaded right atrium (VO) and 12 patients without overload were studied. Each group was further divided into patients less than and older than 12 months of age. Only in the younger patients SERCA2a was significantly reduced in the VO group. In younger patients PLB mRNA level tended to be lower in VO. The PLB:SERCA protein ratio was significantly reduced in the VO group. Age itself did not influence the SERCA2a and PLB expression, if the hemodynamic overload was not taken into account. This study is the first to show a combined influence of volume overload and age on atrial SERCA2a expression.

The effect of a single 2 h bout of aerobic exercise on ectopic lipids in skeletal muscle, liver and the myocardium.

AIMS/HYPOTHESIS Ectopic lipids are fuel stores in non-adipose tissues (skeletal muscle [intramyocellular lipids; IMCL], liver [intrahepatocellular lipids; IHCL] and heart [intracardiomyocellular lipids; ICCL]). IMCL can be depleted by physical activity. Preliminary data suggest that aerobic exercise increases IHCL. Data on exercise-induced changes on ICCL is scarce. Increased IMCL and IHCL have been related to insulin resistance in skeletal muscles and liver, whereas this has not been documented in the heart. The aim of this study was to assess the acute effect of aerobic exercise on the flexibility of IMCL, IHCL and ICCL in insulin-sensitive participants in relation to fat availability, insulin sensitivity and exercise capacity. METHODS Healthy physically active men were included. [Formula: see text] was assessed by spiroergometry and insulin sensitivity was calculated using the HOMA index. Visceral and subcutaneous fat were separately quantified by MRI. Following a standardised dietary fat load over 3 days, IMCL, IHCL and ICCL were measured using MR spectroscopy before and after a 2 h exercise session at 50-60% of [Formula: see text]. Metabolites were measured during exercise. RESULTS Ten men (age 28.9 ± 6.4 years, mean ± SD; [Formula: see text] 56.3 ± 6.4 ml kg(-1) min(-1); BMI 22.75 ± 1.4 kg/m(2)) were recruited. A 2 h exercise session resulted in a significant decrease in IMCL (-17 ± 22%, p = 0.008) and ICCL (-17 ± 14%, p = 0.002) and increase in IHCL (42 ± 29%, p = 0.004). No significant correlations were found between the relative changes in ectopic lipids, fat availability, insulin sensitivity, exercise capacity or changes of metabolites during exercise. CONCLUSIONS/INTERPRETATION In this group, physical exercise decreased ICCL and IMCL but increased IHCL. Fat availability, insulin sensitivity, exercise capacity and metabolites during exercise are not the only factors affecting ectopic lipids during exercise.

Rigor mortis at the myocardium investigated by post-mortem magnetic resonance imaging

INTRODUCTION Post-mortem cardiac MR exams present with different contraction appearances of the left ventricle in cardiac short axis images. It was hypothesized that the grade of post-mortem contraction may be related to the post-mortem interval (PMI) or cause of death and a phenomenon caused by internal rigor mortis that may give further insights in the circumstances of death. METHOD AND MATERIALS The cardiac contraction grade was investigated in 71 post-mortem cardiac MR exams (mean age at death 52y, range 12-89y; 48 males, 23 females). In cardiac short axis images the left ventricular lumen volume as well as the left ventricular myocardial volume were assessed by manual segmentation. The quotient of both (LVQ) represents the grade of myocardial contraction. LVQ was correlated to the PMI, sex, age, cardiac weight, body mass and height, cause of death and pericardial tamponade when present. In cardiac causes of death a separate correlation was investigated for acute myocardial infarction cases and arrhythmic deaths. RESULTS LVQ values ranged from 1.99 (maximum dilatation) to 42.91 (maximum contraction) with a mean of 15.13. LVQ decreased slightly with increasing PMI, however without significant correlation. Pericardial tamponade positively correlated with higher LVQ values. Variables such as sex, age, body mass and height, cardiac weight and cause of death did not correlate with LVQ values. There was no difference in LVQ values for myocardial infarction without tamponade and arrhythmic deaths. CONCLUSION Based on the observation in our investigated cases, the phenomenon of post-mortem myocardial contraction cannot be explained by the influence of the investigated variables, except for pericardial tamponade cases. Further research addressing post-mortem myocardial contraction has to focus on other, less obvious factors, which may influence the early post-mortem phase too.

Targeted overexpression of protein kinase C β2 isoform in myocardium causes cardiomyopathy

Increased cardiovascular mortality occurs in diabetic patients with or without coronary artery disease and is attributed to the presence of diabetic cardiomyopathy. One potential mechanism is hyperglycemia that has been reported to activate protein kinase C (PKC), preferentially the β isoform, which has been associated with the development of micro- and macrovascular pathologies in diabetes mellitus. To establish that the activation of the PKCβ isoform can cause cardiac dysfunctions, we have established lines of transgenic mice with the specific overexpression of PKCβ2 isoform in the myocardium. These mice overexpressed the PKCβ2 isoform transgene by 2- to 10-fold as measured by mRNA, and proteins exhibited left ventricular hypertrophy, cardiac myocyte necrosis, multifocal fibrosis, and decreased left ventricular performance without vascular lesions. The severity of the phenotypes exhibited gene dose-dependence. Up-regulation of mRNAs for fetal type myosin heavy chain, atrial natriuretic factor, c-fos, transforming growth factor, and collagens was also observed. Moreover, treatment with a PKCβ-specific inhibitor resulted in functional and histological improvement. These findings have firmly established that the activation of the PKCβ2 isoform can cause specific cardiac cellular and functional changes leading to cardiomyopathy of diabetic or nondiabetic etiology.

Should we be evaluating the ventricle or the myocardium? Advances in tissue characterization

The assessment of left ventricular (LV) dysfunction has become the most frequent indication for echocardiography, a growth that has been driven by the epidemic of heart failure. The value of echocardiography for assessing LV dysfunction is unquestionable, the quantification of both LV systolic and diastolic dysfunction being a reliable indicator of mortality. 1,2 Nonetheless, whereas the ejection fraction and diastolic assessment are important clinical parameters, they are highly dependent on loading and may produce abnormal results under unusual loading conditions. Moreover, in a number of situations where the LV is evaluated, although the overall function is an important finding, the referring clinician is really requesting an assessment of the nature of the underlying myocardial tissue (Table 1). Indeed, in some situations (eg, among family members of patients with a cardiomyopathy) questions arise about the presence of pathology despite the presence of normal ventricular function. Traditionally, it has been difficult to obtain this information because of the lack of sufficiently sensitive parameters, but a number of new developments have shown such success in this area that the clinical application of tools to assess the myocardium in routine practice appears finally to be a realistic proposition.

Functional serotonin 5-HT4 receptors in porcine and human ventricular myocardium with increased 5-HT4 mRNA in heart failure

Serotonin (5-hydroxytryptamine, 5-HT) increases contractile force and elicits arrhythmias through 5-HT4 receptors in porcine and human atrium, but its ventricular effects are unknown. We now report functional 5-HT4 receptors in porcine and human ventricle. 5-HT4 mRNA levels were determined in porcine and human ventricles and contractility studied in ventricular trabeculae. Cyclic AMP-dependent protein kinase (PKA) activity was measured in porcine ventricle. Porcine and human ventricles expressed 5-HT4 receptor mRNA. Ventricular 5-HT4(b) mRNA was increased by four times in 20 failing human hearts compared with five donor hearts. 5-HT increased contractile force maximally by 16% (EC50=890 nM) and PKA activity by 20% of the effects of (-)-isoproterenol (200 muM) in ventricular trabeculae from new-born piglets in the presence of the phosphodiesterase-inhibitor 3-isobutyl-1-methylxanthine. In ventricular trabeculae from adult pigs (3-isobutyl-1-methylxanthine present) 5-HT increased force by 32% (EC50=60 nM) and PKA activity by 39% of (-)-iso-proterenol. In right and left ventricular trabeculae from failing hearts, exposed to modified Krebs solution, 5-HT produced variable increases in contractile force in right ventricular trabeculae from 4 out of 6 hearts and in left ventricular trabeculae from 3 out of 3 hearts- range 1-39% of (-)-isoproterenol, average 8%. In 11 left ventricular trabeculae from the failing hearts of four beta-blocker-treated patients, pre-exposed to a relaxant solution with 0.5 mM Ca2+ and 1.2 mM Mg2+ followed by a switch to 2.5 mM Ca2+ and 1 mM Mg2+, 5-HT (1-100 muM, 3-isobutyl-1-melhylxanthine present) consistently increased contractile force and hastened relaxation by 46% and 25% of (-)-isoproterenol respectively. 5-HT caused arrhythmias in three trabeculae from 3 out of I I patients. In the absence of phosphodiesterase inhibitor, 5-HT increased force in two trabeculae, but not in another six trabeculae from 4 patients. All 5-HT responses were blocked by 5-HT4 receptor antagonists. We conclude that phosphodiesterase inhibition uncovers functional ventricular 5-HT4 receptors, coupled to a PKA pathway, through which 5-HT enhances contractility, hastens relaxation and can potentially cause arrhythmias.

Relationship of extent and nature of dysfunctional myocardium to brain natriuretic peptide in patients with ischemic left ventricular dysfunction

We studied the relationship between brain natriuretic peptide (BNP) levels and viable myocardium and ischemic myocardium, regional scar and regional contractile function. Fifty-nine patients underwent dobutamine echocardiography and magnetic resonance imaging and resting BNP levels were determined. By magnetic resonance imaging, total extent of dysfunctional myocardium correlated strongest with BNP (r = 0.60, p < 0.0001). The extent of scar, viability and ischemia also correlated. At dobutamine echocardiography, a composite of dysfunctional and ischemic myocardium was the strongest correlate of BNP (r = 0.48, p < 0.0001), with less strong correlations by global parameters. The extent of dysfunctional myocardium, rather than its nature determines BNP levels.