Truncus arteriosus from prenatal diagnosis to clinical outcome: a single-centre experience.

BACKGROUND: The aim of this study was to review our institution's experience with truncus arteriosus from prenatal diagnosis to clinical outcome. METHODS: and results: We conducted a single-centre retrospective cohort study for the years 2005-2020. Truncus arteriosus antenatal echocardiographic diagnostic accuracy within our institution was 92.3%. After antenatal diagnosis, five parents (31%) decided to terminate the pregnancy. After inclusion from referring hospitals, 16 patients were offered surgery and were available for follow-up. Right ventricle-to-pulmonary artery continuity was preferably established without the use of a valve (direct connection), which was possible in 14 patients (88%). There was no early or late mortality. Reinterventions were performed in half of the patients at latest follow-up (median follow-up of 5.4 years). At a median age of 5.5 years, 13 out of 14 patients were still without right ventricle-to-pulmonary artery valve, which was well tolerated without signs of right heart failure. The right ventricle demonstrated preserved systolic function as expressed by tricuspid annular plane systolic excursion z-score (-1.4 ± 1.7) and fractional area change (44 ± 12%). The dimensions and function of the left ventricle were normal at latest follow-up (ejection fraction 64.4 ± 6.2%, fractional shortening 34.3 ± 4.3%). CONCLUSIONS: This study demonstrates good prenatal diagnostic accuracy of truncus arteriosus. There was no mortality and favourable clinical outcomes at mid-term follow-up, with little interventions on the right ventricle-to-pulmonary artery connection and no right ventricle deterioration. This supports the notion that current perspectives of patients with truncus arteriosus are good, in contrast to the poor historic outcome series. This insight can be used in counselling and surgical decision-making.

Comparison of Four-Dimensional Flow MRI, Two-Dimensional Phase-Contrast MRI and Echocardiography in Transposition of the Great Arteries.

Pulmonary artery (PA) stenosis is a common complication after the arterial switch operation (ASO) for transposition of the great arteries (TGA). Four-dimensional flow (4D flow) CMR provides the ability to quantify flow within an entire volume instead of a single plane. The aim of this study was to compare PA maximum velocities and stroke volumes between 4D flow CMR, two-dimensional phase-contrast (2D PCMR) and echocardiography. A prospective study including TGA patients after ASO was performed between December 2018 and October 2020. All patients underwent echocardiography and CMR, including 2D PCMR and 4D flow CMR. Maximum velocities and stroke volumes were measured in the main, right, and left PA (MPA, LPA, and RPA, respectively). A total of 39 patients aged 20 ± 8 years were included. Maximum velocities in the MPA, LPA, and RPA measured by 4D flow CMR were significantly higher compared to 2D PCMR (p < 0.001 for all). PA assessment by echocardiography was not possible in the majority of patients. 4D flow CMR maximum velocity measurements were consistently higher than those by 2D PCMR with a mean difference of 65 cm/s for the MPA, and 77 cm/s for both the RPA and LPA. Stroke volumes showed good agreement between 4D flow CMR and 2D PCMR. Maximum velocities in the PAs after ASO for TGA are consistently lower by 2D PCMR, while echocardiography only allows for PA assessment in a minority of cases. Stroke volumes showed good agreement between 4D flow CMR and 2D PCMR.

Cardiac regeneration from activated epicardium.

In contrast to lower vertebrates, the mammalian heart has a very limited regenerative capacity. Cardiomyocytes, lost after ischemia, are replaced by fibroblasts. Although the human heart is able to form new cardiomyocytes throughout its lifespan, the efficiency of this phenomenon is not enough to substitute sufficient myocardial mass after an infarction. In contrast, zebrafish hearts regenerate through epicardial activation and initiation of myocardial proliferation. With this study we obtain insights into the activation and cellular contribution of the mammalian epicardium in response to ischemia. In a mouse myocardial infarction model we analyzed the spatio-temporal changes in expression of embryonic epicardial, EMT, and stem cell markers and the contribution of cells of the Wt1-lineage to the infarcted area. Though the integrity of the epicardial layer overlaying the infarct is lost immediately after the induction of the ischemia, it was found to be regenerated at three days post infarction. In this regenerated epicardium, the embryonic gene program is transiently re-expressed as well as proliferation. Concomitant with this activation, Wt1-lineage positive subepicardial mesenchyme is formed until two weeks post-infarction. These mesenchymal cells replace the cardiomyocytes lost due to the ischemia and contribute to the fibroblast population, myofibroblasts and coronary endothelium in the infarct, and later also to the cardiomyocyte population. We show that in mice, as in lower vertebrates, an endogenous, epicardium-dependent regenerative response to injury is induced. Although this regenerative response leads to the formation of new cardiomyocytes, their number is insufficient in mice but sufficient in lower vertebrates to replace lost cardiomyocytes. These molecular and cellular analyses provide basic knowledge essential for investigations on the regeneration of the mammalian heart aiming at epicardium-derived cells.

Epicardially derived fibroblasts preferentially contribute to the parietal leaflets of the atrioventricular valves in the murine heart.

The importance of the epicardium for myocardial and valvuloseptal development has been well established; perturbation of epicardial development results in cardiac abnormalities, including thinning of the ventricular myocardial wall and malformations of the atrioventricular valvuloseptal complex. To determine the spatiotemporal contribution of epicardially derived cells to the developing fibroblast population in the heart, we have used a mWt1/IRES/GFP-Cre mouse to trace the fate of EPDCs from embryonic day (ED)10 until birth. EPDCs begin to populate the compact ventricular myocardium around ED12. The migration of epicardially derived fibroblasts toward the interface between compact and trabecular myocardium is completed around ED14. Remarkably, epicardially derived fibroblasts do not migrate into the trabecular myocardium until after ED17. Migration of EPDCs into the atrioventricular cushion mesenchyme commences around ED12. As development progresses, the number of EPDCs increases significantly, specifically in the leaflets which derive from the lateral atrioventricular cushions. In these developing leaflets the epicardially derived fibroblasts eventually largely replace the endocardially derived cells. Importantly, the contribution of EPDCs to the leaflets derived from the major AV cushions is very limited. The differential contribution of EPDCs to the various leaflets of the atrioventricular valves provides a new paradigm in valve development and could lead to new insights into the pathogenesis of abnormalities that preferentially affect individual components of this region of the heart. The notion that there is a significant difference in the contribution of epicardially and endocardially derived cells to the individual leaflets of the atrioventricular valves has also important pragmatic consequences for the use of endocardial and epicardial cre-mouse models in studies of heart development.

Cardiac myocyte follistatin-like 1 functions to attenuate hypertrophy following pressure overload.

Factors secreted by the heart, referred to as "cardiokines," have diverse actions in the maintenance of cardiac homeostasis and remodeling. Follistatin-like 1 (Fstl1) is a secreted glycoprotein expressed in the adult heart and is induced in response to injurious conditions that promote myocardial hypertrophy and heart failure. The aim of this study was to investigate the role of cardiac Fstl1 in the remodeling response to pressure overload. Cardiac myocyte-specific Fstl1-KO mice were constructed and subjected to pressure overload induced by transverse aortic constriction (TAC). Although Fstl1-KO mice displayed no detectable baseline phenotype, TAC led to enhanced cardiac hypertrophic growth and a pronounced loss in ventricular performance by 4 wk compared with control mice. Conversely, mice that acutely or chronically overexpressed Fstl1 were resistant to pressure overload-induced hypertrophy and cardiac failure. Fstl1-deficient mice displayed a reduction in TAC-induced AMP-activated protein kinase (AMPK) activation in heart, whereas Fstl1 overexpression led to increased myocardial AMPK activation under these conditions. In cultured neonatal cardiomyocytes, administration of Fstl1 promoted AMPK activation and antagonized phenylephrine-induced hypertrophy. Inhibition of AMPK attenuated the antihypertrophic effect of Fstl1 treatment. These results document that cardiac Fstl1 functions as an autocrine/paracrine regulatory factor that antagonizes myocyte hypertrophic growth and the loss of ventricular performance in response to pressure overload, possibly through a mechanism involving the activation of the AMPK signaling axis.

Comprehensive gene-expression survey identifies wif1 as a modulator of cardiomyocyte differentiation.

During chicken cardiac development the proepicardium (PE) forms the epicardium (Epi), which contributes to several non-myocardial lineages within the heart. In contrast to Epi-explant cultures, PE explants can differentiate into a cardiomyocyte phenotype. By temporal microarray expression profiles of PE-explant cultures and maturing Epi cells, we identified genes specifically associated with differentiation towards either of these lineages and genes that are associated with the Epi-lineage restriction. We found a central role for Wnt signaling in the determination of the different cell lineages. Immunofluorescent staining after recombinant-protein incubation in PE-explant cultures indicated that the early upregulated Wnt inhibitory factor-1 (Wif1), stimulates cardiomyocyte differentiation in a similar manner as Wnt stimulation. Concordingly, in the mouse pluripotent embryogenic carcinoma cell line p19cl6, early and late Wif1 exposure enhances and attenuates differentiation, respectively. In ovo exposure of the HH12 chicken embryonic heart to Wif1 increases the Tbx18-positive cardiac progenitor pool. These data indicate that Wif1 enhances cardiomyogenesis.

Epicardium and myocardium originate from a common cardiogenic precursor pool.

During development, the epicardium, an epithelial layer that covers the heart, gives rise to a large portion of the nonmyocardial cells present in the heart. The epicardium arises from a structure, called the proepicardium, which forms at the inflow of the developing heart. By epithelial-to-mesenchymal transformation, mesenchymal cells are formed that will subsequently populate the stroma of the proepicardium and the subepicardium. Based on labeling analysis, the proepicardium and part of the myocardium have been shown to be derived from a common cardiogenic precursor population. In this review, we will discuss the common cardiogenic origin of proepicardial and myocardial cells, the underlying processes and factors that play a role in the separation of the lineages, and their potential role in cardiac regenerative approaches.

Wt1 and retinoic acid signaling in the subcoelomic mesenchyme control the development of the pleuropericardial membranes and the sinus horns.

RATIONALE: The cardiac venous pole is a common focus of congenital malformations and atrial arrhythmias, yet little is known about the cellular and molecular mechanisms that regulate its development. The systemic venous return myocardium (sinus node and sinus horns) forms only late in cardiogenesis from a pool of pericardial mesenchymal precursor cells. OBJECTIVE: To analyze the cellular and molecular mechanisms directing the formation of the fetal sinus horns. METHODS AND RESULTS: We analyzed embryos deficient for the Wt1 (Wilms tumor 1) gene and observed a failure to form myocardialized sinus horns. Instead, the cardinal veins become embedded laterally in the pleuropericardial membranes that remain tethered to the lateral body wall by the persisting subcoelomic mesenchyme, a finding that correlates with decreased apoptosis in this region. We show by expression analysis and lineage tracing studies that Wt1 is expressed in the subcoelomic mesenchyme surrounding the cardinal veins, but that this Wt1-positive mesenchyme does not contribute cells to the sinus horn myocardium. Expression of the Raldh2 (aldehyde dehydrogenase family 1, subfamily A2) gene was lost from this mesenchyme in Wt1(-/-) embryos. Phenotypic analysis of Raldh2 mutant mice rescued from early cardiac defects by retinoic acid food supply revealed defects of the venous pole and pericardium highly similar to those of Wt1(-/-) mice. CONCLUSIONS: Pericardium and sinus horn formation are coupled and depend on the expansion and correct temporal release of pleuropericardial membranes from the underlying subcoelomic mesenchyme. Wt1 and downstream Raldh2/retinoic acid signaling are crucial regulators of this process. Thus, our results provide novel insight into the genetic and cellular pathways regulating the posterior extension of the mammalian heart and the formation of its coelomic lining.

Epicardium and myocardium separate from a common precursor pool by crosstalk between bone morphogenetic protein- and fibroblast growth factor-signaling pathways.

RATIONALE: The epicardium contributes to the majority of nonmyocardial cells in the adult heart. Recent studies have reported that the epicardium is derived from Nkx2.5-positive progenitors and can differentiate into cardiomyocytes. Not much is known about the relation between the myocardial and epicardial lineage during development, whereas insights into these embryonic mechanisms could facilitate the design of future regenerative strategies. OBJECTIVE: Acquiring insight into the signaling pathways involved in the lineage separation leading to the differentiation of myocardial and (pro)epicardial cells at the inflow of the developing heart. METHODS AND RESULTS: We made 3D reconstructions of Tbx18 gene expression patterns to give insight into the developing epicardium in relation to the developing myocardium. Next, using DiI tracing, we show that the (pro)epicardium separates from the same precursor pool as the inflow myocardium. In vitro, we show that this lineage separation is regulated by a crosstalk between bone morphogenetic protein (BMP) signaling and fibroblast growth factor (FGF) signaling. BMP signaling via Smad drives differentiation toward the myocardial lineage, which is inhibited by FGF signaling via mitogen-activated protein kinase kinase (Mek)1/2. Embryos exposed to recombinant FGF2 in vivo show enhanced epicardium formation, whereas a misbalance between FGF and BMP by Mek1/2 inhibition and BMP stimulation causes a developmental arrest of the epicardium and enhances myocardium formation at the inflow of the heart. CONCLUSION: Our data show that FGF signaling via Mek1/2 is dominant over BMP signaling via Smad and is required to separate the epicardial lineage from precardiac mesoderm. Consequently, myocardial differentiation requires BMP signaling via Smad and inhibition of FGF signaling at the level of Mek1/2. These findings are of clinical interest for the development of regeneration-based therapies for heart disease.

Role of bone morphogenetic proteins in cardiac differentiation.

Bone morphogenetic proteins (BMP) are involved in the regulation of a plethora of processes underlying cardiovascular development. This review summarizes the effects of BMP and the signaling pathways that regulate the differentiation of cardiomyocytes from mesoderm in the heart-forming region and at the distal borders of the heart tube from the second heart field. Subsequently, the role of BMPs in the formation of the ventricular chambers and septovalvulogenesis in the atrioventricular canal and outflow tract is described. Finally, the effects of BMPs in stem cell biology and cardiac regeneration are discussed.

BMP and FGF regulate the differentiation of multipotential pericardial mesoderm into the myocardial or epicardial lineage.

Proepicardial cells give rise to epicardium, coronary vasculature and cardiac fibroblasts. The proepicardium is derived from the mesodermal lining of the prospective pericardial cavity that simultaneously contributes myocardium to the venous pole of the elongating primitive heart tube. Using proepicardial explant cultures, we show that proepicardial cells have the potential to differentiate into cardiac muscle cells, reflecting the multipotency of this pericardial mesoderm. The differentiation into the myocardial or epicardial lineage is mediated by the cooperative action of BMP and FGF signaling. BMP2 is expressed in the distal IFT myocardium and stimulates cardiomyocyte formation. FGF2 is expressed in the proepicardium and stimulates differentiation into the epicardial lineage. In the base of the proepicardium, coexpression of BMP2 and FGF2 inhibits both myocardial and epicardial differentiation. We conclude that the epicardial/myocardial lineage decisions are mediated by an extrinsic, inductive mechanism, which is determined by the position of the cells in the pericardial mesoderm.