Heart development: An introduction

Risk of maternal exposure to mixed air pollutants during pregnancy for congenital heart diseases in offspring

OBJECTIVE

To explore the risk of maternal exposure to mixed air pollutants of particulate matter 1 (PM ₁), particulate matter 2.5 (PM _2.5), particulate matter 10 (PM ₁₀) and NO ₂ for congenital heart disease (CHD) in offspring, and to estimate the ranked weights of the above pollutants.

METHODS

6038 CHD patients and 5227 healthy controls from 40 medical institutions in 21 cities in Guangdong Registry of Congenital Heart Disease (GRCHD) from 2007 to 2016 were included. Logistic regression model was used to estimate the effect of maternal exposure to a single air pollutant on the occurrence of CHD in offspring. Spearman correlation coefficient was used to analyze the correlation between various pollutants, and Quantile g-computation was used to evaluate the joint effects of mixed exposure of air pollutants on CHD and the weights of various pollutants.

RESULTS

The exposure levels of PM ₁, PM _2.5, PM ₁₀ and NO ₂ in the CHD group were significantly higher than those in the control group (all P<0.01). The correlation coefficients among PM ₁, PM _2.5, PM ₁₀ and NO ₂ were greater than 0.80. PM ₁, PM _2.5, PM ₁₀ and NO ₂ exposure were associated with a significantly increased risk of CHD in offspring. Mixed exposure of these closely correlated pollutants presented much stronger effect on CHD than exposure of any single pollutants. There was a monotonic increasing relationship between mixed exposure and CHD risk. For each quantile increase in mixed exposure, the risk of CHD increased by 47% ( OR=1.47, 95% CI: 1.34-1.61). Mixed exposure had greater effect on CHD in the early pregnancy compared with middle and late pregnancy, but the greatest effect was the exposure in the whole pregnancy. The weight of PM ₁₀ is the highest in the mixed exposure (81.3%).

CONCLUSIONS

Maternal exposure to the mixture of air pollutants during pregnancy increases the risk of CHD in offspring, and the effect is much stronger than that of single exposure of various pollutants. PM ₁₀ has the largest weights and the strongest effect in the mixed exposure.

Anuran heart development and critical developmental periods: a comparative analysis of three Neotropical anuran species

The heart begins to form early during vertebrate development and is the first functional organ of the embryo. This study aimed to describe and compare the heart development in three Neotropical anuran species, Physalaemus albonotatus, Elachistocleis bicolor, and Scinax nasicus. Different Gosner Stages (GS) of embryos (GS 18-20) and premetamorphic (GS 21-25), prometamorphic (GS 26-41) and metamorphic (GS 42-46) tadpoles were analyzed using stereoscopic microscopy and Scanning Electronic Microscopy. Heart development was similar in the three analyzed species; however, some heterochronic events were identified between P. albonotatus and S. nasicus compared to E. bicolor. In addition, different patterns of melanophores arrangement were observed. During the embryonic and metamorphic periods, the main morphogenetic events occur: formation of the heart tube, regionalization of the heart compartments, development of spiral valve, onset of heartbeat, looping, and final displacement of the atrium and its complete septation. Both periods are critical for the normal morphogenesis and the correct functioning of the anuran heart. These results are useful to characterize the normal anuran heart morphology and to identify possible abnormalities caused by exposure to environmental contaminants.

Maternal exposure to ambient air pollution and congenital heart defects in China

BACKGROUND

Evidence of maternal exposure to ambient air pollution on congenital heart defects (CHD) has been mixed and are still relatively limited in developing countries. We aimed to investigate the association between maternal exposure to air pollution and CHD in China.

METHOD

This longitudinal, population-based, case-control study consecutively recruited fetuses with CHD and healthy volunteers from 21 cities, Southern China, between January 2006 and December 2016. Residential address at delivery was linked to random forests models to estimate maternal exposure to particulate matter with an aerodynamic diameter of ≤ 1 µm (PM₁), ≤2.5 µm, and ≤10 µm as well as nitrogen dioxides, in three trimesters. The CHD cases were evaluated by obstetrician, pediatrician, or cardiologist, and confirmed by cardia ultrasound. The CHD subtypes were coded using the International Classification Diseases. Adjusted logistic regression models were used to assess the associations between air pollutants and CHD and its subtypes.

RESULTS

A total of 7055 isolated CHD and 6423 controls were included in the current analysis. Maternal air pollution exposures were consistently higher among cases than those among controls. Logistic regression analyses showed that maternal exposure to all air pollutants during the first trimester was associated with an increased odds of CHD (e.g., an interquartile range [13.3 µg/m³] increase in PM₁ was associated with 1.09-fold ([95% confidence interval, 1.01-1.18]) greater odds of CHD). No significant associations were observed for maternal air pollution exposures during the second trimester and the third trimester. The pattern of the associations between air pollutants and different CHD subtypes was mixed.

CONCLUSIONS

Maternal exposure to greater levels of air pollutants during the pregnancy, especially the first trimester, is associated with higher odds of CHD in offspring. Further longitudinal well-designed studies are warranted to confirm our findings.

Maternal exposure to traffic-related air pollution and birth defects in Massachusetts

Exposures to particulate matter with diameter of 2.5µm or less (PM2.5) may influence risk of birth defects. We estimated associations between maternal exposure to prenatal traffic-related air pollution and risk of cardiac, orofacial, and neural tube defects among Massachusetts births conceived 2001 through 2008. Our analyses included 2729 cardiac, 255 neural tube, and 729 orofacial defects. We used satellite remote sensing, meteorological and land use data to assess PM2.5 and traffic-related exposures (distance to roads and traffic density) at geocoded birth addresses. We calculated adjusted odds ratios (OR) and confidence intervals (CI) using logistic regression models. Generalized additive models were used to assess spatial patterns of birth defect risk. There were positive but non-significant associations for a 10µg/m(3) increase in PM2.5 and perimembranous ventricular septal defects (OR=1.34, 95% CI: 0.98, 1.83), patent foramen ovale (OR=1.19, 95% CI: 0.92, 1.54) and patent ductus arteriosus (OR=1.20, 95% CI: 0.95, 1.62). There was a non-significant inverse association between PM2.5 and cleft lip with or without palate (OR=0.76, 95% CI: 0.50, 1.10), cleft palate only (OR=0.89, 95% CI: 0.54, 1.46) and neural tube defects (OR=0.77, 95% CI: 0.46, 1.05). Results for traffic related exposure were similar. Only ostium secundum atrial septal defects displayed significant spatial variation after accounting for known risk factors.

Ambient air pollution and congenital heart disease: a register-based study

Maternal exposure to ambient air pollution has increasingly been linked to adverse pregnancy outcomes. The evidence linking this exposure to congenital anomalies is still limited and controversial. This case-control study investigated the association between maternal exposure to ambient particulate matter with aerodynamic diameter less than 10 μm (PM(10)), sulfur dioxide (SO(2)), nitrogen dioxide, nitric oxide (NO), ozone (O(3)), and carbon monoxide (CO) and the occurrence of congenital heart disease in the population of Northeast England (1993-2003). Each case and control was assigned weekly average (weeks 3-8 of pregnancy) of pollutant levels measured by the closest monitor to the mother's residential postcode. Using exposure as both continuous and categorical variables, logistic regression models were constructed to quantify the adjusted odds ratios of exposure to air pollutants and the occurrence of each outcome group. We found exposure to CO and NO to be associated with ventricular septal defect and cardiac septa malformations. CO was also associated with congenital pulmonary valve stenosis and NO with pooled cases of congenital heart disease and tetralogy of Fallot. Findings for SO(2), O(3) and PM(10) were less consistent.

Association between maternal exposure to ambient air pollution and congenital heart disease: A register-based spatiotemporal analysis

Recent studies have linked maternal exposure to air pollution with a range of adverse pregnancy outcomes. However, the available evidence linking this exposure to congenital anomalies is still limited and controversial. The present case-control study tested the hypothesis that maternal exposure to ambient black smoke and sulfur dioxide is a risk factor for the occurrence of congenital heart disease. The authors used registry-based data on congenital heart disease for the population of the northeast of England in 1985-1996. A 2-stage spatiotemporal model was developed to predict weekly black smoke and sulfur dioxide levels at each maternal place of residence. Controls were frequency-matched to cases by year of birth (control-to-case ratio of 4:1). Two sets of analyses were performed, using predicted mean values of exposure and 1,000 simulated scenarios of exposure. The analyses were adjusted for birth year, socioeconomic status, infant sex, season of conception, and degree of urbanity. The authors found a weak association between maternal exposure to black smoke and congenital malformations of cardiac chambers and connections only when using exposure as a continuous variable. When the authors used quartiles of exposure, odds ratios did not show a dose-response relation for consecutive quartiles. For sulfur dioxide, the results were not indicative of any association.

Association of congenital cardiovascular malformations with 33 single nucleotide polymorphisms of selected cardiovascular disease-related genes

INTRODUCTION

Clark (1996) proposed that abnormal blood flow is related to some congenital cardiovascular malformations (CCVMs), particularly CCVM with obstruction to blood flow. Our hypothesis is that CCVMs may relate to genes that affect blood coagulation or flow. We studied whether polymorphisms of such genes are related to CCVMs; previous association of these SNPs to conotruncal CCVMs is described.

METHODS

We assessed risk of pulmonary stenosis (PS, N = 120), atrial septal defect (ASD, N = 108), aortic stenosis (AS, N = 36), and coarctation of the aorta (CoAo, N = 64), associated with 33 candidate genes, selected for their relationship to blood flow affected by homocysteine metabolism, coagulation, cell-cell interaction, inflammation, or blood pressure regulation.

RESULTS

Effects were specific to cardiac phenotype and race. CoAo was associated with MTHFR (-667) C>T (odds ratio [OR] for TT 3.5, 95% confidence limits [CI] 1.4-8.6). AS was associated with a polymorphism of SERPINE1, G5>G4, OR = 5.6 for the homozygote with 95% CI 1.4-22.9. Unique polymorphisms were associated with increased risk of ASD and PS: NPPA 664G>A with ASD (OR of 2.4, 95%CI 1.3-4.4) and NOS3 (-690) C>T with PS (OR 6.1; 95% CI 1.6-22.6 in the African American population only). For ASD, the NPPA (-664) G>A SNP there was increased risk from the variant genotype only in maternal smokers (OR 2.6; 95% CI 1.0-7.2).

CONCLUSIONS

Genes affecting vascular function and coagulation appear to be promising candidates for the etiology of cardiac malformations and warrant further study.

The outflow tract of the heart in fishes: anatomy, genes and evolution

A large number of congenital heart defects associated with mortality in humans are those that affect the cardiac outflow tract, and this provides a strong imperative to understand its development during embryogenesis. While there is wide phylogenetic variation in adult vertebrate heart morphology, recent work has demonstrated evolutionary conservation in the early processes of cardiogenesis, including that of the outflow tract. This, along with the utility and high reproductive potential of fish species such as Danio rerio, Oryzias latipes etc., suggests that fishes may provide ideal comparative biological models to facilitate a better understanding of this poorly understood region of the heart. In this review, the authors present the current understanding of both phylogeny and ontogeny of the cardiac outflow tract in fishes and examine how new molecular studies are informing the phylogenetic relationships and evolutionary trajectories that have been proposed. The authors also attempt to address some of the issues of nomenclature that confuse this area of research.

Conus arteriosus of the teleost heart: Dismissed, but not missed

The heart outflow tract (OFT) of primitive fish is formed by two portions: a proximal conus arteriosus and a distal bulbus arteriosus. The OFT of modern teleosts is considered to be formed by a single component, the bulbus, the conus having been lost through evolution. This article challenges the concept of the disappearance of the conus arteriosus in the teleost heart. A total of 28 teleost species belonging to 19 families and 10 orders were analyzed. The hearts were divided into two large groups: those having entirely trabeculated ventricles, and those possessing a compacta. In the hearts having entirely trabeculated ventricles, the conus arteriosus appears as a distinct segment interposed between the ventricle and the bulbus arteriosus, being formed by compact vascularized myocardium. However, the conus of several species lacks vessels. In these cases, the conus presents large intercellular spaces bounded by collagen. In the hearts possessing a ventricular compacta, the conus either appears as a muscular ring of variable length connecting the ventricle and the bulbus or forms a crown or ring of myocardium apposed to the ventricular base. In all the teleosts studied, the conus can be recognized as an anatomic entity different from the ventricle. Furthermore, the conus appears as a distinct heart segment in the developing fish. Therefore, the conus arteriosus has not been lost in evolution and constitutes a fundamental part of the teleost OFT. In all the species studied, the conus supports the OFT valves, which should properly be named conus valves.

Ventricle and outflow tract of the African lungfish Protopterus dolloi

We report a morphologic study of the heart ventricle and outflow tract of the African lungfish Protopterus dolloi. The ventricle is saccular and appears attached to the anterior pericardial wall by a thick tendon. An incomplete septum divides the ventricle into two chambers. Both the free ventricular wall and the incomplete ventricular septum are entirely trabeculated. Only a thin rim of myocardium separates the trabecular system from the subepicardial space. The outflow tract consists of proximal, middle, and distal portions, separated by two flexures, proximal and distal. The proximal outflow tract portion is endowed with a layer of compact, well-vascularized myocardium. This portion is homologous to the conus arteriosus observed in the heart of most vertebrates. The middle and distal outflow tract portions are arterial-like, thus being homologous to the bulbus arteriosus. However, the separation between the muscular and arterial portions of the outflow tract is not complete in the lungfish. A thin layer of myocardium covers the arterial tissue, and a thin layer of elastic tissue underlies the conus myocardium. Two unequal ridges composed of loose connective tissue, the spiral and bulbar folds, run the length of the outflow tract. They form an incomplete division of the outflow tract, but fuse at the distal end. The two folds are covered by endocardium and contain collagen, elastin, and fibroblast-like cells. They appear to be homologous to the dextro-dorsal and sinistro-ventral ridges observed during the development of the avian and mammalian heart. Two to three rows of vestigial arterial-like valves appear in the dorsal and ventral aspects of the conus. These valves are unlikely to have a functional role. The possible functional significance of the "gubernaculum cordis," the thick tendon extending between the anterior ventricular surface and the pericardium, is discussed.

Differentiation of the cardiac outflow tract components in alevins of the sturgeonAcipenser naccarii(Osteichthyes, Acipenseriformes): Implications for heart evolution

Previous work showed that in the adult sturgeon an intrapericardial, nonmyocardial segment is interposed between the conus arteriosus of the heart and the ventral aorta. The present report illustrates the ontogeny of this intermediate segment in Acipenser naccarii. The sample studied consisted of 178 alevins between 1 and 24 days posthatching. They were examined using light and electron microscopy. Our observations indicate that the entire cardiac outflow tract displays a myocardial character during early development. Between the fourth and sixth days posthatching, the distal portion of the cardiac outflow tract undergoes a phenotypical transition, from a myocardial to a smooth muscle-like phenotype. The length of this region with regard to the whole outflow tract increases only moderately during subsequent developmental stages, becoming more and more cellularized. The cells soon organize into a pattern that resembles that of the arterial wall. Elastin appears at this site by the seventh day posthatching. Therefore, two distinct components, proximal and distal, can be recognized from the fourth day posthatching in the cardiac outflow tract of A. naccarii. The proximal component is the conus arteriosus, characterized by its myocardial nature and the presence of endocardial cushions. The distal component transforms into the intrapericardial, nonmyocardial segment mentioned above, which is unequivocally of cardiac origin. We propose to designate this segment the "bulbus arteriosus" because it is morphogenetically equivalent to the bulbus arteriosus of teleosts. The present findings, together with data from the literature, point to the possibility that cells from the cardiac neural crest are involved in the phenotypical transition that takes place at the distal portion of the cardiac outflow tract, resulting in the appearance of the bulbus arteriosus. Moreover, they suggest that the cardiac outflow tract came to be formed by a bulbus arteriosus and a conus arteriosus from an early period of the vertebrate evolutionary story. Finally, we hypothesize that the embryonic truncus of birds and mammals is homologous to the bulbus arteriosus of fish.