Ethnic differences in childhood right and left cardiac structure and function assessed by cardiac magnetic resonance imaging

The prevalence of cardiovascular disease differs between ethnic groups [1‐4]. Studies in the USA suggest that adults from Hispanic and African American background have higher risks of cardiovascular disease than adults from European background [1, 2]. Similarly, in the UK, cardiovascular disease risk is higher among adults from West-African and South-Asian background than among Caucasians [3, 5]. In the Netherlands, lower cardiovascular mortality was reported among adults from Morocco, but higher mortality was observed among the Surinamese than among native Dutch adults [5]. These possible differences are increasingly relevant with the number of migrants in Western Europe [6, 7].

Differences in common risk factors for cardiovascular disease such as body mass index (BMI), blood pressure, and lipid and insulin concentrations can already be observed in childhood and track to adulthood [8‐11]. We previously reported ethnic differences in common cardiovascular risk factors in childhood in the Netherlands, which were mainly explained by early life factors [10]. Although cardiac structures are independent risk factors for mortality in adults, and tend to track from childhood to adulthood, ethnic differences in cardiac structure and function have been studied less extensively [12, 13].

Greater left ventricular end-diastolic volume (LVEDV), left ventricular mass (LVM), and lower LV ejection fraction (LVEF) have been observed in Americans from African background than European background [14]. In the UK, adults from Indian Asian background had smaller LVEDV and LVM than those from European background [15]. Studies in children do not show consistent results [16, 17]. In childhood, lean body mass explains most of the variation in LVM and might differ between ethnicities [10, 18]. Differences in lean mass and other early life factors may influence the ethnic differences in cardiac structure. Most previous studies used echocardiography to evaluate cardiac structures. However, cardiac magnetic resonance imaging (cMRI) has been found to be more accurate and reproducible than echocardiography, and enables studies on volumes of the right side of the heart, another independent risk factor for cardiovascular mortality [19‐21].

We examined ethnic differences in left and right cardiac structure and function in children using cMRI in a multi-ethnic population-based study among 2317 children in Rotterdam, the Netherlands, and examined whether any difference was explained by differences in fetal and childhood factors.

In this multi-ethnic population-based prospective cohort study among 10-year-old children born in the Netherlands, children from Cape Verdean, Surinamese-Hindustani, and Turkish background had smaller RVEDV and LVEDV, relative to their current BSA than Dutch children. These differences were only partly explained by fetal and childhood factors. We did not find consistent associations of ethnicity with RVEF, LVEF, LVM, or LMVR after adjusting for fetal or childhood factors.

Several studies have shown a difference in cardiovascular disease between ethnic groups [1‐5]. In the Netherlands, higher cardiovascular mortality has been observed in adults of Surinamese background [5]. Adults from Moroccans background generally show lower risk of cardiovascular mortality [5]. Although self-reported cardiovascular disease was higher in adults from Turkish background, studies on cardiovascular outcomes have reported conflicting results [5,30].

In our current study, we observed lower RVEDV and LVEDV in children from Cape Verdean, Surinamese-Hindustani, and Turkish background, as compared to Dutch children. The differences in RVEDV and LVEDV in children from Cape Verdean, Surinamese-Hindustani, and Turkish background attenuated slightly after adjustment for fetal and childhood factors. In childhood, cardiac size is mainly determined by lean body mass [18]. Although we standardized the cardiac outcomes on BSA and adjusted for lean body mass percentage, other unaccounted factors of body size and composition might explain part of the differences in cardiac structure that we observed. Also, it is known that well-trained athletes have a larger LVEDV [31]. In the current study, we do not have detailed information on cardiovascular fitness and overall physical activity available, and we were not able to examine if differences in fitness could explain the associations of ethnicity with cardiac structure.

In adults a larger heart and higher LVM as well as RVEDV and LVEDV, are generally associated with higher risk of cardiovascular disease [12, 32]. A higher LMVR is associated with adverse cardiac outcomes, independent from LVM [33]. We observed a lower LVM and a higher LMVR in children from Surinamese-Hindustani background compared to Dutch children, but these associations attenuated fully after adjustment for fetal factors.

Our findings suggest that ethnicity is associated with cardiac structure at school-age, and this association is only partly explained by fetal and childhood factors. The differences we observed were small, and within normal ranges. Further studies are needed to explore whether these differences relate to adult cardiovascular disease. Multiple studies have established Z-scores for cardiac MRI. However, many of these studies are based on a relatively small study population. It would be interesting to create normal values in a large study population across all age-groups taking account for differences between ethnic subgroups.

To our knowledge, this is the first study focused on the associations of children’s ethnicity with cardiac structure and function using cMRI in a large and diverse multi-ethnic prospective cohort. The major advantages of cMRI instead of echocardiography are more accurate measurements and information about the right cardiac structures [19]. Some limitations need to be considered. Of the original cohort, 60% of the children visited the research center at the age of 10 years. Of these children, 72% also attended the MRI center. Lower attendance is due to later start of the MRI study. cMRI was not performed in 15% of children that underwent body MRI. Reasons for not performing cMRI were often logistical, such as malfunctioning of equipment or time constraints. Also, we were not able to analyze 16% of the cMRI scans due to poor quality of the scans. This was partly due to using an 3.0T MRI scan, which is less ideal for imaging of the body [20, 19]. Height and weight used to calculate BSA were measured during an earlier visit than the MRI scan. Around 65% of children visited the MRI within 2 months after the BSA visit, with a median time difference of 1.28 months (95% range (0, 24.2)). Even though we adjusted for the time difference, measurement error can cause attenuation of the observed associations. Finally, it is possible that the observed differences are explained by residual confounding. This could be due to specific factors such as physical activity, blood pressure and arterial hypertension, clustering of cardiovascular risk factors diet or possible comorbidities such as diabetes mellitus or chronic kidney disease (either diagnosed or subclinical), hyperlipidemia, or parental smoking exposure or other parental and childhood lifestyle characteristics [34, 35]. We previously reported ethnic differences in well-known cardiovascular risk factors [10]. Adjustment for these factors did not explain all ethnic differences in cardiovascular risk factors.

Right and left cardiac dimensions differ between ethnic groups in childhood. These differences are only partly explained by fetal and childhood factors. Further research is necessary to examine how ethnic differences in cardiac structure progress during and after adolescence, and if this contributes to later cardiovascular disease.