Sex differences in the determinants of left ventricular mass in childhood. The Medical College of Virginia Twin Study

The cardiovascular exercise response in children with overweight or obesity measured by cardiovascular magnetic resonance imaging

BACKGROUND

Overweight and obesity are among the main causes of cardiovascular diseases. Exercise testing can aid in the early detection of subtle cardiac dysfunction not present in rest. We hypothesized that the cardiovascular response to exercise is impaired among children with overweight or obesity, characterized by the inability of the cardiovascular system to adapt to exercise by increasing cardiac volumes and blood pressure. We performed a cardiovascular stress test to investigate whether the cardiovascular exercise response is altered in children with overweight and obesity, as compared to children with a normal weight.

SUBJECTS

A subgroup of the Generation R population-based prospective cohort study, consisting of 41 children with overweight or obesity and 166 children with a normal weight with a mean age of 16 years, performed an isometric exercise.

METHODS

Continuous heart rate and blood pressure were measured during rest, exercise and recovery. Cardiovascular magnetic resonance (CMR) measurements were performed during rest and exercise.

RESULTS

Higher BMI was associated with a higher resting systolic and diastolic blood pressure (difference: 0.24 SDS (95% CI 0.10, 0.37) and 0.20 SDS (95% CI 0.06, 0.33)) and lower systolic and diastolic blood pressure increases from rest to peak exercise (-0.11 SDS (95% CI -0.20, -0.03) and -0.07 SDS (95% CI -0.07, -0.01)). BMI was also associated with a slower decrease in systolic and diastolic blood pressure during recovery (p values < 0.05). Higher childhood BMI was associated with lower BSA corrected left ventricular mass, end-diastolic volume and stroke volume (p values < 0.05). There were no associations of childhood BMI with the cardiac response to exercise measured by heart rate and CMR measurements.

CONCLUSION

Childhood BMI is, across the full range, associated with a blunted blood pressure response to static exercise but there were no differences in cardiac response to exercise. Our findings suggest that adiposity may especially affect the vascular exercise reaction without affecting cardiac response.

Echocardiographic Comparison of Left Ventricular Systolic Function and Aortic Blood Flow Velocimetry in Children with Ventricular Septal Defect

BACKGROUND

The assessments of left ventricular (LV) longitudinal systolic dynamics in children with ventricular septal defect (VSD) have achieved a major milestone in the evaluation of LV systolic function.

OBJECTIVES

This study aims to evaluate the LV function, LV mass (LVM), and the descending aorta blood flow in children with VSD compared to that obtained in age and sex-matched controls.

RESULTS

The mean LVM of the control, 113.5 ± 123.9 was higher than that of those who had VSD, 75.8 ± 83.9, and the difference in mean was found to be statistically significant (Mann-Whitney U = 2.322, P = 0.022). The mean EF of the control, 67.9 ± 10.3 was comparable to that of those with VSD, 65.6 ± 13.9, (Student's t = 1.223, P = 0.223). Similarly, the mean descending aorta blood flow of control, 1.6 ± 2.2 was comparable to that of those with VSD, 3.9 ± 16.1, (Mann-Whitney U = 1.002, P = 0.321). There was a very weak positive correlation between LVM and descending aorta blood flow among the subjects (n = 85, r = 0.117, P = 0.425). There was a very weak negative correlation between LVM and descending aorta blood flow among control. (n = 85, r = -0.065, P = 0.609).

CONCLUSION

The LVM among children with VSD is lower than controls but there is no difference between LV function in subjects and controls. There is a linear increase of LVM with descending aorta blood flow.

Heart failure in the young: Insights into myocardial recovery with ventricular assist device support

Background

Data on ventricular unloading-promoted myocardial recovery and post-weaning outcome in children is scarce. We analyzed the weaning outcome in children with heart failure (HF) supported with ventricular assist device (VAD).

Methods

A multi-institutional data on VAD implanted in 193 children and adolescents with HF between April 1990 and November 2015 was reviewed. Among them, 25 children (mean age 3.4±3.0, range, 0.058-16.3 years, 15 females) were weaned from VAD. Etiology of HF were myocarditis (n=11), dilated cardiomyopathy (DCMP) (n=7), ischemic HF (n=3), arrhythmogenic CMP (n=1), post-correction of congenital heart disease (CHD) (n=1) and acute graft failure (n=1). Mean duration of HF before VAD implantation was 59.4±3 days.

Results

Age, duration of HF, DCMP, cardiac arrest and duration of VAD are essential clinical characteristics to delineate who may have the potential to myocardial recovery. Echocardiographic parameters pre-implantation, during the final off-pump trial and during the post-explantation follow-ups revealed that LVEF, LVEDD and relative wall thickness (RWT) showed significant differences (P<0.001) among patients stratified by outcome to assess recovery. Presently, 21 (84.0%) of the weaned patients are alive with their native hearts 1.3-19.1 years after VAD explantation. An additional weaned patient had HF recurrence 3 months post-weaning and was transplanted.

Conclusions

Post-weaning myocardial recovery and cardiac stability of children with HF from several etiologies supported with a VAD appears sustainable and durable. Young patients with short HF duration are more likely to recover. Absence of cardiac arrest, cardiac size, geometry and function may prospectively identify patients who may be likely to have myocardial recovery.

Left ventricular mass normalization in child and adolescent athletes must account for sex differences

Background

To assess left ventricular hypertrophy, actual left ventricular mass (LVM) normalized for body size has to be compared to the LVM normative data. However, only some published normative echocardiographic data have been produced separately for girls and boys; numerous normative data for the pediatric population are not sex-specific. Thus, this study aimed to assess whether the LVM normative data should be developed separately for girls and boys practicing sports.

Methods

Left ventricular mass was computed for 331 girls and 490 boys, 5–19 years old, based on echocardiography. The effect of sex on the relationship between LVM and body size was evaluated using a linear regression model. Seven sets of the LVM normative data were developed, using different methodologies, to test concordance between sex-specific and non-specific normative data. Every set consisted of normative data that was sex-specific and non-specific. Upon these normative data, for every study participant, seven pairs of LVM z-scores were calculated based on her/his actual LVM. Each pair consisted of z-scores computed based on sex-specific and non-specific normative data from the same set.

Results

The regression lines fitted to the data points corresponding to LVM of boys had a higher slope than of girls, indicating that sex affects the relationship between LVM and body size. The mean differences between the paired LVM z-scores differed significantly from 0. The percentage of discordant indications, depending on the normalization method, ranged from 66.7% to 100% in girls and from 35.4% to 50% in boys. Application of the LVM normative data that were not sex-specific made relative LVM underestimated in girls and overestimated in boys.

Conclusion

The LVM normative data should be developed separately for girls and boys practicing sports. Application of normative data that are not sex-specific results in an underestimation of relative LVM in girls and overestimation in boys.

Division of Myocardial Enzyme Reference Intervals in Population Aged 1 to <18 Years Old Based on Fisher's Optimal Segmentation Method

Background

Reference interval (RI) research is to make it a concise, effective, and practical diagnostic tool. This study aimed to establish sex- and age-specific RI for myocardial enzyme activity in population aged 1–<18 years old in Changchun, China.

Methods

Healthy subjects (n = 6,322, 1–<18 years old) were recruited from communities and schools. Aspartate aminotransferase (AST), lactate dehydrogenase (LDH), creatine kinase (CK), and creatine kinase isoenzyme (CKMB) were measured using an automatic biochemical analyzer. Fisher's optimal segmentation method was used to partition by including percentiles as impact factors, aiming at minimizing the sum of the squares of the total dispersion into groups as splitting sequence of ordered data.

Results

AST decreased gradually and was partitioned as 1, 2∼<10 and 10∼<18 years old. LDH presented disparate descending rate among 1∼<4, 4∼<12, and 12∼<18 years old. CK stood quite stable with the same RI in all ages. CKMB began to differ at 6 years of age sexually and then remained stable during 6∼<14 years old for male while it continued to decline in female. Cardiac development was partitioned as 1∼<6, 6∼<13, and 13∼<18 years old using multiple percentiles from massive data that reflect characteristics of totality as impact factors.

Conclusions

Fisher's optimal segmentation method excelled for multidimensionality, continuity, and loop calculating as dealing with RIs for myocardial enzymes activity and cardiac development process despite limitations. In future, impact of partition on the overall interval should be delved into.

Proportionality at birth and left ventricular hypertrophy in healthy adolescents

BACKGROUND

Perinatal growth has important implications for cardiac development. Low birth weight is associated with cardiovascular (CV) events and mortality, and animal studies have shown that fetal growth restriction is associated with cardiac remodeling in the perinatal period leading to a permanent loss of cardiomyocyte endowment and compensatory hypertrophy.

AIMS

To determine associations of birthweight (BW) and multiple proportionality indexes (body mass index (BMI); weight/length² and Ponderal index (PI); weight/length³) at birth on one hand, with left ventricular (LV) structure and function during adolescence.

SUBJECTS

379 healthy adolescents aged 14-18 years in Augusta, Georgia.

OUTCOME MEASURES

LV structure and function parameters, including intraventricular septal thickness in diastole (IVSd), LV internal dimension in diastole (LVIDd), LV internal diameter in systole (LVIDs), LV posterior wall thickness in diastole (LVPWd), relative wall thickness (RWT), midwall fractional shortening (MFS), and ejection fraction, were assessed by echocardiography.

RESULTS

When associations of birthweight, birth BMI, and birth PI with LV structure and function parameters were separately evaluated with linear regression adjusting for age, sex, race, Tanner stage, socioeconomic status, and physical activity, significant positive associations of BW with LVIDd (P = 0.004), birth BMI with LV mass index (P = 0.01), and birth PI with IVSd (P = 0.02), LVPWd (P = 0.03), and LV mass index (P = 0.002) were identified. When LV structure and function parameters were compared across PI tertiles, a significant U-shaped trend for LV mass index (P_quadratic = 0.04) was identified.

CONCLUSIONS

Our adolescent data suggest that proportionality at birth may identify associations between perinatal growth and cardiac remodeling independent of birthweight alone.

Reference Intervals and Percentile Curves of Echocardiographic Left Ventricular Mass, Relative Wall Thickness and Ejection Fraction in Healthy Children and Adolescents

Despite the clinical utility of echocardiography to measure cardiac target organ injury (TOI) there are scarcities of data about the reference intervals (RIs) and percentiles of left ventricular (LV) mass (LVM) and derived indexes (LVMI and LVMI^2.7), relative wall thickness (LVRWT) and ejection fraction (LVEF) from population-based studies in children and adolescents. The aim of this study was to generate reference intervals RIs of LVM and derived indexes (LVMI and LVMI^2.7), LVRWT, and LVEF obtained in healthy children, adolescents, and young adults from a South-American population. Echocardiographic studies were obtained in 1096 healthy subjects (5-24 years). Age and sex-specific RIs of LVM, LVMI, LVMI^2.7, LVRWT, and LVEF were generated using parametric regression based on fractional polynomials. After covariate analysis (i.e., adjusting by age, body surface area) specific sex-specific RIs were evidenced as necessaries. Age and sex-specific 1st, 2.5th, 5th, 10th, 25th, 50th, 75th, 90th, 95th, 97.5th, and 99th percentile and curves were reported and compared with previously reported RIs. RIs showed high concordance and complementarity with what was previously reported for the population of North-American children (0-18 years old). In conclusion, in children and adolescents the interpretation of the LVM, LVMIs, LVRWT, and LVEF RIs requires sex-related RIs. This study provides the largest Argentinean database concerning RIs and percentile curves of LVM, LVMIs, LVRWT, and LVEF as markers of cardiac TOI obtained in healthy children and adolescents. These data are valuable in that they provide RIs values with which data of populations of children, adolescents can be compared.

Lifetime risk: childhood obesity and cardiovascular risk

In a recent report, the worldwide prevalence of childhood obesity was estimated to have increased by 47% between 1980 and 2013. As a result, substantial concerns have been raised about the future burden of cardiovascular (CV) disease that could ensue. The purpose of this review is to summarize and interpret (i) the evidence linking early life obesity with adverse changes in CV structure and function in childhood, (ii) the lifetime risk for CV disease resulting from obesity in childhood, and (iii) the potential effects of lifestyle interventions in childhood to ameliorate these risks.

Factors influencing left ventricular hypertrophy in children and adolescents with or without family history of premature myocardial infarction

BACKGROUND

Cardiovascular diseases are the highest ranking cause of mortality. The prevalence of cardiovascular diseases is increasing among people in developed and developing countries. Since left ventricular hypertrophy is one of the risk factors leading to extremely dangerous heart diseases and even sudden death at early ages, investigating its contributing factors can be beneficial. The purpose of this study was to determine factors contributing to left ventricular hypertrophy in students aged 7-18 years in Isfahan. Statistical population of this case-control study was the 7-18 year old students in Isfahan, who were studied in two groups of children with premature myocardial infarction in their parents and the control group.

MATERIALS AND METHODS

After determining the sample size of 138 people, a two-part questionnaire was designed and demographic characteristics and anthropometric measures were recorded in students' profiles. The obtained information was analyzed using SPSS15 software and logistic regression model and the results were reported at P < 0.05.

RESULT

The results showed that among the studied variables, gender, age, body mass index, and blood pressure were associated with the left ventricular hypertrophy.

CONCLUSION

Considering the results and previous studies in this field, it was observed that left ventricular hypertrophy exists at early ages, which is very dangerous and can lead to heart diseases at early ages. Factors such as being overweight, having high blood pressure, and being male cause left ventricular hypertrophy and lead to undiagnosable heart diseases.

Sex-related difference in left ventricular mass in nonhypertensive young adults: role of arterial pressure

BACKGROUND

Blood pressure (BP) is higher in men than in women at similar ages through adult life. Interestingly, a similar pattern is detected in left ventricular mass (LVM), classically attributed to differences in body size. However, the existing difference in BP between sexes might be relevant in determining LVM and it has been not fully investigated. Therefore, we set out to determine the impact of nonhypertensive levels of BP on the sex-associated LVM difference.

METHODS

We conducted population-based study including 283 young students (52% male; age 20.62 ± 1.31 years). BP was determined twice using standard mercury sphygmomanometers in 2 occasions. LVM was determined with M-mode echocardiography. To dissect the relative contribution of BP, volume load, and body size to the sex-related difference in LVM, an analysis of covariance was performed.

RESULTS

Mean systolic and diastolic BP were 10.00 ± 0.96 and 4.59 ± 0.78 mm Hg higher and LVM was 34.87 ± 3.12 g larger in men than in women, respectively (P < 0.01, t test). When LVM was adjusted to mean BP, the sex difference was reduced by 16%. When LVM was adjusted to body size and hemodynamic load, this difference was reduced by 68.5%.

CONCLUSIONS

We report in a sample of young nonhypertensive students a difference in LVM between women and men that is partially explained (16%) by sex differences in BP, supporting an early effect of BP on cardiac mass even in the absence of hypertension. A more relevant effect could be expected as the population ages.

Left ventricular structure and function in children with and without developmental coordination disorder

Children with developmental coordination disorder (DCD) are more likely to develop cardiovascular disease risk factors such as obesity and reduced cardio-respiratory fitness. However, there is limited data using laboratory measures for assessing the risk of cardiovascular disease associated with DCD. The purpose of this study was to examine differences in left ventricular structure and function between children with DCD and healthy controls. The study involved 126 children (aged 12-13 years) with significant motor impairment (n = 63) and healthy controls (n = 63) matched for age, sex, and school. The Movement ABC test (M-ABC2) was used to classify children as probable DCD (p-DCD). Cardiac dimensions were measured using ultrasound echocardiography. Left ventricular mass (LVM) was elevated in children with p-DCD (89 ± 17 g) compared to controls (87 ± 21 g), however, this difference was not significant. When LVM was normalized to height(2.7), no difference was evident between groups (26 g and 26 g for the p-DCD and controls, respectively). However, the p-DCD group demonstrated significantly elevated stroke volume (p = 0.02), cardiac output (p<0.001), end-diastolic volume (p = 0.03), and left ventricle diameter in diastole (p = 0.02). Also, peak VO(2) normalized for fat free mass (FFM) was significantly lower (p = 0.001) and systolic blood pressure (p = 0.01), body mass index (p = 0.001), heart rate (p = 0.005) and percent body fat (p<0.001) were significantly higher in p-DCD. In regression analyses, p-DCD was a significant predictor of stroke volume and cardiac output even after accounting for height, FFM, VO(2FFM), and sex. Children with p-DCD do not demonstrate significantly elevated LVM or depressed systolic function compared to healthy controls. However, cases with p-DCD demonstrate significantly elevated end-diastolic volume, diastolic chamber size, stroke volume, and cardiac output. These differences indicate obesity related changes in the left ventricle and may represent the early stages of developing left ventricle hypertrophy.

Effects of body size and body fatness on left ventricular mass in children and adolescents: Project HeartBeat!

BACKGROUND

Left ventricular mass (LVM) is a strong predictor of cardiovascular disease in adults. Available study findings on effects of body fatness on LVM in children are inconsistent. Understanding the impact of body fat on LVM in children may help prevent excessive LVM through measures to reduce overweight and obesity.

METHODS

Healthy children (n=678) aged 8, 11, and 14 years at baseline were examined at 4-month intervals for up to 4 years (1991-1995); 4608 valid measurements of LVM were obtained with M-mode echocardiography. A multilevel linear model was used for analysis. The impact of body size was examined by adding separately nine body-size indicators to a basic LVM-gender-age model. The impact of body fatness was tested by introducing four body-fatness indicators into the nine models, yielding 36 models.

RESULTS

All body-size indicators showed strong, positive effects on LVM. In models containing weight or body surface area (measuring both fat-free and fat contributions to body size), additional effects of body fatness were negative; in models containing fat-free mass (FFM) or height (both measuring body size independent of body fat), increased body fatness was related to a significant increase in LVM. For example, in models with FFM as a body-size indicator, a 1-SD increase in percent body fat or fat mass was related to a 5.4- or 7.2-g increase in LVM, respectively.

CONCLUSIONS

Effects of body size on LVM attributable to fat-free body mass can be distinguished from those attributable to fat body mass; both are independent, positive predictors, but the former is the stronger determinant. When a body-size indicator not independent of body fat is used as a predictor, effects of fat-free body mass and fat body mass are forced to relate to the same indicator; because their magnitudes are estimated to be equal, the effect of fat body mass is overestimated. Thus, when an additional body-fatness indicator is included in the prediction of LVM, the additional estimated effect related to the indicator appears to be negative.

Differences in left ventricular mass between overweight and normal-weight preadolescent children

This study examined cardiac and arterial differences between overweight and normal-weight preadolescent children. Twenty children (10.2 +/- 0.4 years of age) classified as overweight, on the basis of age-appropriate body mass index (BMI) cutoffs, were compared with 43 normal-weight controls. Height, mass, and body surface area were measured. Relative body fat and lean body mass were estimated from skinfold thickness. Each child's weekly physical activity metabolic equivalent (PAME) was calculated using a standardized questionnaire, and his or her sexual maturation was self-assessed using the Tanner scale. Peak aerobic power was assessed using a cycle ergometer and normalized to lean body mass. Mean arterial pressure was calculated from systolic and diastolic blood pressure (DBP) measurements taken with a Finapres. Cardiac dimensions were measured, using Mu-mode 2-dimensional echocardiography, and normalized to body surface area and height2.7. Left carotid artery pulse pressure (CaPP) was assessed with applanation tomometry. Overweight boys and girls had a higher left ventricular mass (LVM) and LVMHT2.7 than normal-weight boys and girls. CaPP was signficantly lower in the overweight than in the normal-weight groups, whereas PAME and relative peak aerobic power were significantly higher in the boys than the girls. Although overweight children had significantly higher stroke volumes and cardiac outputs than normal-weight children, ejection fraction was similar in the weight groups. Adjusted LVMHT2.7 was associated with cardiac volume measurements, BMI, and DBP in normal-weight children, whereas in the overweight children LVMHT2.7 did not significantly correlate with any variable. In conclusion, we found that cardiovascular adaptations can be seen in prepubescent overweight children as young as 10 years of age.

Sex difference in peak oxygen uptake in prepubertal children

Prepubertal boys' greater aerobic fitness (peak V O(2)) has been attributed to their larger lean body mass (LBM); this bestowing a greater heart size and consequent larger maximum cardiac output. No difference in peak arterio-venous (A-VO(2)) difference is thought to exist. However other work indicates that boys' aerobic fitness remains 5% higher even after controlling for differences in LBM. Consequently the purpose of this study was to investigate whether peak V O(2), heart size, peak cardiac output and peak A-VO(2) difference would be comparable between a group of boys and girls with a similar LBM. A group of 9 prepubertal boys and 9 prepubertal girls with a similar mean LBM (27.0+/-1.4 boys vs. 27.0+/-2.0 kg girls) were selected. Left ventricular mass (LVM) and end diastolic volume (LVEDV) were measured using cardiac magnetic resonance imaging. Peak V O(2) was determined on a cycle ergometer following an incremental exercise protocol to exhaustion, and cardiac output was recorded using thoracic bioimpedance. Boys' peak V O(2) (1.41+/-0.18 L min(-1) vs. 1.23+/-0.08 L min(-1)) and A-VO(2) difference (14.8+/-2.1 mL 100mL(-1) vs. 12.6+/-1.6 mL 100mL(-1)) were significantly (p<0.05) higher than girls' values, but there were no significant sex differences in peak cardiac output (10.0+/-1.4 L min(-1) vs. 9.9+/-1.40 L min(-1)), LVM (97+/-13g vs. 93+/-20g) or LVEDV (77+/-8 mL vs. 70+/-13 mL). Central factors of heart size and peak cardiac output are proportional to the LBM of the individual and sex independent. Sex differences in peripheral factors such as muscle fibre type profile, may affect A-VO(2) difference and underlie prepubertal boys' higher peak V O(2).

Assessment of the interaction of heritability of volume load and left ventricular mass: the HyperGEN offspring study

BACKGROUND

Left ventricular mass (LVM) is more closely associated with volume load than pressure load. We assessed whether part of the genetic heritability of LVM can be explained by stroke volume (SV) inheritance.

METHODS

Echocardiographic LVM, SV and peripheral resistance were measured in 527 families with at least two relatives from the HyperGEN study (51% African-American, 43% men, 44% obese, 53% hypertensive). Included were 1792 subjects without prevalent cardiovascular disease, diabetes and renal failure. Ethnic-specific genetic correlations were estimated using a variance components procedure (SOLAR).

RESULTS

Significant genetic correlations existed between LVM and SV after adjusting for age, sex, race, field center, systolic blood pressure, number of antihypertensive medications, and body mass index (rhog = 0.93 in African-Americans and 0.70 in Caucasians; both P < 0.0001). Urinary Na excretion or serum creatinine did not influence these correlations. After adjusting for covariates, heritability of LVM was greater (h = 0.46 in African-Americans and 0.47 in Caucasians; both P < 0.0001) than that for SV (h = 0.18 in African-Americans and 0.29 in Caucasians; both P < 0.02). Heritability of LVM slightly decreased in African-Americans (h = 0.34), but not in Caucasians (h = 0.45; both P < 0.0001) when SV was added to covariates. Heritability of SV almost disappeared by addition of LVM into the model in African-Americans (h = 0.04, P = not significant), whereas it was slightly reduced in Caucasians (h = 0.20, P < 0.005).

CONCLUSION

LVM and SV share a common genetic profile, but with only a modest reciprocal influence. Variability of LVM has some effect on calculated heritability of SV, especially in African-Americans, whereas the role of heritable volume load in determining the variability of LVM was modest only in African-Americans.

Heritability and major gene effects on left ventricular mass in the Chinese population: a family study

Background

Genetic components controlling for echocardiographically determined left ventricular (LV) mass are still unclear in the Chinese population.

Methods

We conducted a family study from the Chin-San community, Taiwan, and a total of 368 families, 1145 subjects, were recruited to undergo echocardiography to measure LV mass. Commingling analysis, familial correlation, and complex segregation analysis were applied to detect component distributions and the mode of inheritance.

Results

The two-component distribution model was the best-fitting model to describe the distribution of LV mass. The highest familial correlation coefficients were mother-son (0.379, P < .0001) and father-son (0.356, P < .0001). Genetic heritability (h²) of LV mass was estimated as 0.268 ± 0.061 (P < .0001); it decreased to 0.153 ± 0.052 (P = .0009) after systolic blood pressure adjustment. Major gene effects with polygenic components were the best-fitting model to explain the inheritance mode of LV mass. The estimated allele frequency of the gene was 0.089.

Conclusion

There were significant familial correlations, heritability and a major gene effect on LV mass in the population-based families.

Relation of increase in adiposity to increase in left ventricular mass from childhood to young adulthood

This study evaluated the influence of adiposity on the progression of left ventricular (LV) mass from childhood to adulthood and the relation of LV mass to insulin resistance in young adulthood. One hundred thirty-two healthy children recruited into a longitudinal study at a mean age of 13 years and reevaluated at 27 years, at which time insulin resistance studies were also performed, were studied. Echocardiographic assessment of LV mass was made and indexed for height. Body mass index (BMI) at 13 years was highly correlated with BMI at 27 years, as was LV mass index at 13 and 27 years. The cross-sectional correlation of LV mass index and BMI at 13 years (r = 0.38, p < 0.0001) had strengthened considerably by 27 years (r = 0.55, p < 0.0001). A BMI increase > or = 5.5 kg/m2 from 13 to 27 years was associated with a significantly greater increase in the LV mass index (p < 0.0001) than a BMI change < 5.5 kg/m2, and this relation was similar in children who were thin and heavy at baseline. In young adulthood, the relation of LV mass index to lean mass was weaker than that of LV mass index to fat mass. The association of LV mass with insulin resistance was dependent on adiposity. In conclusion, adiposity and LV mass are related in childhood, and this association tracks and becomes stronger in young adulthood. Moreover, the increase in LV mass from childhood to young adulthood is related to the degree of increase in BMI, independent of BMI at 13 years, suggesting that an excessive increase in LV mass could be limited by controlling gain in body fat during adolescence.

Genetic contribution to the variance in left ventricular mass: the Tecumseh Offspring Study

OBJECTIVE

To estimate the contribution of heredity to the variance in left ventricular mass (LVM), and to ascertain whether genetic factors may interact with non-genetic factors in promoting LVM growth.

SUBJECTS AND SETTING

The study population consisted of 290 healthy parents and 251 healthy children living in Tecumseh, Michigan, USA.

MAIN OUTCOME MEASURE

Correlation of parents' LVM with offspring's LVM adjusting for a number of clinical variables.

METHODS

LVM in parents and offspring was measured with M-mode echocardiography by the same investigators.

RESULTS

Parents unadjusted LVM was unrelated to offspring unadjusted LVM, but after removing the confounding effect of age, sex, anthropometric measurements, systolic blood pressure, plasma insulin and urinary sodium excretion, parent-child correlation for LVM was 0.28 (P = 0.006). The relative contribution of parental-adjusted LVM and of several offspring phenotypic and environmental variables on offspring LVM was evaluated by multivariable regression analysis. When age, gender, anthropometric measurements and systolic blood pressure were accounted for, adjusted LVM of parents explained only 1.6% of the total variance in offspring LVM. However, after inclusion of insulin and urinary sodium in the model heredity explained 7.6% of the total variance in offspring LVM, and its predictive power was second only to that of child's height. Furthermore, an interactive effect of parental LVM with offspring systolic blood pressure was found on child's left ventricular mass.

CONCLUSION

Heredity can explain a small, but definite proportion of the variance in LVM. Higher blood pressure favors the phenotypic expression of the genes that regulate LVM growth.

Left ventricular mass and correlated atherosclerotic risk factors in young adolescents: report from Chin-Shan community cardiovascular study in Taiwan

Various subclinical disease indicators can be used as an early stage marker of atherosclerosis. Left ventricular (LV) mass has been related to cardiovascular morbidity and mortality. The distribution of LV mass in Chinese is rarely studied and nothing is known about its relationships with various atherosclerotic risk factors in young teenagers, in particular, aspects of lipid profiles. We performed a community-based survey of 523 males and 555 females, aged 12-15, in Chin-Shan, a suburb area near Taipei, Taiwan. LV mass was calculated from the Penn convention. Normalized LV mass by height with power of 2.7 was defined. LV mass and normalized LV mass were significantly greater in males than in females. There were significant positive correlation coefficients between LV mass and age, blood pressure, body mass index, low density lipoprotein cholesterol (LDL-C), apolipoprotein (Apo) B, fasting insulin levels and significant negative correlation coefficients between LV mass and high density lipoprotein cholesterol (HDL-C) and Apo A1 level in both genders. Multiple linear regression models showed gender and body mass index (BMI) were important factors associated with LV mass or normalized values for adolescents. Age and systolic blood pressure were also significant predictors of LV mass, but not of normalized LV mass values. LV mass values were found to be negatively associated with HDL-C values at marginal statistically significant level. Age and BMI are the most significant factors of echocardiographic LV mass distributions in young adolescent in Taiwan. LV mass may also be associated with atherosclerotic risk factors.

Insulin resistance and cardiovascular risk in the pediatric patient

The insulin resistance syndrome, a cluster of potent risk factors for atherosclerotic cardiovascular disease and type 2 diabetes in adults, is composed of hyerinsulinemia, obesity, hypertension and hyperlipidemia. In addition, left ventricular hypertrophy and its precursor increased left ventricular mass, is known to be a powerful predictor of adverse cardiovascular events, both as an independent risk factor and by association with the insulin resistance syndrome. Obesity appears to have a major role in the relations between the components of the insulin resistance syndrome, and their association with increased heart mass. Of significant impact in the adult population, atherosclerotic cardiovascular disease and death are rarely seen in the young, but the pathologic processes and risk factors associated with its development have been shown to begin during childhood. Recent studies revealed the presence of components of the insulin resistance syndrome also in children and adolescents, however, their associations are not well understood. A direct link between obesity and insulin resistance has also been reported in the young, as has the link between insulin resistance and abnormal lipid profile. There is an increasing amount of data to show that being overweight during childhood and adolescence is significantly associated with insulin resistance, abnormal lipids and elevated blood pressure in young adulthood. Weight loss in these situations results in a decrease in insulin concentration and an increase in insulin sensitivity toward normalcy. Moreover, it has been determined that increased left ventricular mass is present in childhood, and is related to other risk factors, namely obesity and insulin resistance. Based on current knowledge, it is reasonable to suggest that weight control, and lifestyle modification, could alter the incidence of the syndrome of insulin resistance, and improve the risk profiles for cardiovascular disease as children make the transition toward adolescence and young adulthood.

Obesity in the pediatric patient: cardiovascular complications

The prevalence and severity of obesity are increasing in children and adolescents. This raises concerns about the accompanying cardiovascular complications. Such complications include hypertension, dyslipidemia, type II diabetes which may accelerate vascular disease, left ventricular hypertrophy and pulmonary hypertension due to obstructive sleep apnea. The evaluation of an obese child or adolescent should include careful consideration of these possible cardiovascular complications. If they are present, treatment should be directed at both obesity and the risk factor abnormality. This treatment may be important for prevention of future cardiovascular morbidity and mortality. In addition, research is necessary to better understand the mechanisms by which obesity increases the risk of cardiovascular disease.

Determinants of left ventricular structure and mass in young subjects with sympathetic over-activity. The Tecumseh Offspring Study

OBJECTIVE

In this study, we tested the hypothesis that sympathetic over-activity may cause metabolic abnormalities and affect left ventricular (LV) structure and mass early in life.

SUBJECTS AND SETTING

The study population consisted of 111 healthy adolescents and young adults living in Tecumseh, Michigan (USA).

MAIN OUTCOME MEASURES

Correlations of LV mass and structure with several clinical variables in relation to the activity of the sympathetic nervous system.

METHODS

Power spectrum density estimates of heart rate variability were calculated with an auto-regressive method, and subjects were divided by cluster analysis into two groups according to low-frequency and high-frequency components. LV data were obtained by echocardiographic assessment

RESULTS

Subjects with signs of sympathetic over-activity (n = 38, group 1) had higher heart rate, blood pressure (BP), waist/hip ratio and cholesterol levels than the rest of the group (n = 73, group 2). In group 1 subjects, insulin emerged as the strongest univariate correlate of interventricular septum and posterior wall thicknesses (P< 0.001 for both) and of LV mass (P= 0.009). These relationships remained significant when body mass index was accounted for. By contrast, the marginal univariate relationship with diastolic BP did not remain significant in multivariate analysis. In group 2 subjects, BP was strongly correlated with LV wall thickness and mass both in univariate (P values from 0.03 to < 0.001) and multivariate analyses, while insulin was not. The interactive effect of sympathetic activity and insulin on echocardiographic data was confirmed by multivariate analyses performed in the subjects grouped together (P values from 0.02 to 0.001 for the sympathetic activity x insulin interaction term).

CONCLUSIONS

In young subjects with heightened sympathetic activity and initial metabolic abnormalities, insulin is a strong determinant of LV wall thickness and geometry, while in subjects with normal autonomic nervous system activity, the main determinant of left ventricular size is the haemodynamic load.

Predicting heart growth during puberty: The Muscatine Study

OBJECTIVES

During childhood, heart growth is closely associated with somatic growth including increases in body weight, fat-free body mass (FFM), and height. However, with age, greater variability in heart size in relationship to body size is observed, presumably attributable to the increased effect of cardiac workload. At this time, little is known as to what functional attributes (eg, aerobic fitness) contribute to cardiac workload and the relative contribution of these attributes to heart growth during childhood and adolescence. In this article, we report cross-sectional and longitudinal relationships among aerobic fitness, body size, blood pressure (BP), and left ventricular mass (LVM) through puberty including the predictors of heart growth during puberty and the tracking of LVM from pre-puberty to late and post-puberty. Describing the predictors of heart size and heart growth and establishing the likelihood that a large heart, relative to peers, may (or may not) remain a large heart should aid pediatricians in discerning between normal developmental increases in LVM and increases in LVM suggestive of excessive heart growth (left ventricular hypertrophy).

METHODOLOGY

Using a repeated-measures design, we assessed aerobic fitness, FFM, fatness, weight, height, sexual maturation, resting BP, peak exercise BP, and LVM in 125 healthy children (mean baseline age: 10.5 years) for a period of 5 years. All subjects were either in prepuberty or early puberty at the beginning of the study. At follow-up, 110 subjects attempted all research procedures (87% of the initial cohort). Using anthropometry and bioelectrical impedance, we measured FFM, fatness, weight, and height quarterly (once every 3 months) for a total of 20 examinations. Resting BP and LVM (2-dimensional echocardiography) were also assessed quarterly. Aerobic fitness, peak exercise BP, and sexual maturation (staging of secondary sex characteristics and, for boys, serum testosterone) were measured annually (5 examinations). The same field staff conducted all examinations. Statistical methods included Spearman rank correlation coefficients (r(s)) calculated to estimate how well the year 5 LVM was predicted by LVM at earlier years. We also categorized the LVM data into tertiles and reported the percentage who remained in the extreme tertiles in year 5, given they began in that tertile in year 1. Gender-specific stepwise multivariate analysis was used to evaluate predictors of follow-up LVM and predictors of changes in LVM. The latter model examined whether the variability in the changes in LVM, as quantified by subject-specific slopes, could be explained by changes in predictor variables, also quantified by subject-specific slopes.

RESULTS

At baseline and at follow-up, boys tended to be taller, leaner, more aerobically fit, and had greater LVM than girls. Rate of change for these variables was also greater in boys than girls. For example, LVM increased 62% in boys and 48% in girls. At year 5, subjects had advanced at least 1 stage in genital or breast development and over 80% of the subjects were in late- or post-puberty. Significant and strong tracking of heart size (r(s) =.65-.87) was observed. The likelihood that a subject would be in an extreme tertile for heart size at follow-up was approximately doubled if he or she started there at baseline. In boys, baseline FFM explained 54% of the variability in follow-up LVM. Change in aerobic fitness and change in FFM explained 55% of the variability in change in LVM. In girls, baseline aerobic fitness and fatness explained 45% of the variability in follow-up LVM. Because FFM did not enter in this model, we constructed an alternative model in which baseline aerobic fitness adjusted for FFM was entered. Using this approach, 43% of the variability in follow-up LVM was explained by baseline FFM, fatness, and adjusted aerobic fitness. Change in FFM explained 58% of the variability in change in LVM. (ABSTRACT TRUNCATED)

Interpretation of echocardiographic measurements: a call for standardization

BACKGROUND

Although echocardiography is used extensively in clinical medicine, guidelines for quantitative interpretation of echocardiographic measurements are unavailable. The goals of this investigation were to provide an overview of scientific standards for formulating reference values, with clinical chemistry used as a model, to evaluate published echocardiographic reference limits, to survey clinical echocardiography laboratories regarding their interpretation of echocardiographic measurements, and to provide recommendations for improving the interpretation and reporting of echocardiographic measurements.

METHODS AND RESULTS

We reviewed the original reports of the International Federation of Clinical Chemistry on guidelines for formulating reference values. We obtained published reports on echocardiographic reference limits through searches of electronic databases supplemented by a manual search of relevant bibliographies. We also surveyed echocardiographic laboratories in 35 adult acute-care hospitals in Eastern Massachusetts. Studies on echocardiographic reference values were evaluated with the use of guidelines from clinical chemistry. Responses from the 29 participating echocardiographic laboratories were evaluated for their practice of quantitative echocardiographic interpretation. There is considerable heterogeneity in the echocardiographic reference values available in the literature. There is also a lack of agreement in the literature and among echocardiographers regarding the partitioning of reference values (by sex, ethnicity, or age), the anthropometric measure to be used for indexation, and the choice of cut-points for categorizing values within the abnormal range.

CONCLUSIONS

We advocate that echocardiographic reference limits be standardized and a consensus generated regarding the partitioning of reference limits and the indexation of echocardiographic measurements. Such measures can aid in quantitative echocardiographic interpretation and render the results more scientific and consistent.

The relationship between R amplitude in lead V5 (RV5) and left ventricular mass in the groups of adolescent subjects classified by body composition

How the amplitude of the R wave in lead V5 (RV5) of the ECG represents the left ventricular (LV) mass was investigated in 894 students aged 15 (boys: 545, girls: 349). The influence of body composition [ie, percentage of body fat (%fat)] was taken into consideration. A significant correlation was found between RV5 amplitude and LV mass for both genders. However, the relationship was stronger for boys than for girls. The students were then divided into 3 groups; that is, those at either the top or bottom 10th percentile (low or high-fat range) and the rest of the students (middle-fat range), depending on the % fat calculated by the bioelectrical impedance method. The significant correlation between RV5 and LV mass was found only for the 2 groups of boys whose percentage fat was in the low or middle-fat range. The correlation coefficients were 0.40 and 0.34, respectively. Moreover, in the boys' low-fat range, the RV5 of students whose LV mass was large (> or =90th percentile), was significantly higher (p<0.01) than in the other ranges. Setting a particular cutoff point of RV5 in the low-fat range of boys improved sensitivity as well as specificity (20-30% better among all boys) for detecting large LV mass. These observations suggest that classification of subjects by body composition could be improve the reliability of ECG assessment for left ventricular hypertrophy, although the gender and number of subjects in whom improvement is expected are limited.

The associations of body size and body composition with left ventricular mass: impacts for indexation in adults

OBJECTIVES

We investigated the relationship between body size, body composition and left ventricular mass (LVM) in adults, and assessed the impact of different indexations of LVM on its associations with gender, adiposity and blood pressure.

BACKGROUND

The best way to normalize LVM for body size to appropriately distinguish physiologic adaptation from morbid heart morphology was discussed.

METHODS

We undertook a community survey of 653 men and 718 women, aged 25 to 74 years. Lean body mass (LBM) was determined by bioelectric impedance analyses and LVM was assessed by two-dimensional guided M-mode echocardiography.

RESULTS

After traditional indexations to body height, body height2.7, or body surface area, men had higher LVM than women (p < 0.001). These gender differences disappeared (p > 0.05) when LVM was indexed to LBM. The type of indexation also modified the strength of the association between adiposity and LVM. The estimated impact of body fat on LVM indexed to LBM was less than half that obtained with traditional indexations. In contrast, the magnitude of the associations of blood pressure with LVM was entirely independent of the type of indexation.

CONCLUSIONS

This study showed the prominent influence of body composition on adult heart size. Indexation for LBM removed gender differences for LVM and reduced the impact of adiposity, but left the effects of blood pressure unchanged. We suggest that this approach be used for clinical and research applications.

Modeling the influence of body size and composition on M-mode echocardiographic dimensions

The purpose of this study was to determine the optimal index for normalizing left ventricular (LV) echocardiographic dimensions for differences in body size. M-mode echocardiograms defined LV internal dimension at end diastole (LVIDD) and LV wall thickness (LVWT) in 107 adults (59 male, 48 female). Allometric relations were assessed between cardiac dimensions (Y) and body size variables (X) of fat-free mass (FFM), height (H), body surface area (BSA), and fat mass (FM). Further to confirmation of homogeneity of regression slopes, size exponents common to both genders were fitted by a log-linear model: ln Y = ln a + c.gender + b.ln X, where a is the proportionality coefficient, b is the size exponent, and c is the gender coefficient. For LVIDD, mean body size exponents (95% confidence interval) were FFM0.35 (0.22-0.47), H0.68 (0.32-1.03), and BSA0.44 (0.26-0.62). For LVWT, the derived exponents were FFM0.43 (0.20-0.65), H0.65 (0-1.3), and BSA0.56 (0.23-0.89). Body fatness (expressed by FM) had no influence on LV dimensions, with exponents not different from zero (P > 0.05). The root-mean-squares error from the separate regression models indicated that the FFM index was the optimal solution. Indexation of LV dimensions by H was associated with the greatest error. Because the 95% confidence interval for the FFM exponents included 0.33, we recommend that linear LV dimensions be indexed by the cube root of FFM. In the absence of FFM data, the root of BSA was found to be the best surrogate index.

Prediction of left ventricular mass in youth with family histories of essential hypertension

To determine predictors of left ventricular mass (LVM) and hypertrophy (LVH), 56 black and 30 white normotensive healthy youths (mean age 12.6 +/- 2.3 years at initial visit) were studied twice, 2.5 years apart. During the initial visit, anthropometric variables and hemodynamics were measured at rest and before, during, and after 4 physical and behavioral stressors. 2-D directed M-mode echocardiography was performed to derive LVM. Hierarchical multiple regression analyses indicated that follow-up LVM was predicted by initial LVM, weight, height (ht), and gender (males > females; total model R2 = 0.77, P < 0.0001). Predictors of LVM/ht2.7 were initial LVM/ht2.7, weight, ethnicity (blacks > whites), and the aggregate index of blood pressure reactivity (total model R2 = 0.66, P < 0.0001). Youth with LVH at follow-up were taller, heavier, and exhibited greater blood pressure reactivity at initial evaluation. These findings are important since interventional strategies can be developed that target obesity and exaggerated reactivity to stress.

Anthropometric, demographic, and cardiovascular predictors of left ventricular mass in young children

Left ventricular (LV) mass is a strong independent predictor of cardiovascular morbidity and mortality. Few longitudinal studies have examined predictors of LV mass in children. This study assessed the contributions of anthropometric, demographic, and cardiovascular parameters (at rest and after exposure to laboratory stressors) as predictors of LV mass 3.6 years after the initial examination in a sample of 68 Caucasian and African-American children 7.9 +/- 0.7 years old. At the initial examination, all subjects had standard anthropometrics measured and hemodynamics assessed at rest and during 3 stressors: postural change, forehead cold stimulation, and treadmill exercise. On the follow-up examination 3 to 4 years later, echocardiographic evaluations were conducted to estimate LV mass and related LV geometry. LV mass and LV internal diameter in diastole were adjusted for linear growth (LV mass/height2.7 and LV internal dimension during diastole/height0.80, respectively). Hierarchical stepwise multiple regression analyses were conducted using parameters significant in univariate comparisons (p < 0.05). Initial weight (R2 = 0.38), height (R2 = 0.42), and cardiac output reactivity to standing and treadmill exercise (final model R2 = 0.55) were significant predictors of LV mass, whereas LV mass/height2.7 was predicted by initial adiposity (R2 = 0.07) and cardiac output and systolic pressure reactivity to postural change (final model R2 = 0.25). Follow-up relative wall thickness was significantly predicted by ethnicity (African-Americans greater than Caucasians, R2 = 0.15), adiposity (R2 = 0.20), and systolic pressure reactivity to postural change (final model R2 = 0.28). These findings suggest the potential benefit of weight control in childhood as a primary prevention for later onset of cardiovascular disease.

Multivariate Analysis of Left Ventricular Mass Determinants in Adults: Different Patterns in Men and Women

Echocardiographic left ventricular mass (LVM) estimates are strong predictors of subsequent mortality and cardiovascular events. It is known that blood pressure (BP), weight (WT), and age are significantly correlated with LVM. We hypothesized that stroke volume (SV) measured by Doppler echocardiography would also be correlated with LVM. Two hundred and thirteen patients referred for routine echocardiography had determination of LVM, cuff BP, and Doppler SV. Those with localized LV disease, valvular disease, or cor pulmonale were excluded. In both men and women, systolic BP (SBP) was more closely correlated with LVM than was diastolic blood pressure or mean arterial pressure, and SV was more closely correlated with LVM than cardiac output or cardiac index. Stepwise regression, followed by multiple regression showed that four variables (WT, SV, SBP, and AGE) explained 32.3% of the variability in LVM in men and 48.5% of the variability in LVM in women. WT and SV were significant determinants of LVM in both men and women. Age was also significant in men and SBP was also significant in women. For both men and women, SV was more significantly correlated with LVM than was SBP. The changes in LVM associated with 1 SD increments of SV and SBP, respectively, were 8 and 5 g for men and 13 and 11 g for women. We conclude that men and women have different patterns of variables influencing LVM. Doppler echocardiographic SV is a newly described determinant of LVM that has a greater correlation with LVM than does SBP. This study reemphasizes the importance of WT as the major determinant of LVM. (ECHOCARDIOGRAPHY, Volume 13, January 1996)

Left ventricular mass estimation by echocardiography: is it clinically useful?

Echocardiographic determination of left ventricular mass provides prognostic information that is independent of blood pressure. This prognostic information has a graded and continuous relationship with outcome, and is independent of traditional risk factors. This article addresses the prognostic and clinical utility of echocardiography for detection of left ventricular mass. Recommendations will be offered regarding the use of echocardiography for screening in select individuals.