Change of genetic determinants of left ventricular structure in adolescence: longitudinal evidence from the Georgia cardiovascular twin study.

BACKGROUND: Genetic contribution to left ventricular (LV) structure is generally recognized, but whether and how this influence varies by ethnicity or with age is unknown. METHODS: Participants were 517 European-American (EA) and African-American (AA) twin pairs (mean age: 14.6 +/- 3.0) at visit 1 and 422 EA and AA twin pairs at follow-up 4.1 years later. Echocardiograms were obtained on both visits. Data were analyzed using the structural equation modeling software Mx. RESULTS: Body mass index (BMI) was a strong predictor for all LV measures at both visits 1 and 2, accounting for 3.5-24.2% of the total variance. Hemodynamics explained up to 4.5% additional LV measures variance. After adjusting for BMI, LV measures showed substantial heritability (range: 21-71%). Best-fitting longitudinal models revealed considerable novel genetic effects on the interventricular septum, posterior wall-, and relative wall thickness (RWT) (but not LV internal diameter), accounting for 32-41% of the phenotypic variance at visit 2, with no significant gender and ethnic effects. There was a gender difference for LV mass index in AAs (P < 0.01), with a significant influence of novel genetic effects in males (47%), but not in females. No gender difference was seen in EAs, with 34% of the phenotypic variance at visit 2 attributable to novel genetic effects. CONCLUSIONS: The heritability of cardiac structure and geometry was equally substantial in both AAs and EAs. Significant novel genetic influences were detected for all measures but LV inner diameter and LV mass index in AA females. Further developmental genetic studies are warranted to elucidate the nature of the emerging gene effects during the transition from adolescence to adulthood.

Relations of adiposity and effects of training on the left ventricle in obese youths.

PURPOSE: 1) To determine the relations of left ventricular (LV) structure and function to total body composition, visceral adipose tissue (VAT), and hemodynamics in obese children; 2) to determine the effects of 4-month of physical training (PT) on LV structure and function and hemodynamics; and 3) to explore determinants of individual variability in response to PT. METHODS: Measurements included LV structure/function with echocardiography, total body composition with dual-energy x-ray absorptiometry, VAT with magnetic resonance imaging (MRI), and resting and exercising hemodynamics with a Dinamap monitor and Doppler-echocardiography. Youths were randomly assigned to engage in PT for the first or second 4-month periods of the 8-month intervention period. RESULTS: Correlation and regression at baseline showed that elevated LV mass was associated with excess general and visceral adiposity, and elevated cardiac output. Although the PT had favorable effects on percent body fat and VAT, no significant changes were found in LV or hemodynamic variables. Over the 4-month period of the PT intervention, those who increased the most in VAT tended to increase the most in LV mass. CONCLUSION: General and visceral adiposity were associated with elevated LV mass. However, no evidence was provided that 4 months of PT had a significant effect on LV or hemodynamic variables.

Left ventricular structure and function in obese adolescents: relations to cardiovascular fitness, percent body fat, and visceral adiposity, and effects of physical training.

OBJECTIVE: Little is known about the relations of fitness and fatness to left ventricular structure and function in obese adolescents. This project had 2 purposes: 1) to determine the correlations of cardiovascular fitness and adiposity to left ventricular parameters in obese adolescents; and 2) to see the effect of 8 months of physical training (PT) at low and high intensities. DESIGN: Obese 13- to 16-year-olds (N = 81) were tested at baseline and then randomly assigned to lifestyle education (LSE) alone, LSE plus moderate-intensity PT, or LSE plus high-intensity PT. Follow-up testing was conducted 8 months later. Because no significant differences were found between moderate-intensity and high-intensity PT, the groups were combined to form a LSE + PT group. INTERVENTION: Eight months of PT, offered 5 days per week with the target energy expenditure for all PT participants being 250 kcal/session, and LSE every 2 weeks. Outcome Measures. Left ventricular mass divided by height to the 2.7th power (LVM/Ht(2.7)), midwall fractional shortening (MFS), and relative wall thickness (RWT) were measured using M-mode echocardiography. Cardiovascular fitness was measured by a maximal multistage treadmill test; percent body fat (%BF) with dual-energy radiograph absorptiometry; and visceral adipose tissue (VAT) with magnetic resonance imaging. RESULTS: At baseline, high levels of VAT were associated with higher RWT (r = 0.30) and lesser MFS (r = -0.29). Compared with the LSE-alone group, the LSE + PT group significantly improved in cardiovascular fitness and decreased in %BF and VAT. However, there were no significant differences between groups on changes in LVM/Ht(2.7), MFS, or RWT. Individual changes in cardiovascular fitness, %BF, and VAT did not correlate significantly with interindividual changes in left ventricular structure and function. CONCLUSIONS: High levels of VAT were associated with unfavorable left ventricular structure and function. However, no evidence was provided that an 8-month PT program, which improved cardiovascular fitness and reduced general and visceral adiposity, improved left ventricular structure and function. Future studies consisting of longer training programs and/or greater weight reductions are needed to see whether the adverse left ventricular effects of obesity can be ameliorated by exercise training.