Heritability of cardiac size: an echocardiographic and electrocardiographic study of monozygotic and dizygotic twins

The inheritance of left ventricular structure and function assessed by imaging and Doppler echocardiography

The heritability of left ventricular structure and function was studied in 53 pairs of monozygotic and dizygotic twins, aged 18 to 31 years, by means of M-mode and Doppler echocardiography. A significant fraction of the phenotypic variances of left ventricular wall thickness was explained by genetic variance. For the left ventricular internal dimension, however, no genetic effect was found after correction for body weight. After appropriate adjustment a genetic component of 32% was found for aortic peak flow velocity, 55% for stroke distance, and 47% for minute distance. The early and late diastolic peak flow velocities at the mitral valve showed a genetic component estimated at 43% and 26%, respectively. The inheritance of the late/early diastolic peak flow velocity ratio was estimated at 53%. In conclusion, these data suggest a significant genetic component for left ventricular structural features but not for cavity dimension. A significant influence of heredity was detected for left ventricular inflow and outflow characteristics.

Maximum oxygen uptake and cardiac size and function in twins

The contribution of heredity to the interindividual variability of maximum oxygen uptake and of cardiac size and function of healthy male twins, age 18 to 31 years, was studied to evaluate the role of the heart in the inheritance of aerobic power. Twelve pairs of monozygotic and 12 pairs of dizygotic twins were examined. Weight (p less than 0.05), relative weight (Quetelet index) (p less than 0.01) and skinfold thickness (p less than 0.01) were found to be genetically determined, as well as heart rate at rest (p less than 0.05) and systolic blood pressure (p less than 0.05). Genetic variation was significant (p less than 0.05) both for absolute and for weight-adjusted oxygen uptake, measured at peak exercise on the bicycle ergometer. However, the influence of inheritance on aerobic power was not associated with a significant genetic effect on the end-diastolic left ventricular internal diameter or on its fractional shortening as assessed by echocardiography. Genetic variation had a significant (p less than 0.05) effect on left ventricular mass, but this could be attributed to the inheritance of body size. These data indicate that cardiac factors are not significantly involved in the inheritance of aerobic power and suggest that cardiac hypertrophy in athletes is secondary to training.