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

Objective In this study, we tested the hypothesis that sympathetic over-act ivity may cause metabolic abnormalities and affect left ventricular (LV) st ructure and mass early in life. Subjects and setting The study population consisted of 111 healthy adolesce nts and young adults living in Tecumseh, Michigan (USA). Main outcome measures Correlations of LV mass and structure with several cl inical variables in relation to the activity of the sympathetic nervous sys tem. Methods Power spectrum density estimates of heart rate variability were cal culated with an auto-regressive method, and subjects were divided by cluste r analysis into two groups according to low-frequency and high-frequency co mponents. 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 s eptum and posterior wall thicknesses (P < 0.001 for both) and of LV mass (P = 0.009). These relationships remained significant when body mass index wa s accounted for. By contrast, the marginal univariate relationship with dia stolic BP did not remain significant in multivariate analysis. In group 2 s ubjects, BP was strongly correlated with LV wall thickness and mass both in univariate (P values from 0.03 to < 0.001) and multivariate analyses, whil e insulin was not The interactive effect of sympathetic activity and insuli n on echocardiographic data was confirmed by multivariate analyses performe d in the subjects grouped together (P values from 0.02 to 0.001 for the sym pathetic activity x insulin interaction term). Conclusions In young subjects with heightened sympathetic activity and init ial metabolic abnormalities insulin is a strong determinant of LV wall thic kness and geometry, while in subjects with normal autonomic nervous system activity, the main determinant of left ventricular size is the haemodynamic load. J Hypertens 2000, 18:769-775 (C) Lippincott Williams & Wilkins.