Subclinical Myocardial Dysfunction and Cardiac Autonomic Dysregulation Are Closely Associated in Obese Children and Adolescents: The Potential Role of Insulin Resistance

BACKGROUND: The prevalence of obesity is increasing among children/adolescents. Subtle cardiovascular abnormalities, responsible for a higher mortality later in life, have been reported in obese children/adolescents. The aims of the study were to evaluate cardiovascular autonomic regulation, by means of spectrum analysis of R-R interval variability, and myocardial function, by means of standard and tissue Doppler echocardiography, in a group of non-hypertensive asymptomatic obese children and adolescents; furthermore, the influence of insulin resistance was tested. SUBJECTS AND METHODS: R-R interval variability was analyzed during both the 70° head-up tilt and 24-hour electrocardiographic holter monitoring. Spectrum analysis of R-R interval variability provided the indices of sympathetic (low frequency [LF(RR)]) and vagal (high frequency [HF(RR)]) modulation of the sinoatrial node. Homeostasis model assessment of insulin resistance (HOMA-IR) was used to classify obese children/adolescents (n=72) as insulin resistant (n=37) and non-insulin resistant (n=35). RESULTS: In obese subjects: a) left ventricular mass was significantly (p<0.05) increased, whereas both the e/a ratio and the e'/a' ratio were decreased; b) at rest, HF(RR) was lower, and the LF(RR)/HF(RR) ratio was higher; c) during tilting, magnitude of tilt-induced inhibition of HF(RR) was lower; d) during 24-hour electrocardiographic holter monitoring, LF(RR) and the LF(RR)/HF(RR) ratio were higher, whereas HF(RR) was lower; e) HOMA-IR inversely correlated with both the e'/a' ratio (r=-0.655; p<0.001) and the tilt-induced LF(RR)/HF(RR) ratio (r=-0.933; p<0.001); and, f) the e'/a' ratio correlated with the tilt-induced LF(RR)/HF(RR) ratio (r=0.501; p<0.001). Moreover, HF(RR) at rest, magnitude of tilt-induced HF(RR) reduction, and the e'/a' ratio in insulin resistant obese children/adolescents were markedly lower when compared with the remaining subjects. CONCLUSIONS: Subclinical abnormalities of myocardial function and of cardiac autonomic regulation were closely associated in obese children/adolescents and both correlated with the degree of insulin resistance.