Ventricular Ectopic Activity, Left Ventricular Mass, Hyperinsulinemia, and Intracellular Magnesium in Normotensive Patients with Obesity

Abstract

Insulin resistance, a well-known feature of obesity, is associated with several pathological changes, which are potentially arrhythmogenic. Ventricular ectopic activity in normoten sive obese patients has not been studied in detail. Therefore the authors designed a study to investigate potential relationships among ventricular ectopic activity, left ventricular mass, hyperinsulinemia, and intracellular magnesium concentration in obese patients. Thirty-two obese patients and 32 nonobese control subjects, who were referred to outpa tient department because of ventricular ectopy, participated in the study. The groups were matched for age and gender. All had normal glucose tolerance. All subjects underwent a 75-g glucose tolerance test, and blood samples were obtained at 30, 60, and 120 minutes thereafter for determination of glucose and insulin concentrations. Echocardiography was performed and left ventricular mass index was calculated. The number of ventricular ectopic beats per hour (VEB/hour) was recorded by 24-hour ECG Holter monitoring. Plasma and erythrocyte magnesium concentrations were determined by atomic absorption spectrophotometer. Obese patients had higher body weight, body mass index, heart rate, and left ventricular mass index. Obese subjects had higher fasting insulin as well as insulin/glucose ratio and broader area under the curve of insulin (AUC-I) compared to nonobese subjects. Insulin sensitivity appeared to be lower in the obese group. Holter monitoring showed more VEB/hour in the obese group. Magnesium concentration in serum and in erythrocytes was lower in obese persons. In the obese group a positive correlation was found between left ventricular mass index and fasting insulin ( r=0.345, p=0.027), insulin/glucose index ( r=0.351, p=0.049), and AUC-I ( r=0.405, p=0.011). The number of VEB/hour in obese patients was in positive corre lation with age ( r=0.681, p<0.001), left ventricular mass index ( r=0.542, p=0.001), fasting insulin ( r=0.380, p=0.016), and AUC-I ( r=0.493, p=0.002) and in negative correlation with magnesium concentration in erythrocytes ( r=-0.457, p=0.004). Multiple regression analysis showed that age and AUC-I are the only determinants of VEB/hour and together explained 56% of the variability in the obese subjects. It appears that in obese normotensive subjects, ventricular ectopic beats are related to age, insulin resistance, left ventricular mass index, and decreased intracellular magnesium content.