Relation Between Body Fat–Corrected ECG Voltage and Ambulatory Blood Pressure in Patients With Essential Hypertension

Because adipose tissue has high electric resistance, the amount of body fat influences ECG voltage. In this study, body fat weight of patients with essential hypertension was measured by means of the impedance method and was used to correct mean ECG voltage. Then the relation between body fat-corrected mean ECG voltage (Vfm) and ambulatory blood pressure (BP) was investigated. The subjects were 172 patients with essential hypertension (88 men, 84 women, none receiving medication) between the ages of 30 and 75 years. Ambulatory BP was measured by a multi-biomedical recorder. Minimum sleep-time BP (base BP) was calculated to correspond with minimum sleep-time heart rate. The tetrapolar bioelectric impedance method was used to measure body fat (kg). Left ventricular mass (LVM) was obtained by echocardiography. Then comparisons were made with standard 12-lead ECG, and the statistical mean ECG voltage (Vm) and Vfm were derived by multivariate statistical analysis. The following formula was devised to obtain Vfm resulting from the multivariate analysis that demonstrated a high correlation with LVM (r=0.85): Vfm=0.175(Body Fat)1/3xVm+0.5 (mV). The coefficient of correlation (r) between Vfm and ambulatory BP was not smaller than that between LVM and ambulatory BP. Base systolic BP demonstrated a significantly higher r value (r=0.83) with Vfm/BSA1/2 (where BSA is body surface area) than mean daytime SBP (r=0.65). In many subjects with white-coat hypertension, Vfm/BSA1/2 was <1.33 mV/m (34 of 38 cases; sensitivity, 89%; specificity, 89%). These results indicate that Vfm is a better indicator of hypertensive left ventricular hypertrophy and that it may be useful in estimating minimum sleep-time systolic BP and in diagnosing white-coat hypertension in the outpatient clinic.