LINEAR REGRESSION MODELS FOR LEFT VENTRICULAR MASS BY ECHOCARDIOGRAPHY IN NORMAL IRAQI SUBJECTS

Left ventricular mass (LVM) is an independent risk factor for cardiovascular outcome. M-mode echocardiography, the most commonly used technique for estimation of LVM. The purpose of this study is to establish the regression models for prediction of LVM, measure the normal values of the LVM in normal Iraqi subjects and to compare them with values obtained in Europe, American and Arab people. Keyword: left ventricular mass (LVM), Relative Wall thickness (RWT), Echocardiography, Left ventricular mass index (LVMI). Introduction It is well known that increased left ventricular mass (LVM) is an independent risk factor for cardiovascular morbidity and mortality (1, 2, 3). Regression of the LVM index has been found to be associated with lower rates of clinical cardiovascular events (4). Several authors suggest that it may be a useful parameter in risk stratification and guiding treatment, especially for hypertensive patients at low or medium risk (5, 6). For these reasons, accurate estimation of LVM has crucial importance. Echocardiography is the most commonly used technique for the estimation of LVM (7, 8, 9, and 10). Devereux et al (11, 12) proposed a formula for estimation of LVM and found that the LVM calculated by this formula was consistent with the necropsy data. Calculation of LVM by this formula requires some geometric assumptions. Also, it is found good correlation between echocardiography LVM and true anatomic LVM (11). The relation between race-ethnicity and LVM has not been fully explored (13). Blacks are more likely to have increased LVM than whites (14, 15). While the values of LVM in Arab people are not significantly different from that obtained in Europe and North America (16). To the best of our knowledge, prediction models for left ventricular mass have not been established in Iraqi people. This study aimed to establishing linear regression models, and to develop normal data for LVM based on age, sex, body weight, height, and body surface area to look if these data are significantly different from their estimated values by Mmode echocardiography method for blacks, whites and Arab-people. Materials and Method A total of one hundred Iraqi subjects were studied in Baghdadteaching hospital/ Eachocardiography unit between the january2009 to April-2009. One hundred normal subjects were recruited as 50 males and 50 females. Their ages ranged from 19 years to 70 years with mean ages standard deviations of 46.46 15.73 and 43.96 15.44 for men and women respectively. Any subject with evidence of heart disease, hypertension or other systemic disease was excluded. Examination included measurements of blood pressure, height, weight, body surface area (BSA), and body mass index (BMI). The body mass index (BMI) was calculated as (BMI = weight/height) (17). Body surface area (BSA) was calculated by: [BSA in (m) = 0.0001 * 71.84 (weight in Kg) 0.425 (Height in cm)* 0.725] (18). Echocardiography was performed with Philips ultrasound system with a 3 MHz transducer and measurements were taken by standard two-dimensional (2-D) protocol according to the guidelines of the American Society of Echocardiography (ASE) (19). Posterior wall thicknesses (PWT) in diastole, Septal Wall thickness (SWT) in diastole and end diastolic diameter (EDD) were measured Ramaq Ghassan Wahbi Al-Kadi 76 in all subjects. Relative wall thickness (RWT) was calculated as the ratio of 2 [posterior wall thickness / end diastolic diameter] (17). Left ventricular mass was calculated according to the formula published by Devereux and Reichek (11): LVM = 1.04 [ (SWT + LVID + PWT) (LVID) ] 13.6. LVM was then indexed to body size by dividing raw LVM by height to allometric power of 2.7 and analyzed as a continuous variable (20, 21). Data Analysis Pearson s correlation coefficients were derived relating indexed and un-indexed values of LVM measured by M-mode echocardiography and measures body size, weight, height, and body surface area. LVM was also correlated to age. Means SD were calculated for continuous variables. Linear regression models for continuous variables were performed. Statistical significance was determined at the = 0.05 level using two sided-tests. Statistical analyses were conducted using WINKS SDA-statistical Data Analysis Version 6.0. 5 computer software. Results One hundred Iraqi subjects were enrolled in this study. Equal numbers of men and women enrolled into the study (fifty each) were healthy and free of any medical disease Subjects ages ranged from 19 to 70 years with mean age SD of 46.46 15.73 and 43.96 15.44 in men and women, respectively. The characteristics of the study subjects are summarized in Table (1). Table (1) Descriptive statistics of cardiac parameters in 100 healthy subjects (males and females).