Study design and setting
This is a case-control study conducted at the Centre Médical de Kinshasa (CMK) between January and December 2019. The CMK is a reference clinic, working on international standards and norms, with a cardiology unit named « pôle de cardiologie » with highly qualified and regularly retrained personnel, that provides cardiovascular explorations such as doppler echocardiography, coronary scanner and cardiopulmonary exercise testing. A cardiovascular rehabilitation unit, the only one in central Africa, is also operational there.
Consecutive asymptomatic patients with probably essential hypertension aged 20 years or more attending the outpatient clinic at the CMK Pôle de cardiologie between January and December 2019 were screened for clinical or laboratory evidence of secondary hypertension, renal or hepatic disease. They were invited by writen informed consent to participate in the present study. Those with high blood pressure unrelated heart disease were not enrolled. Each participant who met the criteria for echocardiographic diagnosis of LVH was matched for gender and age with two hypertensive patiens without left ventricular hypertrophy.
A total of 267 participants were screened, 106 with left ventricular hypertrophy and 161 without left ventricular hypertrophy. Of these, 47 were excluded due to dilated cardiomyopathy in 20 participants (8 with LVH and 12 without LVH), ischemic cardiopathy in 14 participants (5 with LVH and 9 without LVH), significant valvulopathy in 5 participants (2 with LVH and 3 without LVH), pericardidis in 5 participants without LVH, and hypertrophic cardiomyopathy in 3 participants with LVH. The final analysis therefore included 220 participants 88 (40%) with and 132 (60%) without left ventricular hypertrophy.
Demographic data (age, sex), lifestyle habits (heavy alcohol consumption, current smoking, sedentary behavior), medical history including cardiovascular risk factors (age at diagnosis of high blood pressure, history of diabetes mellitus, dyslipidemia, hyperuricemia, menopause) and previous cardiovascular events (stroke, ischemic heart disease, heart failure, Chronic Kidney Disease, cardiovascular surgery), and current medication use for chronic disease (antihypertensive treatment, anti-diabetic treatment and other treatments including statins, antiplatelet agents, hypouricemics, oral contraception, hormone replacement therapy) were collected during an in-person directed interview using ad hoc questionnaire.
Anthropometric parameters were measured by a final year medical student who had also undergone a study-training session held by the authors. The student measured both primary variables (weight, height, waist size, hip measurement) according to WHO recommendations and a derived variable (body mass index (BMI) as :
- Body weight was measured to the nearest 100 g using a validated electronic balance the participants upright in light clothing without shoes ;
- The height was obtained to the nearest centimeter using a measuring rod, , with the participant standing, barefoot and bareheaded;
- The waist circumference to the nearest 0.1 cm, was mesured using a measuring tape applied directly to the skin along a horizontal line passing through the umbilicus.
- The body surface area (BSA) was calculated using the DuBois formula  as follows: BSA = Height 0.725 × Weight 0.425 × 0.007184.
- BMI was obtained by dividing the weight (Kg) by the square of height (m2)
BP was measured non-invasively by 24 hour-ambulatory blood pressure monitoring (ABPM) using a TONOPORT V (GE Health care, Freiburg, GERMANY) type recorder. During this recording, the participant was asked to maintain his usual way of life.
Left ventricular measurements were taken according to the 2015 American Society of Echocardiography and the European Association of Cardiovascular Imaging updated guidelines for cardiac chamber quantification  using a Vivid T8 (GE) type ultrasound system equipped with 3.5 MHz transducers. Two-dimensional guided M-mode echocardiography was performed on a parasternal long-axis view. Interventricular septum (IVS) thickness in diastole (IVSd), left ventricular posterior wall (PW) thickness in diastole (LVPWd), and left ventricular end-diastolic diameter (LVEDd), all measured in mm were assessed at a level just below the mitral valve leaflets at end-diastole. Simultaneous ECG was done to correlate left ventricular measurements with the cardiac cycle. Diastolic wall thickness was measured at the onset of the QRS wave. LVM was calculated based on the American Society of Echocardiography simplified cubed equation linear method using the following equation : LVM (grams) = 0.8 × 1.04 × [(LVEDd + IVSd + LVPWd)3- (LVEDd)3] + 0.6 g. LVM was indexed to BSA and to height as mass/BSA and mass/height2.7. The relative wall thickness (RWT) of the left ventricle (LV) was calculated as follows: (2 × LVPWd) / LVEDd. In accordance with international recommendations , the parameters of LV diastolic function were measured by recording transmitral flow velocity using conventional doppler echocardiography. With pulsed wave Doppler (PW), transmitral flow velocity was recorded from the apical transducer position with the sample volume situated between the mitral leaflet tips. E (Peak E-wave velocity) and A (Peak A-wave velocity) and Deceleration time of early filling (DT), were recorded in apical four-chamber with color flow imaging for optimal alignment of PW Doppler with blood flow. PW Doppler sample volume (1–3 mm axial size) was placed between mitral leaflet tips, using low wall filter setting (100–200 MHz) and low signal gain, so that the optimal spectral waveforms should not display spikesand. Both E, A and DT were measured as the averages of five consecutive cardiac cycles The E/A ratio was calculated. Tissue Doppler echocardiography, which measures the velocity of the regional cardiac wall, was performed by activating the tissue doppler echocardiographic function, as for two dimensional and M-mode echocardiography. Mitral annular velocities were recorded from the apical window. Sample volumes were located at the lateral site of the mitral annulus. Peak early diastolic mitral annular velocity (E′, cm/s) was measured over five cardiac cycles and the mean calculated. The ratio E/e′ was used as a parameter of left atrial pressure, which is elevated with progression of LV diastolic dysfunction. These parameters, obtained by tissue doppler echocardiography, were also used as parameters of LV diastolic function.
For all analyses, a blood sample was taken from the cubital vein between 7 a.m. and 9 a.m. following an overnight fast that started at 10pm the previous day. All analyses were carried out at the CMK laboratory. Blood was collected in a dry tube for the assessment of serum uric acid level, total cholesterol, LDL-cholesterol, HDL-cholesterol and triglycerides,. Serum was used for the analysis. The assay was performed by the standard colorimetric method. Readings were measured using the colorimetric spectrophotometer brand HELIOS Epsilon (Milwaukee, USA). The blood glucose test was performed on plasma oxalate by colorimetric method using standard reagents Biolabo.
The insulin dose was assessed on EDTA plasma by ELISA. Ooptical density reading was done on a string read from the firm HUMAREADER HUMAN (Germany).
Assessments of glycated hemoglobin were performed on plasma treated with EDTA by the electrophoretic method using HYRYS HYDRASIS from the firm SEBIA (France).
Serum creatinine was measuredby the method of simple colorimetric Jaffe. Readings were assessed by colorimetric spectrophotometer (Spectrum 2100 brand, South Africa).
Sedentary was defined as sitting for more than 7 hours a day .
Cigarette smoking was defined as regular smoking for at least 30 days preceding the interview date regardless of the number of cigarettes smoked .
Excessive alcohol consumption was defined as drinking more than 2 glasses of beer or its equivalent every day for at least a year .
Overweight was defined as a BMI between 25 and 29.9 Kg/m2 of body surface area .
Obesity was defined as a BMI equal to or greater than 30 Kg/m2 of body surface area . Abdominal obesity was been defined as a waist circumference of more than > 102 cm and > 88 cm for men and women respectively .
Poor control of arterial hypertension was defined as an average systolic blood pressure greater than 130 mmHg and/or average diastolic BP greater than 80 mmHg on 24-hour ambulatory blood pressure monitoring .
Diabetes mellitus was defined as a fasting blood glucose ≥ 10 mmol/l with a glycated hemoglobin level greater than 7% .
Hyperinsulinemia was been defined as fasting insulin > 90 mmol/L.
Insulin resistance was defined as a HOMAIR of ≥ 2.5 .
Dyslipidemia was defined as a HDL-cholesterol level of <1.03 mmol/L for males or <1.04 mmol/L for females, and/or an LDL-cholesterol level ≥ 3.38 mmol/L, and/or a total cholesterol level ≥ 5.17 mmol/L, and/or a triglyceride level ≥ 1.69 mmol/L .
The atherogenicity index (AI) was calculated by the total cholesterol to HDL-C ratio. The atherogenicity index was considered high when this ratio was greater than 5 .
Hyperuricemia was defined as a uric acid of > 420 mmol/L .
Normal LVM was defined as ≤115 g/m2 or ≤ 48 g/m2.7 for males and ≤ 95 g/m2 or ≤44 g/m2.7 for females ; LVH was defined as LVM exceeding these values in males and female patients respectively. Four LV geometric patterns were defined as follows [51, 52] : normal geometry (normal LVM and RWT ≤ 0.42), concentric remodeling (normal LVM and RWT > 0.42), eccentric hypertrophy (LVH and RWT ≤ 0.42) and concentric hypertrophy (LVH and RWT > 0.42).
Three patterns of diastolic dysfunction (DD) were defined as follows [53, 54]: abnormal relaxation (grade I of DD: E/A ratio <1 and prolonged deceleration time), pseudonormal relaxation (grade II: E/A ratio >1 and intermediate values of deceleration time), and restrictive patterns (reversible and irreversible, grade III–IV respectively; E/A ratio > 2 and shortened deceleration time).
The dilation of the left atrium was defined as an area of the OG of > 20 cm2 of body surface .
Data were presented in the form of absolute (n) and relative (%) frequencies for categorical variables and as averages (± standard deviation) for quantitative variables. Paired comparisons between the cases and controls were made using Pearson square Chi-square test or the Fisher Exact test as appropriate for categorical variables and using Student's t-test for continuous variables.
Linear regression was used to determine factors predictive of LVM variations. The following variables were entered in the univariate analysis : parameters of obesity (WC, HC, BMI), parameters of glucose metabolism (Fasting glucose, HBA1c, fasting insulinemia, and HOMAIR), parameters of lipid metabolism (TC, HDL-c, LDL-c, Triglycerides), parameters of renal function (creatinine and uricemia), parameters of phosphocalcic metabolism (calcium, ionized calcium, phosphore). When significant associations were observed between LVM and the independent variables, the effect of potential confounders was studied by adjustment in multiple linear regression.
Simple logistic regression was used to determine factors predictive of LVH. The following variables were entered in the univariate analysis : Medical & social history (Known HTN, ND HTN, Cigaret smoking, excessive alcohol consumption, Menopausal), sedentary, uncontrolled HTN, dislipidemia, High AI, diabetes mellitus, hyperinsulinemia, hyperuricemia and insulin resistance. When associations were observed between LVH and the independent variables, the effect of potential confounders was studied by adjustment in conditional logistic regression (multivariate analysis).
The significance threshold retained was then p <0.05. Statistical analyzes were performed using XLStat 2020 and SPSS (Statistic Package for Social Sciences) for Windows version 24 software
This research was conducted in strict compliance with the recommendations of the Helsinki Declaration III. Approval to conduct the study was obtained from the ethics committee of the University of Kinshasa School of Public health. Each participant provided written informed consent for to participate in the study. All respondents were debriefed on the results of the study.