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Echocardiographic evaluation of normal adult left Ventricular geometry in a Nigerian population

Background Differences have shown to exist in some echocardiographic measurements that were attributed to racial, ethnic and gender. This study determined echocardiographic baseline data of normal adult left ventricular (LV) geometry in our locality. Methods The study was performed on 1,192 apparently healthy adults. Participants below the age of 18 years or those with congenital or acquired cardiac abnormalities and history of long-term regular physical training were excluded. Trans-thoracic echocardiography was performed with Vivid T8 GE dedicated echocardiography machine with probe frequency of 1.7 to 3.2 MHz with integrated electrocardiography (ECG) recording electrodes. The study determined normal dimensions of interventricular diamensions. All measurements were indexed to body surface area (BSA) to obtain echocardiographic baseline normal reference values. Results The mean + SD values of LV parameters for male and female participants were: LVIDd (44.80 ± 5.71 mm vs 42.75 ± 5.21 mm), LVIDs (33.54 ± 5.37 mm vs 30.38 ± 4.81 mm), and LVPWd (8.32 ± 1.26 mm vs 7.51 ± 1.22 mm). Females had more statistically significant interventricular septum in diastole (IVSd) (8.20 ± 1.38 mm vs 7.05 ± 1.27 mm) and interventricular septum in systole (IVSs) (9.08 ± 1.42 mm vs 8.99 ± 1.33 mm) (P < 0.05). Conclusion This research established echocardiographic baseline normal adult left ventricular geometry in the study population because in order to detect abnormalities, accurate definition of normal values of echocardiographic measurements is of utmost importance for a reliable clinical decision making.


Introduction
Measurement of the size of the left ventricle of the heart provides diagnostic clues and prognostic information, and enables the clinician to follow patients in respect of disease progression or improvement [1]. Echocardiography is the most widely used non-invasive imaging tool for the assessment of the heart structure and functions [2]. Various measurements can be performed to determine the size, diameter, length and area of the left ventricle. These measurements are performed at distinct time points of the cardiac cycle, i.e the end of diastole and the end of systole. The end of diastole is seen when the volume of the ventricle is largest, shortly before the mitral valve closes and the mitral annulus descends [3,4]. The end of systole is the time when the volume of the ventricle is smallest, shortly before the mitral valve opens. Therefore, in order to detect abnormalities, accurate definition of normal values of echocardiographic measurements is of utmost importance in order to be a reliable guide for decision making [3,4]. Therefore the aim of this study is to determine echocardiographic baseline data of normal adult left ventricular (LV) geometry in Nnewi community setting of Anambra state, Nigeria.
Every effort has been made in establishing normal cardiac dimensions. Such diagnoses include macroscopic examination, genetic studies, electrocardiography, cardiac magnetic resonance imaging (MRI), histological studies and echocardiography [5].
Echocardiography remains the gold standard to determine the structure and fuction of the heart [2]. It is also readily available and cheap when compared to other imaging modalities in Nigeria. The normal baseline values of echocardiographic measured left ventricule of the heart in the literature are mostly based on Caucasian populations [6]. Moreover, there is paucity of literature on the normal echocardiographic values of the left ventricle among adults in our locality. It is of great clinical importance to differentiate between normal and abnormal left ventricles and to explore the normal anatomical variation of these parameters.
This will prove more difficult if the ranges of normal values are unknown for each clime.
Therefore, the aim of this study is to evaluate specific normal reference values of adult left ventricular geometry in our locality in a cross sectional study. The findings will be useful in understanding the pathological changes, treatment and management of cardiac patients in the locality.

Materials and methods
A prospective cross-sectional design was adopted for this study. It was carried out on 1,192 apparently healthy volunteers above 18 years of age who presented for echocardiography study at our center between March 2017 and August 2018. Participants were excluded if they had congenital or acquired cardiac abnormality, had history of long-term regular physical training and If they had any systemic disease (endocrine, collagen, metabolic, nutritional or infectious), hypertension, diabetes mellitus, chronic kidney diseases, and/or chest disease.
The participants who wished their relatives to witness the procedure were obliged. This is to give the participants confidence so as to achieve maximum co-operation for better quality results.
Weights were measured with commercially available weighing scale (Hana model). Heights were measured by a meter rule. Height and weight were used to estimate body mass index (BMI) in kg/m 2 and body surface area (BSA) in m 2 . Where BSA = square root of ([height in cm x weight in kg]/3600).

Sample size estimation
The minimum sample size for this study is given by: For a finite population ( Lwanga and Tyre, 1986).
Where: n = minimum Sample size. Z = 1.96 at 95% confidence interval, that is the standardized Z -score. P = estimated population proportion.
Since this proportion for the population under study is not known, a value of 50% (0.5) is assigned to obtain maximum value for P. d = absolute precision required on either side of the proportion = 50% (0.05).
Substituting the values of z, p and d in the above equation: Therefore in order to minimize sample error, sample size of 1,192 apparently healthy subjects was used for the study.
Scanning protocol or technique: The participants were scanned using 2D, M-mode and Doppler measurements. Standard trans-thoracic echocardiographic studies with machineintegrated ECG recording were performed using Vivid T8 GE machine with sector probe of frequency range from 1.7 to 3.2 MHz. The choice of the probe was to get adequate visualization of the heart through the intercoastal space. All studies were done with patients lying in the left lateral decubitus position and breathing quietly [7,8]. Ultrasound gel was applied to ensure proper coupling of the transducer and good transmission of the ultrasound beam into the subjects. From the parasternal window, parasternal long axis views were obtained by placing the transducer in the left third or fourth intercostal space adjacent to the sternum with the knob pointing toward the right shoulder. After confirming a true long axis view that was perpendicular to the centre of the true long axis of the left ventricle (LV), Mmode image was taken between the papillary muscle and at the tip of the mitral valve [9].
Measurements were made from the leading edge of the septal endocardium to the leading edge of posterior wall endocardium [8]. Measurements for the interventricular septum at end diastole (IVSd), LV internal dimensions at end diastole (LVEDd) and LV posterior wall thickness at end diastole (LVPWd) were obtained. Also the measurements were obtained at end systole for each of the parameters mentioned above. All measurements were done on a frozen M-Mode image.
All measurements were divided by BSA to obtain indexed measurements [2,6].

Statistical analysis
The data collected were analyzed using 53.6% of these subjects were males while 46.4% were females.

Established baseline normal echocardiographic reference values of the left ventricular dimensions in the study population.
The mean septum in diastole and systole were 8.12 ± 1.33 mm and 9.03 ± 1.37 mm respectively. The LV diameter in diastole was 44.78 ± 5.48 mm and the LV diameter in systole was 33.47 ± 5.12 mm. Post wall in diastole and systole, were 8.31 ± 1.24 mm and 9.47 ± 1.26 mm respectively. While relative wall thickness was 0.38 ± 0.08 mm, (table 4).       and LV mass 120.92 ± 31.91kg were observed among the overweight. Highest mean post wall in diastole 8.47 ± 1.34kg and septum in systole 9.26 ± 1.41kg were observed among the obese.

Baseline normal Echocardiographic Values of the Left Ventricle
In this study, various measurements of the left ventricular dimensions in apparently normal subjects were obtained and indexed to BSA. This agrees with findings from other similar studies which reported that indexing echocardiographic parameters to BSA produces more reliable data [2,6]. The study by [10] described only the profile of cardiomyopathy in Nigeria among children in Jos Northern part of Nigeria. Another study by [9] in western Nigeria also described only the profile of cardiomyopathy in Nigeria among children in the region. Thus there is still need for echocardiographic normal values in adult population in Nigeria.
In this study, 1192 apparently healthy subjects were studied to establish baseline normal reference values of left ventricular dimensions. In general it was discovered that left ventricular dimensions increases with increase in age and morphology until mid age in this present study. This was in agreement with the work done by [2] which stated that the size and morphology of the left ventricle varies with age and from person to person. This study, were higher in females (p < 0.001). These were similar with a study on normal reference values of echocardiographic measurements in young Egyptian adults where males also had larger values than females in these parameters [2]. The study showed that a linear correlation existed between all echocardiographic measurements with age, height, weight, BMI and BSA which is similar to the findings of [11]. These imply that echocardiographic parameters can be indexed to body surface area to obtain a more reliable normal reference values in our locality.

3 Baseline normal echocardiographic values indexed to BSA
Producing normal values for dimensions and functions of the heart is very important to avoid misclassification of normal persons into the high risk category and the reverse [12] Studies have shown that using measurements indexed to BSA provides more reliable information [13]. In this study, participants' absolute LV dimesions and LV mass were smaller than the ASE-recommended normal values. These differences were significantly minimized when the values were indexed to BSA. These findings imply that the practice of using absolute values for defining normality of various cardiac chamber dimensions in our locality should be discouraged. The BSA-indexed left ventricular baseline normal reference values in our locality should be used during echocardiography investigations because there is welldeveloped fact that indexing allows comparisons in subjects with different body sizes [14,15,8].These changes have also been observed among different races and ethnicities which raised the importance of this study keeping in mind that today's baseline normal values are widely based on data from North American cohorts obtained in the 1970s and 80s [16,17,18,4].
Specifically, males had higher indexed post wall diastole, indexed LV diameter in diastole (LVEDD) and indexed LV diameter in systole (LVEDS). Females had higher mean in indexed septum diastole, indexed septum systole, indexed post wall systole (5.11 ± 0.8) and indexed LV mass (63.94 ± 19.6). Therefore males had larger left ventricular dimensions than females in this study.

Comparing the study values to international reference values
Measurements obtained from this study were compared with the reference values of On examining these results, it was found that our locality LV dimensions were smaller than those of the caucasian population. The males in this study had a higher upper reference limit of normal for LVEDD, LVESD and IVSd. Females had a higher upper reference limit of normal for indexed LV mass. These confirmed that in this study, males had higher indexed left ventricular internal diameters while the females had thicker left ventricular walls. Moreover, poor image quality and oblique views made it difficult to perform measurements.

Limitations of the study
Also, this work did not measure LV volume which is obtained by 2D measurement of LV length and width, thus further studies should adopt 2D measurement of the LV volume as this work used M-Mode tracing.

Conclusion:
This study established data for baseline normal values for normal left ventricle of the heart in a population of one thousand one hundred and ninety two (1,192)

Availability of data and material:
The dataset generated and analysed during the current study are not publicly available but are available from the corresponding author on reasonable request.

Competing interest: Not applicable.
Funding: Not applicable.
Patient consent for publication: Not applicable.

Conflict of interest: Daniel Chimuanya Ugwuanyi, Charles Ugwoke Eze, Chukwudi
Thaddeus Nwagbara, Hyacinth Uche Chiegwu and Joseph Chukwuemeka Eze declare that they have no conflict of interest.

List of abbreviations: Not applicable.
Human rights statements and informed consent: All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1964 and later revisions. Informed consent was obtained from all patients for being included in the study.