|Year : 2015 | Volume
| Issue : 1 | Page : 12-17
Electrocardiographic Pattern of Apparently Healthy Primary School Children Aged 5-15 Years, in Kano
Ibrahim Aliyu, Mu'uta Ibrahim
Department of Paediatrics, Aminu Kano Teaching Hospital, Bayero University Kano, Kano, Nigeria
|Date of Web Publication||14-Mar-2015|
Department of Paediatrics, Consultant Paediatrician, Aminu Kano Teaching Hospital, Kano
Source of Support: None, Conflict of Interest: None
Background: Electrocardiography (ECG) is a simple, noninvasive, and relatively cheap investigative tool used for cardiac evaluation. However, there are limited electrocardiographic studies of Nigerian children. Adult studies of ECG have shown significant differences between Black and Caucasian populations. These differences may also be seen in children, hence, the need to develop local reference values. Materials and Methods: This was a cross-sectional study and multistage random sampling method was applied to select 650 subjects. The ECG machine was a portable heated stylus direct writing AT-2 Swiss made electrocardiograph (Schiller AG Cardiovit CH6341). Results: There were 350 males (53.3%) and 300 females (46.7 %), with a male:female ratio of 1.2:1. The mean heart rate decreased with increasing age. R-wave amplitudes were higher in the left precordial leads, in keeping with left ventricular dominance. Mean values were higher in boys than girls in the three age-groups in most of the precordial and limb leads. In V 4 R, V 2 , and V 3 highest mean R wave voltages of 0.5 ± 0.1, 1.4 ± 0.3, and 1.4 ± 0.2 mV, respectively, were recorded in the 5-7-year-old. While in V 5 and V 6 , the mean R waves were higher in the 12-15-year-old age group (3.7± 0.5 and 2.5±0.4 mV, respectively). The S-waves showed progressive decrease in its amplitude on the left precordial leads with increasing age. Conclusion: The mean values in heart rate, QRS duration, PR interval, and P-wave amplitude showed higher amplitudes in boys. Similarly higher amplitudes of R-waves in boys were recorded in precordial leads V 2 , V 3 , V 5 , and V 6 in the three age groups.
Keywords: African children, electrocardiography, reference values
|How to cite this article:|
Aliyu I, Ibrahim M. Electrocardiographic Pattern of Apparently Healthy Primary School Children Aged 5-15 Years, in Kano. Heart India 2015;3:12-7
|How to cite this URL:|
Aliyu I, Ibrahim M. Electrocardiographic Pattern of Apparently Healthy Primary School Children Aged 5-15 Years, in Kano. Heart India [serial online] 2015 [cited 2019 Jul 18];3:12-7. Available from: http://www.heartindia.net/text.asp?2015/3/1/12/153280
| Introduction|| |
Electrocardiography (ECG) is a harmless, painless, noninvasive, easy to perform, and relatively inexpensive technique of obtaining information on cardiac activity.  It is invaluable in the evaluation of patients with suspected cardiac diseases which is practicable in a resource limited country like Nigeria.
In interpreting pediatric ECG, integration of the clinical history, physical examination findings with the ECG report is vital to making a reasonable diagnosis. Interpretation of pediatric ECG is age-dependent and reference standards are required for comparison. While ECG reference standards in Nigerian adults , have been established, there is dearth of information on Nigerian children. The current practice of comparing ECG measurements of Nigerian children with Caucasian values should be discouraged because it maybe error prone; it is well-established that, there are racial differences in the ECG characteristics between adult Blacks and Whites ,, which may also be existent in children. Therefore, there is the need to develop local reference standards.
Although there are pioneer works on ECG on apparently healthy Nigerian children, , these studies had limitations which has affected their clinical application. This study seeks to establish reference ranges and any gender differences in the ECG characteristics of Nigerian children.
| Materials and methods|| |
The study involved 650 apparently healthy Nigerian children aged 5-15 years in Kano metropolis who were free of any illness at the period of this study carried out between the months of June 2008 and November 2009.
Those whose blood pressure were more than the 95 percentile for age, sex, and height;  those with dysmorphic facie; those on any medication known to affect the cardiovascular system;  and those with any chronic illness were excluded from the study.
Approval to carry out the study was obtained from the Medical Ethics Committee of Aminu Kano Teaching Hospital and Universal Basic Education board of Kano state. Informed consent was obtained from parents, caregivers, and older children.
This study was cross-sectional. A multistage random sampling technique was adopted ,, to select participants.
The ECG machine was a portable heated stylus direct writing AT-2 Swiss made electrocardiograph (Schiller AG Cardiovit CH6341), with frequency of 150 Hz and sampling frequency of 1,000 Hz. Unipolar, bipolar limb leads, and chest leads with European color coding system were used to record the ECG variables. The machine has two speeds, 25 and 50 mm/s; with three levels of sensitivity at 5, 10, and 20 mm/mV. 'Aqua sonic 100' electrode jelly  was used to provide effective contact between the skin and electrode. The subjects were classified into age groups; 5-7, 8-11, and 12-15 year age groups, respectively.
Standardization and measurement
The ECG machine's control switch was set at a pen calibration to give a deflection of 10 mm/mV with a recording speed of 25 mm/s. Where deflections were small or too large, standardization was doubled or halved, respectively, in order to identify the wave pattern. A minimum of five cardiac cycles were recorded per ECG lead; measuring along the vertical line of the ECG graph paper, 10 mm represented 1 mV, whilst 1 mm along the horizontal line represented 0.04 s (40 ms). Using the TP line as the isoelectric line, positive deflection was measured from the upper margin of the baseline to the tip of the deflection whilst negative deflection was measured from the lower margin of the baseline to the lowest point of the deflection. 
The small box method was used for the calculation of the heart rate for ECGs in sinus rhythm, while the 6-s method was used for those ECGs with irregular rhythm pattern. ,,
PR interval was measured in lead II, from the beginning of P-wave to the beginning of R-wave along the horizontal line of the ECG paper. P-wave duration was measured in II, from the beginning of the P-wave to the end of P-wave along the horizontal line of the ECG paper.
QRS complex duration was measured in lead V 5 , from the beginning of Q wave to the end of the S wave along the horizontal line of the ECG paper. All measurements were done manually by visual inspection using magnifying glass.
Definition of terms
Second percentile was defined as the lower limit of normal, whilst the 98 th percentile was defined as the upper limit of normal. 
An apparently healthy child in this study was defined as any child who was ambulant, clinically free of any disease, and not on any medication at the time of study.  Age was defined as the age at last birthday. 
Data entry and analysis were carried out using a computer software package; the Statistical Package for Social Sciences version 13. The mean and standard deviation of various ECG variables were determined for both sexes,  and 2 nd and 98 th percentiles of measurement distribution were determined.
| Results|| |
Six hundred and fifty children in Kano metropolis were studied. There were 350 boys (53.3%) and 300 girls (46.7%) with male to female ratio of 1.2:1. There were 38.3, 42.9, and 18.8% of the 5-7 year, 8-11 year, and 12-15 year age-group, respectively.
The heart rate increased with increasing age and the female groups had higher mean values than the male groups.
Electrical axis of the heart
The electrical axis of the heart in the frontal plane was represented by the QRS-axis. The mean QRS-axis in the three age groups lay within the normal axis of 0-90 o . The axis progressively increased with age and higher mean values were recorded in the male population.
In the three age groups, the mean P-wave axes lay within 0-90 o . The lowest mean P-wave axis was recorded in the 8-11 year age group, whilst the highest mean value was in the 5-7 year age group.
The mean T-wave axes for the three age groups were within 0 - 90 o . The lowest mean T-wave axis was 30 ± 9 o , whilst the highest mean value was 50 ± 8 o in the three age groups.
P-wave amplitude was determined using lead II. Higher amplitudes were recorded in 8-11 year age group and 12-15 year age groups.
Longer duration was recorded in the older children, in the 12-15 year age group.
The PR interval was recorded using lead II. The PR interval showed variation with age. There was progressive increase in the PR interval with increasing age and higher mean values were documented in the male population.
Bazett's formula was used to calculate the corrected QT interval, which was measured from precordial lead V 5 . The QT and QTc increased with increasing age in the male population, while they were of almost same values in the female population.
The mean duration of the QRS complex increased with increasing age. The lowest mean value was 56 ± 10 milliseconds, whilst the highest mean of 80 ± 15 milliseconds was recorded in the three age groups [Table 1]. Furthermore, females had relatively lower mean QRS duration when compared to the males of all the three age groups.
|Table 1: Lead-independent ECG indices according to agegroups and gender; showing the mean, standard deviation, 2nd, and 98th percentiles values|
Click here to view
In lead II, the lowest mean Q-wave amplitude was 0.2 ± 0.1 mV, whilst the highest mean value of 0.3 ± 0.1 mV was recorded in the three age groups. Highest amplitude was recorded in males of the 8-11 year age group. In lead III, the lowest mean Q-wave amplitude was 0.10 ± 0.1 mV, whilst the highest mean value of 0.26 ± 0.1 mV was recorded in the three age groups. Highest amplitude was recorded in the 12-15 year age group. In lead aVF, the lowest mean value was 0.1 ± 0.1 mV, whilst the highest mean value of 0.2 ± 0.1 mV was recorded in the three age groups. Highest amplitude was recorded in the 8-11 year age group. In lead V 5 , the lowest mean value was 0.2 ± 0.1 mV, whilst the highest mean of 0.3 ± 0.1 mV was recorded in the three age groups. Highest amplitudes were recorded in the 5-7 and 12-15 year age groups. In lead V 6 , the lowest mean Q-wave amplitude was 0.1 ± 0.1 mV, whilst the highest mean of 0.3 ± 0.1 mV was recorded in the three age groups. Highest amplitude was recorded in the 5-7 year age group.
In [Table 2], tall R-waves were predominant in the left precordial leads V 5 and V 6 . The tallest amplitude was recorded in V 5 , with a mean value of 3.7 ± 0.5 mV in the 12−15 year age group. Lead aVR recorded the lowest amplitude in the 5-7 year age group with mean value of 0.2± 0.1 mV. Progressive increase in the magnitude of the R-wave from the right-sided precordial leads to the left precordial leads was recorded. In the three age groups, males had higher R-wave amplitudes in the left precordial leads than females.
|Table 2: R-wave amplitude in the precordial and limb leads; showing the mean (M) and standard deviation (SD)|
Click here to view
[Table 3] depicts the S-wave amplitudes of the study population. There were predominant S waves in the right precordial leads in the three age groups. Highest amplitude was recorded in lead V 2 in the three age groups. There was progressive decrease in the magnitude of the amplitude when traced from V 1 on the right to lead V 6 . In the limb leads, aVR recorded the highest amplitude amongst the three age groups.
|Table 3: S-wave amplitude in the precordial and limb leads; showing the mean (M) and standard deviation (SD)|
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The highest amplitude was recorded in the 12-15 year age group; whilst the lowest amplitude recorded was in the limb lead aVR. There was a gradual increase in the amplitude in the T-wave on the precordial leads with increasing age [Table 4].
|Table 4: T-wave amplitude in the precordial leads according to agegroups and gender; showing the mean (M),|
standard deviation (SD), 2nd, and 98th percentiles values
Click here to view
| Discussion|| |
ECG parameters recorded were analyzed based on age groups; 5-7, 8-11, and 12-15 year similar to that used by Davignon et al.  The lowest mean heart rates was 75 ± 7 beats/min, whilst the highest mean was 96 ± 12 beats/min in the three age groups. The 5-7 year age group had higher mean heart rate than the older age groups. Physiologically, the heart rate decreases with increasing age and is attributed to increased autonomic nervous system activity.  This observation was similar to those reported by Davignon et al.,  Dickson,  and Rijnbeek et al.  Furthermore, females had relatively higher mean heart rates than their male counterparts. These findings were similar to those reported by Edemeka and Ojo,  Rijnbeek et al.,  Sedat et al.,  and Sun et al. 
Mean P-wave amplitude in lead II remains remarkably unchanged from birth until at least the age of 16 years. After the age of 6-12 months, the 98 th percentile value is 0.25 mV. For the diagnosis of right atrial enlargement, P-wave amplitude should be greater than the upper limit of normal. The 98 th percentile value in this study using lead II was within 0.25 mV, which was in conformity with the reports of Davignon et al.,  Dickson,  and Rijnbeek et al. 
The P-wave duration and PR interval measurements were comparable to Caucasian standards. , The PR interval increased with increasing age. The lowest PR interval value recorded was in the 5-7 year age group. This could be due to the fact that the heart rate has influence on the PR interval; the higher the heart rate, the shorter the PR interval. 
Typical features of a normal Q-wave are that; it has amplitude not more than 0.4 mV and a width of not more than 40 ms.  The mean Q-waves fulfilled these physiologic characteristics in our study. The presence of Q-wave of more than 0.4 mV alone or in association with tall symmetrical T-waves in lead V 5 or V 6 is often accepted as a sign of left ventricular hypertrophy.  The upper limit of Q-wave amplitude recorded in V 5 was 0.4 mVin boys of all the age groups. These were comparable to the findings of Rijnbeek et al.,  but contrasted with that of Davignon et al.,  who documented a 98 th percentile value of 0.3 mV. This disparity may be attributed to the difference in their sampling rate. While a sampling rate of 1,000 Hz was used in this study, Davignon et al.,  used a sampling rate of 333 Hz. Q-wave is a high frequency wave, therefore using a low sampling rate may result in recordings of lower voltages.
The QRS duration had a lowest mean value of 56 ± 10 ms, whilst the highest mean value was 80 ± 15 ms in the three age groups. This finding was comparable to those of Edemeka and Ojo  Davignon et al.,  and Rijnbeek et al.  There was progressive increase in the duration of QRS complex with increasing age which was similar to that of Macfarlene et al. 
Tall R-waves were observed in this study. Highest amplitude recorded was in the precordial lead V 5 . These mean values were higher than those of Davignon et al.  This trend compared with the report of Rijnbeek et al.  who also reported higher R wave amplitudes in the left precordial leads than those of Davignon et al.  This difference could be attributed to differences in sampling rate in their studies. Furthermore, higher amplitudes were equally documented in this study when compared to that of Rijnbeek et al.  Although taller R-waves have been reported to be common among Africans, ,,, differences in modality of ECG reading should be recognized, whilst Rijnbeek et al.,  used 'Modular ECG Analysis System,' manual reading was done in this study.
S-waves were predominant on the right precordial lead in the three age groups. This is because left ventricular dominance is already established by the age of 5years.  S-waves were deeper on the right precordial leads in the 8-11 year age group when compared to other age groups. This trend was similar to the findings of Rijnbeek et al.  Similarly, higher amplitude S waves were recorded in this study for the three age groups when compared to that of Rijnbeek et al.  This may be due to racial differences between black and Caucasian children.
| Conclusion|| |
ECG pattern in apparently healthy Nigerian primary school children aged 5-15 years were determined and the mean values of some of the ECG variables such as the R- and S-wave were higher than those reported for Caucasian children. However, there was a significant sex difference in the R-wave amplitude in the precordial leads V 2 , V 3 , V 5 , and V 6 in the three age groups; the male population having higher amplitudes than the female, which is similar to previous reports among Caucasian children.
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[Table 1], [Table 2], [Table 3], [Table 4]