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Cardiovascular risk factors and electrocardiographic pattern in two rural communities of Osun State in South West Nigeria

Curr Res Cardiol Vol 4 No 2 Summer 2017 15 Department of Medicine, College of Health Sciences, Osun State University, Osogbo, PMB 4494, Osogbo, Osun State Nigeria, Department of Community Medicine, College of Health Sciences, Osun State University, Osogbo, PMB 4494, Osogbo, Osun State Nigeria, Department of Surgery, College of Health Sciences, Osun State University, Osogbo, PMB 4494, Osogbo, Osun State Nigeria, Department of Medical Microbiology, College of Health Sciences, Osun State University, Osogbo, PMB 4494, Osogbo, Osun State Nigeria, Department of Chemical Pathology, College of Health Sciences, Osun State University, Osogbo, PMB 4494, Osogbo, Osun State Nigeria

Several studies have shown high prevalence of hypertension and obesity/ overweight in West Africa and also in immigrants of industralised countries from this sub-region (20).
There is therefore an urgent need to start generating data on prevalence, morbidity, mortality and risk factors of CVD in Africa. These data can then serve as template for the government to formulate concrete public health policy on CVD prevention, in order to stem the tide of this imminent CVD epidemic. We therefore embarked on this study to determine the prevalence of CVD risk factors, LVH inclusive (with ECG as tool) and also describe the ECG pattern in 2 rural communities of Osun State; Alajue and Ibokun, South West, Nigeria.

Study design
This was a community-based descriptive cross-sectional study of cardiovascular risk factors carried out in these two rural communities in March 2011 during the research outreach that formed a part of the activities marking the celebration of the World Kidney Day and World Glaucoma Day.

Setting
The study areas included two rural communities in Osun State namely Alajue and Ibokun, with a total population of about five thousand people according to the 2006 Nigerian national population census. Majority of the dwellers were farmers while some were artisans and traders. There is a primary health care center in each of the communities.

Participants
The inclusion criteria were that all eligible participants be permanent residents in either community for at least 5 years, should be aged >18 years and were able to provide informed consent. The Nigerian demographic structure is such that only about 55% of the total population could normally be eligible (age >18 years) (21); then the total number of eligible population could be estimated at 2750. All consenting adults who met the inclusion criteria were screened. Due to limitation of funding in this low resource setting (research was self-funded) a subgroup of all respondents (about 25%) was randomly selected and ECG was performed on them.

Ethical approval
Ethical approval to conduct the study was obtained from the Ethical Research Committee of Osun State University College of Health Sciences, and further permissions were given by concerned LGA authorities and community Kings. Written informed consent was obtained from each participant before commencement of the study.

Data source
This study was carried out as a part of a larger community-based screening programme to raise awareness towards kidney diseases. Two of three senatorial districts (Osun west and Osun East) were selected at random, employing simple balloting. One Local Government Area (LGA) per district and eventually one rural town (categorized as highly populated) per LGA were randomly selected also by simple balloting. These emerged as Alajue and Ibokun communities.
After paying series of advocacy visits to community gatekeepers, members of the two communities were mobilized to a town hall meeting and sensitized on the importance of screening for non-communicable diseases most especially cardiovascular diseases. At the meetings, community members eligible for the study were encouraged to come out en-masse, with the assurance that all who consented to the exercise would have it done for free.

Research instruments
An interviewer administered pre-tested questionnaire was used to collect some basic data pertaining to socio-demographic characteristics and cardiovascular risk factors among respondents. To standardize survey measurements and procedures, ten research assistants were trained with specially prepared survey manuals that conformed to recommended non-communicable disease survey protocols. Before the main study, a field test was carried out to finetune survey procedures.

Operational definitions and screening procedures
Venous blood samples for various biomarkers were collected by venepuncture after an overnight fast of 8-12hr, stored at 12 o C and delivered to the laboratory unit of the College of Health Sciences same day. Lipids profile and glucose levels were measured by qualified laboratory Technologists within the services of the Osun State University College of Health Sciences. Serum Creatinine was measured by enzymatic method. ECG was conducted by trained ECG Technicians and reported by two consultant cardiologists.

Measurements and calculations
ECG Measurements: After 10 minutes rest, each subject had a resting 12 lead ECG with a long rhythm strip of lead II recorded. Three portable ECG machines (model Cardiovit AT_1ECG Machines) and a generator were utilized in the communities for the screening. A generator was needed to prevent incessant power outages from militating against the exercise. Each ECG recording was independently reported by two cardiologists. Left ventricular hypertrophy (LVH) was assessed using Araoye (23) and Sokolow-Lyon (24) criteria independently.
Body weight was measured (to the nearest 0.5 kg) with the subject standing motionless on the calibrated weighing scale, with feet about 15 cm apart and weight equally distributed on each leg. Subjects were instructed to wear minimum outwear (as culturally appropriate) and no footwear while the weight was being measured. Height was measured (to the nearest 0.5 cm) using a calibrated tape and with the subject standing in an erect position against a vertical surface, and the head positioned so that the top of the external auditory meatus was level with the inferior margin of the bony orbit.
After the subjects rested quietly for 5 minutes, blood pressure (BP) was measured in the sitting position with an appropriate-sized cuff encircling the arm. With the right arm of the subject held at the level of the heart, the maximum inflation level was determined with a mercury sphygmomanometer, using a stethoscope and a cuff of appropriate size (a cuff of larger width was used for large arms) (22). BP was measured to the nearest 2 mmHg on two occasions at an interval of one to two minutes. BP measurements were made on the right arm of each study subject. Subjects were not permitted to smoke. In cases where the two readings differed by over 10 mmHg, a third reading was obtained, and the three measurements were averaged (22). The pressures at which sound appeared and disappeared were taken as systolic blood pressure (SBP) and diastolic blood pressure (DBP) respectively. BP was classified as normal, hypertensive or isolated systolic or diastolic hypertension.
A subject was considered to have diabetes mellitus if (i) the fasting venous blood glucose >7.0 mmol/L (126 mg/dL), or (ii) the subject was taking a hypoglycaemic drug or insulin. Normal fasting blood glucose was taken as 3.3-5.5 mmol/L and pre-diabetes or impaired fasting glucose as 5.6-6.9 mmol/L based on the American Diabetes Association criteria (27). Body Mass Index was calculated as weight in kilograms divided by height in meters squared. Based on their BMI, individuals were classified into four groups: thin (BMI <18.5 kg/m 2 ), normal (BMI=18.5-24.9 kg/m 2 ), overweight (BMI = 25.0-29.9 kg/m 2 ) and obese (BMI >30.0 kg/m 2 ); all according to WHO classification.

Data analysis
The Statistical Package for Social Sciences (SPSS) software version 17 (IBM Corporation Armonk, NY, USA) was used for data entry and analysis. Validity of data was ensured by double entry and random checks for errors and outlier values. Blood chemistry variables were recorded based on normal and abnormal values for that variable. Relevant frequency distributions tables and summary indices were generated. The Chi-square test was used to demonstrate relationships between categorical variables (in only those respondents who had complete and comprehensive test results), while level of significance was set at P-values ≤ 0.05 and confidence interval of 95% for all inferential analysis of categorical variables.

Study limitations
Not all the study participants completed all the necessary tests. Only 64 were able to complete all tests including ECG due to fund limitation and informed consent. Another limitation to this study was our not asking questions related to smoking of cigarette, the duration and frequency of smoking.

RESULTS
A total of 259 subjects volunteered to participate in the study. Table 1 shows the socio-demographic data of the subjects.
The ST segment was normal in 95.3% of the subjects and only 4.7% had non-significant ST changes; similarly, the T wave was also normal in 85.9%, inverted in 7.9% and nonspecific in 6.2%. By Araoye criteria, no LVH was found. However, a total of 1 (1.6%) of male and 7 (11.0%) of females had   Table 4 showed that a statistically significant association was found between obesity and gender of respondents, and blood pressure (p<0.05) while none existed between obesity and HDL levels, total cholesterol levels and fasting blood glucose level. (p>0.05). A statistically significant association was found between hypertension and age of respondents (p<0.05) while none existed between hypertension and gender, HDL levels, total cholesterol levels and fasting blood glucose level. (p>0.05). Similarly, there was no statistically significant association when those with normal and prolonged QTc were compared with either hypertension or obesity as a status (p>0.05).
While age is not a predictor of obesity (OR 1.08), respondents older than 45 years of age were three (1/0.34) times more likely to have developed hypertension compared to those respondents less than 45 years old (OR 0.34, 95% CI 0.192-0.616, p-0.001) and this observation was found to be statistically significant.

DISCUSSION
The prevalence of hypertension and other CVS risk factors in Nigeria is on the upward trend portending increase in morbidity and mortality attributable to CVD. This current study supports this dangerous trend as reported in some other rural communities across the nation. (18,19,28). This study showed a systemic hypertension prevalence rate of 23.9% in the two rural communities studied. The total prevalence of hypertension in this study included the patients with known hypertension as they still had their BP elevated showing poor BP control either due to inadequate dosing or poor drug compliance. This shows an increase when compared with an earlier community study in another rural area amongst the same Yoruba tribe of South West Nigeria where a prevalence of 20.8% was reported (18). Other studies in Nigeria reported the rural prevalence of hypertension in both sexes to be between 13.5 and 46.4% (29).
An isolated study however showed a 66.4% prevalence of hypertension in a rural Yoruba community (19). This higher prevalence was because majority (56.7%) of the participants were older, aged between 60-79 years; mean age of 66.77 ± 12.06 years, age range 40-88 years whilst the subjects in this current study have an age range of 18-90 years and a mean age of 49 ± 1.6. The prevalence of hypertension increases with age (29,30). The association between hypertension and age >45 years was statistically significant (OR 0.34, 95% CI 0.192-0.616, p=0.001). This is supported by all other previous studies that showed a good correlation between age and hypertension in which BP increased steadily with age (29,30). Other predictors of hypertension in this study included high total cholesterol and low HDL levels as shown in This may be due to regular interaction of health workers, students and researchers with these two communities. The mean age of these rural dwellers was 49.7 ± 1.6 years. This is also very close to the mean age of 42.1 ± 21.6 years of the subjects in one of the earlier Nigerian studies (18).
Obesity was also found to be statistically significantly associated with hypertension in this study (p=0.050); this is supported by other studies (30,31). Obese respondents were 1.7 (1/0.60) times more likely to become hypertensive compared to the non-obese (OR 0.60, 95% CI 0.284-1.291, p-0.102). Obesity was found in 11.5% of the subjects while overweight was present in 19.6% of them. This is similar to 11.12% obesity obtained in a study conducted in the South East of Nigeria using selected urban and rural Igbo communities (32) but much higher than the 3.9% obtained for general obesity in another study (18). Our finding on the prevalence of obesity also falls within the range of the prevalence of obesity in Nigeria as reported in a systematic review of literature by Chukwonye et al. (33).
Obesity was significantly associated with the female sex (p=0.050). Female respondents were 1.4 times more likely to be obese compared with males (OR 1.43, 95% CI 0.61-3.157, p -0.188). Although more females (2.4%) were obese in the earlier study as against 1.5% of the males, there was however no association calculated with which to compare our study (18). A study done in Latin America and the Caribbean lends credence to this with the females having higher prevalence of obesity than the males (34). This study also showed that high total cholesterol level and low HDL were predictors of obesity (Table 4). A chinese study supports that low HDL was associated with obesity and overweight (BMI) and the association was stronger with central obesity using waist circumference (p<0.001) (35). Respondents with high total cholesterol levels were 1.5 times more likely to be obese compared to those with normal or low total cholesterol level (OR 1.54, 95% CI 0.441-5.386, p-0.264). Similarly, respondents with a low HDL level were 5 times more likely to be obese compared to those with high HDL (OR 1.49, 95%CI 0.718-3.103, p-0.144). A 26 year follow up of participants in the Framingham Heart Study found obesity to be an independent risk factor for cardiovascular diseases in both sexes (36). This was similarly observed amongst Finnish men and women after adjusting for confounding factors (37). About onetenth of our respondents had pre-hypertension; this is much lower than the prevalence of 31.0% reported in the study in American adults (38).
This is expected as westernization of diet and lifestyle is at its peak in America. A meta-analysis from 18 prospective cohort studies showed elevated CVD risk in patients with pre-hypertension, after adjusting for multiple cardiovascular risk factors (39). Diabetes mellitus was detected in 19 (7.3%) of the subjects, lower prevalence was reported in rural areas in the South West and South East of Nigeria (2.5%, 4.8%, and 3.6% respectively) (18,19,29). Impaired fasting glucose was also present in 14.8% of the people. These people with impaired glucose are likely to progress to full blown diabetes mellitus if lifestyle changes are not adopted. Hypercholesterolemia was found in 46 (17.8%) of the patients; 99 (38.2%) had hypertriglyceridemia and 35 (13.5%) had high LDL. This contrasts with lower figures of 2.5%, 1.9% and 0.9% reported for hypercholesterolemia, hypertriglyceridemia and high LDL respectively in an earlier study (18). This may suggest that the newly studied rural communities have adopted more westernized lifestyle. In this study also, 49.8% had low HDL as against 43.1% and 30.0% with low HDL in other studies in the same tribe (18,19). The serum creatinine and urea were elevated in 1 (0.3%) and 12 (4.6%) respectively. Elevated serum urea without concomitant increase in serum creatinine is most likely due to dehydration, more so that the study was carried out during the hot season of the year. Only 0.3% was deemed to have had renal impairment which itself is a risk factor for cardiovascular disease (12).
Physical activity lasting at least 30 minutes a day was very common in the respondents with 236 (91.1%) of them belonging into this group. This is similar to the earlier study in which 96.8% of the rural participants were also physically active (18). This is not unexpected as there are no commercial vehicles for intra village transportation, also the road in Alajue was not motorable as at the time of data collection so people had to trek or ride bicycles to their farms and for moving around. This was advantageous to the villagers as regular physical activity and a normal weight can reduce the risk of cardiovascular disease (37). Another study however showed a lower proportion, 70.2% of the rural community was physically active; the plausible explanation here was the subjects were much older (19).
The ECG pattern of majority of these rural dwellers were normal as shown in Table 3, this was expected as they were apparently normal healthy subjects within the community. Majorities (82.8%) of the people had normal heart rates and were in normal sinus rhythm whilst 9.4% and 7.8% had sinus bradycardia and sinus tachycardia respectively. Sinus bradycardia occurs in people accustomed to exercise such as trained athletes (40), we opine that those with sinus bradycardia might be doing more trekking and farming activities than others. Sinus tachycardia could also have occurred in some subject's due to fear since they had never had ECG run on them before.
First degree heart block was present in 4 (6.3%) whilst one subject (1.6%) had second degree heart block (Type 1). Morbitz type 1 heart block originally considered to be benign has now been found not to be benign in those aged ≥ 45 years (41). The QRS frontal plane electrical axis was normal in 76.5% of the people with 10.9% having left axis deviation (LAD), another 4.7% having right axis deviation (RAD) and 7.8% having indeterminate axis. Although majority of the subjects had their QRS frontal plane electrical axis within the normal range but their percentage (76.5%) was lower than the 97.0% reported in normal healthy adult Nigerians by Araoye (42); conversely the proportion of those with LAD (10.9%) and RAD (4.7%) were higher in this study than the 2.9% and 0.1% obtained respectively in the earlier study (42). The LAD is likely to be because 57.0% of this study subjects were in the age group ≥ 50 years as shown in Table 1. There is a normal leftward shift of the QRS axis with age, RAD could also be a variant of normal (43). The indeterminate axis seen in 7.8% of the subjects however calls for more investigations of those affected as this is rare in normal subjects and when present it indicates serious cardiac condition (43). There were no atrial premature complexes but occasional ventricular premature complexes (VPCs) occurred in 4 (6.3%) of the subjects. Occasional VPCs can be found in normal subjects but as long as they are not frequent or lethal. This has been reported in 1-4% of the normal population on regular 12 lead resting ECG (44), and in 40-75% of subjects on 24-48 hours holter monitoring (45).
There was no ECG evidence of ischaemic heart disease in any of the subjects as majority (95.3%) of them had normal ST segment, only 4.7% had nonsignificant ST changes; similarly, the T wave was also normal in 85.9%, inverted in 7.9%, nonspecific in 6.2% and there were no pathological q waves. Although ischaemic heart disease was not found in these two communities but there is already a constellation of risk factors within these rural communities buttressing an earlier study that the rural communities are also not left out of the epidemiologic transition from communicable diseases to non-communicable diseases (NCDs) (18). Also, it had been shown in our earlier study that the NCDs are now emerging as the most common cause of hospital admission in Nigeria (46). Furthermore, hypertension and its related complications have been shown to be the commonest cause of sudden death in Nigeria (47).
QTc interval was prolonged in 23.4%, this is rather high and caution must be exercised in administering drugs that are known to prolong QTc interval especially antibiotics such as the macrolides (Erythromycin>Clarith romycin>Azithromycin), trimetoprim-sulfamethoxazole, pentamidine, azoles and the fluoroquinolones (sparfloxacin, ciprofloxacin) to them in these two communities so as to avoid lethal arrhythmias, torsades des pointes and sudden death (48). Also, the 23.4% may not be representative of the community because only 25% of those screened had ECG done and this is a limitation of the study. It is also pertinent to note that none of the patients who had ECG was on any illicit drug such as methadone, halofantrine or any other drugs that could prolong the QTc.
This study appears to be the first in Nigeria that will do a community survey incorporating ECG. This is because of logistic problems associated with this, some of these we were able to surmount by carrying portable ECG machines and a generator for the supply of electricity into these two communities. The seemingly apparently normal rural dwellers were found to have the above stated ECG abnormalities. It is also the first time LVH will also be assessed alongside with some other risk factors. LVH on its own predisposes an individual to sudden death irrespective of its cause on account of the lethal arrhythmias it induces hence aggressive management of those with it is the ultimate goal (49)(50)(51).
The preponderance of multiple risk factors as seen in this study further compounds the possible epidemic of CVD and its sequelae. Multiple risk factors were present in 73 respondents (28.2%) and 51 (69.9%) had double while 18 (24.7%) had triple risk factors (Figure 1). This is higher than what was reported in an earlier study amongst a rural Yoruba community in South West Nigeria in which multiple cardiometabolic risk factors were reported in 2.1% of men and 2.7% of women (18). It is also noteworthy that a minor percentage had four or five risk factors as shown in Figure 1. This may be an indication of continuing urbanization and westernization of our rural communities. A study in Abuja among the aboriginal inhabitants of Abuja comparing the prevalence of cardiovascular risk factors among the urban population with that of the rural population corroborates this; despite the same ancestry of these two communities, urbanization increased the prevalence of most of the traditional CVS risk factors (52).
This study also showed that 23.4% of respondents that had ECG done on them had prolonged QTc in both communities. This is a significant finding, because prolonged QTc calls for caution in the administration of contraindicated drugs. Therefore, this work has the potential of furthering our understanding and makes primary prevention efforts in rural areas of Nigeria more feasible.
All the subjects identified to be having these risk factors were counseled and sent to our cardiology clinic at the Ladoke Akintola University Teaching Hospital for more thorough investigations and appropriate treatment; after which they were sent back to the primary health centre or comprehensive health centre to continue their treatment and follow up. A few of the patients however opted for continuation of their treatment in the teaching hospital and are still being followed up.

CONCLUSION
It is important to conclude that obesity/overweight, physical inactivity, existence of hypertension, pre-hypertension, diabetes, impaired fasting glucose, and dyslipidemia are all modifiable risk factors that could be tackled to prevent emergence of cardiovascular diseases in epidemic proportions. Concerted effort must be made by all stakeholders in the health sector to increase awareness and knowledge among the rural communities where there is usually limited access to electronic and print media as a means of health education. Thus, stakeholders should devise acceptable methods of reaching these remote areas with appropriate messages that would address modifiable risk factors for non-communicable diseases as well as strengthen the health systems to take care of non-modifiable and other risk factors and determinants thereby preventing a future epidemic of CVD.