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| ORIGINAL ARTICLE |
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| Year : 2016 | Volume
: 13
| Issue : 1 | Page : 33-38 |
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Initial experience with 24-h ambulatory blood pressure monitoring in Nigerian patients with hypertension
Godsent Chichebem Isiguzo1, Dainia Baugh2, Geoffery Chibuzor Nwuruku1, Kenechukwu N Mezue3, Chichi Madu4, Ernest Chijioke Madu2
1 DOCS Heart Centre, Enugu; Cardiology Unit, Department of Internal Medicine, Federal Teaching Hospital Abakaliki, Ebonyi State, Nigeria
2 DOCS Heart Centre, Enugu, Nigeria; Depatment of Cardiology, Heart Institute of the Caribbean, Kingston, Jamaica, USA
3 Department of Medicine, Einstein Medical Center, Philadelphia, Pennsylvania, USA
4 Department of Medicine, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| Date of Web Publication | 13-Jan-2016 |
Correspondence Address:
Godsent Chichebem Isiguzo
DOCS Heart Centre, 164 Ogui Road, Enugu, Nigeria
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0189-7969.173851
Context: Ambulatory blood pressure monitoring (ABPM) is superior to office blood pressure (OBP) in predicting hypertension control/outcome. Despite the growing burden of hypertension in Africa, ABPM use remains rudimentary.
Aims: To report our initial ABPM experience in Nigeria.
Setting and Design: Ongoing prospective descriptive study, involving consecutive recruitment of consenting patients' ≥18 years, presenting at DOCS Heart Centre Enugu Nigeria.
Methods: The study involved 78 hypertensive patients attending the clinic from May, 2013. OBP was taken in sitting position, using oscillometric BP device. Each patient was then monitored over 24 h with a Tonoport V (GE CS V6 71[21]), interpreted using GE CardiosoftTM ABPM software in accordance with British Medical Council guidelines.
Statistical Analysis: Data were analyzed using EPI Info (version 3.3.5). Continuous variables were expressed as means ± standard deviation. Differences between group means were tested using two-tailed Student's t-test. Proportions were reported as percentages and compared between groups with Chi-square.
Results: The study involved 78 adult hypertensive patients; mean age of the patients was 53 ± 13 years and body mass index 30.0 kg/m2, 53.8% were males. Control on OBP was 17.9%, on ABPM 24.4%. The mean 24-h BP was 144 ± 16/88 ± 10 mmHg; daytime BP, 146/90 ± 17/11 mmHg; night-time BP, 139/81 ± 17/9 mmHg; and waking BP 149/88 ± 20/14 mmHg. Borderline hypertension was seen in 4.5%, sustained hypertension in 36.4%, white coat hypertension in 13.6%, and nocturnal hypertension in 22.7%. The majority of patients had abnormal dipping pattern, with enormous BP load, 89.2% having a high load.
Conclusion: BP control was better represented by ABPM more than OBP in the patients; showing that to optimize management, greater use of ABPM is a more pragmatic approach to mitigate the adverse outcomes among hypertensive patients. Keywords: Ambulatory blood pressure monitoring, hypertension, Nigeria
How to cite this article:
Isiguzo GC, Baugh D, Nwuruku GC, Mezue KN, Madu C, Madu EC. Initial experience with 24-h ambulatory blood pressure monitoring in Nigerian patients with hypertension. Nig J Cardiol 2016;13:33-8 |
How to cite this URL:
Isiguzo GC, Baugh D, Nwuruku GC, Mezue KN, Madu C, Madu EC. Initial experience with 24-h ambulatory blood pressure monitoring in Nigerian patients with hypertension. Nig J Cardiol [serial online] 2016 [cited 2023 May 31];13:33-8. Available from: https://www.nigjcardiol.org/text.asp?2016/13/1/33/173851 |
| Introduction | |  |
Noncommunicable diseases (NCDs) such as hypertension is increasing in epidemic proportions in Africa, accounting for 22% of the total deaths in the region in 2000, with cardiovascular diseases (CVDs) causing 9.2% of the total deaths.[1] According to the WHO database on disease incidence, in Nigeria, the age-standardized death rate from CVDs (estimated at approximately 400 deaths/100,000) is more than that from HIV, respiratory infections, malaria, and tuberculosis.[2] African countries like Nigeria now face a “double burden” of both NCDs, which affects the affluent countries, and communicable (infectious) disease.[3]
Hypertension is one of the major risk factors for CVD, responsible for at least 45% of deaths due to heart disease and 51% of deaths due to stroke.[4] The number of people with hypertension worldwide rose from 600 million in 1980 to 1 billion in 2008, at which time approximately 40% of adults aged 25 and above had been diagnosed with hypertension.[4] In Nigeria, the incidence of hypertension is rising even faster. A nation-wide survey done in 1997 showed that 11.2% of adults in the country were hypertensive, but recent studies done in different parts of the country have shown prevalence rates that ranged from 28.8% to 36.6%.[5],[6] Hypertension is more common among urban Africans than among “truly rural dwellers.” This may indicate that the rising prevalence of hypertension is due to the changing lifestyles, diet, and level of activity in urban Africa, which may be a true reflection of an epidemiological transition.[3],[7]
Improved control of hypertension is needed to reduce the public health burden of CVD in Nigeria, and better monitoring of blood pressure (BP) among patients with hypertension is one element of a program to improve control of this condition. Ambulatory BP monitoring (ABPM) is gaining prominence in clinical practice as a better tool for recording patient BP.[8],[9] There is overwhelming evidence of its superiority in predicting outcome in patients with hypertension compared to office BP (OBP).[10] The National Institute for Health and Care Excellence guidelines support the use of ABPM in all patients with a clinic BP of above 140/90 mmHg.[11] The United States Center for Medicare and Medicaid Services has approved reimbursement for ABPM for the identification of individuals with “white-coat hypertension.” The large numbers of readings obtained with ABPM during patient daily activities provide information on BP variability, circadian changes, and the effects of environmental and emotional conditions on BP levels.[12] ABPM has also been documented to predict the risk of morbid events better than OBP.[13],[14]
Despite the increased interest in the role of ABPM in the current evaluation and management of hypertension globally, and the huge burden of hypertension in Africa, its use in most of Africa is still rudimentary. Increased use of ABPM could lead to better characterization of the burden of hypertension in Sub-Saharan African countries. In addition, improved management based on ABPM should lead to the prevention of complications of uncontrolled hypertension. This descriptive study is one of the first to assess the use of ABPM in the Nigerian setting.
| Methods | | |
The study was approved by the Ethics Committees of DOCS Heart Centre, Nigeria and Federal Teaching Hospital Abakaliki, Nigeria, and the participants gave informed written consent. It is part of a prospective ongoing data collection, started in May 2013. The study population consists of adults hypertensive 18 years and above referred to DOCS Heart Centre Enugu, Nigeria, who gave consent to be part of the study. Participants were consecutively recruited, demographic data, medical history, medications, smoking and alcohol history were collected from the electronic medical record. Height and weight were measured using a stadiometer, and body mass index (BMI) was calculated as weight (kg)/height (m) 2; patients were classified as overweight if BMI was 25 kg/m 2 to 29.5 kg/m 2, and obese if BMI ≥ 30 kg/m 2. OBP was measured in both arms with an oscillometric BP device, the GE Dinamap Procure 400 monitor (GE Medical systems information technologies Inc. Milwaukee Wisconsin, USA) while the patient was sitting. The arm with the higher reading was taken as the patients BP after an average of three readings. Systolic and diastolic (Phase V) BP were determined to the nearest 2 mmHg in accordance with European Society of Hypertension recommendation. Ambulatory BP was measured with the Tonoport V monitor (GE CS V67 [21]) for a minimum of 24 h, using a similar sized cuff as was used in the OBP measurement. Ambulatory monitors were checked monthly against a mercury manometer and deviation by > 4 mmHg warranted recalibration. The ABP monitor measured BP at 15-min intervals from 0600 h to 2200 h (representing daytime) and 30-min intervals from 2200 to 0600 h (representing night-time). Participants kept a diary card for the duration of the record to note bedtime and waking time to define day and night and to check the transition time. ABPM data were interpreted in accordance with British Heart Association guidelines.[15]
Data analysis
ABPM data processing was performed using the GE Cardiosoft ™. Ambulatory Blood Pressure software (PAR Medizintechnik GmbH Sachsendammb D-10829, Berlin, Germany). Management of data and statistical analysis were performed with EPI Info 3.5.3 (CDC, Atlanta, Georgia). Proportions were reported as percentages and compared between groups with Chi-square.
| Results | | |
The study consist of 82 adult hypertensive patients, however, 78 patients had complete data for analysis. The mean age of the cohort was 53 ± 13 years, with 53.8% of subjects male. None of the patients were smokers, alcohol use was not significant, and only 1 patient was diabetic. The mean BMI of 30.0 kg/m 2 showed that a good percentage of the cohort was overweight. BP increased with age, and BP control was suboptimal as shown from the mean of both OBP 152 (21)/88 (10) mmHg and 24-h ABP 144 (16)/88 (10) mmHg [Table 1]. OBP measurement showed that 17.9% and 24-h ABPM showed that 24.4% of the cohort had controlled BP, respectively. The night-time BP was above the cut-off definition for nocturnal hypertension (NHTN) and many of the cohort showed a nondipping pattern, with reverse dipping also seen in some, and nondipping more common with advancing age [Table 2]. The systolic nondipping pattern was seen in 47.6% of males and 38.9% of female participants while diastolic nondipping was seen in 41.7% of females and 57.1% of males [Table 3]. In addition, 11.9% of females and 19.4% of males had diastolic reversed dipping.
There was sustained hypertension (SHTN) in 40.3% (47/78), nocturnal hypertension (NHTN) in 14.1% (8/78), so also was white coat hypertension, while masked hypertension was seen in 1.3% (1/78) [Figure 1]. The mean waking BP among patients with masked and SHTN, 147/99 mmHg and 153/99 mmHg, respectively, and when this was compared between those with SHTN and NHTN, it was 154 (20)/91 (14) mmHg and 140 (14)/90 (17) mmHg (P = 0.005), an increase of 14/1 mmHg. | Figure 1: ABP pattern of participants. Sys+ Di HTN (Sustained hypertension) WCH (White coat hypertension)
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The BP load i.e a percentage of BP above normal target showed that eight subjects (10.8%) had low BP load defined as <50% higher than threshold [Table 5].
Comparing low BP load against controlled 24 h ABP, at 95% confidence interval, gave a Chi-square of 0.0612, and P value of 0.042.
| Discussion | | |
This study is a descriptive study of ABPM conducted in Nigeria. The results showed that only 24.4% of patients had normal BP by ABPM compared to 17.9% based on OBP, suggesting that ABPM may be a more sensitive method for assessing BP control than OBP.
The use of ABPM is still not common in Nigeria and most of Sub-Saharan Africa (SSA), though ABPM has been shown to be superior to OBP in prognostication of hypertension-related outcomes in several studies [Table 4].[16],[17] The findings from this study, though limited by the small sample size, show the increasing burden of hypertension among our patients, and re-emphasize the need for more routine use of ABPM to reveal the true perspective. It is hoped that future prospective studies with larger cohorts will make the picture clearer.
Given that Blacks are more prone to hypertension-related complications than Whites,[18] with more harmful cardiac remodeling even in the early stages of hypertension,[19] ABPM will probably be very useful in the outpatient management of hypertension in the Nigerian population. However, in a previous study in South Africa, nurse-recorded auscultatory BP and ABPM were equivalent in predicting target organ changes in a randomly selected population sample (n = 458).[20] Our results may be different from this South African study because we used automated measurement rather than using auscultatory measurements of OBP.
As expected based on earlier studies using OBP, we found increasing BP with age among our patients using ABPM. While BP is known to increase with age, the reported high burden of end organ damage in African Blacks may also be a reflection of the common practice of African patients to present only at the onset of complications. This has been characterized as “lack of early, accurate diagnosis in economically depressed environments,”[21] and suggests that there may be a large potential benefit for improved screening for hypertension. If ABPM is confirmed to be more sensitive for the detection of clinically relevant hypertension in larger studies in Africa, it could play a role in screening, although it is relatively expensive for wide use in resource-limited settings.
NHTN was present in 22.7% of the cohort and worsened with age. It has been shown to be a better indicator of CVD target organ damage compared to OBP and daytime ambulatory BP [22] and worse in patients with obesity and increased waist circumference.[23] A good proportion of our cohort were overweight with average BMI of 29.9 (5.3) kg/m 2. A study comparing ABPM results in newly diagnosed African and European cohorts found that untreated Black hypertensive patients systematically present higher clinic and ABP values and a lower night-time BP fall than untreated White hypertensive patients for all spectra of age distribution.[24]
Another concerning result from this study is the abnormal dipping pattern, with systolic nondipping seen in 47.8% of the cohort, and noted to worsen with age. This is similar to findings in South Africa, where Black students had higher systolic and diastolic BP throughout the day, night and critical time periods compared with the Indian students.[25] BP load was higher in Black (40.8%) than in Indian participants (29.6%; P < 0.05) and there was less dipping at night. In another study comparing nocturnal BP in 22 South African Black patients with age, sex and daytime mean pressure-matched American Black and White patients, there was a smaller percentage reduction in mean BP at night in American Blacks compared with the other groups with the South African cohort having similar nocturnal BP as the white group.[26] These data suggest that the differences in diurnal BP between American Blacks and Whites do not represent a true racial difference, but may be environmental in origin. The absence of the normal decline of BP at night may place patients at an increased risk of CVD, especially with elderly patients. This has been identified as an early marker of microalbuminuria in diabetic patients.[27] An ABPM study of 235 individuals of East African descent in Seychelles showed that the capacity to excrete sodium during daytime is a significant determinant of nocturnal BP and dipping.[28]
As noted above, more of our patients had controlled BP by OBP compared with ABP (32.6% vs. 19.6%), suggesting that there may be an undiagnosed and therefore under-treated reservoir of hypertension that would benefit from a more thorough evaluation and more aggressive therapeutic approach. Such “masked hypertension” was first elaborated on by Pickering [29] and shown to predict patients with left ventricular hypertrophy (LVH), stroke and other indices of the poor cardiovascular outcome.[30] The prevalence of masked hypertension from different studies analyzed in a meta-analysis varies between 8% and 48%, with risk factors including the use of alcohol, tobacco, and caffeine as well as physical inactivity.[31] In the Pressioni Arteriose Monitorate E Loro Associazioni population, patients with masked hypertension had a prevalence of LVH that was much greater than that of normotensive subjects.[32] It has been suggested that inappropriate target organ disease (i.e., inappropriate for OBP levels), therefore, should trigger suspicion of masked hypertension and motivate physicians to expose a susceptible patient to 24-h ABPM.
Another issue raised by this study is the early morning surge of BP which has been shown to be associated with CVD morbidity and mortality.[33] Although there are some conflicting data, a recent meta-analysis showed that an exaggerated increase in morning BP is associated with increased CVD risk.[34] Identifying a morning surge in BP is important since appropriate treatment to control BP throughout the early morning hours can reduce the associated risk.[31] The BP load was also noticed to be high, this concept was first described by White in who showed that BP load was a better predictor of cardiac target organ effects than the corresponding mean AB P values.[35]
| Conclusion | | |
BP is a very labile hemodynamic parameter, varying from heartbeat to heartbeat, from morning to evening, from winter to summer, from sleeping to waking, and from sitting to standing, such that making treatment decisions based on casual office reading is fraught with limitations. The results of this study contribute to the literature on 24-h ABPM as a better marker of CVD risk than OBP, and specifically suggest that ABPM has a role in African patients. If these results are confirmed in larger investigations among African patients, then ABPM may become a part of a more pragmatic approach to hypertension diagnosis and management in SSA. However, the use of ABPM in routine patient management must be carefully considered, as the potential benefits will have to be weighed against the expense in countries in need of overall health system strengthening.
Acknowledgments
The comments and contributions of 2014 Level 3 Faculty of Pan-African Thoracic Society Methods in Epidemiologic, Clinical and Operational Research is highly appreciated and acknowledged.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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