Can common carotid intima media thickness serve as an indicator of both cardiovascular phenotype and risk among black Africans?

Osuntokun Award Lecture 2021: Challenges of Measuring the Burden of Stroke in Africa

BACKGROUND

Over recent years non-communicable diseases have dramatically increased in low- and middle-income countries, including those of sub-Saharan Africa. With continuing high levels of infectious disease, these countries now face the double burden of disease. Stroke has emerged as a major cause of hospital admission, disability, and mortality for which the major modifiable risk factor is hypertension, which is often not diagnosed and, even if diagnosed, not treated and, even if treated, not controlled.

METHODS

In this award lecture paper I outline my personal experience of measuring the burden of, and risk factors for, stroke in sub-Saharan Africa, along with the challenges faced. I will specifically describe the measurement of mortality and case fatality, prevalence and incidence as well as commenting on aetiology and risk factors and reflect on future initiatives and directions.

RESULTS

Over the past 5 decades there has been a dramatic increase in numbers of stroke patients admitted to hospital throughout sub-Saharan Africa, with high in hospital mortality rates, also reflected in high case fatality rates in those cohorts followed up following discharge from hospital. Community-based surveys assessing mortality from stroke using verbal autopsy have demonstrated very high age-adjusted rates. Age adjusted prevalence rates assessed by door-to-door surveys have generally shown lower prevalence than high income countries. The Tanzanian stroke incidence study, which incorporated verbal autopsy for those patients dying before reaching hospital, demonstrated some of the highest age-adjusted stroke incidence rates in the world. There were high rates of stroke in younger ages and high rates of intracranial haemorrhage though not as high as previously shown in hospital-based studies. Hypertension is the main modifiable risk factor but other risk factors such as HIV are important while, certainly in rural populations, raised cholesterol remains rare as does carotid artery stenosis and history of transient ischemic attack. Other vascular disease such as ischemic heart disease and peripheral vascular disease is also less common.

CONCLUSIONS

There is already a large burden relating to stroke in sub-Saharan Africa and this will only escalate further as the population ages. Hypertension is the biggest risk factor for mortality worldwide and in sub-Saharan Africa prevalence rates are very high with the majority of people suffering with stroke not being diagnosed with their hypertension prior to their stroke. The most important challenge is to improve primary prevention for which improving diagnosis and control rates for hypertension is the number one priority. For those who do have stroke there is a need to increase the number of suitably staffed stroke units as these have been shown to have a very large impact on improving both mortality and morbidity in high income countries. There are still many unanswered questions and a need for more research throughout sub-Saharan Africa on risk factors, and treatment, for stroke.

Stroke in Africa: profile, progress, prospects and priorities

Stroke is a leading cause of disability, dementia and death worldwide. Approximately 70% of deaths from stroke and 87% of stroke-related disability occur in low-income and middle-income countries. At the turn of the century, the most common diseases in Africa were communicable diseases, whereas non-communicable diseases, including stroke, were considered rare, particularly in sub-Saharan Africa. However, evidence indicates that, today, Africa could have up to 2-3-fold greater rates of stroke incidence and higher stroke prevalence than western Europe and the USA. In Africa, data published within the past decade show that stroke has an annual incidence rate of up to 316 per 100,000, a prevalence of up to 1,460 per 100,000 and a 3-year fatality rate greater than 80%. Moreover, many Africans have a stroke within the fourth to sixth decades of life, with serious implications for the individual, their family and society. This age profile is particularly important as strokes in younger people tend to result in a greater loss of self-worth and socioeconomic productivity than in older individuals. Emerging insights from research into stroke epidemiology, genetics, prevention, care and outcomes offer great prospects for tackling the growing burden of stroke on the continent. In this article, we review the unique profile of stroke in Africa and summarize current knowledge on stroke epidemiology, genetics, prevention, acute care, rehabilitation, outcomes, cost of care and awareness. We also discuss knowledge gaps, emerging priorities and future directions of stroke medicine for the more than 1 billion people who live in Africa.

Cardiovascular disease risk and its determinants in people living with HIV across different settings in South Africa

Objectives

Socio‐economic factors and lifestyle are known to differ across geographies and populations, which may result in distinct risk profiles for cardiovascular disease (CVD). This study assessed carotid intima‐media thickness (CIMT), a proxy for CVD, and its determinants in two groups of people living with HIV (PLHIV) in two different settings in South Africa.

Methods

A cross‐sectional analysis was conducted comparing data from the Ndlovu Cohort Study in the Limpopo Province (group 1) and from three clinical trials in Johannesburg (group 2). The association between demographics, conventional CVD risk factors, HIV‐related factors and CIMT in groups 1 and 2 was analysed with two separate multivariable linear regression models.

Results

Group 1 consisted of 826 participants (mean age 42.2 years) and mean (± standard deviation) CIMT was 0.626 ± 0.128 mm. In this group, sex, age, body mass index (BMI), cholesterol, glucose and antiretroviral therapy (ART) duration (β = 0.011 mm per 5 years; P = 0.02) were associated with higher CIMT. There were positive interactions between age and ART duration and age and cholesterol. Group 2 consisted of 382 participants (mean age 39.5 years) and mean (± standard deviation) CIMT was 0.560 ± 0.092 mm. In this group, only sex, education level, BMI and cholesterol were associated with higher CIMT, albeit with weaker associations than in group 1.

Conclusions

Conventional CVD risk factors were the main drivers of CIMT. The impact of some of these risk factors appeared to increase with age. Differences in sample size, age and viral suppression might explain why an effect of ART was observed in group 1 but not in group 2.

Cardiovascular disease risk in an urban African population: a cross-sectional analysis on the role of HIV and antiretroviral treatment

BACKGROUND

Life expectancy is increasing in the HIV-positive population and age-related non-communicable diseases, such as cardiovascular disease, (CVD) are seen more frequently. This study investigated to what extent HIV and antiretroviral therapy (ART) is associated with CVD risk in an urban African population.

METHODS

A cross-sectional study was performed in Johannesburg, South Africa, between July 2016 and November 2017. Both HIV-positive adults (ART-naïve, or on first- or second-line ART), as well as age and sex matched HIV-negative controls who were family or friends of the HIV-positive participants were included. Data were collected on demographics, cardiovascular risk factors, HIV-related characteristics, carotid intima-media thickness (CIMT) and carotid distensibility. The association between HIV, ART and CIMT and distensibility was analysed with linear regression models, adjusting for age, gender and CVD risk factors.

RESULTS

The study included 548 participants, 337 (62%) females, age 38.3 ± 9.5 years of whom 104 (19.0%) were HIV-positive, ART-naïve; 94 (17.2%) were on first-line ART; 197 (35.9%) were on second-line ART; and 153 (27.9%) were HIV-negative. Participants on second-line ART had higher CIMT and lower distensibility compared to the other groups (p < 0.001). After adjustment for age, these outcomes were similar between groups. Further adjustment for CVD and HIV-related factors did not alter the findings.

CONCLUSION

Neither HIV nor ART was associated with CIMT or carotid distensibility in this urban African population. Longitudinal studies are needed to fully understand the relationship between HIV and CVD across different populations.

Classical Cardiovascular Risk Factors and HIV are Associated With Carotid Intima-Media Thickness in Adults From Sub-Saharan Africa: Findings From H3Africa AWI-Gen Study

Background Studies on the determinants of carotid intima-media thickness ( CIMT ), a marker of sub-clinical atherosclerosis, mostly come from white, Asian, and diasporan black populations. We present CIMT data from sub-Saharan Africa, which is experiencing a rising burden of cardiovascular diseases and infectious diseases. Methods and Results The H3 (Human Hereditary and Health) in Africa's AWI-Gen (African-Wits-INDEPTH partnership for Genomic) study is a cross-sectional study conducted in adults aged 40 to 60 years from Burkina Faso, Kenya, Ghana, and South Africa. Cardiovascular disease risk and ultrasonography of the CIMT of right and left common carotids were measured. Multivariable linear and mixed-effect multilevel regression modeling was applied to determine factors related to CIMT. Data included 8872 adults (50.8% men), mean age of 50±6 years with age- and sex-adjusted mean (±SE) CIMT of 640±123μm. Participants from Ghana and Burkina Faso had higher CIMT compared with other sites. Age (β = 6.77, 95%CI [6.34-7.19]), body mass index (17.6[12.5-22.8]), systolic blood pressure (7.52[6.21-8.83]), low-density lipoprotein cholesterol (5.08[2.10-8.06]) and men (10.3[4.75- 15.9]) were associated with higher CIMT. Smoking was associated with higher CIMT in men. High-density lipoprotein cholesterol (-12.2 [-17.9- -6.41]), alcohol consumption (-13.5 [-19.1--7.91]) and HIV (-8.86 [-15.7--2.03]) were inversely associated with CIMT. Conclusions Given the rising prevalence of cardiovascular diseases risk factors in sub-Saharan Africa, atherosclerotic diseases may become a major pan-African epidemic unless preventive measures are taken particularly for prevention of hypertension, obesity, and smoking. HIV -specific studies are needed to fully understand the association between HIV and CIMT in sub-Saharan Africa.

Deciphering Endothelial Dysfunction in the HIV-Infected Population

Cardiovascular disease (CVD), as a possible consequence of endothelial dysfunction, is prevalent among HIV-infected patients despite successful administration of antiretroviral drugs. This warrants the routine clinical assessment of endothelial function in HIV-positive patients to circumvent potential CVD events. Several different non-invasive strategies have been employed to assess endothelial function in clinical research studies yielding inconsistencies among these reports. This review summarises the different techniques used for assessing endothelial function, with a focus on proposed blood-based biomarkers, such as endothelial leukocyte adhesion molecule-1 (E-selectin), soluble intercellular adhesion molecule-1 (sICAM-1), soluble vascular cell adhesion molecule-1 (sVCAM-1), von Willebrand factor (vWF), TNF-α, interleukin 6 (IL6) and soluble thrombomodulin (sTM). The identification of suitable blood-based biomarkers, especially those that can be measured using a point-of-care device, would be more applicable in under-resourced countries where the prevalence of HIV is high.

Stroke, cerebrovascular diseases and vascular cognitive impairment in Africa

With increased numbers of older people a higher burden of neurological disorders worldwide is predicted. Stroke and other cerebrovascular diseases do not necessarily present with different phenotypes in Africa but their incidence is rising in tandem with the demographic change in the population. Age remains the strongest irreversible risk factor for stroke and cognitive impairment. Modifiable factors relating to vascular disease risk, diet, lifestyle, physical activity and psychosocial status play a key role in shaping the current spate of stroke related diseases in Africa. Hypertension is the strongest modifiable risk factor for stroke but is also likely associated with co-inheritance of genetic traits among Africans. Somewhat different from high-income countries, strokes attributed to cerebral small vessel disease (SVD) are higher >30% among sub-Saharan Africans. Raised blood pressure may explain most of the incidence of SVD-related strokes but there are likely other contributing factors including dyslipidaemia and diabetes in some sectors of Africa. However, atherosclerotic and cardioembolic diseases combined also appear to be common subtypes as causes of strokes. Significant proportions of cerebrovascular diseases are ascribed to various forms of infectious disease including complications of human immunodeficiency virus. Cerebral SVD leads to several clinical manifestations including gait disturbance, autonomic dysfunction and depression. Pathological processes are characterized by arteriolosclerosis, lacunar infarcts, perivascular spaces, microinfarcts and diffuse white matter changes, which can now all be detected on neuroimaging. Except for isolated cases of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy or CADASIL, hereditary arteriopathies have so far not been reported in Africa. Prevalence estimates of vascular dementia (2-3%), delayed dementia after stroke (10-20%) and vascular cognitive impairment (30-40%) do not appear to be vastly different from those in other parts of the world. However, given the current demographic transition in both urban and rural settings these figures will likely rise. Wider application of neuroimaging modalities and implementation of stroke care in Africa will enable better estimates of SVD and other subtypes of stroke. Stroke survivors with SVD type pathology are likely to have low mortality and therefore portend increased incidence of dementia.

HIV and risk of cardiovascular disease in sub-Saharan Africa: Rationale and design of the Ndlovu Cohort Study

Background The largest proportion of people living with HIV resides in sub-Saharan Africa (SSA). Evidence from developed countries suggests that HIV infection increases the relative risk of cardiovascular disease (CVD) by up to 50%. Differences in lifestyle, gender distribution, routes of HIV transmission and HIV subtype preclude generalisation of data from Western countries to the SSA situation. The Ndlovu Cohort Study aims to provide insight into the burden of cardiovascular risk factors and disease, the mechanisms driving CVD risk and the contribution of HIV infection and its treatment to the development of CVD in a rural area of SSA. Design The Ndlovu Cohort Study is a prospective study in the Moutse area, Limpopo Province, South Africa. Methods A total of 1000 HIV-positive and 1000 HIV-negative participants aged 18 years and older with a male to female ratio of 1:1 will be recruited. Measurements of CVD risk factors and HIV-related characteristics will be performed at baseline, and participants will be followed-up over time at 6-month intervals. The burden of CVD will be assessed with repeated carotid intima-media thickness and pulse wave velocity measurements, as well as by recording clinical cardiovascular events that occur during the follow-up period. Conclusion This project will contribute to the understanding of the epidemiology and pathogenesis of CVD in the context of HIV infection in a rural area of SSA. The ultimate goal is to improve cardiovascular risk prediction and to indicate preventive approaches in the HIV-infected population and, potentially, for non-infected high-risk populations in a low-resource setting.

Carotid IMT is more associated with stroke than risk calculators

BACKGROUND

It is unclear whether a natural marker of atherosclerosis (carotid intima-media thickness: CIMT) or calculated risk score is more associated with stroke. We therefore comparatively examined the relationship between CIMT as well as two cardiovascular risk calculators (Omnibus Risk Score -ORS and Framingham Risk Score- FRS) and the occurrence of stroke among hypertensive African patients.

METHODS

CIMT was measured in 555 consecutive consenting hypertensive adults (377 stroke patients and 178 stroke-free subjects). The 10-year cardiovascular risk was calculated for each participant with the FRS and ORS. The strengths of association between FRS, ORS, CIMT, and stroke occurrence were examined using logistic regression. The discriminative capacity of FRS, ORS, and CIMT for stroke occurrence was assessed with c-statistics.

RESULTS

Higher average CIMT (OR 11.71; 95% CI 1.65-83.07; P = 0.01) was strongly associated with stroke after adjusting for age, sex, blood pressure, serum cholesterol, and blood sugar. Neither the FRS (OR: 1.03; CI: 0.89-1.19, P = 0.68) nor the ORS (OR: 1.08; CI: 0.90-1.30; P = 0.41) was significantly associated with stroke. CIMT had a higher c-statistic for differentiating stroke patients from hypertensive controls (right: c = 0.63, P < 0.001; left: c = 0.67, P < 0.001; average: c = 0.66, P < 0.001) than some conventional risk factors. Neither FRS (P = 0.39) nor ORS (P = 0.55) was able to independently differentiate between stroke and hypertensive patients.

CONCLUSION

CIMT, but neither FRS nor ORS, is independently associated with stroke among Nigerian African hypertensive patients. CIMT may be a better tool for estimating the overall risk of stroke than FRS or ORS in this population.