Editorial

Hypertension is a global public health challenge affecting approximately 1.5 billion people worldwide and is the premiere modifiable risk factor for strokes and other cardiovascular diseases (CVDs).1 Although effective lifestyle and drug treatments are available for the management of hypertension, blood pressure (BP) control is suboptimal worldwide and the greatest burden of uncontrolled BP is reported in low and middle-income countries (LMICs) where rates of CVDs are rapidly rising.2 3 The need for improvement in hypertension control is particularly urgent in LMICs with two-thirds of global burden of hypertension.4 For instance, sub-Saharan Africa is now reported to have the highest estimated effect size of hypertension for stroke causation worldwide.5 The population attributable risk (PAR) of hypertension for stroke occurrence in Africa from the Stroke Investigative Research & Educational Networks study is 90.8% (95% CI 87.9% to 93.7%), with 86.6% (95% CI 81.6% to 91.6%) being for ischaemic stroke and 96.6% (95% CI 94.4% to 98.9%) for haemorrhagic stroke.5 These background observations highlight the importance of hypertension for stroke occurrence in regions of the world with severely challenged health systems to provide the needed care for the devastating consequences of uncontrolled hypertension. It has been suggested that differences in levels of knowledge, awareness and treatment of hypertension across regional blocks of the world may influence the occurrence of CVDs emanating from uncontrolled hypertension, in particular stroke. However, no previous study has provided rigorous evidence to support this view.

In their study, O’Donnell and colleagues sought to provide empirical evidence to substantiate a hypothesis that country income-level variations in knowledge, detection and treatment of hypertension could contribute differentially to occurrence of stroke and its primary types.6 The authors deployed a case–control methodology with data involving nearly 13 500 stroke cases with age, sex and site matched controls recruited from 32 countries involved in the INTERSTROKE study.7 The authors demonstrated a graded association between countries’ gross national income (GNI), hypertension knowledge, awareness, and treatment and stroke occurrence. Countries with low GNI had the lowest levels of knowledge, awareness and treatment of hypertension culminating in higher risk of stroke, younger onset of stroke and larger proportion of intracerebral haemorrhage relative to higher income countries. The PAR of hypertension for stroke across all regions of the globe was 47.9%, with 37.2% being for high-income countries (HICs), 45.4% for upper middle-income countries—1 (UMICs), 47.6% for UMICs—2 and 53.6% for lower middle and low-income countries (LMICs). The authors partitioned the PAR of hypertension for stroke occurrence according to three control categories: aware and treated hypertension, aware but untreated hypertension and unaware of hypertension. Comparing HICs with LMICs, the PAR of aware and treated hypertension for stroke was 22.2% vs 17.3%, aware but untreated was 4.8% vs 20.4% and unaware of hypertension was 5.6% vs 15.9%, with UMICs demonstrating intermediate risks between HICs and LMICs. The PAR refers to the proportion of the incidence of a disease (ie, stroke) in the population (exposed and unexposed) that is due to the exposure (ie, hypertension) or the incidence of a disease (stroke) in the population that would be eliminated if exposure (hypertension) were eliminated. However, as the authors correctly conceded, the PAR provides an aspirational and theoretical estimate rather than a realistic estimate of reduction in stroke achievable with elimination in hypertension because complete elimination of hypertension is currently an unlikely possibility.

With these limitations of the PAR estimates in mind, the authors further used generalised impact fraction estimators to provide an estimate of the proportion of stroke that would be reduced if hypertension as a risk factor was modified on the basis of summary estimates of association between treated and untreated hypertension for stroke occurrence. This information has pragmatic relevance from a health policy implementation perspective. The impact fraction estimates provide a measure of the extent to which the control of hypertension at a population level using available management options such as use of antihypertensive medications would reduce the occurrence of stroke. Based on the INTERSTROKE study data, the authors reported that 10.3% of the global burden of stroke could be mitigated by treating individuals known to have hypertension without necessarily achieving BP control and, second, use of at least two antihypertensive agents would eliminate 17.6% of stroke worldwide. Of note, the impact fraction of hypertension control was substantially higher for intracerebral haemorrhage at 32.4% compared with ischaemic stroke at 13.5% strongly emphasising the compelling associations between untreated hypertension for intracerebral haemorrhage relative to ischaemic stroke which has a more diverse risk factor profile. These impact fraction estimates were all higher for LMICs relative to HICs.

Implications

The central message from this study is that strategic deployment of population-level interventions aimed at improving knowledge, awareness and treatment of hypertension would substantially impact on the prevention of stroke across the globe. While hypertension control measures have been implemented in HICs with resultant declines in the burden of stroke and other CVDs in these countries, the findings from the study6 show there is still room for improvement in these regions with particular reference to the proportions of treated hypertensives achieving treatment goals. Thus, audacious initiatives such as the Million Hearts, a US Department of Health and Human Services initiative which has a goal of preventing 1 million heart attacks and strokes over a 5-year period, are highly salutary. The overarching objective of efforts of Million Hearts in the clinical setting is on the ABCs of heart health (aspirin use when appropriate, BP control, cholesterol management and smoking cessation) with improving hypertension control as a prime focus.

In LMIC regions, however, more effort is urgently required to reverse or bend downwards the curve of the hypertension-triggered stroke epidemic currently raging in these regions. Priority should be given to addressing the gaps in knowledge through public education through print and electronic media. Coupling hypertension control (an asymptomatic disease) educational messages with occurrence of a devastating medical disorder such as stroke will accentuate the immediacy and relevance of these public education interventions in these regions. Furthermore, deficits in awareness of hypertension status at an individual level should be addressed through large hypertension screening initiatives targeting the population such as the May Measurement Month for hypertension initiated by the International Society of Hypertension. Finally, given the multidimensional nature of hypertension treatment deficiencies, multimodal interventions centred around the chronic care model, task shifting to non-physician healthcare workers, deployment of group clinics, self-management and perhaps practice facilitation may be deployed to address this critical gap. The fact is primary healthcare systems across LMICs are oriented towards the management of communicable diseases and are not yet attuned to the changing trends in CVD burden. Health workers have inadequate skills to manage hypertension and its complications, lack relevant guidelines and lack medical doctors at primary care facilities with the few experts that are available in-country working in tertiary/teaching hospitals. Tailored and efficacious BP control programmes which comprehensively address the contributors of poor BP control at systemic, provider and patient levels are needed to avert preventable mortality and morbidity in LMICs.