Prehypertension and target organ changes in an African population

Mokwena, Caroline Motheo
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Hypertension (HT) remains the leading risk factor for cardiovascular diseases (CVDs) and a leading cause of death globally. It is estimated that HT causes 10.4 million deaths annually. Studies showed that even individuals who are in the normotensive( NT) range show indications of target organ damage. This gave rise to a new category of HT called pre-hypertension(pre-HT). Prior 2017, HTwas defined as a blood pressure (BP) ≥ 140/90 mm Hg and pre-HT was defined as a BP of 120 mm Hg to 139 mm Hg. In 2017 these guidelines were revised by the American College of Cardiology (ACC) and the American Heart Association (AHA). According to these new guidelines, HTis defined as BP≥ 130 mm Hg and pre-HTas BP of 120 mm Hg to 129 mm Hg. However, both the South African Hypertension Society (SAHA) and European Society of Cardiology/European Society of Hypertension (ESC/ESH) do not recommend these new guidelines. Both organisations still recommend the definition of HTas a BP ≥ 140/90. Even though the ESC/ESH guidelines are accepted by the SAHA, there is no evidence to indicate which of the guidelines are more appropriate for African communities since all the studies were conducted in western countries like the United States of America (USA) and the United Kingdom (UK). Therefore, in this study we recruited South African peoplefrom South Africa, determined the prevalence of HT and pre-HT assessed cardiovascular target organ changes.We recruited 1211 participants of African ancestry and measured both conventional and ambulatory blood pressure (ABP). To asses cardiac changes we used echocardiography to measure early-to-late diastolic filling and left ventricular wall thickness. To measure vascular changes we used the SphygmoCorto measure pulse wave velocity (PWV). Blood samples were collected to measure plasma hormone concentrations and 24-hour urine samples were collected to measure urinary electrolyte excretion. Anthropometric measurements were taken and body mass index (BMI) was calculated as weight divided by height squared. A standardised questionnaire was administered to determine intake of medication and lifestyle habits like alcohol intake and cigarette smoking. Our results indicate that the average age of the population was 44.05±18.29 years. There were more female(65%) participants than male (5%). The overall population was overweight with a BMI of 29.47±8 kg/m2. Fifteen percent (15%) of the sample population were smokers. Participants who consumed alcohol were 21%. When the AHA guidelines were used, more participants were hypertensive (41.5%) compared to those who were pre-hypertensive (18.6%). On the other hand when the ESC/ESH guidelines were used, more participants were pre-hypertensive (34.2%) compared to those who were hypertensive (25.9%). The night-time BP of the pre-hypertensives and grade-1 (HT1) was within normal range while the night-time BP of the grade 2 (HT2) and grade 3 (HT3) was elevated. The pre-hypertensives and the three HT groups had an attenuated decline in nocturnal BP. Compared to the NT, the PWV and left ventricular mass index (LVMI) of all the HT groups, including the pre-HT were significantly higher. As the HT stages progressed there was a reduction in diastolic function observed.In conclusion our results indicate that according to the SAHS/ESH that are currently applied in SA, pre-HT is overestimated while HT is underestimated. Furthermore, using the AHA guidelines, our findings indicate that cardiovascular target organ changes increase significantly fromthe pre-HTto the HT1 stage. Since both stages (pre-HT and HT1) are considered NT according to the SAHS/ESC/ESH guidelines, by the time they reach HT2 stage which is the first stage considered as hypertensive, target organ damage may have progressed significantly. Therefore, these results indicate that the AHA/ACC guidelines are more appropriate for the SA population. If these guidelines can be adopted for HT treatment, CVD target organ damage can be significantly reduced.
A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Medicine, 2021