Noninvasive imaging in children with hypertension

Abstract

Clearly not all children with a high blood pressure (BP) reading need imaging investigation, so some form of selection must be applied. First, the significance of the BP should be established. Measurements made in a clinic may overestimate (or less commonly underestimate) a child’s hypertensive status. To avoid this problem 24-h ambulatory blood pressure monitoring (ABPM) is often used to provide a more comprehensive assessment. ABPM avoids the problem of overestimating hypertension caused by a “white coat effect.” It also allows assessment of BP during sleep, which may be important because absence of nocturnal dipping appears to be a strong indicator of clinically significant hypertension [10]. Nevertheless, hypertension in children is defined as a BP greater than the 95th centile for age, gender and height on three different occasions [5, 11]. (By definition, then, exactly 5% of children should be hypertensive. Why, then, are only 3–4% of children hypertensive? The reason is likely to be regression to the mean, i.e. measuring BP on three separate clinic visits decreases the probability that all will exceed the 95th centile. Another way of looking at this is that the normative values are too high. An alternative explanation is that we are getting systematically lower BP readings because of the replacement of mercury sphygmomanometers.) Prehypertension is defined as BP between the 90th and 95th centiles (or more than 120/80 mmHg, even if this is below the 90th centile). Prehypertension is not normally treated with drugs unless the child has comorbidities such as diabetes mellitus, chronic kidney disease or left ventricular hypertrophy. All children with BP >90th centile should be given advice about lifestyle changes, including weight loss for those who are overweight or obese (body mass index >30 kg m−2), instituting a healthy, low-sodium diet and getting regular physical activity. Adolescents should be advised to avoid tobacco and alcohol [12, 13, 14, 15]. Although this seems a sensible attempt at primary prevention in children, there is actually very little evidence that it is effective in reducing BP. The threshold for commencing drug treatment in children is stage 2 hypertension, which is defined as BP >99th centile plus 5 mmHg. There is a good case that stage 2 patients should be referred to centers with special expertise in the diagnosis and treatment of pediatric hypertension [11, 16, 17]. Children with stage 1 hypertension are only treated if they have comorbidities or symptoms or fail to respond to lifestyle changes [16].