The Birth of Pediatric Primary Hypertension

When I was a kid so many things were different: we listened to music on cassette mixtapes, had to carry around quarters in case we needed to use a pay phone, and we weren't diagnosed with hypertension unless our blood pressure was above the adult threshold values of 140 / 90mm Hg. Given that high a threshold, it is not surprising that almost all kids with hypertension back them had some underlying secondary cause¹. Whether it was renal, vascular, or endocrine, almost everyone with hypertension during childhood or adolescence had some identifiable contributing factor. These cases were rare and often carried significant morbidity, either related to the underlying condition or from the effects of that severe level of hypertension. Our understanding of the epidemiology of hypertension in children started to change in the late 1970s with the first National High Blood Pressure Education Program task force². For the first time, hypertension in children was defined as >95 percentile of normative values from children based off age and gender. In the mid-1980s, height was also recognized as an important factor in determining normal values of blood pressure and was added to the percentile thresholds³.

These 95^th percentile pediatric blood pressures are usually much lower than adult thresholds; with the advent of those lower normative values for childhood blood pressures, a new category of essential pediatric hypertension was discovered. Though blood pressures need to be repeated both within a visit and across several visits to make a definitive diagnosis⁴, approximately 3 to 4% of all children in the United States have sustained blood pressures that are above normative thresholds⁵. Most recent guidelines have recognized that since so many teens have elevated blood pressure above even adult thresholds, using percentile-based definitions are not appropriate beyond puberty. As such, new AAP guidelines recommend adult cut points of 120/80 starting at age 13 years⁶. In most cases, the 120/80 threshold is notably lower than the corresponding 95^th percentile. With this lowering of blood pressure thresholds for teens and older adolescents by the AAP Clinical practice guidelines, the prevalence of elevated blood pressure and primary hypertension has gone up in this age range, though still nowhere near adult prevalence⁷.

Unfortunately, not all of the change that we have seen in the epidemiology of hypertension in youth is attributable to those changing thresholds and improved definitions. Like the rest of America, youth continue to increase in obesity, a major contributing factor to hypertension at all ages including children⁵. Data suggests that obesity related hypertension may be increasing in prevalence in recent decades to now become the most common etiology in children and adolescents^{8, 9}. Though the exact mechanism is likely multifactorial, the AHA scientific statement introduces the multiple links between obesity and childhood hypertension. Though difficult to separate from the risk of obesity, sedentary lifestyle and poor physical conditioning are additional risk factors for hypertension onset in children and youth.

A major limitation in the management and treatment of hypertension in youth remains poor diagnostic accuracy. Several studies have demonstrated that pediatricians often fail to diagnose blood pressures that are in the hypertensive range, particularly among younger patients whose threshold is lower than 120 / 80. Though the simplified BP threshold table created by the AAP CPG were designed to facilitate identification of abnormally high blood pressures, no data has emerged to ascertain whether there has been an improvement since the 2017 publication of the GPG. Also unknown is the effect of recommendations regarding the addition of the AAP blood pressure thresholds into EMR systems to automatically notify providers of abnormally high blood pressures.

Ideally the thresholds separating normal blood pressure in youth from high blood pressure should not be based on population norms and the arbitrary 95^th percentile threshold. Research to generate blood pressure thresholds based off target-organ-injury risk is ongoing. The recently completed systolic hypertension in pediatrics- adult hypertension onset in youth (SHIP AHOY) study measured cardiovascular and neurocognitive outcomes in children with varying degrees of elevated blood pressure to determine whether 95^th percentile thresholds are adequate to capture target organ risk in children with elevated blood pressure¹⁰. Though analysis is ongoing, it appears that cardiovascular risk, in the form of left ventricular hypertrophy and altered pulse wave velocities, begins at blood pressures even lower than current threshold cut points^{11, 12}.

Another sequalae of the changing epidemiology towards primary pediatric hypertension as the leading etiology in children is a streamlining of the initial evaluation and workup of youth with high blood pressure. Before primary hypertension was recognized as the most common clinical scenario, children with hypertension underwent an extensive and expensive evaluation¹³. All children received both renal and cardiac ultrasounds (echocardiograms) as well a battery of blood and urine tests to identify underlying cause of blood pressure abnormalities. While that approach is still appropriate for the severe levels of blood pressure elevation that defined hypertension (>140/>90mmHg) decades ago, children with more mildly elevated pressures can likely undergo much less comprehensive evaluations. The AAP CPG propose that kidney ultrasound be reserved for children under age 6 unless there is suspicion of kidney disease based off urine studies or serum creatinine; echocardiograms should be deferred unless pharmacologic treatment is planned⁶. The guidelines further recommend forgoing additional specialized tests such as endocrine evaluation, sleep study, or drug testing except where such issues are clinically suspected.

Finally, it should be noted that there remains some controversy about the utility of screening for primary hypertension in children. Though perhaps guilty of improperly framing the question, the US Preventative Task force recently concluded that the evidence to support screening blood pressure in children and adolescents is insufficient to assess benefit on cardiovascular mortality¹⁴. Mortality? Given that pediatric definitions of hypertension did not exist until roughly 45 years ago, it is not surprising that little data directly ties childhood blood pressure abnormalities to eventual cardiovascular mortality. Children of the 1970's who were diagnosed with hypertension using the lower normative thresholds are just now reaching their 50's, the age when cardiovascular mortality starts to climb. Several studies demonstrate that elevated blood pressure and hypertension track from adolescence into young adulthood and beyond^{15, 16}, so it would not be surprising if such long-term cardiovascular outcomes do become established in the following few decades. In the meantime, we know that precursors of morbidity, including LVH and subtle neurocognitive effects, appear reversible with appropriate blood pressure management during childhood^{17, 18}. Waiting for definitive associations between blood pressure in children and adult mortality seems unwise. Evidence supports that primary hypertension leads to deleterious effects on vasculature even in young patients.

The American Heart Association scientific statement on pediatric primary hypertension provides an excellent overview of current definitions and recommendations for the evaluation and management of children and adolescents with elevated blood pressure. Considering etiology, evaluation, management, and even primary prevention, the committee lays out a comprehensive approach to the increasingly common condition.