Ambulatory Blood Pressure Monitoring in Children: Ready for Primetime

In this paper, Flynn and colleagues present an update to the 2008 AHA scientific statement on Ambulatory Blood Pressure Monitoring (ABPM) in Children and Adolescents.¹ In the 6 years since the original statement, data not only continue to support the use of ABPM in children, but also reveal additional situations where ABPM is especially useful in establishing an accurate diagnosis and ensuring effective treatment.

The committee did an excellent job updating the 2008 statement on ABPM in children. The report, though necessarily lengthy, is easily readable and accessible and represents a definite improvement over previous recommendations. The statement provides not only rationale but also extensive detail to aid clinicians in running a successful ABPM program. These recommendations give essentials about machine use and care and monitoring specifics such as placement and frequency issues, and provide an improved framework for interpretation. Given that most ABPM devices use oscillometric techniques, the addition of mean arterial pressure to the normative tables is commendable. Their classification schema for ABPM interpretation is greatly improved, correcting several ambiguities from the original statement. As the authors point out, missing from classification are those with normal clinic BP but elevated ambulatory BP loads (generally defined as >25%) and those with hypertension in clinic but elevated BP loads. Their case-by-case approach is reasonable given the myriad of indications for ABPM. The CKiD study chose to classify their cohort as hypertensive whenever the BP load was elevated, regardless of the clinic blood pressures.² This inclusive definition of hypertension can be justified by the significant cardiovascular risk among children with chronic kidney disease (CKD).^3,4 Among otherwise healthy children, however, the clinical significance of an elevated load is less clear. Any BP load over 25%, regardless of clinic BP and ambulatory mean, is likely abnormal. Whether an isolated high load is enough to warrant the classification of ambulatory pre-hypertension is still unclear.

Tying abnormal blood pressure values in childhood to both short- and long-term health risk has been an ongoing focus of longitudinal research. This update summarizes the evidence that childhood blood pressures do correlate to measureable increases in atherosclerosis, thickening of cardiac muscle, carotid intima-media thickness, left ventricular mass (LVM), and rates of eccentric left ventricular geometry occurring during childhood. One of the first papers from the Bogalusa longitudinal study used autopsy results from accidental deaths in children and young adults to document increased lesions in the coronary arteries in subjects with higher systolic and diastolic blood pressures.⁴ In 2011, Urbina showed there was a strong positive relationship between arterial stiffness and LVM index in children as well as strong correlation of LVM index and systolic blood pressure independently of age, body mass index, heart rate, hemoglobin A1c, sex, and arterial stiffness.⁵ Furthermore, ABPM has proven to be a more sensitive measure than clinical blood pressures in identifying the presence of end-organ damage compared to clinical blood pressures alone. Sorof et al demonstrated in children with both ABPM and clinical BP measurements that LVM determined by ECHO correlated only with ABPM measures but not with clinical BPs.⁶ McNiece further showed that using ABPM to classify hypertension status was more strongly associated with left-ventricular hypertrophy (LVH) than when classifying by clinic blood pressures alone.⁷ Lande et al confirmed the presence of LVH in over one quarter of children with hypertension confirmed by ABPM but no cases of LVH among those with white coat hypertension, emphasizing the importance of ABPM in distinguishing sporadic hypertension in the clinical setting from sustained ambulatory hypertension.⁸ Upon review of this evidence, an expert panel on cardiovascular risk reduction in children recently recommended treatment of hypertension in children in order to avoid further end-organ damage.⁹

The report expands the recommendations from prior guidelines, and can be interpreted as recommending routine ABPM in the initial assessment of all children with sustained elevated office blood pressure readings. The 2004 4^th Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents suggested ABPM as a useful adjuvant in diagnosing blood pressure abnormalities in children.¹⁰ The report stopped short of recommending universal adoption, and Table 7 from that report lists ABPM not as routine in evaluation, but only “as indicated” when white coat HTN is suspected. Similarly, the original AHA 2008 guideline states that ABPM “may prove useful.”¹¹ The current update calls for routine performance of ABPM. I agree that ABPM should be routinely performed in the diagnosis of suspected HTN. ABPM confirms sustained hypertension and is better at predicting end organ damage, such as left ventricular hypertrophy, than clinic blood pressures alone. White coat hypertension, which is common in children,¹² can only be diagnosed by ABPM and will rule out unnecessary evaluation and treatment in children who are only nervous at a doctor’s visit. ABPM has also been shown to be a cost effective initial first step in the evaluation of children with office hypertension.¹³

Though ABPM remains useful in confirming the diagnosis and aiding in the management of pediatric hypertension, there are still several unanswered questions. As the authors point out, current normative values for threshold blood pressures in children are derived from a single study of White Central European children.^14,15 Whether these thresholds are appropriate for our multicultural population is unclear. Certainly minority populations tend to have higher prevalence of hypertension and, at least in adults, much more end organ damage. Whether minority threshold values are and should be the same depend primarily on when end organ damage occurs. No normative values for minorities currently exist, nor have any differential studies evaluated organ damage by race. Creating normative values for US children should remain an important research goal.

Despite the remaining gaps in knowledge regarding the utility of ABPM in children, the current AHA update advances the field and provides detailed instruction on the use and interpretation of this important diagnostic technique.