Researchers identify possible mechanisms for childhood primary hypertension
Overactivity presenting as elevated heart rate, left ventricular ejection velocity and proximal pulse wave velocity are potential sources of primary hypertension among children, researchers reported.
According to a study published in the Journal of the American College of Cardiology, children aged 8 to 18 years with primary hypertension (n = 31) were compared with normotensive children (n = 50). Researchers assessed these cohorts based on:
- peripheral and carotid BP waveforms and carotid-femoral pulse wave velocity measured via tonometry;
- LV outflow velocities and ejection fraction measured by echocardiography; and
- wave separation and intensity analysis to assess pressure wave propagation.
In this U.K. study, investigators found that elevated mean arterial pressure in the hypertensive cohort compared with the normotensive group (90 mm Hg vs. 76 mm Hg; P < .001, respectively) was associated with increased heart rate and cardiac output adjusted for age and sex (5.3 L/min vs. 4.5 L/min; P < .05) and not elevated systemic vascular resistance (18 mm Hg/min/mL vs. 19.3 mm Hg/min/mL; P = .374).
In addition, an elevated peripheral pulse pressure in the hypertensive cohort (66 mm Hg vs. 46 mm Hg; P < .001) was associated with elevated proximal aortic stiffness (3.3 m/s vs. 2.5 m/s; P < .005) and increased LV ejection velocity (1.33 m/s vs. 1.21 m/s; P < .05).
Two major findings
“To the best of our knowledge, this is the first comprehensive characterization of central hemodynamics in children with primary hypertension. There are two major findings. First, increased mean arterial pressure, the steady-state component of BP, in hypertension is attributable to an increase in heart rate and cardiac output rather than increase in systemic vascular resistance,” Ye Li, PhD, research associate at the King’s College London British Heart Foundation Centre, London, United Kingdom, and colleagues wrote. “Second, increased pulsatility of BP in children with primary hypertension, which is more marked than the increase in mean arterial pressure, is explained by a combination of increased proximal aortic stiffness and increased LV ejection velocity.
“While backward wave components were also increased, this was likely secondary to the increase in the forward wave. Increased pressure wave ‘reflection,’ usually inferred from pressure wave morphology, has been implicated in systolic hypertension in adults,” the researchers wrote. “However, in the present study, we found no evidence of increased reflection as measured by augmentation index or by the ratio of backward to forward wave components in hypertensive children.”
Participants were referred to a tertiary center for evaluation. Researchers stated that although noninvasive measures of hemodynamics and calibration of waveforms derived from radial tonometry and brachial and diastolic BP are subject to error, it was unlikely they influenced values in the analysis of the hypertensive group compared with the normotensive group.
Further studies needed
“We studied a relatively small number of hypertensive children and were not able to meaningfully stratify our analysis by age and sex,” the researchers wrote. “Further studies are required to characterize hypertension in different age groups and according to other characteristics. Many of our hypertensive children were on some antihypertensive treatment, and although adjustment for treatment or analysis in untreated children made no difference to our conclusions, further studies on a larger group of untreated children are indicated.”