Dilation of the main pulmonary artery (MPA) and narrowing of the peripheral pulmonary artery are both characteristic of PAH. Previous studies have shown that MPA dilation is linked to higher pulmonary artery pressure, and is therefore a known risk factor in adult PAH. But no studies have analyzed the clinical impact of MPA diameter on clinical outcomes in children.
The study, “Impact of Main Pulmonary Artery Dilatation on Outcome in Pediatric Idiopathic and Heritable Pulmonary Arterial Hypertension,” appeared in the Circulation Journal, researchers aimed to assess clinical differences between pediatric PAH with and without MPA dilation.
Researchers at Tokyo’s Toho University Omori Medical Center studied 66 Japanese children with PAH and 166 healthy controls from 1998 to 2013. All were under the age of 18 at the time of diagnosis.
Using non-invasive chest X-rays, researchers found that median MPA diameter was 31.1 mm in PAH patients, versus 17.3 mm in controls. higher in PAH patients compared to controls (31.1 mm vs 17.3 mm). Median MPA diameter to thorax (MPA/T) ratio (taking into account the patient’s thorax diameter), was also higher in PAH patients (13.4 mm) than in controls (7.7 mm).
Furthermore, within the PAH patient group, those with higher MPA/T ratios had more severe hemodynamic parameters such as pulmonary vascular resistance, as well as adverse outcomes such as hospitalization. This suggests a link between MPA dilation and both disease progression and a more severe disease outcome.
The team also reported that MPA size measurements using X-ray could be used to assess adverse effects in pediatric PAH patients. This is important because the use of conventional chest X-ray to measure MPA/T ratios carries a lower risk of radiation exposure than the widely used computerized tomography (CT) scan to measure MPA diameter in PAH patients.
Despite the small number of patients enrolled, researchers concluded, “this study has described an association between PA [pulmonary artery] trunk dilatation and clinical characteristics; and shown that PA dilatation on single, non-invasive, chest X-ray can be used to evaluate disease severity and prognosis in children with idiopathic and heritable PAH as a homogeneous group.”