CT scan marker could flag PH risk in pulmonary fibrosis patients

Among people with progressive pulmonary fibrosis, PH was linked to a larger pulmonary artery-to-aorta (PA/Ao) ratio on CT scans, an indirect sign that has been reported as a proxy of PH. The researchers also found that PH develops at similar rates in both progressive and idiopathic pulmonary fibrosis (PF), so “screening using this factor may enable timely and detailed examinations and treatment interventions,” they wrote.

The study, “Prevalence and predictors of pulmonary hypertension in patients with progressive pulmonary fibrosis: A retrospective study,” was published in Respiratory Investigation. 

Pulmonary hypertension refers to abnormally high blood pressure in the blood vessels that carry blood from the heart to the lungs. When PH develops alongside interstitial lung disease (ILD) — a broad group of disorders that cause inflammation and scarring in the lungs  — it is associated with worse outcomes.

Idiopathic PF is one type of ILD, characterized by lung scarring with no known cause. Most studies of PH associated with ILD have focused on idiopathic PF. Much less is known about PH in progressive PF, which describes a fibrotic pattern that is worsening, including how often it occurs and whether it affects survival.

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Medical records provide clues

To learn more, researchers in Japan reviewed medical records of 139 ILD patients with a median age of 70 who underwent echocardiography (a procedure that uses sound waves to visualize the heart and blood flow) between January 2017 and December 2021. PH was established based on criteria from echocardiography and right heart catheterization, the gold standard method for diagnosing pulmonary hypertension, in which a flexible tube is guided to the right side of the heart and the pulmonary artery to measure pressure.

Seventy-six patients (54.7%) were diagnosed with PH during follow-up. In the group of 61 participants who developed progressive PF, more were women (57.4% vs. 10.6%) and most were younger (median age 67 vs. 74) than the 47 participants who developed idiopathic PF. No significant difference was found between the proportion of patients with either progressive or idiopathic PF who had PH (60.7% vs. 63.8%).

Lung function was broadly similar between the two groups. Median predicted forced vital capacity, which measures how much air can be forcibly exhaled after a full breath, was 67.9% in the progressive group and 65.6% in the idiopathic group.

During the three-year follow-up, 40 patients died and six underwent lung transplant, including five with progressive PF. Among those with this form of PF, having pulmonary hypertension was not significantly associated with shorter transplant-free survival or with a higher risk of earlier death.

Among patients with PH, pulmonary vasodilators (medications that widen blood vessels in the lungs to lower pulmonary pressure) were used in 14 patients with progressive and 10 with idiopathic PF. Vasodilator users tended to have preserved lung function, although the differences were not statistically significant.

The researchers then looked for predictors of PH among people with progressive PF. PH was associated with lower FEV1 (a measure of how much air can be forcibly exhaled in one second) and lower diffusing capacity of the lungs for carbon monoxide (a measure of how much oxygen moves from the lungs to the blood on inhalation). Patients with PH also had higher levels of brain natriuretic peptide (a marker of heart strain), and were more likely to show signs of right-heart strain.

But in a multivariable analysis, which considers several factors at the same time, the PA/Ao ratio was the only independent predictor of PH.

Using a receiver operating characteristic (ROC) analysis, a statistical measure of the distinction between people with and without a condition, the cutoff for the PA/Ao ratio was set at 0.97. That cutoff correctly identified about 76% of patients with PH and correctly ruled it out in about 88% of those without PH.

“Chest CT is essential for the assessment of ILD and is regularly performed in patients with ILD,” the investigators wrote. “By focusing on the PA/Ao ratio, it may be possible to predict the early development of PH.”

The scientists noted that their study had some limitations, including that it was conducted at a single center and involved only patients with ILD who had undergone echocardiography, meaning the group could already have had a higher likelihood of PH.

Overall, the study suggests that PH is similarly common in progressive and idiopathic PF, and that the PA/Ao ratio on routine chest CT scans could offer a tool for identifying people who need further PH evaluation.

“In the future, this study’s results should be validated through research involving patients diagnosed with PH by right heart catheterization,” the team wrote.