Main pulmonary artery parameters predict PAH outcomes, study finds
MPA diameter requires single measurement vs. multiple for other risk scores
A higher diameter and a faster enlargement rate of the body’s main pulmonary artery — dubbed the MPA, it carries oxygen-poor blood out of the heart toward the lungs — are independent predictors of poor outcomes among people with pulmonary arterial hypertension (PAH), a new study reports.
In predicting patients’ risk of hospitalization for right heart failure, needing a lung transplant, or death, MPA diameter performed just as well as existing risk stratification scores already used in clinical practice to estimate prognosis, according to the researchers.
The possible benefit of MPA diameter is that it only requires a single measurement, while other risk scores require multiple different data, the team noted.
“MPA diameter is a significant independent predictor of adverse clinical events in PAH patients without congenital heart disease [heart-affecting birth defects],” the researchers wrote. “It may potentially be a novel prognostic marker in addition to the existing risk scores.”
The study, “Prognostic Value of Main Pulmonary Artery Diameter in Pulmonary Arterial Hypertension,” was published in the journal CHEST.
Researchers cite ‘ongoing need’ for noninvasive outcome measures
PAH, a form of pulmonary hypertension, is characterized by a narrowing of the pulmonary arteries, which are the blood vessels that transport blood from the heart to the lungs. Such narrowing leads to increased blood pressure that ultimately makes it harder for the heart to pump blood.
Treatment decisions in PAH are guided by risk stratification models, which take into account various clinical, laboratory, and imaging parameters to estimate a patient’s prognosis. Among these models are the REVEAL 2.0, REVEAL Lite 2, and one from the European Society of Cardiology/European Respiratory Society.
However, these models rely on several different parameters, some of which are not easily obtained.
“Therefore, there is ongoing need for noninvasive and accessible parameters to prognosticate clinical outcomes,” the researchers wrote.
The MPA — sometimes referred to as the pulmonary trunk — is the wide pulmonary artery that carries blood directly out of the heart. It later splits into the left and right pulmonary arteries, which deliver oxygen-poor blood to their respective lungs.
This main artery is commonly enlarged in PAH patients, which has been linked to worse clinical outcomes. MPA diameter has therefore emerged as a possible prognostic factor in PAH, though studies to date have yielded conflicting results.
Now, a team of researchers in Australia set out to better characterize the prognostic value of MPA diameter in PAH. To that end, they retrospectively analyzed data from 351 PAH patients without congenital heart disease who were seen at two large centers in Sydney.
Participants underwent initial (baseline) MPA imaging a median of about six months after their PAH diagnosis. Clinical outcomes were collected a mean of four years after baseline imaging.
The mean baseline MPA diameter was about 35 mm, with more than 90% of patients exceeding normal sex-specific thresholds, the researchers noted.
For patients with serial imaging results available, MPA diameter was increased in more than half (56%). It remained unchanged for 31% with such data, and shrank for 13%. The overall mean MPA growth rate was 0.4 mm/year, with a larger MPA diameter and worse risk scores at baseline predicting faster MPA enlargement.
People with idiopathic PAH — in which the disease does not have a known cause — showed significantly slower MPA enlargement than those with PAH related to connective tissue disease.
“MPA enlargement is frequent in PAH, with progressive growth being the norm,” the researchers wrote.
Higher risk seen for each 5 mm increase in main pulmonary artery
During follow-up, 190 people reached a primary composite outcome of lung transplant, hospitalization for right heart failure, or death. The results overall showed that baseline MPA diameter and MPA growth rate were significant predictors of these poor outcomes.
Every 5 mm larger MPA diameter at baseline was significantly associated with a 31% higher risk of reaching this composite outcome, the data showed.
Baseline MPA diameter remained an independent predictor of poor outcomes in various patient subgroups, including across PAH subtypes, and in statistical analyses adjusted for the three well-established PAH risk scores and their components.
MPA diameter may serve as a simple and readily accessible alternative to the multiparametric risk scores. … [It also] offers incremental risk stratification values when added to existing risk stratification scores.
This parameter was also a predictor of secondary outcome measures, including a composite of death or lung transplant, and a composite of death, lung transplant, hospitalization for right heart failure, and start of epoprostenol treatment. Epoprostenol is an intravenous, or into-the-vein, PAH therapy (sold as Flolan and Veletri).
Independently of baseline MPA diameter, MPA growth was also a predictor of the primary composite outcome: Specifically, every 1 mm/year of growth was significantly associated with a 79% increased risk.
Final statistical models indicated that baseline MPA diameter had a similar ability to predict clinical outcomes as the other three PAH risk scores. When this parameter was combined with the REVEAL 2.0 risk score, 23% of patients were “more appropriately classified into a lower risk category,” the team wrote.
Overall, “MPA diameter may serve as a simple and readily accessible alternative to the multiparametric risk scores,” the researchers wrote, adding that it also “offers incremental risk stratification values when added to existing risk stratification scores.”
The team noted, however, that given the study’s retrospective design, these findings need to be confirmed in studies that follow patients over time “before this novel parameter can be integrated into clinical practice.”
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