In patients with cystic fibrosis or chronic obstructive pulmonary disease, relative enlargement of the pulmonary artery on chest computed tomography (CT) may be a marker of respiratory exacerbations and adverse outcomes. Results from recent studies show that pulmonary vascular pruning, which is present in chronic obstructive pulmonary disease and emphysema, may also be a marker of respiratory exacerbations. The objective of this study was to determine if similar findings are present in asthma and whether they are explained by differences in left and right ventricular size.
Researchers used data from adults with severe and nonsevere asthma who were part of a prospective, multicenter investigation called the Severe Asthma Research Program III (ClinicalTrials.gov Identifier: NCT01761630). They obtained volumetric, non-contrast, non-electrocardiogram (ECG) gated CT chest scans and assessed a number of imaging characteristics including pulmonary artery and aorta diameter. The researchers also estimated right, left, and total epicardial cardiac ventricular volume (eETVVI) indices in this cohort. Pearson correlation was used to assess associations between cardiac and pulmonary artery measures and clinical measures of asthma severity, and multivariable linear and zero-inflated negative binomial regression were used to evaluate associations with asthma severity and exacerbations.
Of the patients who had clinical and imaging data available for analysis (N=237), cardiac segmentation was successfully performed in 233. There were 10 healthy controls in this group. The mean age was 46.2 years, and the mean duration of disease was 27.6 years. Of those who received cardiac segmentation, 65.7% were women, 28.3% had mild or moderate asthma, and 67.4% had severe asthma.
Results revealed that asthma severity and exacerbations were associated with smaller left and right ventricular volumes prior to enrollment and at follow-up. For example, those with severe asthma (n=157) had 36.1 mL/m² smaller eETVVI than healthy controls (P =.003) and 14.1 mL/m² smaller eETVVI than those with mild or moderate asthma (n=66; P =.011). Patients with an eETVVI less than the median had a 57% higher rate of exacerbations during follow-up compared with those with eETVVI greater than the median (P =.020). Asthma severity and exacerbations were not associated with pulmonary artery to aorta diameter ratio or estimated right ventricular to estimated left ventricular volume ratio.
This study had several limitations. First, the researchers used an automated technique to measure estimated ventricular volume based on non-contrast, non-ECG gated CT imaging, which limited conclusions drawn from estimated right ventricular to estimated left ventricular volume ratio findings. Second, because the CT images were non-ECG gated, the researchers obtained a temporal average of ventricular size across the cardiac cycle instead of the end-diastolic values typically reported.
Third, the researchers lacked expiratory imaging for cardiac analyses and used inspiratory imaging instead. Fourth, they were unable to identify effects related to recent asthma exacerbations because CT scans were not always obtained on the same day as a study visit. Lastly, due to limitations in study size and asthma event rates, the researchers could not investigate relationships between findings and biologic variables.
The study researchers concluded that severe asthma as well as a higher rate of exacerbations may be associated with smaller cardiac ventricular size, and that this finding may lead to new treatments and discoveries surrounding asthma etiology.
Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.
Ash SY, Sanchez-Ferrero GV, Schiebler ML, et al; for the SARP Investigators. Estimated ventricular size, asthma severity and exacerbations: the SARP III cohort [published online September 12, 2019]. CHEST. doi:10.1016/j.chest.2019.08.2185