CT shows promise in predicting COPD exacerbation risk

Measurement of the pulmonary artery-to-aorta (PA:A) ratio can predict the risk for exacerbations in patients with chronic obstructive pulmonary disease (COPD), particularly those that require hospitalization, say the authors of a US study.

They add that as a routinely used and inexpensive method of assessing lung patients, the computed tomography (CT) scan analysis could become a useful clinical tool.

"The ability to predict which patients are likely to experience an exacerbation of their COPD symptoms requiring hospitalization is clinically significant," said lead author, Michael Wells (University of Alabama, Birmingham, USA) in a press release. "Physicians armed with this knowledge may be able to employ a more aggressive treatment to this population in an attempt to reduce their risk of hospitalization."

The researchers used data from 3464 participants of the COPDGene study who were all current or previous smokers, aged 45-80 years old, with a Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification of II to IV. They were followed up for a median of 2.1 years.

In addition, Wells et al validated their findings using data from 2005 participants from the 3-year ECLIPSE study.

The authors found that, in the COPDGene study, a PA:A ratio greater than 1 was shown to be predictive for future severe exacerbations after adjustment for confounding factors, conferring a 3.44-fold increase in the odds for severe exacerbation during follow up.

The authors made similar findings in the ECLIPSE validation cohort, which showed that at both 1 and 3 years, a PA:A ratio greater than 1 was the factor most strongly associated with severe exacerbations.

They also reported associations between PA:A measurements and overall rates of exacerbations in both data cohorts during follow up.

Additionally, PA:A ratios greater than 1 were associated with an increased rate of severe exacerbations during the year before enrollment.

Previous studies have showed that CT measures of PA:A correlate with pulmonary artery pressure, which in turn is associated with COPD exacerbations. However, the authors believe theirs is the first study to directly examine the association between CT measurements and exacerbations.

"The PA:A ratio also appears to outperform many established risk factors for exacerbation including GERD [gastroesophageal reflux disease], St George's Respiratory Questionnaire [SGRQ], score, breathlessness, chronic bronchitis, and [forced expiratory volume in one second] FEV₁," they write in The New England Journal of Medicine.

They add that the method has practical benefits: "The technique requires minimal training, is reproducible and can be obtained from routine CT images without the need for contrast or special software," principal investigator, Mark Dransfield (University of Alabama, Birmingham, USA) said in a press release. "We suggest that the measurement of the ratio between the pulmonary artery and the aorta should be encouraged as a clinical tool."

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