What is the prevalence of airflow obstruction in UK Biobank participants with Coronary Heart Disease and what is the relationship with mortality?

Problem

Comorbidity of Coronary Heart Disease (CHD) and Chronic Obstructive Pulmonary Disease (COPD) is common. A number of studies conducted in cardiology units of patients with CHD have demonstrated a high prevalence of airflow obstruction (AO) established by spirometry, the majority of which was previously undiagnosed. While this has been cited as evidence of a high prevalence of undiagnosed COPD, there is concern that spirometry criteria in isolation may overestimate the prevalence of COPD, particularly in asymptomatic non-smokers. The prevalence of AO in those with CHD has not previously been evaluated in a community cohort. Furthermore only one, small (n=133) study has assessed the impact of AO on mortality.We aim (i) to assess the prevalence of AO in UK Biobank participants with CHD and (ii) to assess the impact of AO on mortality in this cohort.

Approach

Anonymised data from the UK Biobank community research cohort (n=502,640) were reviewed. CHD and COPD were defined by participant self-report during nurse-led interview. AO was defined as forced expiratory volume in 1 second (FEV1)/forced vital capacity <0.7, based on the best available valid spirometry measurement from the UK Biobank assessment centre. All-cause mortality was available for a median follow-up period of 7 years (Interquartile range 76 months to 93 months) using data linkage with national mortality records. Hazard Ratios (HR) were calculated to examine the association between all-cause mortality and the presence of AO (divided into COPD and undiagnosed AO). Results were adjusted for age, sex, socio-economic status, smoking, body mass index (BMI), diabetes and hypertension.

Findings

Of the 22,731 UK Biobank participants with self-reported CHD, valid spirometry measurements were available for 13,863. Of these, 3,245 (23%) had AO. 2,329 (72%) of those with AO had no previous diagnosis of COPD, asthma or bronchiectasis. 315 (10%) had known COPD. Those with COPD were more likely than those with undiagnosed AO to report shortness of breath or wheeze (91% vs 34%, p<0.01) or to have a history of smoking (92% vs 79%, p<0.01). Compared with those with no airflow obstruction, mortality was higher among CHD participants with known COPD (HR 2.30, 95% confidence intervals (CI) 1.75-3.02) and those with undiagnosed airflow obstruction (HR 1.41, 95% CI 1.21-1.65). Results were adjusted for age, sex, socio-economic status, smoking, BMI, hypertension and diabetes. After adjusting for severity of AO, mortality remained significantly higher in the COPD group compared with undiagnosed AO.

Consequences

A high proportion of those with CHD have AO, most of which is undiagnosed, and which is associated with increased risk of mortality. Smoking status, symptoms and mortality risk differ between undiagnosed AO and COPD. Spirometry, along with clinical history, may therefore be valuable to aid risk stratification in those with CHD.