Co-morbidity in COPD: the effects of cardiovascular drug therapies

Cardiovascular disease is a major co-morbidity in chronic obstructive pulmonary disease (COPD) patients and is a predictor of all-cause mortality. This paper reviews the study design and data analyses of observational studies of cardiovascular drug effects in patients with COPD and evaluates the potential for bias on the validity of their findings. Three recent observational studies of statin use in the setting of COPD show surprisingly high efficacy results which, by their magnitude, demand closer analysis. Such analysis reveals that immortal time and immeasurable time biases likely accounted for dramatic findings of reduced mortality with aggressive treatment for cardiovascular disease. After removing these sources of bias, the effects are mitigated or may disappear entirely. Investigation of methods and results in the statin studies reviewed in this article reveals significant bias that has skewed the results of these early studies. Correcting these methodological flaws with proper statistical analysis may attenuate or even eliminate these apparent benefits.