Background
Discrepancy exists amongst studies investigating the effect of comorbid heart failure (HF) on the morbidity and mortality of chronic obstructive pulmonary disease (COPD) patients.

Methods
MEDLINE and Embase were searched using a pre-specified search strategy for studies comparing hospitalisation, rehospitalisation, and mortality of COPD patients with and without HF. Studies must have reported crude and/or adjusted rate ratios, risk ratios, odds ratios (OR), or hazard ratios (HR).

Results
Twenty-eight publications, reporting 55 effect estimates, were identified that compared COPD patients with HF with those without HF. One study reported on all-cause hospitalisation (1 rate ratio). Two studies reported on COPD-related hospitalisation (1 rate ratio, 2 OR). One study reported on COPD- or cardiovascular-related hospitalisation (4 HR). One study reported on 90-day all-cause rehospitalisation (1 risk ratio). One study reported on 3-year all-cause rehospitalisation (2 HR). Four studies reported on 30-day COPD-related rehospitalisation (1 risk ratio; 5 OR). Two studies reported on 1-year COPD-related rehospitalisation (1 risk ratio; 1 HR). One study reported on 3-year COPD-related rehospitalisation (2 HR). Eighteen studies reported on all-cause mortality (1 risk ratio; 4 OR; 24 HR). Five studies reported on all-cause inpatient mortality (1 risk ratio; 4 OR). Meta-analyses of hospitalisation and rehospitalisation were not possible due to insufficient data for all individual effect measures. Meta-analysis of studies requiring spirometry for the diagnosis of COPD found that risk of all-cause mortality was 1.61 (pooled HR; 95%CI: 1.38, 1.83) higher in patients with HF than in those without HF.

Conclusions
In this systematic review, we investigated the effect of HF comorbidity on hospitalisation and mortality of COPD patients. There is substantial evidence that HF comorbidity increases COPD-related rehospitalisation and all-cause mortality of COPD patients. The effect of HF comorbidity may differ depending on COPD phenotype, HF type, or HF severity and should be the topic of future research.