A propensity-matched study of the effect of diabetes on the natural history of heart failure: variations by sex and age

Background

Poor prognosis in heart failure (HF) patients with diabetes is often attributed to increased co‐morbidity and advanced disease. Further, this effect may be worse in women.

Objective

To determine whether the effect of diabetes on outcomes and the sex‐related variation persisted in a propensity score‐matched HF population, and whether the sex‐related variation was a function of age.

Methods

Of the 7788 HF patients in the Digitalis Investigation Group trial, 2218 had a history of diabetes. Propensity score for diabetes was calculated for each patient using a non‐parsimonious logistic regression model incorporating all measured baseline covariates, and was used to match 2056 (93%) diabetic patients with 2056 non‐diabetic patients.

Results

All‐cause mortality occurred in 135 (25%) and 216 (39%) women without and with diabetes (adjusted HR = 1.67; 95% CI = 1.34 to 2.08; p<0.001). Among men, 535 (36%) and 609 (41%) patients without and with diabetes died from all causes (adjusted HR = 1.21; 95% CI = 1.07 to 1.36; p = 0.002). Sex–diabetes interaction (overall adjusted p<0.001) was only significant in patients ⩾65 years (15% absolute risk increase in women; multivariable p for interaction = 0.005), but not in younger patients (2% increase in women; p for interaction = 0.173). Risk‐adjusted HR (95% CI) for all‐cause hospitalisation for women and men were 1.49 (1.28 to 1.72) and 1.21 (1.11 to 1.32), respectively, also with significant sex–diabetes interaction (p = 0.011).

Conclusions

Diabetes‐associated increases in morbidity and mortality in chronic HF were more pronounced in women, and theses sex‐related differences in outcomes were primarily observed in elderly patients.Diabetes is common in heart failure (HF) and is associated with poor outcomes.^1,2 HF patients with diabetes are sicker and have a higher burden of co‐morbidity than those without diabetes.^1,2 Diabetes is also associated with activation of the renin–angiotensin–aldosterone and sympathetic nervous systems.^3,4 There is mounting evidence that diabetes adversely affects collagen production in fibroblasts and calcium homeostasis in cardiac myocytes.^5,6 However, it is not clear to what extent the diabetes‐associated poor outcomes in HF are due to the direct effects of diabetes.Although outcome‐based multivariable risk adjustment models can account for these confounding covariates to some extent, concerns for residual bias limit interpretation of these results.⁷ To address this concern, propensity score matching can be used to assemble cohorts of patients with and without an exposure who would be well balanced in all measured baseline covariates.^8,9,10 More importantly, as investigators remain blinded during the design phase of a randomised clinical trial, this process of bias reduction and study cohort assembly can be done without any knowledge or use of the outcomes data, and the magnitude of bias reduction may be objectively assessed using standardised differences.^7,9,10,11Data from patients with coronary artery disease and elderly patients hospitalised with systolic HF suggest that the effect of diabetes might be worse in women than in men.^12,13,14 However, little is known about the sex‐related variation in the effect of diabetes on outcomes in a more stable younger ambulatory patient population with mild to moderate systolic and diastolic HF. It is also unknown if this sex‐related difference in the effect of diabetes on HF is a function of age. The purpose of this study thus is to determine the effect of diabetes on mortality and hospitalisation in propensity score‐matched ambulatory HF patients and to determine if the effect varies by sex and if the sex‐related differences vary by age.