Discussion
In this study, we provide the first comprehensive summary of trends of HF-related inpatient admissions and non-admitted ED visits in the USA among adults with and without diabetes and note several important findings. First, rates of HF-related inpatient admissions and ED visits were three to five times higher in adults with versus without diabetes, and this excess risk has increased over time. Second, while absolute rates remained lowest in the youngest age groups, the greatest relative increases in HF-related inpatient admissions and ED visits were observed in young adults with diabetes. Third, increases in HF-related utilization among adults with diabetes was observed in both inpatient and ED settings, suggesting broader underlying causes rather than a shift in treatment setting.
Our results are consistent with the few studies that have reported changes in HF incidence over time. In the USA, a NIS-based study reported a 3.6% annual decline in HF inpatient admissions among adults ≥35 years with diabetes between 1998 and 2014.13 This decline was likely driven by significant decreases in the earlier period (ie, 1998–2006) and explains why we, in contrast, observed a non-significant decline in HF-related inpatient admissions from 2006 to 2013. Another study, also using the NIS, reported an overall 38.9% decline in primary HF admissions in people with diabetes between 1995 and 2015.12 This decline also appeared to be driven by reductions in the earlier study period as non-significant increases were observed between 2013 and 2015.12 In Spain, a significant 5.4% annual increase in HF hospitalizations was observed between 1997 and 2010 in patients with diabetes, broadly similar to findings in the current study.23 However, the NIS-based studies and the Spanish study did not compare changes in HF incidence in people with versus without diabetes. This comparison is necessary to understand whether diabetes is an underlying cause of changing HF rates and to develop targeted interventions to reduce the HF burden in this subpopulation. Only one other study has compared rates of HF hospitalizations in people with versus without diabetes. In Sweden, a 29% decrease in HF hospitalization rates, defined as primary of contributory cause, among persons with type 2 diabetes was observed between 1999 and 2013, and this decline was greater than what was observed for people without type 2 diabetes.24 Unfortunately, data beyond 2013 were not available, and thus, it remains to be elucidated whether the recent increase in HF hospitalizations seen in our US data is also occurring in other populations and settings.
The increasing rates of HF among people with diabetes, especially young adults with diabetes, are consistent with a recent resurgence of other diabetes-related complications in the USA.25 Between 2010 and 2015, national data show increases in lower extremity amputations (LEAs)26 and hyperglycaemic crises among adults with diabetes,27 while long-term declines in end-stage renal disease, acute myocardial infarction (AMI) and stroke have stalled.25 These trends appear to be driven by increases in young (aged 18–44 years) and middle-aged (aged 45–64 years) adults, among whom the risk of hyperglycaemic crisis, AMI, stroke and LEAs each increased by more than 25% between 2010 and 2015.25 We add to this growing body of literature that increases in HF also disproportionally affect young people with diabetes at or around the same time. There are several possible reasons to explain this observed increase. First, we have observed a changing profile of newly identified diabetes cases that are more obese and may have more poorly managed risk factors (eg, blood pressure and lipids) as compared with earlier years, particularly among younger adults.4 Second, a longer average duration of diabetes may be leading to a shift in risk of complications. Third, the younger age group may include a larger relative proportion of type 1 diabetes who may be at increased risk for HF. However, accumulating evidence suggests that diabetes complication rates may be higher in young adults with type 2 diabetes as compared with type 1 diabetes.28 Fourth, changes in healthcare policy such as the introduction of high-deductible health plans have led to reductions in early preventive care in people with diabetes.29 30 Fourth, increased costs of insulin and other diabetes medications may have led patients to cut back on treatment to minimize costs, thus exposing them to increased risk for complications including HF.31 Last, in 2012, the US Centers for Medicare and Medicaid Services implemented the Hospital Readmissions Reduction Program, which financially penalized hospitals with high 30-day readmission rates for HF.32 The role of this policy in influencing HF trends in the current study is unclear as NIS and NEDS do not identify hospital readmission. Overall, it is most likely that a combination of these factors explains the increases in HF-related ED visits and hospitalization among US adults with diabetes.
The results of this study offer important implications for public health and healthcare practice. First, in this study, we show that diabetes is associated with an almost fivefold increased risk for HF-related inpatient and non-admission ED visits. The continued increase in the prevalence of diabetes is likely to increase the number of people with HF in the future and will have important implications for both outpatient and hospital burdens, pharmacotherapies and resource allocation. Second, we hypothesize that increasing risk for HF may lead to an increase in subsequent HF-related mortality with some early evidence to support this hypothesis. For example, Cheng et al33 reported an increase in HF-related mortality among young US adults with diabetes between 1988 and 2015, despite mortality rates for several other CVDs declining in that time, and an Australian study reported no change in HF-related mortality despite declines for other CVD outcomes.34 Third, improved awareness by healthcare providers that diabetes is an important risk factor for HF might stimulate more intensive and focused prevention and management opportunities. For example, post hoc analysis of the Steno-2 trial in Denmark demonstrated a reduction in HF hospitalizations among patients with diabetes receiving intensive (vs conventional) therapy.35 Furthermore, emerging trial data of sodium-glucose cotransporters 2 (SGLT2) inhibitors show promising findings for HF. For example, randomized trials of SGLT2 inhibitors (vs placebo) have shown a pooled 31% reduction in HF hospitalizations in type 2 diabetes patients at high risk of CVD,36 as well as improved outcomes among those with existing diabetes and HF.37 Real-world studies, such as CVD-REAL (Comparative Effectiveness of Cardiovascular Outcomes in New Users of SGLT-2 Inhibitors), have also demonstrated the positive effects of SGLT-2 inhibitors in HF prevention in patients with type 2 diabetes, irrespective of atherosclerotic disease status.38 39
This is the largest study to explore rates of HF over time in USA adults with and without diabetes in two nationally representative patient datasets. Nonetheless, there are limitations to be considered. First, NIS and NEDS represent hospital discharges, not individual persons and therefore may include multiple hospital stays for some persons. This may lead to an increase in population-based rates, especially in certain subpopulations at higher risk for recurrence, including those with diabetes.40 However, the primary objective of this study was to examine changes in HF admissions over time in people with versus without diabetes. To that end, and in the absence of contrary data, we assume that the risk of readmission in people with versus without diabetes remained constant during the study period and readmissions are, therefore, unlikely to impact our key conclusions. Second, because of the inability to differentiate diabetes type in the NHIS survey data, we were not able to report trends in HF by diabetes type. Therefore, all types of diabetes are included in the current analysis with the assumption that the vast majority (~90%–95%) have type 2 diabetes.41 In addition, the NHIS is self-reported and does not include undiagnosed diabetes and thus likely underestimates the number of people with diabetes in the population. Furthermore, the underlying characteristics of people with diagnosed diabetes could be changing over time. However, there have not been adequate data or studies to characterize such changes. Third, a shift from ICD-9-CM to ICD-10-CM in October 2015 may have affected our observed rates. However, observed changes in trends occurred before this period, and therefore, it is unlikely that this coding shift influenced the overall patterns that we observed in this study. Furthermore, coding changes do not explain differential increases in people with versus without diabetes and in younger versus older adults. Fourth, admissions for hypertensive heart disease with HF were not included in the current analysis. Fifth, NIS and NEDS do not report HF stages and we were unable to explore differential impacts of diabetes on HF stages, though this is an important future direction. Sixth, location (urban/rural) and poverty status, although available in NHIS, were not categorized in the same way in NEDS and NIS, so these factors were excluded from rate calculations. In addition, the race/ethnicity variable in NIS was incomplete prior to 2012, and so trends were not calculated by race/ethnicity. Finally, this is a descriptive observational study designed to assess the relative burden of HF hospitalizations in people with versus without diabetes over time. Future studies with more appropriate datasets (ie, with individual level data) are needed to tease out the underlying mechanisms with which diabetes leads to an increase in HF hospitalization, particularly among young adults.