A nationwide registry study on heart failure in Norway from 2008 to 2018: variations in lookback period affect incidence estimates

Abstract

Background: The incidence of heart failure (HF) has declined in Europe during the past two decades. However, incidence estimates from registry-based studies may vary, partly because they depend on retrospective searches to exclude previous events. The aim of this study was to assess to what extent different lookback periods (LPs) affect temporal trends in incidence, and to identify the minimal acceptable LP. Further, we wanted to estimate temporal trends in incidence and prevalence of HF in a nationwide population, using the minimal acceptable LP.

Methods: We identified all in- and out-patient contacts for HF in Norway during 2008 to 2018 from the Norwegian Patient Registry. To calculate the influence of varying LP on incident cases, we defined 2018 with 10 years of LP as a reference and calculated the relative difference by using one through 9 years of lookback. Temporal trends in incidence rates were estimated with sensitivity analyses applying varying LPs and different case definitions. Standardised incidence rates and prevalence were calculated by applying direct age- and sex-standardization to the 2013 European Standard Population.

Results: The overestimation of incident cases declined with increasing number of years included in the LP. Compared to a 10-year LP, application of 4, 6, and 8 years resulted in an overestimation of incident cases by 13.5%, 6.2% and 2.3%, respectively. Temporal trends in incidence were affected by the number of years in the LP and whether the LP was fixed or varied. Including all available data mislead to conclusions of declining incidence rates over time due to increasing LPs.

Conclusions: When taking the number of years with available data and HF mortality and morbidity into consideration, we propose that 6 years of fixed lookback is sufficient for identification of incident HF cases. HF incidence rates and prevalence increased from 2014 to 2018.

Trial registration: Retrospectively registered.

Keywords: Heart failure; Incidence; Lookback period; NPR; Prevalence; Wash-out period.

Fig. 1

Schematic overview of different lookback approaches. 1; 4 years fixed LP (2012–2018), 2; 6 years fixed LP (2014–2018), 3; 8 years fixed LP (2016–2018); 4, All available data (2012–2018 allowing minimum 4 years of LP resulting in varying LPs). In case examples A and B, the red arrows represent the retrospective lookback period and grey arrows represent deletion of historical data when applying a fixed LP

Fig. 2

Estimated overestimation (relative difference) of incident HF cases by applying 1–9 years of lookback when using 2018 as year of reference

Fig. 3

Incidence rates utilizing different approaches to lookback period. Incidence rates are age- and sex standardised per 1000 PY. Grey line; 4 years fixed LP, Black line; 6 years fixed LP, Green line, 8 years LP; Blue line; including all available data from 2014. PY person years, LP lookback period, AAD all available data

Fig. 4

Incidence rates from 2014 to 2018 applying different case definitions of heart failure. Incidence rates are age- and sex standardised per 1000 person-years using 6 years fixed lookback. a I11.0, I13.0, I13.2, I42, I50 in any position; b Only hospitalized I11.0, I13.0, I13.2, I42, I50, excluding outpatients visit; c Only primary diagnosis I11.0, I13.0, I13.2, I42, I50; d Only I50.x diagnosis

Fig. 5

Temporal trends in incidence rates and prevalence from 2014 to 2018 with 6-year fixed lookback period. Age-and sex-standardised a incidence rates per 1000 person-years per calendar year and b prevalence (%). Blue lines; men, red dashed lines; women, grey; total