Dynamics in cardiac surgery: trends in population characteristics and the performance of the EuroSCORE II over time

Abstract

Objectives: The aim of this study was to investigate the performance of the EuroSCORE II over time and dynamics in values of predictors included in the model.

Methods: A cohort study was performed using data from the Netherlands Heart Registration. All cardiothoracic surgical procedures performed between 1 January 2013 and 31 December 2019 were included for analysis. Performance of the EuroSCORE II was assessed across 3-month intervals in terms of calibration and discrimination. For subgroups of major surgical procedures, performance of the EuroSCORE II was assessed across 12-month time intervals. Changes in values of individual EuroSCORE II predictors over time were assessed graphically.

Results: A total of 103 404 cardiothoracic surgical procedures were included. Observed mortality risk ranged between 1.9% [95% confidence interval (CI) 1.6-2.4] and 3.6% (95% CI 2.6-4.4) across 3-month intervals, while the mean predicted mortality risk ranged between 3.4% (95% CI 3.3-3.6) and 4.2% (95% CI 3.9-4.6). The corresponding observed:expected ratios ranged from 0.50 (95% CI 0.46-0.61) to 0.95 (95% CI 0.74-1.16). Discriminative performance in terms of the c-statistic ranged between 0.82 (95% CI 0.78-0.89) and 0.89 (95% CI 0.87-0.93). The EuroSCORE II consistently overestimated mortality compared to observed mortality. This finding was consistent across all major cardiothoracic surgical procedures. Distributions of values of individual predictors varied broadly across predictors over time. Most notable trends were a decrease in elective surgery from 75% to 54% and a rise in patients with no or New York Heart Association I class heart failure from 27% to 33%.

Conclusions: The EuroSCORE II shows good discriminative performance, but consistently overestimates mortality risks of all types of major cardiothoracic surgical procedures in the Netherlands.

Keywords: Cardiothoracic surgery; Population dynamics; Prediction models.

Figure 1:

Observed and expected mortality of the EuroSCORE II over time. Upper graph, solid lines: average of observed/EuroSCORE II calculated mortality at specific time points; dahsed lines: overall average observed/EuroSCORE II calculated mortality; dotted lines: trend line (LM) of observed/EuroSCORE II calculated mortality, lower graph, solid line: observed:expected ratios; dashed line: trend line (locally weighted smoothing) of the observed:expected ratio.

Figure 2:

Area under the receiver-operating characteristic curve with 95% confidence interval of the EuroSCORE II over time. Dots: average interval AUC; Wider area: 95% confidence intervals of interval AUC; dashed line: overall average AUC. AUC: area under the receiver-operating characteristic curve.

Figure 3:

EuroSCORE II performance per major procedure type. Upper lines: average of EuroSCORE II calculated mortality; Lower lines: observed mortality for the 4 major procedure types: aortic valve surgery (top left), isolated coronary artery bypass graft (coronary artery bypass grafting; top right), major aortic surgery (bottom left), and mitral valve surgery (bottom right).

Figure 4:

Trends in values of individual EuroSCORE II model predictors over time. Solid lines: proportions of individual predictors; dashed lines: trend line (locally weighted smoothing) of predictor dynamics. AE: active endocarditis; CABG: coronary artery bypass grafting; CCS4: CCS class 4 angina; CPD: chronic pulmonary disease; Critical: critical preoperative state; ECA: extracardiac arteriopathy; IDDM: insulin-dependent diabetes mellitus; LV function: left ventricular function; N/M mob: neurological or musculoskeletal dysfunction severely affecting mobility; NYHA: New York Heart Association; PA systolic: pulmonary artery systolic pressure; Recent MI: recent myocardial infarction; Redo: previous cardiac surgery. Weight of procedure ‘1 non-CABG’: single major cardiac procedure which is not isolated CABG; 2: 2 major cardiac procedures; 3+: 3 or more major cardiac procedures.