Society of Thoracic Surgeons Risk Score and EuroSCORE-2 Appropriately Assess 30-Day Postoperative Mortality in the STICH Trial and a Contemporary Cohort of Patients With Left Ventricular Dysfunction Undergoing Surgical Revascularization

Abstract

Background: The STICH trial (Surgical Treatment for Ischemic Heart Failure) demonstrated a survival benefit of coronary artery bypass grafting in patients with ischemic cardiomyopathy and left ventricular dysfunction. The Society of Thoracic Surgeons (STS) risk score and the EuroSCORE-2 (ES2) are used for risk assessment in cardiac surgery, with little information available about their accuracy in patients with left ventricular dysfunction. We assessed the ability of the STS score and ES2 to evaluate 30-day postoperative mortality risk in STICH and a contemporary cohort (CC) of patients with a left ventricle ejection fraction ≤35% undergoing coronary artery bypass grafting outside of a trial setting.

Methods and results: The STS and ES2 scores were calculated for 814 STICH patients and 1246 consecutive patients in a CC. There were marked variations in 30-day postoperative mortality risk from 1 patient to another. The STS scores consistently calculated lower risk scores than ES2 (1.5 versus 2.9 for the CC and 0.9 versus 2.4 for the STICH cohort), and underestimated postoperative mortality risk. The STS and ES2 scores had moderately good C statistics: CC (0.727, 95% CI: 0.650-0.803 for STS, and 0.707, 95% CI: 0.620-0.795 for ES2); STICH (0.744, 95% CI: 0.677-0.812, for STS and 0.736, 95% CI: 0.665-0.808 for ES2). Despite the CC patients having higher STS and ES2 scores than STICH patients, mortality (3.5%) was lower than that of STICH (4.8%), suggesting a possible decrease in postoperative mortality over the past decade.

Conclusions: The 30-day postoperative mortality risk of coronary artery bypass grafting in patients with left ventricular dysfunction varies markedly. Both the STS and ES2 score are effective in evaluating risk, although the STS score tend to underestimate risk.

Clinical trial registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT00023595.

Keywords: coronary artery bypass; coronary artery disease; heart failure; risk stratification.

Figures

Figure 1:

Inclusion process for patients in the contemporary cohort that had isolated CABG for ischemic LV dysfunction. §Seven patients were lost to follow-up within the first 30 days following surgery. *Non-MV procedure refers to any procedure combined with CABG other than repair/replacement of the mitral valve (SVR, aortic valve/ tricuspid valve repair or replacement, left atrial appendage closure, septal defect repair, tumor resection, and surgery on thoracic aorta). †Unstable refers to: Any cardiopulmonary resuscitation or mechanical ventilation before the start of the procedure; Pre-operative shock, peripheral hypoperfusion or end-organ damage; Critical pre-operative state; Surgery during the acute phase of myocardial infarction; Any sustained ventricular arrhythmia or aborted sudden cardiac death. ‡ Emergent refers to operation before the beginning of the next working day after decision to operate; Salvage refers to patients requiring cardiopulmonary resuscitation prior to induction of anaesthesia. §Seven patients were lost to follow-up within the first 30 days following surgery.

Figure 2:

Distribution of STS and EuroSCORE-2 risk scores across the STICH (left) and the contemporary cohorts (right) for patients with isolated CABG.

Figure 3:

Cumulative distribution of the predicted risk of operative mortality assessed using the STS and the EuroSCORE-2 in both cohorts in patients with isolated CABG. Red: the STS score in STICH patients, Blue: the EuroSCORE-2 in STICH patients, Black: the STS in contemporary patients, Green: the EuroSCORE-2 in contemporary patients. Vertical dashed lines refer to median values for overall STS (1.23) and EuroSCORE-2 (2.63).

Figure 4:

Actual vs. predicted 30-day postoperative mortality using the EuroSCORE-2 and the STS models in both cohorts (STICH patients (N=814), left and contemporary patients (N=1239, 7 patients were lost to follow-up), right) in patients with isolated CABG.