Computed tomography derived segment involvement score and coronary artery calcium score when used in clinical routine— <i>data from a Swedish Registry Cohort</i>

AIMS: This study aimed to evaluate the prognostic value of segment involvement score (SIS) from coronary computed tomography angiography (CCTA) and compare it with coronary artery calcium score (CACS) in clinical practice. METHODS AND RESULTS: Patients undergoing CCTA for suspected coronary artery disease between 2006 and 2022 at 27 centres were included. SIS was defined by the number of segments with plaque. CACS was calculated using the Agatston method. Patients were followed for all-cause death and/or myocardial infarction (MI). A total of 23,034 patients were followed for a median of 2.5 years. SIS = 0 was found in 61.4% of patients, SIS = 1 in 12.6%, SIS = 2 in 8.2%, SIS = 3 in 5.7%, and SIS ≥ 4 in 12.2%. Compared with SIS = 0, SIS ≥ 4 was associated with higher adjusted risk of death (HR [95% CI]: 1.39 [1.17-1.66]), MI (3.53 [2.72-4.59]), and death or MI (1.88 [1.62-2.18]). Obstructive stenosis (≥50%) was also independently associated with all outcomes but showed lower discrimination than SIS in receiver operating characteristic curve analyses. SIS and CACS had similar ability to predict death or MI (Area under the curve: 0.70 [0.67-0.74] vs. 0.68 [0.65-0.72], P = 0.08) and MI alone (0.72 [0.67-0.77] vs. 0.72 [0.67-0.78], P = 0.69). CACS performed better than SIS in predicting death (0.70 [0.66-0.74] vs. 0.67 [0.63-0.70], P = 0.008). CONCLUSION: Both the extent of coronary atherosclerosis, measured by SIS, and the presence of obstructive disease are important predictors of outcomes. However, they do not provide additional prognostic value over CACS when used in routine clinical practice.