Introduction and objectives: The association between apolipoprotein B (apoB) and residual cardiovascular (CV) risk in patients with chronic coronary syndrome (CCS) remains unclear. We aimed to investigate the association between apoB levels and CV outcomes in statin-treated CCS patients.

Methods: We enrolled 8641 statin-treated CCS patients at Fuwai Hospital. The patients were divided into 5 groups based on to apoB quintiles (Q1 to Q5). The primary endpoint was 3-year CV events, including CV death, nonfatal myocardial infarction, and nonfatal stroke.

Results: During a median follow-up of 3.17 years, there were 232 (2.7%) CV events. After multivariable adjustment, a restricted cubic spline illustrated a J-shaped relationship between apoB levels and 3-year CV events, with the risk remaining flat until apoB levels exceeded 0.73 g/L, after which the risk increased (nonlinear P < .05). Kaplan-Meier curves showed the lowest CV event rate in the Q3 group (0.68-0.78 g/L). Compared with the Q3 group, multivariable Cox regression models revealed that both low (Q1, ≤ 0.57 g/L) and high (Q5, > 0.93 g/L) apoB levels were associated with an increased risk of major adverse cardiac events (all P < .05). Notably, patients with low apoB levels (Q1) had the highest risk of CV death (HR, 2.44; 95%CI, 1.17-5.08).

Conclusions: Our analysis indicates that both low and high levels of apoB are associated with elevated CV risk, with the risk being particularly pronounced at higher levels (> 0.73 g/L).