Carotid Plaques and Type 2 Diabetes as Predictors of Cardiovascular Events and Mortality: Insights from the LitHiR Prospective Cohort Study

Background/Objectives: Type 2 diabetes mellitus (DM) and carotid atherosclerosis are established risk factors for cardiovascular disease (CVD). However, their relative and combined prognostic significance in individuals without known CVD remains uncertain. This study aimed to evaluate the independent and combined associations of carotid plaques and DM with cardiovascular events and mortality in a high-cardiometabolic-risk primary prevention cohort. Methods: This prospective cohort study followed 6138 participants (3571 men [57%] and 2567 women [43%]; median age 53 years, IQR 48–58) enrolled in the Lithuanian High Cardiovascular Risk (LitHiR) primary prevention program from 2006 to 2023. All individuals underwent clinical assessment and carotid ultrasonography. Participants were stratified by DM status and the presence of carotid plaques. Associations with cardiovascular events, major adverse cardiovascular events (MACE, including non-fatal ischaemic stroke, non-fatal myocardial infarction, and cardiovascular death), and all-cause mortality were evaluated using Cox proportional hazards models. Results: During follow-up (median 6.5 years, IQR 4.5–9.0), 954 participants (16%) experienced composite cardiovascular events (MACE, including non-fatal ischaemic stroke, non-fatal myocardial infarction, and cardiovascular death). Bilateral carotid plaques were more common in individuals with cardiovascular events (23.3% vs. 19.4%; p = 0.007). Individuals with both DM and carotid plaques had the highest risk of MACE (HR = 1.696; 95% CI: 1.346–2.136; p < 0.001), myocardial infarction (MI; HR = 4.089; 95% CI: 1.590–10.516; p = 0.003), and all-cause mortality (HR = 1.802; p = 0.015). The presence of carotid plaques without DM was independently associated with increased risk of MACE (HR = 1.234; 95% CI: 1.062–1.433; p = 0.006) and MI (HR = 2.492; 95% CI: 1.176–5.278; p = 0.017), but not all-cause mortality (HR = 0.986; 95% CI: 0.689–1.413; p = 0.941). In contrast, DM without carotid plaques was not significantly associated with any outcome examined. Conclusions: In this high-cardiometabolic-risk primary prevention cohort, carotid plaques were independently and more strongly associated with cardiovascular outcomes than diabetes alone. Individuals with both carotid plaques and diabetes showed the highest observed risk of adverse cardiovascular events and all-cause mortality. These findings are associational and apply to a high-risk metabolic syndrome cohort; extrapolation to the general population requires further study. The results support the prognostic value of carotid plaque assessment as an adjunctive tool in cardiovascular risk evaluation.