Impact of Age and Sex on Subclinical Coronary Atherosclerosis in a Healthy Asian Population

Background The influence of age and sex on clinical atherosclerotic cardiovascular disease is well reported, but literature remains sparse on whether these extend to the disease in its preclinical stage. Objectives The purpose of this study was to report the prevalence, risk factors, and impact of age and sex on the burden of subclinical coronary atherosclerosis in a healthy Asian population. Methods Healthy subjects age 30 to 69 years, with no history of cardiovascular disease or diabetes were recruited from the general population. Subclinical coronary atherosclerosis was quantified via the coronary artery calcium score (CAC) with CAC of 0 indicating absence of calcified plaque, 1 to 10 minimal plaque, 11 to 100 mild plaque, and >100 moderate to severe plaque. Results A total of 663 individuals (mean age 49.4 ± 9.2 years; 44.8% men) were included. The prevalence of any CAC was 29.3%, with 9% having CAC >100. The prevalence was significantly higher in men than women (43.1% vs 18.0%; P < 0.001). Multivariable analysis revealed significant associations of increasing age, male sex, higher blood pressure, increased glucose levels, and higher low-density lipoprotein cholesterol levels with the presence of any CAC. Low-density lipoprotein cholesterol was more significantly associated with CAC in women compared with men (Pinteraction = 0.022). Conclusions The prevalence of preclinical atherosclerosis increased with age, and was higher in men, with sex-specific differences in associated risk factors. These results will better inform individualized future risk management strategies to prevent the development and progression of coronary artery disease within healthy individuals.

A therosclerosis is a long, complex process that involves the gradual accumulation of fat, inflammation, scar tissue, and calcium deposits within the walls of arteries (1). Due to the long latent period of atherosclerosis and its initial development during early life (1,2), increasing focus has now been placed on the primordial prevention of atherogenic risk factors, and the identification and possible intervention of this process at its preclinical phase (3).
The influence of age and sex on patterns of coronary artery disease (CAD) is well reported in literature, with epidemiological, clinical, and experimental data providing evidence for sex-specific differences in the development, prevalence, presentation, and progression of CAD (4)(5)(6)(7). In addition, the prevention and treatment outcomes of CAD differ across age and sex (8,9). What is less understood however, is whether-and to what extent-these age and sex differences extend to the extent of coronary atherosclerosis at its preclinical phase. This holds important implications for screening and preventative strategies designed toward the early evaluation and risk assessment of CAD in asymptomatic individuals.
Coronary artery calcium (CAC) is a highly specific and well-established subclinical marker of coronary atherosclerosis, with consistent evidence linking CAC with major cardiovascular outcomes (10)(11)(12)(13)(14)(15). In our present study, we use the CAC score to quantify the extent of preclinical coronary atherosclerosis, and report on the baseline prevalence, associated risk factors, and influence of age and sex on the extent of the preclinical atherosclerotic burden within a healthy Asian population without known cardiovascular disease. We also evaluate the potential utility of the CAC score as a risk enhancing factor in this asymptomatic Asian population.

METHODS STUDY POPULATION.
SingHEART is a prospective population-based study of healthy Asian adults living in Singapore. The full details have previously been published (16,17). In summary, the SingHEART study aims to evaluate the development of cardiovascular disease among asymptomatic healthy individuals (16). Healthy subjects age 21 to 69 years were recruited from the general population from October 2015 to July 2020 and were enrolled according to approved standardized protocol. Inclusion criteria were as follows:  (14,19).

CARDIOVASCULAR RISK
CLASSIFICATION. The MESA (Multi-Ethnic Study of Atherosclerosis) coronary heart disease (CHD) risk score was used to classify participants by cardiovascular risk. The MESA CHD risk score is an algorithm that incorporates various atherosclerotic risk factors to predict the 10- year risk of CHD (20,21). The score comprises of 2 models, one largely relying on the traditional Framingham risk variables, and another model that additionally incorporates subclinical atherosclerotic risk as measured by the CAC score. The MESA risk scores for all participants were generated both with and without the incorporation of CAC scores.
Participants with higher CAC scores were likely to have higher 10-year CHD risk scores (Fisher's exact P < 0.001). In particular, 16.7% of participants with CAC >100 had 10-year CHD risk scores of $5%, in comparison to just 1.5% of participants with CAC ¼ 0 (P < 0.001) (Supplemental Table 1). After the incorporation of CAC scores, there was a significant increase in the mean AE SD 10-year CHD risk scores of our population from 1.78 AE 0.01% to 2.20 AE 0.01% (P < 0.001). Furthermore, we observed significant reclassification of individual risk, with 35 individuals (5.56%) reclassified from a "low" to an "elevated" risk of CHD (P < 0.001) (Supplemental Table 2).

DISCUSSION
In this cross-sectional study of 663 healthy individuals, the overall prevalence of preclinical coronary atherosclerosis (as measured by CAC) was 29.3%, with 9.0% having moderate-severe degrees of CAC. The prevalence of coronary atherosclerosis was higher in men than women, and increased with age, both overall and within each sex. We also observed sex-specific differences in the associations of LDL  all also reported similar prevalence values to ours. We also observed a higher burden of preclinical atherosclerosis in men compared with women, and with the It should be noted, however, that atherogenesis is a complex process, and sex-specific differences in atherogenic risk factors extend past differences in lipid profiles alone and may also include differences in systemic and vascular inflammatory profiles (8,42,43). Evidence also indicates that sex hormones (and the lack thereof postmenopause) have a role in modulating the immune response, resulting in different atherosclerotic phenotypes across sexes (6,44,45). However, literature specifically examining sex differences in the role of inflammatory mechanisms, mediators, and markers during the atherogenic process remain sparse (44). Regardless of these potential sex differences in proatherogenic inflammatory and lipid profiles, firm evidence exists for the role of lipid-lowering statins, which are also known to have anti-inflammatory effects, in the primary prevention of future cardiovascular events (46).
We also observed significant reclassifications in the cardiovascular risk of asymptomatic individuals upon incorporation of the CAC score. A total of 35 individuals (5.56%) within our population were reclassified from a "low" to an "elevated" risk of CHD.  Abbreviations as in Table 2. of CAC scores to prediction models significantly improved the classification of risk, and placed more individuals in higher-risk categories (21,47). The CAC score has potential utility in improving the risk stratification for CAD in asymptomatic healthy Asian populations, and this will be the work of further research.
STUDY LIMITATIONS. Limitations of our study include the cross-sectional nature of our study. The CAC score is a surrogate marker of subclinical atherosclerotic disease, and further research on actual clinical outcomes is required. As part of the SingHEART study, these patients are currently being followed up for long-term clinical events, and these clinical outcomes will subsequently be reported.
There is also a potential for bias, as these participants were volunteers recruited from the general population; such individuals might have a higher regard for their health and potentially have more favorable health-related lifestyle choices. It should also be noted that the interpretation of CAC scores may be complicated by variations across sex and ethnic groups (10). We acknowledge that the lower prevalence of moderate-severe CAC (CAC >100) within women may not necessarily translate to a lower risk of CAD in such individuals, as age-sex specific percentiles, rather than the traditional absolute thresholds may be more important in translating CAC to cardiovascular risk (48,49).

CONCLUSIONS
In this healthy asymptomatic population, preclinical coronary atherosclerosis was present in about 3 of 10 subjects. This prevalence increased with age, and was higher in men than women, with sex-specific differences in associated risk factors. The potential utility of the CAC score in CAD risk stratification was also highlighted. These results will better enable the optimization of age and sex-specific risk management strategies to prevent the development and progression of clinical CAD in healthy individuals.

FUNDING SUPPORT AND AUTHOR DISCLOSURES
The Lee Foundation provided grant support for the SingHeart study conducted at National Heart Centre Singapore. This work was also supported by core funding from SingHealth and Duke NUS through their institute of Precision Medicine (PRISM) and by a center grant awarded to National Heart Centre Singapore from the National atherosclerosis is present in about 3 of 10 subjects. The prevalence of preclinical coronary atherosclerosis in asymptomatic Asian individuals increases with age, is higher in men than women, and is subject to sex-specific differences in associated risk factors.

COMPETENCY IN PATIENT CARE AND PROCEDURAL
OUTCOMES: The CAC score has the potential to improve the risk stratification for CAD in asymptomatic healthy Asian populations.