Elsevier

Atherosclerosis

Volume 238, Issue 1, January 2015, Pages 126-131
Atherosclerosis

Improving the relationship between coronary artery calcium score and coronary plaque burden: Addition of regional measures of coronary artery calcium distribution

https://doi.org/10.1016/j.atherosclerosis.2014.11.008Get rights and content

Highlights

  • The Agatston coronary artery calcium (CAC) score predicts cardiovascular events.

  • Measuring regional CAC distribution may improve atherosclerosis prediction.

  • We compared the addition of regional CAC to Agatston score on coronary CT.

  • Addition of regional CAC improves association of Agatston score with plaque burden.

Abstract

Background: The Agatston coronary artery calcium (CAC) score predicts cardiovascular events through its association with overall burden of coronary atherosclerosis. It is unclear whether adding regional measures of CAC distribution to the Agatston score improves this association. Methods: We studied 920 consecutive patients (mean age 57 ± 12, 53% female), referred for 64-slice Coronary CT angiography (CCTA) who had concomitant CAC scoring. Total atherosclerosis burden was quantified as the segment involvement score (SIS), which describes the number of coronary segments with plaque on CCTA. We studied the heterogeneity between CAC group (0, 1–100, 101–400, >400) and the number of vessels with CAC (0–4), and related this to SIS on CCTA. In patients with multi-vessel disease, we examined the relationship of concentrated vs. diffuse CAC (> or ≤75% total CAC in one vessel) with SIS. Results: When CAC was intermediate (1–400), considerable heterogeneity was noted between CAC group and the number of vessels with CAC (CAC 1–100: 53% 1-vessel, 29% 2-vessel, 16% 3-vessel, 2% 4-vessel; CAC 101–400: 9% 1-vessel, 28% 2-vessel, 43% 3-vessel, 20% 4-vessel). Within each CAC group, increase in the number of vessels with CAC was significantly associated with increased SIS. In multi-vessel disease, a higher SIS was associated with diffuse versus concentrated CAC (CAC 1–100: 3.8 vs. 2.8, CAC 101–400: 5.5 vs. 4.3 [both p < 0.01]). These associations persisted after adjustment for age, gender, and the absolute Agatston CAC score (p < 0.01). Conclusion: Addition of measures of regional CAC distribution improves the association of the Agatston CAC score with total plaque burden.

Introduction

Coronary artery calcium (CAC) scoring has established utility in refining cardiovascular risk stratification among intermediate-risk patients [1] and in those in whom treatment decisions are uncertain [2]. This is thought to be the result of the strong association between the presence of CAC and the overall burden of coronary atherosclerosis [3], inclusive of non-calcified, mixed calcified and fully calcified coronary plaque.

Agatston et al. [4] developed the most commonly used method for calculating the burden of CAC in the late 1980s. The Agatston score involves multiplying the area of each individual calcified plaque by a factor derived from the maximal plaque density (CT attenuation) in Hounsfield Units, and then adding the values obtained for all coronary plaques identified. The Agatston CAC score is thus an aggregate score and does not account for the regional distribution of CAC. In addition, this method disproportionally weights increased coronary plaque density, meaning that heavily calcified plaque contributes more to the score than less calcified “mixed” plaque. Recent research has demonstrated that cardiovascular events may in fact be inversely related to plaque density, and probably more closely linked to total coronary plaque volume [5].

Characterizing the regional distribution of CAC may be important for two reasons. First, patients with more diffuse coronary artery disease (CAD) have worse cardiovascular outcomes when compared to patients with more focal CAD [6]. The PROSPECT study [7] demonstrated the importance of total plaque burden in predicting cardiovascular events, while a sub-study of the COURAGE trial noted the superiority of coronary plaque burden over ischemic burden in predicting the risk of myocardial infarction [8]. Furthermore, while highly dense local plaque may correlate with local coronary artery stenosis severity, focusing on coronary stenosis has the inherent potential to underestimate coronary plaque burden [9], due to the outward remodeling of coronary plaque, as originally described by Glagov et al. [10].

Whether accounting for regional CAC distribution improves the association of the Agatston CAC score with overall coronary atherosclerotic plaque burden has not been rigorously evaluated. We studied whether the addition of measures of increasingly diffuse CAC distribution improves the association of CAC scoring with overall coronary atherosclerotic plaque burden on concomitant coronary CT angiography (CCTA).

Section snippets

Study population

A total of 920 consecutive patients (93% symptomatic) who underwent multi-detector CT coronary angiography (CCTA) between January 2006 and December 2009 were included in this study. This is a cross-sectional study, the details of which have been previously published [11]. The institutional review board at the study institution approved the study, and patients' informed consent requirement was waived. Exclusion criteria were known CAD, iodine allergy, and chronic kidney disease (creatinine

Results

The mean age of the study population was 57 ± 12 years old, and 53% were female. The ethnic composition was 58% White, and 34% African American. A total of 93% were symptomatic, with 80% presenting with chest pain and 36% identifying dyspnea. There was a high prevalence of cardiovascular risk factors (Table 1, hypertension: 73%, diabetes mellitus 20%, hyperlipidemia 66%, smoking 17%, positive family history of premature CAD 33%). Of those who had prior stress testing performed (n = 421), 69%

Discussion

In this analysis of the regional distribution of CAC in relation to total atherosclerosis burden on CCTA, we demonstrated that while the Agatston CAC score is associated with total coronary plaque burden, measures of increasingly diffuse CAC distribution further stratify patients with an increased SIS, increasing the correlation of the Agatston CAC score with SIS on CCTA. The ability to improve the Agatston CAC score by adding measures of regional CAC distribution is inherent in the way the

Limitations

Our dataset did not allow a definition of total coronary plaque burden on CCTA defined by the volumetric analysis of plaque burden. While highly correlated with SIS, assessment of total plaque volume has been demonstrated to be a superior method of determining coronary atherosclerotic burden, and has a higher predictive value for acute coronary syndrome compared to luminal stenosis and Agatston CAC scoring [21]. Data on cardiovascular outcomes for this dataset is also not available to

Conclusion

Addition of regional measures of CAC, including the number of coronary arteries with CAC and a measure of concentrated versus diffuse CAC, provide a more accurate description of overall plaque burden than the absolute Agatston CAC score alone. Within the intermediate CAC score groups (1–100, 101–400), the number of CAC-positive coronary arteries improves the association with the overall coronary plaque burden on CCTA. Future studies are needed focusing on the prognostic importance of new

Author disclosures

None.

References (22)

  • M.H. Criqui et al.

    Calcium density of coronary artery plaque and risk of incident cardiovascular events

    JAMA

    (2014)
  • Cited by (34)

    • Coronary Artery Calcium Volume and Density: Potential Interactions and Overall Predictive Value: The Multi-Ethnic Study of Atherosclerosis

      2017, JACC: Cardiovascular Imaging
      Citation Excerpt :

      Additionally, the density score used here is only the average density for each participant, and range of density scores may also be important to consider. Another limitation is that traditional CAC scoring does not account for the location (proximal vs. distal, focal vs. diffuse) or dispersion of the density, which may also affect the risk for cardiovascular events (18–20). The inverse association of CAC density with incident CHD and CVD events is consistent across all levels of CAC volume, and across multiple strata of other risk variables.

    View all citing articles on Scopus
    View full text