Association of Muscle Radiodensity and Muscle Mass With Thoracic Aortic Calcification Progression in Dialysis Patients

Abstract

Background: Recent findings have spotlighted sarcopenia as a critical factor exacerbating cardiovascular risk in dialysis patients. However, no studies have investigated the relationship of muscle characteristics with thoracic aortic calcification (TAC). We explored whether skeletal muscle radiodensity (SMD) and skeletal muscle index (SMI) are associated with TAC in dialysis patients.

Methods: In this study, 2517 dialysis patients (between January 2020 and June 2023) from four centres with chest computed tomography (CT) scans were analysed cross-sectionally. A cohort of 544 initial-dialysis patients (between January 2014 and December 2020) was followed for TAC progression. Chest CT images were used to assess SMD and SMI at the L1 level, as well as to measure the scores of TAC, including ascending TAC (ATAC), aortic arch calcification (AoAC) and descending TAC (DTAC). Multivariable linear regression models were employed to assess the effects of SMD and SMI on TAC and its progression. Restricted cubic spline was used to assess the potential non-linear relationships of SMD and SMI with TAC progression.

Results: The mean (SD) age for the cross-sectional study was 54.8 (14.0) years, with males accounting for 58.2%. Over a mean (SD) follow-up duration of 3.45 (1.82) years, 85.7% showed TAC progression. Comparing the highest quartile of SMD to the lowest quartile, a significant inverse association was observed with TAC (β, -1.08 [-1.42 to -0.75]; p < 0.001); similar trends were noted for SMI (β, -0.42 [-0.74 to -0.10]; p = 0.011). SMD and SMI as continuous variables were also both significantly negatively correlated with TAC. In the longitudinal study, multivariable linear regression models revealed that an increase of 1 SD in SMD resulted in a decrease of 0.10 SD (95% CI, -0.17 to -0.02; p = 0.011) in TAC progression, and an increase of 1 SD in SMI resulted in a decrease of 0.12 SD (95% CI, -0.20 to -0.04; p = 0.003) in TAC progression. Restricted cubic spline models excluded non-linear trends for the relationships of SMD and SMI with TAC progression. The associations of SMD and SMI with DTAC were consistent with those observed for TAC, but neither showed a significant association with ATAC.

Conclusions: Higher SMD and higher SMI were significantly associated with lower TAC and its progression in dialysis patients. Improving SMD and SMI could be a new approach for reducing TAC.

Keywords: cardiovascular diseases; computed tomography; dialysis; skeletal muscle index; skeletal muscle radiodensity; thoracic aortic calcification.

FIGURE 1

Correlation of SMD and SMI with TAC in dialysis patients. SMD and SMI exhibited significant inverse correlations with log (TAC + 1), as depicted in Graphs (A) and (B), respectively. The correlation with SMD was notably stronger, as indicated by a higher R ² value. The blue dashed line represents the threshold for significant TAC, defined at a log (TAC + 1) value of 4.42, while the red dashed line indicates the corresponding SMI or SMD value at this threshold. TAC indicates thoracic aortic calcification; SMD, skeletal muscle radiodensity; SMI, skeletal muscle index.

FIGURE 2

Illustrating the relationship between SMI, SMD and TAC with visual examples in CT imaging. An axial noncontrast composite CT image at the L1 level illustrates the segmentation of muscle (in red), and TAC can be evaluated by CT (in purple) within the same scan. Scale bars are shown in each panel, each measuring 10 cm, to provide a clear visual reference for the dimensions of the anatomical structures displayed in the CT images. (A) Body composition values in a 69‐year‐old man who underwent chest CT in 2022. Patient body composition values: L1 SMI = 29.3 cm²/m², L1 SMD = 17.6 HU and (B) TAC = 14024.9 mm³. (C) Body composition values in another 69‐year‐old man who underwent chest CT in 2021, L1 SMI = 50.9 cm²/m², L1 SMD = 39.0 HU and (D) TAC = 0.2 mm³. TAC indicates thoracic aortic calcification; ATAC, ascending thoracic aortic calcification; AoAC, aortic arch calcification; DTAC, descending thoracic aortic calcification; SMI, skeletal muscle index; SMD, skeletal muscle radiodensity.

FIGURE 3

Restricted cubic splines analysis of SMD and SMI on TAC progression. Regression coefficients (β) of TAC progression with SMD (A) and SMI (B) depicted in fully adjusted models. These coefficients were derived after adjusting for age, sex, SMI (SMD model), SMD (SMI model), BMI, smoking history, history of hypertension, history of diabetes, log WBC, log (TG + 1), LDL cholesterol, log iPTH, serum phosphate, corrected serum calcium, vitamin D use and log (baseline TAC + 1). The shaded area represents the 95% confidence interval. SMD indicates skeletal muscle radiodensity; SMI, skeletal muscle index; TAC, thoracic aortic calcification; BMI, body mass index; WBC, white blood cell count; TG, triglycerides; LDL, low‐density lipoprotein; iPTH, intact parathyroid hormone.

FIGURE 4

Subgroup analyses of the association between SMD/SMI and TAC. Estimated from multivariable linear regression. The multivariable model was adjusted for age, sex, SMI (SMD model), SMD (SMI model), BMI, smoking history, history of hypertension, history of diabetes, log WBC, log (TG + 1), LDL cholesterol, log iPTH, serum phosphate, corrected serum calcium, vitamin D use and log (baseline TAC + 1). All β are standardized coefficients. SMD indicates skeletal muscle radiodensity; SMI, skeletal muscle index; TAC, thoracic aortic calcification; CI, confidence interval; BMI, body mass index; WBC, white blood cell count; TG, triglycerides; LDL, low‐density lipoprotein; iPTH, intact parathyroid hormone.