Rationale and Objectives
In the Calcium Acetate Renagel Evaluation (CARE)-2 study, the effects of calcium acetate plus atorvastatin (Lipitor) on the progression of coronary artery calcifications (CACs) are evaluated versus those of Renagel, monitored using dual electron beam tomography (EBT) scans (two scans at study initiation and two at follow up). The aim of this study is to estimate the interscan variation for the Agatston score and for the volume score determined in patients with end-stage renal disease (ESRD) in the CARE-2 study.
Materials and Methods
CAC score and volume were measured at study initiation in 463 ESRD subjects (mean age: 59.4 ± 12.5 years, 48.3% female). All patients underwent dual scanning using an EBT, as first scan of two needed to measure the progression of CAC when treated with sevelamer (Renagel) compared with calcium acetate with or without atorvastatin. All scans in all participants were completed by using an EBT system (GE Imatron, South San Francisco, CA). Interscan variability was defined by the following formula: abs (scan A − scan B) ÷ (0.5 × scan A + 0.5 × scan B) × 100%, where A and B denote the first and second scan, respectively, of the dual scan procedure performed before treatment. We evaluated the reproducibility of the cutpoints commonly used for calcium scores clinically, namely 1–30, 31–100, 101–400, and >400.
Results
The CAC interscan variability was 11.8% using the Agatston score and 10.3% using the volume score. The reproducibility was then assessed using cutpoints 1–30, 31–100, 101–400, and >400. Agatston score variability for the four subgroups was 61.3%, 23%, 16.1%, and 8.2%, respectively (mean variability, 11.8%). Volume score variability was 60.0%, 14.4%, 14.6%, and 7.7%, respectively (mean variability, 10.3%). The correlation coefficient for scan A to scan B goes up significantly with increasing calcium scores and reaches 0.99 for scores greater than 400 ( P < .0001).
Conclusion
Interscan variability was sufficiently small for patients with calcium scores greater than 30. Our study thus demonstrates a sufficient reproducibility of the calcium score using EBT. This score allows for accurate serial assessment of these patients and for comparing different therapies.
Coronary artery calcium (CAC) assessment for diagnosis of atherosclerosis and obstructive disease as well as risk stratification for future cardiac events has undergone significant validation over the past 20 years ( ). An important limitation is, however, the significant interscan variation (ISV), especially in patients with lower calcium scores, which can limit longitudinal studies with this modality ( ). But the mean scores of patients with end-stage renal disease (ESRD) are quite high, so that ISV should be lower among this population, allowing for serial evaluation. We evaluated the ISV of the 524 persons who underwent dual scanning at the origin of the Calcium Acetate Renagel Evaluation – 2 (CARE-2) study.
Methods
Population
The CARE-2 study is a prospective, multicenter, randomized clinical trial comparing the effects of calcium acetate plus atorvastatin (Lipitor) versus sevelamer HCl (Renagel) with or without atorvastatin on progression of CAC in patients with ESRD. Randomized patients met the inclusion criteria for serum phosphorus (P) > 5.5 mg/dl, LDL level > 80 mg/dL, and EBT-measured CAC score of 30 to 7000 (average score of dual study initiation scans). A total of 524 patients were screened for the CARE-2 study and 463 cases with positive calcium scores on both scans were included in our analysis. The mean age of the participants (48.3% female) was 59.4 ± 12.5 years.
Coronary Calcium Imaging Procedure
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Statistical Analysis
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Results
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Table 1
Profile of Interscan Variability and R Values of Four Groups in Agatston and Volume Scores
Groups No.R Value Interscan Variability By Score Agatston Score Volume Score Agatston Score Volume Score Group 1 Scores 1–30 33 .75 .88 61.3 ± 67.6 60.0 ± 65.0 Group 2 Scores 31–100 40 .65 .79 23.0 ± 19.2 14.4 ± 21.8 Group 3 Scores 101–400 127 .81 .85 16.1 ± 18.5 14.6 ± 16.6 Group 4 Scores >400 263 .99 .99 8.2 ± 10.4 7.7 ± 9.1 Mean 463 11.8 ± 21.2 10.3 ± 19.0
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Discussion
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