Measurement of vascular calcification using CT fistulograms

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Abstract

Background

Vascular calcification (VC), precipitated by calcium and phosphate imbalance, is a major contributor to cardiovascular disease (CVD) in chronic kidney disease (CKD). Electron-beam computed tomography (EBCT) quantitatively assesses coronary artery calcification (CAC), with VC scores predictive of atherosclerosis and cardiac events in the general and CKD population. EBCT is not readily available but spiral CT can also provide quantitative assessment of the extent of VC. CT fistulograms can be used as initial investigation for arterio-venous fistula (AVF) problems in haemodialysis (HD). The images obtained include thoracic aorta, brachio-cephalic, subclavian and common carotid arteries which allow assessment of the extent of VC in these vessels. No study to date has combined the CT fistulogram with concurrent determination of VC.

Methods

We hypothesize that a single investigation for AVF management may also provide information on VC. We retrospectively analysed CT fistulograms on 28 HD patients determining VC scores (in Hounsfield units) in AVF, subclavian and carotid arteries and aorta. We correlated these scores with patient demographics, serum markers of mineral metabolism (time averaged for the period 6 months prior to CT) and calcium-based phosphate binders.

Results

Patients (60.7% male) had a median age of 59 years and 46.4% were diabetic. The mean duration of dialysis was 17.5 months. CT fistulograms showed predominantly aortic (75% of patients) and subclavian (75%) calcifications, with only 21.4% having carotid VC and minimal VC at the level of AVF. Median VC scores were 619.8 (0–1481.4) for aorta and 521.7 (0–1139.6) for subclavian (scores of >400 indicate severe atherosclerotic disease), but there was no significant correlation with serum markers or duration of HD. Increasing age correlated significantly with greater VC in aortic (R=0.53, P=0.003) and subclavian (R=0.40, P=0.03) vessels, as well as with the number of VC sites involved. CAC was present in most patients (89.3%) but CAC scores were not able to be determined because of cardiac movement.

Conclusion

Concurrent determination of the degree of calcification in certain vessels may be possible from CT studies assessing AVF structure. VC scores provided by CT fistulograms could contribute to HD patient CVD risk assessment but studies with larger patient numbers are required to determine their relevance.

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