Electron Beam Computed Tomography Evaluation of the Rapid Progression of Coronary Artery Calcification in Chronic Hemodialysis Patients

patients and is the leading cause of death (1, 2). In such patients the prevalence of coronary artery disease (CAD) is 20-fold higher than in the general population (3, 4). As chronic dialysis patients are at increased risk of death from CAD (5,6), early detection and treatment of CAD may improve their survival rate. At present, coronary angiography is the gold standard for the diagnosis of CAD, but it is too invasive to be recommended for every dialysis patient. A recent study showed that non-invasive tests for CAD (such as electrocardiography, echocardiography, and dipyridamole thallium-201 scintigraphy) are of limited value in hemodialysis patients because of their low sensitivity (7). Coronary artery calcification can be evaluated non-invasively by electron beam computed tomography (EBCT). EBCT scanners offer high-speed imaging and capture a clear image of the beating heart. Serial transaxial images synchronized with the cardiac cycle at mid-diastole are obtained in 100-ms slices of 3to 6-mm thickness to detect coronary artery calcium. Thirty to forty adjacent axial scans are obtained during 1 to 2 breath-hold intervals. EBCT software permits quantification of a total calcium score by multiplying the area of calcification by a weighted density score. T h e calcified portion of atherosclerotic plaque represents a small portion of the total plaque volume, and the extent of calcification correlates closely with the total plaque burden (8). A meta-analysis of EBCT in non-dialysis patients has shown that the degree of coronary artery calcification (coronary artery calcification score, CACS) determined by E B C T has reasonable sensitivity and specificity for the diagnosis of ischemic heart disease (9). The CACS also has high predictive value for future cardiac events in nondialysis patients (10 ). The CACS is now being used increasingly in the screening of asymptomatic patients for the presence of CAD and risk of a cardiac event, as well as in symptomatic patients for diagnosis of obstructive CAD. Whether this increased use is occurring in the dialysis population is not c l e a r. Arterial calcification in uremic patients can be different from that in the general population. In the general population, intimal wall calcification occurs frequently with atherosclerosis (11). Medial wall calcification, however, is more common in chronic dialysis patients. In an autopsy s t u d y, coronary plaque in dialysis patients was characterized by increased medial thickness and marked calcification (12). A high CACS obtained by EBCT suggests the presence of arterial calcification of the intima, the media, or both. Three papers have now been published indicating that CACS in dialysis patients are high (13-15). Several correlates such as sex, duration of dialysis, serum phosphate level, daily calcium intake (13), and hypertension (14) were reported in cross-sectional studies. Braun et al evaluated 49 dialysis patients and found that the CACS in these patients was from 2.5to 5.0-fold higher than that in non-dialysis patients (13). CACS correlated with age and hypertension, but not with factors associated with calcium metabolism. Goodman et al studied 39 young dialysis patients ranging from 7 to 30 years of age. Fourteen of the 16 patients aged 20 to 30 years had a high CACS. Significant correlates with CACS were serum phosphate level, calcium-phosphorus product, and daily calcium intake (14). We examined the relation between coronary risk factors, factors associated with metabolism of calcium and other minerals, and CACS progression in 24 dialysis patients. The CACS was measured twice in each patient, with a mean interscan period of 17 months. Patients showing rapid increase in CACS had a significantly higher prevalence of dyslipidemia such as high triglyceride and low HDLcholesterol levels (15). No association was found with other traditional risk factors of atherosclerosis or indicators of disturbed calcium metabolism. Our observations support the notion that uremic lipoprotein abnormalities may be important in the acceleration of atherosclerosis in dialysis patients (16). Obviously, more data are needed to confirm our findings; and our results would need to be Editorial The International Journal of Artificial Organs / Vol. 24 / no. 12, 2001/ pp. 835-837