Autopsy studies have shown that there is a close link between coronary artery calcification and the extent of vascular stenosis with a subsequent risk of myocardial infarction. A variety of imaging modalities has been used for detecting coronary artery calcifications of which, plain chest radiography and fluoroscopy have the lowest sensitivity. CT imaging is superior to fluoroscopy for detecting coronary calcifications1
Ultrafast CT has high-resolution contrast, a rapid image acquisition, and allows elimination of image blurring caused by heart movement. Due to these features, ultrafast CT has a high sensitivity for detecting calcium in the coronary arteries3. In different series, the sensitivity and specificity of the examination ranged from 88 to 100% and 43 to 100%, respectively2,4,5.
Arterial calcification occurs in the intima of the blood vessels, as a part of atherosclerosis. In general population, coronary artery calcification correlates with the atherosclerotic plaque burden and with coronary vessel stenosis, and has consistently been shown to be predictive for future cardiac events6-9.
Coronary segments with a luminal obstruction greater than 50% are likely to have some calcification that is detectable with electron-beam CT. In a trial, it was shown that, a 0 calcium score had a 100% predictive value in the exclusion of angiographic evidence of obstructive epicardial coronary lesions. The higher the calcium score, the more likely the presence of angiographic obstructive disease10.
Results of autopsy studies indicate that coronary artery calcification is invariably associated with the presence of atherosclerotic plaque11. In a previous study performed with 450 consecutive patients, Callaway et al found atherosclerotic plaques in 26% of male and 15.6% of female scans. The incidence increased to 48% from 41.6% when they have determined a threshold of 40 years for age12.
Coronary calcification is strongly associated with the prognosis. Indeed, the extent of coronary atherosclerosis (total calcium score) is the most powerful predictor of subsequent or recurrent cardiac events. This was true in the former years when calcium was detected with fluoroscopy and conventional CT13.
Janowitz et al., analyzed the evolution of the amount of calcium in atherosclerotic plaques by ultrafast CT in patients with and without coronary artery disease3. Ninety-eight percent of the calcium deposits identified on the initial examination were confirmed in consequent imagings, and there was a significant increase in the calcification volume and in the total calcified area of the atherosclerotic plaque in the evolution. Patients with coronary artery disease have a large amount of new calcium deposits, which are not found in asymptomatic patients. In patients with no evidence of calcification, both in the first approach and later, the prevalence of ischemic heart disease is extremely low.
In a study searching the presumptive detection of coronary stenosis on the basis of existing calcification by means of CT, higher sensitivities have been found in the calcified arteries (78% for LAD, 63% for the circumflex and 16% for RCA). Specificities were 78%, 80% and 100%, and positive predictive values (PPV) were 88%, 83% and 100%, respectively. The high PPV suggested that significant coronary artery disease was likely to be present when coronary calcification was seen on CT14. In a study performed by Shirazi et al,, of the total 100 patients (62 males), 69 had coronary artery obstruction (>50% stenosis was detected by angiography). Angiography was normal in the rest. For the diagnosis of coronary artery disease, a spiral CT scan had a sensitivity of 94% and a specificity of 61%. PPV and negative predictive value (NPV) were 84% and 79%, respectively1.
In their series performed with double-helix CT, Shemesh et al., stated that calcification was significantly more prevalant in patients with coronary artery obstructive disease (>83%) than in patients with normal coronary arteries (27%) or in healthy control subjects (34%, p<0.1). The researchers found a high sensitivity (91%), however, the specificity was low (52%) due to calcification in non-obstructive lesions15. When CT and angiographic findings were compared, CT was found to have 84% accuracy with PPV and NPVof 89% and 59%, respectively15.
In contrast, some investigators claim that the technique is useless16. Detrano et al., in their series performed with 1196 asymptomatic high-coronary-risk subjects that underwent risk-factor assessment and cardiac CT, showed that CT calcium score did not add significant incremental information to risk factors in clinical screening. The researchers claimed that neither risk-factor assessment nor the calcium detected with CT was an accurate event predictor in high-risk asymptomatic adults16.
Our study had some limitations. Our sample size was small and a relatively old CT technology was used. Moreover, there was no gold standard angiographic demonstration of stenotic effects of the calcium deposits.
In conclusion, coronary calcifications were easily discernible with CT. Our study showed that calcified deposits were more frequently encountered with increasing age and male gender. In addition, to the increased association of coronary calcification with the male gender, a relationship to diabetes mellitus, hypercholesterolemia and cardiomegaly was detected.
There was no financial support for this study.