Results
Coronary segments with a luminal obstruction of greater than 50% are likely to have some calcification that is detectable with electron-beam CT (EBCT). In one trial, 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 disease. In another study,[3] a calcium score greater than 371 had a 90% specificity in the detection of a luminal obstruction of greater than 70%. Specificity tends to decrease with advanced patient age, but it increases with the number of calcified vessels as well as the total calcium score.[4]
In a study in which calcium scores and thallium stress test results were compared, almost one half of the patients with scores greater than 400 had a normal thallium stress result.[5] Such testing may not be contradictory in terms of the pathophysiology; thallium detects inducible ischemia, not plaque burden.
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 early days when calcium was detected with fluoroscopy and conventional CT.
When EBCT calcium scores became available, the prognostic value of coronary calcification was again affirmed. The higher the calcium score, the worse the prognosis.[6, 7, 8] The degree of coronary calcium was a good predictor of the development of symptomatic cardiovascular disease. In a study by Agatston et al, the mean calcium score for patients with a cardiovascular event was 399, compared with a mean score of 76 in those without such an event. One study suggested that the detection of coronary calcification at EBCT was a better predictor of subsequent events than many traditional risk factors, including those evaluated in the Framingham database.[9]
Cardiac events do occur in patients with low calcium scores, but the incidence is low. Intravascular ultrasonographic studies show that as many 30% of coronary plaques are devoid of calcium. In an autopsy study,[10] the benefit of combined assessment of coronary artery calcification and risk factors (Framingham Risk Index) in predicting sudden cardiac death was apparent. In the study, 79 consecutive adults with sudden cardiac death were evaluated by using a Framingham Risk Index and histologic findings of coronary calcification. The risk classifications with the 2 techniques agreed in a majority of the patients. Patients with plaque erosion (as opposed to plaque rupture) who were dying of sudden cardiac death had significantly less coronary calcification and lower Framingham Risk Indexes.
Clearly, in establishing the cardiac risk, traditional coronary artery disease risk factors and coronary calcification may be most useful when used in combination. Whether risk stratification is further enhanced with the use of novel risk factors is yet to be determined.[6, 11, 12]
In a study in which calcium scores and thallium stress test results were compared, almost one half of the patients with scores greater than 400 had a normal thallium stress result.[5] Such testing may not be contradictory in terms of the pathophysiology; thallium detects inducible ischemia, not plaque burden.
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 early days when calcium was detected with fluoroscopy and conventional CT.
When EBCT calcium scores became available, the prognostic value of coronary calcification was again affirmed. The higher the calcium score, the worse the prognosis.[6, 7, 8] The degree of coronary calcium was a good predictor of the development of symptomatic cardiovascular disease. In a study by Agatston et al, the mean calcium score for patients with a cardiovascular event was 399, compared with a mean score of 76 in those without such an event. One study suggested that the detection of coronary calcification at EBCT was a better predictor of subsequent events than many traditional risk factors, including those evaluated in the Framingham database.[9]
Cardiac events do occur in patients with low calcium scores, but the incidence is low. Intravascular ultrasonographic studies show that as many 30% of coronary plaques are devoid of calcium. In an autopsy study,[10] the benefit of combined assessment of coronary artery calcification and risk factors (Framingham Risk Index) in predicting sudden cardiac death was apparent. In the study, 79 consecutive adults with sudden cardiac death were evaluated by using a Framingham Risk Index and histologic findings of coronary calcification. The risk classifications with the 2 techniques agreed in a majority of the patients. Patients with plaque erosion (as opposed to plaque rupture) who were dying of sudden cardiac death had significantly less coronary calcification and lower Framingham Risk Indexes.
Clearly, in establishing the cardiac risk, traditional coronary artery disease risk factors and coronary calcification may be most useful when used in combination. Whether risk stratification is further enhanced with the use of novel risk factors is yet to be determined.[6, 11, 12]
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