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Asymptomatic patients Numerous cohort studies have shown that the presence of coronary calcium demonstrated by EBCT in asymptomatic individuals is a prognostic parameter regarding the development of cardiac events (e.g., coronary death, nonfatal MI, the need for revascularization procedures).
A meta-analysis including 6 cohort studies published between 2003 and 2005 in 27622 patients (n=395 CHD death or MI) found that the 3 to 5 year risk of any detectable calcium elevates a patient's CHD risk of events by nearly 4-fold. The analysis also found that patients without detectable calcium have a very low rate of CAD death or MI (0.4%) over 3 to 5 years of observation (n = 49 events/11 815 individuals). (Greenland, 2007) The Heinz Nixdorf Recall study (HNR) is currently in progress in Germany. This study recruited a total of 4814 participants aged 45-74 years. (Schmermund et al., 2006) Detrano et al., as part of the MESA trial, studied 6741 asymptomatic participants. CAC was measured by using duplicate CT scans. Results showed a total of 3355 participants; 49.8% had calcium (Agatston score 0) detected on at least one of the two scans. Overall agreement between scans was high (95.9%). The authors stated that CT coronary calcium assessments can be performed with equivalent reproducibility using either EBCT or MDCT. Detrano et al. noted that for both types of scanners, volume-based coronary calcium measurements result in only minimally improved rescan reproducibility ( 2% difference) compared with that of Agatston score. (Detrano, 2005) LaMonte et al. followed 10746 adults for 3.5 years (Copper Clinic Study). There were 81 hard events (i.e., coronary heart disease death, nonfatal MI) and 287 total events (i.e., hard events plus coronary revascularization) that occurred. Ageadjusted rates (per 1,000 person-years) of hard events were computed according to four CAC categories: no detectable CAC and incremental sex-specific thirds of detectable CAC; these rates were, respectively, 0.4, 1.5, 4.8, and 8.7 for men and 0.7, 2.3, 3.1, and 6.3 for women. CAC levels also were positively associated with rates of total CHD events for women and men. The association between CAC and CHD events remained significant after adjustment for CHD risk factors. CAC was associated with CHD events in persons with no baseline CHD risk factors and in younger (aged 65 years) study participants. (LaMonte, 2005) Pletcher et al. performed a meta-analysis of four of the early cohort studies and found that the risk of major CHD events increased 2.1-fold and 10-fold for scores ranging from 1 to 100 and 400, respectively, as compared with scores of 0.
Cardiac Computed Tomography (CT), Coronary Artery Calcium Scoring and Cardiac CT Angiography - Commercial Medical Management Guideline This relationship has been established when predicting all-cause mortality, cardiovascular events, CHD death or nonfatal MI, and overall CHD events. (Pletcher, 2004) In a prospective, observational population-based study of 1461 asymptomatic adults with coronary risk factors, Greenland et al. reported that a high CAC score was predictive of high risk among patients with an intermediate-high FRS greater than 10% (p less than 0.001) but not in patients with a low risk FRS (i.e., score less than 10%). (Greenland, 2004) Based on data collected as part of the Prospective Army Coronary Calcium (PACC) study, O'Malley, et al. focused on the efficacy of using EBCT as a motivational tool to influence asymptomatic individuals to change behavior and modify cardiovascular risk factors. The results of the randomized controlled trial that involved 450 active-duty Army personnel found that the use of coronary calcification screening was not associated with improvement in cardiovascular risk factors at 1 year. (O'Malley, 2003) Symptomatic patients The utility of coronary artery calcium measurement in symptomatic patients has been widely studied as a noninvasive diagnostic technique for detecting obstructive CAD.
To define CAC test characteristics and compare it with other noninvasive tests, a meta-analysis was performed and published in the 2000 ACC/AHA consensus statement. Patients were included if they had no prior history of CAD or cardiac transplantation. A total of 3683 patients were considered among 16 studies evaluating the diagnostic accuracy of CAC measurement. On average, significant coronary disease (greater than 50% or greater than 70% stenosis by coronary angiography) was reported in 57.2% of the patients. Presence of CAC was reported on average in 65.8% of patients (defined as a score greater than 0 in all but one report). All of the studies evaluated the sensitivity and specificity of electron beam CT (EBCT) to predict CAD. Sensitivities ranged from 68%-100% and specificities ranged from 21%The pooled statistics revealed a 91% sensitivity and a 49% specificity. The authors concluded that, in a symptomatic population, EBCT was associated with a high sensitivity for CAD, a much lower specificity, and an overall predictive accuracy of approximately 70% in a typical CAD patient population. (O'Rouke et al., 2000) Knez et al. evaluated 2115 consecutive symptomatic patients with no prior diagnosis of CAD. These patients were being referred to the cardiac catheterization laboratory for diagnosis of possible obstructive coronary artery disease, without knowledge of the CAC scan results. The scan result did not influence the decision to perform angiography. Overall sensitivity was 99%, and specificity was 28% for the presence of any coronary calcium being predictive of obstructive angiographic disease. With volume calcium score greater than 100, the sensitivity to predict significant stenoses on angiography decreased to 87% and the specificity increased to 79%. (Knez, 2004).
Large, multi-center studies have been reported using fast CT for diagnosis of obstructive CAD in symptomatic persons (n = 1851), who underwent coronary angiography for clinical indications. The overall sensitivity was 95%, and specificity was 66% for coronary calcium score to predict obstructive disease on invasive angiography. Increasing the cut-point for calcification markedly improved the specificity, but decreased the sensitivity. In the same study, increasing the CAC cutpoint to greater than 80 decreased the sensitivity to 79% while increasing the specificity to 72%. (Budoff, 2002) In another large study (n = 1764) comparing CAC to angiographic coronary obstructive disease, use of a CAC score greater than 100 resulted in a sensitivity of 95% and a specificity of 79% for the detection of significant obstructive disease by angiography (Haberl, 2001).
Noncalcified plaque (NCP) There is growing interest concerning the ability of contrast-enhanced CT coronary angiography to detect (and possibly to quantify and to further characterize) non-calcified coronary atherosclerotic plaque. Data on the accuracy of CT Cardiac Computed Tomography (CT), Coronary Artery Calcium Scoring and Cardiac CT Angiography - Commercial Medical Management Guideline angiography to detect non-calcified plaque are limited to a small number of studies that have compared CT angiography with intravascular ultrasound (IVUS). The fact that there is currently a lack of prospective clinical data that would support the use of contrast-enhanced CT angiography for the assessment of non-stenotic plaque does not allow clinical applications in asymptomatic individuals for the purpose of risk stratification. However, the tremendous potential of CT angiography for visualization and characterization of coronary plaques must be recognized and further research is strongly supported. (Schroeder, 2008) Professional Societies/Government Organizations American College of Cardiology (ACC)/American Heart Association (AHA) In a 2007 consensus document, the ACC and the AHA, in collaboration with the Society of Atherosclerosis Imaging and Prevention (SAIP) and the Society of Cardiovascular Computed Tomography (SCCT), made the following clinical
recommendations on coronary artery calcium (CAC) scoring:
1. It may be reasonable to consider the use of CAC measurement in asymptomatic patients with intermediate CHD risk (between 10% and 20% 10-year risk of estimated coronary events) based on the available evidence that demonstrates incremental risk prediction information in this patient group. This conclusion is based on the possibility that such patients might be reclassified to a higher risk status based on high CAC score, and subsequent patient management may be modified.
2. The use of CAC measurement in patients with low CHD risk (below 10% 10-year risk of estimated CHD events is not recommended. The committee also does recommend screening of the general population using CAC measurement.
3. CAC measurement in asymptomatic patients with high CHD risk (greater than 20% estimated 10-year risk of estimated CHD events, or established coronary disease or other high-risk diagnoses) is not advised as they are already judged to be candidates for intensive risk reducing therapies based on current NCEP guidelines.
4. No evidence is available that allows the committee to make a consensus judgment to reduce the treatment intensity in patients with calcium score = 0 in patients who are considered intermediate risk before coronary calcium score.
Accordingly, the Committee felt that current standard recommendations for treatment of intermediate risk patients should apply in this setting.
5. The question whether there is evidence that coronary calcium measurement is better than other potentially competing tests in intermediate risk patients for modifying cardiovascular disease risk estimate cannot be adequately answered from available data.
6. There is no clear evidence that additional non-invasive testing in high risk patients with high coronary calcium score (e.g., CAC greater than 400) will result in more appropriate selection of therapies.
7. Evidence indicates that patients considered to be at low risk of coronary disease by virtue of atypical cardiac symptoms may benefit from CAC testing to help in ruling out the presence of obstructive coronary disease. Other competing approaches are available, and most of these competing modalities have not been compared head-to-head with CAC.
8. CAC data are strongest for Caucasian, non-Hispanic men. Caution in extrapolating CAC data derived from studies in white men to women and to ethnic minorities is recommended.
9. Current radiology guidelines should be considered when determining need for follow-up of incidental findings on a fast CT study.
For the symptomatic patient, exclusion of measurable coronary calcium may be an effective filter before undertaking Cardiac Computed Tomography (CT), Coronary Artery Calcium Scoring and Cardiac CT Angiography - Commercial Medical Management Guideline invasive diagnostic procedures or hospital admission. Scores less than 100 are typically associated with a low probability (less than 2%) of abnormal perfusion on nuclear stress tests and less than 3% probability of significant obstruction (greater than 50% stenosis) on cardiac catheterization. The presence of CAC by fast CT is extremely sensitive for obstructive (greater than 50% luminal stenosis) CAD (95% to 99%), but has limited specificity. CAC studies of over 7600 symptomatic patients demonstrate negative predictive values of 96% to 100%, allowing for a high level of confidence that an individual with no coronary calcium (score=0) has no obstructive angiographic disease.
Because progression of CAC is not clearly modifiable through standard risk reducing therapies, and CAC measurement involves both costs and radiation exposure, clinical monitoring of CAC progression through serial fast CT scanning is not recommended at this time.
There have been no clinical trials to evaluate the impact of calcium scoring on clinical outcomes in either symptomatic or asymptomatic patients. However, the Writing Committee's position reflects that calcium scoring can be considered reasonable where there is evidence that the test results can have a meaningful impact on medical decision-making.
(Greenland, 2007) American Heart Association (AHA) In a scientific statement (Budoff, 2006), the AHA made the following recommendations on coronary artery calcium (CAC) scoring:
Class IIb Recommendations (Usefulness/efficacy is less well established by evidence/opinion)
1. In clinically selected, intermediate-risk patients, it may be reasonable to measure the atherosclerosis burden using EBCT or MDCT to refine clinical risk prediction and to select patients for more aggressive target values for lipidlowering therapies.
2. Coronary calcium assessment may be reasonable for the assessment of symptomatic patients, especially in the setting of equivocal treadmill or functional testing.
3. Patients with chest pain with equivocal or normal ECGs and negative cardiac enzyme studies may be considered for CAC assessment.
4. CACP measurement may be considered in the symptomatic patient to determine the cause of cardiomyopathy.
Class III Recommendations (Not useful/effective and in some cases may be harmful)
1. Individuals found to be at low risk (20% 10-year risk) do not benefit from coronary calcium assessment.
2. It is not recommended to use CACP measure in asymptomatic persons to establish the presence of obstructive disease for subsequent revascularization.
3. Serial imaging for assessment of progression of coronary calcification is not indicated at this time.
American College of Radiology (ACR) While the role of coronary artery calcium scoring is currently being refined, data support its use for risk stratification and therapeutic decision making in select patients with intermediate risk for a significant ischemic cardiac event. An additional indication is the localization of myocardial and pericardial calcium. (ACR, 2006b) National Cholesterol Education Program (NCEP) Adult Treatment Panel III ATP III supports the conclusions of the American Heart Association's Prevention Conference V and the ACC/AHA report that high coronary calcium scores signify and confirm increased risk for CHD when persons have multiple risk Cardiac Computed Tomography (CT), Coronary Artery Calcium Scoring and Cardiac CT Angiography - Commercial Medical Management Guideline factors. Therefore, measurement of coronary calcium is an option for advanced risk assessment in appropriately selected persons, provided the test is ordered by a physician who is familiar with the strengths and weaknesses of noninvasive testing.