These three articles show how EBCT compares with other modalities used in the diagnosis of coronary heart disease (CHD). The first article demonstrates that a simple equation using the calcium scores in the left anterior descending and the circumflex arteries plus two other risk factors can very accurately predict the presence or absence of left main or three vessel disease in patients with symptoms suggestive of cardiovascular heart disease (CHD). The second article indicates that EBCT is more powerful than stress thallium testing or risk factors in predicting the presence of angiographically significant CHD. The third article shows that EBCT is a powerful tool for risk-stratifying patients into groups with low, intermediate, or high likelihood of having abnormal myocardial perfusion on radionuclide stress testing. Taken together, these articles provide a useful cross-section of the many articles in the literature that have shown the validity of the coronary calcium score as a predictor of significant CHD. Conversely, low scores are indicative of a low probability for angiographically significant CHD.

1. An Algorithm for Noninvasive Identification of Angiographic Three Vessel and/or Left Main Coronary Artery Disease in Symptomatic Patients on the Basis of Cardiac Risk and Electron Beam Computed Tomographic Calcium Scores

Objectives: We sought an algorithm for noninvasive identification of angiographically obstructive three-vessel disease based on conventional cardiac risk assessment and site and extent of coronary calcium determined by EBCT.
Methods: Examined 291 patients with suspected, but not previously diagnosed, CAD who underwent coronary Angiography for clinical indications. Cardiac risk factors were determined as defined by the National Cholesterol Education Program. An EBCT scan was performed in all patients, and a coronary calcium score (Agatston method) was computed. Total per-patient calcium scores and separate scores for major arteries were generated. These scores were also analyzed for localization of coronary calcium in the more distal versus proximal tomographic sections. These parameters and the risk factors were considered for the model described in the following section.
Results: Sixty-eight patients (23%) had angiographic three-vessel and/or left main CAD. Multiple logistic regression analysis determined male sex, presence of diabetes and left anterior descending (LAD) and circumflex (LCx) coronary calcium scores, independent from more distal calcium localization, as independent predictors for identification of three-vessel and/or left main CAD. Based on this four variable model, a simple noninvasive index (NI) was constructed as the following: loge(LAD score) + loge(LCx score) + 2[if diabetic] + 3[if male]. Receiver operating characteristic analysis for this NI yielded an area under the curve of 0.88 +/-0.03 (p<0.0001) for separating patients with versus without Angiographic three-vessel and/or left main CAD. Various NI cutpoints demonstrated sensitivities from 87-97% and specificities from 46-74%. The NI values >14 increased the probability of Angiographic three-vessel and/or left main CAD from 23% (pre-test) to 65-100% (post-test), and NI values <10 increased the probability of no three-vessel and/or left main CAD from 77% (pre-test) to 95-100% (post-test).
Conclusions: On the basis of a simple algorithm ("noninvasive index"), EBCT calcium scanning in conjunction with risk factor analysis can rule in or rule out angiographically severe disease, i.e., three-vessel and/or left main CAD, in symptomatic patients.

2. Independent and Incremental Value of Coronary Artery Calcium for Predicting the Extent of Angiographic Coronary Artery Disease

Objectives: The study was done to test the ability to predict the extent of angiographically determined coronary artery disease (CAD) by quantification of coronary calcium using electron beam computed tomography (EBCT) and to compare it with more conventional parameters for delineating the angiographic extent of CAD, that is, cardiovascular risk factors and radionuclide single-photon emission computed tomography (SPECT).
Background: The angiographic extent of CAD is a powerful predictor of future events. Use of EBCT may be able to define it by virtue of its ability to determine plaque burden.
Methods: We examined 308 patients presenting with suspected but not previously known CAD who underwent selective coronary Angiography. As measures of the angiographic extent of CAD, coronary artery greater even 20 (CAGE ³ 20) and CAGE ³ 50 scores represented the total number of coronary segments with ³ 20% or ³ 50% stenoses, respectively. The EBCT-derived total calcium scores were obtained in 291 patients, risk factors as defined by the National Cholesterol Education Program in 239 patients, and SPECT scans in 136 patients.
Results: Using multiple linear regression analysis, total calcium scores were better independent predictors of both CAGE ³ 20 and CAGE ³ 50 scores than either a SPECT-derived radionuclide perfusion score or the risk factors age, male gender and ratio of total/high density lipoprotein (HDL) cholesterol. The association between EBCT and angiographic scores remained highly significant after excluding the influence of all interrelated risk factors and SPECT variables (r = 0.65; p < 0.001 for CAGE ³ 20 scores, r = 0.50; p < 0.001 for CAGE ³ 50 scores).
Conclusions: Coronary calcium predicts the angiographic extent of CAD in symptomatic patients and provides independent and incremental information to the more conventional clinical parameters derived from SPECT or risk assessment.

3. Severity of Coronary Artery Calcification by Electron Beam Computed Tomography Predicts Silent Myocardial Ischemia

Background: Detection of subclinical coronary artery disease (CAD) before the development of life-threatening cardiac complications has great potential clinical relevance. Electron beam computed tomography (EBCT) is currently the only noninvasive test that can detect CAD in all stages of its development and thus has the potential to be an excellent screening technique for identifying asymptomatic subjects with underlying myocardial ischemia.
Methods and Results: Over 2.5 years, we prospectively studied 3,895 generally asymptomatic subjects with EBCT, 411 of whom had stress myocardial perfusion tomography (SPECT) within a close (median, 17 days) time period. SPECT and exercise treadmill results were compared with the coronary artery calcium score (CACS) as assessed by EBCT. The total CACS identified a population at high risk for having myocardial ischemia by SPECT although only a minority of subjects (22%) with an abnormal EBCT had an abnormal SPECT. No subject with CACS < 10 had an abnormal SPECT compared with 2.6% of those with scores from 11-100, 11.3% of those with scores from 101 to 399, and 46% of those with scores ³ 400 (p < 0.0001). CACS predicted an abnormal SPECT regardless of subject age or sex.
Conclusions: CACS identifies a high-risk group of asymptomatic subjects who have clinically important silent myocardial ischemia. Our results support the role of EBCT as the initial screening tool for identifying individuals at various stages of CAD development for whom therapeutic decision making may differ considerably.