High-quality, noninvasive coronary imaging requires high spatial resolution and a high acquisition speed because of the small size, tortuous course, and continuous motion of the coronary arteries. Computed tomography (CT) has emerged as the most effective technique to visualize the coronary arteries noninvasively. Electron beam computed tomography (EBCT), which was introduced in the mid-1980s, is a high-speed CT scanner designed for cardiac imaging. Although mostly used for the detection and quantification of coronary calcium, EBCT also allows contrast-enhanced coronary angiography. Since the early 2000s, multislice computed tomography (MSCT) scanners with cardiac imaging capabilities have been developed. MSCT scanners can be used to detect and quantify coronary calcium, but were primarily developed to image the coronary arteries. Current state-of-the-art scanners are equipped with 64 or more detector rows. Dual-source scanners are available that allow even faster acquisition of images. In this chapter, we will discuss the value of coronary calcium scoring and total coronary plaque burden as assessed by CT, and the role of CT coronary angiography in the evaluation of patients presenting with acute coronary syndromes.
Prediction of Adverse Cardiovascular Events
Computed Tomography Coronary Calcium Scoring
Coronary calcium is easily identified by CT because the roentgenographic attenuation of calcium is much higher compared with that of the surrounding tissues ( Fig. 16-1 ). Histologic studies have shown that a CT tissue density of greater than or equal to 130 HU is highly correlated with calcified coronary plaques. The presence of coronary calcium is evidence of the presence of coronary atherosclerosis. The extent of coronary calcium correlates with the overall atherosclerotic plaque burden (i.e., presence of calcific and noncalcific atherosclerosis), although the calcific plaques constitute only 20% of the total coronary plaque burden. A large amount of coronary calcium is associated with an increased likelihood of vulnerable plaque present somewhere in the coronary tree, but does not identify the site of a specific vulnerable plaque. Absence of coronary calcium does not exclude coronary atherosclerosis, including the presence of a high-risk plaque, but its presence is very unlikely.
The amount of coronary calcium can be quantified in different ways. The most widely used method is the Agatston calcium score, based on the peak CT density (>130 HU) and the area of the calcific plaque (≥1 mm 2 ). For each calcified lesion, the area is multiplied by a factor determined by the peak CT density: 1 for a peak density of 130 to 199 HU, 2 for 200 to 299 HU, 3 for 300 to 399 HU, and 4 for 400 HU or more. By adding up the individual plaque scores, the total Agatston score can be determined. Several large-scale long-term follow-up studies have assessed the value of calcium scoring to predict cardiovascular events in high-risk asymptomatic populations ( Table 16-1 ). A coronary calcium score of 0 is associated with a very low risk (<0.4% annual risk) of the occurrence of an adverse cardiovascular event and there is a strong direct relationship between the magnitude of the calcium score and the occurrence of adverse events ( Tables 16-2 and 16-3 ).
| Study (Year) | No. of Patients | Age (yr) | Follow-up (yr) | Completeness Follow-Up (%) | Predictive Calcium Score | Prevalence NP * | Comparative Group Calcium Score (Prevalence) † | End Point (NP) | RR |
|---|---|---|---|---|---|---|---|---|---|
| Shaw et al (2003) | 10,377 | 53 ± 0.1 | 5 | 100 | >40 | 935 | ≤10 (5946) | All-cause mortality (249) | 6.2 |
| Greenland et al (2004) | 1312 | 66 ± 8 | 7 | 88 | >300 | 221 | 0 (316) | Cardiac death/MI (84) | 3.9 |
| Arad et al (2005) | 4613 | 59 ± 6 | 4.3 | 94 | ≥100 | 1136 | <100 (3477) | Cardiac death or MI (119) | 9.2 |
| Taylor et al (2005) | 1627 | 43 ± 3 | 3 | 99 | >0 | 364 | 0 (1363) | Death or MI UA (9) | 11.8 |
| Vliegenthart et al (2005) | 1795 | 71 ± 6 | 3.3 | 99 | >1000 | 196 | 0-100 (905) | Death/MI (40) | 8.1 |
| LaMonte et al (2005) | 6835 (men) | 54 ± 10 | 3.5 | 70 | >250 | 1380 | 0 (2692) | Cardiac death or MI (81) idem | 8.7 ‡ |
| 3911 (women) | >113 | 376 | 0 (2780) | 6.3 ‡ | |||||
| Budoff et al (2007) | 25,253 | 56 ± 11 | 6.8 | 100 | >10 | 14,207 | 0 (11,046) | All-cause mortality | 1.7 |
* Number of patients with predictive calcium score.
† Number of patients in this group with defined calcium score as comparison.
| Calcium Score | No. of Patients (%) | All-Cause Death (%) | RRR | RRR (Adjusted Risk Factors) * |
|---|---|---|---|---|
| ≤10 | 5946 (57) | 1.0 (62) | — | — |
| 11-100 | 2044 (20) | 2.6 (53) | 2.5 | 1.7 |
| 101-400 | 1432 (14) | 3.8 (54) | 3.6 | 1.8 |
| 401-1000 | 623 (6.0) | 6.3 (39) | 6.2 | 2.6 |
| >1000 | 332 (3.2) | 12.3 (41) | 12.3 | 4.0 |
* 10,377 asymptomatic individuals; total deaths = 2.4% ( N = 249).
| Calcium Score | No. of Patients (%) | RRR | RRR (Adjusted Age + Risk Factors) |
|---|---|---|---|
| 0 | 11,046 (44) | — | — |
| 1-10 | 3567 (14) | 2.6 | 1.5 |
| 11-100 | 5033 (20) | 6.7 | 3.6 |
| 101-400 | 3177 (13) | 13 | 3.9 |
| 401-1000 | 1469 (6) | 23 | 6.2 |
| > 1000 | 965 (4) | 38 | 9.4 |
* 25,253 asymptomatic individuals; all-cause death, 2% ( N = 510).
A meta-analysis of the prognostic value of coronary calcium was recently performed ( Tables 16-4 and 16-5 ). Overall, the relative risk ratio of having calcium compared with the absence of calcium was 4.3 (95% confidence interval [CI], 3.5 to 5.2) and the relative risk ratios revealed a close relationship with higher calcium scores associated with higher event rates and higher relative risk ratios.
| Parameter | Results |
|---|---|
| Total no. of patients | 27,622 |
| Follow-up (yr) | 3-5 |
| CHD death or MI | 395 |
| High- vs. low-risk events | |
| 364/19,039 events | CS > 0 |
| 49/11,815 events | CS = 0 |
| Relative risk ratio | 4.3 (95% CI, 3.5-5.2) |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
