The Acute Scrotum
Coronary Artery Calcification Scanning
Its Time Has Arrived

by Robert J. Optican, M.D. Fall 2000

As a new tool in the armamentarium of preventive cardiology, computed tomography has emerged as a useful screening tool for the detection of coronary atherosclerosis in asymptomatic patients. For many years, calcification within the coronary arteries detected on plain film or fluoroscopy has been recognized as a marker of advanced coronary artery disease (CAD).

The emergence of sub-second CT scanning provides the ability to image even tiny amounts of calcium in the coronary arteries. This ability gives physicians an opportunity to detect atherosclerosis early, before symptoms develop. It should be remembered that calcification does not occur in normal coronary arteries; when present, it is always associated with coronary atherosclerosis. CT scanning has been around for a long time; why is this test so new?

Sub-second CT scanning is necessary to image the coronary arteries in order to reduce motion artifact sufficiently to achieve diagnostic image quality. Electron-beam CT scanners were the first scanners developed with the capacity to achieve sub-second scans. Electron beam scanners utilize a moving stream of electrons to produce x-rays necessary create an image. Unfortunately, electron beam scanners have proven difficult to maintain, are much more expensive than mechanical scanners, and provide substandard image quality for examination of the brain and abdomen. In the past few years, technology has emerged which allows sub-second scanning to be performed on modern helical scanners requiring only minor modifications. This technology requires EKG-gating, allowing data acquisition during the resting phase (diastole) of the cardiac cycle. These modifications were recently made to the scanner located at BMH Collierville. This scanner is currently (as of November 2000) the only scanner in the Baptist system capable of the sub-second scan time required.

What does the "calcium score" represent?

The detection of any degree of coronary calcium on CT indicates that CAD is present. The "calcium score" (a number derived from a combination of the size and density of calcified plaques) provides a quantitative estimate of plaque burden. In general, the higher the "score" the larger the plaque burden and the higher the risk of subsequent cardiac events. Although the relationship between the calcium score and the degree of angiographic stenosis is not exact, data regarding specific thresholds exists to help utilize the score in clinical context.

Does a score of zero eliminate any possibility of coronary disease? No. One limitation of calcium scoring is that although calcium deposition occurs relatively early in the atherosclerotic process, plaque material is not initially calcified. Therefore very early atherosclerosis may be undetected by this technique. This is important since early non-calcified plaque could potentially become unstable (plaque rupture) and cause symptoms (unstable angina or acute MI); if it is not accompanied by calcified plaque, a patient's calcium score could still be "zero." Therefore, any patient with typical chest pain should receive an appropriate evaluation, and calcium scoring at this time does not play a role in the evaluation of chest pain.

How can a physician utilize the calcium score?

The following guiding principles should be used in interpreting a patient's score: The presence of any detectable coronary calcium implies the presence of coronary artery disease. This can affect patient management by providing impetus for more aggressive hypertension control, lipid lowering, and low-dose aspirin therapy. Investigators have also noted that patients, when informed of their score, or shown actual images, have displayed much more willingness to undertake healthy lifestyle changes. Since patients with very high scores (e.g., over 400) have a high likelihood of harboring a significant stenosis, they should probably undergo stress testing to evaluate for inducible ischemia. Patients with intermediate scores may require further testing based upon other factors (age, other risk factors, etc). In an asymptomatic patient, a score of zero would imply no need for further imaging tests for coronary disease.

Calcium Score Guidelines:

Calcium Score---Plaque Burden---Probability of Significant CAD--- Implications for future risk (MI, unstable angina)---Recommendations

0 ---No identifiable (calcified) plaque---Very low, generally less than 5%---Very Low---Reassure patient. Discuss general public health guidelines for primary prevention of CV disease.

1-10---Minimal identifiable plaque burden---Very unlikely, less than 10%---Low---Discuss general public health guidelines for primary prevention of CV diseases

11-100 ---Definite, at least mild plaque burden---Mild or minimal coronary stenoses likely---Moderate---Counsel about risk factor modification, strict adherence with&Mac240;primary prevention goals. Daily ASA.

101-400 ---Definite, at least moderate plaque burden---Non-obstructive CAD highly likely, although obstructive disease possible---Moderately High---Institute risk factor modification and secondary prevention goals. Consider exercise testing for further risk stratification. Daily ASA

>400&Mac240;---Extensive plaque burden---High likelihood (>90%) of at least one significant coronary stenosis---High---Institute very aggressive risk factor modification. Consider exercise for pharmacologic nuclear stress testing to evaluate for inducible ischemia. Daily ASA.

Indications for Coronary Calcium Scanning

A calcium scoring evaluation may be useful in those patients in whom the documentation of the presence of coronary artery disease would be expected to change or influence therapy. Patients with borderline lipid levels, or mild hypertension may be ideal candidates, helping stratify whether more aggressive secondary prevention therapies are appropriate. Patients with a relatively early family history of coronary disease may benefit from the enhanced risk stratification offered by calcium scoring.

If premature CAD is detected, this may lead to a search for less "traditional" risk factors, such as homocysteine levels, Lp(a), and wider screening of family members for these and other cardiac risk factors. In the setting of dilated cardiomyopathy, calcium scoring may be utilized to help assess whether the cardiomyopathy is likely ischemic in etiology. A relatively low calcium score would suggest that the cardiomyopathy is probably idiopathic, viral or metabolic, and that the patient would not be expected to derive clinical benefit from undergoing coronary angiography.

In general, most studies have evaluated patients 40-70 years of age, although younger individuals may be appropriate candidates depending upon their risk factor profile. Incremental clinical benefit is unlikely in individuals over the age of 70, and generally calcium scoring is not recommended in these individuals. Contraindications for Coronary Calcium Scanning: Patients who already have documented CAD are not appropriate for calcium scoring evaluation. The results of the scan would not be expected to change management in this population. Patients with arrhythmias or resting tachycardia should not undergo scanning, because adequate cardiac gating will be difficult to accomplish, compromising image quality.

Does calcium scoring replace other imaging modalities for coronary artery disease?

Sub-second CT is sensitive for the detection of early CAD, and extent of plaque burden. But it is not helpful in defining the location or severity of coronary artery stenosis. The most powerful imaging tool for defining clinical prognosis in patients with coronary artery disease is nuclear stress testing, and therefore patients with significant coronary calcium deposition should be preferentially considered for an exercise or pharmacologic nuclear stress test for further evaluation. CT is not a replacement for coronary angiography. At the present time, coronary angiography represents the only reliable technology to accurately assess luminal narrowing within the coronary circulation.

Recommend reading: Wexler L, et al. Coronary artery calcification: pathophysiology, epidemiology, imaging methods, and clinical implications. A statement for health professionals from the American Heart Association. Writing Group. Circulation, 1996 Sep, 94:5, 1175-92. Budoff MJ, et al. Ultrafast computed tomography as a diagnostic modality in the detection of coronary artery disease: a multicenter study. Circulation, 1996 Mar, 93:5, 898-904.

Dr. Optican received fellowship training in Cardiac Radiology at the Cleveland Clinic Foundation from 1993-1994.