Coronary Calcium Scanning: A Guide for Physicians, Elizabeth Klodas, M.D.
Coronary artery calcification scanning affords the opportunity to determine very accurately and noninvasively whether or not underlying coronary artery disease is present, as well as provide an estimate of the extent and severity of coronary disease. This information can then be utilized to optimize patient care, helping to appropriately tailor prevention goals and to determine further evaluation and follow up, if needed.
The purpose of this guide is to provide you with some background information regarding coronary calcium scanning. We hope that this will allow you to gain some appreciation of the technology itself, its capabilities and weaknesses, and its potential role in the milieu of already established testing modalities (from stress testing to angiography).
According to 1996 estimates:
- Nearly 59 million Americans have one or more forms of cardiovascular disease.
- Coronary heart disease caused nearly 500,000 deaths in 1996 and is the single leading cause of death in America today.
- From 1979 to 1996, the number of cardiovascular operations and procedures increased 355 percent according to the American Heart Association.
Normal: No Identifiable Plaque
Moderate: Definite Plaque Burden
High: Extensive Atherosclerotic Plaque Burden
Rationale for Coronary Calcium Evaluation
The Technology Involved
Heart CT at CMC is the noninvasive method to assess the extent of coronary artery calcification utilizing gated helical CT imaging.
Capabilities and Limitations of Coronary Calcium Scanning
- qualitative evaluation of the presence or absence of coronary calcium
- quantitative evaluation of the degree/extent of calcification
The presence of ANY coronary calcium signifies that underlying CAD is present. The “calcium score” (an amalgamation of total size and density of the calcific deposits found throughout the coronary tree) provides a quantitative evaluation of extent of plaque burden.
A limitation of coronary calcium scanning is that although calcium deposition occurs relatively early in the atherosclerotic process, plaque material very initially is not calcified. Therefore, very minimal atherosclerotic changes may be missed by this technique. It is important to keep this point in mind – and the results of the scan should be viewed as only one, albeit powerful, component in the assessment and management of a particular patient.
Understanding the Calcium Score
A score between 10 and 400 indicates a moderate plaque burden, and is associated with an intermediate, although significant risk of future cardiac events, especially when scores are >100. The odds ratio of developing symptomatic cardiovascular disease has been reported to be as high as 7:1 in patients with scores >50, 20:1 in patients with scores >100 and 35:1 in those with scores >160.
The clinical significance of a particular score is influenced by the patient’s age and gender. A score of 150 may be “average” for a 70 year old man, but would be considered markedly abnormal for a 40 year old woman. The correlation between calcium score and plaque burden is identical in men and women; however, just as clinical manifestations of CAD are delayed in women as compared to men, so is the development of coronary calcium. Table 1 displays expected percentile ranges of calcium scores stratified by sex and age.
Table 1 – Percentile Range of Coronary Artery Calcium Score in Asymptomatic Women and Men as a Function of Age
Utilizing the Heart CT Results/Score
In the absence of coronary calcium, no further functional testing is likely to be required.
These recommendations are summarized in Table 2:
Table 2 – Calcium Score Guidelines
Probability of Significant Coronary Artery Disease
Implications for CV risk
|0||No identifiable plaque||Very low, generally 5%||Very low||Reassure patient, discuss general public health guidelines for primary prevention of CV disease|
|1-10||Minimal identifiable plaque burden||Very unlikely, under 10%||Low||Discuss general public health guidelines for primary prevention of CV disease|
|11-100||Definite, at least mild atherosclerotic plaque burden||Mild or minimal coronary stenoses likely||Moderately||Counsel about risk factor modification, strict adherence with primary prevention goals. Daily ASA.|
|101-400||Definite, at least moderate atherosclerotic 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+||Extensive atherosclerotic 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
- Patients with borderline lipid levels or mild hypertension may be ideal candidates, helping stratify whether more aggressive and expensive secondary prevention therapies are clearly appropriate for these individuals.
- Patients with a relatively early family history of coronary disease may benefit from the enhanced risk stratification offered by Heart CT. 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, Heart CT may be utilized to noninvasively determine the extent of underlying CAD, helping to 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.
- Some centers have used coronary calcium scanning to help risk stratify patients who present with chest pain, especially young persons with atypical symptoms. This may represent another useful, cost effective application of the technology.
- 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 to be substantial in individuals over the age of 70, and generally Heart CT is not recommended in these individuals.
There is no data to support mass imaging of asymptomatic individuals at the present time. Patients who already have documented CAD are not appropriate for Heart CT evaluation. The results of the scan would not be expected to change management in this patient population.
Scanning is accomplished at rest, without contrast administration, without the need for IV access, and in a nonfasting state. No changes in patient medication are required. There are no restrictions with respect to pacemakers or prosthetic devices.
Patients with arrhythmias (chronic atrial fibrillation, very frequent extrasystoles) or patients with relative resting tachycardia (HR>90-95 bpm) should not undergo Heart CT scanning, because adequate cardiac gating will be difficult to accomplish, compromising image quality. Because scanning does involve minimal x-ray exposure, women who are pregnant or potentially pregnant should not undergo this evaluation.
How does Heart CT fit in with other cardiac tests?
The most powerful cardiology tool for defining clinical prognosis is nuclear stress testing, and, therefore, patients with significant coronary calcium deposition should be preferentially considered for an exercise or pharmacological nuclear stress testing for further evaluation.
In general, echocardiography is superior for evaluating valvular structures and valvular function. Although left ventricular function assessment is possible with CT scanning, this involves contrast infusion, a less than desirable requirement in view of the potential side effects of iodinated contrast administration.
Cardiac CT scanning may be utilized to evaluate the pericardium in patients with suspected constrictive pericarditis, and may be useful in evaluating the right ventricle in rare patients with suspected right ventricular dysplasia. For nearly all other indications, non-CT imaging modalities are more appropriate and/or clinically useful.
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Comparison of Electron Beam and Helical CT in the Detection of Coronary Artery Calcification, K.D. Hopper, M.D., Hershey, PA, D.C. Strollo, M.D., D. Mauger, PhD. Radiologic Society of North America, 1998 Scientific Program.
Dr. Klodas’ professional affiliations include the American Heart Association, the American College of Cardiology and the American Society of Nuclear Cardiology, of which she is a founding member of the Upper Midwest Working Group.