Coronary Artery Calcium Scoring (CACS) has been used for cardiovascular risk assessment for over 20 years. Statements from the American Heart Association, the American College of Cardiology and others such as the Royal College of Radiologists, have now firmly endorsed its role in primary cardiovascular disease prevention.
Primary prevention of CAD requires identification of at-risk individuals, to enable effective intervention. Unfortunately, traditional Framingham risk assessment can predict only 60-65% of hard cardiac events (acute myocardial infarction or sudden death). In approximately 50% of men and 64% of women with CAD the first manifestation of disease is a heart attack or death, demonstrating the need to improve risk prediction, especially in asymptomatic patients. Despite the widespread adoption of Framingham risk assessment, there remains a huge number of at risk patients who are not currently identified and treated appropriately.
‘Functional’ imaging such as treadmill exercise ECG, stress echocardiogram and myocardial perfusion scans work on the premise that a flow limiting coronary stenosis is present and that a sufficient workload can be induced to precipitate ischaemia. When negative, such tests give no information as to the presence of a significant plaque burden and do not identify patients with sub-clinical atherosclerosis. These patients remain at risk.
Who should be screened?
The radiation dose for a typical CAC scoring examination is approximately 1.5 mSv compared with the background radiation exposure in the UK of 2 to 3 mSv per year. The theoretical risk of radiation-induced cancer from any source, however small, decreases with advancing age. For this reason, CT screening for CAD should be limited to patients older than 40 (exceptions include those with a strong family history of premature CAD). Any theoretical risk from this exposure is either too small to measure or insignificant. Similarly, since risk predictions from CAC scoring are based on 2 to 5 year intervals, it is not necessary to routinely scan patients on an annual basis. Since 2001, the National Cholesterol Education Program (NCEP) Adult Treatment Panel III specifically recommends the use of CAC scoring to assist in risk stratification for these intermediate risk patients, as well as the elderly, in whom traditional risk factors lose some of their predictive power. European guidelines also support the use of CAC scoring in patients found to be of intermediate risk from a Framingham risk assessment. The Society of Atherosclerosis Imaging has recommended CAC scoring in primary prevention for men 35 years of age and older, and for women 45 years of age and older if any traditional risk factors are present. The SHAPE taskforce (Screening for Heart Attack Prevention and Education. www.shapesociety.org ) advocates mass screening of men over 45 and women over 55 using CACS or carotid artery Intima-Media Thickness (IMT).
Significance of CAC scores
Recommendations for patient management are based on the total calcium score and the score relative to a reference population. Patients with very low scores whose score is also below average for their age do not generally require any thing other than lifestyle advice such as a healthy diet and stopping smoking etc. Patients with higher scores (>100) or who are above average for their age and sex (>75th centile) would be advised to start medical treatment with low dose aspirin and statins. Patients with high scores (>400) should also be considered for formal exercise testing as well as more aggressive risk factor modification. There is no requirement to proceed to angiography unless there is good evidence of ischaemia from further exercise testing or functional imaging. Angiography should be reserved for those patients who are likely to benefit from revascularisation. The site of calcified plaque shows poor correlation with the site of any underlying coronary artery stenosis.
Conclusion
Atherosclerosis and coronary artery disease remain huge health concerns in the developed World. They constitute the largest single cause of death and are responsible for billions of pounds of health care spending annually. It is well known that lifestyle modification and drug therapy can reduce the risk of hard cardiac events, but current Framingham risk assessment is suboptimal. Coronary artery calcification as measured by CT has been shown to be the most powerful independent predictor of hard cardiac events. According to current guidelines from multiple agencies, CAC scoring should be considered to increase the accuracy of risk stratification for intermediate-risk individuals and to direct further testing and treatment.
Dr John Giles FRCP FRCR Consultant Radiologist, |
Dr M Faris MRCP SPR Radiology, |
The above is an extract from an article originally published in Rad Magazine in April 2007.
Further reading - Cardiac calcification scoring
Quantification of coronary calcification using ultrafast computed tomography.
Agatston AS, Janowitz WH, et al
J. Am Coll Cardiology 1990; 15: 827 – 832.
Coronary artery Calcification as an indicator of Preclinical coronary artery disease.
Stanford W.
Radiographics, 1999; 19: 1409-1419.
CT imaging of Coronary Artery Calcium as an Indicator of Atherosclerotic Disease: An Overview.
Janowitz WR.
Journal of Thoracic Imaging. 2001; 16: 2-7.
Comparison of Electron beam and ungated Helical CT in detecting coronary arterial calcification by using a working heart phantom and artificial coronary arteries.
Hopper K, Strollo D, Mauger D.
Radiology vol 222, 474 - 482.
Coronary Angigraphy with multi-slice Computed Tomography.
Nieman K, Oudkerk M et al,
Lancet 2001. Feb 24;357: 599-603.
Atherosclerosis imaging and coronary calcification: The UK perspective.
Morgan-Hughes G, Roobottom C, Marshall A,
British Journal of Cardiology 2002; vol 9: 373- 376.
Cost effectiveness of coronary calcification scanning using EBCT
in intermediate and high risk asymptomatic individuals.
Rumberger J,
Journal of Cardiovascular Risk 2000; 7: 113-119.
Reliable non-invasive Coronary angiography with fast submillimeter multislice CT.
Nieman K. et al.
Circulation, October 2002.
