Information about Coronary Artery Calcium scoring

Coronary Artery Calcium Scoring (CACS) has been used for cardiovascular risk assessment for over 25 years. Statements from the Royal College of Radiologists, the American Heart Association, the American College of Cardiology and others have now firmly established its role in primary cardiovascular disease (CVD) prevention.

Primary prevention of CVD requires identification of individuals who are at greater risk of future cardiovascular problems such as heart attack and stroke, to enable effective intervention.  Unfortunately, traditional risk assessment methods such as the Framingham risk assessment tool 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 Coronary Artery Disease the first manifestation of disease is a heart attack or death. The majority of these events occur in patients traditionally considered to be of intermediate risk, demonstrating the need to improve risk prediction, especially in asymptomatic patients. Despite the widespread adoption of assessment tools such as Framingham, there remains a huge number of at risk patients who are not currently identified as being at risk and therefore not 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 high levels of sub-clinical plaque build up. These patients remain at risk. The risk of death or heart attack is directly related to the overall build up of plaque with most events occurring secondary to non obstructive plaque which are not identified with exercise testing.

Who should be screened?

At least 1 in 3 people will die of cardiovascular disease. Despite this statistic there is very little to be gained in screening those who are traditionally considered to be very low risk for example individuals aged less than 40 years and without any other recognised risk factors such as a history of smoking or a high cholesterol or blood pressure. Patients who have already suffered an event such as a heart attack, stroke or had previous coronary intervention such as angioplasty and or stent placement will not benefit from screening as they should already be on maximum secondary prevention.

Screening is primarily aimed at those who are considered to be of intermediate risk, allowing them, with confidence, be reclassified as either low or high risk based upon the presence and amount of plaque.

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. Similar 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 functional tests such as exercise testing or nuclear medicine testing. Likewise, Coronary Angiography should be reserved for those patients who are likely to benefit from revascularisation once they have developed symptoms or are suspected of having significant obstructive disease identified by functional testing. The site of calcified plaque shows poor correlation with the site of any underlying coronary artery stenosis.

Are there any risks?

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.

Patients identified as being of increased risk can reduce the risk of future events by at least 30% by modifying risk factors and medical management with statins.

Further information about and risks can be found here and here

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.

The above is adapted from an article originally published in Rad Magazine in April 2007.

Dr John Giles FRCP FRCR
Consultant Radiologist,
Clinical Director Lifescan UK

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.
http://content.onlinejacc.org/cgi/content/abstract/15/4/827

Coronary artery Calcification as an indicator of Preclinical coronary artery disease.
Stanford W.
Radiographics, 1999; 19: 1409-1419.
http://radiographics.rsna.org/content/19/6/1409.full.pdf+html

CT imaging of Coronary Artery Calcium as an Indicator of Atherosclerotic Disease: An Overview.
Janowitz WR.
Journal of Thoracic Imaging. 2001; 16: 2-7.
http://journals.lww.com/thoracicimaging/Fulltext/2001/01000/CT_Imaging_o...

Coronary artery calcium screening: sufficient evidence for accurate risk assessment?
Ernst E. van der Wall , Joanne D. Schuijf , J. Wouter Jukema , Jeroen J. Bax
Int J Cardiovasc Imaging (2008) 24:907–909
http://www.springerlink.com/content/83n6128105906n7p/fulltext.pdf

Coronary artery calcium screening: current status and recommendations from the European Society of Cardiac Radiology and North American Society for Cardiovascular Imaging
Matthijs Oudkerk , Arthur E. Stillman , Sandra S. Halliburton ,Willi A. Kalender , Stefan Mo¨hlenkamp , Cynthia H. McCollough ,Rozemarijn Vliegenthart , Leslee J. Shaw , William Stanford , Allen J. Taylor , Peter M. A. van Ooijen , Lewis Wexler , Paolo Raggi.
Int J Cardiovasc Imaging (2008) 24:645–671
http://www.springerlink.com/content/44x4033t77666313/fulltext.pdf

Expert review on coronary calcium
Matthew J Budoff, Khawar M Gul.
Vascular Health and Risk Management 2008:4(2) 315–324
http://www.biomedsearch.com/attachments/00/18/56/15/18561507/vhrm-0402-3...

2010 ACCF/AHA Guideline for Assessment of Cardiovascular Risk in Asymptomatic Adults
Philip Greenland, MD, FACC, FAHA, Chair et al.
Journal of the American College of Cardiology Vol. 56, No. 25, 2010
http://content.onlinejacc.org/cgi/content/full/56/25/e50