CT Coronary Calcium Scoring

20-12-2006Back to Article

CT Coronary Calcium Scoring – Predicting your 10 year Risk for a Heart attack. The basic question that arises in all our minds is why all these new tests when the Exercise TMT is the most economical way of selecting people for aggressive interventional management or conservative medical management. The ACCF/AHA Expert Consensus Document on Coronary Artery Calcium Scoring published in 2007 discusses on this aspect after, Gianrossi et al. investigated the reported diagnostic accuracy of the exercise ECG for CAD obstructive disease in a meta-analysis. One hundred forty-seven (147) consecutively published reports involving 24 074 patients who underwent both coronary angiography and exercise testing were summarized. Wide variability in sensitivity and specificity was found (mean sensitivity (the ability of a test to correctly pick a positive patient) was 68% only, with a range of 23% to 100% and a standard deviation (variation from person to person who did the study) of 16%; mean specificity (a positive patient to have been rightly diagnosed meaning the right positive among the positive cases) was 77% only, with a range of 17% to 100% and a standard deviation of 17%)(variation from person to person who did the study).

This signifies that based on sensitivity – 68% were rightly picked (Out of every 100 patients only 68 were positive) and from specificity - 77% (Out of 100 patients who were TMT positive only 77 were actually positive, with some degree of disease). On an average 40% of all TMT studies done are non specific and therefore to avoid interventional procedures in potentially normal patients from being subject to intervention and cost burdens other added more specific risk factors were looked at.

In the west to increase specificity to the selection criteria – the most widely used test since the last 2 decades is a test called stress thallium “Myocardial perfusion scan”. This is done by injecting – a small amount of 99mTc MIBI/ Tetrofosmine into a peripheral vein at the peak of the TMT Exercise test and later imaging under a gamma camera to understand the decrease in blood supply to the cardiac muscle. This test is totally non invasive and can be performed on patients who cannot undergo a treadmill stress test by way of a pharmacological stress test. The sensitivity of this test was – 93% and the specificity was 97% that means only 7% would be missed in comparison with the 32 % being missed on TMT stress alone, and the Specificity that is the false positive rate was only 3% compared to the 23% of TMT stress alone. Other valuable information on function, Contractility of the heart muscle, Vessel territory, Extend of decrease in blood supply (Functional significance) was very clearly understood. Cost per examination prevented it from being employed as a routine screening test and was placed to further select the patients with an intermediate Stress TMT positive meaning – patients who were not very strongly positive on TMT stress.

 

If the Coronary Calcium Score (CAC) is:	1-year risk is:	10-year risk is:	Rounded
0	1.1%	10.5%	10%
1-100	1.9%)	17.2%	17%
101-400	3.3%	28.6%	29%
>400	4.7%	38.5%	38%

Any one with a 10 year risk score of 15% and above should have a TMT stress done.

 

A simple pathway to calculate your risk and what to do next.

 

• Use the risk calculator on our web site home page to Calculate your 10 year risk / mail us to know your risk.

• If you have a 10 year risk > 10% - CAC scoring or TMT stress is suggested. (To access your further risk).

• Based on Your TMT Stress Test Results - Suggestions.

  • Stage 1 positive : Interventional Catheter Angiography.
  • Stage 2 positive: Interventional catheter Angiography.
  • Stage 3,4, Recovery positive: CT Angiography or Myocardial Perfusion Scan.

• Simple one short – 15 second screening tests – CT Angiography.

(This is an easy, simple and cost effective method of evaluation mentioned and practiced widely in many western countries. Personal practice views might vary from doctor to doctor and this is being given just to give a wide view of what is available among interventional and non-interventional methods to screen yourselves and select the right choice of treatment).

Issued in Public Health Interest by DDNMRC Radiology as Part of Identifying the possibly affected but asymptomatic population so timely treatment can be initiated by giving appropriate advice in risk management, in preventing heart attacks and sudden cardiac deaths from occurring.

Procedure and Precautions.

CT Coronary Calcium Scoring is a simple, non invasive 4 seconds procedure available in all Cardiac CT centres all across the country and are charges for the tests vary between Rs 1000 – Rs 2500/- from centre to centre all across the country. Calcium scoring is a technique where the extent of calcification in the coronary arteries is measured and scored. It has been around for many years and was initially performed using EBCT (electron beam CT), but is now increasingly performed using mult-slice / 64slice CT. As a rule, the faster the scanner, the more accurate is the calcium scoring. There is a direct correlation between the extent of calcium in the coronary arteries and the risk of a future cardiac event. For example, a calcium score of more than 400 is considered severe and it would be necessary to take steps to prevent further advancement of atherosclerosis and plaque formation. The higher the calcium score, more likely is there a chance of severe stenosis as well. The attributed risk to calcium score and the risk is mentioned in the table above. A calcium score of 0 does not rule of soft plaques, but statistically rules out significant coronary artery disease. Though the calcium score does not show soft plaques (which however are best seen on a CT angiogram), the higher the calcium score, the more is it likely that there are soft plaques as well. Rupture of a soft plaque is the commonest cause of an acute coronary syndrome (i.e. a heart attack). Calcium scoring is offered as a separate stand-alone test, but more and more, since we are reliably able to assess the coronary arteries themselves, it is being performed as an initial part of the entire cardiac CT examination.