Plaque Detector/ Coronary Artery Calcium Scan
Coronary artery calcification is 100% specific for presence of atherosclerotic plaque
Many heart attack patients do not experience any warning signs, the heart attack itself being the first sign of heart disease. It is called the silent killer for this very reason, and remains the top cause of mortality in most countries.
Who should have a Coronary Artery 'Calcium' Scan (CAS) Scan?
Stress testing in all its various modalities attempt to detect coronary artery disease from functional changes in the heart resulting from ischaemia (lack of oxygen), but the heart artery blockage has to be severe before that will happen. Treadmill stress ECG, SPECT, stress echocardiography and other current non-invasive diagnostic tools cannot detect the presence of a mild or non-obstructive CAD(<50%) narrowing. Yet mild or less than 50% lesions are responsible for 70% of heart attacks. (Falk et al Circulation 1995; 92:657-671)
One can have a negative stress test but still be at risk of having a heart attack.
Scientific Background
CT scanning of heart, or heart scan (CAS), is an imaging technique that detects calcium deposits in coronary arteries with a high sensitivity of 95%. There is no question that coronary artery calcification is part of the development of atherosclerosis. Calcification occurs exclusively in atherosclerotic arteries and is absent in the normal vessel wall. The presence of a heavy calcium load certainly indicates an atherosclerotic process and a greater likelihood that the plaques of interest are present.
CAS is useful in screening of asymptomatic people to assess those at high risk for developing coronary heart disease and cardiac events, as well as for the diagnosis of obstructive coronary artery disease(CAD) in symptomatic patients
CAS test is 95% sensitive. In other words, it will pick up 95% of all patients with coronary atherosclerosis, even at a very early stage. It is 100% specific for presence of coronary atherosclerosis; there is no false positive result. A person with no coronary atheroslerosis will not get a false alarm from an erroneous positive scan.
A negative CAS test makes the presence of atherosclerotic plaque, including unstable plaque, very unlikely.
A negative test is highly unlikely in the presence of significant luminal obstructive disease.
Negative tests occur in the majority of patients who have angiographically normal coronary arteries.
A negative test may be consistent with a low risk of a cardiovascular event in the next 2-5 years.
A positive CAS result confirms the presence of a coronary atherosclerotic plaque.
The greater the amount of calcium, the greater the likelihood of occlusive CAD, but it is not a 1-to-1 relationship, and findings may not be site specific.
The total amount of calcium correlates best with the total amount of atherosclerotic plaque, although the true “plaque burden” is underestimated.
A high calcium score may be consistent with moderate to high risk of a cardiovascular event within the next 2 to 5 years.
A consistent finding of ALL published studies is that CAS calcium scores in asymptomatic patients provide an index of future cardiac risk ranging from 2 to 10 times greater than that predicted by conventional (Framingham) risk analysis.(Ref:Rumberger Mayo Clin Proc 1999;94:243-252)
The primary purpose of CAS is to find early heart disease (coronary plaque) prior to the development of a major blockage. This test is uniquely qualified to do this and should not be compared to stress testing for this purpose, which is abnormal only when there is already advanced coronary disease.
Published data indicate that CAS is a cost effective alternative to conventional stress testing in many common clinical situations. CAS is very effective in determining who does NOT need further testing.
The calcium score has been advocated by Scott Grundy, Chairman of National Cholesterol Education Program and Framingham Heart Study as a potential surrogate for age in risk-assessment models. (ref: Scott Grundy AJC 1999;83:1455-1457)
The AHA Prevention 5 Scientific Committee stated that CAS has the greatest potential for further determination of risk particularly in elderly asymptomatic patients and others at intermediate risk. When a screening of risk factors is done first, there is a fairly large group that may be at moderate risk. CAS in that setting could be very useful in identifying patients who, if they have a high score, might be candidates for aggressive risk factor modification with medication. Conversely a low or absent score on CAS would help define a low-risk population.
CAS has also been proposed as a useful technique for assessing the progression or regression of coronary artery disease in response to treatment of risk factors such as hypercholesterolemia. (ref: Budoff AJC 2000;86:8-11)
Recent study published in the Journal of the American College of Cardiology in Nov 2018, shows that coronary artery calcium scoring can identify with a high degree of accuracy, patient who will or will benefit from statins (cholesterol medicines) treatment. The study was based on over 13,500 patients followed for nearly 10 years.
* Coronary Artery Calcium Scan cannot determine the degree of narrowing in the heart arteries. CT Angiogram or Conventional angiogram is the procedure for this purposes.