What is a CT coronary angiogram ?
Computed tomography coronary angiography (CTCA) uses X-rays to provide images of the coronary arteries and the heart muscle. Combined with an intravenous contrast material, CTCA provides high-resolution, three-dimensional images of the heart and the coronary arteries. These images show whether there is furring or blockage of the coronary arteries (arteriosclerosis).
What is a calcium score ?
Calcium is deposited during the process of furring of the arteries. Generally, a high calcium score is associated with a high risk of future heart attacks. Your GP may have requested a calcium scoring scan if you are thought to be at risk of developing coronary heart disease. A high calcium score carries a higher risk of developing heart attacks than a low score. A high score, however, does not give any information as to whether the coronary arteries are blocked or likely to be the source of a heart attack. On the other hand, a low calcium score is associated with a low risk of future heart attacks, it does not necessarily mean that the arteries are not furred up. This is why it is essential that you discuss the value of your calcium score with your cardiologist.
Coronary calcium is a marker for atherosclerosis (hardening of the arteries). The presence and amount of calcium detected in a coronary artery by the CT scan, indicates the presence and amount of atherosclerotic plaque. These calcium deposits appear years before the development of heart disease.
A calcium score is computed for each of the coronary arteries based upon the volume and density of the calcium deposits. This can be referred to as your calcified plaque burden. It does not correspond directly to the percentage of narrowing in the artery but does correlate with the severity of the underlying coronary atherosclerosis. This score is then used to determine the calcium percentile, which compares your calcified plaque burden to that of other and women of the same age. The calcium score, in combination with the percentile, enables your physician to determine the future risk of a heart attack.
A score of zero indicates that there is no calcified plaque. This implies that there is no significant coronary artery narrowing and a very low likelihood of a cardiac event over at least the next 3 years. It does not absolutely eliminate the possibility of a cardiac event in the long term.
A score greater than zero indicates at least some coronary artery disease. As the score increases, so does the likelihood of a significant coronary narrowing and the likelihood of a coronary event over the next 3 years, compared to people with lower scores. Similarly, the likelihood of a coronary event increases with increasing calcium percentiles.
What does a CTCA show?
A CTCA provides an image of coronary arteries and provides information about:
• Furring or blockage of the coronary arteries (arteriosclerosis).
• Calcification of the coronary arteries, which in arteriosclerosis.
• Cholesterol build-up (‘soft’, or 'unstable' plaque).
• The degree to which arteriosclerosis narrows the coronary arteries.
• Structural abnormalities of the coronary arteries.
Why have a CTCA ?
A CTCA may be considered in the following circumstances:
• When the cause of chest pain is uncertain
• Chest pain with features that suggest a cardiac cause.
• Inconclusive stress test (treadmill, stress echocardiogram).
• A negative stress test but continuing chest pain.
• Unexplained breathlessness during physical exertion.
• Suspicion of an underlying coronary artery anomaly
• Investigation of coronary artery disease before cardiac surgery.
What does a CTCA involve ?
A CTCA takes less than 10 minutes to perform. You lie down on a special couch which takes you into the bore of the scanner. A small canula is inserted into a vein in your arm so that we can give the contrast substance that highlights the coronary arteries. Sometimes, we may need to give a beta-blocker intravenously to slow down the heart rate. You may be asked to lie still and to hold your breath at intervals. After contrast injection, some patients experience a metallic taste in the mouth or they may fell flushed. These effects are, however, short-lived. The scan will need to be analysed in in detail by the cardiologist. It is essential that the results are discussed with you afterwards.
Calcium score and CTCA references:
Greenland P et al. ACCF/AHA 2007 clinical expert consensus document on coronary artery calcium scoring. J Am Coll Cardiol 2007;49:378-402
Hendel RC et al. ACCF/ACR/SCCT/SCMR/ASNC/NASCI/SCAI/SIR 2006 appropriateness criteria for cardiac computed tomography. J Am Coll Cardiol 2006;48:1475-97.
Carr JJ, et. al., Evaluation of Subsecond Gated Helical CT for Quantification of Coronary Artery Calcium and Comparison with Electron Beam CT.; AJR 2000; 174: 915-921
A 3D reconstruction of a CT coronary angiogram
A CT scanner
Example of calcium score result