CT Coronary Angiogram

CT scanning uses a series of two-dimensional X-ray images taken from a single axis of rotation to build a three-dimensional picture of an area of the body. CT scanning has an increasingly application in diagnostic and therapeutic imaging, although it is only in recent years that it has proved particularly useful for imaging the heart; the heart is more elusive than other organs because it is in a constant state of motion, and sometimes irregularly so. The latest technological innovations have resolved this issue to a great extent, giving us an additional technique with which to explore, understand and treat a number of heart conditions.

coronary artery calcium scoring

Its simplest application for cardiologists is a scan called the coronary artery calcium score. The patient lies in the scanner and CT images of the heart are acquired in a matter of minutes, using a low dose of radiation. The scanner is not claustrophobic and no needles or injections are required. The scan detects calcium build-up in the coronary arteries, a component of the furring up process of coronary artery disease. A calcium score of zero, i.e. no calcium detected in the arteries, equates with a minimal, though not zero, risk of underlying coronary artery disease. Occasionally there is only cholesterol build-up, soft plaque, which has not calcified and which the scanner would therefore not detect; this is more likely in younger patients, since it takes time for calcium deposits to develop. All the same, the calcium score is an excellent screening method for refining an individual’s risk of underlying coronary artery disease; the higher the calcium score, the greater the risk of a future heart attack, and so individuals with a high score can be offered treatment, such as statin therapy, to reduce their risk.

CT coronary angiography

Using the same technology as coronary artery calcium scoring it is possible to view the coronary arteries and their major branches, not only looking for calcium deposits but also for any signs of narrowing within them. This technique detects both calcium deposits and “soft plaque”, and is called a CT coronary angiogram. It is an established alternative to conventional coronary angiography, which necessitates an admission to hospital, usually as a day case, and entails a higher risk of complication. In addition to providing information about the blood supply to the heart, a CT angiogram can also assess the pumping action of the heart and provide information about other structures surrounding the heart.

Preparing for a CT coronary angiogram

The patient should not eat for two to four hours prior to the scan and caffeine should be avoided for 12 hours beforehand, but water can be consumed freely. Better quality images are obtained at slower heart rates, and so a tablet or injection of a beta blocker may be given to slow the heart rate adequately, and the patient will be attached to an ECG monitor for the duration of the scan. The patient might also be given either a tablet or a spray of GTN under the tongue to dilate the arteries and ensure that the best quality images are obtained. Since the test entails the use of a radiographic dye (contrast) to outline the arteries, a recent blood test may be needed to check renal function beforehand, since the dye will be excreted through the kidneys into the urine. If necessary this blood test can sometimes be performed at the time of the scan. It is very important that caffeine is not consumed in the 12 hours before the scan. Caffeine is found in more food, drink and medicines than one might think, and we have listed some of these below. The patient can otherwise eat and drink as normal up to two hours before the scan time.

Food Caffeine (mg/100ml) Medicine Caffeine (mg/pill)
Dark Chocolate 71.4 Panadol Extra 65
Milk Chocolate 21.4 Solpadeine Plus 30
Chocolate Cereal 3 Benylin Cold and ‘Flu 25
Drink Caffeine (mg/100ml) Drink Caffeine (mg/100ml)
Espresso 173.6 Pepsi 10.7
Fresh Coffee 45.4 Green Tea 10.6
Red Bull 32 Diet Pepsi 10.1
Monster 32 Coca Cola 9.7
Instant Coffee 24.1 Chocolate SlimFast 8.4
Tea 19.9 Hot Chocolate 3.8
Diet Coke 12.7 Lipton Iced Tea 2.8
Lucozade 12.1 Decaf Coffee 2.4
Dr Pepper 11.8 Cocoa 2.1

after the scan

A CT coronary angiogram is an outpatient procedure lasting approximately 45 minutes, and the patient can leave the department immediately after the scan and resume normal activities. After the data from the scan have been collected, it is now possible to undertake something called an FFRCT analysis to gain further information about any narrowings in an artery and the impact of those narrowings on blood flow to the heart. This analysis takes place once the patient has left the department and involves applying mathematical equations to 3D models of the arteries in order to assess pressure and flow, and determine whether any lesions detected on the CT scan are restricting blood flow to the heart and therefore require treatment.

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