Cardiac CT - Coronary CT Angiography
Cardiac computed tomography (cardiac CT) includes coronary CT angiography (CTA) as well as using CT technology to assess disease of the cardiac valves, aorta and pericardium.
This examination requires appropriate patient selection and preparation to complete a high quality examination and answer the clinical question. Beta-blockers are frequently given to lower heart rate minimizing motion artifact. Iodinated intravenous contrast is administered and the timing of the contrast bolus is crucial. Sublingual nitroglycerine is used to dilate the coronary arteries for better visualization. Depending on the CT scanner being used and the software available, there are numerous variations in protocol. Coronary CT studies can be retrospectively gated (acquiring data throughout the cardiac cycle) or prospectively gated to reduce radiation exposure (acquiring data only at certain points in the R-R interval).
There are appropriateness criteria to help guide physicians as to the indications for coronary CT angiography. The scoring system used in these criteria is 1-9 with scores of 1-3 being inappropriate indications, 4-6 uncertain indications and 7-9 appropriate indications. Note that the higher the pretest probability of coronary disease and when potential anginal symptoms are present, invasive coronary angiography is usually indicated and not coronary CT angiography according to these criteria.
The appropriate indications for coronary CTA that received a score of 7-9 are:
1. Discordant exercise ECG and imaging results (a.k.a. an equivocal stress test)
2. A previously normal stress test with persistent symptoms concerning for angina
3. Uninterpretable ECG in a patient able to exercise and an intermediate pretest probability for coronary disease
4. Uninterpretable ECG or unable to exercise with low or intermediate pretest probability for coronary disease
5. Evaluation of patency coronary artery bypass grafts
1. Normal ECG and cardiac markers with low or intermediate pretest probability for coronary disease
2. ECG uninterpretable (old left bundle branch or paced rhythm) with low or intermediate pretest probability for coronary disease
3. Non-diagnostic ECG or equivocal cardiac biomarkers with low to intermediate pretest probability
1. Newly diagnosed heart failure with reduced ejection fraction, no prior coronary disease and no anginal symptoms
2. Coronary evaluation prior to non-coronary cardiac surgery (i.e. heart valve surgery) in a patient with intermediate pretest probability for coronary disease
3. Evaluation of coronary anomalies and complex congenital heart disease