Summary:
- CT coronary angiography is a non-invasive scan that detects blocked heart arteries.
- It is recommended for patients with chest pain or who have an intermediate risk of coronary artery disease.
- The scan itself takes only seconds, although the entire appointment usually lasts 30–60 minutes.
- A normal CTCA makes significant coronary artery disease very unlikely.
- Early detection allows treatment that may reduce the risk of future heart attacks.
Heart disease often develops silently. Many people only discover they have blocked heart arteries after suffering a heart attack. Fortunately, advances in medical imaging now allow us to look directly at the heart arteries using a CT coronary angiogram (CTCA), without having to undergo surgery.
This is important because coronary artery disease remains one of the leading causes of death worldwide. In Singapore, nearly one in three deaths in 2024 was due to cardiovascular disease, including heart disease and stroke.1 Heart attacks are becoming increasingly common, and approximately one in nine patients had no symptoms before their heart attack.2
A CTCA is one of the non-invasive tests available to detect narrowed or blocked coronary arteries, allowing cardiologists to detect coronary artery disease before it causes a heart attack, enabling preventive treatment to be considered earlier.
In this article, we’ll explain everything you need to know about CT coronary angiography, including who should have one, how to prepare, what happens during the scan, and what the results mean.
What is a CT Coronary Angiogram?
A CT coronary angiogram (CTCA) is also commonly referred to as a “CT heart scan”, “heart CT scan”, or “CT angiogram of the heart”. It is a specialised CT scan that uses X-rays, intravenous contrast dye, and advanced computer technology to produce highly detailed 3-dimensional images of the coronary arteries— the blood vessels supplying oxygen to the heart muscle.
Unlike a conventional coronary angiogram which is invasive, a CT coronary angiogram does not require a catheter to be inserted into the heart arteries. Instead, contrast dye is injected through a vein in your arm while the CT scanner rapidly acquires images of your heart.
What Can a CT Coronary Angiogram Detect?
The scan can detect:
- Narrowing (stenosis) of the coronary arteries
- Complete blockages
- Calcified plaque
- Soft (non-calcified) plaque
- Mixed plaque
- Congenital abnormalities of the coronary arteries
- Coronary artery aneurysms
Modern CT scanners can acquire images of the entire heart in just a few heartbeats, while exposing patients to relatively low radiation doses.
Severe stenosis seen in the mid LAD on CTCA (left panel) and coronary angiogram (right panel).
Why is a CT Coronary Angiogram Important?
Coronary artery disease often develops silently over many years. Plaque gradually builds up inside the arteries without causing symptoms until blood flow becomes significantly reduced or a plaque suddenly ruptures, resulting in a heart attack.
Importantly, CTCA does more than detect severe blockages. It can also detect early atherosclerosis. For many patients, identifying coronary plaque before it progresses or causes symptoms provides an opportunity to prevent, rather than simply treat, a heart attack.
Who Should Get a CT Coronary Angiogram?
Not everyone requires a CT coronary angiogram. The test is most useful when there is a reasonable possibility of coronary artery disease, but uncertainty about whether significant blockages are present.
You may benefit from CTCA if you have:
1) Chest discomfort, especially if symptoms occur during exercise or emotional stress.
Such symptoms include:
- Chest tightness, pressure, pain, or discomfort
- Burning sensation in the chest
- Jaw pain
- Neck pain
- Shoulder pain
- Arm discomfort
- Unexplained upper back discomfort
2) Shortness of breath
Some people, especially women, older adults, and patients with diabetes, may experience breathlessness as their only symptom of heart disease, instead of chest pain.
3) Multiple cardiovascular risk factors
Risk factors include:
- Diabetes
- High cholesterol
- High blood pressure
- Smoking
- Obesity
- Family history of premature heart disease
- Elevated Lipoprotein(a) levels [Lp(a)]
- Chronic kidney disease
4) Abnormal cardiac investigations
A CT coronary angiogram may be recommended after:
- Abnormal ECG finding
- Abnormal, equivocal, or inconclusive treadmill stress test
- Abnormal stress echocardiogram
- Abnormal nuclear stress test
- Abnormal cardiac MRI finding
5) Intermediate likelihood of coronary artery disease
International guidelines now recommend CT coronary angiography as a first-line investigation for many patients with stable chest pain because of its diagnostic accuracy.3,4
Large clinical trials, particularly SCOT-HEART5, have shown that CTCA can improve diagnostic certainty and guide preventive therapy. Longer-term follow-up from SCOT-HEART also demonstrated a reduction in coronary heart disease death or non-fatal heart attacks among patients managed with CTCA-guided care.
Who May Not Be Suitable for CT Coronary Angiogram?
CT coronary angiogram may not be appropriate if you:
- Have severe kidney impairment
- Have had a previous severe reaction to iodinated contrast
- Are unable to hold your breath briefly
- Have very rapid or irregular heart rhythms that significantly reduce image quality (although newer CT scanners have improved substantially)
- Are pregnant unless absolutely necessary
Your cardiologist will determine whether another test, such as a stress echocardiogram, cardiac MRI, nuclear perfusion imaging, or invasive coronary angiography, is more appropriate.
How Accurate is a CT Coronary Angiogram at Detecting Blocked Heart Arteries?
CT coronary angiogram is one of the most accurate non-invasive tests for detecting coronary artery disease. It has very high sensitivity and an excellent negative predictive value for detecting significant coronary artery disease, making it particularly useful in ruling out significant disease in appropriately selected patients.6
In simple terms, a normal CT coronary angiogram makes significant coronary artery disease very unlikely.
What are the Limitations of a CT Coronary Angiogram?
A CT coronary angiogram may not always provide diagnostic-quality images in patients with extensive coronary artery calcification, very rapid or irregular heart rhythms (such as atrial fibrillation), or severe obesity.
In such situations, other cardiac investigations may be more appropriate.
What Should I Do Before My CT Coronary Angiogram?
Preparation helps ensure the best image quality.
Your doctor may advise you to:
- Avoid caffeine: Avoid coffee, tea, energy drinks and cola for approximately 12–24 hours before the scan, as caffeine increases heart rate.
- Avoid smoking: Nicotine also increases heart rate and may reduce image quality.
- Continue medications unless instructed otherwise: Your doctor will advise if any medications need to be stopped before the scan. Metformin (a diabetic medication) is sometimes stopped on the day of the CTCA and for 48 hours after the scan, particularly if kidney function is impaired.
- Drink water: Good hydration helps to flush out the contrast and supports kidney function unless you have been advised to restrict fluids.
- Wear comfortable clothing: You may be asked to change into a hospital gown.
Why Are Heart Rate-Lowering Medications Given?
The slower the heart rate, the clearer the heart images and the more accurate the diagnosis. Because the heart is constantly moving, doctors often aim for a heart rate around 60 beats per minute or lower.
Do come early for the scan so that you have time to rest and allow your heart rate to stabilise.
In addition, you may receive:
- Oral beta-blockers or ivabradine before coming for the scan
- Intravenous or oral beta-blockers immediately before imaging if required
These medications temporarily slow the heart and improve image quality. Some patients also receive nitroglycerin spray under the tongue to widen the coronary arteries, allowing better visualisation.
What Happens During The CT Coronary Angiogram?
The scan itself is surprisingly quick.
The typical process4 includes:
Step 1: ECG leads are placed on your chest to synchronise image acquisition with your heartbeat.
Step 2: A small intravenous cannula is inserted into a vein in your arm.
Step 3: Contrast dye is injected through the cannula.
You may briefly experience:
- A warm sensation throughout the body
- A metallic taste in the mouth
- A temporary feeling as though you need to pass urine
These sensations are normal and usually disappear within seconds.
Step 4: You will be asked to hold your breath for approximately 5–10 seconds while the scanner acquires images.
The entire appointment usually lasts 30–60 minutes, although the actual scan often takes less than 10 seconds.
What Happens After the CT Coronary Angiogram?
Most patients can return to their normal daily activities immediately.
You should:
- Drink extra water to help flush out the contrast dye, unless you have been advised to restrict your fluid intake.
- Resume normal eating unless instructed otherwise.
- Continue medications unless advised differently. Metformin (a diabetic medication) is sometimes stopped on the day of the CTCA and for 48 hours after the scan, particularly if kidney function is impaired.
If you received medications to lower your heart rate, you may be observed briefly before going home.
What are the Risks of a CT Coronary Angiogram?
A CT coronary angiogram is a safe and minimally invasive investigation. Serious complications are uncommon, and for most people, the benefits of accurately diagnosing coronary artery disease far outweigh the risks. However, like any medical test, there are some potential risks to be aware of.
1) Radiation exposure
A CT coronary angiogram uses X-rays to create detailed images of the heart arteries, which means you will be exposed to a small amount of radiation. Modern CT scanners have dramatically reduced radiation doses compared with older scanners.
For most patients, the radiation dose is comparable to or only modestly higher than natural background radiation accumulated over a few years. The potential benefit of accurately diagnosing significant coronary artery disease generally outweighs the small theoretical radiation risk when the test is appropriately indicated.
2) Allergic reaction to contrast dye
A CT coronary angiogram requires an iodine-containing contrast dye to clearly visualise the coronary arteries.
Most people tolerate the contrast without any problems. Mild reactions, such as itching, a skin rash, or nausea, are uncommon and usually resolve quickly. Severe allergic reactions are very rare, but emergency medications and trained medical staff are always available should they occur.
Be sure to inform your doctor if you have had a previous allergic reaction to iodinated contrast or have a history of severe allergies.
3.) Effects on kidney function
The contrast dye is filtered by the kidneys. In people with normal kidney function, this rarely causes problems. However, patients with significant kidney impairment may have a higher risk of kidney injury following iodinated contrast administration. Your doctor may arrange a blood test to check your kidney function before and a few days after the scan if necessary.
Drinking plenty of water after the procedure helps the body to reduce the risk of kidney injury, unless you have been advised to restrict your fluid intake.
4.) Temporary side effects from heart rate-lowering medication
To obtain clear images, many patients are given medications such as beta blockers or ivabradine before the scan to slow the heart rate.
These medications are generally well tolerated but may occasionally cause:
- A very slow heart rate
- Low blood pressure
- Mild dizziness
- Fatigue
These effects are usually short-lived and resolve after a few hours.
5.) Temporary headache
Some patients may receive a spray of nitroglycerin under the tongue just before imaging to widen the coronary arteries and improve image quality.
Some people may experience:
- A mild headache
- Facial flushing
- Light-headedness
These side effects are usually temporary and typically disappear within a few minutes.
6.) Contrast leakage at the injection site
Occasionally, a small amount of contrast dye may leak outside the vein during injection.
This can cause temporary pain, swelling, or bruising around the injection site. Significant tissue injury is very uncommon and usually resolves with simple measures such as elevating the arm and applying a cold compress.
Serious Complications Are Rare
Overall, CT coronary angiography is safe. Serious complications, such as severe allergic reactions or significant kidney injury, are uncommon, particularly when patients are appropriately selected and screened beforehand.
Your cardiologist will review your medical history, allergies, medications, and kidney function before recommending the test to ensure it is both safe and appropriate for you.
Understanding Your CT Coronary Angiogram Results
Your cardiologist will explain whether the scan shows:
- Normal coronary arteries: No evidence of coronary artery disease.
- Mild narrowing: Mild atherosclerotic plaque which is often managed with lifestyle modification and appropriate cholesterol-lowering medication.
- Moderate narrowing: Further assessment may sometimes be recommended, depending on symptoms, the location, and appearance of the plaques.
- Severe narrowing: Significant blockages may require additional investigations such as invasive coronary angiography, with possible coronary angioplasty (stenting) if appropriate.
Remember, treatment decisions are based not only on the scan findings but also on your symptoms, risk factors, and overall clinical assessment.
Speak To Our Experienced Cardiologists About A CT Coronary Angiogram in Singapore
A CT coronary angiogram is a powerful non-invasive tool for detecting blocked heart arteries. It provides detailed images of the coronary arteries, helps diagnose coronary artery disease at an early stage, and guides treatment to reduce the risk of future heart attacks.
Coronary artery disease is often silent, but it doesn’t have to remain undetected. If you are experiencing chest pain, shortness of breath, or have multiple cardiovascular risk factors such as diabetes, high cholesterol, high blood pressure, smoking, or a strong family history of heart disease, speak to your cardiologist about whether a CT coronary angiogram is appropriate for you. Detecting disease early could make all the difference to your long-term heart health.
Not sure whether you need a CT coronary angiogram or a CT calcium score? Read our guide: CT Calcium Score vs CT Coronary Angiogram: Which Heart Scan Is Right for You?
FAQs on CT Coronary Angiogram in Singapore
Can a CT coronary angiogram detect a heart attack?
CT coronary angiography is not the primary test used to diagnose an acute heart attack. If you have symptoms suggestive of a heart attack, you need urgent medical assessment, including an ECG and blood tests such as cardiac troponin.
If you are experiencing severe or persistent chest pain, shortness of breath, sweating, or other symptoms suggestive of a heart attack, seek emergency medical attention immediately.
Can a CT coronary angiogram detect blocked arteries?
Yes. A CT coronary angiogram is specifically designed to detect narrowing or blockages in the coronary arteries. It can identify both calcified and non-calcified plaques and is an accurate non-invasive test for diagnosing coronary artery disease.
Is a CT coronary angiogram painful?
No. The scan is non-invasive. Apart from insertion of the intravenous cannula, most patients experience little or no discomfort.
Is a CT coronary angiogram better than a treadmill stress test?
The two tests answer different questions.
- A stress test is a functional test that evaluates how the heart responds to exercise and detects severe blockages that significantly reduce blood flow during exercise.
- A CT coronary angiography is an anatomical test that directly visualises the coronary arteries and can detect even minor narrowings. However, it does not directly assess whether blood flow to the heart muscle is significantly compromised.
In many patients with stable chest pain, CTCA is an appropriate first-line investigation and provides detailed anatomical information about the coronary arteries.
Will I need a coronary angiogram afterwards?
Not necessarily. Many patients can avoid invasive coronary angiography if CTCA shows normal arteries or only mild disease. However, patients with severe narrowing or uncertain findings may still require invasive assessment.
Can I drive after the scan?
Most patients can drive home afterwards unless they have received medications that make them feel unwell or their doctor advises otherwise.
- Principal Causes of Death in Singapore 2024. https://www.moh.gov.sg/others/resources-and-statistics/principal-causes-of-death/
- Singapore Myocardial Infarction Registry Annual Report 2023. www.nrdo.gov.sg/docs/librariesprovider3/default-document-library/singapore-myocardial-infarction-registry-annual-report-2023.pdf
- Gulati M, Levy PD, Mukherjee D, et al. 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR Guideline for the Evaluation and Diagnosis of Chest Pain: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2021;144:e368–e454. doi:10.1161/CIR.0000000000001029.
- Vrints C, Andreotti F, Koskinas KC, et al.; ESC Scientific Document Group. 2024 ESC Guidelines for the management of chronic coronary syndromes. Eur Heart J. 2024;45(36):3415–3537. doi:10.1093/eurheartj/ehae177.
- Newby DE, Adamson PD, Berry C, et al.; SCOT-HEART Investigators. Coronary CT Angiography and 5-Year Risk of Myocardial Infarction. N Engl J Med. 2018;379(10):924–933. doi:10.1056/NEJMoa1805971.
- Narula J, Chandrashekhar Y, Ahmadi A, et al. SCCT 2021 Expert Consensus Document on Coronary Computed Tomographic Angiography: A Report of the Society of Cardiovascular Computed Tomography. J Cardiovasc Comput Tomogr. 2021;15(3):192–217. doi:10.1016/j.jcct.2020.11.001.
