Video: This video illustrates the main differences between the CT Coronary Angiogram and CT Calcium Scoring and when each test is indicated.
The heart has been the primary focus of intensive research over the past century, leading to significant advancements in cardiology and cardiac imaging techniques. The CT Coronary Angiogram (CTCA) and the CT Coronary Artery Calcium Score (CAC Score) are commonly used non-invasive diagnostic tools for assessing cardiac health. While the CTCA serves primarily as a diagnostic test, the CT calcium score is a “risk assessment” tool without diagnostic implications. Understanding the distinctions between these two imaging techniques is essential for patient management, as overlooking their differences can lead to severe, life-threatening consequences. In this article, I delineate the differences, limitations, and indications of these imaging techniques.
CT Coronary Angiogram (CTCA)
A CT Coronary Angiogram is a specialized computed tomography (CT) scan that captures detailed images of the coronary arteries. It uses intravenous contrast dye to highlight blood vessels, allowing physicians to evaluate blood flow and identify any narrowing or blockages due to plaque build-up.
Indications for CTCA:
- Suspicion of coronary artery disease (CAD) in patients with chest pain or other symptoms suggestive of angina.
- Evaluation of patients with abnormal stress echocardiogram results.
- Assessment of coronary artery bypass grafts (CABG) or stents.
- Preoperative evaluation before non-cardiac surgery for patients with known CAD or multiple risk factors.
Limitations of CTCA:
- Exposure to ionizing radiation and iodinated contrast dye, which may cause allergic reactions or kidney damage in some patients.
- Inability to accurately evaluate calcified plaques, as they can cause blooming artifacts that may obscure the lumen.
- Inability to measure the physiological significance of stenosis (i.e., whether the stenosis has compromised blood flow).
- Not recommended for patients with known allergy to iodinated contrast dye, severely impaired kidney function, or pregnant women.
CT Coronary Artery Calcium Score (CAC Score)
The coronary artery calcium score measures the amount of calcified plaque in the coronary arteries. It uses a non-contrast CT scan to quantify calcium deposits, which are then used to calculate a score. A higher score indicates a higher risk of future cardiac events.
Indications for CAC Score:
- Asymptomatic patients with low to intermediate risk for CAD to help redefine risk stratification and guide preventive strategies.
- Patients with a family history of premature CAD.
- Evaluate patients with atypical chest pain after a normal functional test like a stress echocardiogram or myocardial perfusion scan.
Limitations of CAC Score:
- Exposure to ionizing radiation, albeit at a lower dose compared to CTCA.
- Inability to detect non-calcified plaque, which can still cause significant stenosis and contribute to CAD.
- No information about the severity of luminal narrowing or blood flow impairment.
The CT Coronary Angiogram and CT Calcium Score are valuable diagnostic tools for assessing cardiac health. CTCA is typically used for individuals experiencing symptoms such as chest pain or when abnormalities are detected during a stress echocardiogram. Although CTCA offers a detailed evaluation of coronary arteries, it involves higher radiation exposure and the use of contrast dye.
In contrast, CAC Score quantifies calcified plaque burden. It aids in risk stratification but lacks information about non-calcified plaque or blood flow impairment. CAC Score is recommended for individuals without symptoms or those with a normal stress echocardiogram to assess future heart attack risk and guide therapy. It’s essential to note that CAC Score should not be used for high-risk individuals, such as those with multiple risk factors for CAD, or Familial Hypercholesterolemia (FH), as it may not detect non-calcified plaques and blockages. This crucial point about CAC Score is further explained in this post, along with a real case study for better understanding.