Cardiac CT

Cardiac CT has been around for approximately 30 years, but has exploded in popularity over the past few years. In my view is now one of the most miss used test we do, partly through public demand and partly through Doctor Ignorance. We need to remember the reason for performing any test- will it change the outcome to the patient or change our management, and is the downside justified!

Which Cardiac CT Scan to have?

Like most tests in Medicine, to answer this we should look at what the question is and why we are doing the test.

A CT Calcium score tells us nothing about blockages or narrowing’s, just whether there is, and how much calcium is present in the arteries as a marker of plaque. It’s synonymous with having a skin check and being told whether you have Sun damaged skin. We expect people with higher risk factors for Coronary disease (Family History/Smoking/Blood pressure/Diabetes/High Cholesterol) to have higher calcium scores. In my view the only role for CT Calcium scoring is to assess peoples “artery Age” to risk stratify them about the benefit of treating the above risk factors. ( which arguably we should do anyway!)

A CT Coronary Angiogram on the other hand can tell us a Calcium score and also the presence of plaque that may have not become Calcified yet- much more likely at a younger age. It also can give an ‘estimate’ of Coronary Narrowing. For this CT scanning has become much more accurate in later years but is still usually quantified with wide ranges. It is a valuable test for assessing the major Coronary Arteries, such as the so called ‘Widow Maker’ which certainly effect treatment options. However, compared with a CT calcium it is more valuable for risk stratifying,particularly in younger people who are more likely to have non-calcified plaque.

What is Cardiac CT scanning?

CT scanning, or Computed Tomography is widely used in medicine. Commonly miss understood is that there are broadly speaking 2 types of Cardiac CT scans: CT Calcium scans, and CT Coronary Angiography (CTCA) and they do provide different information.

CT Calcium scan is a non contrast scan that essentially simply measures and quantifies any Calcium in your coronary arteries and where in the arteries it is- it tells us nothing about narrowing’s or blockages. However, coronary plaque usually becomes calcified over time so Calcium is a marker of Plaque burden, and the higher the calcium present, the higher probability of narrowing’s. We will all get plaque in our arteries, almost from the day we are born, so some degree of Calcification is normal. That is why the absolute CT calcium score is usually graded related to your age expected- although it would be lovely to have Zero calcium, a percentile Calcium score of 50% places you at age predicted calcification.

A CTCA on the ther hand does involve contrast and aims to look to see if there are any narrowing’s of the Coronary Arteries- if you like, a “Virtual Angiogram”. It usually also includes a Calcium score. It will aim to quantify any plaque and narrowing’s, and importantly will be able to document ‘non-calfified’ plaque!

Is there a down side to Cardiac CT Scanning?

There is very little down side or risk, although serious Allergic reactions can occur with inta-venous Contrast.

The radiation dose fro Cardiac CT scanning is not insignificant and has getting lower- for a CT Calcium Scan it is approximately 3mSv ( about the same as 30 Chest X-rays), for a CT Angiogram 12 mSv (about the same as 120 Chest X-rays).