ct coronary calcium scores hdr

Why Heart Disease Is Like Street Crime - CT Coronary Calcium Scores

Why Heart Disease Is Like Street Crime

Broken windows theory was proposed in 1982 by Political Scientist James Quinn Wilson and Criminologist Geroge Kelling. The idea was that small crimes and misdemeanours inevitably led to serious crimes. This idea was taken on by New York Police Commissioner William Bratton. He cracked down on petty crimes and as a result, serious crime in New York fell. 

Some people have a lipid profile that puts them at increased risk of cardiovascular disease. If you have a high Apolipoprotein-B (Apo-B) and high LDL particle number (LDL-p), for example, you are at higher risk of cardiovascular disease. This is because a high LDL particle number means that LDL is likely to break into the wall of the artery, cause inflammation and lead to coronary heart disease. It gets into the wall of the artery thanks to Apo-B. Having high Apo-B and LDL-p is analogous to living in a bad neighbourhood. If you have high Apo-B and LDL you are likely to have a break-in (to the arterial wall). Coronary calcium is a sign that damage has occurred in the arterial wall and reflects the body’s healing in response to damage. It is like having a boarded-up window after it has been smashed by a hooligan in a bad neighbourhood. We know from commissioner Bratton that broken windows inevitably lead to serious crime. In much the same way, coronary calcium is a signal that something serious is going to happen in the arterial wall. 

Coronary artery calcium scoring (CACS) examines calcium deposits in the coronary arteries that occur during atherosclerotic plaque formation. The study takes around 10 minutes, doesn’t use contrast and the radiation dose is low (approximately 1 mSv). This amount of radiation is comparable to around two screening mammograms. The average person is exposed to approximately 2.7mSv radiation per year in the UK according to Public Health England. 

Calcification in the arteries is due to the repair of the damage caused by the formation of atherosclerotic plaque. CACS provides an overall assessment of the amount of calcification, most commonly using the Agatston Score. As an interesting aside, Arthur Agatston not only developed the scoring system for measuring coronary artery calcium but also the South Beach Diet. 

The initial evidence of the value of coronary calcium was provided by the landmark Multiethnic Study of Atherosclerosis (MESA). This was a study of 6814 individuals from four major ethnic groups. The study found a strong association between calcium score and adverse coronary events over almost 4 years of follow-up.  Subsequent studies have shown the benefit of calcium scoring in a variety of ages, sexes and clinical risk factor burdens.

The addition of calcium scoring to our traditional risk estimation improves our identification of a patients chance of cardiovascular disease. It is particularly useful who allowing us to better understand who would and would not benefit from having medications to prevent cardiovascular disease such as statins or aspirin.

A key advantage of calcium scoring is that while high scores are associated with elevated cardiovascular risk, the absence of coronary calcium is a negative risk marker that confers a good prognosis. This is what is known as negative predictive value. The negative predictive value of zero coronary calcium appears to be greatest in individuals at intermediate risk by traditional risk calculators. 45% of these patients will have CAC = 0, placing them at low cardiovascular risk and removing the need for preventive therapy such as statins. Conversely, the power of zero coronary calcium is limited in individuals who are already at high risk. Nearly 50% of fatal MIs occur in non-calcified areas of coronary arteries.  So even if the calcium score is zero, the patient may still need aggressive intervention if they live in a ‘bad neighbourhood.’ That is, even if they have a normal CAC but have very high ApoB and LDL-p. This is because they may have soft plaque and CAC does not show soft plaque.  

European Society of Cardiology guidance on CVD prevention, dyslipidaemia, and chronic coronary syndrome have all recognised the important role of CACS in the CVD risk assessment on an individual patient screening basis. They advised that CACS may improve risk classification in patients without symptoms in the moderate or low-risk categories. At levels of risk above this, significant lifestyle changes and potential medications are indicated. 

So, CACS, seeing the amount of boarded-up windows in your neighbourhood, can considerably improve our estimation of your risk of cardiovascular disease and can be extremely helpful in guiding decisions on preventative treatment. 

Dr J Hugh Coyne

Private GP