Coronary CT angiography

Should all Indians above 40 years of age undergo screening with coronary CT angiography to detect coronary disease ?

Recently, a 56 year old man, a non smoker, who had no prior symptoms, had sudden severe chest pain and collapsed in his house with cardiac arrest. He was a regular tennis player, without hypertension, diabetes or obesity. The only adverse history was that both his parents had coronary heart disease and some cousins too at young age.

Could we have done a test earlier which could have help us predict his heart disease and helped us prevent it? Something like treadmill stress test? Or CT coronary angiography ?

CT coronary angiography is a test in which a liquid (called ‘contrast’ or ‘dye’) is injected into a vein, the subject is asked to hold his/her breath for few seconds, and the heart is scanned under a CT scanner. What comes out as a result are pictures of one’s coronary arteries. One can then see whether his/her coronary arteries have blockages or not.

What is the accuracy of the test- vis a vis the usual invasive coronary angiography ? or vis a vis treadmill stress test?

Well, a negative test is highly reliable. In other words, if your CT coronary angiogram is normal, there is about 98% likelihood that it is truly normal. On the other hand a “positive” test result is not so reliable – which means that if there are blockages, these may be over or under diagnosed and an invasive angiogram MAY be necessary if the physician so feels.

But the advantage of this test is not only that it is convenient, non invasive and can be done in a few minutes on an out-patient basis, but that it also shows the state of coronary artery wall- whether it is thickened due to “plaque” or fat build up on the inner lining. This can tell whether the patient is at a future risk of a heart attack caused by rupture of that “plaque” and clot formation on top of it.

A treadmill stress test does not tell you this and there is the issue of lot of false positives and false negatives in a treadmill test.

So the million dollar question is whether to subject all above 40 years to CT coronary angiography, given the high propensity of the disease in young Indians ? (Almost 4 times our western brothers).

That brings us to the disadvantages of the test. Firstly, it exposes the individual to radiation which is potentially carcinogenic. Secondly it exposes the individual to the “dye” load which can harm kidneys if they are already compromised. Finally the cost (Rs 8000 to 12000) may prohibit usage on a mass scale.

Hence selection of the test for only some high risk individuals is the key. At present, due to its inherent dangers, recent “appropriateness criteria” from bodies such as the American Heart Association mention that the test is definitely ‘inappropriate’ for low or intermediate risk patients but its value is “uncertain” for high risk individuals. *

“Uncertain” means that the authors were equally divided between agreeing and disagreeing with the appropriateness of the test and opine that the test “may be generally acceptable and may be a reasonable approach for the indication”.

So, on the one hand we have a test which can easily tell us whether disease is present or not – a disease which takes away or damages young lives in India. On the other hand we may expose normal people (already exposed to a host of pollutants and radiation) to harmful radiation.

Although the balance is thus evenly placed, one would like to tilt it in favor of doing the test in high risk individuals especially young Indians who are inherently at a risk higher than western counterparts (to whom the appropriateness criteria properly apply).

So, to answer the question posed at the beginning: “Should all Indians above 40 years of age undergo screening with coronary CT angiography ?”

Well, not all, but only those at high risk of any age may undergo the test..

It may be very useful in a young man of 35 with risk factors, esp a strong family history of premature heart disease, while it may not be useful and cause more harm than benefit in a man of 60 with low risk.

Thus in view of the wide prevalence of severe coronary artery disease in young Indians, coronary CT angiography may be used for “routine screening” of high risk individuals based on the number and severity of risk factors such as diabetes, hypertension, abnormal lipids and family history of premature heart disease (below age 56 in brothers or father and below 65 yrs in mother or sisters). Then, if presence of disease is confirmed by the test, vigorous life style changes and even preventive medications like statins and aspirin may make a difference between life and death for these individuals.


*People are divided into low, intermediate or high risk for heart attack in next ten years based on the presence and severity of ‘risk factors’ in them.
Low risk correlates with a 10-year absolute CHD (coronary heart disease) risk <10%, intermediate risk correlates with a 10-year absolute CHD risk between 10% to 20% and high risk is defined as a 10-year absolute CHD risk of >20%, the presence of diabetes mellitus in a patient 40 years of age, peripheral arterial disease or other coronary risk equivalents (prior angina, heart attack etc) This ‘scoring’ of risk is done by noting risk factors in an individual like hypertension, diabetes, abnormal cholesterol levels, smoking, family history of premature heart disease etc. and logging on to :
http://www.framinghamheartstudy.org/risk/coronary.html
http://hp2010.nhlbihin.net/ATPiii/calculator.asp