CT

Screening CT Coronary Angiography, Our Experience

About 10 per cent of the population at large has CAD which is undiagnosed, since they do not have any manifesting symptom like chest pain

"We read every day about health checkup programmes by various hospitals to assess the overall fitness of an individual. But, none of the hospitals does CT coronary angiography as part of the health checkup protocol" - Dr Anand M Rahalkar Consultant Radiologist Sahayadri Hospital Pune

Coronary Artery Disease (CAD) is assuming large proportions in the population due to various factors like changing lifestyles, lack of exercise, stress and habits like alcohol and smoking. CAD leads to a large number of deaths. We in India do not have any specific statistics regarding the numbers as in US. However, it is well known that we are more prone to it than the western world due to lack of health awareness, genetic causes and our eating habits also contribute to it. The urban population is having prevalence of 7.9 per cent to 11 per cent in subjects above 20-years and 14.3 per cent in subjects above 40 years of age. CAD is also the cause of death in 25.1 per cent in urban Indian population.

We read everyday about health checkup programmes by various hospitals to assess the overall fitness of an individual. But, none of the hospitals does CT coronary angiography as part of the health checkup protocol. We, at Sahyadri Hospital, do screening CT coronary angiography and hence the need for writing our experience and findings. We can also boast of the maximum number of CT coronary angiographies done on any single day in India and in most parts of the world.

Calcium Scoring

Calcium Scoring is a good way of assessing the risk for CAD. It gives us an idea of the amount of calcium load in the coronaries. Statistically, higher the calcium load, higher is the risk of developing CAD. However, it does not rule out CAD, when calcium score is minimal or zero. Therefore, though an excellent marker for screening purposes, it falls short of being an ideal marker to exclude CAD absolutely. Also, the patient or client doesn't usually understand the significance or seriousness of having high calcium score and therefore may not necessarily make necessary lifestyle changes.

If the calcium score is very high, ie. exceeds 400-500, we do not do CT coronary angiogram and ask the client to undergo catheter angiography. This is because such high calcium score usually indicates a significant coronary lesion and higher calcium also makes assessment of luminal stenosis difficult on CT scan.

Coronary Angiography

Sahyadri Hospital has done over 10,000 coronary angiographies over the last four years. We have the state-of-art Siemens Definition Dual Source CT since the last one-year and it has helped us immensely in increasing our numbers. We have successfully done away with beta blocking the client, unless the heart rate exceeds 100.

We have an average positive rate of 10 per cent in the asymptomatic population. This means that about 10 per cent of the population at large has CAD which is undiagnosed, since they do not have any manifesting symptom like chest pain. Here lies the most important issue, as to why CT coronary angiography is excellent as a screening tool. This is precisely because all other methods of cardiac risk assessment like echo, ECG and stress test are an indirect way of assessment and have false positive and negative results to it. CT coronary angiography is the only direct non-invasive way of assessing coronaries, which can detect disease much before it manifests.

The other advantage is that the client becomes more motivated to change lifestyles and other methods to try and reduce his risk. The client and the consulting doctor can directly visualise the narrowing in his or her coronaries on CT scan.

All clients are screened with echo and ECG before a CT scan and contrast related risks are explained to the client. Serum creatinine is always done before CT to prevent unwarranted injection of contrast in renal impaired clients.

Statistics

In the past one month, we have done 900 coronaries. Eighty-three clients showed significant stenosis on CT coronary angiographies. Forty-two clients showed high calcium score, who were advised catheter angiography for further evaluation. So, the total positive clients who need catheter angiography are 120 out of 900, which come to 12-13 per cent. Clients having more than 70 per cent narrowing on CT are directly referred for catheter angiogram and the cardiologist then decides about the future plan of action required. The others need medical management or lifestyle modification, according to the cardiologist's opinion. High calcium score clients also need catheter angiography.

Issues

Radiation is the most important issue in CT coronary angiogram today. We have therefore restricted our health checkup study to clients over 40 years of age, who are at more risk than the younger ones. However, we do see significant narrowing in clients under 40 also, though occasionally. The CT coronary angiogram, if positive, outweighs the amount of radiation received by the client. Hence, we feel that it should not be a stumbling block for doing screening CT coronary angiograms.

Conclusion

It is definitely worth screening clients with CT coronary angiography. The issue raised by most cardiologists about radiation is baseless. The amount of radiation incurred by CT coronary angiography is slightly more than that by CT chest or abdomen. CT chest and abdomen are done very frequently and even recommended by some without having an ultrasound done. With over 10 per cent positive rate in our institution, we think that screening CT coronary angiography is definitely useful. Also, with newer CT machines the radiation exposure is decreasing.

CT calcium scoring is also a useful screening test. If the calcium score is high, it is definitely a good indicator for CAD. However, it should be kept in mind that a low calcium score does not rule out CAD.

anand.rahalkar@gmail.com