Q: What were the results of the CorE 64 trial? How accurate is Multislice CT Angiography (CTA) as compared with standard angiography performed in the catheterization lab?
Dr. Poon: I think the study was well-done. It showed that, as a test to rule out the presence of significant coronary disease, CTA is capable of doing a rather good job. But at this moment it’s still not the test that you would use to compete with diagnostic angiography for accuracy. I think that’s the conclusion that we can draw from the CorE 64 data.

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Q: During the panel discussion after the CorE 64 presentation at last week's AHA, Dr. Michael Lauer, who left the Cleveland Clinic this year for the National Heart, Lung and Blood Institute, voiced strong objections to the widespread use of Cardiac CT. But don't the results of the CorE 64 trial basically reinforce previous studies, for example the CATSCAN study from Cleveland Clinic.
Dr. Poon: CTA is a great test to rule out the presence of disease. Its negative predictive value is very high. That basically has always been what the data’s been showing. I don’t understand why Dr. Lauer was being so negative. The fact is that it cannot completely replace diagnostic cath. Yet he went ballistic. And I said, “Whoa!” He wanted to put a two year moratorium on this technology, which I think will be detrimental to patients who could benefit from this test.

Nobody in my view is thinking that CT will replace diagnostic cath. In fact, that was the reason Dr. Lauer was objecting to CT, he said “You see -- the CorE 64 shows that this test is nowhere near the accuracy of a diagnostic cath.” We never claimed that CT is going to replace diagnostic cath. We said that the accuracy of CT is very good when it comes to ruling out the presence of disease. We never said that CT is as accurate as diagnostic cath. So, you have to look at the two ends of the spectrum. When you look at the disease process, it goes from no disease to a lot of disease. So, CT is focusing on one end, which is the “no disease” end. Diagnostic cath is focused on the other end, which is “how bad is your disease.” So, CTs job is to rule out the presence of disease on the low-to-intermediate risk group.

Dr. Poon with a patient

Q: So if patient selection is important, who are the patients that can best benefit from CTA? Dr. Poon: Again, we are not advocating doing this on everybody. We are not advocating doing CTA on a patient who is asymptomatic. We have very clear guidelines, based on the published Appropriateness Criteria. I was on the writing committee and we specifically stated that this test is indicated in patients with symptoms suggestive of the presence coronary artery disease, in lieu of doing invasive angiography, which is a test that can be 30-40% negative for coronary artery disease.

Just look at the National Cardiovascular Data Registry (NCDR) for the the percentage of unnecessary caths, meaning that after the diagnostic cath, the operator decided that there is no need for further intervention. In other words the test could have been avoided. And it’s close to 40%. So the strength of cardiac CT is to help this group of patients to have a test which is non-invasive, and can rule out the presence of significant coronary disease, so they don’t have to go to the cath lab and subject themselves to an invasive procedure which carries a percentage of potential complications, both mortalities and morbidities.

Q: What are those percentages? Mortality is very low, but we’ve heard 3-4% quoted for vascular
Dr. Poon: 3-4% is a pretty conservative estimate. As for some of the groin complications, they may be minor, but you wouldn’t want to be the one who has it. And there is no long-term follow up on the impact of these complications on the individual.

Q: Yes, we have a number of patients writing into our Forums two or three months after a cath with problems in their leg that started right after the cath.
Dr. Poon: Exactly.

Q: What about the radiation exposure with CT compared to standard catheterization. The popular press quoted a figure of 10 times greater. That’s not true is it?
Dr. Poon: No, that’s not true. There are very widely published data on that. The number we quote is from an article published by Cynthia McCullough of the Mayo Clinic, and based on her study, the amount of radiation that you get from a 64 slice CT is somewhere between 7-14 millisieverts (mSv) and the conventional diagnostic cath can go as high as 5-10 mSv. So it’s absolutely not a ten-times more procedure in terms of radiation exposure. And furthermore there are many ways that you can lower the dose.

The whole issue about radiation risk is a very hypothetical one, because walking around in NYC over the course of a year, you randomly get an amount of radiation that is about 2-3 mSv. Just from the sunlight. So one 64 slice CT will be getting the amount of radiation you would normally be exposed to in 3 years. So do people after three years of existence automatically get cancer? No. So people really need to be educated about the risks.

You also have to look at the alternative modality that nobody questions about the radiation exposure: the nuclear stress test, which is the most common diagnostic test for patients with chest pain. The total number of nuclear stress exams is 8 million a year. Yet the radiation exposure of nuclear stress test, based on Dr. McCullough’s estimate, is equal if not higher than 64 slice CT.

Q: Is that why some cardiologists think that cardiac CT Angiography will impact the nuclear stress test more than it will standard angiography. What is the role of a nuclear stress test, and does CTA really answer those questions?
Poon: That's a very good question, because one of the problems with a high percentage of patients going to the cath lab and then finding out that they don't have disease is that the nuclear stress test carries a very high false positive rate. If you look at the eight million nuclear stress tests done a year, because of the sensitivity and specificity, it's only somewhere between seventy-five to eighty-five percent, even in good hands. Therefore, nuclear generates close to twenty-five or thirty-five percent of false positives.

Q: That seems like a lot.
Poon: That's a lot, and these patients go on to the cath lab and to potentially getting complications from the tests -- and the number, as we just talked about, is between 3-4% that have vascular complications. And I'm sure that number is underreported. So, the role of CT in many expert eyes is that maybe, before we do nuclear, we should do a CT first. And if the CT is normal, then you don't need anything. And if the CT is abnormal, then you may want to do a nuclear at that point to find out whether it's significant or not. So you basically help nuclear to focus on what it's good at by not sending everybody to nuclear, because nuclear, if you do that, will carry a very high false positive rate.

Q: As well as significant radiation dose.
Poon: That's right, and the radiation from nuclear is no less than CT. In fact, probably a lot more, depending on the way that you do the test. Whether you use sestamibi or whether you use thallium. The dose from thallium is two or three times higher than CT, and no one talks about that.

And we put out a very good training program, the CTA Academy - Practicum. This is a joint collaboration between the American College of Cardiology and the Society for Cardiovascular CT. We are now running regular training programs at the Heart House in Washington, D.C. to train people who are interested in seeking Level 2 certification in cardiac CT.

So our society's emphasis is not turf war, but collaboration. We have eminent radiologists on our board, like Jack Ziffer, Norbert Wilke and Larry Boxt, and we work on multiple task forces together to promote cross-pollination, and maintenance of high quality study and training programs. We promote a lot of research, and collaboration between the American College of Cardiology (ACC) and the American College of Radiology (ACR). In fact a lot of the advocacy efforts that we are working on are joint efforts between ACC and ACR. I think that's the most effective way of getting the politicians, and the vendors and the health care providers to listen to us, that we are working together.

Q: Do you see then that invasive X-ray catheterization and CT are not really at odds with each other?
Poon: No, I don't think so. In fact, I've worked with the Cardiology Research Foundation (CRF) and we are looking into future collaboration between CT and the cath lab. Perhaps CT can provide additional insight to the invasive cardiologists on what lesion would require what kind of intervention. And also to help them perhaps cut down the amount of radiation time required in the cath lab, if we can provide them with some of the computer-aided diagnostic techniques using CT image. To give you an example, the CT can tell you exactly at which orientation the coronary artery is coming out of the aorta, so that automatically can help you to select the catheter required to do the test, so you don't have to guess.

Q: So here's an example where CT can actually reduce the radiation dose.
Poon: Absolutely, absolutely! So you don't have to fish around to find the right catheter.

Q: At the TCT I saw that Jeff Moses used the Stereotaxis system, where CT and conventional angiography are combined, in order to open a Chronic Total Occlusion (CTO) which was quite impressive.
Poon: This is exactly what I'm talking about. I see mutual benefits from working together, and new technology provides you with new ways of looking at things. I remember when I was a fellow, sometimes I had no idea what catheter to use -- sometimes you'd go through ten to find one. CT can tell you exactly which one you need. So, I think it's an important technology to be recognized, that this is not a new layer that we add to the diagnostic algorithm. We are providing a new approach that potentially can cut down costs, cut down the risks involved, and also save the operator in the cath lab a lot of unnecessary radiation.