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Cardiac Computed Tomography: What does it mean for the cath lab?
You have seen cardiac CT evolve over time. With the advent of CTs offering faster rotation speeds and better coverage, where do you feel CT fits into a cardiologist’s arsenal of medical equipment today?
I think CT has become sufficiently robust to use it clinically, provided that the scanner is a 64-slice, and that the person operating the scanner and reading the data has sufficient experience. Both are absolute prerequisites. If both are fulfilled, then CT can be used quite accurately to rule out the presence of coronary stenosis.
One clinical situation where this can be useful is in patients coming to the emergency room with acute chest pain, but with a lack of EKG findings or lab tests to indicate that there is a very high likelihood for an acute coronary syndrome. If a patient comes in with chest pain, but they have a normal EKG and no elevated myocardial enzymes, this is a situation where CT can be very helpful, because many of these patients do not have coronary artery disease. If the CT scan is normal, you can then immediately rule out coronary disease, saving both time and money. The other situation where CT is useful is in patients with stable symptoms that are equivocal, or who have symptoms and a stress test that is equivocal. CT is helpful in a situation where there is remaining doubt after the stress test and it is possible, but not likely, that coronary artery stenosis is present. Instead of referring these patients to an invasive angiogram, which will probably be normal, it is a very good alternative to do a CT scan. Then, if it is normal, you have avoided the invasive angiogram. Ultimately, CT should be used to rule out coronary stenosis in situations where it is possible that coronary stenoses are present but not very likely, in patients with acute chest pain, or in patients with stable symptoms, in order to avoid the invasive angiogram.
There is a group of professional societies that have issued “appropriateness criteria” for cardiac CT and cardiac magnetic resonance imaging (MRI). The criteria also list these two situations as appropriate for using CT, exactly as I outlined them: the acute chest pain patient with intermediate likelihood of disease, normal EKG and normal myocardial enzymes, and the patient with more stable symptoms, who has an equivocal stress test.
How has the Siemens Definition Dual Source CT impacted your workflow and patient mix?
The Definition Dual Source has one big advantage, which is the fact that the temporal resolution is higher than that of conventional 64-slice CT scanners. In conventional 64-slice CT, without the dual source design, it is very important to lower the patient’s heart rate to 65 beats per minute or less. Optimally, we even try to get the heart rate down to 60 beats per minute or less, which usually requires pre-medication. In most cases, beta blockers are used to lower the heart rate. With the dual source CT, it is still the case that image quality might be slightly better if the heart rate is low, but you get diagnostic image quality at almost any heart rate, and this has been confirmed by several studies. Patients who come with a higher heart rate can also be scanned. While it is my feeling that the dual source CT image quality is better than conventional 64-slice CT, even for low heart rates, the main impact of the dual-source CT is mostly the fact that having a low heart rate is not as crucial.
What types of vascular or cardiac exams might see the greatest improvement with dual source scanning?
In peripheral arterial disease, a potential advantage with dual source CT is that the two tubes can be used with two different energies (called “dual energy” scanning). This can help to identify calcium and remove it from the data set, done in post-processing. Dual energy scanning is mainly done for peripheral arterial disease, not so much for coronary disease, where the high temporal resolution is the big advantage.
How is the patient base expanding as the technology grows?
We are still looking, in most cases, for the same information. Do the coronary arteries have stenosis or can we rule it out? Of course, as scanners become more advanced, we can send more and more patients to have these examinations. Previously, with the older scanner generations, there was a real challenge in interpreting the data sets of patients who had large amounts of calcification inside the coronary arteries; today, with scanners that can eliminate artifact caused by motion, calcification is less of a problem. In the future, it may be possible to use CT in patients who have arrhythmias or atrial fibrillation, which so far has not been possible. It’s not that we are looking for completely different diseases, but by making the scanners better, we can have more and more patients with suspected coronary disease scanned by CT.
What types of patients do you see in your own practice?
I work in a university hospital, department of cardiology, in Germany. The way in which we use CT is what I outlined before: first, patients who come to our hospital, our outpatient setting or are sent to us with symptoms, stable symptoms that are not typical. Maybe they had a stress test that really didn’t help, because either the stress test was contradictory to the clinical presentation or the stress test itself was not interpretable, and there is a possibility of coronary disease. In these cases, if the likelihood of stenosis being present is not very high, then we use CT to avoid the invasive angiogram. The other type of patients we see are of course from the emergency room, where we have patients every day coming in with acute chest pain. We do a CT scan in many cases, and can often discharge the patient immediately after showing that the coronary arteries are free of coronary artery disease.
Is there something you would like the interventional community to know about CT and the interpretation of images?
First of all, I think it would be great, and in our institution it is the case, that the interventional people (I am an interventionalist myself) work closely with CT, because it can provide information to the interventionalist that is not so easily obtainable from the invasive angiogram. For example, the amount of calcification, the exact angle of bifurcations and the distribution of plaque. Often, CT can help visualize occluded vessels or side branches that are not easily identifiable in the invasive angiogram. I would think that the interventional cardiologist should not be negative about CT, but in fact should welcome it as an option to learn more about the exact coronary anatomy of the patient. I do see that the interest in cardiac CT is increasing in more and more interventional centers, as well as at the big interventional conferences.
What I would like to see on the side of the vendors is the ability to very easily integrate the CT information into the cath lab so you can, as you are in the cath lab, pull up the CT images and look at the CT. That is possible, but so far not available in a widespread fashion, so it is something that should be improved.
Do you see diagnostic catheterizations eventually being eliminated by cardiac CT?
No, I don’t think they will ever be completely eliminated. There is always a tradeoff. As soon as the likelihood that the patient has coronary artery disease is above a certain threshold, the CT doesn’t make a lot of sense anymore, because you expect a stenosis will be present. It’s better in this case to send the patient to invasive angiography, because then if there is a stenosis confirmed, a stenosis that had been expected with very high likelihood, then the intervention can be done immediately. CT is really for those patients where the likelihood of stenosis is considered to be rather low and CT is done to avoid the invasive angiogram.
Many patients have typical chest pain and a positive stress test. In these cases, the likelihood for having a coronary stenosis is often more than 80% or 90%. At this point, it makes more sense to send the patient to the cath lab, because then you can do the diagnosis and intervention right away. It really depends on the likelihood of disease, so I do not think that diagnostic angiograms will ever go away completely. Diagnostic angiography is very safe, it is not awfully expensive and it is quite accurate. CT will help in reducing the number of negative angiograms. Normal angiograms can never be eliminated, but at least they can be reduced.
There are also patients where both current-generation and future CT scanners will not be able to provide sufficient image quality. For example, take patients who have small implanted coronary artery stents, which are very difficult to analyze by CT. Also difficult are patients who have renal disease. They often have tremendous amounts of coronary calcification, and then CT has problems. Injection of contrast agent may also be a problem in these patients. So there are some patient groups that cannot be studied very well by CT, and in these patients, the invasive angiogram will always remain the clinical test that will help us decide whether or not they have coronary disease.
What about reimbursement?
Currently, we are in a phase of turmoil in every country. Nobody knows exactly how and under which circumstances this test should be reimbursed, but I am certain this is all going to level out in the years to come. As we have larger studies — and many of them are coming out right now — insurers will recognize that if this test is used reasonably and according to the guidelines, it can actually save them money. Of course, the concern is for an initial phase where the test is perhaps not being done in a qualified fashion (and that is sometimes the danger), meaning that the results are not very helpful. Then I can understand that insurance might be initially reluctant to reimburse for the test. If people look very closely at the data we have now and limit the use of CT to patients where it is truly appropriate, they will clearly see that it can save money, and work for the benefit of the patient and society. That is why I believe the payers will eventually decide to pay for this test; I hope it will be very soon. This holds true for every country. In Germany, we do not have reimbursement at the moment, but we see it coming, slowly. In the United States, I know that a great deal hinges on the decision of CMS as to whether there should be a positive or negative national coverage determination for the reimbursement of CTA in Medicare patients, which is completely open at the moment that we are having this interview — but it might be finalized when it is published. It is going to be interesting to see what happens. Even if the decision were negative, I think it will be only a temporary problem. Eventually, in the long run, if this technique is used reasonably and cost-effectively, it will be recognized and reimbursed.
You are involved with the Society of Cardiovascular CT (SCCT). Can you describe the purpose and work of the society?
The Society is an amazing phenomenon. I was fortunate enough to be the founding president of this group, which started early in the year 2005, when there were two separate groups involved in cardiac CT. Each group felt a professional organization was necessary to get behind all of the problems we mentioned: reimbursement, advocacy, education, training, verification and credentialing. As cardiac CT grows, all of that is important. There definitely needed to be a society devoted exclusively to cardiac CT in order to manage these issues, without inherent competing interests. Out of this desire arose two different groups very early in 2005. One group first met in Atlanta, and the other in Chicago, on the same date (by total coincidence), independently from one another, seeking to start a professional society. Very soon it was recognized that it would not make any sense to have two societies competing. With the massive help of the American College of Cardiology (ACC), a process ensued that, within a few weeks, led to the fusion of these two initial organizations. In March 2005 in Orlando, Florida, the Society of Cardiovascular CT was founded. The two original groups merged and leadership was elected, consisting of representatives from both initiatives. In the first two years, SCCT grew to more than 4000 members, which, we were told, was the fastest-growing society that has ever been seen in this field. SCCT continues strongly, with 4,473 active members as we speak. It is very active in issues of education; for example, doing courses with the ACC, providing input to international meetings of the radiology and cardiology societies, and in the SCCT Annual Meetings, which are attended by close to 1000 people each year. There is a verification program of training experience as well as a credentialing program that we helped create. A journal has been created, the Journal of Cardiovascular CT, which is free of charge to all of our members. It has turned out to be a very nice resource of up-to-date information about the clinical applications and science of cardiac CT. We have also started our first international chapter, in Japan. I am happy to see that SCCT has grown to be very strong within a very short period of time.
Any advice for those physicians referring patients for cardiac CT?
I am deeply convinced that cardiac CT is a tremendously useful test, if it is used in the right patient and if it is done appropriately. If you use inadequate technology, or if the person who uses the technology, who does the scan and interprets the scan, is not sufficiently experienced, that can be a problem. Then the quality will not be good. It is not a terribly difficult test to perform, but the equipment has to be good and a few things have to be taken care of and done right. Then the scans are usually of very high quality. Low-quality scans are impossible to interpret, and if interpreted, the result is likely to be wrong. Getting trained and having a high level of quality at the site that performs the scan is very important. Anyone who thinks about referring a patient to a cardiac CT scan should only refer the patient to a center that has sufficient experience. In some places, they do one cardiac CT per week, and it is likely to be bad. The quality has to be good and the volume has to be high. Then it is a very, very useful test.
