Cardiac CT Goes for the Gold Standard

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Cardiac CT Goes for the Gold Standard

Cardiac catheterization has been the gold standard for detecting the extent of coronary artery disease (CAD) for years. But that paradigm is changing…quickly. Thanks to the jump-start of 16-slice cardiac CT angiography, more recently the huge surge in 64-slice scanner sales and the growing excitement around Dual Source CT systems, multidetector CT is providing a faster, cheaper, and noninvasive method for obtaining much of the same information.

Clinical studies have shown that cardiac CT has 95 to 99 percent accuracy (sensitivity and specificity) when it comes to ruling out coronary artery disease (CAD)—in a single patient breath hold. Similar advantage is seen in detecting peripheral vascular disease (PVD), namely in vertebral and carotid arteries, aneurysms, arch vessel disease, infrapopliteal and calcified vessels, evaluating stents and bypass grafts and in trauma evaluation. And more potential exists in lumen reduction and atherosclerotic plaque identification, characterization and quantification that some day, researchers hope, will help in more effective risk stratification as well as statin dosing and therapy management.

In a field where new advancements come fast and furiously, cardiologists and radiologists—most often working in collaboration—are embracing the techniques even as validation studies are still in the works. And with heart disease as the leading killer of Americans and most developed countries, there’s no time to waste.

“Coronary CTA is stretching the physical boundaries of CT in imaging such small and more rapidly moving anatomy,” says Stephan Achenbach, MD, president of the Society of Cardiovascular CT (SCCT) who spoke at the society’s 1st annual meeting mid-July in Arlington, Va. He is an assistant professor of medicine at the University of Erlangen in Germany and was described at the meeting as the “grandfather of coronary CTA,” albeit at a young age, by other leaders in the field.

Multidetector CT scanning has taken the cardiac imaging arena by storm—based on the fastly surging number of facilities offering CCTA scanning and physicians being trained in the evaluation of images. That the current multidetector CT scanner has sufficient spatial and temporal resolution to image the coronary arteries means physicians can detect the presence, extent and location of coronary calcifications. Note that the cath lab maintains the advantage in spatial and temporal resolution, offering spatial resolution of 0.2 mm vs. 0.4mm in CCTA, and temporal resolution of 8 milliseconds vs. 80 to 200 ms for CCTA. It’s also important to note that right now there is a tendency for CCTA to overestimate stenosis slightly when compared with cath lab findings.

Yet, CCTA’s recent technological advances mean high resolution, three-dimensional images that may soon replace cardiac catheterization in many cases. In other cases, cardiac CTA may help lock in the decision that it’s best to send a patient to the cath lab for stenosis repair or directly to surgery when cardiac bypass is essential. Achenbach urges physicians to ask the scanner: “Is this a patient who does NOT need a cardiac cath?” If the CT is normal, he sees no reason for further workup.

The choice

When Baylor Heart and Vascular Hospital in Dallas opened in 2002, leadership decided to go with a 16-slice CT scanner rather than focusing on MRI. The cardiologists at the 50-bed facility had to bet on what would be the next big technological advance in cardiac imaging. “It was a huge gamble,” said Jeffrey Schussler, MD. “CT looked very promising but we didn’t realize it was going to be as big as it has become.” They did hedge their bets—if heart CT evaluation didn’t work out, the facility could still use the scanner for peripheral angiography.

But, the scanner “really does what it says it’s going to do,” Schussler says, “which is look at heart arteries without being inside them. The fundamental question is: Is there a blockage that needs to be fixed? A CT scan can answer that question very well.”

The facility was so pleased with its 16-slice scanner that it added a 64-slice CT scanner from GE Healthcare to its arsenal a year and a half ago.

A new standard of care

64-slice CT scanning is the new standard of care for cardiac imaging because it offers an accurate, noninvasive image for about one-sixth of the cost of a cardiac catheterization, let alone the patient care benefits.

“We spend over $10 billion a year [in the U.S.] on cardiac catheterization,” says Claudio Smuclovisky, MD, director of South Florida Medical Imaging Diagnostic Center in Boca Raton, Fla. Up to 40 percent of those procedures are negative. Current tests, such as nuclear stress tests, aren’t very efficient. Stress tests miss significant disease 10 percent of the time and the false positive rate is about 10 percent as well. Many patients go on to have a catheterization that could have been avoided, he says.

With a CT scan, physicians no longer have to treat patients based on indirect information from lab results and statistics, and screenings that only show the likelihood of a future event. “Now we have a direct test that shows evidence” of a problem, Smuclovisky says. “It’s quite clear that this will have a huge impact on patient management.” Some 1.4 million Americans a year suffer a heart attack and about 50 to 70 percent of them die on the first event. (Worldwide, more than 19 million people die from a heart attack each year.) “Many didn’t have any symptoms,” Smuclovisky says. An imaging test that can rapidly rule out significant CAD reduces unnecessary invasive testing and helps hospitals triage chest pain patients more effectively. Cardiac CT also allows physicians to see more of any blockages in vascular beds in other areas of the body such as in the kidneys and lower extremities—red flags for future coronary problems.

Calcium scoring is another measure in which CT scanning can improve outcomes. One of the most valuable findings in a symptomatic patient is a cardiac CT scoring exam that is negative for coronary calcium. The patient can then be evaluated for noncardiac sources of chest pain, eliminating the need for an invasive procedure. But, if the cardiac CT score is high, there is evidence that stress testing or coronary angiography is the next appropriate step.

Findings of an excessively high coronary score on a symptomatic patient can be highly predictive of the presence of advanced coronary plaque and risk of an acute cardiac episode. These results provide evidence that the patient probably should be admitted for further evaluation—studies show that between 5 and 10 percent of chest pain patients discharged from emergency rooms in the United States have a myocardial infarction. Calcium scoring can help these patients get the care they need rather than have their heart attack go undetected and untreated and their life at risk.

David Gorra, MD, COO of the New York Heart Center, installed a 64-slice CT scanner from Philips last fall because its “state-of-the-art for diagnosing the arteries of the heart. We wanted to be ahead of the curve.” While cardiac catheterization can take several hours, Gorra says a 64-slice coronary angiogram takes about 20 minutes to acquire the scan (including patient prep) and 15 minutes for the doctor to read. “This is cutting edge. This is where every cardiology practice should be.”

How to Optimize Coronary CT Angiography
Among the parameters Coronary CTA experts agree need to be met to optimally image the coronary arteries:
  • 16-slice, 64-slice or Dual Source CT system with excellent spatial and temporal resolution
  • Maintain optimal patient heart rate between 60 and 65 beats per minute – most often controlled with oral or IV beta blockers*
  • Regular cardiac rhythm
  • Reasonable body mass index (BMI)
  • Iodine-based contrast injection via IV
  • Administration of nitrates just prior to CCTA
  • Patient cooperation:
    • Ask patient to take normal medications morning of scan, with the exception of erectile disfunction medications
    • Ask patient to avoid use of caffeine day of the scan, stay hydrated.
    • Tech should review scan procedure with patient, practicing breath holds and commands and preparing for table movement
    • Ask patient to stay still to avoid motion artifacts
    • Closely monitor patient blood pressure, heart rhythm and anxiety level throughout prep and exam, administer additional beta blockers when necessary
* Dual Source CT does not dictate heart rate modulation and users claim good image quality as high as 135 bpm. The systems also can compensate somewhat for variations in cardiac rhythm.

Source: Speakers from the Society of Cardiovascular CT (SCCT) annual meeting, July 13-16, 2006, Arlington, Va.

Ongoing collaboration needed

Successful 64-slice CT scanning takes some work, however. Michael Radien, MD, of Pacific Coast Image in Southern California, says ongoing collaboration between cardiologists and radiologists is essential. His practice is a hybrid of the two specialties. Physicians there read the scans together. Cardiologists joining the group get training in cardiovascular CT and radiologists learn what cardiologists need to glean from the images to provide good care. “These techniques don’t belong to one specialty or another. When you collaborate, you get the best product possible,” he says.

Good training for the technologists is important, Radien says. And, all patients are assessed one or two days before their procedure by a cardiac nurse. The nurse administers a beta blocker that optimizes the heart rate.

Having all the components in place is vital, says Smuclovisky. “You don’t just buy a machine and start diagnosing with accuracy. This is a complex study.” Acquiring the scanner is just the beginning. “The learning curve is huge,” he says. “It takes time, commitment and money.” And, liability is a significant issue. “If you misdiagnose, you may have a huge problem.”

Just as an airplane requires many components to work perfectly to fly, including an experienced pilot, cardiac CT needs to be an integrated program with all the components in place. That includes cardiologists and radiologists working together. “Both have pieces of the puzzle and it takes a concerted cooperative effort for the best results,” Smuclovisky says.

Technique training

Training physicians how to read cardiac CT is a big part of successful cardiac imaging. Competency statements are beginning to emerge from groups such as the American College of Cardiology, American Heart Association and American College of Radiology to guide physicians, technologists and facilities as to criteria needing to be met to dictate competence in CCTA scanning and evaluation. Interest is growing in CCT training at medical conferences and via CCT fellowships, too.

For a list of training courses, see the Cardiac CT Training Guide.

The Top 10 Indications for Coronary CT Angiography
Here is CCTA guru and SCCT President Stephen Achenbach, MD’s list of the hottest applications as presented at the annual SCCT meeting in mid-July.
 Application Where the competition is coming from
 1. Cardiac calcification None
 2. Coronary calcification Other cardiac risk assessment
 3. Anomalous coronary arteries MRI
 4. Rule out coronary stenoses Stress tests
 5. Bypass graft patency & location Stress tests & MRI
 6. Congenital heart disease Echocardiography & MRI
 7. Cardiac masses Echocardiography & MRI
 8. Pulmonary veins MRI
 9. Cardiac veins None
 10. Valvular disease - prostheses Echocardiography & MRI
Sneak Peak: What might rise to take a place on the list? Stent, plaque and perfusion imaging.

The American College of Cardiology Foundation/American Heart Association (ACCF/AHA) Clinical Competence Statement on Cardiac CT and MR which was developed and endorsed by several organizations, including SCCT, requires that physicians read 150 CT cases to be qualified, according to Matthew Budoff, MD, FACC, FAHA, associate professor of medicine, division of cardiology and director of cardiac CT at Harbor UCLA Medical Center in Torrance, Calif., and author of the statement. Budoff detailed the requirements at the July SCCT meeting. The CT competency includes watching 50 live or videotaped CCT cases, another 50 in which the physician has the ability to manipulate data on the workstation and another 50 in which the physician is directly involved in both scanning and interpreting the case. Budoff added that there is no CT Board Exam yet, but that is in the works and is likely “a couple years out.” Neither accreditation of facilities conducting cardiac CT or certification of technologists is yet available. For a copy of the ACCF/AHA competency statement, visit: http://www.americanheart.org/presenter.jhtml?identifier=3031865.

The statement on noninvasive cardiac imaging from the American College of Radiology calls for board-certified radiologists to have supervised and interpreted 75 cardiac CT cases, excluding those performed exclusively for calcium scoring over the past 3 years or a physician can complete an Accreditation Council for Graduate Medical Education (ACGME)-approved radiology residency program and thus fulfill the requirements above. Both groups must complete at least 40 hours of category I continuing medical education in cardiac imaging, including cardiac CT, anatomy, physiology, and/or pathology or documented equivalent supervised experience in a center actively performing cardiac CT. For more information visit: http://www.duerinckx.com/CVI-documents/Rad-CT-ACR-Consensu-2005.pdf.

“As this technology explodes, I see the biggest issue in training and credentialing physicians in reading the studies,” says Peter Fail, MD, CT director for the Cardiovascular Institute of the South in Houma, La. The Institute has teamed up with Toshiba America Medical Systems to provide a hands-on educational program geared for cardiologists, vascular surgeons and administrators concerning the use of 64-slice CT technology in cardiovascular medicine.

Fail agrees that acquiring the technology is just the first step. “We must also ensure that it’s being used correctly and to its fullest capabilities,” Fail says. His organization has been involved in multidetector CT scanning for several years. “We were excited about the 16 slice scanner several years ago for peripheral CTA. We felt that the technology had reached a point where it made sense to provide a noninvasive way to delineate the vascular bed of those patients with peripheral artery disease. When the 64-slice came along and we were able to do coronaries more reliably, we felt that was an important addition.”

Noninvasive cardiac imaging has affected facility real estate as well. Barry Katzen, MD, medical director of the Baptist Cardiac & Vascular Institute in Miami, began to see the shift toward less invasive technology to gradually replace invasive technology six or seven years ago. So, he began to install less invasive imaging instead of adding cath labs. One of unique aspects in the Institute’s physical plan is that CT devices, and MR too, are mixed in with invasive devices. Katzen’s facility may just be one of many to move the equipment for a time-consuming, costly, invasive and often unnecessary cardiac cath procedure aside and let CT and MRI usher in new advances in cardiac imaging.

MR gaining ground in cardiac imaging

Magnetic resonance to seek out cardiac disease is the other noninvasive imaging technique gaining ground in the cardiac imaging arena. Albeit a few steps out of the spotlight that now focuses so strongly on cardiac CT, the volume of MR angiographies is increasing. What would boost acceptance even further? More speed, says Barry Katzen, MD, medical director of the Baptist Cardiac & Vascular Institute in Miami. “Cardiac MR is extremely useful for certain types of disease but it competes with other noninvasive procedures such as echocardiography which is readily available and less expensive.”

Among the conditions MR shines in evaluating are myocarditis and dilated cardiomyopathy, namely related to the risk of sudden death, and quantitative aortic regurgitation. And since MR offers excellent soft tissue characterization, it can help in identifying infarcted heart tissue following a coronary occlusion.

But, standalone cardiac MR is not a financially viable proposition at this point, Katzen says. “It’s very difficult to get a sufficient number of cardiac cases to sustain cardiac MR.” But, considerable research is underway to define how MR can best detect obstructive coronary artery disease and structural heart disease.

MR does have definite advantages over CT, says Mark Winkler, MD, of Steinberg Diagnostic Medical Imaging Centers in Las Vegas. “The sequences available today are far more robust and far more advanced than those of five to 10 years ago,” he says. Back then, the coils were made up of just one element. Now the technology uses 16-element coils which allow for faster sequences, better signal and therefore, less sensitivity to motion and artifact.

MR cardiac imaging is strong for viewing congenital abnormalities in children, aortic dissection, masses in and around the heart, pulmonary veins, post atrial fibrillation ablation evaluation and right ventricular dysplasia in adults. In the university medical center setting, MR is used for advanced cardiac function analysis and coronary artery disease. These procedures are pretty advanced for the average radiology practice, Winkler says. But, MR also can be used for cardiac viability—delayed enhanced images allow physicians to conduct infarction analysis to see whether a patient has had a heart attack and what tissue is still viable. “MR is better at looking at flow dynamics, which is good for valvular disease, such as stenosis or regurgitation,” Winkler says. MR is designed to acquire these “black blood” images, which are useful for cardiac anatomy.

Relatively speaking, CT is easier to set up and requires less technologist expertise and less physician interaction, says Winkler. It also is more reproducible. “A CT scan is done one way for every problem,” he explains. “MR is less robust and there is more machine-to-machine variability. It is very customized, depending on the problem. If you image 50 different patients, you could do each differently.”

MR cardiac imaging will increase as cardiac CT scanning increases, Winkler says. As with most new technology, people are reluctant to commit to the relatively steep and long learning curve of MR. But, “if they don’t do the techniques done in the large university medical centers, and just stick to basic anatomic and infarction imaging, more practices would do it,” Winkler says. “Clearly, there is a role for cardiac MR.”  —B.W.