| |||||||||||||||
|
Home
|
For other articles and previous issues click here. April 10, 2006
Coronary CT in the Emergency Department Evaluating and diagnosing chest pain remains an enormous challenge in the emergency department (ED). According to the National Hospital Ambulatory Medical Care Survey, unspecified chest pain represents the second most common reason for a trip to the ED, accounting for approximately 5 million visits annually (by some estimates, as many as 8 million). However, only approximately one third of patients presenting with chest pain are eventually diagnosed with acute coronary syndrome (ACS), according to the American College of Emergency Physicians. Yet nearly one half of all ED patients complaining of chest pain are admitted to the hospital, which means that a substantial number each year are admitted unnecessarily. Still more troubling, studies show that 4% to 5% of such patients are discharged wrongly, suffering from undiagnosed disease that too often results in a more severe cardiac event soon after the ED visit. By some estimates, as many as one fourth of patients erroneously discharged from the ED subsequently die from unidentified myocardial infarction (MI). Triage
Options Available noninvasive imaging modalities can include x-rays, stress ECG, and perfusion studies using MR and/or SPECT. In many instances, those findings also prove inconclusive, leaving the diagnosticians back where they started—unable to comprehensively rule in or rule out serious but noncardiac causes of severe chest pain. Soon, however, many more emergency physicians may be able to order a single, noninvasive, comprehensive test for evaluating chest pain and suspected ACS. Essentially generating three simultaneous studies in one, coronary CT angiography (CCTA) provides an inclusive set of images for evaluating the three primary culprits: pulmonary embolism (blood clot), aortic dissection (aneurysm), and MI (coronary artery stenosis). Pioneering applications of cardiac CT developed two different protocols: one for imaging and reconstructing the thorax (noncoronary anatomy) and a separate set for the coronary vessels (arteries). One problem with that split approach is that by confirming or eliminating one diagnosis, you could potentially fail to search for another. Now the newest 64-slice multidetector computed tomography (MDCT) systems enable visualizing the entire chest region in full detail, so a single study yields usable data for all three vascular beds. This so-called “triple rule-out” covers the heart and lungs, as well as all of the thoracic aorta plus the upper part of the abdominal aorta. “The science is still lagging just a little bit to suggest using the CCTA for every [chest pain patient] in the emergency setting,” says David A. Dowe, MD, medical director and chief operating officer of Atlantic Medical Imaging and attending radiologist at AtlantiCare Regional Medical Center in Galloway, N.J. “But the triple rule-out … is going to have a lot of power in that setting.” Image
Acquisition Keeping the heart rate between the optimal 65 to 70 beats per minute usually means pretreating with a beta-blocker. The typical CCTA protocol calls for the ordering physician to give oral beta-blockers, followed by additional intravenous beta-blockers if needed. But for certain patients already diagnosed with heart disease, beta-blocker use can be a problem, as can tachycardia or arrhythmia. That’s one of several areas where emerging protocols are being tailored specifically for 64-slice systems, according to Charles White, MD. White, who is a professor of radiology and internal medicine at the University of Maryland School of Medicine and director of thoracic imaging at University of Maryland Medical Center, led one of the first studies of CCTA in emergency settings in 2005. He says, “Even if we don’t succeed in getting the heart rate down to below 70—ideally under 65 [beats per minute]—with the 64-slice, we can certainly get acceptable images above that rate. Even with a heart rate in the 70s and 80s, scans are of sufficient quality for diagnostic interpretation.” (For full details of the original study, see: White C, Kuo D, Kelemen M, et al. Chest pain evaluation in the emergency department: Can MDCT provide a comprehensive evaluation? Am J Roentgenology. 2005;185:533-540.) Since CCTA is a gated study, other complications crop up if the patient is unable to maintain a breath hold—a situation more likely to arise when the patient does, in fact, have coronary disease or a lung condition. However, White points out that the newer protocol for the 64-slice scanner helps out there, too. “Because of the length you have to cover and because you have to make as fine a spiral as you can in order to get a good look at the coronary arteries, we start at the bottom going up. Doing that, the scan time is on the order of 15 seconds, and if the patient can hold a breath just seven or eight seconds, you’re already through the heart, which is where [imaging] is most sensitive to motion.” Admittedly, reversing the traditional cardiac protocol by going from base to apex is something of a compromise because it slightly changes the cardiac phase used for image acquisition. However, White believes the quality and proximal quantity of images using the 64-slice system more than compensate. “Unless you have some problem with gating, it’s not really an issue.” Radiation
Questions Even so, the highest-powered scanners offer a vast improvement in image quality, and being able to complete the total scan in as little as 10 to 15 seconds aids in limiting radiation exposure. While a 16-slice MDCT typically uses a 500-millisecond gantry speed, the 64-slice helical MDCT system reduces that to roughly 350 milliseconds (some vendor tests claim even less) to obtain the same quality of imaging. White notes that while initially his group used a 16-slice scanner for the comprehensive exam, “there are some substantial limitations to [the older system] for this sort of protocol. You need to cover the entire chest and you need to do it in low pitch to make a fairly tight spiral, and that’s very much less demanding for a 64-slice scanner. Using the comprehensive chest protocol as opposed to just the dedicated cardiac scan, our general image quality improved substantially with the 64-slice scanner.” White emphasizes that the decision to do CCTA should take into account competing technologies, many of which subject the patient to significant radiation dosages as well, including catheterization and nuclear stress testing. Any universal emergency protocol for CCTA testing will necessarily account for age and gender as well as thrombolysis in MI risk assessment, he says. “Maybe it’s not appropriate for every 30-year-old woman, but when you’re dealing with a 50-year-old man … and you’re triaging a life-threatening issue, the comprehensive scan allows you to rule out the most serious diagnosis as quickly as possible.” Both experts also hold out high hopes that ongoing enhancements in the equipment will resolve this issue. “Currently, image acquisition and post processing are highly technology dependent,” says Dowe. In his lab, scanning the heart itself takes six seconds, and a full triple rule-out study takes 12 seconds. While such speeds were unthinkable just five years ago, they’re snail-paced in comparison with the 256-slice detector system being tested in Japan. Unveiled as an experimental prototype at March’s American College of Cardiology (ACC) meeting, the 256-slicer reportedly delivers “one-beat whole-heart imaging,” completing the heart scan in 1.5 seconds using a 14.2 mSv radiation dosage. The designers project that 256-slice CTs could be commercially available within another year or two. New image acquisition techniques, such as controlling table motion between cardiac cycles, are also being explored. False
Positives Dowe notes, “You will always have your fair share of false positives because if someone has a large amount of calcified plaque, you will always be obligated to say [it might indicate] a significant stenosis. But we know that CCTA has a 99% negative predictive value, which means that when CCTA says the patient is negative, it’s right 99-plus percent of the time.” Positive predictive value, he also notes, “is running anywhere between 80% to 90%.” For example, in the original 2005 study White led (using a 16-slice system), 75% of patients had negative CCTA findings. The scans confirmed diagnosed significant cardiac and noncardiac results in 19% of patients. Only 3% of patients were overdiagnosed for a coronary stenosis; another 3% had clinically significant stenosis that the scan failed to diagnose. Sensitivity and specificity for cardiac causes of chest pain were 83% and 96%, respectively; sensitivity and specificity for noncardiac causes was 87% and 96%, respectively. “CCTA remains most appropriate for that group of patients whose chest pain symptoms are neither strikingly worrisome in terms of coronary disease, nor is it strikingly trivial, nor does it fit into any of the other disease classes. It’s in that group where a universal chest pain protocol might be worth thinking about,” says White. Accumulating literature shows that many of these patients’ exams turn up entirely negative for coronary disease, which, he says, should give physicians more confidence in giving an early discharge to patients whose studies come back negative. Dowe adds, “We know 13% of CCTA patients are going to be these potentially false positive patients. You’ve still done a tremendous service with the negative predictive value. You’ve declared 84% of the patients safe to be discharged. It’s real-world medical management.” It’s also worth noting, he points out, that stress tests have a much higher false-positive rate, and that approximately 40% of elective diagnostic cardiac catheterizations come back normal (showing no significant stenosis). “It’s those catheterizations that CCTA can help prevent.” Cost
Comparisons “We need to balance [those outlays] against the cost of unnecessary admissions,” he adds. “If you can safely discharge many more of these patients directly from the ED instead of admitting them, I think those savings more than outweigh the costs of the scans. And our study, as well as others that have recently come out, suggests that these scans are saving a lot of admissions. Ultimately, that may be the most significant factor.” Dowe concurs: “Right now, the number of unnecessary admissions for chest pain is resulting in a $5 billion problem. The length of stay for an acute chest pain patient who does not have an MI is 48 to 72 hours, and hospitals are getting creamed on the length of stay. The triple rule-out will be a big helper in terms of determining who gets admitted and who doesn’t, and in decreasing length of stay.” Mounting evidence certainly seems to validate the specialists’ expectations. Two further studies previewed at the ACC’s 2006 meeting showed that performing CCTA with a 64-slice scanner can cut by more than half both initial diagnostic costs and average length of stay. (For details on ACC preliminary research, visit www.acc.org/2006ann_meeting/multimedia/multimedia.htm.) Dowe cautions, however, that “it remains to be seen how the medical community is going to deal with the 24/7 CCTA world. It’s going to be very difficult from a manpower standpoint, particularly finding the technologists who are capable of doing this and enough radiologists who are technologically on board. Radiologists will largely be handling this work out of the ED. No matter what they say, cardiologists are not going to be willing to stick around to 10 or 12 o’clock at night to sit at a workstation to process the next study.” CCTA
Beyond the ED He continues, “Even if CCTA is not used in the ED, it will definitely be used very early after chest pain patients are admitted. Say the radiologist leaves the medical center at 5:30 and the chest pain patient comes in at 5:31. Well, if the radiologist can do CCTA the next morning at 7 am, the patient’s length of stay is now 131/2 hours instead of maybe 72 hours. With CCTA, whatever workload accumulates overnight can be quickly dispensed with the next day. And medically that’s very acceptable, because, as we know, nobody comes to do a stress test in the middle of the night.” White agrees: “There’s definitely a tendency to push for 64-slice scanners to replace older systems, with the idea that they will have the potential to do cardiac work, and do it optimally.… It’s a pretty strong potential that it’s going to become the standard capability for looking at the coronary region.” What’s more, he believes, “When you’re talking about a comprehensive study, you’re talking about the cardiologist continuing to rely exclusively on the radiologist—or spending a lot of time in the radiology lab learning about the rest of the thorax. Most probably the radiologist will be doing the bulk of the comprehensive protocol, and learning enough of the cardiac medicine to provide feedback and to answer the cardiologist’s questions.” — J. K. Bucsko is a freelance healthcare and technology writer based in Westville, N.J., and a frequent contributor to Radiology Today.
The ACR’s Clinical Statement on NonInvasive Cardiac Imaging specifically differentiates between CT exams conducted for calcium scoring and studies done to evaluate more acute coronary conditions. To establish and maintain coronary CT angiography (CCTA) competency, physicians are required to complete 40 hours of Category One CME, and to meet a minimum cardiac case requirement of 75 every 36 months. The AHA/ACCF’s jointly issued Clinical Competence Statement on Cardiac Imaging with Computed Tomography and Magnetic Resonance, developed with contributions from a number of other cardiology groups (including the recently founded Society of Cardiovascular Computed Tomography), calls for three levels of special training: introductory, independent practice, and director of cross-sectional cardiac imaging functions. At the independent practice level, becoming credentialed requires eight weeks of training and 200 cases; maintaining that status requires continuing experience with at least 50 cardiac cases annually, as well as completing 20 CME hours every three years. ...But
the New Codes Are Clear • 0146T — CCTA of coronary arteries without quantitative coronary calcium evaluation; • 0147T — CCTA of coronary arteries with quantitative coronary calcium evaluation; • 0148T — cardiac structure and morphology, and CCTA of coronary arteries without quantitative coronary calcium evaluation; and • 0149T — cardiac structure and morphology, and CCTA of coronary arteries with quantitative coronary calcium evaluation. Most importantly, the new codes hold the billing physician responsible for interpreting all findings, including any incidental noncardiac pathologies. And unlike the older Category I codes associated with relative value units (RVUs) that help determine reimbursement levels, the new codes are listed as Category III, used for data gathering on emergent procedures. Because they don’t carry RVUs, reimbursement may prove tricky in many arenas. Notes David A. Dowe, MD, medical director and chief operating officer of Atlantic Medical Imaging and attending radiologist at AtlantiCare Regional Medical Center in Galloway, N.J. “As far as reimbursing out of the ED for the acute chest pain setting, right now that’s still a medical decision, not a reimbursement decision.” Hopefully, adds White, “as the technology and the protocol for its use evolve, the reimbursement issues will prove temporary.” You can find more details at the following Web sites: http://new.cms.hhs.gov/manuals/downloads/ncd103c1_Part4.pdf www.acc.org/clinical/competence/imaging/index.pdf www.ama-assn.org/ama/pub/category/3113.html — JKB
|
 |
|
3801 Schuylkill Rd • Spring City, PA 19475 Publishers of Radiology Today All rights reserved. |