Supported by a growing base of clinical studies, cardiac CT angiography (CCTA) has shown its utility in improving cardiac patient management and ruling out heart disease with greater than 99 percent accuracy, while also offering fiscal benefits that can be found by limiting unnecessary diagnostic cardiac catheterization procedures on low- to intermediate-risk patients presenting with acute chest pain.
It’s no wonder CCTA system installations have surged in recent years, in university hospitals and medical centers as well as in community hospitals and outpatient imaging center settings. There were approximately 4.3 million CTA procedures performed in 2007, according to IMV Medical Information Division.
Diagnostically, CCTA is a good fit for patients with low to intermediate likelihood of coronary artery disease (CAD) with atypical chest pain and/or prior equivocal or non-diagnostic other tests (e.g. stress testing, nuclear myocardial perfusion imaging). It also has proved valuable in the detection and exclusion of obstructive CAD, the severity of stenosis, as well as plaque volumes, composition and remodeling.
Clinical evidence suggests CCTA will revolutionize patient management for the treatment of heart disease. However, the future implications of the procedure remain unclear as CMS noted in its final ruling that “questions remain on the indications of use.”
CCTA in clinical practice
One question that has been answered is whether there is enough evidence to justify incorporating CCTA into clinical practice for assessing heart disease. The answer is unanimous and unequivocal—absolutely. “If used appropriately, CCTA is an extremely beneficial tool in clinical practice,” says U. Joseph Schoepf, MD, cardiac radiologist, Medical University of South Carolina (MUSC). “The main reason is that it has an extremely high negative predictive value—almost 100 percent.”
From the patient viewpoint, the value is in replacing one invasive procedure, invasive coronary angiography, with a non-invasive one. For the institution, value is gained by inserting CT into the clinical algorithm for patients with suspected CAD. A substantial number of patients with normal arteries can be eliminated from the cath lab schedule, creating a much more specific selection of patients who need interventional procedures meaning time can be more cost-effectively spent on the more lucrative coronary interventions. For the healthcare system, significant cost-savings can be realized by ruling out CAD with a test (i.e. CCTA) that typically runs at one-third of the cost of diagnostic coronary catheterization. “Thus, if patient management is based on CTA’s exceedingly high negative predictive value, this test can be beneficial on many levels,” Schoepf adds.
CCTA offers a financial incentive for institutions operating a CT scanner and a cath lab to use the procedure to fill the schedules with patients who are reasonably expected to need an intervention, Schoepf says.
He is among researchers at MUSC who have developed a dual-source CT scanner technique using the Somatom Definition from Siemens Medical Solutions, enabling a comprehensive diagnosis of heart disease based on a single CT scan.
Normally, heart disease is difficult to diagnose because it not only requires a detailed view of structures like heart valves and blood vessels, but also blood flow to the heart muscle. By adding two x-ray spectrums with varying degrees of energy, researchers have gained a static image of the coronary arteries and the heart muscle, and thus the ability to map blood distribution and pinpoint areas of decreased blood supply. The technique, which requires only a single CT scan within a breath-hold of 15 seconds or less, brings better accuracy for detecting coronary stenosis, Schoepf says.
“We have gained the ability to better see those lesions and grade them, differentiating between lesions that are non-obstructive versus those lesions that cause significant decrease in blood supply,” he says. “This is revolutionary because you historically needed a combination of tests—invasive coronary angiography and myocardial perfusion imaging—to determine the significance of the lesion and its affect on blood supply,” he notes. “Now, we bring them together into one single, non-invasive test, which bodes well for the work up of patients with suspected CAD.”
By dropping the use of beta blockers, they also have seen improvements in workflow—now cardiac CT is like a regular CT scan. “It can be done in the same time slot without a radiology nurse on hand for IV protocols,” he adds.
CCTA has reached the point where it should be the first test—instead of nuclear stress testing—for the initial evaluation of patients with suspected CAD, according to Harvey S. Hecht, MD, FACC, director of cardiovascular CT at Lenox Hill Hospital in New York City. “It is more sensitive, more specific and more accurate, plus you obtain information about the amount of calcified plaque—usually a strong prognosticator of coronary disease,” Hecht says.
A second area where CCTA is beneficial is in guiding the practice of coronary stenting, which “tells you how long the stenosis is to size the stent appropriately, and tells you the size of the vessel to facilitate the procedure,” Hecht notes. Lenox Hill is using a Brilliance 64-slice CT scanner and a 256-slice Brilliance iCTscanner from Philips Healthcare.
Despite the obvious benefits to CCTA, challenges remain. If CAD is found, CT is still somewhat limiting in grading the degree of stenosis and in determining the hemodynamic significance of the lesions on myocardial perfusion. Additionally, Hecht says contrast agents can be a potential problem in patients with renal disease and for patients allergic to them.
While it would be easy to send everyone with chest pain through a CT scanner, it does not make economical, clinical or ethical sense, due to the radiation doses, especially in younger patients, who need to be closely monitored for radiation exposure. According to Jerry Hines, MD, president and CEO of Illinois Heart and Vascular in Hinsdale, Ill., a single-specialty private practice with 27 cardiologists, aside from eliminating needless testing, there have been protocol changes to CCTA that have lowered radiation exposure for patients.
“By lowering our Kv from 120 to 100, by dose modulating all of our studies and by using prospective gating, we were able to considerably lower radiation exposure for our patients,” Hines says.
With the Lightspeed VCT from GE Healthcare, which has SnapShot Pulse technology for cardiac dose control, in addition to dose modulation, cardiologists are able to have x-ray on all the time, but at a lower dose in portions of the cardiac cycle that are not as clinically relevant. “Pulse technology has the potential to lower radiation exposure from 10 percent of normal levels—normally 10 to 15 millisieverts to approximately 2 millisieverts.” Hines notes this is not applicable to all patients.
If a patient has suspected cardiac disease symptoms, and if there are no indications of an acute ischemic event, then that patient should be considered for CCTA. “If there is evidence of acute ischemic event, then an elective CT scan is not our first choice,” he adds. “In patients with atypical chest pain, or with chest pain that is clearly not cardiac in origin, CT has been a marvelous tool in ruling out coronary disease to avoid invasive procedures and associated radiation risks.”
Despite volumes of research data available that promote the proven benefits of CCTA, it is still a technology in development. Further studies need to be conducted to show an appropriate use of the test in appropriate populations, says Julie Miller, MD, assistant professor of medicine at Johns Hopkins Hospital in Baltimore. Miller was the lead investigator for the CorE 64 study, who presented the results at the 2007 American Heart Association meeting in Orlando, Fla.
The nine-center, seven-country, multi-site Coronary Artery Evaluation using 64-Row Multidetector Computed Tomography (CorE-64) showed that 64-row multidetector CT, for coronary artery evaluation in patients with suspected CAD and with calcium scores less than 600, could assess the presence of significant CAD just as well as cardiac catheterization. Using the Toshiba Aquilion 64 CFX multidetector CT scanners from Toshiba America Medical Systems for imaging, the study was the first step taken by the industry to realize the full potential of CT imaging in predicting CAD.
“CorE-64 was the first step because assessing the diagnostic accuracy in symptomatic patients was necessary, but now it is time to look toward how to use it in clinical practice to actually alter care,” Miller adds. “We need to show an appropriate diagnostic use of the test in the appropriate population. If the diagnosis can be made by other means that do not involve radiation, that would be better. But, if we can identify patients earlier or not send out patients from the ER who then have a cardiac event, that is useful.”
With the first step taken, many within the industry feel the next step is to determine whether CCTA can be used as a screening tool. “Obviously we would not want to screen everyone—but for high-risk, asymptomatic patients, if we could identify those patients at very high risk, we might be able to change their medical therapy,” Miller notes.
Patients at very high risk, such as diabetic patients, are thought to be more susceptible to heart disease, but there are many asymptomatic patients who die from cardiac events that are the first sign of coronary disease. “We do not have proof that screening asymptomatic patients with CCTA, and then treating them based on what we find, actually saves lives or prevents heart attacks,” says J. Bret Muhlestein, director of cardiology research at Intermountain Medical Center in Murray, Utah.
Intermountain is embarking on a new study that will determine whether CT scans can prevent heart attacks and strokes by finding dangerously clogged arteries in patients who otherwise have no symptoms of heart disease. The first-of-its-kind study could change the way heart disease is diagnosed and treated, Muhlestein notes.
The FaCTor64 study will use new 64-slice CT scanning technology as an early warning system to find dangerously clogged arteries in 1,100 patients with diabetes, a disease that leaves them particularly vulnerable to heart disease, but otherwise have no symptoms of heart disease. Physicians then will treat patients in an attempt to pre-empt heart attacks, strokes and death.
Currently, CMS does not reimburse for CCTA for asymptomatic screening, but Muhlestein says CMS “is waiting for a study like this to provide proof that CTA helps asymptomatic patients before they will pay for it.”
Intermountain deliberately chose a patient population that was high risk and asymptomatic so that researchers could, in an affordable number of patients, have enough expected events to determine a sudden reduction statistically in screened patients compared to those left to standard care methods.
“Our hope is that if we demonstrate a significant reduction in death and heart attack and result in therapies that will improve the life of patients we screen—then CMS will pay for it. If it does not, then we will look at other ways of capturing and aiding the 25 percent of patients who die of a cardiac event before receiving care,” he says.
As the technology continues to develop, and as further studies are conducted, the lingering questions surrounding the efficacy and utility of CCTA, for both symptomatic and asymptomatic patients, may finally be answered.