CCTA Gains Ground for Low-Risk Chest Pain

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CT angiography of the left circumflex shows a stenosis less than 70 percent. (Source: Frank Rybicki, MD, Brigham and Women’s Hospital in Boston)
Triage methods for low-risk chest pain lack consensus. However, a recent scientific statement and appropriate use criteria (AUC) have recommended best practices, paying particular attention to coronary CT angiography (CCTA) as a triage tool.

Let’s get clinical

More than eight million U.S. patients with chest pain or other symptoms associated with potential coronary disease visit the emergency department (ED) annually—a majority of whom do not have coronary artery disease (CAD) or acute coronary syndromes (ACS). Low-risk patients with ACS are typically identified as those “with no hemodynamic derangements or arrhythmias, a normal or near-normal electrocardiogram (ECG), and negative initial cardiac injury markers,” according to a recent American Heart Association (AHA) scientific statement (Circulation 2010;122:756-776).

“Those patients who present to the ED with no instability of hemodynamics or rhythm, negative CK-MB and a normal ECG, but have chest discomfort are automatically classified as low risk for a coronary event,” explains Ezra A. Amsterdam, MD, professor of medicine in the division of cardiovascular medicine at the University of California, Davis Health System in Sacramento and lead author of the AHA statement.  
To further examine these patients, clinicians can employ various tests, such as an exercise treadmill exam, a stress echo, SPECT imaging or a CCTA scan. Due to the attention paid to excessive imaging over the past few years, some are advocating a return to more basic assessments.

“It has been demonstrated that among patients presenting to the ED with chest pain, those with less than 5 percent probability of MI can be identified from the presenting symptoms, past history and ECG,” according to the statement. “[A]lthough the cause of chest pain in these patients is frequently elusive, basic clinical tools provide powerful estimates of cardiac risk.”

However, the authors state that non-invasive imaging, such as CCTA, could have a role. “[U]nlike exercise treadmill testing, SPECT myocardial perfusion imaging and stress echo, CCTA provides anatomic rather than functional information regarding coronary patency by producing a noninvasive coronary angiogram.”

Joseph A. Ladapo, MD, PhD, from the department of ambulatory care and prevention at Harvard Medical School in Boston, agrees. “While CCTA has limitations with localizing vulnerable plaque, the test can identify patients who are vulnerable for CAD via their atherosclerotic burden through the calcification of the coronary arteries. CCTA can help identify those patients who require further treatment.”  

The statement highlights several potential limitations of CCTA, including suboptimal coronary artery visualization caused by extensive calcium, and radiation exposure. However, it cites a recent study that reported new methodology that could reduce radiation dose by 50 percent, but this finding needs further validation.

Appropriate use criteria (AUC)

Amsterdam notes that each practicing clinician has his or her test preference. “Clinicians bring different perspectives into practice, which they apply in the best interests of their patients,” he says. However, new multi-society AUC could make the choice of when to intervene with CCTA as a triage tool less subjective (J Am Coll Cardiol 2010;56:1864-1894).

In the criteria, CCTA is deemed appropriate for patients with chest pain whose preliminary tests suggest low or intermediate pre-test probability for CAD, because CCTA helps exclude the presence of CAD with time sensitivity, says the criteria’s lead author Allen J. Taylor, MD, co-director of non-invasive imaging at Washington Hospital Center, Washington, D.C.  

“There is a real dearth of information about the effectiveness of imaging, especially in relation to improved patient outcomes because these diagnostic tests are only a part of the spectrum of patient care and not the only driver of outcomes,” Taylor says.

As a result, the AUC authors hope that the updated criteria will better inform decision making: “Facilities and payors may choose to use these criteria either prospectively in the design of protocols and preauthorization procedures, or retrospectively for quality reports. … It is hoped that payors would use these criteria as the basis for the development of rational payment management strategies.”

Cost considerations

Utilizing CCTA as a triage tool in low-risk patients who present to the ER may not increase costs to the ED or the hospital setting. In a cost-effectiveness analysis, Ladapo et al found that CCTA-based triage for patients with low-risk chest pain was modestly more cost effective than the standard of care (SOC), and cost saving in women (Am J Roentgenol 2008;191:455-463). “Using the modality is cost saving in women because they are more likely to be ruled out with CCTA,” explains Ladapo.  

Employing a microsimulation model, researchers found that using CCTA to triage 55-year-old men with acute chest pain increased ED and hospital costs by $110 and raised total healthcare costs by $200. In 55-year-old women, the technology was cost saving: ED and hospital costs decreased by $410, and total healthcare costs decreased by $380. Compared with the standard of care, CCTA-based triage extended life expectancy by 10 days in men and by six days in women, which translated into corresponding improvements of 0.03 and 0.01 quality-adjusted life years (QALYs), respectively. They found the incremental cost-effectiveness ratio for CCTA was $6,400 per QALY in men.  

In another study using the same computer simulation model, Ladapo et al found that CCTA raised overall costs, partly through the follow up of incidental findings, and when performed with stress testing, its incremental cost-effectiveness ratio ranged from $26,200/QALY in men to $35,000/QALY in women (J Am Coll Cardiol 2009;54:2409-2422). In this study, the authors noted that health outcomes were marginally less favorable in women when radiation risks were considered.

While Ladapo characterizes the societal burden of increased costs due to imaging utilization as a “legitimate concern,” he suggests the solution “isn’t to go after a specific modality, such as CCTA. Instead, the solution lies on a nationwide systemic level, which should better evaluate why certain tests are performed for certain patient populations, even low-risk patients.”  

The findings of Ladapo et al now are being put to the test in a randomized, controlled trial that is assessing CCTA’s clinical efficacy as well as the economic considerations in low-risk patients with chest pain. Supported by the National Heart, Lung and Blood Institute, the PROMISE trial is comparing CCTA with functional stress tests—exercise ECG, stress echocardiography and stress nuclear imaging. This study will include 10,000 participants at 150 sites with low- to intermediate-CAD risk who present to the ED, and will be followed for about 2.5 years.    

“Never before have we looked at diagnostics in this way to understand the value they bring to patient care. In the past, our focus has been on determining if the tests are accurate and specific, but not if they improve people’s health,” primary investigator Pamela Douglas, MD, from Duke University Medical Center in Durham, N.C., has said about PROMISE.

Defining appropriateness

While awaiting the results of the PROMISE trial, cardiovascular practices and departments have the new scientific statement and AUC by which to judge their diagnostic methodology.

Specifically, the criteria state that CCTA is “appropriate primarily for situations involving a low or intermediate pretest probability of obstructive CAD.” However, Taylor acknowledges there is a “gap” between AUC and clinical practice.  

Widespread AUC adoption is still in its “very early stages,” says Todd D. Miller, MD, from the nuclear cardiology department at Mayo Clinic in Rochester, Minn. While clinical studies suggest the inappropriate use of cardiac SPECT is 15 percent across the U.S., for example, Miller says that it could be as high as 50 percent in some practices based on the national rate of imaging growth.  

To counteract this lack of AUC utilization across imaging modalities, Taylor suggests that integration of AUC into computer physician order entry systems and clinical decision support tools could facilitate appropriate utilization. “Having these AUC and other guidelines implemented into EMR will allow for them to be translated into practice more efficiently,” Taylor says.