The growing role of coronary CTA in stable CAD
With advances across multiple imaging modalities, decision-making regarding the optimal test for the evaluation of CAD can be challenging. However, the role of coronary CT angiography has become more important in the wake of recent trials.
The decision to pursue functional testing vs. anatomic imaging via coronary CT angiography (CCTA) is one facing many clinicians today.
A recently released article summarizing the recommendations of an American College of Cardiology-led CCTA Summit suggested the use of CCTA as a first-line test for evaluating patients with stable chest pain with low or intermediate pretest probability of obstructive CAD. It also states that CCTA can be used in high-risk patients to rule out significant left main disease. The goal of this analysis is to explore some of the research and data behind the recommendations.
The expanding role of CCTA
Recent clinical trials and observational data provide compelling evidence for a CCTA-first strategy. The SCOT-HEART trial found that the use of CCTA results in a significantly lower rate of CHD death or MI at 5 years compared with standard care alone, likely due to greater rate of initiation of and adherence to preventive therapies. A large Danish registry of patients undergoing evaluation for suspected CAD similarly found lower rates of MI and higher rates of preventive therapy use among patients referred to CCTA compared with those referred to functional testing.
The PROMISE trial did not find CCTA to be superior to functional testing in regard to outcomes, including all-cause death, nonfatal MI, hospitalization for unstable angina or major procedure-related complications, but a prespecified subgroup analysis of patients with diabetes found significantly lower risk for CV death and MI among those who underwent CCTA as opposed to functional testing.
Invasive interventions such as PCI have not been shown to provide long-term benefit over optimal medical therapy for those with established CAD and controlled angina symptoms, but improved control of modifiable risk factors improves survival.
Unfortunately, data consistently show poor attainment of these goals. The SCOT-HEART trial suggests that knowledge of the presence and amount of plaque could provide the impetus for successful implementation of secondary prevention strategies.
Additionally, CCTA — which assesses the total burden and severity of atherosclerotic disease — has been found to be a strong predictor of cardiac events. Indeed, in some studies, plaque burden is a stronger predictor of CV events than ischemic burden. Predicting which patients will go on to have clinical events remains difficult, but CVD risk increases with increasing disease and plaque burden.
Accordingly, CCTA assessment can be used to risk-stratify patients and refer those who are at high risk for more intensive lifestyle interventions. Most functional testing techniques do not detect nonobstructive disease, and many patients who have nonobstructive disease detected on CT will have a normal stress test. Thus, the detection of plaque by CCTA offers an important opportunity for secondary prevention in patients with underlying nonobstructive CAD. Plaque detection can also be achieved by adding coronary artery calcium testing to functional tests, but this is rarely done in clinical practice.
In addition to providing prognostically important information regarding the amount of underlying plaque, CCTA also provides information on high-risk plaque features such as low-attenuation plaque or positive remodeling. The presence of such plaque has been shown to be associated with higher risk for events, especially in the presence of nonobstructive plaque. This information could help guide shared decision-making with clinicians and patients regarding the intensity of preventive therapies or, in selected cases, the need for more testing.
FFR-CT as an additional tool
There is also growing evidence that shows favorable outcomes when CT-derived fractional flow reserve is used with CCTA to guide the decision to pursue catheterization or opt for medical management. Although FFR has traditionally been performed invasively, FFR-CT allows the noninvasive measurement of lesion-specific flow limitation.
The U.K.’s National Institute for Health and Care Excellence (NICE) guidelines currently recommend the use of FFR-CT to potentially avoid unnecessary invasive angiography in patients with known CAD. Of note, clinicians need to remember that more aggressive risk reduction can also improve borderline FFR readings over time.
A CCTA-first strategy has the potential to assist in implementing a patient-centered approach by providing tangible evidence of the presence of plaque and increasing the likelihood of implementing and adhering to lifestyle changes and pharmacotherapies. Incorporating the use of FFR-CT has the potential to select those who would benefit from undergoing invasive coronary angiography and limit unnecessary procedures in patients for whom a medical management strategy is effective.
An appropriate criticism of CCTA has been that it can lead to a higher use of invasive angiography and revascularization, but in the SCOT-HEART trial, this was not observed at 5 years. The PROMISE study, which started enrollment more than a decade ago, did show that CCTA was associated with higher use of downstream invasive testing. However, this was at a time when little guidance was provided to clinicians on how to manage patients based on the CCTA results.
Published statements provide clear recommendations on how to act on the results of CCTA and advise that, in the vast majority of cases, invasive testing is not needed. Furthermore, results of the ISCHEMIA trial, first presented at the American Heart Association Scientific Sessions in November 2019, have further emphasized the safety of medical therapy, even in the presence of severe CAD, and have given clinicians greater reassurance in deferring invasive testing when patients do not have unacceptable symptoms. CCTA has the potential to help patients avoid unnecessary invasive testing, but there is also an important need to educate clinicians on how to best manage patients to avoid excess testing after CCTA.
When CCTA is performed as a first-line testing strategy in stable patients, the majority of patients would have no CAD or nonobstructive CAD. Patients who have multivessel obstructive CAD or left main stenosis may benefit from direct referral for invasive angiography. Approximately 10% to 20% may have moderate or severe stenosis where the functional significance is uncertain, and either FFR-CT (if available) or another type of functional testing approach can be provided.
The use of a CCTA-first strategy centers on appropriate patient selection for CCTA, and each center needs to consider the availability and expertise in CCTA as well as other testing techniques. In addition, one has to ensure that patients who are referred for CCTA can have good image quality. This test should generally be avoided in patients who have morbid obesity (BMI > 40 kg/m2) or those who have tachycardia that cannot be controlled. CCTA may not be a useful test for patients who have extensive coronary artery calcifications, as this could interfere with the ability to estimate the severity of stenosis.
In cases where CCTA is not available, where high-quality images cannot be obtained or in patients with known CAD, functional testing (eg, nuclear stress testing, stress echocardiography) has an important role. An exercise treadmill stress test can determine whether patients have exertional symptoms and provides useful prognostic data related to functional capacity.
The evolving paradigm shift from functional to anatomical testing for evaluation of patients with stable CAD has important challenges. The wide availability of CT scanners means little upfront investment in new equipment for some hospitals, but this approach requires investment in education programs.
Another challenge is that CCTA has relatively low CMS reimbursements, a factor which effectively disincentivizes hospitals from performing CCTAs, as the current payment rate to hospitals is often lower than the cost of providing these services. Obtaining prior authorization from some insurance companies represents an additional barrier, although this may change as CCTA is more broadly incorporated into guidelines.
The CCTA Summit report proposes solutions starting with a national registry for data collection and monitoring, and calls for the U.S. to collaborate with U.K. and European societies whose rollout of CCTA with FFR-CT proved to be successful in changing practice norms and reducing health care costs. It calls for reclassification of CCTA to an ambulatory payment group that more appropriately reflects the time and technology associated with the test, advocates for bundled payments for cardiac testing as a means to reduce costs, and calls for eliminating prior authorizations for those participating in the registry.
A national CCTA registry would provide valuable data for future areas of research, which could include an evaluation of downstream medical therapy, resource utilization and outcomes after CCTA. Future improvement in plaque analysis technique may enhance the performance of CCTA.
Promoting a CCTA-first strategy
The CCTA Summit, evolving worldwide guidelines and recent scientific data all support a CCTA-first strategy for stable patients presenting with concern for obstructive CAD. CCTA can be performed as an effective first-line test. Such a strategy will improve outcomes among patients with stable symptoms who do not have known CAD by increasing the likelihood of implementing lifestyle modifications and pharmacotherapies. Because the cost of CCTA is severalfold lower than other testing approaches, this strategy may also result in lower cost if downstream testing can be avoided.
Among patients who require cardiac testing for known or suspected CAD, the use of a patient-centered imaging approach is essential. Clinicians will need to learn how to select between the available testing approaches and understand the anticipated impact of test results on patient management and outcomes. Future guidelines and education efforts should emphasize which patient characteristics may favor particular testing strategies, especially given the growing role of CCTA.
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For more information:
Chloe Duvall, MD, is a resident at Johns Hopkins Hospital.
Richard Ferraro, MD, is a resident at Johns Hopkins Hospital and a member of the Johns Hopkins Ciccarone Center for the Prevention of Heart Disease.
Ron Blankstein, MD, is the associate director of the cardiovascular imaging program, the director of cardiac computed tomography and co-director of the cardiovascular imaging training program at Brigham and Women’s Hospital and professor of medicine at Harvard Medical School.
Roger S. Blumenthal, MD, is the director of the Ciccarone Center for the Prevention of Cardiovascular Disease and professor of medicine at Johns Hopkins University School of Medicine. He is also the editor of the Prevention section of the Cardiology Today Editorial Board. The authors can be reached at Johns Hopkins Ciccarone Center for the Prevention of Cardiovascular Disease, Division of Cardiology, Johns Hopkins University School of Medicine, 600 N. Wolfe St., Halsted 560, Baltimore, MD 21827.