Tiered CT Protocol Boosts Efficiency, Speed of CAD Diagnosis

Liam Davenport

January 09, 2018

ROTTERDAM — A tiered cardiac computed tomography (CT)–based protocol that includes myocardial perfusion imaging (MPI) is a faster and more efficient alternative to standard functional testing in patients with stable angina, while reducing rates of unnecessary procedures, results of the CRESCENT-II trial suggest.[1]

The protocol, comprising calcium scanning and CT angiography (CTA) if calcium was present, followed by dynamic MPI in those with greater than 50% stenosis on CTA, significantly reduced the rate of invasive coronary angiography without a class 1 indication for revascularization compared with functional testing (primarily exercise electrocardiography) at 6 months (1.5% vs 7.2%; P = .035).

The overall rate of invasive angiography was similar in both groups, while the proportion of patients with a revascularization indication was higher with the CT protocol (88% vs 50%; P = .017).

Furthermore, the proportion of patients who required further testing was more than halved with the tiered CT protocol compared with functional testing (13% vs 37%; P < .001).

The findings, published online December 13 in JACC: Cardiovascular Imaging, extend those of previous studies, including SCOT-HEART, in which CTA helped reclassify coronary artery disease (CAD) and angina diagnoses and resulted in more focused treatment than standard clinical care in patients with new-onset chest pain.

It is not clear, however, whether this results in improvements in hard clinical endpoints.

For example, the PROMISE study of over 10,000 symptomatic patients indicated no significant impact on clinical outcomes with CTA vs functional testing in patients suspected of having CAD.

In contrast, a recent meta-analysis suggested that CTA is associated with significantly fewer myocardial infarctions than is standard functional stress testing in patients suspected of having CAD and acute or stable chest pain, albeit with more downstream invasive procedures.

Lead author, Dr Marisa Lubbers (Erasmus MC, Rotterdam, the Netherlands), told theheart.org | Medscape Cardiology that it would not be expected that the efficiencies gained in CRESCENT-II would translate into improved outcomes.

She explained it is "hard to improve hard outcomes like deaths and myocardial infarction" because the overall survival of outpatients with chest pain is very high due to few events and even fewer deaths.

CRESCENT-II was therefore focused "especially on improving efficiency, like the time to diagnosis and the number of downstream diagnostic tests necessary to reach a diagnosis," Lubbers said.

Results of the CRESCENT-I trial[2] showed that adding calcium scanning into a tiered CT strategy was safe and effective. However, the ability of the strategy to assess the hemodynamic importance of angiographic lesions was limited.

Building on a Tiered CT Approach

In CRESCENT-II, the researchers prospectively randomly assigned 268 patients who had chest pain symptoms and a greater than 10% probability of CAD to the tiered CT protocol, including adenosine-stress MPI or standard guideline-directed functional testing.

In the cardiac CT group, the mean calcium score was 5 and 50 (39%) patients had no detectable calcium. CT angiography was performed in 79 (61%) patients with a positive calcium scan and in a further 5 patients with no detectable calcium but a pretest probably of CAD of greater than 80%.

Twenty patients had greater than 50% stenosis, of whom 19 (66%) had myocardial ischemia on perfusion imaging. Fourteen patients underwent invasive angiography and 13 were revascularized. Two patients with a normal CT-MPI result later underwent percutaneous coronary intervention.

Cardiac CT patients were more likely to receive their final clinical diagnosis on the same day than those who had functional testing (87% vs 64%; P < .001).

While the index costs were higher with cardiac CT, the mean cumulative diagnostic expenses did not significantly differ between cardiac CT and functional testing ($515 [€435] vs $533 [€450]; P = .827).

There was also no significant difference in the proportion of patients reporting absent anginal symptoms at 6 months between the cardiac CT and functional testing groups (38% vs 28%; P = .118). Improvements in quality of life scores were also similar between the two groups.

Over an average follow-up of 250 days, the adverse event rate was the same in the two groups, at 3% in each. However, the median cumulative radiation dose was higher for the CT group than the functional testing group (3.1 mSv vs 0 mSv; P < .001).

The team writes: "In patients with stable angina and a typically low CAD prevalence the challenge is to accurately rule out CAD in the majority by relative simple means, while comprehensively assessing those who may benefit from revascularization."

"A tiered, comprehensive cardiac CT protocol, including dynamic perfusion imaging, appears to be a fast and efficient alternative to standard functional testing in these patients."

While acknowledging that there are "multiple more established stress imaging techniques," the researchers believe that CT-MPI has "practical advantages," such as allowing for the comprehensive assessment of anatomy and function.

Importantly, Lubbers noted that the protocol, if used in full, "can be cost-effective."

By using the CT calcium score to exclude CAD in almost 40% of patients, the researchers were able to direct them to "a very 'cheap' and safe diagnostic test to exclude severe disease," Lubbers said.

"By adding CT perfusion for patients with greater than 50% stenosis on CT angiography, you also save costs, because almost half of patients with greater than 50% stenosis on CT angiography do not have a significant perfusion defect, and do not have to continue to invasive angiography," she added.

In an accompanying editorial,[3] Dr Leslee J. Shaw (Emory University School of Medicine, Atlanta, GA) and colleagues point out that having 40% of patients with no detectable coronary calcium "calls into question whether many patients should have undergone a diagnostic imaging evaluation at all."

"Our approach to patient selection desperately needs revision and more appropriate tools for identifying at-risk patients," they write, noting that "[c]urrent pretest risk scores are challenged and inaccurate in many younger, female, and diverse patient subgroups."

While lamenting the lack of robust trial evidence to support cardiac imaging, they concede that large-scale randomized controlled trials are unlikely because of high costs and the difficulties in controlling nonimaging factors that contribute to outcomes, including downstream use of test information and less than optimum post-test patient care strategies.

They say: "We have yet to identify trial designs which consistently identify evaluation algorithms of superior or suboptimal effectiveness, safety, or efficiency."

"It is perhaps time for the imaging community to establish focused discussions on future trial designs, pragmatic yet clinically meaningful trial end points and novel approaches for assessing comparative effectiveness."

The study was supported by the Erasmus University Medical Centre and ZonMW. Lubbers reports grant support from the Dutch Heart Foundation; coauthor disclosures are listed in the paper. The editorialists have disclosed no relevant financial relationships.

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