Marlene Busko

July 06, 2016

ORLANDO, FL — Debaters at the Society of Cardiovascular Computed Tomography (SCCT) 2016 Annual Scientific Meeting agreed that an initial CT test is best to rule out CAD in low-risk patients but squared off over whether this strategy is best for intermediate-risk patients[1].

Recent studies show that "coronary CT angiography should be the first diagnostic test for coronary artery disease," said Dr Todd C Villines (Walter Reed National Military Medical Center, Bethesda, MD), arguing for the "pro" side in the debate.

Not so fast, countered Dr Paul Knaapen (VU University Medical Center, Amsterdam, Netherlands), presenting his case for the "con" side. Doing a CT test first in patients with intermediate risk of suspected CAD is associated with more referrals to the cath lab, more revascularization, increased medical therapy, and higher costs, "whereas the outcome doesn't really change," he said.

Knaapen did agree that a "CT-first" strategy is called for in patients with a low risk of CAD. "I think it is wise to take a step back and say 'CT is the first one for low likelihood of disease,' because its strength lies in ruling out disease, not ruling in disease," he concluded.

He also noted, however, that "depending on what you have in your facility, you chose the best for the patient, to the best of your abilities, which may not be CT." At his center they have "a super PET program that far surpasses the diagnostic accuracy of CT, but it's one of the rare places in the world."

But Villines had an ace up his sleeve. "I would say be 'NICE' and do CT first. It's not just me; the entire UK agrees with me," he said, pointing to planned amendments to the National Institute for Health and Care Excellence guidelines. "CT improves health outcomes in the low- to medium-risk patients without known disease, identifies disease stages, and leads to more appropriate catheterization and more appropriate use of preventive medicine," he summarized.

Invited to comment, Dr Matthew J Budoff (Los Angeles Biomedical Research Institute at Harbor-University of California, Los Angeles Medical Center) told heartwire from Medscape that "obviously there's no winner or loser in this type of debate, because ultimately it comes down to local expertise. . . . We also have to understand that not all centers are equipped to do all tests."

But he said that Villines made a strong case for CT first based on recent data and that the United Kingdom's new NICE guidelines are moving in that direction for almost all patients. "I think we will follow that model; it's just going to take a while for our systems to adapt to more CT and less functional testing."

Reasons for Not Using CT First

"I find myself at the SCCT . . . to tell you not to use CT. So I think I'm very much in the lion's den here," said Knaapen at the start of the debate.

"What we really want in a diagnostic test in intermediate-likelihood patients is to see whether or not they have obstructive CAD" that can be defined as a fractional flow reserve below 0.8, he said.

In a meta-analysis by Danad et al[2] that compared the diagnostic performance of coronary CT angiography, single-photon emission computed tomography (SPECT), stress echocardiography, invasive coronary angiography, and cardiac MRI vs a fractional flow reference standard, CT angiography had a high sensitivity and a high negative predictive value but low specificity and positive predictive value. MRI and SPECT had higher specificity.

An analysis of data from the Study of Myocardial Perfusion and Coronary Anatomy Imaging Roles in Coronary Artery Disease (SPARC) registry[3] that compared the treatment costs of patients who had different noninvasive tests to evaluate suspected CAD showed that "even if your CT is pretty normal, you end up with a stent or bypass, whereas for SPECT that doesn't happen; the index test with CT is low cost, but the things that follow are very expensive," Knaapen said.

In the PROMISE study of 10,003 symptomatic patients with suspected CAD, a strategy of initial CT angiography vs functional testing (exercise electrocardiography, nuclear stress testing [SPECT], or stress echocardiography) did not improve clinical outcomes over a median follow-up of 2 years.

Patients with initial CT angiography as opposed to a functional test were referred more frequently to the cath lab (12.2% vs 8.1%), had higher radiation exposure (12.0 mSv vs 10.1 mSv), and higher rates of revascularization (6.2% vs 3.2%) and were twice as likely to undergo CABG (72 patients vs 38 patients). However, both groups had similar rates of the primary outcome (death, MI, hospitalization for unstable angina, or major procedural complication): 3.3% and 3.0%, over a median follow-up of 2 years.

"The impact would have to be superb with such a low incidence of end points," Knaapen noted. "So the doctor orders you a CT test and now you're going to get bypass surgery; I would want SPECT to still walk around without the scar on my chest."

A study by Hulten et al[4] showed that the medical treatment "changed dramatically" in patients who had an initial CT test for suspected CAD. For example, in patients with no obstructive CAD on CT, aspirin prescribing went from 10% to 46% after the CT test. "That is odd; aspirin for life, yet I have a normal CT, and we know that aspirin doesn't work in primary prevention," Knaapen observed.

"What about the elephant in the room, the SCOT-HEART trial? Wasn't that a positive trial outcome?" he asked rhetorically. "Actually, it wasn't." None of the prespecified end points were reached. "They were borderline significant, but borderline significance isn't significant, especially if you randomize 4000 patients."

This all adds up to show that a strategy of "CT first is debatable in patients with an intermediate likelihood of CAD risk," Knaapen concluded.

Reasons for Using CT First

"I would argue that CT angiography should be the first diagnostic test," and then physicians can "use data derived from CT coronary angiography to subsequently change management of patients," Villines countered.

On average, patients in PROMISE were 60 years old and had a high rate of invasive angiography—8% to 12%. "Are we cathing the right people?" Villines asked. "Using current functional testing, less than half of the patients who end up in a cath lab around the world have obstructive disease. We simply can do better."

For example, a study of data from the National Cardiovascular Data Registry, US Veterans Affairs, and PROMISE showed that among patients who had noninvasive testing for suspected cardiac chest pain and then had elective cardiac catheterization, 72.1% of patients in the CT-test group vs 47.5% of patients in the functional-test group had obstructive CAD.

"Without initial CT we are seeing a lot of people who don't need this invasive procedure," according to Villines.

In SCOT-HEART, the primary end point was certainty of the diagnosis of angina secondary to CAD at 6 weeks. At that time, the diagnosis of CAD changed in 27% of participants in the CT-angiography arm vs 1% of participants in the standard-care arm, and similarly, the diagnosis of angina due to CAD changed in 23% vs 1%, respectively (P<0.001 for both).

Thus, CT angiography "clarifies the diagnosis in one in four" patients, Villines noted.

There was no significant increase in revascularization or coronary invasive angiography.

However, there was a fourfold increase in aspirin and/or statin use that was associated with a 50% reduction in an incident fatal or nonfatal MI. "This is something that resonates with your patients, and this was seen with just 2 years of therapy," Villines pointed out.

A new analysis from the Computed Tomography Versus Exercise Testing in Suspected Coronary Artery Disease (CRESCENT) trial[5] recently reported that for patients with suspected stable CAD, "a tiered cardiac CT protocol offers an effective and safe alternative to functional testing, [and] incorporating the calcium scan into the diagnostic workup was safe and lowered diagnostic expenses and radiation exposure."

And the recent Cardiac CT in the Treatment of Acute Chest Pain (CATCH) trial[6] reported that "a coronary CT angiography–guided treatment strategy appears to improve clinical outcome in patients with recent acute-onset chest pain and normal electrocardiograms and troponin values vs standard care with a functional test."

"May I remind you that the majority of patients who undergo CT do not have obstructive disease?" Villine said. "Being able to rapidly exclude coronary disease is a strength of the procedure."

So in the end, both debaters agreed on a CT-first strategy for patients with a low likelihood of CAD, but they agreed to differ (for the debate) about the merits of this strategy for intermediate-risk patients.

Knaapen and Villines have no relevant financial relationships. Budoff receives research grant support from GE Healthcare and the National Institutes of Health.

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