CT Angiography Moves to Forefront in Assessment of Chest Pain in UK

New UK recommendations for the assessment of chest pain are prioritizing the use of CT angiography in cases where a diagnosis of stable angina cannot be excluded on the basis of a clinical assessment alone.

The National Institute for Health and Care Excellence (NICE) is now recommending CT angiography as the first-line investigation for patients with stable chest pain with typical or atypical symptoms, as well as those with nonanginal chest pain with ECG changes suggestive of coronary artery disease.

The 2016 NICE clinical update, which was published in late November, suggests the use of noninvasive functional imaging if CT coronary angiography shows coronary artery disease of uncertain functional significance or is nondiagnostic. Invasive coronary angiography is the third-line test in situations where the results of noninvasive functional imaging are inconclusive.

“It would be fair to say that CT angiography is now being recognized for the powerful test it is, not just for excluding significant coronary artery disease but as a first-line investigation for those with intermediate- and intermediate-to-high pretest probability of coronary disease,” Ed Nicol, MD (Royal Brompton Hospital, London, England), told TCTMD.

Nicol, the president of the British Society of Cardiovascular Imaging and British Society of Cardiovascular CT (BSCI/BSCCT), said there will likely remain “quite a few” patients who will undergo second-line functional testing based on the CT angiogram. The most powerful aspect of CT coronary angiography is its ability to exclude significant coronary artery disease, not necessarily to determine the percentage of stenosis in an individual with moderate or severe disease, he said.

“I think we’re going to equally see a number of areas with increased use of [myocardial perfusion with single-photon emission computed tomography], stress echocardiography, and perfusion MRI,” said Nicol. “The reality is that if hospitals only have a 64-slice scanner, there will be things like calcification and artifact which make it very difficult to say whether the lesion is likely to be flow-limiting or not.”

For Michael Blaha, MD (Johns Hopkins Medical Institute, Baltimore, MD), the prioritization of CT angiography is appropriate and “a pretty big deal for the CT community.” What with the time spent in the emergency room, cost, radiation, and the number of times patients go to the cath lab only to return with a negative result, the use of CT angiography makes sense. “We don’t have evidence that [CT angiography] saves lives, but that’s not what this is about in this case,” said Blaha. 

NICE is an independent organization responsible for providing evidence-based guidance and advice to the National Health Service in the United Kingdom.

Future CT Angiography Landscape in the UK

Speaking with TCTMD, Nicol said he is excited that CT is being recognized for the “powerful tool that it is” but also urged caution as CT angiography is pushed front and center in patient care. In fact, the BSCI/BSCCT published a statement in response to the NICE clinical update highlighting some of their concerns.

“A pretty big deal for the CT community.” Michael Blaha

“Our biggest concern as a society is essentially a delivery problem,” said Nicol. “CT scanners are already used in most [National Health Service (NHS)] hospitals and are pretty much at capacity. Historically, [we have had] a relatively low number of consulting radiologists compared with our European partners. And CT coronary angiography is not an established technique in a very significant number of hospitals in the UK. To go overnight from one set of guidelines to another doesn’t really take into account significant investment in the CT scanner base, which in the NHS is under quite significant financial pressure.”

Even if the CT scanners were in place, Nicol noted that CT angiography performed poorly can lead to a high dose of radiation with little practical benefit. “It requires training and experience for radiographers, radiologists and cardiologists to make sure the quality of the scans is high enough to be of diagnostic use with the lowest possible dose of radiation,” he said. “There’s a whole raft of things that need to happen in the NHS to make this a reality.”

According to the BSCI/BSCCT, the United Kingdom has a very low number of CT scanners compared with other countries. In Germany, Spain, and France, there are 19, 17, and 14 CT scanners per million inhabitants compared with just 9 million scanners per million inhabitants in the UK. Currently, there are 228 cardiac-capable CT scanners in the UK (minimum 64-slice detector technology), or 4 scanners per million patients. The BSCI/BSCCT estimate that an additional 200,000 patients may require CT angiography under the new NICE stable chest pain guidelines, a 700% increase in cardiovascular CT delivery.    

Other Changes in the NICE Guidelines

As part of the old treatment paradigm for patients with chest pain, patients with a very low pretest probability—those with a less than 10% likelihood of coronary artery disease—required no additional investigation. Patients with a low pretest probability—those with a 10% to 29% likelihood of coronary disease—were referred for coronary artery calcium (CAC) screening. Depending on their CAC score, these patients either had no further testing, underwent CT angiography, or were sent directly to the catheterization laboratory for invasive angiography.

Patients with a 30% to 60% pretest probability of coronary disease were referred for functional testing and those with a more than 60% probability were referred directly for invasive angiography.  

Nicol said CAC screening has always been “a bit contentious in the UK,” noting that younger patients can have significant coronary artery disease without calcification. “With CT angiography, you can still see the calcification, but you can also see the noncalcified plaque,” he said. “If you’re going to do a test to confirm or exclude significant coronary artery disease, CT angiography is almost certainly the right test.”

Regarding pretest probability, which was based on the patient’s age, symptoms, and risk factors, among other variables, Nicol said the evidence suggests physicians are not very good at estimating the likelihood of coronary disease, with most assessments overestimating risk. “This meant a lot of people were going straight to invasive angiography, which probably wasn’t the best test, and was increasing the number of people with normal invasive angiograms and all the risks associated with it,” said Nicol.

Blaha told TCTMD physicians should still use their clinical judgement, but he pointed out that under the older guidelines, CT angiography was considered appropriate for chest pain patients with an intermediate likelihood of disease. In this setting, intermediate risk was defined as anything from a 10% to 90% likelihood of obstructive coronary artery disease.

“Everyone but the lowest of lows and the highest of highs,” said Blaha. “And those numbers are so misleading anyway. There’s no population that has a 90% risk of obstructive coronary artery disease unless they’re having a heart attack. Who’s to say what the difference is between 5% and 11%, for example. There’s no tool to accurately predict, so my response is that they’re removing something that never really had any great evidence to support it anyway.”

NICE is also recommending the use of high-sensitivity troponin testing in patients who arrive at the hospital.