Marlene Busko

August 07, 2017

WASHINGTON, DC — A large, single-center, retrospective study of patients who presented to the emergency department with acute chest pain and low- to intermediate-risk of acute coronary syndrome (ACS) showed that a coronary artery calcium (CAC) score of zero was highly predictive of not having obstructive coronary artery disease (CAD)[1].

In symptomatic patients with low- to medium-risk of ACS, just over half had a CAC of zero, and of these, only 0.7% had obstructive CAD (>50% stenosis).

However, the rate of obstructive CAD was doubled in smokers and patients with type 2 diabetes.

But experts differed about whether these findings mean that a CAC of zero could be used as a "gatekeeper" to rule out ACS in these types of patients.

"CAC has a very high negative predictive value [and] can be used for a screening test" in low- to intermediate-risk patients with acute chest pain in the ER," Dr Gowtham R Grandhi (Baptist Health South Florida, Miami) reported, in an oral session at the Society of Cardiovascular Computed Tomography (SCCT) 2017 Annual Scientific Meeting.

But "do the findings lead you to use CAC alone when CAC is zero?" session comoderator Dr Daniele Andreini (Centro Cardiologico Monzino, Milan, Italy) wanted to know.

"This could be used [alone], but we need more studies," Grandhi replied.

In an email to | Medscape Cardiology, senior author Dr Khurram Nasir (Baptist Health South Florida, Miami) said, "I see a clear value of absence of CAC acting as a gatekeeper for more advanced testing, adding value to managing the majority of the low-risk patients with [acute chest pain] in the emergency department."

The risk of having an acute event or missing an obstructive disease with a CAC of zero is lower than a normal nuclear stress myocardial perfusion imaging test or stress echocardiography, which is routinely employed in a majority of hospitals in the country, Nasir said.

But he agreed that for smokers and patients with type 2 diabetes, "caution can be applied, [since the] risk of obstructive disease with CAC=0 is slightly above the accepted threshold of 1%."

The two session comoderators, however, were not convinced that low-/intermediate-risk patients with CAC of zero could be discharged safely.

The overall rate of obstructive CAD was very low, but it was not zero, Andreini stressed to | Medscape Cardiology. "We are speaking about safe discharge of patients after just [a coronary] calcium score," he said. "I think it's not enough."

Similarly, comoderator Dr Mona Bhatia (Fortis Escorts Heart Institute, New Delhi, India) said that in India, most patients with acute coronary disease are younger than 45, before the age when coronary calcium begins to develop.

"If a patient comes with any kind of chest pain or any kind of symptoms or is at high risk, then just a coronary calcium is really not enough, in India," she said, "because a lot of [patients] have soft plaques that are not going to show up on the calcium score.

CAC Scores and Plaque Burden in Acute Chest Pain

"CAC testing has been established as a risk-stratifying tool in asymptomatic individuals," but few studies have investigated its role for patients presenting to the emergency department with acute chest pain, Grandhi said.

To examine the relationship between CAC scores and coronary plaque burden, they identified 5129 patients with acute chest pain who presented to the emergency department at their center from 2010 to 2015 and who had level 4, low- to intermediate-risk of ACS.

That is, they had a TIMI risk score <2, negative troponins, and a normal or nondiagnostic ECG. According to their center's protocol, these patients undergo a coronary CT scan.

The study patients had a mean age of 53.5, and slightly more than half were women (55%) or Hispanic (53%).

More than half (2895 patients; 56%) had a CAC score of zero, and most of these patients (2762 patients; 95.4%) had no coronary artery stenosis.

Of the remaining patients with CAC=0, 112 patients (3.9%) had nonobstructive CAD and 21 patients (0.7%) had obstructive CAD.

Of the 21 patients with no coronary artery calcium and obstructive disease, 11 patients had undergone stenting.

The rate of obstructive CAD was twice as high in smokers vs nonsmokers (1.9% vs 0.7%) and patients with vs without type 2 diabetes (1.4% vs 0.7%), and it was also higher in patients older than 60 vs younger patients.

The CAC test had a high sensitivity (96%) and negative predictive value (99.3%), but a lower specificity (62.4%) and a much lower positive predictive value (22.4%). It had a diagnostic accuracy of 65.8%.

Study limitations include that the population was largely Hispanic, so the findings may not be generalizable, and risk factors were based on patient recall, authors note.

"In general, most hospitals in the US do not have well-developed emergency-department infrastructure and processes to support a robust coronary CTA program for ruling out ACS for these low- to intermediate-risk chest-pain patients," Nasir said.

However, "there is a slow uptake to adopt these programs that can help reduce the length of stay and associated costs, compared with traditional pathways . . . using stress testing with or without imaging after observing the patients for at least 8 to 12 hours."

Grandhi, Nasir, Andreini, and Bhatia had no relevant financial relationships.

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