Could a Coronary Calcium Test Rule Out CAD in Chest Pain?

For patients with chest pain who are at low risk of acute coronary syndromes, a coronary artery calcium (CAC) score of zero rules out CAD and the need for revascularization in the vast majority of patients, according to results from a new study.

The findings, say investigators, suggest that incorporating CAC testing into the evaluation of patients with chest pain might be one way to identify those who don’t need any additional testing, such as with CT angiography or myocardial perfusion imaging, and could save the healthcare system money.

“Almost 90% of all the nuclear scans that happen for chest pain assessment in our country are normal,” senior investigator Khurram Nasir, MD (Houston Methodist DeBakey Heart and Vascular Center, Texas), told TCTMD. “Even if you look at the PROMISE study and other studies, even [among] people who are considered higher risk with chest pain who undergo a CT scan, only about 11% have some form of obstructive disease, which is what we’re trying to find. With our current methodologies, which include the pretest probability of disease, it’s very clear that we overestimate risk.”

With that overestimation, he said, many patients are sent unnecessarily for advanced and expensive imaging.

“Right now, we’re moving towards value-based medicine,” said Nasir. “We don’t have infinite resources, and we have to be prudent in what we use. What we’ve suggested for a long time in cardiology circles is that maybe a simple, cheap, widely-available calcium scan can help as a gatekeeper.”

To TCTMD, Marc Dweck, MBChB, PhD (University of Edinburgh, Scotland), said that in contemporary clinical practice, patients with chest pain are assessed with a clinical history, physical exam, ECG, and high-sensitivity troponin, and there will be situations of diagnostic uncertainty where use of additional testing will help physicians. However, he’s not convinced that CAC testing will trump CT angiography in this setting.

“It just seems that contrast CT angiography holds advantages,” he said. “It tells you about calcific plaque, it tells you about noncalcific plaque, it tells you about luminal stenosis. But it also tells you about differential diagnoses, most notably pulmonary embolism and aortic dissection. This is the reason a lot of the imaging was done in the first place, the triple rule-out scenario.”

He emphasized that patients in the new study were low-risk patients where physicians “didn’t really think they were having an acute coronary syndrome.” In that setting, Dweck acknowledged, CAC performed well and demonstrated some value in identifying patients unlikely to have obstructive or nonobstructive CAD.

“I think it’s interesting and thought-provoking, but I don’t think it changes practice,” said Dweck. “I don’t think we should be ordering noncontrast scans in these patients. I still think contrast CT offers a lot more value because with that you don’t miss anyone and the penalty is slightly higher radiation exposure, which isn’t of too much clinical relevance for what is an important diagnosis to get right.”

The study was published online recently in JACC: Cardiovascular Imaging, with Gowtham R. Grandhi, MD (Miami Cardiac and Vascular Institute, Baptist Health of South Florida, Miami, and MedStar Union Memorial Hospital, Baltimore, MD), as first author.

CAC in the Emergency Department

In the recent European NSTE ACS guidelines, CT angiography is a class I (level of evidence A) recommendation as an alternative to coronary angiography for exclusion of ACS in patients at low-to-intermediate risk of CAD and normal or inconclusive ECG and troponin test results. While CAC testing is widely acknowledged as a helpful decision tool for identifying stable patients with coronary atherosclerosis who would benefit from treatment, such as the initiation of statins, it is not used as a gatekeeper in patients with chest pain in the emergency department.

To test whether CAC might be used as an initial test in patients with chest pain—a population where physicians do not want to miss the presence of significant CAD—the researchers evaluated its use in 5,192 patients (54% women; mean age 53.5 years) presenting to a Baptist Health South Florida emergency department who were referred for cardiac CT angiography (or triple rule-out CT angiography). All patients were at low risk for ACS based on a normal/nondiagnostic ECG, normal cardiac enzyme levels, and a TIMI score ≤ 2.

Overall, 56% of patients had a CAC score of zero. Of these 2,902 patients, 95.4% did not have any evidence of CAD on CT angiography. Among the 135 patients with no calcification but CAD, 114 (3.9%) had nonobstructive disease and 21 (0.7%) had obstructive disease. As for the 2,290 patients with coronary calcification (CAC > 0), 77% had obstructive CAD, 11% had moderate stenosis, and 12% had severe stenosis.

For the detection of obstructive CAD, the sensitivity and specificity of CAC were 96.2% and 62.4%, respectively. The positive predictive value and negative predictive value of CAC for obstructive CAD were 22.4% and 99.3%, respectively.

To TCTMD, Nasir said that the negative predictive value of CAC for ruling out obstructive CAD or ACS is higher than the reported results of any stress imaging testing, including stress echocardiography and SPECT-myocardial perfusion imaging. These are standard-of-care tests physicians are comfortable using to discharge patients with chest pain, said Nasir. “If CAC score testing is not safe, then stress myocardial perfusion imaging is not safe,” he observed. “We can’t have different views about one test because those tests miss obstructive disease more than a calcium score.”

In terms of downstream testing, just two patients with a CAC score of zero and nonobstructive CAD underwent functional stress testing and one was sent for invasive coronary angiography because of a positive result on the stress test. None of the patients required any coronary intervention and thus were discharged. Of the 21 patients with a CAC score of zero and obstructive CAD, 12 patients were sent to invasive coronary angiography and 11 were revascularized with PCI.

Value-Based Medicine

Simon Winther, MD, PhD (Gødstrup Hospital, Herning, Denmark), whose work has previously shown that adding clinical risk factors and a CAC score to the conventional diagnostic algorithm for chest pain improved the prediction and discrimination of patients with suspected CAD, said that most European centers will send low-to-intermediate-risk patients for CT angiography. This newest study, he said, is quite similar to theirs and shows that the absence of coronary calcification can safely identify chest pain patients without obstructive CAD.

“If the calcium score is zero, the probability of having any disease is very, very low,” said Winther. The new data suggest that it is possible for the coronary calcium score to identify patients who need further testing and those for whom CAD can be safely ruled out, he explained “I think it’s important to say the coronary calcification score is not a diagnostic test—you don’t diagnose obstructive disease—but it’s a tool to help us risk stratify patients.”

Winther added that if a patient has a high CAC score, then CT angiography is not a very useful tool for identifying CAD because there is a higher risk the test will be inconclusive. In that way, the CAC score might even help select patients who would be best suited for invasive coronary angiography. “That’s one solution, also,” he said. “You can risk-stratify patients and manage them based on their calcium score.” 

Dweck pointed out that some patients who present to the emergency department may have had a recent CT scan for another reason. In those patients, CAC may assist physicians in shoring up a diagnosis of CAD, particularly if the previous CT scan suggested the presence of coronary atherosclerosis. “To me, I think that’s where this study adds some value,” he said. “It encourages me to maybe make use of a CT scan done recently for another purpose.” 

Nasir is hopeful that the new chest pain guidelines, which are expected very soon from the American College of Cardiology/American Heart Association, will acknowledge the usefulness of CAC and the “power of zero.” The data are extremely robust, he said, and “confirm what we’ve known for the last 20 years: a calcium score of zero in chest pain patients is safe and is actually safer than many other traditional, standard-of-care tests.”