乌鸦传媒

Cardiac CT angiography (CTA) adds prognostic value to existing risk scores for patients who present to the emergency department with acute chest pain and for those who have undergone a coronary artery bypass graft, two studies showed.

In the first study, cardiac event rates increased with worsening severity of coronary artery disease as seen with CTA in patients presenting to the emergency department with acute chest pain (P<0.0001), according to Quynh Truong, MD, MPH, of Massachusetts General Hospital in Boston, and colleagues.

In the second, event rates among patients who had undergone CABG increased with a greater number of unprotected coronary territories seen with CTA (P<0.001), according to Benjamin Chow, MD, of the University of Ottawa Heart Institute, and colleagues.

Both studies, which were reported in the May issue of JACC: Cardiovascular Imaging, demonstrated that adding the information from the CT scans to clinical risk models improved the prediction of cardiac events.

The authors of both studies, however, called for future multicenter studies to confirm the findings.

John Reilly, MD, of the Ochsner Health System in New Orleans, told 乌鸦传媒 that "the role for CT angiography is primarily in the patients who are in the lower-risk group."

The CT scans may allow patients with chest pain, who have normal levels of cardiac biomarkers and normal electrocardiographic findings when they present to the emergency department, to go home sooner than they typically would.

Even these low-risk patients often spend 12 to 24 hours in the hospital for observation to rule out an impending myocardial infarction, according to Reilly, a spokesman for the Society for Cardiovascular Angiography and Interventions.

Using cardiac CT may compress the time spent in the emergency department to about three hours in patients with normal lab tests and normal scans, he said, a strategy that is already becoming more widely adopted.

"This is more time efficient and in many hospitals more cost efficient" because of the lower use of resources, including nursing services and additional blood tests, Reilly said.

ED Study Looks at CT in Acute Cases

The study by Truong and colleagues extended the findings from a previous report, which showed that low-to-intermediate risk patients presenting to the emergency department with acute chest pain had a very low chance of cardiovascular events through one year if they had no evidence of coronary artery disease on cardiac CT. The current study followed patients through nearly two years.

They analyzed 368 patients who were participating in the ROMICAT trial. All had low-to-intermediate risk of acute coronary syndrome, negative initial troponin, and a nonischemic electrocardiogram.

All of the patients underwent contrast-enhanced 64-slice CT. Both the caregivers and the patients remained blinded to the results, so the findings would not influence clinical outcomes.

"Given the acceptance of cardiac CT into clinical practice, such a study design is unlikely to be possible nowadays," the authors noted.

The CT scans showed that 18.5% of the patients had stenosis and 12.5% had left ventricular regional wall motion abnormalities.

Through follow up, 6.8% of the patients had a major adverse cardiovascular event (MACE). There were no cardiac deaths, 12 MIs, and 23 revascularizations.

The rate climbed from 0% for patients with no evidence of coronary disease, and 4.6% for those with nonobstructive disease, to 30.3% for those with obstructive disease (P<0.0001), "which provides support for at least a two-year MACE-free warranty period in patients with normal CT findings in the emergency department patient cohort," according to the authors.

There was a similar pattern when information on the presence of coronary disease and regional wall motion abnormalities was combined, with the highest rate in patients with stenosis and regional wall motion abnormalities (62.4%).

When added to the clinical TIMI risk score, information from CT improved the prediction of risk, as assessed using the area under the receiver-operator characteristic curve (P<0.0001).

"Although the presence of no coronary artery disease (CAD) on CT may lead to an early and safe hospital discharge of patients, the detection of nonobstructive CAD, obstructive CAD, and regional wall motion abnormalities should require a more conservative triage approach and aggressive management strategy by caregivers," Truong and colleagues wrote.

CABG Study Broadens Data on CT

Commenting on the study by Chow and colleagues, Reilly said the investigation of the prognostic value of CT angiography in patients who have undergone CABG was important because these patients have been excluded from previous studies of cardiac CT.

He said that was because of technical limitations of performing scans in this population, including a tendency for more diffuse and more heavily calcified disease and the presence of surgical clips.

Chow's team analyzed data from 250 patients who had undergone CABG. All had their cardiac risk calculated using the National Cholesterol Evaluation Program/Adult Treatment Panel III.

All underwent 64-slice CT to determine the number of unprotected coronary territories. A territory was considered unprotected if an ungrafted native coronary artery had a significant stenosis; a significant stenosis in the native artery was distal to the graft insertion; and a native artery and its graft both had significant stenoses.

The primary endpoint was a composite of cardiac death or MI.

Through a mean follow-up of 20.8 months, 9.2% of patients had an event -- 15 cardiac deaths and eight nonfatal MIs.

The cumulative event rate increased with the number of unprotected coronary territories -- 3.9%, 9.5%, 16.2%, and 45.5% for patients with 0, 1, 2, and 3 unprotected territories.

A multivariate analysis controlling for clinical variables showed that the presence of unprotected coronary territories was associated with about double the risk of having an event (HR 2.08, 95% CI 1.40 to 3.10).

As in the study by Truong and colleagues, adding CT information to the clinical risk model improved prognostic value (P=0.001).

In an accompanying editorial, Patrick O'Gara, MD, and Ron Blankstein, MD, of Brigham and Women's Hospital in Boston, said the study by Chow and colleagues "provides important evidence that the anatomic information provided by coronary CT angiography is prognostically important and can identify patients with a high rate of cardiovascular death or myocardial infarction."

They added that future studies in this patient population should include multiple centers and a longer duration of follow-up.

In another editorial, Paul Schoenhagen, MD, of the Cleveland Clinic, and colleagues said that both studies demonstrate the prognostic value of cardiac CT in the respective patient populations, adding, however, that "what we truly need are large, prospective clinical trials that connect diagnostic testing with clinical endpoints."

"We urgently need large-scale trials so that clinical guidelines based on comparative effectiveness data, rather than expert consensus alone, will direct individual patients to the most appropriate diagnostic approach and further treatment," they wrote. "Tremendous opportunities are in our hands -- it is up to us to use them to the maximum benefit of the patients who entrust us with their well-being."

In terms of limitations, authors of both studies noted the use of data from single centers and the use of a radiation dose that was higher than in previous studies -- 11.4 mSv in the study by Truong and colleagues; 23.2 in the study by Chow and colleagues. Studies with prospective triggered CT protocols have reported exposures as low as 2 mSv to 4 mSv.

Chow and colleagues explained that, in their study, "this likely relates to the greater scan length needed to ensure coverage of bypass grafts ... Understanding the potential harm of radiation exposure, the authors stress the importance of radiation reduction techniques and that such techniques should be used whenever possible."