Chest pain is an unwieldy problem bordering on unmanageable. As many as 6 million patients are admitted to emergency departments every year in the U.S. for the assessment of chest pain. And while test results are frequently inconclusive, they are always expensive. Coronary CT angiography (CTA), despite real limitations, has been shown to diagnose some patients quickly and accurately.
In a new study, 64-slice CTA provided the correct diagnosis in 95% of patients with low-risk acute chest pain, leading the authors to conclude that CTA was well suited to diagnosing this population at least. Still, a quarter of the patients needed additional examination to determine that CT had been correct all along.
Significant limitations apply in 64-slice multidetector-row CT (MDCT), particularly in the assessment of intermediate-grade stenoses for which CT's results are often inconclusive, cautioned Dr. James Goldstein and colleagues from William Beaumont Hospital in Royal Oak, MI. But compared with the standard of care (SOC) -- electrocardiography followed by cardiac enzymes and stress testing -- MDCT patients were more likely to remain discharged over a six-month follow-up period.
"Failure to diagnose myocardial ischemia as the cause of acute chest pain has serious public health consequences and causes substantial malpractice litigation," Goldstein and colleagues wrote in this week's Journal of the American College of Cardiology.
"Although 50% of acute chest pain cases represent noncardiac conditions, symptoms are often atypical and clinical presentations frequently overlap, contributing to the challenge of rapidly establishing a correct diagnosis," they wrote. "Accordingly, emergency department (ED) chest pain units employ standard of care (SOC) rule-out-myocardial infarction algorithms with serial electrocardiograms followed by rest and/or stress imaging studies. This approach has reduced diagnostic error but is time-consuming, expensive, and not always definitive" (JACC, February 27, 2007, Vol. 49:8, pp. 863-871).
The study by Goldstein and his colleagues Drs. Michael Gallagher, William O'Neill, Michael Ross, Brian O'Neil, and Gilbert Raff sought to compare the safety, diagnostic efficacy, and efficiency of MDCT with the standard of care for patients with low-risk chest pain.
Eligible patients were age 25 or older, with chest pain and a low predicted risk of infarction or complications. Exclusion criteria included known coronary artery disease, ECG results diagnosing cardiac infarction or ischemia, elevated biomarkers or previously known cardiomyopathy, irregular heart rhythms, renal insufficiency, and contraindications to contrast.
After determining that four-hour ECGs and serum biomarkers were normal, the researchers randomized 197 low-risk patients with chest pain to either 64-slice MDCT (n = 99) or SOC (n = 98) protocols.
After administering beta-blockers to achieve heart rates of 65 beats per minute (bmp) or less, patients underwent contrast-enhanced CT imaging according to standard protocols. The protocol included 60-100 mL of contrast (Visipaque, GE Healthcare, Chalfont St. Giles, U.K.) followed by a saline chaser. Using a 15-segment model, lesions were classified by maximal luminal diameter and graded on a severity scale from 0 to 5, with 5 indicating total occlusion.
Patients whose CT results showed minimal disease were discharged and sent home, while those with intermediate stenoses (greater than 70%) were sent for stress testing.
The SOC protocol included serial electrocardiograms, cardiac biomarkers, and nuclear stress testing (standard stress-rest myocardial perfusion single-photon emission CT imaging).
Both diagnostic approaches were found to be safe, with no adverse events reported. MDCT alone was able to exclude or identify coronary artery disease as the source of chest pain in 75% of patients, "including 67 with normal coronary arteries and eight with severe disease referred for invasive evaluation," Goldstein and colleagues noted.
The remaining quarter of patients needed stress tests, due either to lesions of intermediate severity or nondiagnostic CT scans. Of these patients, 21 of the 24 (87.5%) had negative stress test results and were discharged.
"Overall 88 of 89 (94.9%) patients in the (MDCT) group were directly discharged from the ED during the index visit."
Among the SOC patients 93 of the 98 (94.9%) patients had normal nuclear scans and were discharged. Three of five patients with abnormal results underwent invasive angiography, and two were discharged for in-patient follow-up.
"In the (MDCT) group, 12 of 99 (12.1%) patients underwent invasive angiography for (MDCT) abnormalities, including seven cases with MDCT finding of significant coronary stenosis ≥ 70% in at least one coronary segment," the authors wrote.
During the index visit, evaluation with MDCT reduced diagnostic time compared with the SOC cohort (3.4 hours versus 15.0 hours, p < 0.0001), lowering the costs of care ($1,586 for SOC versus $1,872 for MDCT, p < 0.001) and requiring fewer repeat evaluations for chest pain (MDCT 2/99, 2%) compared to SOC (7/99, 7%, p = 0.10).
The total cost of care was derived by calculating patient charges in the emergency department, multiplied by the hospital's ED cost-to-charge ratio. The cost of additional stress testing was added in cases in which it was needed, and the cost of waiting for scanners during off-hours was also factored in.
The MDCT was more time- and cost-effective than SOC, but "our analysis did not include 'global' costs or time incurred from protocol-driven invasive procedures, or those related to additional cardiovascular testing," the authors explained. "Also, the present study did not address the comparative value of alternative standard-of-care noninvasive strategies employing ECG-only stress testing, stress echocardiography, or rest-only nuclear scanning."
Both modalities are safe and ultimately provide the correct diagnosis, the team concluded. CT's main advantage is its "ability to delineate the absence of coronary artery disease or the presence of severe stenosis, thereby establishing an immediate diagnosis in nearly 75% of cases, which facilitates more rapid discharge."
Thus MDCT can serve as the definitive evaluation for the vast majority of low-risk patients by virtue of its ability to delineate normal coronary arteries and severe stenoses.
Even in the quarter of cases that needed further testing, MDCT was found to produce a correct diagnosis 95% of the time. And MDCT's value in depicting noncardiac thoracic pathology is another big advantage.
Among its limitations, MDCT may lead to unnecessary catheterization in some cases due to an inability to provide physiological blood flow data in moderately stenosed lesions. Other disadvantages of CT include the radiation dose and exposure to iodinated contrast.
"Caution must be applied when extrapolating these results to patients with higher risk," particularly those with ischemic ECG changes or positive biomarkers, they noted, and low-risk patients also have inherently low event rates.
CT's main limitation is in the evaluation of intermediate-level stenoses, followed by poor image quality. In these cases, stress echocardiography or cardiac MR might be used as a subsequent exam to avoid irradiating the patient twice, the authors suggested.
"Future studies will be necessary to determine how to best use this diagnostic technique," they wrote.
By Eric Barnes
AuntMinnie.com staff writer
March 7, 2007
Related Reading
Radiation dose slashed in 64-slice coronary CTA, February 15, 2007
64-slice CT takes on dual-source in cardiac radiation dose, January 26, 2007
Inflammatory view: Imaging blind to plaque risk, December 7, 2006
Cardiac CT evolves on multiple fronts, November 15, 2006
Dual-source imaging promises better CT scanning, June 15, 2006
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