New research has concluded that multidetector-row CT (MDCT) may be an efficient method of triaging patients who present to the emergency department with acute chest pain.
In 40 patients with acute chest pain who underwent CT angiography to rule out acute coronary syndrome (ACS), Dr. Udo Hoffmann and colleagues at Massachusetts General Hospital and Harvard Medical School in Boston found that MDCT has "tremendous potential" to decrease unnecessary hospital admissions for patients presenting with acute chest pain, but with nondiagnostic ECG results and normal cardiac enzymes.
"Early triage of these patients is important both for prognosis and treatment but it remains difficult," the authors wrote. "Patients at highest risk for adverse outcomes derive the greatest benefit from glycoprotein IIb/IIIa inhibitor therapy and early revascularization. By contrast, patients at low risk may be discharged without long-term impact on their risk of death or myocardial infarction, and can safely be assessed further as outpatients."
Multidetector CT is becoming more widely available in emergency departments. Recent data from 64-slice CT studies have shown sensitivities of 78% to 100% (specificity 96% to 100%) for detecting stenoses in smaller side branches, with positive predictive values of 87% to 100% and negative predictive values of 97% to 100%, the group noted.
The study examined CT's ability to stratify risk in patients with acute chest pain but normal cardiac enzymes. Patients received standard care and underwent MDCT scans to evaluate the feasibility of detecting significant coronary artery stenosis as a triage decision criterion compared with clinical outcome.
The pilot study examined 40 patients with CT (53% men; mean age 57 ± 13 years) who were awaiting admission to a hospital for the evaluation of suspected acute cardiac ischemia. All had acute chest pain but normal enzymes and a lack of diagnostic ECG changes, the authors explained.
Following administration of 320 mg iodixanol (Visipaque, GE Healthcare, Chalfont St. Giles, U.K.) as a contrast agent, and 5-15 mg of IV metroprolol as a beta-blocker, CT images were acquired on a either a Sensation 16 or Sensation 64 scanner (Siemens Medical Solutions, Malvern, PA). The 16-slice protocol (n = 17) used 16 x 0.75-mm collimation, 420 msec rotation speed, 120 kVp, and 500 mAs; the 64-detector images were acquired at 64 x 0.6-mm collimation, 330 msec rotation speed, 120 kVp, and 850 mAs, the group reported.
Images were reconstructed using a medium-sharp convolution kernel at a slice thickness and interval of 1.0/0.5 mm (16-slice) or 0.75/0.4 (64-slice) using an ECG-gated half-scan algorithm and retrospective ECG gating. Reconstruction windows were optimized to reduce motion artifacts.
Physicians caring for the patients were blinded to the MDCT results. "An expert panel established the presence or absence of ACS based on American Heart Association (AHA) guidelines," Hoffman and his team wrote. The AHA categories include ST-segment elevation myocardial infarction, non-STEMI myocardial infarction, and unstable angina pectoris.
In all, 61 of the108 patients were deemed ineligible due to elevated creatinine, positive troponin or ECG changes indicative of myocardial ischemia, and seven refused participation.
"The average clinical pretest probability as assessed by emergency department staff at the time of triage was 30% ± 24% (range, 1% to 90%)," they wrote.
Of the remaining 40 eligible patients, all five with ACS (12.5%) including one with non-ST elevation myocardial infarction and four with unstable angina pectoris, had at least one significant coronary stenoses, for a CT sensitivity of 100% (95% CI, 49% to 100%). CT ruled out ACS in the remaining 35 patients, and the presence of significant coronary stenosis (> 50% occlusion) was used to make the triage decision with regard to admission.
The mean heart rate during the scan was 62 ± 8 beats per minute for patients in both scanners. For the 17 patients imaged at 16-slice CT, image quality was limited in six patients, good in six patients, and excellent in five patients. For the 23 patients imaged at 64-slice CT, image quality was limited in two patients, good in eight, and excellent in 13 (p = 0.01).
The presence of significant stenosis was excluded in 26 patients. The presence of any significant stenosis was either detected or could not be excluded in 14 patients, the group noted.
In nine patients in whom ACS was ruled out by standard clinical evaluation, significant stenoses were either diagnosed (n = 2) or could not be excluded (n = 7) at CT, the authors wrote. The average hospital stay for standard clinical care was 30.5 ± 17.3 hours (range 7.6-76.2) compared to the MDCT-based strategy of 7.8 ± 3.1 hours (range, 4-11.4) (p < 0.01), a potential savings of 598 hospital hours with CT. Event rates in patients who were discharged without an ACS diagnosis were less than 1%.
"Although risk stratification schemes have been suggested for patients with acute chest pain on the basis of clinical presentation and risk factors to identify patients with low risk of ACS, translation of these schemes into clinical decision-making has been difficult," the team wrote. "This diagnostic dilemma is emphasized by a wide range (1% to 90%; mean 30% ± 24%) of clinical pretest probabilities in our patient cohort as assessed by emergency department staff at the time of triage. In these patients, triage based on traditional risk stratification is ineffective."
The study showed the feasibility of performing CT in patients awaiting hospital admission, with 100% sensitivity and 74% specificity to appropriately admit patients with suspected ischemia using the detection of significant stenosis as a triage criterion, Hoffmann and colleagues wrote. MDCT improves early risk stratification, and a larger study is warranted to determine if this finding will change patient management.
MDCT may be limited in patients with prior stenting, bypass, or severe calcification, the authors cautioned. Again, more studies are needed to better assess which patients should be excluded, they wrote.
MDCT is feasible in acutely ill patients, and the modality has great potential for decreasing the number of hospital admissions "without reducing appropriate admissions in patients who have nondiagnostic ECG results and normal cardiac enzymes," the authors concluded.
By Eric Barnes
AuntMinnie.com staff writer
November 1, 2006
Related Reading
CT assesses plaque composition, but with difficulty, September 18, 2006
MDCT correlates ACS to mixed plaques, April 20, 2006
Study: 16-MDCT yields too many nonevaluable artery segments, July 26, 2006
CTA proves faster and cheaper for assessing chest pain in ER, April 11, 2006
CT doesn't hurt when evaluating emergency chest pain, August 15, 2005
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