ASNC: SPECT Scan Can Identify ACS Patients Hours after Symptoms End

SAN DIEGO, Sept. 12 -- SPECT imaging of fatty acid metabolism can detect or rule out suspected acute coronary syndrome (ACS) with good accuracy, even hours after symptoms have resolved, investigators reported here.
Imaging with iodinated BMIPP achieved a sensitivity of 85% and negative predictive value of 91% in a multi-center evaluation, James Udelson, M.D., of Tufts University in Boston reported at the American Society of Nuclear Cardiology meeting.
Among patients with troponin-positive MI, the imaging technique had 100% sensitivity, he said.
"BMIPP imaging demonstrated sensitivity and negative predictive value for ACS similar to that reported for rest myocardial perfusion imaging," said Dr. Udelson. "However, these data were seen even though BMIPP imaging was performed up to 30 hours after cessation of symptoms."
For evaluation of patients with suspected ACS, molecular imaging of fatty acid metabolism with 123I-BMIPP (β-methyl-P-[123I]-iodophenyl-pentadecanoic acid) offers the advantage of "ischemic memory"-the ability to identify "the imprint of ischemia" hours after symptoms subside, Dr. Udelson said. The technique also minimizes radiation exposure and might eliminate the need for pharmacologic or exercise stress testing, he noted.
Investigators at nine sites in the United States performed BMIPP imaging during initial emergency department evaluation of patients with suspected ACS. All patients were stratified into low, intermediate, and high risk on the basis of gender-specific criteria that included ECG findings, initial troponin levels, and medical history.
BMIPP SPECT imaging was performed within 30 hours of symptom cessation, following rest injection of the contrast material, said Dr. Udelson. BMIPP dose ranged from 2.5 to 5.4 mCi, and SPECT imaging began about 10 minutes following injection. No attenuation or scatter correction was employed.
As indicated by clinical findings, patients had coronary angiography and revascularization. Patients who did not have angiography had SPECT myocardial perfusion imaging for final diagnosis. Telephone follow-up at 30 days assessed safety and clinical events.
An abnormality on SPECT was defined as 3% of left ventricular extent. Investigators used risk-stratified criteria for quantitative analysis of BMIPP defects. For patients with a high likelihood of ACS, a defect was defined as two standard deviations, 2.5 for intermediate risk, and three for low-risk patients.
"The quantitative threshold was varied based on the likelihood of ACS, such that if it was a low-likelihood patient, the defect had to be more severe to be called abnormal," said Dr. Udelson.
A total of 97 patients had complete data: 49 at low risk, 20 at intermediate risk, and 28 at high risk. Adjudicated final diagnoses showed that a total of 26 patients had diagnoses of ACS: three low-risk patients, four intermediate-risk patients, and 19 high-risk patients. SPECT-BMIPP imaging was performed an average of 14 hours after symptom cessation, Dr. Udelson noted.
Performance characteristics of BMIPP imaging for detecting ACS included 85% sensitivity, 59% specificity, 91% negative predictive value, and 43% positive predictive value.
Additionally, the SPECT assessment of fatty acid metabolism correctly identified all patients who had positive cardiac troponin tests, consistent with myocardial infarction.
Comparing SPECT results in ACS-positive and negative patients, Dr. Udelson said the median defect size in patients with ACS was 16.6% of the left ventricle versus 1% in ACS-negative patients (P<0.0001).
Even when SPECT results were falsely positive, median abnormality size differed significantly from patients with true-positive scans (6% versus 28.6%, P=0.005).
No patient discontinued the study because of adverse events. The lone serious adverse event was deemed unrelated to the study drug.
In conclusion, Dr. Udelson said, "The ability to image prolonged post-ischemic abnormalities in fatty acid metabolism, allowing imaging long after symptoms subside, is unique in this setting. These data support the performance of larger pivotal trials, which are now ongoing, in this patient population."
Dr. Udelson said all investigators in the trial received support from Molecular Insight Pharmaceuticals, which funded the study. Additionally, Dr. Udelson and another investigator are consultants for MIP, and the principal investigators included MIP employees. Primary source: American Society of Nuclear CardiologySource reference: Udelson JE et al. "Phase 2B study of the safety and efficacy of [123I]-BMIPP for identification of ischemic myocardium using SPECT in adults admitted to the ED for evaluation of an acute coronary syndrome." American Society of Nuclear Cardiology 2007. Abstract LB-04.