From Theheart.org JUNE 10, 2010 | Reed Miller
Salt Lake City, UT – Coronary computed-tomography angiography (CCTA) can identify which intermediate-sized plaques are most likely to cause ischemia without requiring follow-up perfusion imaging, a new study shows .
This week here at the Society of Nuclear Medicine 2010 Annual Meeting, Dr Haim Shmilovich (Cedars-Sinai Medical Center, Los Angeles, CA) presented results from a retrospective analysis of 34 coronary disease patients whose stenotic plaque obstructed between 70% and 89% of the lumen. All of the patients under
went CCTA and myocardial perfusion imaging within six months.
The results suggest that severely stenotic plaques containing certain adverse plaque characteristics that appear on CCTA, especially a lipid core, are more likely to produce significant ischemia than plaques without those characteristics.
Shmilovich presented the examples of a patient who had an 81% stenosis but no ischemia and another with 70% stenosis with ischemia. “Ischemia is not just a matter of the severity of the blockage in the coronary artery but the composition of the plaque,” Shmilovich told heartwire. “We tend to just look at severity and manage patients according to the numbers of the severity of the ischemia. But now we understand that the composition of the plaque also matters.”
If these results are confirmed in larger studies, patients with plaques with these characteristics on CCTA could be referred to intervention without the need to confirm the ischemia with a myocardial perfusion imaging modality such as single-photon-emission computed tomography (SPECT) or positron-emission tomography (PET), he explained. “In the future, it might imply better management of the patient.”
The adverse plaque characteristics analyzed in the study include lipid cores detected as areas of low radiation attenuation on the CCTA, discrete “spotty” calcifications less than 3 mm in length and occupying less than an 180° arc of short-axis vessel circumference, and positive remodeling, defined as a maximal outer vessel diameter along the plaque exceeding the diameter of the proximal reference vessel segment by at least 5%.
Significant inducible ischemia on the myocardial perfusion image was defined as a stress total perfusion defect exceeding the rest total perfusion defect by at least 5%. The researchers used chi-square and multivariable logistic regression tests to analyze the relationship between individual adverse plaque characteristics and total number of adverse plaque characteristics to the presence of significant inducible ischemia.
Overall, 38.2% of the patients in the study had significant inducible ischemia, and corresponding regional ischemia was far more prevalent in plaques with lipid core than those without (80% vs 21%, p=0.001) after adjustment for the measured stenosis severity and other plaque characteristics, but a similar relationship was not found with spotty calcification or positive remodeling. The number of adverse plaque characteristics exhibited a significant positive correlation with the stress-rest total perfusion defect score even after adjustment for the measured severity of the stenosis.
For this study, the researchersfocused on plaques obstructing 70% to 89% of the lumen because it is in this intermediate range of stenotic severity where the composition of the plaque makes the biggest difference to whether the obstruction causes ischemia. Hemodynamic studies have shown that plaques covering over 90% or more of the lesion are almost certainly ischemic and therefore should be referred for intervention, while plaques covering 70% or less are unlikely to cause ischemia, and plaques covering 50% or less are almost certainly unable to cause ischemia.
To confirm the results of this small study and to help define the limits of where plaque composition is a more important determinant of ischemia than stenosis severity, Shmilovich and colleagues are currently conducting a larger study with patients with stenoses ranging from 50% to 99% of the lumen.
- Shmilovich H, Cheng V, Tamarappoo B, et al. Adverse characteristics in coronary arterial plaques causing severe stenoses on coronary computed tomography angiography (CCTA) predict inducible ischemia on myocardial perfusion imaging MPI. Society of Nuclear Medicine 2010 Annual Meeting; June 8, 2010; Salt Lake City, UT. Abstract 430.