64-MDCT Better Evaluates Noncalcified Lesions Located Proximally

The objective of a recent study was to determine the accuracy of 64-MDCT for the evaluation of nonculprit coronary lesions compared with invasive coronary angiography.

On 64-MDCT, the degree of stenosis caused by nonculprit lesions can be accurately assessed if the plaque if of mixed type or noncalcified and if located in a proximal coronary artery segment whereas evaluation is more limited if the plaque is calcified or occurring in coronary vessels less than or equal to 3 mm in diameter, remains limited.

Participants
29 patients who presented with acute coronary syndrome (ACS) and underwent invasive coronary angiography.

Methods
Stents were placed within culprit lesions. All patients subsequently underwent 64-MDCT 24 to 48 hours afterwards.

A culprit lesion was labeled on the basis of the association of its invasive angiography depiction with ECG changes or ischemia as determined by stress testing. Invasive coronary angiography was assessed for nonculprit lesions, which were evaluated with quantitative coronary angiography (QCA) software.

64-MDCT was performed with retrospective ECG gating. IV metoprolol was administered as needed to maintain a heart rate <65 bpm. Sublingual glyceryl nitrate was administered prior to imaging.

CT readers were aware of the nonculprit lesion location on invasive coronary angiography, but were unaware of the grade of stenosis on QCA. Lesions causing >=30% stenosis were analyzed. Five post-processing techniques were analyzed on CT:

1. cross-sectional 1-mm slice thickness multiplanar reformat (MPR) manually measured diameters;
2. 5-mm slice thickness maximum intensity projection (MIP) manually measured diameters;
3. coronary lumen cross-sectional areas (CSA) outlined manually from MPRs created perpendicular to the center of the coronary artery segment;
4. coronary software-diameter; and,
5. coronary software-area.

All lesions were characterized as causing 30% to 50% stenosis, 51% to 70% stenosis, and >70% stenosis.

All reference coronary arteries were characterized as <=3 mm or >3 mm in diameter. All plaque was characterized as calcified, mixed, or noncalcified.

Results
On QCA, 65 segments had >=30% stenosis. Of these, 46 could be evaluated on MDCT; 16 segments were excluded because the calcified plaque caused complete visual loss of the vessel lumen and 3 were excluded because of motion artifact. When nonculprit lesions were subgrouped by reference vessel diameter, there was strong correlation for vessels >3 mm (R = 0.78 to 0.91; P <0.01) and poor correlation for vessels <=3 mm (R = 0.1 to 0.07).

When nonculprit lesions were subgrouped by plaque type, there was moderate to strong correlation for mixed plaque (R = 0.58 to 0.75; P <0.01) and noncalcified plaque (R = 0.44 to 0.61; P <0.01) and poor correlation for calcified plaque (R = 0.01 to 0.30). Of the 5 post-processing techniques evaluated on CT, CSA had the best overall correlation with QCA (R = 0.56; P <0.01).

Conclusions
The degree of stenosis caused by nonculprit lesions can be accurately assessed if the plaque is of mixed type or noncalcified and if located in a proximal coronary artery segment. Evaluation of the degree of stenosis caused by nonculprit lesions, which are calcified or occurring in coronary vessels <=3 mm in diameter, remains limited.

Reviewer’s Comments
The authors have nicely demonstrated the strengths and limitations of 64-MDCT with regard to both lesion characterization and post-processing methodology.

Author: Vineet R. Jain, MD

Reference:

Dodd JD, Rieber J, et al. Quantification of Nonculprit Coronary Lesions: Comparison of Cardiac 64-MDCT and Invasive Coronary Angiography. AJR; 2008; 191(August): 432-438