Korean J Radiol.  2017 ;18(4):655-663. 10.3348/kjr.2017.18.4.655.

Assessment of Myocardial Bridge by Cardiac CT: Intracoronary Transluminal Attenuation Gradient Derived from Diastolic Phase Predicts Systolic Compression

• Yu M
• Zhang Y
• Li Y
• Li M
• Li W
• Zhang J

• KMID: 2427234
• DOI: http://doi.org/10.3348/kjr.2017.18.4.655

Abstract

OBJECTIVE
To study the predictive value of transluminal attenuation gradient (TAG) derived from diastolic phase of coronary computed tomography angiography (CCTA) for identifying systolic compression of myocardial bridge (MB).
MATERIALS AND METHODS
Consecutive patients diagnosed with MB based on CCTA findings and without obstructive coronary artery disease were retrospectively enrolled. In total, 143 patients with 144 MBs were included in the study. Patients were classified into three groups: without systolic compression, with systolic compression < 50%, and with systolic compression ≥ 50%. TAG was defined as the linear regression coefficient between intraluminal attenuation in Hounsfield units (HU) and length from the vessel ostium. Other indices such as the length and depth of the MB were also recorded.
RESULTS
TAG was the lowest in MB patients with systolic compression ≥ 50% (−19.9 ± 8.7 HU/10 mm). Receiver operating characteristic curve analysis was performed to determine the optimal cutoff values for identifying systolic compression ≥ 50%. The result indicated an optimal cutoff value of TAG as −18.8 HU/10 mm (area under curve = 0.778, p < 0.001), which yielded higher sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy (54.1, 80.5, 72.8, and 75.0%, respectively). In addition, the TAG of MB with diastolic compression was significantly lower than the TAG of MB without diastolic compression (−21.4 ± 4.8 HU/10 mm vs. −12.7 ± 8 HU/10 mm, p < 0.001).
CONCLUSION
TAG was a better predictor of MB with systolic compression ≥ 50%, compared to the length or depth of the MB. The TAG of MB with persistent diastolic compression was significantly lower than the TAG without diastolic compression.

Keyword

Coronary computed tomography angiography; Myocardial bridge; Systolic compression; Transluminal attenuation gradient; TAG; Ischemic heart disease; Coronary artery disease

MeSH Terms

Adult
Aged
Aged, 80 and over
Area Under Curve
Blood Pressure/physiology
Coronary Angiography
Female
Humans
Image Processing, Computer-Assisted
Linear Models
Male
Middle Aged
Myocardial Bridging/diagnosis/*diagnostic imaging
ROC Curve
Retrospective Studies
Sensitivity and Specificity
Severity of Illness Index
*Tomography, X-Ray Computed
Young Adult

Figure

• 

  Fig. 1 Bland-Altman analysis plot comparing observer 1 and observer 2 for measurement of TAG in 40 randomly selected cases.Mean difference of TAG measured by two raters was -5.4 HU/10 mm. HU = Hounsfield units, SD = standard deviation, TAG = transluminal attenuation gradient

• 

  Fig. 2 Representative case of MB with dynamic compression.A. CPR image of end-systolic phase (35% of R-R interval) showed presence of MB at middle LAD with significant compression (white arrows). B. CPR image of mid-diastolic phase (70% of R-R interval) showed presence of MB at middle LAD (white arrows). MB depth and length were 2.2 and 27.4 mm, respectively. C. CPR image of end-diastolic phase (5% of R-R interval) showed presence of MB at middle LAD (white arrows) with persistent compression. D. VR image confirmed overlay of myocardium at middle LAD (black arrows). E. TAG of MB vessel was -30 HU/10 mm. CPR = curved planar reformation, HU = Hounsfield units, LAD = left anterior descending, MB = myocardial bridge, TAG = transluminal attenuation gradient, VR = volume rendering

• 

  Fig. 3 Representative case of MB with dynamic compression.A. CPR image of end-systolic phase (35% of R-R interval) showed presence of MB at middle LAD without compression (white arrows). B. CPR image of mid-diastolic phase (70% of R-R interval) showed presence of MB at middle LAD (white arrows). MB depth and length were measured as 1.3 and 15.8 mm, respectively. C. CPR image of end-diastolic phase (5% of R-R interval) showed presence of MB at middle LAD (white arrows). D. VR image confirmed overlay of myocardium at middle LAD (black arrows). D. TAG of MB vessel was -6.14 HU/10 mm. CPR = curved planar reformation, HU = Hounsfield units, LAD = left anterior descending, MB = myocardial bridge, TAG = transluminal attenuation gradient, VR = volume rendering

• 

  Fig. 4 ROC curve analysis of CCTA-derived parameters for identifying MB with systolic compression ≥ 50%.TAG showed largest AUC and best diagnostic performance compared with MB depth and MB length (TAG vs. depth, p = 0.01; TAG vs. length, p = 0.057; length vs. depth, p = 0.475). AUC = area under curve, CCTA = coronary computed tomography angiography, CI = confidence interval, MB = myocardial bridge, ROC = receiver operating characteristic, TAG = transluminal attenuation gradient

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