Skip to main content
NCBI home page
Radiology: Cardiothoracic Imaging logoLink to Radiology: Cardiothoracic Imaging
. 2020 Aug 20;2(4):e190203. doi: 10.1148/ryct.2020190203

Relationship between Coronary Iodine Concentration Determined Using Spectral CT and the Outcome of Percutaneous Coronary Intervention in Patients with Chronic Total Occlusion

Jeong Yoon Lee 1, Yu-Whan Oh 1, Do-Sun Lim 1, Cheol Woong Yu 1, Jae Hyoung Park 1, Hyung Joon Joo 1, Hwan Seok Yong 1, Eun-young Kang 1, Cherry Kim 1, Ki Yeol Lee 1, Sung Ho Hwang 1,✉
PMCID: PMC7977875  PMID: 33778600

Abstract

Purpose

To evaluate the feasibility of coronary iodine concentration (CIC) by using spectral CT in the assessment of the outcome of percutaneous coronary intervention (PCI) for chronic total occlusion (CTO).

Materials and Methods

In total, 50 consecutive patients underwent preprocedural coronary CT angiography with spectral CT prior to their staged PCI for CTO between June 2017 and July 2018. Iodine density maps, referred to as iodine-no-water maps throughout, with spectral CT provided the CIC at proximal CTO (CTO-CIC). Depending on the outcome of PCI, all CTO lesions were divided into two groups: failed PCI and successful PCI. The receiver operating characteristic curve was used to determine the cutoff values of CTO-CIC in the assessment of the outcome of PCI for CTO.

Results

Of the 50 CTO lesions in 50 patients, 34 (68%) and 16 (32%) were assigned to the successful PCI and failed PCI groups, respectively. The mean CTO-CIC was significantly less in the failed PCI group than in the successful PCI group (1.3 mg/mL ± 0.9 [standard deviation] vs 5.2 mg/mL ± 2.5; P < .001). A low CTO-CIC (≤ 2.5 mg/mL) predicted failed PCI with 87% sensitivity, 79% specificity, 79% positive predictive value, and 90% negative predictive value. At multivariable analysis, the low CTO-CIC was significantly associated with the failed PCI (odds ratio, 27.0; 95% confidence interval: 4.9, 147.6; P < .0001).

Conclusion

The CTO-CIC determined by using spectral CT may be useful in the assessment of the outcome of staged PCI for CTO.

See also the commentary by Rubinshtein and Blankstein in this issue.

© RSNA, 2020

Summary

By using spectral CT for coronary angiography before percutaneous coronary intervention (PCI) for chronic total occlusion (CTO), a low coronary iodine concentration (≤ 2.5 mg/mL) at the entry of the CTO lesion is associated with failure of successful antegrade PCI for CTO.

Key Points

  • ■ The coronary iodine concentration at the entry of the chronic total occlusion lesion is significantly less with failed percutaneous coronary intervention than with successful percutaneous coronary intervention (mean, 1.3 mg/mL ± 0.9 [standard deviation] vs 5.2 mg/mL ± 2.5; P < .001).

  • ■ Setting the optimal cutoff point of coronary iodine concentration to 2.5 mg/mL to predict failed percutaneous coronary intervention resulted in a sensitivity of 87%, specificity of 79%, positive predictive value of 66%, and negative predictive value of 93%.

  • ■ The results of a multivariable logistic regression analysis show a low coronary iodine concentration of 2.5 mg/mL or less at the entry of the chronic total occlusion lesion is significantly associated with the failed antegrade percutaneous coronary intervention (odds ratio, 27.0; P < .0001).

Introduction

Coronary chronic total occlusion (CTO) is an obstructive coronary artery disease for which patients are commonly referred for percutaneous coronary intervention (PCI) (1). The prevalence of CTO has been reported to be up to 30% among patients with a clinical indication of coronary angiography (2). Revascularization of the coronary arteries by PCI improves symptoms, quality of life, left ventricular function, and survival in patients with CTO (3). However, despite recent technological advances and improvements in interventional strategies, the success rate of PCI for the revascularization of CTO has remained low (4,5).

The pathologic characteristics of CTO encompass the presence of calcification, inflammation, and neovascularization within the totally occluded segment (6). The degree of calcification, negative remodeling, and the presence of necrotic core along the occluded segment of the CTO help explain the success rates of PCI for CTO (7). In particular, small microvessel recanalization and loose fibrous tissue of CTO lesions are associated with the success rate of PCI (8). Coronary CT angiography is a valuable imaging method for the characterization of CTO (9–11). In clinical practice, the scoring systems based on the coronary CT angiography manifestations of CTO have been used for treatment planning and proper selection of candidates for PCI. Li et al (12) reported that the presence of contrast enhancement within the occluded segment of the CTO on coronary CT angiograms may be associated with microvessel formation or recanalization of the lumen of the CTO. However, the visual assessment of contrast enhancement in the occluded segment of the CTO on coronary CT angiograms may be subjective, depending on the reader’s experience.

Spectral CT based on the dual-energy CT technique can quantify iodine content, which is a major component of the contrast media used at coronary CT angiography (13,14). The quantification of iodine content by using the dual-energy CT technique may provide a more reliable evaluation of contrast enhancement than an assessment based on Hounsfield units (15). We hypothesized that the characterization of CTO at coronary CT angiography may benefit from iodine-specific reconstruction by using spectral CT. Thus, the objective of this study was to measure the coronary iodine concentration (CIC) of CTO lesions with coronary CT angiography by using spectral CT and to evaluate the feasibility of CTO-CIC in the assessment of the outcome of PCI for CTO.

Materials and Methods

Study Population

This retrospective study was approved by our institutional review board, and the requirement for informed consent was waived. Between June 2017 and July 2018, 70 consecutive patients with CTO who underwent coronary CT angiography and PCI sequentially within 1 month were retrospectively reviewed. The inclusion criteria were (a) a diagnosis of CTO confirmed at invasive coronary angiography and (b) previous imaging with preprocedural coronary CT angiography with spectral CT. The exclusion criteria were (a) the presence of a coronary stent at the occluded segment of the CTO (n = 9), (b) congestive heart failure (n = 8), or (c) an uninterpretable coronary CT angiographic examination (n = 3). Finally, 50 patients were enrolled into this study (Fig 1).

Figure 1:

Flowchart shows patient inclusion and exclusion criteria. CCTA = coronary CT angiography, CTO = chronic total occlusion, PCI = percutaneous coronary intervention.

Open in a new tab

Flowchart shows patient inclusion and exclusion criteria. CCTA = coronary CT angiography, CTO = chronic total occlusion, PCI = percutaneous coronary intervention.

Coronary CT Angiographic Examination

All coronary CT angiographic examinations were performed using a dual-layer spectral CT scanner (IQon; Philips, Best, the Netherlands). Patients with no contraindication to β-blockers and with initial heart rates above 65 beats per minute were administered an oral dose of 2.5 mg β blocker (Concor; Merck, Darmstadt, Germany) 1 hour before coronary CT angiography. The mean heart rate during coronary CT angiography was 60 beats per minute ± 16 (standard deviation) (range, 45–81 beats per minute). Isosorbide dinitrate was sprayed into the patient’s oral cavity before contrast material administration. All patients were administered intravenous contrast material (370 mg/mL iodine [Iopamiro; Bracco, Milan, Italy]) through an 18-gauge catheter placed in the antecubital vein. The injection protocol included an initial injection of 60–80 mL of contrast material at the rate of 5–6 mL/sec, according to the patient’s body mass index, followed by 30 mL of saline at the same rate. Imaging was performed in the cranial-caudal direction during an inspiratory breath-hold with retrospective electrocardiographic gating. The bolus-tracking technique was used with a trigger threshold of 100 HU in the ascending aorta. The imaging parameters were as follows: voltage, 120 kVp; current, 158–300 mAs; collimation, 64 mm × 0.625 mm; pitch, 0.16; rotation time, 0.27 sec; field of view, 257 mm; image matrix, 512 × 512; slice thickness, 0.9 mm; and slice increment, 0.45 mm. The virtual monoenergetic image obtained at 60 keV and quantitative iodine-no-water maps of the coronary arteries obtained at the late diastolic phase were reconstructed from the same spectral dataset, with a section thickness of 1 mm and a section increment of 0.5 mm (12).

During coronary CT angiography, the CT dose–length product (in milligrays · centimeter) was recorded. The effective dose (in millisieverts) was estimated by multiplying the dose–length product and a conversion factor for chest examination (k = 0.017 mSv/mGy ⋅ cm) (16).

CT Image Reconstruction and Analysis

Coronary CT angiography data were transferred to an offline workstation (IntelliSpace Portal, version 9.0; Philips Medical Systems, Best, the Netherlands) for image analysis. The coronary CT angiography data were analyzed by two experienced radiologists (S.H.H. and J.Y.L.) with 15 years and 4 years, respectively, of experience in cardiac imaging. The reviewers were independently blinded to the clinical histories and outcomes of PCI. Any disagreement between the two reviewers was resolved by consensus.

At coronary CT angiography, the CTO lesion was defined by the complete absence of luminal enhancement in the coronary artery. Furthermore, the anatomic characteristics of whole CTO lesions were assessed using the cross-sectional curved multiplanar reformatted images from coronary CT angiography. The reviewers recorded the presence or absence of high-risk coronary CT angiographic findings related to failed PCI in every CTO lesion. The high-risk coronary CT angiography manifestations of CTO consisted of (a) long CTO (with a total lesion length > 2 cm), (b) severe calcification (with calcifications ≥ 50% of the vessel cross-sectional area), (c) CTO bending (with an angle ≥ 45° at the occlusion site), and (d) blunt stump (without any tapered stump at the entry of the CTO) (Fig 2) (9).

Figure 2a:

High-risk findings of coronary CT angiography related to failed percutaneous coronary intervention for chronic total occlusion (CTO). (a) On a curved multiplanar reformatted (MPR) image from coronary CT angiography, the CTO length between the proximal (A) and distal (B) CTO margins is measured along the vessel axis. A CTO length greater than 2 cm is defined as a long CTO. (b) On a curved MPR image from coronary CT angiography, the CTO entry site without tapering (arrow) is categorized as a blunted stump (arrowhead). (c) On a cross-sectional image of the CTO entry site, severe calcification (arrow) is defined on the basis of calcifications greater than or equal to 50% of the vessel cross-sectional area. (d) On a curved MR image, the angle at the occlusion site is 54.34°. CTO bending is defined as an angle greater than or equal to 45° at the occluded segment.

Open in a new tab

High-risk findings of coronary CT angiography related to failed percutaneous coronary intervention for chronic total occlusion (CTO). (a) On a curved multiplanar reformatted (MPR) image from coronary CT angiography, the CTO length between the proximal (A) and distal (B) CTO margins is measured along the vessel axis. A CTO length greater than 2 cm is defined as a long CTO. (b) On a curved MPR image from coronary CT angiography, the CTO entry site without tapering (arrow) is categorized as a blunted stump (arrowhead). (c) On a cross-sectional image of the CTO entry site, severe calcification (arrow) is defined on the basis of calcifications greater than or equal to 50% of the vessel cross-sectional area. (d) On a curved MR image, the angle at the occlusion site is 54.34°. CTO bending is defined as an angle greater than or equal to 45° at the occluded segment.

Figure 2b:

High-risk findings of coronary CT angiography related to failed percutaneous coronary intervention for chronic total occlusion (CTO). (a) On a curved multiplanar reformatted (MPR) image from coronary CT angiography, the CTO length between the proximal (A) and distal (B) CTO margins is measured along the vessel axis. A CTO length greater than 2 cm is defined as a long CTO. (b) On a curved MPR image from coronary CT angiography, the CTO entry site without tapering (arrow) is categorized as a blunted stump (arrowhead). (c) On a cross-sectional image of the CTO entry site, severe calcification (arrow) is defined on the basis of calcifications greater than or equal to 50% of the vessel cross-sectional area. (d) On a curved MR image, the angle at the occlusion site is 54.34°. CTO bending is defined as an angle greater than or equal to 45° at the occluded segment.

Open in a new tab

High-risk findings of coronary CT angiography related to failed percutaneous coronary intervention for chronic total occlusion (CTO). (a) On a curved multiplanar reformatted (MPR) image from coronary CT angiography, the CTO length between the proximal (A) and distal (B) CTO margins is measured along the vessel axis. A CTO length greater than 2 cm is defined as a long CTO. (b) On a curved MPR image from coronary CT angiography, the CTO entry site without tapering (arrow) is categorized as a blunted stump (arrowhead). (c) On a cross-sectional image of the CTO entry site, severe calcification (arrow) is defined on the basis of calcifications greater than or equal to 50% of the vessel cross-sectional area. (d) On a curved MR image, the angle at the occlusion site is 54.34°. CTO bending is defined as an angle greater than or equal to 45° at the occluded segment.

Figure 2c:

High-risk findings of coronary CT angiography related to failed percutaneous coronary intervention for chronic total occlusion (CTO). (a) On a curved multiplanar reformatted (MPR) image from coronary CT angiography, the CTO length between the proximal (A) and distal (B) CTO margins is measured along the vessel axis. A CTO length greater than 2 cm is defined as a long CTO. (b) On a curved MPR image from coronary CT angiography, the CTO entry site without tapering (arrow) is categorized as a blunted stump (arrowhead). (c) On a cross-sectional image of the CTO entry site, severe calcification (arrow) is defined on the basis of calcifications greater than or equal to 50% of the vessel cross-sectional area. (d) On a curved MR image, the angle at the occlusion site is 54.34°. CTO bending is defined as an angle greater than or equal to 45° at the occluded segment.

Open in a new tab

High-risk findings of coronary CT angiography related to failed percutaneous coronary intervention for chronic total occlusion (CTO). (a) On a curved multiplanar reformatted (MPR) image from coronary CT angiography, the CTO length between the proximal (A) and distal (B) CTO margins is measured along the vessel axis. A CTO length greater than 2 cm is defined as a long CTO. (b) On a curved MPR image from coronary CT angiography, the CTO entry site without tapering (arrow) is categorized as a blunted stump (arrowhead). (c) On a cross-sectional image of the CTO entry site, severe calcification (arrow) is defined on the basis of calcifications greater than or equal to 50% of the vessel cross-sectional area. (d) On a curved MR image, the angle at the occlusion site is 54.34°. CTO bending is defined as an angle greater than or equal to 45° at the occluded segment.

Figure 2d:

High-risk findings of coronary CT angiography related to failed percutaneous coronary intervention for chronic total occlusion (CTO). (a) On a curved multiplanar reformatted (MPR) image from coronary CT angiography, the CTO length between the proximal (A) and distal (B) CTO margins is measured along the vessel axis. A CTO length greater than 2 cm is defined as a long CTO. (b) On a curved MPR image from coronary CT angiography, the CTO entry site without tapering (arrow) is categorized as a blunted stump (arrowhead). (c) On a cross-sectional image of the CTO entry site, severe calcification (arrow) is defined on the basis of calcifications greater than or equal to 50% of the vessel cross-sectional area. (d) On a curved MR image, the angle at the occlusion site is 54.34°. CTO bending is defined as an angle greater than or equal to 45° at the occluded segment.

Open in a new tab

High-risk findings of coronary CT angiography related to failed percutaneous coronary intervention for chronic total occlusion (CTO). (a) On a curved multiplanar reformatted (MPR) image from coronary CT angiography, the CTO length between the proximal (A) and distal (B) CTO margins is measured along the vessel axis. A CTO length greater than 2 cm is defined as a long CTO. (b) On a curved MPR image from coronary CT angiography, the CTO entry site without tapering (arrow) is categorized as a blunted stump (arrowhead). (c) On a cross-sectional image of the CTO entry site, severe calcification (arrow) is defined on the basis of calcifications greater than or equal to 50% of the vessel cross-sectional area. (d) On a curved MR image, the angle at the occlusion site is 54.34°. CTO bending is defined as an angle greater than or equal to 45° at the occluded segment.

For evaluating the CIC (Fig 3), the cross-sectional virtual monoenergetic image obtained at 60 keV and the iodine-no-water map obtained perpendicular to the coronary artery centerline were reconstructed for each CTO lesion. On the virtual monoenergetic image obtained at 60 keV, the regions of interest (ROIs) were manually drawn at the proximal CTO (at 2 mm from the entry of the CTO, excluding the calcification) and the reference vessel (at the unaffected vessel immediately proximal to the CTO within a 1-cm interval). The ROI at the reference vessel covered the entire vessel lumen. The ROI at the proximal CTO represented the largest noncalcified area in the occluded segment of the CTO. The ROI area of the reference segment (reference ROI area, in millimeters squared) and the ROI area of the proximal CTO (CTO-ROI area, in millimeters squared) were recorded. Thereafter, the CICs of the reference vessel (reference CIC, in milligrams per milliliter) and the proximal CTO (CTO-CIC, in milligrams per milliliter) were measured by applying the ROIs to the iodine-no-water maps. Eventually, the reviewers measured the reference areas, CTO area, reference CIC, and CTO-CIC by using the virtual monoenergetic image obtained at 60 keV and iodine-no-water map from coronary CT angiography (Fig 3).

Figure 3a:

Evaluation of the chronic total occlusion (CTO) coronary iodine concentration (CIC) by using the cross-sectional virtual monoenergetic image obtained at 60 keV and iodine-no-water map by using spectral CT. (a) Cross-sectional images of the proximal CTO (at 1 mm from the entry of CTO, red box) and unaffected reference vessel (blue box) are selected on the virtual monoenergetic image (MonoE) obtained at 60 keV. (b) At the reference vessel, the region of interest (ROI) is manually drawn to cover the entire vessel lumen. The ROI area refers to the reference vessel lumen area. (c) At proximal CTO, the ROI is manually drawn to cover the noncalcified occlusion on the virtual monoenergetic image obtained at 60 keV. The determined ROI is reapplied into the iodine-no-water map to quantify the CTO-CIC in the noncalcified area. Ar = area, Av = average, Equiv = equivalent, Perim = perimeter, SD = standard deviation.

Open in a new tab

Evaluation of the chronic total occlusion (CTO) coronary iodine concentration (CIC) by using the cross-sectional virtual monoenergetic image obtained at 60 keV and iodine-no-water map by using spectral CT. (a) Cross-sectional images of the proximal CTO (at 1 mm from the entry of CTO, red box) and unaffected reference vessel (blue box) are selected on the virtual monoenergetic image (MonoE) obtained at 60 keV. (b) At the reference vessel, the region of interest (ROI) is manually drawn to cover the entire vessel lumen. The ROI area refers to the reference vessel lumen area. (c) At proximal CTO, the ROI is manually drawn to cover the noncalcified occlusion on the virtual monoenergetic image obtained at 60 keV. The determined ROI is reapplied into the iodine-no-water map to quantify the CTO-CIC in the noncalcified area. Ar = area, Av = average, Equiv = equivalent, Perim = perimeter, SD = standard deviation.

Figure 3b:

Evaluation of the chronic total occlusion (CTO) coronary iodine concentration (CIC) by using the cross-sectional virtual monoenergetic image obtained at 60 keV and iodine-no-water map by using spectral CT. (a) Cross-sectional images of the proximal CTO (at 1 mm from the entry of CTO, red box) and unaffected reference vessel (blue box) are selected on the virtual monoenergetic image (MonoE) obtained at 60 keV. (b) At the reference vessel, the region of interest (ROI) is manually drawn to cover the entire vessel lumen. The ROI area refers to the reference vessel lumen area. (c) At proximal CTO, the ROI is manually drawn to cover the noncalcified occlusion on the virtual monoenergetic image obtained at 60 keV. The determined ROI is reapplied into the iodine-no-water map to quantify the CTO-CIC in the noncalcified area. Ar = area, Av = average, Equiv = equivalent, Perim = perimeter, SD = standard deviation.

Open in a new tab

Evaluation of the chronic total occlusion (CTO) coronary iodine concentration (CIC) by using the cross-sectional virtual monoenergetic image obtained at 60 keV and iodine-no-water map by using spectral CT. (a) Cross-sectional images of the proximal CTO (at 1 mm from the entry of CTO, red box) and unaffected reference vessel (blue box) are selected on the virtual monoenergetic image (MonoE) obtained at 60 keV. (b) At the reference vessel, the region of interest (ROI) is manually drawn to cover the entire vessel lumen. The ROI area refers to the reference vessel lumen area. (c) At proximal CTO, the ROI is manually drawn to cover the noncalcified occlusion on the virtual monoenergetic image obtained at 60 keV. The determined ROI is reapplied into the iodine-no-water map to quantify the CTO-CIC in the noncalcified area. Ar = area, Av = average, Equiv = equivalent, Perim = perimeter, SD = standard deviation.

Figure 3c:

Evaluation of the chronic total occlusion (CTO) coronary iodine concentration (CIC) by using the cross-sectional virtual monoenergetic image obtained at 60 keV and iodine-no-water map by using spectral CT. (a) Cross-sectional images of the proximal CTO (at 1 mm from the entry of CTO, red box) and unaffected reference vessel (blue box) are selected on the virtual monoenergetic image (MonoE) obtained at 60 keV. (b) At the reference vessel, the region of interest (ROI) is manually drawn to cover the entire vessel lumen. The ROI area refers to the reference vessel lumen area. (c) At proximal CTO, the ROI is manually drawn to cover the noncalcified occlusion on the virtual monoenergetic image obtained at 60 keV. The determined ROI is reapplied into the iodine-no-water map to quantify the CTO-CIC in the noncalcified area. Ar = area, Av = average, Equiv = equivalent, Perim = perimeter, SD = standard deviation.

Open in a new tab

Evaluation of the chronic total occlusion (CTO) coronary iodine concentration (CIC) by using the cross-sectional virtual monoenergetic image obtained at 60 keV and iodine-no-water map by using spectral CT. (a) Cross-sectional images of the proximal CTO (at 1 mm from the entry of CTO, red box) and unaffected reference vessel (blue box) are selected on the virtual monoenergetic image (MonoE) obtained at 60 keV. (b) At the reference vessel, the region of interest (ROI) is manually drawn to cover the entire vessel lumen. The ROI area refers to the reference vessel lumen area. (c) At proximal CTO, the ROI is manually drawn to cover the noncalcified occlusion on the virtual monoenergetic image obtained at 60 keV. The determined ROI is reapplied into the iodine-no-water map to quantify the CTO-CIC in the noncalcified area. Ar = area, Av = average, Equiv = equivalent, Perim = perimeter, SD = standard deviation.

PCI Procedure

All PCIs were performed by two interventional cardiologists (C.W.Y. and J.H.P.) with 20 years and 15 years, respectively, of experience in coronary intervention. CTO lesions were defined as the obstruction of the native coronary artery with no luminal continuity and interruption of antegrade blood flow at conventional coronary angiography. PCI with an initial antegrade approach of the angioplasty guidewire for CTO could be defined as failed PCI if (a) the antegrade progress of the guidewire failed; (b) complications such as coronary dissection, perforation, or hemodynamic instability occurred; or (c) the PCI operator believed that the prolongation of the procedure would not benefit the patient (12). However, successful opening of the CTO and restoration of flow with PCI were defined as successful PCI.

Statistical Analysis

Quantitative variables were expressed as means ± standard deviations. The Student t test or Mann-Whitney U test was used to compare between failed CTO and successful CTO, if appropriate. The CTO-CIC was treated as a categorical variable by using the best cutoff values obtained with the receiver operating characteristic curve. Intraobserver and interobserver reproducibility of quantitative measurements were evaluated by using the intraclass correlation coefficient. An intraclass correlation coefficient of 0.7 or greater was considered statistically reproducible (17). κ statistics were used to assess the intraobserver and interobserver agreements for the evaluation of low CTO-CIC. The strength of agreement was interpreted using κ values. A κ value of 0.6 or greater was considered as showing good agreement (18). Univariable statistical tests were first performed with binary logistic regression to identify variables associated with successful PCI. A multivariable model for predicting PCI failure was fitted with a forward stepwise selection, with the iterative entry of variables based on the test results. The removal of variables was based on likelihood ratio statistics with a probability of 0.1.

Statistical analysis was performed by using MedCalc Statistical Software, version 15.8 (MedCalc Software, Ostend, Belgium). A P value less than .05 was considered statistically significant.

Results

All 50 patients with CTO (mean age, 65 years ± 13; range, 37–89 years; 40 men [mean age, 62 years ± 13; range, 37–89 years] and 10 women [mean age, 74 years ± 10; range, 60–86 years]) were included (Table 1). Depending on the outcome of PCI, 34 (68%) and 16 (32%) of the 50 patients were assigned to the successful PCI and failed PCI groups, respectively. When considering clinical histories that included smoking, hypertension, diabetes mellitus, and dyslipidemia, no significant difference was observed in their incidence between the successful PCI and failed PCI groups (Table 1). The mean dose–length product of coronary CT angiography was 410 mGy · cm ± 75 (range, 310–489 mGy · cm), which corresponded to 5 mSv ± 3 (range, 4–7 mSv). PCI was performed in all patients at a mean interval of 4 days ± 2 (range, 2–7 days) after coronary CT angiography.

Table 1:

Clinical Characteristics of the Study Cohort

graphic file with name ryct.2020190203.tbl1.jpg

Open in a new tab

In the comparison of coronary CT angiography manifestations (Table 2), the right coronary artery was the most common location of CTO. However, there was no significant difference of PCI result among the locations of CTO. The failed PCI group showed significantly greater incidence of severe calcification (11 of 16 [69%] vs 12 of 34 [35%]; P = .55), blunt stump (10 of 16 [62%] vs six of 34 [18%]; P = .001), and long (>2 cm) CTO (12 of 16 [75%] vs 15 of 34 [44%]; P = .04) compared with the successful PCI group. In the quantitative assessment of the reference vessel at coronary CT angiography, no significant difference was noted in the reference area between the failed PCI and successful PCI groups (mean, 6.4 mm2 ± 2.3 vs 5.9 mm2 ± 2.1, respectively; P = .42). In contrast, the failed PCI group showed significantly less reference CIC than did the successful PCI group (mean, 11.8 mg/mL ± 3.7 vs 14.5 mg/mL ± 4.1; P = .03). In the quantitative assessment of proximal CTO with coronary CT angiography, no significant difference was observed in the CTO-ROI area between the failed PCI and successful PCI groups (mean, 5.0 mm2 ± 1.9 vs 5.2 mm2 ± 1.7; P = .35). In contrast, the failed PCI group showed significantly less CTO-CIC than did the successful PCI group (mean, 1.3 mg/mL ± 0.9 vs 5.2 mg/mL ± 2.5; P < .001). In the reproducibility of the coronary CT angiography analysis (Table 3), the intraclass correlation coefficients of the CTO-ROI area and CTO-CIC were 0.7 or greater, indicating good reproducibility.

Table 2:

Comparison of Coronary CT Angiography Manifestations between Successful PCI and Failed PCI

graphic file with name ryct.2020190203.tbl2.jpg

Open in a new tab

Table 3:

Reproducibility of the Coronary CT Angiography Parameters

graphic file with name ryct.2020190203.tbl3.jpg

Open in a new tab

In the assessment of failed PCI (Figs 4, 5), the area under the receiver operating characteristic curve for CTO-CIC was 0.89 (P < .001). When the cutoff point of low CTO-CIC was set at 2.5 mg/mL to predict failed PCI, the sensitivity was 87% (14 of 16), specificity was 79% (27 of 34), positive predictive value was 67% (14 of 21), and negative predictive value was 93% (27 of 29). In the reproducibility of low CTO-CIC (Table 3), the κ values of low CTO-CIC were 0.6 or greater, indicating fair-to-good reproducibility. Finally, the coronary CT angiographic findings at the CTO proximal entry (severe calcification, blunt stump, and low CTO-CIC) were used as input variables for the multivariable logistic regression analysis (Table 4). In this analysis, low CTO-CIC (odds ratio, 27.0; 95% confidence interval: 4.9, 147.6; P < .0001) was an independent factor for failed PCI.

Figure 4:

Receiver operating characteristic curve for the assessment of failed percutaneous coronary intervention (PCI) with chronic total occlusion coronary iodine concentration (CTO-CIC). AUC = area under the receiver operating characteristic curve.

Open in a new tab

Receiver operating characteristic curve for the assessment of failed percutaneous coronary intervention (PCI) with chronic total occlusion coronary iodine concentration (CTO-CIC). AUC = area under the receiver operating characteristic curve.

Figure 5a:

Representative images of coronary CT angiography in a 56-year-old man who underwent percutaneous coronary intervention for chronic total occlusion (CTO) that failed. (a) A curved multiplanar reformatted (MPR) virtual monoenergetic image obtained at 60 keV shows the complete absence of contrast material filling because of the CTO in the middle right coronary artery (arrow). (b) A cross-sectional iodine-no-water map shows a low CTO coronary iodine concentration (CIC) of 1.9 mg/mL, without severe calcification. (c) Coronary CT angiogram shows the failure of angioplasty guidewire progress through the CTO lesion in the right coronary artery. Ar = area, Av = average, Perim = perimeter, SD = standard deviation.

Open in a new tab

Representative images of coronary CT angiography in a 56-year-old man who underwent percutaneous coronary intervention for chronic total occlusion (CTO) that failed. (a) A curved multiplanar reformatted (MPR) virtual monoenergetic image obtained at 60 keV shows the complete absence of contrast material filling because of the CTO in the middle right coronary artery (arrow). (b) A cross-sectional iodine-no-water map shows a low CTO coronary iodine concentration (CIC) of 1.9 mg/mL, without severe calcification. (c) Coronary CT angiogram shows the failure of angioplasty guidewire progress through the CTO lesion in the right coronary artery. Ar = area, Av = average, Perim = perimeter, SD = standard deviation.

Table 4:

Multivariable Predictors of Failed PCI for CTO

graphic file with name ryct.2020190203.tbl4.jpg

Open in a new tab

Figure 5b:

Representative images of coronary CT angiography in a 56-year-old man who underwent percutaneous coronary intervention for chronic total occlusion (CTO) that failed. (a) A curved multiplanar reformatted (MPR) virtual monoenergetic image obtained at 60 keV shows the complete absence of contrast material filling because of the CTO in the middle right coronary artery (arrow). (b) A cross-sectional iodine-no-water map shows a low CTO coronary iodine concentration (CIC) of 1.9 mg/mL, without severe calcification. (c) Coronary CT angiogram shows the failure of angioplasty guidewire progress through the CTO lesion in the right coronary artery. Ar = area, Av = average, Perim = perimeter, SD = standard deviation.

Open in a new tab

Representative images of coronary CT angiography in a 56-year-old man who underwent percutaneous coronary intervention for chronic total occlusion (CTO) that failed. (a) A curved multiplanar reformatted (MPR) virtual monoenergetic image obtained at 60 keV shows the complete absence of contrast material filling because of the CTO in the middle right coronary artery (arrow). (b) A cross-sectional iodine-no-water map shows a low CTO coronary iodine concentration (CIC) of 1.9 mg/mL, without severe calcification. (c) Coronary CT angiogram shows the failure of angioplasty guidewire progress through the CTO lesion in the right coronary artery. Ar = area, Av = average, Perim = perimeter, SD = standard deviation.

Figure 5c:

Representative images of coronary CT angiography in a 56-year-old man who underwent percutaneous coronary intervention for chronic total occlusion (CTO) that failed. (a) A curved multiplanar reformatted (MPR) virtual monoenergetic image obtained at 60 keV shows the complete absence of contrast material filling because of the CTO in the middle right coronary artery (arrow). (b) A cross-sectional iodine-no-water map shows a low CTO coronary iodine concentration (CIC) of 1.9 mg/mL, without severe calcification. (c) Coronary CT angiogram shows the failure of angioplasty guidewire progress through the CTO lesion in the right coronary artery. Ar = area, Av = average, Perim = perimeter, SD = standard deviation.

Open in a new tab

Representative images of coronary CT angiography in a 56-year-old man who underwent percutaneous coronary intervention for chronic total occlusion (CTO) that failed. (a) A curved multiplanar reformatted (MPR) virtual monoenergetic image obtained at 60 keV shows the complete absence of contrast material filling because of the CTO in the middle right coronary artery (arrow). (b) A cross-sectional iodine-no-water map shows a low CTO coronary iodine concentration (CIC) of 1.9 mg/mL, without severe calcification. (c) Coronary CT angiogram shows the failure of angioplasty guidewire progress through the CTO lesion in the right coronary artery. Ar = area, Av = average, Perim = perimeter, SD = standard deviation.

Discussion

We assessed the CIC of proximal CTO (CTO-CIC) on the iodine-no-water map from coronary CT angiography by using spectral CT just before PCI. Our results showed that patients with a failed PCI had significantly lower mean CTO-CIC than those who underwent a successful PCI (P < .001). Furthermore, the optimal cutoff for low CTO-CIC related to failed PCI was set at 2.5 mg/mL. At multivariable analysis, the low CTO-CIC of 2.5 mg/mL or less was independently associated with failed PCI for CTO.

Many CT features have been identified for defining the treatment strategies for the revascularization of CTO (11,19). In particular, calcification of the CTO lesion is closely associated with difficulty in achieving a successful PCI for CTO. It poses difficulties at all steps of the procedure, hampering successful guidewire passage, lesion predilatation, and adequate stent expansion (20,21). Extensive and large calcifications are the most important reasons for the low success rate of PCI for CTO (20,21). A cross-sectional calcium area of 50% or more serves as the best cutoff value for predicting PCI failure (10). The results of our study reconfirmed that severe calcifications of occluded coronary arteries are independently associated with failed PCI for the treatment of CTO. Interestingly, the absence of severe calcification does not always guarantee successful PCI. Thus, a comprehensive assessment of CTO characteristics, beyond calcifications, has been emphasized for ensuring better treatment strategies for patients with CTO.

CTO of the coronary artery is defined as the total occlusion of the vessel at invasive angiography, with complete interruption of antegrade blood flow. However, CTO lesions at angiography are not always totally occluded. CTO lesions can include a shortly tapered stump, which may represent a high iodine concentration at the entry of the CTO on the iodine map. Furthermore, histologic studies reported that complete occlusion was noted in only 22% of all angiographic CTO lesions (7). At histologic analysis, microvessels (vessel diameter < 200 µm) surrounding loose fibrous tissue may be present in the angiographic CTO. These microvessels and loose fibrous tissue are amenable to PCI owing to the ease with which the wire can penetrate the CTO lesion. Coronary CT angiography can also be used to help identify features that may be overlooked at invasive angiography. Li et al (12) suggested that visible intrathrombus contrast enhancement on coronary CT angiograms could help predict better PCI outcomes for CTO. We hypothesize that the low iodine concentration as found in our study may represent a lack of tissue composition amenable to PCI.

Dual-energy CT can help improve material differentiation by using two different x-ray energy spectra (22). Spectral CT allows dual-energy data acquisition with the use of unique dual-layer energy-resolving detectors (14). More importantly, dual-energy evaluation can be performed retrospectively after spectral CT in all clinical cases. Recently, authors of spectral CT studies have assessed the incremental diagnostic value of iodine quantification (22). When using spectral CT, the iodine-no-water map showing iodine density can be generated using known attenuation properties at high and low energies, which represents the iodine concentration in each voxel (13). The iodine-no-water map reconstructed by using dual-energy techniques also provides excellent resolution of images, with improved iodine contrast-to-noise ratio. In fact, a previous study reported that the use of an iodine map increased the readers’ confidence in detecting the abnormal presence of contrast media, particularly from endoleaks in patients in whom aortic stent graft had been placed (23). This study showed that the quantification of iodine concentration even in small vessels, such as the coronary artery, had the potential to predict failed PCI in patients with CTO.

Our study had several limitations. First, this retrospective study had biases caused by case selection, operator expertise, resources, and image quality of the coronary CT angiograms. Second, a small number of patients and a relatively low portion of failed antegrade PCI could be critical limitations in the generalization of the results of this study. Another limitation of this study was the lack of pathologic correlation. Further validation of the iodine concentration with the histologic morphology of the CTO lesion is desirable. Therefore, further experimental and clinical studies with larger data sets are warranted to define the exact nature of iodine concentration at the site of coronary occlusion and to assess its clinical significance.

In conclusion, by using spectral CT for coronary angiography before PCI for CTO, a low CIC (≤ 2.5 mg/mL) at the entry of the CTO lesion is associated with failure of successful antegrade PCI for the management of CTO.

Supported by a Hyun Jin Kim Research Grant from the Radiology Department and Research Fund of Korea University.

Disclosures of Conflicts of Interest: J.Y.L. disclosed no relevant relationships. Y.W.O. disclosed no relevant relationships. D.S.L. disclosed no relevant relationships. C.W.Y. disclosed no relevant relationships. J.H.P. disclosed no relevant relationships. H.J.J. disclosed no relevant relationships. H.S.Y. disclosed no relevant relationships. E.Y.K. disclosed no relevant relationships. C.K. disclosed no relevant relationships. K.Y.L. disclosed no relevant relationships. S.H.H. disclosed no relevant relationships.

Abbreviations:

CIC
coronary iodine concentration
CTO
chronic total occlusion
PCI
percutaneous coronary intervention
ROI
region of interest

References

  • 1.Stone GW, Reifart NJ, Moussa I, et al. Percutaneous recanalization of chronically occluded coronary arteries: a consensus document—part II. Circulation 2005;112(16):2530–2537. [DOI] [PubMed] [Google Scholar]
  • 2.Werner GS, Gitt AK, Zeymer U, et al. Chronic total coronary occlusions in patients with stable angina pectoris: impact on therapy and outcome in present day clinical practice. Clin Res Cardiol 2009;98(7):435–441. [DOI] [PubMed] [Google Scholar]
  • 3.Prasad A, Rihal CS, Lennon RJ, Wiste HJ, Singh M, Holmes DR Jr. Trends in outcomes after percutaneous coronary intervention for chronic total occlusions: a 25-year experience from the Mayo Clinic. J Am Coll Cardiol 2007;49(15):1611–1618. [DOI] [PubMed] [Google Scholar]
  • 4.Fefer P, Knudtson ML, Cheema AN, et al. Current perspectives on coronary chronic total occlusions: the Canadian Multicenter Chronic Total Occlusions Registry. J Am Coll Cardiol 2012;59(11):991–997. [DOI] [PubMed] [Google Scholar]
  • 5.Galassi AR, Ganyukov V, Tomasello SD, Haes B, Leonid B. Successful antegrade revascularization by the innovation of composite core dual coil in a three-vessel total occlusive disease for cardiac arrest patient using extracorporeal membrane oxygenation. Eur Heart J 2014;35(30):2009. [DOI] [PubMed] [Google Scholar]
  • 6.Sakakura K, Nakano M, Otsuka F, et al. Comparison of pathology of chronic total occlusion with and without coronary artery bypass graft. Eur Heart J 2014;35(25):1683–1693. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 7.Srivatsa SS, Edwards WD, Boos CM, et al. Histologic correlates of angiographic chronic total coronary artery occlusions: influence of occlusion duration on neovascular channel patterns and intimal plaque composition. J Am Coll Cardiol 1997;29(5):955–963. [DOI] [PubMed] [Google Scholar]
  • 8.Katsuragawa M, Fujiwara H, Miyamae M, Sasayama S. Histologic studies in percutaneous transluminal coronary angioplasty for chronic total occlusion: comparison of tapering and abrupt types of occlusion and short and long occluded segments. J Am Coll Cardiol 1993;21(3):604–611. [DOI] [PubMed] [Google Scholar]
  • 9.Li Y, Xu N, Zhang J, et al. Procedural success of CTO recanalization: Comparison of the J-CTO score determined by coronary CT angiography to invasive angiography. J Cardiovasc Comput Tomogr 2015;9(6):578–584. [DOI] [PubMed] [Google Scholar]
  • 10.Opolski MP, Achenbach S. CT angiography for revascularization of CTO: Crossing the borders of diagnosis and treatment. JACC Cardiovasc Imaging 2015;8(7):846–858. [DOI] [PubMed] [Google Scholar]
  • 11.Opolski MP. Cardiac computed tomography for planning revascularization procedures. J Thorac Imaging 2018;33(1):35–54. [DOI] [PubMed] [Google Scholar]
  • 12.Li M, Zhang J, Pan J, Lu Z. Coronary total occlusion lesions: linear intrathrombus enhancement at CT predicts better outcome of percutaneous coronary intervention. Radiology 2013;266(2):443–451. [DOI] [PubMed] [Google Scholar]
  • 13.Rajiah P, Abbara S, Halliburton SS. Spectral detector CT for cardiovascular applications. Diagn Interv Radiol 2017;23(3):187–193. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 14.Lennartz S, Le Blanc M, Zopfs D, et al. Dual-energy CT-derived iodine maps: Use in assessing pleural carcinomatosis. Radiology 2019;290(3):796–804. [DOI] [PubMed] [Google Scholar]
  • 15.van Assen M, Lavra F, Schoepf UJ, et al. Iodine quantification based on rest / stress perfusion dual energy CT to differentiate ischemic, infarcted and normal myocardium. Eur J Radiol 2019;112:136–143. [DOI] [PubMed] [Google Scholar]
  • 16.Macari M, Chandarana H, Schmidt B, Lee J, Lamparello P, Babb J. Abdominal aortic aneurysm: can the arterial phase at CT evaluation after endovascular repair be eliminated to reduce radiation dose? Radiology 2006;241(3):908–914. [DOI] [PubMed] [Google Scholar]
  • 17.Shrout PE, Fleiss JL. Intraclass correlations: uses in assessing rater reliability. Psychol Bull 1979;86(2):420–428. [DOI] [PubMed] [Google Scholar]
  • 18.McHugh ML. Interrater reliability: the kappa statistic. Biochem Med (Zagreb) 2012;22(3):276–282. [PMC free article] [PubMed] [Google Scholar]
  • 19.Escaned J. Percutaneous treatment of chronic total coronary occlusions: The light that came from Japan. JACC Cardiovasc Interv 2017;10(21):2155–2157. [DOI] [PubMed] [Google Scholar]
  • 20.Mollet NR, Hoye A, Lemos PA, et al. Value of preprocedure multislice computed tomographic coronary angiography to predict the outcome of percutaneous recanalization of chronic total occlusions. Am J Cardiol 2005;95(2):240–243. [DOI] [PubMed] [Google Scholar]
  • 21.Soon KH, Cox N, Wong A, et al. CT coronary angiography predicts the outcome of percutaneous coronary intervention of chronic total occlusion. J Interv Cardiol 2007;20(5):359–366. [DOI] [PubMed] [Google Scholar]
  • 22.Goo HW, Goo JM. Dual-energy CT: New horizon in medical imaging. Korean J Radiol 2017;18(4):555–569. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Ascenti G, Mazziotti S, Lamberto S, et al. Dual-energy CT for detection of endoleaks after endovascular abdominal aneurysm repair: usefulness of colored iodine overlay. AJR Am J Roentgenol 2011;196(6):1408–1414. [DOI] [PubMed] [Google Scholar]

Articles from Radiology: Cardiothoracic Imaging are provided here courtesy of Radiological Society of North America

RESOURCES