Methods

A prospective single-center design was used for this study. From January 2014 to December 2014, patients scheduled for CTO intervention who had no specific contraindications for intraprocedural CT scanning were consecutively enrolled. CTO was defined as obstruction of a native coronary artery with Thrombolysis In Myocardial Infarction flow grade 0 and an estimated duration ≥3 months based on the clinical history or previous coronary angiography results. All patients had typical chest pain or positive stress test results in various functional studies. According to Japan–Chronic Total Occlusion score, CTO lesions were classified as easy (score = 0), intermediate (score = 1), difficult (score = 2), and very difficult (score ≥3). The Institutional Review Board of the Yonsei University College of Medicine approved this study. Each enrolled patient received a detailed explanation of the study and provided written informed consent to participate.

We recently reported the first CTO case using the CCTA system. The CCTA system comprises a 640 multislice CT scanner applying double-slice technology (Aquilion ONE; Toshiba Medical Systems, Otawara, Japan) and a coronary angiography system and allows for scanning to be performed during intervention without moving the patient on the table ( Figure 1 ). The CT system has a wide detector width of 16 cm, which allows for a full cardiac CT data set to be acquired within a single heartbeat. In the present study, CT scan was performed using a cranial-to-caudal acquisition with prospective electrocardiogram gating using the following parameters: collimation and slice thickness, 0.5 mm; reconstruction increment, 0.5 mm; tube rotation time, 0.275 seconds; tube voltage, 100 kV(p); current, dose modulation; and reconstruction field of view, 180 mm. The data were reconstructed at 75% of the RR length. If motion artifacts were present, a different cardiac phase was selected. The following modulation was applied to the reconstruction: kernel, FC04; reconstruction algorithm, adaptive iterative dose reduction 3D. Sharp kernel with beam hardening collection was used to reduce metal artifacts. For intraprocedural CCTA scanning, the coronary angiogram system moved backward, and the CT system moved forward for scanning ( Figure 1 ). After scanning, the system operated in the reverse order, and on-site analyses of the CCTA images were performed.

CCTA system. CCTA system consisting of a CT scanner (A) moving forward and backward on a railroad system and a coronary angiography system (B) moving left and right (A) . For an intraprocedural CCTA, the coronary angiogram system moves backward and then the CT scanner moves forward (B and C) . ​MSCT = multislice CT.

For specific cases that required enhancement of the distal part of the CTO, intracoronary contrast injection was used during CCTA ( Figure 2 ). The contrast medium (Visipaque 320 mg/ml; GE healthcare, Princeton) was diluted with normal saline solution to obtain optimal coronary enhancement (300 to –400 HU). The concentration of diluted contrast medium is 12.61 mgI/ml to produce 400 HU of luminal attenuation under the 100 kVp. The diluted contrast medium was delivered with a dual-head power injector (Medrad Stellant Injector; Medrad, Indianola, Pennsylvania) using the following protocols; injection rate of 5 ml/s and volume of contrast medium of 30 ml. The start buttons for the CT and the injector were pressed at the same time for CT scan. The CT scan started 2 seconds after the start button was pressed. The CT scan time was 1.176 seconds, and injection was continued for 6 seconds.

Comparison of CCTA images with or without intracoronary contrast injection. When CCTA evaluation was performed without contrast injection (A to C) , the determination of the vascular contour was difficult at the location crossing the guidewire tip level (b to d in C ). Using intracoronary contrast injection (D to F) , the distal portion of the guidewire tip was enhanced by contrast filling of collateral channels. The course of the artery was then clearly visible and the guidewire tip location was more easily recognizable (b to d in F ). Preprocedural angiographic findings (A and D) ; angiogram indicating the guidewire location, before CCTA (B and E) ; C-MPR images (C and F) and the matched cross-sectional images (a to e). The red broken line and orange arrow indicate the wire-tip level and guidewire, respectively.

Before the CCTA, each patient’s vital signs were evaluated, and a beta-adrenergic blocker (esmolol, 1 mg/kg) was administered intravenously if the heart rate was ≥65 beats/min, and there were no contraindications to the use of beta-adrenergic blocking agents. The dose length product (mGy·cm) for CCTA was recorded. All radiation doses are presented as mSv, calculated as dose length product (DLP) × 0.014. The mean times for scanning and moving of CCTA system, as well as time for CCTA analyses, including data transfer and the total radiation doses were investigated.

Selected CCTA images were transferred to a workstation (Vitrea fX 6.4; Vital Images, Minnetonka, Minnesota), and then analysis for the identification of guidewire locations was performed. The double oblique and curved multiplanar reconstruction (C-MPR) images were obtained throughout the course of the coronary artery segments using a guidewire and were used for the examination of guidewire location in a 360-degree view with the transverse axial images ( Figure 3 ). In addition, the window width and level was adjusted to distinguish between the guidewire and other structures.

Prediction of guidewire location using C-MPR images. Preprocedural angiographic findings (A and F) and angiogram indicating the location of the guidewire before intraprocedural CCTA evaluation (B and G) . Transverse axial images did not reveal the guidewire location (C and H) ; however, the C-MPR images at the different angles clearly indicated the location of guidewire within the coronary artery (D and E , I and J) . The red arrows and boxes indicate the wire-tip level and the corresponding axial images, respectively.

By on-site review of these various results, we discriminated guidewires from the vessel structures and investigated guidewire locations on longitudinal and cross-sectional sections. Based on the findings of CCTA, we predicted the possible locations of the guidewire tip divided into 3 different zones ( Figure 4 ): (1) intraplaque zone (suggestive of true lumen), case in which guidewires were located inside the vessel and clearly differentiated from vessel wall; (2) subintimal zone (suggestive of false lumen); cases in which the tip of the guidewire deviated to the lateral vessel wall and was not differentiated from the vessel wall; and (3) outside-vessel zone, cases in which the guidewire was completely out of the vessel wall.

Classification of the location of the guidewires. The possible locations of guidewire were divided into 3 different zones based on the results of the transverse axial and C-MPR images: (1) intraplaque zone (A) ; (2) subintimal zone (B) ; and (3) outside-vessel zone (C) .

Before coronary intervention, all patients received ≥75 mg aspirin, and a loading dose of 300 mg clopidogrel was administered at least 12 hours before the procedure. The choice of vascular access, CTO intervention techniques/devices, and the use of intravascular ultrasound were left to the discretion of the operators. Successful CTO intervention was defined as a final Thrombolysis In Myocardial Infarction flow grade of 3 and residual stenosis ≤30% by visual assessment after stent implantation.

Continuous variables are expressed as a mean ± SD, and categorical variables are presented as a number (%) and compared by the chi-square test or Fisher’s exact test. McNemar’s test was used for comparisons of changes in incidences. Agreement regarding guidewire location was evaluated using Fleiss’ kappa for multiple raters. In detail, 4 different observers including 2 interventionists and 2 specialized imaging cardiologists with level 3 clinical competence in cardiovascular CT imaging, assessed the location of guidewires. p Values <0.05 were considered statistically significant. Analyses were carried out using SPSS, version 20 (IBM Corporation, Chicago, Illinois) and R, version 3.21 (R Development Core Team, Vienna, Austria).

Results

From January 2014 to May 2015, a total of 61 patients who were scheduled for elective CTO intervention were consecutively enrolled and underwent CCTA and on-site analyses of CCTA images during intervention. The results for the patients’ baseline characteristics and the procedures performed are presented in Table 1 .

A summary of the CCTA evaluation and those results is presented in Table 2 . Patients’ vital signs were stable before and after CCTA evaluations. Intraprocedural CCTA was performed for various CTO types and procedures ( Figure 5 ). In addition to showing the anterograde single wire, CCTA revealed the locations of retrograde and double wires used for parallel wire techniques.

Table 2

Summary of coronary computed tomographic angiographic evaluation

Variable	61 patients
Systolic/ Diastolic blood pressure (mmHg)	137.7±20.2 / 67.8±10.1
Heart rate (beats per minute)	63.9±12.1
Total number of evaluation	72
Time for evaluation (minutes)
Time for scanning and moving computed tomographic system	8.6±2.1
Time for coronary computed tomographic angiographic analyses including data transfer	8.5±1.9
Total time, including test, system-moving, and analyses	17.2±2.9
Radiation dose (mSv)	2.9±1.5
Reasons for coronary computed tomographic angiography
Penetration of proximal chronic total occlusion cap by guidewire	13 (18%) ∗
Location of guidewire within chronic total occlusion segment	48 (67%) ∗
Entrance of guidewire into distal true lumen	11 (15%) ∗
Multiple coronary computed tomographic angiography during intervention	10 (16%)
Evaluation according to the change of the approaches or wiring techniques	4
Evaluation after guidewire progress	6
Use of contrast
Non-contrast scanning	32 (52%)
Scanning with intracoronary contrast injection	29 (48%)
Contralateral	27
Ipsilateral	2
Total diluted contrast volume used (mL)	28.5±9.7
Actual contrast volume used (mL)	1.1±0.4
Status of guidewire during coronary computed tomographic angiography
Single wire	64 (89%) ∗
Parallel wires	3 (4%) ∗
Anterograde and retrograde wires	5 (7%) ∗
Identification of the location of guidewire tip and path
Initial identification only by transverse axial images	34 (56%)
Final identification by multiple modalities	53 (87%) †

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