Magnetic Navigation System and CT Roadmap-Assisted Percutaneous Coronary Intervention: A Comparison to the Conventional Approach

Author(s): 

Ruina Hao, MD1,2*, Qiu Zhang, MD3*, Zhuowen Xu, MD4*, Lijun Tang, MD, PhD5, Zhijian Yang, MD, PhD1, Kejiang Cao, MD, PhD1, Chunjian Li, MD, PhD1

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Abstract: Background. Computed tomography coronary angiography (CTCA) has been successfully integrated with the magnetic navigation system (MNS) to facilitate a roadmap-assisted percutaneous coronary intervention (PCI). The aim of this study was to compare this new approach of PCI versus conventional PCI regarding the difference of contrast usage, x-ray exposure, procedure success, and in-hospital expenses. Methods. Thirty-eight patients with stable coronary artery disease and coronary artery lesions of 70% diameter stenosis diagnosed by both pre-procedure CTCA and coronary angiography (CAG) were enrolled to receive the MNS and CT roadmap-assisted PCI. Another 38 patients were consecutively recruited to receive conventional PCI, matched with the MNS group by the vessel and lesion type base on American College of Cardiology/American Heart Association criteria. Results. Regarding the process of the guidewire placement, wherein the technical difference of the two procedures exists, the median contrast usage for guidewire crossing was significantly lower in the MNS group than in the conventional group [0.0 mL (interquartile range [IQR], 0.0-3.0 mL) vs 5.0 mL (IQR, 3.1-6.8 mL); P<.001], with zero contrast usage in 25 of the 44 guidewire placements in the MNS group, but in none of the conventional group; the radiation dosage for guidewire crossing in the MNS group was also significantly lower than in the conventional group (235.8 µGym2 [IQR, 134.9-455.1 µGym2] vs 364.4 µGym2 [IQR, 223.4-547.2 µGym2]; P=.033). There were no significant differences between the two groups concerning the total contrast usage, total radiation dosage of the PCI, the procedural fees, or the overall in-hospital expenses. All of the enrolled vessels were successfully intervened in both groups. Conclusion. In PCI of simple lesions, the application of CT guidance and magnetic navigation had modest impacts on radiation dosage and contrast usage for wire crossing, but no impact on overall radiation dosage or contrast usage for the procedure. In addition, the use of CT roadmap and MNS was likely more expensive compared to PCI using conventional radiographic technique.  

J INVASIVE CARDIOL 2013;25(4):177-181

Key words: percutaneous coronary intervention, magnetic navigation system, computed tomography coronary angiography, CTCA

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Magnetic navigation system (MNS)-assisted percutaneous coronary interventions (PCI) have been applied in clinical practice for several years. The major technical innovation of this novel procedure exists in the process of the guidewire placement, while the majority of the procedure (balloon dilation, stenting, and postdilation as needed) is the same as conventional PCI.1-5 Recently published studies have shown that MNS-assisted PCI may improve success rate in certain complex cases and reduce contrast usage and radiation exposure, which depends upon different navigation modes and image integration strategies.6-13 More recently, Li et al14 have successfully extracted vessels from computed tomography (CT) images and transferred them to the live fluoroscopic screen after reconstruction, which then functioned as roadmaps to guide the MNS-assisted PCI; however, the advantages of this new PCI approach have not been fully investigated. This study aimed to compare MNS and CT roadmap-assisted PCI with conventional PCI regarding contrast usage, radiation exposure, procedural success rate, and in-hospital expenses.

Methods

Study population. This study was carried out in a single center in a period from January 2011 to July 2011. Thirty-eight patients with stable coronary disease and coronary artery lesions of 70% diameter stenosis diagnosed by both preprocedure CT coronary angiography (CTCA) and percutaneous coronary angiography were recruited to compose the MNS group before initiating the coronary intervention. Patients in the MNS group received MNS and CT roadmap-assisted PCI. The decision for a preprocedure CT scan was at the attending physician’s discretion. Patients who met the following criteria were excluded: (1) acute coronary syndromes; (2) angiographic total occlusion; (3) not eligible for PCI due to severe or diffuse lesions requiring CABG; and (4) contraindication magnet exposure (eg, patients with pacemakers, metal valves, and prosthetic metal hip or knee). The study conformed to institutional guidelines and those of the American Physiological Society. Written informed consent was obtained from each patient.

Another 38 patients who did not receive preprocedure CTCA examination were consecutively recruited to compose the control group on condition that their coronary artery lesions matched with the MNS group by the vessel and lesion type based on American College of Cardiology/American Heart Association (ACC/AHA) criteria. Patients in the control group received conventional PCI.

MNS and CT roadmap-assisted PCI. MNS-assisted PCI has been described in detail elsewhere.14 Briefly, MNS (Niobe II; Stereotaxis) is composed of two large permanent magnets that can be positioned in parallel at the two sides of the operating table during magnetic intervention. They generate a uniform magnetic field of 0.08 T with a diameter of about 6 inches in the center of the patient’s thorax. An MNS-compatible guidewire (Titan; Stereotaxis), which includes a tiny magnet embedded in the tip, is maneuvered by modulating the orientation of the magnetic field, which changes the direction of the guidewire tip. The change of the magnetic field orientation can be achieved by clicking and dragging the vector in the touch screen using the Navigant Workstation (Stereotaxis) located at the table side. The operator thus can manually advance the magnetic guidewire and change the direction of the wire tip in vivo while referring to the roadmap extracted from CT images. Contrast flush is performed to check the wire position according to the operator’s discretion. After the magnetic guidewire is in position, the rest of the procedure is the same as the conventional PCI. The operators in the MNS arm were also using conventional x-ray imaging to evaluate stent positioning, stent deployment and sizing, and final results of stent deployment. The wire is finally pulled out after the stent is deployed, and the two magnets are stowed upon completion of the procedure.

Incorporating CT images into the Navigant software and creating roadmaps have been described in a previous study.14 In brief, CT images were imported into the Navigant workstation (Figure 1A), after which the main branches of the coronary arteries were extracted and reconstructed (Figures 1B and 1C). Meanwhile, two diagnostic cines of the target vessel at least 30° apart were chosen and transferred into Navigant. The datasets were aligned by landmark registration, whereby an intrinsic fiducial vessel marker was selected on two diagnostic cines of the target vessel, after which the same landmark was identified and selected from the CT image, and then the software automatically aligned the x-ray and CT images by aligning the selected landmarks. Manual alignment was allowed if necessary. Finally, the reconstructed CT vessel was transferred onto the live fluoroscopic screen as a roadmap, and the magnetic vector could be changed on the touch screen at the table side referring the route of the roadmap (Figure 2).

The technical parameters for a CT scan were as follows:15 imaging acquisition was performed using a 64-slice dual-source CT scanner (Somatom Definition; Siemens Healthcare). CTCA requires a bolus injection of 80-100 mL of contrast (Ultravist 370; Schering) in the antecubital vein at a velocity of 5 mL/s, followed by flushing with 40 mL of saline. Scanning was automatically triggered by the bolus tracking technique included in the scanner. The scan was performed with the following parameters: rotation time, 330 ms; tube voltage, 120 kV; effective tube current, 380-420 mAs; pitch, 0.2-0.43 (depending on the heart rate); collimation width, 64 × 0.6 mm; slice width, 0.75 mm; reconstruction increment, 0.5 mm; and reconstruction kernel, B26f. An electrocardiogram was recorded during data acquisition, and electrocardiographic pulsing was applied to reduce radiation exposure. Images of the best diastolic phase and the best systolic phase were automatically reconstructed by using the retrospective electrocardiogram gate and the optimal cardiac phase that displayed the minimal motion artifacts, which was individually determined for the cases with arrhythmia.16, 17 It is important to note that patients recruited into the MNS group were exposed to additional radiation and as much as 80-100 mL contrast media in the process of the CT scan; however, the preprocedure CT scans in this study were performed prior to admission at the attending physician’s discretion, while not mandated by the study investigators.  

Procedural definitions. Vessel lesion classifications were based on ACC/AHA criteria. Lesion length and stenosis percentage were determined with the quantitative coronary angiography (QCA) software (Artis; Siemens Healthcare). Procedure success was defined as successful stent implantation without major complications. Contrast usage and x-ray exposure dosage during the guidewire placement were recorded for each case during the period when the guidewire exited from the guiding catheter until it reached its final position, far distal to the lesions. Procedure time was defined as the time from guidewire exiting from the guiding catheter to completion of stent deployment. Total x-ray exposure dosage, total contrast usage in the procedure time, as well as procedural fees and total in-hospital expenses (including the costs of the CT scan and the Stereotaxis guidewire) of the patients were all recorded.  

Statistical analysis. Continuous data were expressed as mean ± standard deviation or median (25%-75% interquartile range [IQR]) where appropriate, and were compared using the two-sided student t-test or Mann-Whitney U-test. Categorical data were expressed as number and percentage, and were analyzed with the Pearson χ2 test. A 2-sided P-value of <.05 was considered statistically significant. Stata 9.2 (StataCorp) statistical software was used for data analysis.


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