Ann Thorac Surg 2006;82:1078-1084
© 2006 The Society of Thoracic Surgeons
New technology
Target Vessel Detection and Coronary Anastomosis Assessment by Intraoperative 12-MHz Ultrasound
Hubert Stein, BS, BMEa,*,
John Michael Smith, MDb,
John R. Robinson, MDb,
Marc R. Katz, MDc
a Intuitive Surgical, Inc, Sunnyvale, California
b Department of Surgery, Division of Cardiothoracic Surgery, Good Samaritan Hospital, Cincinnati, Ohio
c Department of Cardiac Surgery, Henrico Doctor's Hospital, Richmond, Virginia
Accepted for publication March 15, 2006.
* Address correspondence to Mr Stein, Intuitive Surgical, Inc, 950 Kifer Rd, Sunnyvale, CA 94086 (Email: hubert.stein{at}intusurg.com).
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Abstract
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PURPOSE: Our aim was to assess whether the left internal mammary artery, left anterior descending artery, and anastomosis could be visualized by intraoperative ultrasound for safe graft harvesting, optimal anastomotic target selection, and quality control.
DESCRIPTION: In 10 patients, the left internal mammary artery, the left anterior descending artery, and the constructed anastomosis were scanned with 12-MHz epicardial ultrasound. Anastomosis quality was assessed on ultrasound and compared with surgeon score.
EVALUATION: All left internal mammary arteries and left anterior descending arteries could be identified, and pathways could be followed on the ultrasound. Plaque and calcifications were detectable. Deviation from initial coronary anastomotic target was necessary in 2 of 10 patients. None of the constructed anastomoses needed revision. On the anastomotic scans, six anastomoses scored satisfactory and four scored good.
CONCLUSIONS: Epicardial ultrasound was able to evaluate vessel characteristics and coronary anastomosis patency. This can lead to correction of surgical technique related problems in the operating room, possibly improving graft patency. Further advancements could make epicardial ultrasound a cost effective standard for anastomotic quality control. Applying it during robotic-assisted bypass surgery could make this procedure appropriate for more patients.
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Introduction
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The identification and course of the left internal mammary artery (LIMA) and its side branches can be difficult if they are covered by a thick thoracic fat layer or muscular fascia, especially during robotic-assisted endoscopic coronary artery bypass procedures. Finding the "optimal" target area on the left anterior descending coronary artery (LAD) to construct a patent coronary anastomosis can be rendered more difficult when it is deeply embedded in the epicardial fat or myocardium. Identifying the coronary target site under endoscopic conditions can lead to confusion and unintentional grafting of a dominant diagonal branch [1]. Plaque and calcifications in the target segment make anastomosis suturing difficult. Intense bleeding from a septal perforating branch in the occluded coronary segment may make clear visibility unachievable. Perforating branches are difficult to identify because they do not visualize well on preoperative angiograms. To assure excellent surgical outcome with a long-term high patency rate, anastomosis quality should be assessed and technical problems should immediately be corrected in the operating room.
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Technology
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Epicardial ultrasound scanning for evaluating vessel and anastomosis characteristics was described as a potential solution in the 1980s and 1990s [2, 3]. Despite promising results, technical limitations prevented widespread use. The Utrecht group described a 13 MHz epicardial ultrasound transducer for assessment of the LAD and geometry assessment of anastomoses [4, 5].
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Technique
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In our study the goal was to assess whether intraoperative 12 MHz ultrasound scanning was feasible to visualize the LIMA and LAD in patients to allow safe graft vessel harvesting and selection of the optimal anastomotic target site. An additional goal was to determine if epicardial ultrasound could visualize the finished LIMA-LAD anastomosis in sufficient detail to score its quality by a blinded observer and compare it with the surgeon's score. Special attention was paid to the applicability of epicardial ultrasound to endoscopic coronary revascularization with robotic assistance.
Patients
Ten patients were selected for multi-vessel coronary artery bypass grafting through a sternotomy, either on-pump or off-pump (Table 1). The study was limited to scanning of the LIMA, the LAD, and the constructed anastomosis. The study received approval from the institutional review boards at both institutions before conduction on June 3 and July 6, 2005. Informed consent was obtained from all patients prior to surgery.
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Table 1. Patient Characteristics, Results of Left Internal Mammary Artery and Left Anterior Descending Coronary Artery Assessment
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Ultrasound Equipment
A Sonata 2300 Ultrasound Imaging System combined with an epicardial surgery probe TC-603-SUR (Tetrad Corp, Englewood, CO) was used. The TC-603-SUR probe has a maximum scan frequency of 12 MHz and an active scanning surface of 18 mm x 6 mm. The transducer was inserted into a gel-filled sterile sleeve cover for scanning.
Scanning Procedure
After sternotomy the LIMA was scanned for location, path, and flow if it was not visible in full length under direct vision. Before anastomosis construction the coronary artery target was chosen based on preoperative angiography and intraoperative findings. Then the conventionally anticipated target site was scanned for pathway, size, septal perforator branches, and the presence of plaque and calcifications. The scan was performed during stabilization of the coronary artery with either a cardiac stabilizer in the off-pump cases or with the free hand of the surgeon in the on-pump cases before going on bypass. After scoring of the finished anastomosis by the surgeon, a subsequent scan of the anastomosis was performed. The individual surgeons applied the probe to perform the ultrasound scanning. The same trained observer operated the ultrasound system in all cases. Ultrasound images were recorded for off-line analysis.
Anastomosis Scoring Procedure
The surgeon scored the finished anastomosis as usual based on his surgical experience, independent of the ultrasound image, as either "good," "satisfactory," or "poor," which would require revision. The scoring was recorded. One blinded observer scored the finished anastomosis solely based on transverse ultrasound images postoperatively applying the criteria developed by Budde [5] (Table 2). The scoring was recorded.
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Clinical Experience
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LIMA Identification
In 5 of 10 patients the LIMA was not directly visible to the surgeon in its partial or full path (Table 1). All LIMAs could be identified with a transverse scan. With a longitudinal scan the course of the LIMA could be followed (Fig 1). In one patient the longitudinal scan was not possible due to the transducer length. The intercostal spaces were too tight to accommodate the transducer for scanning with good tissue contact.
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Fig 1. The left internal mammary artery (LIMA) identification (patient WRP). Vessel path not visible for the surgeon under direct vision due to fascia and muscle tissue covering the LIMA. (a) Longitudinal scan with color flow Doppler showing LIMA embedded in tissue (red) with a side branch (blue). (b) Transverse scan of the LIMA with color Doppler flow. (c) LIMA course can be followed with transverse scan past the bifurcation (blue).
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Coronary Target Vessel Detection
In 2 of 10 cases the conventionally chosen anastomotic target site on the LAD (based on preoperative angiography and intraoperative findings) was not visible under direct vision (Table 1). All LADs could be identified on the ultrasound, and the course followed by transverse scanning were questionable. Plaque and calcifications were detected in all cases. In 2 of 10 patients, massive plaque, not palpable and not visible under direct vision, and on preoperative angiography at the anticipated anastomotic target site, was detected on ultrasound and made deviation to a "clean" coronary segment necessary. In both cases septal perforator branches could be identified before arteriotomy at the new target site (Fig 2). In 9 of 10 patients the septal perforator branches were identified along the run of the LAD.
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Fig 2. Left anterior descending coronary artery (LAD) detection (patient JKR). (a) Longitudinal scan of anticipated anastomotic target on LAD. (b) Longitudinal scan with color flow Doppler at "clean" coronary segment as the new anastomosis target site. Septal perforator branch (SP) was identified before arteriotomy. (*Plaque and calcification in the artery that have not been palpable and were not visible under direct vision and on preoperative angiography; S = stenosis from plaque.)
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Anastomosis Assessment
In all patients the capture of the LIMA, the LAD, and the anastomotic orifice in one longitudinal image was successful (Fig 3). None of the constructed anastomoses needed revision (Table 3). In all 10 patients the surgeons scored the anastomosis as good, based on experience and independent of the ultrasound image. The score of the anastomotic scans by the blinded observer revealed six anastomosis with satisfactory results and four with good results in applying the Utrecht criteria (Table 2).
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Fig 3. Anastomosis assessment (patient RFL). (a) Longitudinal scan of the anastomosis, no construction errors or similar visible. (b) Same scan with color Doppler flow showing good flow through anastomotic orifice from the internal mammary artery (IMA) into the left anterior descending coronary artery (LAD).
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Follow-Up
Nine of 10 patients had an uneventful postoperative period for as many as 114 days and did not need any reintervention on the LIMA-LAD anastomosis. One patient had a major adverse cardiac event (MACE, defined as death, myocardial infarction, urgent reintervention revascularization) who died on postoperative day 3 (Table 3); an aortic dissection was diagnosed postmortem.
Scanning Time
Even though we did not record the scanning times in this study, a decrease in time to perform the scans was noticed, and it was in the range of 5 minutes at conclusion of the trial.
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Comment
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Readily available methods in the operating room, such as intraoperative angiography, thermal imaging, transit time flow Doppler, audible Doppler probes, and transesophageal echocardiography have not been widely used due to associated major cost, difficult interpretation without anatomical information, missing reproducibility, or inaccuracy [6]. Graft assessment systems based on indocyanine green fluorescent imaging showed good results in an initial study [7], but applications specific to graft and target vessel morphology remain to be demonstrated. Coronary angiography with a computer tomographic system [8] has provided preoperative information about target artery measurements and the internal mammary artery position, but remain currently limited in use, mainly due to the high cost factor. This may change with enhanced augmented reality applications [1].
With epicardial ultrasound and color flow imaging we were able to enhance evaluation of different vessel characteristics and coronary anastomosis patency. Identification was superior, and correction of surgical technique related problems in the operating room was possible. Nevertheless some limitations were found in our study. With the intercostal spaces being very tight in some patients, LIMA scanning longitudinally with sufficient tissue contact was difficult due to the length of the transducer. In a future design the transducer length should be somewhat shortened, but still needs to allow scanning of the anastomotic orifice in one longitudinal image. Left anterior descending coronary artery scanning remained challenging in the on-pump cases because the beating heart was not immobilized with a stabilizer system before cardiopulmonary bypass. We would recommend always using a stabilizer system when scanning the beating heart to maximize image quality and avoid scan misinterpretation. Future transducer heads will be designed to fit between the feet of stabilizers. The ultrasound was effective in locating septal perforating branches and calcifications in the coronary target segments. This led to an ultrasound-guided change of the originally designated anastomotic site in 2 patients, which we believe is an excellent feature to avoid postarteriotomy problems with the anastomosis and enhance clinical outcome. Assessing anastomosis geometry and patency on the ultrasound seemed to be more complex due to limited experience with interpretation of such images. The blinded observer believed that the criteria developed by the Utrecht group provided a good guideline for anastomosis assessment, and his comfort level increased building up "references" [5]. The comparison to the surgeon's score revealed no need for reintervention and showed more satisfactory anastomosis probably due to the fact that the ultrasound image allows a look inside the anastomosis. None of the patients had anastomotic-related problems in the follow-up period. Specific training for assessing anastomotic scans may be necessary to build the comfort level for surgeons to trust the ultrasound image enough to redo an anastomosis based on a scanned image. This would be particularly true for robotic-assisted endoscopic coronary artery bypass procedures. Based on our results, epicardial ultrasound scanning seems to be an extremely valuable tool in the cardiac operating room during coronary artery bypass graft surgery. This also has the potential to improve graft patency and acceptance of minimally invasive coronary artery bypass graft surgery, specifically robotic-assisted endoscopic coronary artery bypass, resulting in a more reliable operation for the patient. Printed or stored image scans could become part of the patient record. Epicardial ultrasound could become a cost-effective standard for anastomotic quality control to be able to replace postoperative angiography when compared in more clinical studies. Immediate reliable confirmation of anastomosis construction, function, and run-off is recognized as an advantage. Through further advancements in the technology, overlapping of ultrasound images onto a robotic system three-dimensional display may make real ultrasonography-guided surgery possible and enable beating heart robotic-assisted endoscopic coronary artery bypass in patients with complex pathology and anatomy. Anastomotic scans could be three-dimensionally rendered and allow excellent quality control on a real three-dimensional model of the constructed anastomosis. The robot-controlling surgeon could see the ultrasound image captured by a specific EndoWrist Instrument (Intuitive Surgical Inc, Sunnyvale CA) on the stereo display and score the LIMA pedicle with a robotic cautery instrument, allowing real time image-guided surgery. This potential has been demonstrated in previous animal studies [9, 10] and clinical evaluation will follow.
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Disclosures and Freedom of Investigation
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The ultrasound imaging system used in this study was purchased with funds from Intuitive Surgical, Inc (Sunnyvale, CA). The authors had full control of the design of the study, methods used, outcome measurements, analysis of data, and production of the written report. None of the authors has a financial relationship with Tetrad Corp.
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Disclaimer
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The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.
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Acknowledgments
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The authors thank Amy Engel and Kathy Loxterkamp (Hatton Research Institute, Cincinnati, OH), as well as Ann Robertson and Tiffany Lange (Cardiac and Thoracic Surgical Associates, Richmond, VA) for support during the study. We also thank Dennis R. Dietz (Tetrad Corp, Denver, CO) for training on the use of the ultrasound system.
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References
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- Falk V, Mourgues F, Adhami L, et al. Cardio navigationplanning, simulation, and augmented reality in robotic assisted endoscopic bypass grafting. Ann Thorac Surg 2005;79:2040-2048.[Abstract/Free Full Text]
- Hiratzka LF, McPherson DD, Lamberth Jr WC, et al. Intraoperative evaluation of coronary artery bypass graft anastomoses with high-frequency epicardial echocardiographyexperimental validation and initial patient studies. Circulation 1986;73(6):1199-1205.[Abstract/Free Full Text]
- Oda K, Hirose K, Fukutomi T, Yamashiro T, Ogoshi S. Intraoperative detection of embedded coronary arteries in MIDCAB using a color Doppler microprobe Ann Thorac Surg 1999;68:263-264.[Abstract/Free Full Text]
- Eikelaar JHR, Meijer R, van Boven WJ, et al. Epicardial 10-MHz ultrasound in off-pump coronary bypass surgerya clinical feasibility study using a minitransducer. J Thorac Cardiovasc Surg 2002;124:785-789.[Abstract/Free Full Text]
- Budde RPJ. Epicardial ultrasound in coronary artery bypass surgery. Thesis Utrecht University with a summary in Dutch. The Netherlands: UMC Utrecht (University Press); 2005.
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- Reuthebuch O, Haussler A, Genoni M, et al. Novadaq SPYintraoperative quality assessment in off-pump coronary artery bypass grafting. Chest 2004;125(2):418-424.[Abstract/Free Full Text]
- Herzog C, Dogan S, Diebold T, et al. Multi-detector row CT versus coronary angiographypreoperative evaluation before totally endoscopic coronary artery bypass grafting. Radiology 2003;229(1):200-208.[Abstract/Free Full Text]
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Abstract
Introduction
