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© 2004 European Association of Cardio-Thoracic Surgery
SPYTM: an innovative intra-operative imaging system to evaluate graft patency during off-pump coronary artery bypass graftingDepartment of Cardiovascular Surgery, Hiratsuka Kyosai Heart Center, Hiratsuka Kyosai Hospital, 9-11, Oiwake, Hiratsuka, Kanagawa 254-8502, Japan
* Corresponding author. Tel.: +81-463-32-1950; fax: +81-463-31-1865 Received October 10, 2003; received in revised form January 14, 2004; accepted January 29, 2004
Off-pump coronary artery bypass grafting (CABG) has been rapidly increased, because of its less invasiveness with low complications. However, graft patency rate highly depends on the operators' capability due to technical difficulties. The SPYTM system, based on the fluorescence of indocyanine green, is an innovative device that permits validation of graft patency intra-operatively. Real time images of grafts are obtained with no need for catheterization, X-rays or iodine contrast medium. High-quality images could be obtained in all 290 grafts of 72 off-pump CABG cases (mean 4.0 grafts per patient). Four anastomoses (1.4%), including two proximal and two distal, were revised because of defects detected by SPY images. In one case, the SPYTM system revealed no blood flow in a radial sequential graft, although transit-time flow meter measurements showed a diastolic dominant pattern. SPY images provide critical information to surgeons to detect non-patent grafts, allowing them to be revised while the patient is still on the operating table. Using the SPYTM system, technical failures could be completely resolved during surgery. The use of the SPYTM system for intra-operative graft validation during off-pump CABG may become the gold standard for surgical management in the near future.
Key Words: Off-pump coronary artery bypass grafting; Intra-operative graft validation; Indocyanine green; SPY system
The incidence of off-pump coronary artery bypass grafting (CABG) has increased rapidly, because of the potential for eliminating complications associated with the use of the bypass pump. However, there are still concerns about reduced graft patency rates due to technical difficulties. If defective grafts can be detected and revised in the operating room, post-operative graft patency rate will approach 100%. The SPYTM intra-operative imaging system (Novadaq Technologies Inc., Toronto, Canada) has been developed as a means for detecting dysfunctional grafts during CABG [1,2]. The SPYTM imaging system acquires fluorescence coronary angiograms using the dye indocyanine green (ICG). The purpose of this study was to evaluate the innovative SPYTM imaging system during off-pump CABG.
2.1. Intra-operative imaging Intra-operative imaging was performed using the SPYTM imaging system. This imaging system makes use of the fluorescence properties of ICG to acquire images of grafts and native coronary arteries. The device incorporates an 806 nm laser light source that illuminates an area of 7.5x7.5 cm2 on the surface of the heart. As ICG passes through this field of illumination it fluoresces, emitting light in a broad band centered at 830 nm. This fluorescence is captured by means of a charged coupled device video camera equipped with appropriate filters to block the passage of laser (and room) light while maximizing transmission of the emitted fluorescence light. Images are captured at a rate of 30/s and downloaded directly to the computer disc. Images of grafts are seen in real time and may also be reviewed immediately following capture. The imaging device is composed of an imaging head that contains the optical components and a mobile cart that contains the electrical controls and the computer. The imaging head is attached to the cart by means of an articulating arm that allows the cart to be positioned approximately 1 m from the operating table. Imaging of each graft takes 2–3 min. The imaging head, enclosed in a sterile drape, is positioned about 30 cm above the heart. Selection of the appropriate field of view is achieved with the aid of a real time image on the monitor. For each image sequence a bolus of ICG (2.5 mg in 1.0 ml) is injected into the central venous line. At the same time the laser is activated by means of a command to the computer. Within 5–6 s fluorescence images of the grafts and coronaries are seen on the monitor. The fluorescence is initially seen in the coronary arteries and grafts, then in the microcirculation as a background flush and finally washing out through the coronary veins. The laser shuts off automatically after 30 s at which time another image sequence can be acquired. Images can only be acquired during the first pass of the bolus of ICG through the field of view. Once the ICG has distributed throughout the blood volume, the concentration is too low for further acquisition. Subsequent image acquisition requires injection of a further bolus of ICG for each image sequence acquired. ICG has been widely used for over 40 years for measuring cardiac output, assessing hepatic function and for ophthalmic angiography. The drug has an excellent safety profile with a low incidence of adverse effects [3,4]. Based on the data from the developing company (Daiichi Pharmaceutical Co., Ltd Tokyo), the adverse drug reaction rate of ICG is lower (0.17%) than iohexol iodine contrast media (2.65%). (Table 1).
The ICG is excreted unchanged by the liver with a half life of 3–5 min, thus there is no potential for nephrotoxic effects for those patients with compromised renal function. 2.2. Surgical management Seventy-two consecutive patients undergoing off-pump CABG in our institute were included in the study. Eight patients underwent minimally invasive direct coronary artery bypass (MIDCAB) via a small incision without sternal splitting. The other 64 patients underwent off-pump CABG via median sternotomy (OPCAB). The average age was 68.5 years, and 21 females were included. Twenty-one (29.2%) patients underwent emergency operation for acute coronary syndrome. Twenty (27.8%) suffered from diabetes mellitus, and six patients were receiving dialysis for chronic renal failure.The internal thoracic artery (ITA) was dissected in a full skeletonized fashion using a harmonic scalpel. The radial artery was also completely skeletonized. Syringe infusion of diluted olprinone hydrochloride (Eisai Co., Ltd, Tokyo) into the interspaces between the radial artery and the fascia was very useful to prevent spasm, when fasciotomy was performed. The DONUTTM Heart Stabilizer (MediVas LLC, San Diego, CA, USA) invented by the author [5–7] was utilized in most patients to achieve a stable operative field on the beating heart. Our operative strategy for isolated coronary artery disease is complete arterial revascularization for all stenosed coronary branches. The total number of distal anastomoses was 290. The average number of distal anastomoses was 1.38 in MIDCAB, and 4.36 in OPCAB. Two patients received maximal nine bypass grafts. One hundred and ninety-one conduits were utilized, including 72 ITAs, 68 RAs, 42 saphenous veins, 8 gastroepiploic arteries, and 1 inferior epigastric artery. 53.4% of conduits were used as single grafts (one distal anastomosis per graft), and 46.6% were sequential grafts (more than one distal anastomosis per graft). Target arteries included 79 (27.2%) left anterior descending (LAD), 40 (13.8%) diagonal, 13 (4.5%) intermediate, 57 (19.7%) obtuse marginal, 31 (10.7%) circumflex, 36 (12.4%) posterior descending, 15 (5.2%) posterior lateral, 12 (4.1%) major right coronary artery, and 7 (2.4%) right ventricular branch. Proximal radial or venous anastomoses were constructed onto the aorta in most cases. Chest computed tomography scan was routinely performed to rule out aortic calcification, or intra-operative direct aortic echocardiogram was performed when the pre-operative computed tomography scan had not been performed in emergent cases.
3.1. Clinical outcomes Off-pump CABG could be safely performed in all 72 patients, even in emergency cases. No adverse drug reactions of ICG were observed. There were no operative deaths, peri-operative myocardial infarction, additional intra-aortic balloon pumping, and cerebral infarction. No major complications occurred post-operatively. 3.2. Imaging results Excellent quality SPY images could be obtained for all 290 distal anastomoses. Examples of the images are shown in Video 1.The skeletonized conduits provided better visualization than pedicled ones. Four anastomoses (1.4%), including two proximal and two distal, were revised because of defects detected by SPY images. In a 66-year-old male patient, images obtained using the SPYTM system indicated no blood flow in the proximal segment of a radial artery sequentially grafted from the aorta to obtuse marginal 1 and the circumflex, although the transit-time flow meter showed a diastolic dominant pattern. After revision of the proximal anastomosis, excellent flow in all segments of the graft could be observed in the SPY images (Fig. 1). Following graft revision the transit-time flow measurement increased to 55 ml/min (from 24 ml/min observed prior to revision). In an 88-year-old female, the left ITA was anastomosed sequentially to the diagonal and the LAD. SPY images showed occlusion of the ITA graft between the diagonal and the LAD. After revision of the anastomosis to the diagonal, excellent flow to the LAD could be observed in the SPY images (Fig. 2 and Video 2).
In several cases of competitive blood flow between the graft and native coronary artery, SPY imaging could demonstrate the anastomotic patency (Fig. 3).
3.3. Comment In this report we have described intra-operative graft validation during off-pump CABG using the SPYTM imaging system. Real time images of grafts are obtained following injection of a low dose of ICG via the central venous line. The imaging is very rapid and safe with no need for catheterization, X-rays or iodine contrast media. SPY images could show the real-time graft flow even in case of competitive graft flow. Several techniques for intra-operative graft validation have been introduced. Transit-time flow measurement [8] is a very easy device to use, however, it cannot show the visual image of the graft. When the graft is subjected to spasm, or the stenosis of the native coronary artery is not very severe, flow measurement data may not be diagnostic (Fig. 3). Epicardial echocardiogram [9] and thermal coronary angiography [10] have been employed as non-invasive graft assessment technologies. However, they are very difficult to use for lateral or posterior wall coronary arteries and additionally provide very poor resolution. Conventional intra-operative X-ray angiography using portable digital subtraction angiographic device requires the use of iodine contrast media, and risky catheter insertion into the ostia of the grafts. The SPYTM system may overcome the problems and deficiencies of the above-mentioned alternate technologies. For surgeons, great courage is necessary to decide whether the anastomosis must be revised or not, even in situations when they are not totally confident in the quality of the anastomosis they performed. SPY images provide critical information to surgeons to confidently detect non-patent grafts, allowing them to be revised while the patient is still on the operating table. Taggart et al. [2] reported that compromised graft flow occurred in 5% of the patients and in 1.9% of all grafts performed. We also revised the anastomoses in 1.4% of all 290 grafts in this series. This device may greatly contribute not only to the patients' life but also to the surgeons' work.
There are some limitations to this technology. First, it does not provide an exact graft flow quantity measurement. Quantitative graft flow measurement software is currently being investigated. Second, the laser light source is of relatively low power to ensure safe clinical use. However, this limits the penetration of the light through tissue to about 1 mm. Thus, clear images could not be obtained when the coronary artery has a deep intra-myocardial location. The pedicled conduits with significant amounts of overlying tissue are also less well visualized. However, we believe that full skeletonization of the arterial conduits is a very useful and important technique for complete arterial revascularization of all the coronary vascular regions. We believe that the use of the full skeletonization technique may optimize the long-term graft patency. In Europe, the cost of the procedure may be around 200–350
The SPYTM system is a very useful technique for intra-operative graft validation. The device has the great advantages of non-invasiveness and safety. The ability to confidently confirm graft patency at the time of surgery encourages the surgeon to attempt challenging techniques and strategies. Off-pump CABG using SPYTM intra-operative validation may become the gold standard for surgical management in the near future.
Conference discussion Dr B. Walpoth (Geneva, Switzerland): I would like to congratulate you on your clinical study with a new promising device. I agree with you that you will have a morphologic imaging and you will know where the problem is, especially if you measure flow and you have a low-flow situation. In occlusions, however, both techniques will confirm the occlusion, but none of the techniques will give you the exact localization. How long does this technique take to do in the operating room and how many injections can you perform and how fast is the washout of the contrast? Dr Takahashi: Two or three minutes to take one picture. I dilute the ICG to 20 ml, and one time I used 1 ml of diluted ICG, so 20 times we can do for the one patient. Dr Walpoth: So the washout is very rapid? Dr Takahashi: Yes. Dr Walpoth: You have no staining of the myocardium? Dr Takahashi: That's right. Dr B. Buxton (Heidelberg, Vic., Australia): An excellent technique. It has potential use for us as surgeons. Did you detect spasm during your technique, particularly in the radial artery grafts, and if so, what steps did you take to eliminate the spasm? Also, could you tell spasm from a mechanical obstruction or narrowing? Dr Takahashi: When the graft is patent? Dr Buxton: When the graft is patent and looked narrowed such as that last demonstration, did you take any steps to eliminate the spasm, with the use of GTN or a PD-III inhibitor? Dr Takahashi: I have never experienced graft occlusion due to spasm after I used full skeletonized arterial graft and PD-III inhibitor to prevent spasm. So I recognized that all the non-functional grafts detected by SPY system cause technical failure. Dr Buxton: Could you see a technical failure on your imaging technique and correct it? Dr Takahashi: Sorry, I can't understand. Dr Dion: The question is, this tool, did it change something to your technique, did you do something differently technically to perform the anastomosis? Did this tool, this imaging, influence your surgical technique for the anastomosis? Dr Takahashi: Yes. I always prefer to use the fully skeletonized radial arterial graft, after SPY system has been introduced in my hospital. The spasm is not a reason for the non-functional graft detected by SPY, just technical failure I think, I believe it.
ICVTS on-line discussion Author: Dr. Hitoshi Hirose, Juntendo Univesity Hospital, Department of Cardiovascular Surgery, Hongo, Bukyo-ku, Tokyo Date: 18-May-2004 Message: The SPY system would be an excellent modality to evaluate the bypass patency in the operating room. One of the advantages of the SPY over the flow prove is the capability to detect sequential bypass. In sequential bypass, if one of the anastomosis is patent, the flow meter may give normal value and normal wave form (false positive), because the flow is dependent on one of the patent anastomoses. By using the SPY, as the figure shown by the authors illustrates, each sequential anastomosis patency can be detected individually. I believe this to be an important point of the SPY system. Author: Dr. Kenji Minakata, The Tominaga Hospital, Division of Cardiovascular Surgery, 1-4-48 Minatomachi, Naniwa-ku, Osaka-city, 556-0017 Japan Date: 26-May-2004 Message: This is a very nice study which introduces a new device to evaluate the quality of graft anastomoses during off-pump CABG. As OPCAB is getting more popular, the issue of long-term graft patency raises a great interest. Clearly, it is necessary to improve the early outcome to have better long-term results. The authors demonstrate in the article that the SPY system can be used both very safely and easily as well as detect potential technical failures during OPCAB thus allowing the surgeons to revise it at the same time. Since I personally observed this device recently, it is absolutely true that the images are quite vivid and impressive with great resolution. I agree with the authors that the SPY system can be a standard tool just like a TEE in the field of modern cardiac surgery, pretty soon.
We gratefully acknowledge the help of Dr John Docherty in the preparation and translation of the manuscript.
Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.icvts.2004.01.018. Presented at the joint 17th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 11th Annual Meeting of the European Society of Thoracic Surgeons, Vienna, Austria, October 12–15, 2003. doi:10.1016/j.icvts.2004.01.018
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Abstract
1. Introduction
. This will include use of the device, ICG and the drape. 
