Interact CardioVasc Thorac Surg 2009;9:150-154. doi:10.1510/icvts.2008.201418
© 2009 European Association of Cardio-Thoracic Surgery
Work in progress report - Coronary |
Preliminary experience for the evaluation of the intraoperative graft patency with real color charge-coupled device camera system: an advanced device for simultaneous capturing of color and near-infrared images during coronary artery bypass graft
Takemi Handaa,b*,
Rajesh G. Katarea,
Shiro Sasagurib and
Takayuki Satoa
a Department of Cardiovascular Control, Kochi Medical School, Nankoku, Kochi 783-8505, Japan
b Department of Surgery 2, Kochi Medical School, Nankoku, Japan
Received 31 December 2008;
received in revised form 10 April 2009;
accepted 14 April 2009
 Financial support: This study was supported by Japan Science and Technology (JST).
*Corresponding author. Tel.: +81-88-880-2309; fax: +81-88-880-2310.
E-mail address: takemi{at}mpd.biglobe.ne.jp (T. Handa).
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Abstract
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We developed a new color charge-coupled device (CCD) camera for the intraoperative indocyanine green (ICG) angiography. This device consists of a combination of custom-made optical filters and an ultra-high sensitive CCD image sensor, which can detect simultaneously color and near-infrared (NIR) rays from 380 to 1200 nm. We showed a comparison between our system and other devices for the preliminary experience. We routinely performed both transit-time flowmetry (TFM) and color images for intraoperative assessment, thallium-scintigraphy for the early postoperative assessment, and then angiography after 1-year surgery. We also obtained intraoperative graft flows and images in 116 grafts. Although TFM indicated a graft patency, the CCD camera suspected perfusion failures in four grafts. Also the analysis of the ICG fluorescence intensity showed the significant hypoperfusion at the perfusion territory distal to the anastomosis (graft vs. perfusion territory; 230±26 vs. 156±13 a.u, P=0.02). When the CCD camera suspected a graft failure, CCD camera and angiography showed a comparable graft failure. The unique device that visualized ICG-enhanced structures against a background of natural myocardial color improved the visibility of abnormality in flow and perfusion. Our findings show that this device may become a standard intraoperative graft and perfusion assessment tool in coronary artery bypass graft (CABG).
Key Words: Indocyanine green angiography; Coronary artery bypass graft; Intraoperative graft assessment; New device
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1. Introduction
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To provide direct visual images, intraoperative indocyanine green (ICG) fluorescence imaging system (SPY; Novadaq Technologies Inc, Toronto, Canada) was used during coronary artery bypass graft (CABG) [1–5]. A comparison of transit-time flowmetry (TFM), SPY system and conventional angiography was reported, and then SPY system can detect clinically significant graft errors than does TFM [6–8]. However, the main drawbacks of SPY system is that the system captured fluorescence image on monochromatic camera and the continuous recording time is limited to 35 s due to the automatic laser shut-off. Therefore, to overcome this issue, our institution developed an advanced ICG fluorescence angiography system (real color CCD camera system), which captured the ICG fluorescence on color charge-coupled device (CCD) camera, illuminated with light emitting diodes (LED) and importantly with a long recording time. Here, we demonstrate a comparison of real color CCD camera, TFM, thallium-scintigraphy, and then angiography for the patency assessment of the graft for preliminary experience.
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2. Methods
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2.1. Real color CCD camera system
ICG is a water-soluble tricarbocyanine dye with a peak spectral absorption at 800–810 nm when dissolved in blood. When illuminated with 806 nm light, ICG emits fluorescence at 830 nm as previously described [1]. However, our preliminary in vitro study showed that the peak spectral absorption for ICG (0.001%) diluted in human blood was 760–780 nm (data not shown). Therefore, we selected 760 nm light source and 840 nm near-infrared (NIR) cut-on filter.
Apart from being expensive, the laser light source cannot be used for long-time recording of the images due to increased heat production. Therefore, we selected LED as our light source as they are less expensive. Importantly, the amount of heat produced on long-time use of LED was negligible, thus making it easier and safer in clinical use. Low-angle ring LED light decreased a glare from the surface of the heart and the cells compared with using the same axle LED light, and its illumination area was 78.5 cm2 (3.14x5 cmx5 cm) on the surface of the heart. For intraoperative image acquisition, the camera was positioned above the area of interest at a distance of  50 cm. ICG dye (2.5 mg/ml) was injected through a central venous catheter. After injection of ICG, image acquisition to the computer was initiated by means of a single command to the computer. The movie was recorded using the conventional laptop computer and the files are stored in avi format which can be immediately replayed in the operating room. The color CCD camera was connected to the imaging monitor with the same axle cable, and the imaging monitor was connected to the laptop computer with USB cable (Fig. 1).
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Fig. 1. Real color CCD camera system. This device consists of a combination of custom-made optical filters and an ultra-high sensitive color CCD image sensor, which can detect simultaneously color and near-infrared (NIR) rays. A light source for excitation of ICG dye is made with an array of light emitting diodes (LED). Recording time is no limitation and movie is replayed on laptop computer using Windows Media Player 9.
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2.2. Patients
Patients undergoing isolate CABG between April 2007 and December 2008 were included in this study. Each patient signed a consent form before the surgery. Exclusion criteria included allergy to ICG dye and cardiogenic shock. Operation was performed by a single surgeon and off-pump coronary artery bypass (OPCAB) was a standard procedure.
2.3. Experimental protocol
To compare two devices, we used routinely both TFM and CCD camera during CABG.
For the intraoperative evaluation of the graft patency and the decision of the graft revision, transit time-flow measurement (TTFM) was performed using MediStim BF 2004 (MediStim AS, Oslo, Norway). Graft patency using TFM was classified according to the following classification system: 1) Normal is >50% DF, a mean flow of >10 ml/min and PI of <5; 2) Abnormal is <50% DF, or a mean flow of <10 ml/min, or PI of >5. If there was no quantifiable flow, a graft was deemed occluded as previously described [9]. As a rule, graft revision was decided according to TFM assessment. In addition, if there was a retrograde flow (RF) in systolic phase, a graft was deemed competitive flow in this study.
Furthermore, ICG angiography was performed on the same grafts using real color CCD camera system after TTFM. We defined graft occlusion as no fluorescence in the graft, and perfusion defect as no fluorescence in the perfusion coronary artery without deep intramyocardial coronary artery. As a rule, when CCD camera captured graft occlusion or perfusion defects, we performed graft revision in this study.
To make a standard for the CCD assessment, we defined normal graft as continuous flow fluorescence on the graft, and functionally patent perfusion as continuous and forward flow fluorescence in the perfusion territory that is dependent on the graft flow, and widely left ventricular perfusion, and then the fluorescence intensity of the target coronary artery is the same as graft intensity.
On the other hand, we classified other visual images of the graft according to the following classification system: 1) competitive flow graft – retrograde or to-and-fro flow fluorescence on the anastomosis; 2) irregular flow graft – forward but intermittent flow in the graft, excluding to-and-fro flow; 3) dissection, kinking, stenosis, or occlusion grafts. Any types of abnormal perfusion were classified according to the following classification system: 1) unfavorable perfusion – flow fluorescence in the perfusion territory is independent on the graft flow, or the fluorescence intensity of the target coronary artery is <70% compared with graft intensity; 2) no quantifiable perfusion because of deep intramyocardial coronary artery. However, to analyze the fluorescence intensity values, we have to make the static images of the perfusion coronary arteries which is a limitation of this preliminary study.
For the postoperative assessment, we routinely performed thallium-scintigraphy within 2 weeks after the surgery, and then angiography after 1-year surgery. However, when angina recurrence was shown or scintigraphy showing any sign of ischemia, angiography was performed within 1 year after the surgery. Each coronary angiogram was independently evaluated by a cardiologist for graft patency. The evaluation of graft patency was classified according to TIMI classification system.
2.4. Statistical analysis
All data were expressed as mean±S.D. or as percentages. An unpaired Student t-test was used to verify the significance of fluorescence intensity between the graft and the perfusion territory, and the  calculation was used to evaluate the agreement of TFM and CCD camera by using StatView 4.5 software (Abacus Concept).
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3. Results
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We obtained the intraoperative graft images in 116 grafts in 39 patients undergoing isolate CABG from April 2007 to December 2008. All 39 patients were undergoing isolate OPCAB procedure. The average age of the patients was 70.5±8.7 years. A total of 149 distal anastomoses were constructed in 116 grafts. The average number of distal anastomoses was 3.8±1.0 per patient. We used 52 in-situ arterial grafts, 33 individual saphenous vein grafts (SVG), 26 sequential SVG, and then five free arterial grafts.
3.1. Results of CCD camera, TFM and scintigraphy assessment
We used TFM, CCD camera and scintigraphy in 116 grafts in 39 patients (Table 1). Ninety-five among 116 grafts (81.9%) indicated the patency of the graft by TFM, and the patency of the graft and perfusion by CCD camera (Video 1). And CCD camera showed that there was no difference in fluorescence intensity between the grafts and the perfusion territory (238±19 vs. 226±26 a.u., P=0.19). The scintigraphy did not show any sign of ischemia in this group.
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Video 1. Patent graft images. LITA to LAD, RA to PL, SVG sequential bypass to 4PD and 4AV are constructed with OPCAB. Real color CCD camera is able to capture the continuous and the graft dependent flow fluorescence in the target coronary arteries. OPCAB, off-pump coronary artery bypass; LITA, left internal thoracic artery; RA, radial artery; SVG, saphenous vein graft; LAD, left anterior descending artery; PL, posterolateral branch; 4PD, posterior descending artery; 4AV, atrioventricular branch.
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Twelve competitive grafts among 116 grafts (10.3%), TFM showed normal flow profile but detected retrograde waveform, and then CCD camera showed to-and-fro flow and functionally patent perfusion (Video 2). When TFM detected a retrograde waveform, CCD camera could capture to-and-fro flow fluorescence. And CCD camera captured normal perfusion that there was no difference in fluorescence intensity between the grafts and the perfusion coronary arteries (231±23 vs. 228±25 a.u., P=0.19). The scintigraphy did not show any sign of ischemia in this group.
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Video 2. Competitive flow images. LITA to LAD, RITA to OM and GEA to 4AV are constructed with OPCAB. Real color CCD camera captures to-and-fro flow (flow competition) on the anastomosis of the LITA graft. OPCAB, off-pump coronary artery bypass; LITA, left internal thoracic artery; RITA, right internal thoracic artery; GEA, gastroepiploic artery; LAD, left anterior descending artery; OM, obtuse marginal branch, 4AV, atrioventricular branch.
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On the other hand, normal grafts assessed by TFM included any type of the abnormal assessment by CCD camera in four grafts (3.4%). Although a mean flow was 19.2±6.0 ml/min, PI was 1.8±0.4, diastolic filling (DF) was 72±12% by TFM, CCD camera detected the abnormality of the perfusion in one graft, the abnormality of the graft and the perfusion in two grafts, and then CCD camera suspected one reverse dissection of ITA. In this group, the fluorescence intensity values in the perfusion territory were <70% compared with the graft intensity (230±26 vs. 156±13 a.u., P=0.02). Three among four grafts were negative assessment by scintigraphy. One graft, which was positive assessment by scintigraphy, showed a graft failure by early postoperative angiography.
In contrast, TFM assessed abnormal but CCD camera assessed normal grafts were three among 116 grafts (2.6%). Although a mean flow was 8.0±0.0 ml/min, PI was 2.9±19, DF was 74.0±10.3%, the perfusion fluorescence was completely dependent on graft flows, and there was no difference in fluorescence intensity value between the graft and the perfusion territory (233±5 vs. 227±3, P=0.14). The scintigraphy did not show any sign of ischemia in this group.
Furthermore, two among 116 grafts (1.7%) indicated the graft failure by both CCD camera and TFM, therefore, we performed graft revision.
However, the calculated for TFM and CCD camera was 0.34, which did not indicate an agreement between the two methods in this study.
3.2. A comparison of TFM, CCD camera and angiography
Angiography was performed for 50 grafts in 14 patients until December 2008 (Table 2). When CCD camera assessed normal perfusion, angiography indicated the patency of the graft. On the other hand, when CCD assessed any type of abnormality, CCD camera and angiography showed a comparable graft failure in this study (Fig. 2). The sensitivity and the specificity of TFM was 93% and 0%, in contrast, the sensitivity and specificity of CCD camera was 100% and 100% in this preliminary study.
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Fig. 2. Reverse dissection of ITA graft. LITA to LAD is constructed with OPCAB. (a) Although TFM indicated the patency of the graft, CCD camera suspected a reverse dissection of ITA graft (circle). (b) Postoperative angiography showed a graft failure of ITA graft (arrow). OPCAB, off-pump coronary artery bypass; LITA, left internal thoracic artery; LAD, left anterior descending artery.
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4. Discussion
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Real color CCD camera system was simultaneous capturing of color and NIR images during ICG angiography. Our system imaged the operative field with vivid real colors; it was easy to verify the localization of the target coronary and myocardial perfusion.
In the present results, the calculation is too weak to be indicative of agreement between TFM and CCD camera, because TFM gave only the local flow information of the graft on its probe, and thus never revealed the quality of CABG-induced restoration of myocardial perfusion at the area distal to the probe. Although the patency of the graft was indicated by TFM, the analysis of the ICG intensity value showed the significant hypoperfusion at the myocardial area distal to the anastomoses. In contrast, when CCD camera shows any type of abnormality, angiography can detect graft failures within 1 year after the surgery and the sensitivity of CCD camera is 100% in this preliminary experience. Here, the present results suggest that the non-occlusive hypoperfusion assessment using CCD camera is a risk factor for the graft failure in the future. Routine completion angiography detected 12% of grafts with important angiographic defects [10], on the other hand, our system detected 11% of graft failures. These findings speculate that real color CCD camera system may become a high-sensitive graft assessment tool because it is able to detect the details of the graft and perfusion failure with visual images.
However, we have two main limitations in this preliminary study. First, although real color CCD camera visualized the abnormality of the graft flow and myocardial perfusion, we did not evaluate the severity of the graft failure which required graft revision yet. We need a multiple-center trial to obtain any non-occlusive graft failure images in multiple graft designs for the evaluation of the severity. Second, we need a postoperative angiography for each graft to evaluate the sensitivity and specificity of our device.
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5. Conclusion
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The unique device that visualized ICG-enhanced structures against a background of natural myocardial color improved the visibility of abnormality in flow and perfusion. Real color CCD camera is useful for the intraoperative assessment of graft flow and patency, which may become a standard surgical management tool in CABG.
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Acknowledgements
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This study was supported by a grant for Science and Technology Incubation Program in Advanced Regions from Japan Science and Technology Agency.
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Abstract
1. Introduction
