Eur J Cardiothorac Surg 2003;24:961-966
© 2003 Elsevier Science NL
Real-time patency control with thermal coronary angiography in 1401 coronary artery bypass grafting patients
Bingür Sönmez,
Harun Arbatli*,
Selim Tansal,
Naci Ya
an,
Mehmet Ünal,
Ergun Demirsoy,
Faruk Tükenmez,
Ouz Yilmaz
Department of Cardiovascular Surgery, Istanbul Memorial Hospital, Piyalepasa Bulvari, Okmeydani, 80270 Istanbul, Turkey
Received 12 March 2003;
received in revised form 29 June 2003;
accepted 10 July 2003.
* Corresponding author. Tel./fax: +90-212-220-8910
e-mail: harbatli{at}hotmail.com
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Abstract
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Objective: Intraoperative coronary angiography has always been favoured by cardiac surgeons. Thermal coronary angiography (TCA) is a useful method for intraoperative control of graft patency. It detects heat differences between tissues, provides easy-to-interpret angiographic images and even measures the flow of the grafts quantitatively. Methods: Between January 2000 and January 2002, TCA has been used in scheduled coronary bypass operations. Upon completion of each distal anastomosis, the perfusion of the distal arterial tree from the graft was evaluated with a thermal camera. Results: TCA was applied to 1401 patients, mean age 60.97±9.61 years, who underwent simple coronary artery bypass grafting (CABG) procedures. A total of 4105 thermal images were obtained including 2161 venous, 1355 single internal thoracic artery (ITA), 56 bilateral ITA and 477 radial artery grafts. Image quality was not sufficient in 34 grafts (1.57%) due to either deep intramyocardial vessels or excessive epicardial fat tissue. Technical failures in three ITA anastomoses were detected and revised before the cross-clamp was removed. Flow-restricting lesions distal to the anastomosis on the left anterior descending artery (LAD) in nine patients were managed with a secondary distal bypass graft (five patients) or plaque splitting and anastomotic revision (four patients). Endarterectomy was combined in seven patients since the graft flow and the distal visualization was not satisfactory, although the anastomoses were performed on a good lumen. Angiographically undetected diagonal arteries were revascularized in 11 patients with totally occluded LAD vessels. Conclusion: Thermal imaging provides decisive coronary angiographies, and detects the perfusion area and flow of the implanted graft. It allows real-time detection of technical failures, reveals unexpected occluding plaques or any kind of flow-restricting lesions, and gives the chance of refinement of the anastomosis during the arrest period. We believe that the thermal imaging technique is a safe, noninvasive and feasible method to document the quality of the myocardial revascularization intraoperatively.
Key Words: Coronary artery bypass surgery • Thermal coronary angiography • Thermal imaging
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1. Introduction
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Intraoperative evaluation of graft patency and distal run-off has always been a challenge in coronary bypass surgery. Some authors have used intraoperative conventional coronary angiography [1,2], but it is not popular since it needs contrast injection and requires preventive measures from radiation, high technology and experienced staff, which add more expenses. Thermal coronary angiography (TCA) allows anastomotic quality control, not only by improved imaging techniques, but also with the recently developed flow measurement feature. Technical failures of the anastomoses as well as distal native coronary artery diseases can be recognized by this method. Although the features of intraoperative use of thermal imaging has been published in the literature since the 1970s [3,4], it has not been used widely until the 1990s following improved reception of images using highly sensitive infrared cameras [5,6].
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2. Methods
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A thermal imaging camera (IVA-2000, Opgal Optronic Industries Ltd., Karmiel, Israel) has been used routinely in our department since January 2000. The TCA device consists of two mobile parts, a camera and a console. The console contains a video recorder, a video printer, a monitor, a wired remote control and an image-processing unit. The camera unit contains an infrared imager, a video camera and a monitor on a post for the surgeon's view (Fig. 1)
. The camera unit is easily placed over the heart from the anesthesia side and the camera can be pointed at the area of interest easily by the surgeon using sterile handles. The console can be placed anywhere in the operating room and used by a technician. The coronary arteries either on the front or the back of the heart can be visualized successfully.
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Fig. 1. Thermal coronary angiography device consists of two mobile parts. The camera unit is placed over the heart and camera can be pointed to the area of interest easily by the surgeon using sterile handles. The console can be placed anywhere in the operating room.
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All patients scheduled for coronary artery bypass grafting (CABG) were evaluated by TCA intraoperatively. Thermal imaging created by infrared technology provides real-time and easy-to-interpret coronary angiographies as well as graft flow measurements. The temperature difference generated between the myocardium and the coronary arteries by injecting either cold or warm cardioplegic solution into the vein or the radial artery from the proximal end of the graft or by the patient's own blood running through an internal thoracic artery graft creates angiographic images. When the temperature of the coronary artery is lower than the myocardium, it shows black images; the other way round gives white images (Fig. 2)
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Fig. 2. (A) Cold saline injected through the graft gives the black image. (B,C) Warm saline through the graft or warm blood through the ITA graft gives white images. (D,E) Technical failure of the anastomosis can be detected by showing the unfilled distal or proximal arterial segments.
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Tepid blood cardioplegia was utilized in all patients delivered via the antegrade and retrograde route with the standard cardioplegia setting. At the initiation of the retrograde cardioplegia, satisfactory myocardial delivery was evaluated by the thermal camera by filling both the anterior cardiac and particularly the right marginal veins. Thermal imaging of the native vessels was inspected with antegrade cardioplegia delivery to localize a mid-arterial stenosis, or a visible plaque was able to be checked if it was obstructing the lumen (Fig. 3)
. Graft and native artery visualization were obtained after completion of each distal anastomosis (Fig. 4) . Particularly on the left anterior descending artery (LAD), efforts were intensified to visualize the proximal and distal part of the anastomosis to evaluate the diagonal arteries filled with blood (Fig. 5)
. Anastomoses were visualized in each coronary artery on sequential grafts to see both vessels filled adequately, and distal flow was measured separately (Fig. 5). Visualization and flow measurements of pedicled internal thoracic artery (ITA) grafts were done immediately after the removal of the bulldog clamp. On the other hand, free grafts (saphenous vein, radial artery, free ITA) were visualized by injecting warm or cold saline from the proximal ends.
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Fig. 3. (A,B) Visible plaque on the coronary artery can be checked by the TCA if it is obstructing the lumen during the delivery of the antegrade cardioplegia.
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Fig. 4. (A) Warm saline injection through the vein graft which shows good filling of the obtuse marginal artery. (B) Cold saline injection through the radial artery which creates black filling of the posterolateral branch of the circumflex artery. (C) Good filling of the obtuse marginal branches of the circumflex artery. (D) Posterolateral branch of the right coronary artery after completion of the anastomoses.
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Fig. 5. (A,B) Visualization of the LAD distally and proximally is essential for the confirmation of a perfect anastomosis. (C,D) Video image of LITA sequential anastomoses to the diagonal and the LAD arteries and intraoperative control of the same graft with the TCA.
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Although TCA failed to visualize the coronary arteries due to excessive epimyocardial fat or intramural artery, flow measurements on the grafts were still helpful in such conditions. Graft flow is measured by capturing the temperature on a fixed point, cooling it down with cold flush and measuring the rewarming time (calculation of time versus rewarming) with the well-known thermodilution technique. The flow measurement site can be the ITA itself, distal anastomotic area or an area close to the proximal anastomosis of veins or radial arteries and others (Fig. 6)
. Since minimal motion is required during the flow measurement, it is advised to measure the flow on the ITA before the cross-clamp is removed. On free grafts, flow measurements were done after the construction of proximal anastomoses on a motionless segment close to the aorta just before weaning from the cardiopulmonary bypass. Flow in the grafts above 70 ml/min was accepted as adequate. When the grafts had no good distal coronary image or unsatisfactory flow, the distal anastomoses were revised (Fig. 7)
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Fig. 6. (A,B) Graft flow measurement accomplished by capturing the temperature on a fixed spot distal to the ITA graft or close to the proximal anastomosis on the free grafts and measuring the rewarming time after cooling down this spot with cold flush.
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Fig. 7. (A) Intraoperative TCA of the LITA sequential anastomoses on diagonal and LAD determined no flow in the LAD. (B) The anastomosis was revised and resulted in excellent flow in the LAD.
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Concerning the effect of intraoperative TCA on the cross-clamp period, we instituted a control group (n=221) and a study group (n=440), with patients who received three distal anastomoses.
Statistical analysis were performed by GraphPad InStat 3.05 for Windows (San Diego, CA).Unpaired t-test, chi-square test and Fisher's exact tests were used.
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3. Results
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TCA was applied to 4105 bypass grafts in 1401 patients. Only 34 very deep intramyocardial coronary arteries or arteries covered with excessive fat tissue on the heart could not be visualized sufficiently (1.57%). However, flow measurements were done on the grafts to confirm the anastomotic patency. No flow in the LAD was determined in three patients, and the anastomoses were revised in all, which resulted in satisfactory flow. Flow-restricting lesions were detected in the mid LAD segment in nine patients and either a secondary vein graft constructed onto the distal LAD was done (n=5) or plaque splitting was performed (n=4). Undetected diagonal arteries with preoperative coronary angiography were revascularized in 11 patients with totally occluded LAD vessels. Poor visualization of flow in the diagonals after construction of the LAD anastomosis led the surgeon to revascularize these vessels. Inadequate left ITA (LITA)–LAD graft flow was detected and endarterectomy was adjoined in seven patients although the anastomoses were constructed onto the good lumen at the first attempt (Fig. 8)
. The ratio of the endarterectomy group was slightly higher than that of the control group (1.71 vs. 0.63%) without statistical importance (P=0.083).
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Fig. 8. (A) Endarterectomy venous patch plasty and LITA anastomosis were performed to the LAD. (B) Intraoperative TCA, showing good filling of the LAD artery.
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Some visible plaques on the coronary arteries proved not to disturb the coronary lumen (external plaque) during the antegrade cardioplegia delivery by the TCA (Fig. 3), so that the grafts were placed proximal to the plaque without any hesitation.
The mean cross clamp time in patients with three distal anastomoses was 57.92±14.87 min in the thermal angiography group as compared to 57.01±11.51 min in the control group (P=0.4254).
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4. Discussion
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Intraoperative evaluation of the perfused region and the function of the graft is a guarantee for the success of the CABG procedure. Several methods for intraoperative assessment of anastomotic quality have been developed to verify the graft patency. Angiography is the gold standard for the assessment of anastomotic quality, but it is invasive, requires nephrotoxic contrast material, is time consuming and expensive, and is not available in most operating rooms during CABG surgery.
High-frequency epicardial echocardiography was used to detect anastomotic failures by some authors with satisfactory results [7,8]. However, segmental calcifications on the arteries may cause some artifacts that complicate the accurate assessment and prolong the investigation time.
Intraoperative perfusion echocardiography by using albumin-coated microbubbles is an indirect method to evaluate the patency of grafts [9]. Nevertheless, this tool is neither cost-effective nor practical.
Angioscopic evaluation is another alternative to assess the quality of anastomosis [10,11]. However, it has the potential danger of intimal injury and is not feasible for in situ grafts, and has never had wide acceptance.
Methods used to quantify the graft flow are either cumbersome or potentially harmful. Using an electromagnetic flowmeter and Doppler equipment can easily mislead the surgeon as regards measuring the retrograde flow or the flow going to the side branches. This was documented by Merin and associates; after the completion of the LAD–LITA anastomosis the flowmeter revealed good flow but thermal angiography showed an obstruction 2 cm distal to the anastomosis, which was corrected intraoperatively [12].
More recently introduced ultrasound-based transit-time flow measurement has been used as a measurement tool for graft flow [13]. The effectiveness of this tool is controversial. D'Ancona and colleagues reported that transit-time flowmetry improved their surgical results by early detection of graft failures. Intraoperative measurements led them to revise 9.9% of distal anastomosis constructed off-pump, which is technically more demanding [14]. Conversely, Hol and associates compared the transit-time flowmeter measurements with perioperative and postoperative coronary angiographic results and mentioned that this instrument could not identify significant lesions in arterial or vein grafts, and that the interpretation of flow measurements alone should be done cautiously [15].
Robicsek and colleagues used thermography to study anastomotic patency and coronary anatomy but they failed to demonstrate severe technical failures [3]. As thermal imaging technology has developed, not only the problems of misinterpretation of nonrestrictive anastomotic strictures or distal coronary artery disease have been overcome, but also the flow rates of these distal arteries can now be obtained intraoperatively.
Perioperative evaluation of anastomotic patency is especially desired in the minimally invasive era. Some surgeons use angiography [16–18], while others prefer to use transit-time flow measurement perioperatively [19,20]. TCA can be utilized in off-pump CABG [21] and even in minimally invasive direct coronary artery bypass (MIDCAB) procedures [22] to determine the function of the graft efficiently. The recently introduced flow quantification feature of the device adds another alternative to evaluate the quality of the implanted graft. The images obtained by thermography show the area perfused by the graft while flow measurement accurately determines the success. It takes less than 1 min to perform TCA per graft, while the flow measurement is done after releasing the cross-clamp. No disposable material is required except cold and warm saline.
Falk and associates reported the rates of anastomotic failure to be 1 and 5.3% for vein and ITA grafts, respectively, which were detected by TCA and revised intraoperatively [6]. Their preoperative myocardial infarction rate and intra-aortic balloon pump use tended to be lower than the control group (3.0 vs. 3.4%), without statistical significance.
In our study, there were only three anastomotic failures detected by TCA (0.007%). On the other hand, TCA helped the surgeon to decide to do an endarterectomy in seven, to do an additional bypass graft to the side branch in 11, to split a plaque on the coronary artery in four and to construct a secondary distal bypass graft in five cases. Perioperative myocardial infarction rate also tended to be lower, although statistically not significant.
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5. Conclusion
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Thermal images derived by TCA are easy to interpret and the flow measurement feature comprises an extra aid in CABG surgery. There are no side effects of contrast media, which are only cold or warm saline, there is no radiation effect on the theatre staff and there is no need for extra staff training. We believe that the thermal camera deserves to be an essential device in coronary artery bypass surgery.
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Abstract
1. Introduction
