Ann Thorac Surg 2007;83:1508-1512
© 2007 The Society of Thoracic Surgeons
New Technology
Superiority of Using Bipolar Radiofrequency Energy for Internal Mammary Artery Harvesting
Thomas A. Vassiliades, Jr, MDa,*,
Ned Cosgriff, MDb,
Amy Denham, BSEEb,
Jessica Olson, MSMEb,
Donald H. Maul, DVMc
a Division of Cardiothoracic Surgery, Emory University School of Medicine, Atlanta, Georgia
b Tyco Healthcare, Boulder, Colorado
c Pre-Clinical Research Services, Colorado State University, Fort Collins, Colorado
Accepted for publication August 4, 2006.
* Address correspondence to Dr Vassiliades, The Emory Clinic Bldg A, 1365A Clifton Rd NE, Suite 2100, Atlanta, GA30322 (Email: thomas.vassiliades{at}emoryhealthcare.org).
Presented at the Basic Science Forum of the Fifty-second Annual Meeting of the Southern Thoracic Surgical Association, Orlando, FL, Nov 10–12, 2005.
| Dr Cosgriff, Ms Denham, and Ms Olson disclose that they have financial relationships with Tyco Healthcare.
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Abstract
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Purpose: The purpose of this study was to observe the acute effects of harvesting the porcine internal mammary artery using a novel bipolar (BP) radiofrequency energy device.
Description: The internal mammary artery from 16 porcine subjects was harvested using monopolar electrosurgery, BP electrosurgery, ultrasonic coagulation, and mechanical dissection with clips. Segments were evaluated with respect to endothelial function and integrity and the strength of side-branch sealing.
Evaluation: Adenosine triphosphate-induced relaxation was greatest with internal mammary artery segments harvested by bipolar electrosurgery in comparison with monopolar electrosurgery (p = 0.0271), ultrasonic coagulation in comparison with monopolar electrosurgery (p = 0.0047), and mechanical clipping in comparison with monopolar electrosurgery (p = 0.0381). The standard error of the mean failed to demonstrate any significant difference in epithelial disruption among the four treatment groups. Clips and bipolar electrosurgery exhibited the most secure ligations with burst pressures exceeding 350 mm Hg.
Conclusions: Internal mammary artery segments harvested using a novel BP electrosurgery retained a greater degree of endothelial function when compared with monopolar electrosurgery and ultrasonic coagulation. Side-branch sealing with BP electrosurgery was as secure as mechanical clips.
The comparative attributes and limitations of different devices for harvesting the internal mammary artery have been reported in the literature [1–3]. Commonly used techniques include monopolar radiofrequency electrosurgery, ultrasonic coagulation, and mechanical dissection with clips. Although bipolar RF electrosurgery has been used extensively in other surgical procedures, performance data on its use in internal mammary artery (IMA) harvesting is limited.
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Technology
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This study was undertaken to evaluate bipolar RF electrosurgery in IMA harvesting with respect to endothelial function and integrity. A direct comparison is made with three established methods currently used in clinical practice.
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Technique
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All animals were cared for according to standard operating procedures of the test facility (Colorado State University, Fort Collins, CO) and in compliance with the 1996 "Guide for the Care and Use of Laboratory Animals" as recommended by the United States National Institutes of Health. The Animal Care and Use Committee of Colorado State University approved all procedures and protocols (ACUC Protocol No. 02-042A-01). Using the same general anesthetic technique in all subjects, sixteen female pigs (70 to 80 kg) underwent a median sternotomy through which both the left and right internal mammary arteries were harvested by a single surgeon (TAV). Segments were surgically dissected without a pedicle using one of four methods: (1) monopolar (MP) RF electrosurgery, (2) Bipolar (BP) RF electrosurgery, (3) ultrasonic (US) coagulation, and (4) mechanical division with a scalpel and ligation with standard titanium clips (CL). Monopolar RF electrosurgery consisted of a hand-switching pencil with a Teflon (polytetrafluoroethylene) coated blade and generator (Valleylab, Boulder, CO). The energy setting was placed on "20/20" coagulation/cutting in all cases. Bipolar RF electrosurgery consisted of a custom vessel sealing technology using specialized bipolar RF energy (Valleylab). Ultrasonic energy technology consisted of the harmonic scalpel with a curved blade and generator (Ethicon Endosurgery, Inc, Cincinnati, OH). Mechanical dissection consisted of clipping side branches with small titanium clips, a single-use clip applier (Premium Surgiclip, Autosuture [US Surgical, Norwalk, CT]) and division with a No. 15 scalpel blade. Four IMA test samples from each animal were obtained by randomly assigning a harvest method to each of four anatomic regions of the IMA: (1) left proximal half, (2) left distal half, (3) right proximal half, and (4) right distal half. Block assignments were distributed evenly among the four anatomic regions and four harvesting modalities to overcome variation in IMA size between subjects.
Vasoreactivity Testing
Harvested IMA segments with ligated side branches and an untreated control segment with side branches that were not ligated were placed in an ice-cold physiological salt solution and transported to the muscle bath laboratory (Cardiovascular Pulmonary Research Laboratory, University of Colorado Health Sciences Center, Denver, CO) within 90 minutes of the ligations. Specimens were submitted to the laboratory without indication of the harvesting method.
In the laboratory, 3 mm to 4 mm-wide rings (containing either a ligated or unligated side branch) were cut from the artery segments, cleaned of connective tissue, mounted on stainless steel hooks, and suspended in 10 mL physiological salt solution in a muscle bath under an optimal resting tension of 2 g (as defined in preliminary studies of contractile responses to KCl). The rings were then allowed to equilibrate in the physiological salt solution maintained at 37°C and were aerated. Some untreated control rings were mechanically denuded of endothelium with a roughened steel hypodermic needle. Artery ring isometric tension was measured by force-displacement transducers (FT03 [Grass Instrument Co, Quincy, MA]) and recorded on a computer-linked system (MP100, Biopac Systems Inc, Goleta, CA). After 60 minutes of equilibration, the rings were stimulated to contract by membrane depolarization with 80 mM KCl to test for viability and to "prime" the vessel contractility, and were then precontracted with 1 µM phenylephrine (
1-adrenoceptor agonist). After the phenylephrine contraction had plateaued, adenosine triphosphate (10–8 to 10–3 M) was cumulatively added to the muscle bath to induce concentration-dependent relaxation, which was expressed as percent reversal of the phenylephrine contraction. The adenosine triphosphate was chosen as the relaxant (vasodilator) after several preliminary experiments showed that other commonly used agents, such as acetylcholine, bradykinin, substance P, and cyclopiazonic acid had caused little or no reversal of the phenylephrine contraction in the control porcine IMA rings.
Burst Pressure Testing
Optical magnification was used to identify and isolate all side branches. Isolated IMA segments containing each side branch were pressurized by a saline-filled, 60 mL syringe pump (Cole Parmer, 74900 series, Vernon Hills, IL) at a rate of 100 mL/hr. Blue dye in the saline provided the visual means of identifying the specific failure location at the ligation. Peak pressure was recorded at the advent of failure of the ligation using a Fluke Pressure Calibrator (Fluke Electronics, Everett, WA).
Scanning Electron Microscopy Preparation
Porcine internal mammary arteries were fixed, stored, and shipped at room temperature to the microscopy lab (Ken Baker Associates, Acton, Ontario, Canada) in 2.5% glutaraldehyde in a 0.2M PO4 buffer. Individual specimens were processed using standard techniques. Each was examined at 10 Kv with a Hitachi S-570 scanning electron microscope equipped with the LaB6 gun (Hitachi High Technologies America Inc, Pleasanton, CA). Digital images were acquired at low (100x), medium (400x), and high (1,000x) magnifications with an emphasis on the endothelial surfaces adjacent to and opposite the side branch ostia. One pathologist, who was blinded to the test, examined all specimens and described the endothelial integrity using the following scoring system: grade 0 = (unaffected) subendothelial architecture distribution obvious and uniform; grade 1 = subendothelial architecture distribution obvious with mild changes; grade 2 = subendothelial architecture distribution apparent but partially obscure; grade 3 = subendothelial architecture distribution mostly obscured; grade 4 = (severe) complete endothelial denudation, subendothelium broadly exposed.
Statistical Analysis
The vasoreactivity data are shown as means ± standard error of the mean. Variations in the percent reversal of phenylephrine contraction were expressed using analysis of variance with Fisher’s post hoc test. Comparison between burst pressures was performed with two-tailed t testing. The Mann-Whitney U test was used to analyze differences between groups in the scanning electron microscopy scores. Statistically significant differences among the four groups were defined as p < 0.05.
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Results
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Harvested IMA segments with a total of 163 side branches were submitted for side branch burst testing. Among the four treatment groups, there were no statistically significant differences in harvesting times, the mean diameter of the side branches, or the ratio of side branch location along the IMA (Table 1). The mean burst pressure of side branches ligated with bipolar RF and metal clips were not significantly different. However, bipolar RF and clips had statistically higher burst pressures compared individually with MP RF and US coagulation (Fig 1).
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Table 1 Internal Mammary Artery Side Branch Size, Location, and Ligation Failures for Four Treatment Groups (n = 163)
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There were no statistically significant differences among the groups in response to KCl or 1 µM phenylephrine, although the denuded rings showed a tendency to contract less. The adenosine triphosphate concentration-relaxation curves in all rings that contracted to phenylephrine are shown in Fig 2. Adenosine triphosphate-induced relaxation was greatest with IMA segments harvested by bipolar electrosurgery in comparison with MP electrosurgery (p = 0.0271), BP in comparison with US coagulation (p = 0.0047), and BP in comparison with mechanical clipping (p = 0.0381).
Using a five-point scale (grades 0–4) to assess the degree of endothelial disruption in the main body of the IMA by the standard error of the mean, the mean score for each of the treatments were as follows: mean control = 0.0; mean MP RF electrosurgery = 2.0; mean BP = 1.75; mean US coagulation = 1.75; and mean clips = 1.75. Although there were no statistically significant differences between treatment groups, there was a slight trend toward more endothelial damage of the IMA wall around and opposite the side branch ostia when harvesting using the MP RF technique (Figs 3A,
3B). None of the specimens exhibited grade 4 damage (Fig 4).
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Fig 3. Representative scanning electron micrographs of porcine internal mammary artery harvested as (A) control (grade 0) and (B) monopolar radiofrequency (RF) electrosurgery (grade 3).
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Fig 4. Distribution of standard error of the mean (SEM) grades for treatment groups (high, mean, low; control, intact = 0.0; control, denuded = 4.0). (BP = bipolar; CL = clips; MP = monopolar; US = ultrasonic.)
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Comment
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Methods currently used to harvest the IMA include MP and BP RF electrosurgery, US coagulation, and dissection with scalpel and clips. Monopolar RF electrosurgery uses alternating current in which the circuit is comprised of a generator, an active electrode, the patient, and a return electrode [4]. In bipolar RF electrosurgery, both the active electrode and return electrode functions are performed at the site of surgery. Only the tissue grasped is included in the electrical circuit [5]. Ultrasonic coagulation consists of an instrument that delivers mechanical vibration rather than an electrical current [6]. Scalpel dissection and clips rely completely on the surgeon’s mechanical dissection without the aid of an external energy source. Although each of these modalities has inherent advantages and limitations, characteristics important to surgeons include ease of use, system efficiency, and safety. Safety includes the security of side branches and the preservation of the normal structure and function of the main body of IMA, specific factors that are addressed in this study.
Results from side branch burst testing demonstrated that each of the four methods had an acceptable performance level in the physiological pressure range. With the size and location of IMA side branches equivalent in all treatment groups, each of the treatment groups had a mean side branch burst pressure at least two to three times normal systemic blood pressure. The data suggest a two-tiered level of performance with clips and BP RF demonstrating a statistically significant higher mean burst pressure and lower side branch failure rate when compared with MP and US coagulation (Table 2). Although electrosurgery and US coagulation both denature the tissue to achieve ligation [7–8], the effectiveness of US coagulation may be more user-dependent than RF electrosurgery. Tissue ligated by ultrasound appears to require more firm tissue apposition.
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Table 2 P Values Comparing Side Branch Failure Rates Between Treatment Groups With Increasing Hydrostatic Pressure (Two-Sided Fischer’s Exact Test)
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This study also attempted to determine whether any of the four different procedures of side branch ligation had an adverse effect on the vasoreactivity of isolated porcine IMA. Although the relaxation response to adenosine triphosphate was blunted in all groups, the specimens harvested using bipolar RF electrosurgery showed the greatest relaxation, statistically different from each of the other three groups.
The third phase of our study was designed to compare specimens harvested from the four treatment groups with respect to endothelial architecture as determined by the standard error of the mean performed by an independent, blinded pathologist. The results failed to reveal any statistically significant conclusions, but we learned that meticulous harvesting techniques using well-established methods and technology may still result in a moderate amount of endothelial disruption.
Study limitations include the use of porcine rather than human IMA specimens. Human samples of IMA might have reacted, particularly with respect to the vasoreactivity experiments. In addition, bias may have entered into the study as a result of the inability to blind the surgeon from the harvesting techniques, or the influence of the surgeon’s prior experience with one method versus another. Finally, as this was not a chronic animal study or a clinical trial, it is difficult to quantify what truly constitutes clinically relevant injury to the IMA.
In summary, several factors must be considered in the design of a system to divide and ligate IMA side branches. Of vital importance is dividing and ligating the side branches to withstand supraphysiological pressure, and in the process, protecting the body of the IMA. The process must be achieved with a low rate of complication, including IMA spasm and thrombosis, side branch bleeding, pulmonary insufficiency, chest wall trauma, sternal infection, and chronic chest wall pain. Other considerations include ease-of-use, time efficiency, and system costs. Each of these factors is also influenced by the individual surgeon’s level of experience and technique, such as harvesting the skeletonized IMA, or as a fascial pedicle, or harvesting the IMA thoracoscopically as opposed to the traditional open technique.
Safety data using MP RF, US coagulation, and mechanical dissection with clips to harvest the IMA have been well documented [9, 10]. However, the use of bipolar RF electrosurgery in harvesting the IMA has not been extensively reported nor widely adopted. As has been demonstrated in this study, bipolar RF electrosurgery can be designed to ligate vessels as reliably as metal clips, while preserving the endothelial function and anatomic integrity better than other techniques using external energy sources. With a properly designed handpiece, bipolar RF can be designed to be easily used, time efficient, and cost effective.
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Disclosures and Freedom of Investigation
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Doctor Vassiliades was financially compensated by Valleylab Corp for his time spent on this project, but he had complete freedom of investigation including full control of the design of the study, methods used, outcome measurements, analysis of data, and production of the written report. There are no undisclosed writers for this article.
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Acknowledgments
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Valleylab Corp funded this entire project including animal studies performed at an independent facility (Colorado State University, Fort Collins, CO), endothelial function studies at an independent laboratory (Cardiovascular Pulmonary Research Laboratory, University of Colorado Health Sciences Center, Denver, CO), and standard error of the mean examinations of the specimens by an independent pathologist (Ken Baker Associates, Acton, Ontario, Canada).
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Footnotes
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Disclaimer 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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References
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- Yoshida H, Wu M, Kouchi Y, et al. Comparison of the effects of monopolar and bipolar cauterization on skeletonized, dissected internal thoracic arteries J Thorac Cardiovasc Surg 1995;110:504-510.[Abstract/Free Full Text]
- Lehtola A, Verkkala K, Jarvinen A. Is electrocautery safe for internal mammary artery (IMA) mobilization?A study using scanning electron microscopy (SEM). Thorac Cardiovasc Surg 1989;37:55-57.[Medline]
- Higami T, Yamahits T, Nohara H, et al. Early results of coronary grafting using ultrasonically skeletonized internal thoracic arteries Ann Thor Surg 2001;71:1224-1228.[Abstract/Free Full Text]
- Gruendemann BJ, Fersebner B. Technology management electrosurgery Comprehensive Perioperative Nursing Volume 1 Principles. Boston, MA: Jones and Bartlett; 1995. pp. 315-323.
- Fortunato NM. Biotechnology: specialized surgical equipment Berry & Kohn’s Operating Room Technique. 9th ed. St Louis, MO: Mosby; 2000. pp. 313-318.
- Wu MP, Ou CS, Chen SL, et al. Complications and recommended practices for electrosurgery in laparoscopy Am J Surg 2000;179:67-73.[Medline]
- Vancallie TG. Electrosurgery: principles and risks. San Antonio, TX: Center for Gynecologic Endoscopy; 1994.
- Foschi P, Cellerino F, Corsi T, et al. The mechanisms of blood vessel closure in humans by the application of ultrasonic energy Surg Endosc 2002;16:814-819.[Medline]
- Blake KL, Watt PA, Smith JM, et al. Randomized comparison of ultrasonic aspiration versus conventional electrocautery for dissection of the human internal thoracic artery J Thorac Cardiovasc Surg 1996;111:1194-1199.[Abstract/Free Full Text]
- Rukosujew A, Reichelt R, Fabricius A. Skeletonization versus pedicle preparation of the radial artery with and without the ultrasonic scalpel Ann Thorac Surg 2004;77:120-125.[Abstract/Free Full Text]
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Abstract
Introduction
= monopolar; 
= bipolar; 
= ultrasonic; 
= clips.
= monopolar radiofrequency (n = 23); 
= clips (n = 24); 
= bipolar radiofrequency (n = 19); 
= ultrasonic (n = 23); 
= control (intact) (n = 16); 
= control (denuded) (n = 8).