Ann Thorac Surg 2000;69:1833-1835
© 2000 The Society of Thoracic Surgeons
Original articles: Cardiovascular
The harmonic scalpel: optimizing the quality of mammary artery bypass grafts
Peter Lamm, MDa,
Gerd Juchem, MDb,
Peter Weyrich, MDc,
Albert Schütz, MDa,
Bruno Reichart, MDa
a Department of Cardiac Surgery, University Hospital Großhadern, Ludwig-Maximilians-Universität München, München, Germany
b Department of Anesthesiology, University Hospital Großhadern, Ludwig-Maximilians-Universität München, München, Germany
c Department of Cardiology, University Hospital Grosshadern, Ludwig-Maximilians-Universität München, München, Germany
Address reprint requests to Dr Lamm, Department of Cardiac Surgery Universität München am Augustinum, Wolkerweg 16, 81375 München, Germany
e-mail: lamm{at}lrz.uni-muenchen.de
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Abstract
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Background. The damage done to the endothelium during the preparation of a graft used in an aortocoronary procedure is a risk factor for early graft failure. We compared the effect on the endothelium of the mammary arteries when the harvest was done either by the harmonic scalpel (HS) or the high-frequency electrocauter (HF).
Methods. Twenty-four mammary arteries were harvested and divided into two groups depending on the use of the HS or the HF. The endothelial damage was analyzed with a scanning electron microscope. The groups were compared in regard to the size of the internal mammary artery (IMA) pedicle.
Results. The endothelial damage of the IMAs taken down with the HS was significantly less than when taken down with the HF if the IMA pedicle size was less than 0.5 cm.
Conclusions. The HS has a positive effect on the endothelial preservation, especially when the preparation is done closely to the IMA. The HS is profitable in minimally invasive procedures, particularly when it is difficult to keep a wide enough distance from the IMA.
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Introduction
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The internal mammary artery (IMA) is the graft of choice in an aortocoronary bypass operation [1, 2]. The use of this graft is the single most important factor in improved survival and freedom from angina [3]. Its long-term patency is significantly superior to that of vein grafts [3, 4]. The success of an aortocoronary bypass operation in general is to a large degree dependent on the structural integrity of the grafts used. The damage done to the endothelium during the preparation and storage of the grafts is presently considered to be of prime importance for early graft failure [5]. With the increasing frequency of minimally invasive aortocoronary bypass procedures associated with a smaller and more complicated access to the mammary arteries [6], this consideration has to be applied to the mammary harvest as well. So far, the left LIMA has already been taken down by use of the harmonic scalpel in minimally invasive direct coronary artery bypass procedures [7]. It has also been used for the harvest of the radial arteries [8] and in laparoscopic surgery [9]. The reported results are altogether promising.
The aim of our study was to evaluate the extent of the damage done to the endothelium when the mammary artery is taken down with the harmonic scalpel as compared with the standard technique by using the high-frequency electrocauter.
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Material and methods
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Dissection instruments
The harmonic scalpel used (Ultrasonic; Ethicon, Hamburg, Germany) consists of a generator, a hand piece with a connecting cable, a blade system (we used the 5-mm blade), and a foot pedal. The blade vibrates longitudinally with a frequency of 55,000 Hz. Different from the high-frequency cauter, there is no conduction of electricity. The effect (the denaturation of proteins) is done completely mechanically. The depth of penetration of the scalpel is regulated by the pressure applied to the scalpel.
For the control group, a conventional high-frequency electrocauter was used (Force 40; Valleylab, Boulder, CO).
Patients
Twenty-four consecutive patients with a proximal left anterior descending artery stenosis whose IMA was harvested during an aortocoronary procedure were randomly split into two groups: group 1 (12 patients), the IMA was harvested using the harmonic scalpel; group 2 (12 patients), the IMA was harvested using the high-frequency electrocauter.
With the patients written informed consent, the IMAs were taken down well over their distal bifurcation. A distal tissue sample for scanning electron microscopic (SEM) evaluation of the endothelium was taken from each graft. Additionally, a second tissue sample from 7 patients of group 1 and 10 patients of group 2 was collected. Those samples were used to compare the effects on the endothelium when either the harmonic scalpel or the high-frequency cauter was used closely to the vessel for about 1 second. Care was taken that there was no direct contact between the IMA and the instruments. All samples were evaluated by SEM by three independent examiners.
Score system
The score system for the description of the endothelial damage [10] was: 1, completely confluent endothelium; 2, partially confluent endothelium; 3, loosely netted endothelium; 4, islands of endothelium; 5, no endothelium. All grafts were macroscopically examined for visible carbonization damages.
Statistical analysis
Results are presented as the mean ± the standard deviation. The Mann-Whitney test was used to analyze differences between groups. A p value of less than 0.05 was considered significant.
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Results
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If a distance of more than 0.5 cm between the IMA and the edges of the IMA pedicle was kept, we could not detect significant morphological differences in the two groups (Figs 1, 2). All samples showed a completely confluent endothelium. When the distance of the pedicle to the IMA was less than 0.5 cm, we found carbonization damages on the outer layer of the IMA on all grafts of group 2; there was no damage in group 1. The endothelial morphology of group 1 was hardly altered, whereas group 2 showed considerable endothelial cell losses (Table 1).

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Fig 1. Completely confluent endothelium after IMA harvest using the harmonic scalpel, with a tissue pedicle of at least 0.5 cm to the IMA.
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Fig 2. Completely confluent endothelium after IMA harvest using the high-frequency electrocauter, with a tissue pedicle of at least 0.5 cm to the IMA.
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If used immediately adjacent to the vessel, we found a dissiminated loosening of the cells from the subendothelial matrix in group 1, but in no instance a total loss of endothelial cells. Group 2 showed a total loss of the vascular endothelium in all samples (Figs 3, 4).

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Fig 3. Beginning detachment of the endothelial cells with no pedicle (IMA harvest with harmonic scalpel).
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Fig 4. Total loss of endothelial cells with no pedicle (IMA harvest with high-frequency electrocauter).
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Comment
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The harmonic scalpel enables a safe harvest of the IMA. Even by accidental contact of the instrument with the IMA, there is no irreversible damage done to the endothelium. Although the IMA takedown is more time consuming using the harmonic scalpel and although the positive effect on the endothelium preservation only seems to be significant when the preparation is done closely to the IMA, the harmonic scalpel should prove itself very helpful when there are anatomical problems to generate a big enough pedicle (especially in slim patients or in patients who undergo reoperations). There should also be a considerable benefit when the IMA is taken down in a minimally invasive technique because of the reduced damage to the endothelium if the vessel is touched accidently. On the other hand, it should be a prerequiste when using the high-frequency electrocauter that there is a big enough tissue pedicle taken down on either side of the IMA. This corroborates with findings from laparoscopic usage of high-frequency electrocoagulation where there is a safe distance from the organ demanded [11]. Our results should also be kept in mind when the IMA is harvested in a skeletonizing technique [12] during a conventional aortocoronary bypass operation.
In conclusion, the harmonic scalpel helps to optimize the quality of IMA bypass grafts by reducing the damage done to the endothelium.
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References
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Accepted for publication December 13, 1999.
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