Ann Thorac Surg 2006;82:1919-1921
© 2006 The Society of Thoracic Surgeons
How To Do It
Protecting the Crossover Right Internal Thoracic Artery Bypass Graft With a Pedicled Thymus Flap
Giuseppe Gatti, MD*,
Aniello Pappalardo, MD,
Livio Gon, MT,
Bartolo Zingone, MD, FECTS
Cardiovascular Department, Division of Cardiac Surgery, Ospedali Riuniti di Trieste, Trieste, Italy
Accepted for publication January 12, 2006.
* Address correspondence to Dr Gatti, Cardiovascular Department, Division of Cardiac Surgery, Ospedali Riuniti di Trieste, Ospedale di Cattinara, Polo Cardiologico, Strada di Fiume, 447, Trieste, 34100 Italy. (Email: giusep.gatti{at}tiscali.it).
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Abstract
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The right internal thoracic artery graft is placed in jeopardy during repeat sternotomy as it crosses the aorta anteriorly to reach its left-sided coronary targets. We have devised a way of protecting it by means of a pedicled flap taken from the thymic remnants. The flap is easily developed without unduly increasing operative time and morbidity, and it is expected to prevent inadvertent injuries to the graft in the case of mediastinal reentry. Starting in 1999, suitable flaps were obtained in 955 of 1,034 patients (92.4%) receiving an anteaortic crossover right internal thoracic artery-to-coronary graft in our division.
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Introduction
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The benefit of using two internal thoracic arteries (ITAs) versus one depends on both grafts being devoted to the left coronary system [1]. Although the right internal thoracic artery (RITA) can be taken down and used as a free graft from either the aorta or the left ITA, many surgeons would regard the in situ RITA grafting of the left coronary branches as an ideal proxy of the successful and well established in situ left ITA to the left anterior descending coronary artery graft.
There is no question that the need for crossing the midline behind the sternum is a distinct disadvantage of the in situ RITA, as it exposes the graft to the risk of injury in the case of mediastinal reentry [2, 3]. We have devised a simple technique to overcome this problem based on a pedicled flap made from the thymic remnants that will completely cover up and protect the RITA.
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Technique
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After complete median sternotomy, loose areolar tissue is cleared off the thymic remnants and the anterior pericardium. Dissection is then started by incising the thin fascia that envelops the thymus at the point where the innominate vein enters the mediastinum from the left. The incision parallels the midline and continues along the left thymic edge down to its caudal end. An anatomical plane is initially developed to dissect the thymus away from the left mediastinal pleura, although aiming somewhat medially to preserve the pleura intact, and hemostasis is carefully pursued while numerous small vessels are divided between hemoclips. Once the pericardium is reached, the thymus is raised by blunt dissection progressing toward the right and cranially until the superior vena cava and the innominate vein are well seen. With leftward tension on the thymus, the flap is then completed by developing an anatomical plane along the right mediastinal pleura until the superior vena cava is reached again. It is useful to raise the flap cranially from the vena cava and have the confluence of the right internal thoracic vein well in sight at this time so as to facilitate later harvesting of the proximal segment of the RITA. Now the thymus hinges on its cranial end, which is carefully preserved to avoid injury to its vascularization. In this manner, flaps of 7 to 14 cm of length can be obtained (Fig 1A). Next, to create as short a pathway as possible for the grafts, the usual pericardial opening is prolonged cranially by dividing its reflections from the aorta on both sides and from the left pulmonary artery as well. The arch is cleared of any intervening fat tissue, carefully clipping mediastinal veins. This provides a deep and fairly straight groove for the left ITA, whereas on the right side the RITA graft lies on the vena cava and the distal ascending aorta. Skeletonizing both ITAs up to their proximal end is made easier and safer by having the thymus already mobilized and the venous structures well exposed beforehand [4].
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Fig 1. (A) The pedicled thymus flap at the end of preparation. (B) The flap at the conclusion of operation; it will cover both the in situ right internal thoracic artery (RITA) graft crossing over the ascending aorta toward the left anterior descending (LAD) coronary artery and the aortic anastomosis of a saphenous vein (SV) graft to the right posterolateral (RPL) coronary artery. The in situ left internal thoracic artery graft to the obtuse marginal coronary artery is not visible.
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At the time of sternal closure, the flap, which had been stored in the jugular recess, is placed back into its natural position over the ascending aorta, completely covering the crossover RITA graft (Fig 1B).
The thymus flap technique has been used consistently at our unit by one surgeon since 1987, and has been gradually adopted by other surgeons. Between January 1999 and October 2005, the in situ RITA anteriorly crossing the aorta toward the left-sided targets was used in 46.2% of patients (n = 1,034) undergoing coronary surgery. Suitable flaps were obtained in 92.4% of patients (n = 955). Sixty-five hypoplastic thymus glands were a priori not used, and 14 thymic flaps with small or poorly vascularized pedicles were rejected.
Twenty-five patients required re-exploration for bleeding. In 26 patients, early mediastinal reentry was required for sternal rewiring (n = 13) or debridement for deep wound infection (n = 13), including mediastinitis in 3 patients. There were no injuries to crossover RITA grafts or complications referable to the flap.
Seven patients with crossover RITAs underwent reoperation during the study period, and a standard re-sternotomy with an oscillating saw was used in 5 of them. Lateral angiography of the ITA grafts was performed prior to each reoperation. In 4 patients with a valve operation, both ITAs were covered with the flap and could be easily preserved, whereas in the fifth patient the RITA graft was occluded. A clamshell approach was used in 2 cases due to uncertainty as to how the RITA had been managed (both initially treated before 1999).
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Comment
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Thymic flaps have been previously reported for use in tracheal and bronchial reconstructive operations [5], although our technique is intended to provide a mechanical protection to the crossover RITA rather than facilitate healing around the graft. In our practice it has proved effective, reproducible, and complication-free at the cost of 5 to 10 minutes of extra operative time. This compares favorably with a number of alternatives including pericardial closure with biological or synthetic fabric patches [6], use of synthetic membranes to wrap around the graft [7], or vascular prostheses to include the graft [8], all of them sharing the disadvantage of introducing foreign materials and the potential for untoward effects [9, 10], not to mention their additional cost. Although the practice of routing the in situ RITA behind the aorta through the transverse sinus is quite straightforward and effective, we have come to prefer the anteaortic course as it extends the scope of the graft and facilitates hemostasis.
Developing the thymic flap as described possesses additional advantages besides preventing the RITA crossover adhering to the sternum. First we have found that mobilizing the thymus before bilateral ITA harvesting greatly facilitates the dissection of the grafts at their cranial end, thus allowing additional length to be gained and providing fairly short and direct pathways to targeted coronary arteries. The flap also contributes to filling with viable autologous tissue an otherwise empty space, probably decreasing the risk of deep wound infection gaining the mediastinum. It causes no tension, distortion, or compression of the RITA graft coursing underneath, which remains accessible for hemostasis. The flap may also give protection to aortic anastomoses of saphenous vein grafts and to the ascending aorta (Fig 1B). Finally, the RITA graft consistently crosses the aorta close to the cannulation site where it will be predictably found in case of reentry. There could be no better trade-off for an usually rejected tissue.
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References
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- Malm T, Bowald S, Bylock A, Busch C. Prevention of postoperative pericardial adhesions by closure of the pericardium with absorbable polymer patches: an experimental study J Thorac Cardiovasc Surg 1992;104:600-607.[Abstract]
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Abstract
Introduction
