Introduction
The excellent long-term outcomes obtained in coronary artery bypass grafting (CABG) using the internal thoracic artery (ITA) as a graft conduit are clearly established . Observational reports suggested improved long-term survival rates with bilateral ITA grafts . However, the harvest of bilateral ITA pedicles has been associated with an increased risk of sternal wound complications, especially in patients with obesity, diabetes, or pulmonary dysfunction .
The risk of sternal wound infection seems to depend partly on the ITA harvesting dissection technique. In patients receiving the bilateral ITA during CABG, some groups have used skeletonization technique and reported a low incidence of sternal wound infection, in contrast to a higher reported rate with ITA pedicle harvesting .
Sternal blood supply is mostly derived from the periosteal plexus fed by sternal branches of the ITA, as demonstrated in Arnold’s human anatomical work . We conducted a study to see the difference in sternal blood flow reduction by two ITA harvesting techniques in a canine model . After ITA pedicle harvesting, sternal blood flow decreased to 15% of the baseline, whereas after ITA skeletonized harvesting, it only fell to 29% of the baseline. This implies that preservation of the ITA’s surrounding tissues, including the internal thoracic vein (ITV), lymphatics, adipose tissue, and fascia, partially alleviates the loss of sternal blood supply. This in turn implies that fine skeletonization of the ITA is the preferable method of harvesting, in which those surrounding tissues are preserved ( Fig. 6.1 ). Dedicated groups have reported better clinical results and low rates of sternal wound complications with bilateral skeletonized ITA among diabetics or high-risk patients . It seems relatively quick and easy to harvest the ITA pedicle, but meticulous attention and considerable extra time are needed to harvest the ITA in skeletonized fashion if one uses fine hemoclips and scissors.
An ultrasonic scalpel (harmonic scalpel, Ethicon Endo-Surgery, Cincinnati, Ohio) was first introduced for harvesting skeletonized ITA by Higami et al. in 2000 . They also conducted a histological study on the harmonic scalpel’s capacity for safe sealing of vessels . The harmonic scalpel simplifies the delicate task of ITA skeletonization. The purpose of this chapter is to specify and explain the method and to show some technical details and pitfalls, in harvesting skeletonized ITA using the harmonic scalpel.
Harvesting of the skeletonized internal thoracic artery using the harmonic scalpel
We believe that there are three important technical tips to effectively perform ITA skeletonization, based on our experience ( Fig. 6.2 ):
- 1.
The ITA harvesting process should begin with an incision into the endothoracic fascia 1 cm medial and parallel to the ITV, after which the edge of the fascia can be grasped with forceps.
- 2.
It is crucial to find an appropriate plane and create a narrow gap between the ITA and the ITV, and between the ITA and the chest wall, preferably using the cold cautery tip (nonactivated electrocautery).
- 3.
Each branch from the ITA should be exposed for at least 2 mm so that the blunt tip of the harmonic scalpel can be applied 1 mm away from the ITA trunk to seal and cut the branch by inducing protein coagulation.
These crucial tips provide the best trauma-free ITA skeletonized harvesting. A secure surgical technique is as follows.
A median sternotomy is performed. Periosteal bleeding is controlled, and a Delacroix ITA retractor is used to elevate the left or right sternal half. The loose mediastinal tissue posterior to the sternum, and the medial part of the parietal pleural reflection, is gently pushed and dissected away using a low power electrocautery (in coagulation mode only). This maneuver exposes the posterior surface of the sternum where one can see or palpate the ITA and ITV through the transversus thoracis fascia.
Dissection usually begins at the midpoint of the ITA course, approximately 1 cm medial and parallel to the ITA and the ITV. The tip of the electrocautery is bent 45 degrees, and an initial cut of a few centimeters is made in the endothoracic fascia. Then the edge of the fascia is grasped with curved-tip forceps (DeBakey type or carbide tipped) and gently pulled posteriorly. The soft tissue is dissected away from the fascia using the cold cautery tip (the nonactivated electrocautery tip) as a dissector. The ITA and ITV are first visualized and exposed ( Fig. 6.3 ). The ITA can be gently teased away from the ITV, to open a narrow gap between the vessels. The ITA attached to the fascia edge is further separated from the chest wall ( Fig. 6.4 ). Forceps can hold the periadventitial soft tissue but should never grasp the ITA trunk. At this stage the perforating branches become visible in the space between the artery and the vein. This cut in the endothoracic fascia is extended distally and proximally, exactly parallel to the course of the ITA. Distally, the transversus thoracis muscle must be divided to expose the ITA down to the level of the xiphoid process. The separated space between the ITA and the ITV is created mostly by gently stroking the groove with the cold cautery tip.
Then, the harmonic scalpel dissecting hook is used. The harmonic scalpel is an ultrasonic instrument that produces mechanical vibration at 55,500 Hz. Application of the tip can raise tissue temperatures to about 80 degrees Celsius, much lower than the 300 degrees Celsius achieved with an electrocautery. The harmonic scalpel causes little charring, with less risk of damage to surrounding tissues. By simply applying the dissecting tip in the space between the ITA and the ITV, while gently pulling the fascia edge with forceps, one can clear away the fatty tissue using the cavitation effect of the harmonic scalpel. This exposes the branches of the ITA more clearly visible, and the blunt tip of the harmonic scalpel is gently touched to each branch at least 1 mm away from the ITA trunk, so as to seal the stump of each branch securely without causing any heat injury to the ITA trunk. Once a few anterior branches have been so treated, the grasped fascia edge is pulled further posteriorly. The intercostal or lateral branches become visible. The adipose tissue between these branches is touched and cleared away before these are sealed and divided. When these are finished, a few centimeters of the ITA trunk can be circumferentially separated from the ITV and chest wall. The tip of the forceps is inserted into the space between the artery and chest wall and gently pulled posteriorly, to further separate the ITA from the chest wall ( Fig. 6.5 ). With this traction the anterior and lateral branches are exposed to view.
