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Ann Thorac Surg 1999;68:1636-1639
© 1999 The Society of Thoracic Surgeons

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Original Articles

Angiographic anatomy of the grafted left internal mammary artery

^a Department of Cardiology and Cardiac Surgery, University "G. D’Annunzio" of Chieti, Chieti, Italy

Address reprint requests to Dr Calafiore, Division of Cardiac Surgery, "G. D’Annunzio" University, S. Camillo de’ Lellis Hospital, Via C. Forlanini, 50, 66100 Chieti, Italy
e-mail: calafiore{at}unich.it

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. The hypothesis that persistence of undivided branches is a common finding after myocardial revascularization using the left internal mammary artery was explored.

Methods. Three hundred seven consecutive postoperative angiographies of the left internal mammary artery were considered. Seven were excluded because of occlusion or malfunction of the conduit or the anastomosis. Of the remaining 300, 150 were harvested through a left anterior small thoracotomy (group A) and 150 through a median sternotomy (group B). The persistence of undivided branches was recorded for each group.

Results. Common origin with other branches of the subclavian artery was present in 55 patients in group A and 54 in group B (p = not significant); the persistence of lateral costal branch was also equally distributed in both groups (15 and 17; p = not significant). The first intercostal artery was present in 5 patients in group A and in none in group B (p = not significant). Branches of 1 mm or more were more frequent in group A (34 versus 4, p < 0.001), as well as branches of less than 1 mm (140 versus 67; p < 0.001). Only 2 patients in group A had no branches versus 48 patients in group B (p < 0.001).

Conclusions. Common origin with other branches of the subclavian artery and persistence of the lateral costal branch are common aspects in the angiographic anatomy of the grafted left internal mammary artery. Moreover, new branches, sometimes wider than 1 mm, develop with time. These findings are independent from the harvesting technique, the left anterior small thoracotomy, or the median sternotomy. If flow competition between the coronary and noncoronary territories was a reality, coronary artery grafting with the left internal mammary artery would be unsuccessful since the beginning.

	Introduction

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The introduction into the clinical practice of the left internal mammary artery grafting through a left anterior small thoracotomy (LAST operation) [1–5] has pushed many surgeons to evaluate the influence of the persistence of undivided branches of the left internal mammary artery (LIMA) on the flow in the left anterior descending (LAD) artery. Even if some investigators reported episodic cases of flow competition, we were able to demonstrate that there was no difference in the flow reserve of partially or totally harvested LIMA [6]. Furthermore, Kern and colleagues [7], studying the flow pattern in a large undivided branch of the LIMA, found that after adenosine injection, it remained systolic, without any influence on the coronary flow, which was basically diastolic.

Three hundred postoperative angiographies were evaluated to determine whether the persistence of undivided branches was a finding present only when the LIMA was harvested during the LAST operation or also with conventional harvesting through a median sternotomy.

	Material and methods

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The last 154 postoperative angiographies obtained in patients who underwent a LAST operation (group A) were compared to the last 153 postoperative angiographies of patients who had myocardial revascularization through a median sternotomy (group B). In this latter group only the LIMA was included in this study. The end point of the study was August 31, 1998, and the study lasted 19 months.

As only the widely patent anastomoses were considered, 4 patients in group A (2 for occlusion and 2 for anastomosis/conduit malfunction) and 3 in group B (1 for occlusion and 2 for anastomotic/conduit malfunction) were excluded. The interval between operation and angiography was 4.2 ± 3.2 months, 2.4 ± 2.1 in group A and 6.0 ± 4.1 in group B. Whereas in group A all the anastomoses were performed on the LAD, in group B the LAD was the target vessel in 82 patients, the LAD and a diagonal branch in 17, a single marginal branch in 39, and two marginal branches in 12 patients. The angiographies were examined to evaluate the presence of a common origin of the LIMA with other branches of the subclavian artery; the lateral costal branch; the first intercostal branch; and branches wider or smaller than 1 mm. The absence of any LIMA branch was also recorded.

Surgical technique
Our technique of harvesting the LIMA during the LAST operation was recently reported [8]. When the median sternotomy was used, the LIMA was harvested in a skeletonized fashion [9].

Statistical analysis
Statistical analysis comparing two groups was performed with ² test. A p value less than 0.05 was considered significant.

	Results

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Table 1 shows the results of this study. Interestingly, new branches wider or smaller than 1 mm were present in the majority of patients, independently from the harvesting technique (Fig 1). Common origin with other branches of the subclavian artery is shown in Figure 2. The thoracic lateral branch was present equally in both groups (Fig 3). Only 2 patients in group A (1.3%) and 48 in group B (32%) showed complete absence of any branch from the LIMA (p < 0.001).

View larger version (77K): [in this window] [in a new window]   Fig 1. The left internal mammary artery, harvested through a median sternotomy, shows a new branch (A) that goes down to reach the epicardium near the anastomosis (B).

View larger version (84K): [in this window] [in a new window]   Fig 2. Common origin with the inferior thyroid artery and the suprascapular artery. The left internal mammary artery is harvested through a median sternotomy (A) and through a left anterior small thoracotomy (B). In B a lateral costal artery is present.

View larger version (81K): [in this window] [in a new window]   Fig 3. Presence of the lateral costal artery. The left internal mammary artery is harvested through a median sternotomy (A) and through a left anterior thoracotomy (B).

	Comment

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When the LAST approach for LAD grafting was reintroduced into the clinical practice, LIMA harvesting was criticized because, under direct vision, division of all the branches was impossible. The possibility of flow competition between the territory perfused by the muscular branches and the coronary territory depending on the LAD, was considered a potential complication of this technique [11]. However, from the physiologic point of view, the muscular and the coronary territories have different flow patterns, with a prevalent perfusion during systole the former, and during diastole the latter one [6].

A recent study by Henriquez-Pino and associates [12] emphasized the surgical anatomy of the mammary artery. They clearly demonstrated that in many patients the internal mammary artery originates together with other branches of the subclavian artery. We evaluated the postoperative angiograms of two groups of patients, according to the LIMA harvesting, to investigate whether the problem of persisting undivided branches was limited to one group or common to both groups.

With postoperative angiograms we found that this common origin with other branches was present in more than one-third of the patients. This means that the harvesting technique never reaches the origin of the mammary artery. These branches would have been the first cause of flow competition, if this existed. The lateral costal branch is present in 10% and 11.3% in group A and group B, respectively. The first intercostal branch was present in 7 patients in group A, but absent in all patients in group B. Interestingly, many new branches, of different sizes, appeared in different segments of the LIMA, where the artery was completely dissected during operation. This was a common finding, as the LIMA, in contact with the pleura, the pericardium, or the epicardium, seems to have the possibility to develop new branches, sometimes wider than 1 mm. Only in 2 patients in group A and in 48 patients in group B the LIMA showed no branches at all. This is attributable, in our opinion, to the mandatory intrapleural route of the LIMA in the LAST operation, which favors a strict contact with the pleura.

This study clearly demonstrates that, when the LIMA is harvested for use as a coronary graft, the persistence of undivided LIMA branches is not the exception but the rule. This is independent from the harvesting technique used. Moreover, the LIMA has a powerful stimulus to develop new branches. As a consequence, the possibility of flow competition is theoretically present not only in patients who undergo the LAST operation, but also in patients who have a median sternotomy. Fortunately, as can be shown physiologically, the amount of coronary flow is independent from the persistence of undivided LIMA branches [13, 14], provided that these branches have no diastolic perfusion themselves. If flow competition was a reality, myocardial revascularization with the LIMA would have caused several problems early on in coronary operations.

	References

Top Abstract Introduction Material and methods Results Comment References

 

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