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Ann Thorac Surg 1997;64:1041-1045
© 1997 The Society of Thoracic Surgeons

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Original Article: Cardiovascular

Surgical Anatomy of the Internal Thoracic Artery

Division of Descriptive Anatomy, Department of Morphology, and Division of Cardiovascular Surgery, Department of Surgery, Escola Paulista de Medicina, Federal University of São Paulo, São Paulo, Brazil

Accepted for publication April 5, 1997.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background. The internal thoracic artery (ITA) has become increasingly important in coronary artery bypass grafting due to the excellent long-term results. This study reviews its anatomic characteristics.

Methods. The ITAs of 100 cadavers were examined and their origin, relation to the phrenic nerve, presence of lateral costal branch; origin of pericardiacophrenic arteries, length, level and type of ITA termination, relation with the transverse muscle of thorax, collateral parietal branches, and distance between the ITA and sternal margins were studied.

Results. The ITA was present in all cases, originating directly from the subclavian artery or from a common trunk with other arteries. Its length was 20.4 cm on average, and the most frequent level of termination was at the sixth intercostal space, existing as a bifurcation in 93% and as a trifurcation in 7%. The pericardiacophrenic artery originated from the ITA in 89%. The lateral costal branch was present in 15% of the cases. The ITA was covered by the transverse muscle of the thorax for 7.5 cm (average) and was crossed anteriorly by the phrenic nerve in 70.0%.

Conclusions. Information provided by this study may contribute to knowledge of its anatomic characteristics and in turn help prevent complications in ITA dissections.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
The internal thoracic artery (ITA) has gained increased importance and extensive use in coronary bypass grafting because of long-term better patency rate and improvement in both the duration and quality of survival of patients when compared with the results of saphenous vein grafts [1–3].

Prior anatomic studies examined this artery, but little emphasis has been placed on its specific characteristics for use in myocardial revascularization. Therefore, a review of its anatomic characteristics is necessary, to pursue the possible extension of its utilization and avoid intraoperative and postoperative complications.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
This study examined 100 fresh adult cadavers of individuals of either sex (56 men and 44 women) and different races (59 white, 41 black and mixed), with ages varying from 20 to 84 years, obtained from Escola Paulista de Medicina of Federal University of São Paulo.

The anterior sternocostal wall of the thorax was removed with a portion of the ascending aorta, the aortic arch, the subclavian and axillary arteries, and the phrenic nerves, the later being sectioned above the subclavian artery. The left ITA (LITA) was injected with yellow Neoprene latex, whereas the right ITA (RITA) was injected with red latex. The specimens were subsequently fixed in 10% formaldehyde solution.

Macroscopic and mesoscopic dissection were performed and the following were studied: (1) origin of the internal thoracic arteries, (2) the relation to the corresponding phrenic nerve, (3) presence of lateral costal branch, (4) origin of pericardiacophrenic arteries, (5) length of ITA, (6) level and (7) type of termination point of ITA, (8) relation with the transverse muscle of thorax, (9) collateral parietal branches (anterior intercostal, sternal and perforating), and (10) the distance between the ITA and sternal margins. Examples of the specimens are shown in Figures 1 through 7.

View larger version (139K): [in this window] [in a new window]   Fig 1. . Left (LITA) and right internal thoracic arteries (RITA), with vertical trajectory, bifurcating (bif.) at the seventh intercostal space. The right superior epigastric (RSEA) and right musculophrenic (RMA) arteries are detailed. The sternal (st) and intercostal (ic) branches also can be seen.

View larger version (141K): [in this window] [in a new window]   Fig 2. . View of the tortuous left (LITA) and right internal thoracic arteries (RITA), covered by the transverse muscle of the thorax (TMT) and accompanied by the right internal thoracic vein (RITV).

View larger version (144K): [in this window] [in a new window]   Fig 3. . The trifurcation (trif.) of the right internal thoracic artery (RITA) is seen, dividing into the right musculophrenic artery (RMA), right superior epigastric artery (RSEA), and the diaphragmatic branch (DB). The accompanying right internal thoracic vein (RITV) also can be seen.

View larger version (136K): [in this window] [in a new window]   Fig 4. . Large lateral costal branch (LCB) originating from the right internal thoracic artery (RITA). Also shown is the pericardiacophrenic artery (PPA) that accompanies the phrenic nerve (PN).

View larger version (148K): [in this window] [in a new window]   Fig 5. . Note the left internal thoracic artery (LITA) originating in a common trunk with the suprascapular (SSA) and the transverse cervical (TCA) arteries from the subclavian artery.

View larger version (144K): [in this window] [in a new window]   Fig 6. . The crossing of the phrenic nerves with the internal thoracic arteries is seen. The left phrenic nerve (LPN) crosses anteriorly with the left internal thoracic artery (LITA), and the right phrenic nerve (RPN) crosses posteriorly the right internal thoracic artery (RITA).

View larger version (149K): [in this window] [in a new window]   Fig 7. . Anterior intercostal branch (ic) and the sternal branch (st) originating from the common trunk (tr) of the right internal thoracic artery (RITA).

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Origin of Internal Thoracic Arteries
The ITA was present in all individuals studied. The LITA originated directly from the subclavian artery in 70% of cases and from a common trunk with other arteries in 30%. In 95% of cadavers studied the RITA originated from the subclavian artery whereas 5% arose from a common trunk with other arteries. The distribution can be seen in Table 1.

Relation With Phrenic Nerves
Both phrenic nerves crossed the ITAs anteriorly in 54% of the cases and posteriorly in 14%. The left phrenic nerve crossed the artery anteriorly and the right phrenic nerve posteriorly in 12% of the cases, whereas the reverse relationship was observed in 20%.

The distance between the origin of the LITA and the point where it crossed the left phrenic nerve varied from 0.5 to 4.4 cm, the average being 1.9 ± 0.7 cm. There was a statistically significant difference between male and female individuals and between white and nonwhite individuals (p = 0.048). The distance between the origin of the RITA and the point where it crossed the RPN varied from 0.3 to 4.5 cm, the average being 1.5 ± 0 7 cm. A statistically significant difference was observed between white and nonwhite individuals (p = 0.043).

When the distance from the origin of the ITAs to the crossing point with the phrenic nerves was compared, there was a statistically significant difference between the right and left side (p = 0.0001).

Presence of Lateral Costal Branch
The lateral costal branch was found in 15% of cases, with all lateral costal branches originating from the ITA. Bilateral presence was observed in 5% and unilateral incidence was 10%.

The distance between ITA origin and lateral costal branch origin varied from 1.3 to 3.8 cm with a mean of 2.5 ± 0.7 cm. On the right side the distance varied from 1.3 to 3.5 cm (mean, 2.3 ± 0.6 cm), whereas on the left side the distance varied from 2.0 to 3.8 cm (mean, 2.9 ± 0.6 cm).

Origin of Pericardiacophrenic Arteries
The pericardiacophrenic arteries originated from the ITA in 89% of cases, from thymic branches in 9.5%, and from the subclavian artery in 0.5%.

The distance between the origin of the ITA and the origin of the pericardiacophrenic artery varied from 1.9 to 7.6 cm, the mean being 4.3 ± 0.9 cm. On the right side the distance varied from 1.9 to 7.2 cm (mean, 4.2 ± 0.8 cm), whereas on the left side the distance varied from 2.5 to 7.6 cm (mean, 4.3 ± 0.9 cm).

Length of Internal Thoracic Artery
From the origin to the termination point, the length of ITA varied from 15.1 to 26.0 cm, with a mean of 20.4 ± 2.1 cm. The LITA varied from 16.2 to 26.0 cm (mean, 20.7 ± 2.1 cm) and the RITA varied from 15.1 to 25.1 cm (mean, 20.1 ± 2.0 cm). In male subjects, the mean length was 21.4 ± 2.0 cm, and in female subjects it was 19.8 ± 1.9 cm. Statistical analysis demonstrated a significant difference in values between male and female individuals and also between the values of RITA and LITA (p = 0.00003). The direction of the ITA was vertically rectilinear in 34% of cases studied, with medial concavity in 30%, a lateral vertical direction in 29%, and a tortuous course in 7%.

Termination Point Level of Internal Thoracic Artery
The most frequent termination point of both ITAs was at the level of the sixth rib. The distribution is detailed in Table 2.

Relation With the Transverse Muscle of the Thorax
The ITA was covered by the transverse muscle of thorax for a distance that varied between 1.7 and 16.6 cm (mean, 7.5 ± 2.7 cm) and its free portion varied from 5.7 to 20.6 cm, with a mean of 12.9 ± 2.5 cm. The LITA was covered for a distance varying from 2.5 to 13.7 cm (mean, 8.2 ± 2.7 cm), and its free portion varied from 5.7 to 19.7 cm (mean, 12.6 ± 2.6 cm). The RITA was covered for a distance varying from 1.7 to 16.6 cm (mean, 6.9 ± 2.7 cm), and its free portion varied from 7.0 to 20.6 cm (mean, 13.2 ± 2.5 cm).

Collateral Parietal Branches of Internal Thoracic Artery
The collateral parietal branches of the ITA are the anterior intercostal, sternal, and the perforating, which may originate isolated from the ITA or forming a trunk together. The anterior intercostal branches varied in number from 4 to 10, the sternal branches varied from 4 to 9, and the perforating from 3 to 6. A description of this distribution is shown in Table 3.

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
In 1895 the Basilea Nomina Anatomica denominated the ITA as the "internal mammary artery", a term largely used by authors in the literature. In 1936, in the Jena Nomina Anatomica, the denomination was changed to "internal thoracic artery", which also was referred to in 1955 in the Paris Nomina Anatomica [4]. "Internal thoracic artery" is considered to be the most appropriate name, as it possesses an informative and descriptive value, as the localization and distribution occur essentially at the interior of the thorax.

The ITA always originates from the subclavian artery, in isolation or in association with another artery. It was observed that the left side was significantly longer than the right. In men the ITA was found to be longer than that in women, probably due to the fact that the length of the thorax in women is generally shorter. It should be noted that the length of the ITA depended on the type of thorax, relating to the constitutional type of the individual.

The close relationship of the ITAs with the phrenic nerves could explain some cases of paralysis of the diaphragm observed postoperatively in myocardial revascularization operations using the ITA [5–7]. The ITA crosses the phrenic nerve obliquely, lateral to medial, sometimes anterior or posterior, tending to be quite variable at the site of intersection. Care should be taken in dissecting the ITA until several centimeters below the origin at the subclavian artery, to avoid inadvertent lesions of the phrenic nerves with the use of electrocautery. Paralysis of the diaphragm also could occur, resulting from ischemia of the phrenic nerve consequent to lesion of the pericardiacophrenic artery.

The loss of surgical result with recurrence of angina pectoris after myocardial revascularization using ITAs can occur by a steal phenomenon when the collateral branches are left unligated [8–10]. Care should be taken with the lateral costal branch, which is present in 15% of cases and which shows a large variability in terms of the level of its origin from the ITA. Also the lateral costal branch may present a similar caliber as the ITA, as shown in Figure 4. In addition, the origin of the left costal lateral branch is found to be in a more inferior position when compared with the right.

The most frequent level of termination of the ITA occurred at the sixth intercostal space, with a bifurcation into two branches in 93% and into three branches in 7% of cases.

The average distance between the ITA and the sternal margin was less at the level of the first intercostal space in relation to the level of the sixth space. It was noted that the ITA becomes more distant from the sternal margin as you descend throughout the thoracic cavity.

The ITA is found covered by the transverse muscle of the thorax in an extension compatible with approximately one third of its full length, being longer on the left side.

The collateral intercostal, sternal, and perforating branches can arise from the ITA in isolation or forming a trunk together. These branches deserve more attention because in ITA dissections, eventually there can be a diminishment of the sternal blood supply, which can lead to necrosis [11, 12]. Figure 7 demonstrates one sternal branch and one anterior intercostal branch arising from a single trunk of the ITA. Preservation of this trunk in ITA dissection can provide flow to the sternal branch through the connection of the anterior intercostal artery with the posterior intercostal branch, which originates from the aorta [13–15]. Small statistically significant anatomic differences were observed between the left and right ITAs.

In conclusion, this anatomic study offers aid to minimize or avoid clinical complications in patients who undergo myocardial revascularization with use of ITAs.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Address reprint requests to Dr Gomes, Division of Cardiovascular Surgery, Department of Surgery, Escola Paulista de Medicina, Federal University of São Paulo. Rua Botucatu 740, São Paulo, SP 04023-900, Brazil.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Enio Buffolo Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Henriquez-Pino, J. A. Articles by Buffolo, E. Search for Related Content PubMed PubMed Citation Articles by Henriquez-Pino, J. A. Articles by Buffolo, E.