A rare case of left internal mammary artery disease before bypass surgery

To the Editor Tripathi et al. (1) presented the interesting case of a patient whose left internal thoracic artery (ITA) contained a tight proximal stenosis thereby it could not be used as a graft to the left anterior descending artery. This case reminds us that although the ITA is highly resistant to atherosclerosis it is not completely immune with a reported angiographic incidence of significant atherosclerosis of only 2% (2). The authors are to be commended because, despite the absence of any clinical clues favoring stenosis of the subclavian artery (SCA) or severe peripheral vascular disease justifying preoperative SCA/ITA angiography they decided to obtain a left ITA angiogram thereby facilitating planning the revascularization procedure with a saphenous vein graft. Consequently, continued postoperative ischemia that would have been the case if an undiagnosed severely narrowed left ITA had been used as a graft, had been avoided (3). Yet, if we hypothesize that the left ITA presented in the article in question was free of significant atherosclerosis, did it show any anatomical feature that could potentially complicate bypass surgery hence requiring surgical attention? The answer is yes and that is the aberrant origin of the left ITA from the third (extrascalenic) part of the SCA that is nicely depicted in the angiographic images illustrating Tripathi et al’s (1) article. The ITA usually arises opposite the origin of the thyrocervical trunk, directly from the inferior surface of the first (intrascalenic) part of the SCA that is medial to the scalenous anterior muscle (4). Origination of the ITA from the third (extrascalenic) part of the SCA that extends from the lateral margin of the sclalenous anterior muscle to the outer border of the first rib is a rare anatomical variation with a reported incidence rate of 0.5% to 1.0% in anatomical studies and 1.5% in one angiographic study. During surgery, the usually arising ITA is frequently mobilized high enough to allow for sequential grafting or prevent graft stretching potentially leading to kinking and consequent continued postoperative ischemia (5). In such cases, surgeons discontinue dissection at the thoracic inlet just beyond the first rib, when the anterior border of the subclavian vein is visualized (6). Accordingly, an ITA with origin from the third (extrascalenic) part of the SCA that follows an oblique extrathoracic course at the inner border of the first rib for a short distance before curving behind the first rib to become endothoracic can easily be injured at the level of the first rib by a surgeon who is not aware of its presence and performs high mobilization assuming that a usually arising ITA that follows a relatively straight course at that site is present (4, 7). Therefore, knowledge of the presence of such a laterally arising ITA in patients undergoing bypass graft surgery is important to allow for preoperative planning of the surgical technique in order to avoid ITA graft injury during harvesting that could potentially lead to continued postoperative ischemia or prolonged surgical times owing to the need for modification of the grafting strategy. Furthermore knowledge of the presence of such an anomalous ITA is important during insertion of central venous catheters or pacemaker leads through the subclavian vein (4, 8). Inadvertent injury of the ITA may occur during such procedures and in contrast to the usually arising ITA, an ITA arising from the third (extrascalenic) part of the SCA is susceptible to such injury anywhere across its extrathoracic course (4); therefore it might be prudent to switch to the contralateral subclavian vein. In conclusion, ITA angiography performed prior to coronary artery bypass surgery should be scrutinized not only for significant atherosclerosis but also for variations in ITA anatomy that are known to influence surgical results. Proper diagnosis of an ITA with aberrant origin from the third (extrascalenic) part of the SCA facilitates safe harvesting during coronary artery bypass surgery. Knowledge of this anomaly is also important in order avoid the erroneous diagnosis of an occluded ITA during postoperative angiography. Conflict of interest: none References 1. Tripathi SP, Kerkar PG, Lanjewar CP, Phadke MS. A rare case of left internal mammary artery disease before bypass surgery. Eur Heart J. 2015 ;36:1349. 2. Singh RN. Atherosclerosis and the internal mammary arteries. Cardiovasc Intervent Radiol. 1983;6:72-7. 3. Ochi M, Yamauchi S, Yajima T, Bessho R, Tanaka S. The clinical significance of performing preoperative angiography of the internal thoracic artery in coronary artery bypass surgery. Surg Today 1998;28:503-8. 4. Andreou AY, Iakovou I, Vasiliadis I, Psathas C, Prokovas E, Pavlides G. Aberrant left internal thoracic artery origin from the extrascalenic part of the subclavian artery. Exp Clin Cardiol 2011;16:62-4. 5. Andreou AY, Georgiou GM, Avraamides PC. Stenting for an internal mammary artery graft kink. Arch Cardiovasc Dis. 2011;104:423-4. 6. LoCicero III J, Hoyne WP, LoCicero MS, Cochard L, Sanders Jr. JH. Anatomic variations of the phrenic nerve at the superior thoracic aperture (thoracic inlet): Implications for the cardiothoracic surgeon. Clin Anat. 1988;1:125-29. 7. Bauer EP, Bino MC, von Segesser LK, Laske A, Turina MI. Internal mammary artery anomalies. Thorac Cardiovasc Surg. 1990;38:312-5. 8. Chemelli AP, Chemelli-Steingruber IE, Bonaros N, Luckner G, Millonig G, Seppi K, Lottersberger C, Jaschke W. Coil embolization of internal mammary artery injured during central vein catheter and cardiac pacemaker lead insertion. Eur J Radiol. 2009;71:269-74.

Title: A rare case of an aberrant and diseased left internal thoracic artery Authors: Andreas Y. Andreou, MD, FESC, FACC Institutional Affiliation: Department of Cardiology, Limassol General Hospital, Limassol, Cyprus Address for correspondence: Andreas Y. Andreou, MD, Department of Cardiology, Limassol General Hospital, Nikeas street, Pano Polemidia, Postal code 3304, PO Box 56060, Limassol, Cyprus Telephone: +357-25801437; Fax: +357-25801432; E-mail: [email protected] To the Editor Tripathi et al. (1) presented the interesting case of a patient whose left internal thoracic artery (ITA) contained a tight proximal stenosis thereby it could not be used as a graft to the left anterior descending artery. This case reminds us that although the ITA is highly resistant to atherosclerosis it is not completely immune with a reported angiographic incidence of significant atherosclerosis of only 2% (2). The authors’ are to be commended because, despite the absence of any clinical clues favoring stenosis of the subclavian artery (SCA) or severe peripheral vascular disease justifying preoperative SCA/ITA angiography they decided to obtain a left ITA angiogram thereby facilitating planning the revascularization procedure with a saphenous vein graft with a consequent avoidance of continued postoperative ischemia that would have been the case if an undiagnosed severely narrowed left ITA had been used as a graft (3). Yet, if we hypothesize that the left ITA presented in the article in question was free of significant atherosclerosis, did it show any anatomical feature that could potentially complicate bypass surgery hence requiring surgical attention? The answer is yes and that is the aberrant origin of the left ITA from the third (extrascalenic) part of the SCA that is nicely depicted in the angiographic images illustrating Tripathi et al’s (1) article. The ITA usually arises opposite the origin of the thyrocervical trunk, directly from the inferior surface of the first (intrascalenic) part of the SCA that is medial to the scalenous anterior muscle (4). Origination of the ITA from the third (extrascalenic) part of the SCA that extends from the lateral margin of the sclalenous anterior muscle to the outer border of the first rib is a rare anatomical variation with a reported incidence rate of 0.5% to 1.0% in anatomical studies and 1.5% in one angiographic study. During surgery, the usually arising ITA is frequently mobilized high enough to allow for sequential grafting or prevent graft stretching potentially leading to kinking and consequent continued postoperative ischemia (5). In such cases, surgeons discontinue dissection at the thoracic inlet just beyond the first rib, when the anterior border of the subclavian vein is visualized (6). Accordingly, an ITA with origin from the third (extrascalenic) part of the SCA that follows an oblique extrathoracic course at the inner border of the first rib for a short distance before curving behind the first rib to become endothoracic can easily be injured at the level of the first rib by a surgeon who is not aware of its presence and performs high mobilization assuming that a usually arising ITA that follows a relatively straight course at that site is present (4, 7). Therefore, knowledge of the presence of such a laterally arising ITA in patients undergoing bypass graft surgery is important to allow for preoperative planning of the surgical technique in order to avoid ITA graft injury during harvesting potentially leading to continued postoperative ischemia or prolonged surgical times owing to the need for modification of the grafting strategy. Furthermore knowledge of the presence of such an anomalous ITA is important during insertion of central venous catheters or pacemaker leads through the subclavian vein (4, 8). Inadvertent injury of the ITA may occur during such procedures and in contrast to the usually arising ITA, an ITA arising from the third (extrascalenic) part of the SCA is susceptible to such injury anywhere across its extrathoracic course (4); therefore it might be prudent to switch to the contralateral subclavian vein. In conclusion, ITA angiography performed prior to coronary artery bypass surgery should be scrutinized not only for significant atherosclerosis but variations in ITA anatomy that are known to influence surgical results. Proper diagnosis of an ITA with aberrant origin from the third (extrascalenic) part of the SCA facilitates safe harvesting during coronary artery bypass surgery and avoiding the erroneous diagnosis of an occluded ITA during postoperative angiography. Conflict of interest: none References 1. Tripathi SP, Kerkar PG, Lanjewar CP, Phadke MS. A rare case of left internal mammary artery disease before bypass surgery. Eur Heart J. 2015 ;36:1349. 2. Singh RN. Atherosclerosis and the internal mammary arteries. Cardiovasc Intervent Radiol. 1983;6:72-7. 3. Ochi M, Yamauchi S, Yajima T, Bessho R, Tanaka S. The clinical significance of performing preoperative angiography of the internal thoracic artery in coronary artery bypass surgery. Surg Today 1998;28:503-8. 4. Andreou AY, Iakovou I, Vasiliadis I, Psathas C, Prokovas E, Pavlides G. Aberrant left internal thoracic artery origin from the extrascalenic part of the subclavian artery. Exp Clin Cardiol 2011;16:62-4. 5. Andreou AY, Georgiou GM, Avraamides PC. Stenting for an internal mammary artery graft kink. Arch Cardiovasc Dis. 2011;104:423-4. 6. LoCicero III J, Hoyne WP, LoCicero MS, Cochard L, Sanders Jr. JH. Anatomic variations of the phrenic nerve at the superior thoracic aperture (thoracic inlet): Implications for the cardiothoracic surgeon. Clin Anat. 1988;1:125-29. 7. Bauer EP, Bino MC, von Segesser LK, Laske A, Turina MI. Internal mammary artery anomalies. Thorac Cardiovasc Surg. 1990;38:312-5. 8. Chemelli AP, Chemelli-Steingruber IE, Bonaros N, Luckner G, Millonig G, Seppi K, Lottersberger C, Jaschke W. Coil embolization of internal mammary artery injured during central vein catheter and cardiac pacemaker lead insertion. Eur J Radiol. 2009;71:269-74.