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Eur J Cardiothorac Surg 2003;23:56-59
© 2003 Elsevier Science NL

Internal thoracic artery flow competition: studies in a canine H-graft model

Division of Cardiothoracic Surgery, Beth Israel Deaconess Medical Center, LMOB 2A, 110 Francis Street, Boston, MA 02215, and Harvard Medical School, Boston, MA, USA

Received 17 July 2002; received in revised form 9 September 2002; accepted 1 October 2002.

* Corresponding author. Tel.: +1-617-632-8381; fax: +1-617-632-8287
e-mail: wcohn{at}caregroup.harvard.edu

Objective: Internal thoracic artery (ITA) flow competition is a diversion of graft flow through intact ITA branches with a net decrease in perfusion to the grafted coronary. Although a widely acknowledged phenomenon, the conditions under which flow competition occurs have not been established. This is examined in a canine H-graft model. Methods: Eight dogs had a right ITA segment interposed (H-graft) between their in situ left ITA (LITA) and the snared left anterior descending (LAD) coronary artery. Proximal LITA and H-graft flows were measured at baseline and during pacing-induced tachycardia, phenylephrine-induced hypertension, and nitroprusside-induced hypotension. Flows were measured with the distal LITA open and occluded. Two additional animals were subjected to eight separate 2-min periods of LAD ischemia, after which post-ischemic H-graft flow measurements were obtained with and without distal LIMA occlusion. Results: During baseline conditions, proximal LITA flow was greater when the distal LITA was open rather than occluded (46±15 versus 35±12 ml/min, respectively; P=0.002), but H-graft flow did not change significantly (32±18 versus 35±18 ml/min, respectively; P=0.21). Similarly, occlusion of the distal LITA had no impact on H-graft flow during tachycardia, hypertension, or hypotension. Only in animals subjected to transient LAD ischemia did H-graft flow increase with distal LITA occlusion, albeit marginally (65±7–70±9 ml/min, occluded versus open, respectively; P=0.04). Conclusions: Mild diversion of flow from the LAD was demonstrated during immediate post-ischemic coronary reperfusion only, and could not be elicited under any other physiologic condition. These data suggest that flow competition is unlikely to constitute a clinically significant limitation to the use of H-grafts or other modalities that leave ITA branches patent.

Key Words: Coronary artery bypass grafting • Internal thoracic artery • Coronary flow

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