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

Eur J Cardiothorac Surg. 2003 Jan;23(1):56-9. doi: 10.1016/s1010-7940(02)00656-5.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Coronary Artery Bypass*
  • Coronary Disease / physiopathology*
  • Coronary Disease / surgery
  • Coronary Vessels / physiology*
  • Coronary Vessels / surgery
  • Dogs
  • Models, Animal
  • Myocardial Reperfusion
  • Postoperative Period
  • Regional Blood Flow
  • Thoracic Arteries / physiology*
  • Thoracic Arteries / surgery