Internal thoracic artery flow competition: studies in a canine H-graft model.
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.
Cohn
William E
WE
Division of Cardiothoracic Surgery, Beth Israel Deaconess Medical Center, LMOB 2A, 110 Francis Street, Boston, MA 02215, USA. wcohn@caregroup.harvard.edu
Ruel
Marc
M
Zhang
Jian Ping
JP
Sellke
Frank W
FW
Johnson
Robert G
RG
D000818:Animals; D001026:Coronary Artery Bypass; D003327:Coronary Disease / Q000503:physiopathology* / Q000601:surgery; D003331:Coronary Vessels / Q000502:physiology* / Q000601:surgery; D004285:Dogs; D023421:Models, Animal; D015425:Myocardial Reperfusion; D011184:Postoperative Period; D012039:Regional Blood Flow; D013895:Thoracic Arteries / Q000502:physiology* / Q000601:surgery