352 
SURGERY AND TRANSPLANTATION 
significant decrease in peripheral CCA pressure 
and a twofold increase in flow in the graft to 
the CCA. This residual CCA peripheral pres- 
sure of 41 mm Hg, as well as the failure of 
graft flow to elevate above 27 cc/min indicated 
an additional source of CCA collateral inflow, 
most likely from the right coronary artery. 
Khouri has observed a similar residual eleva- 
tion of peripheral CCA pressure after tempo- 
rary LAD occlusion, and also attributed this to 
communications with the right coronary artery.^ 
Occlusion of the LAD in the presence of col- 
laterals was always followed by reactive hy- 
peremia in the LAD peripheral bed. Nine of 10 
animals, however, demonstrated no CCA re- 
active hyperemia after graft occlusion, possibly 
indicating lack of ischemia due to collateral 
inflow. Temporary occlusion of the graft was 
accompanied in each animal by an increase in 
LAD flow implying an immediate reduction in 
collateral flow after graft insertion. During 
the two and one-half hour period of observation, 
no further decrease in collateral flow could be 
demonstrated in this model. Khouri has recently 
demonstrated almost complete regression of 
flow through collaterals within three hours 
after release of CCA obstruction in the awake, 
intact dog.3 Our preparation showed a decrease 
in collateral flow, but not a complete regression, 
and this diflference may be due to the length of 
observation, the effects of the anesthetic agent, 
or again to a possible mechanical alteration 
within the collateral vessel wall. 
Reversal of direction of flow through collat- 
eral channels has not been experimentally dem- 
onstrated. In the present study, peripheral CCA 
pressure was markedly decreased by clamping 
the LAD, but there was not a corresponding 
magnitude in reduction of LAD peripheral pres- 
sure after graft occlusion. This may indicate 
unidirectional transmission of pressure through 
collateral channels, but may be influenced by 
communications with the right coronary artery 
as indicated by the control value of LAD periph- 
eral pressure of 23 mm Hg. Observations of 
graft flow and pressure made during insertion 
of human aorto-coronary saphenous vein bypass 
grafts have not clarified this situation.^'S Fur- 
ther human and animal observations are needed 
to determine the ability of flow in collateral | 
vessels to reverse direction. ; 
SUMMARY 
The effects of aorto-coronary artery vein by- | 
pass graft on coronary hemodynamics in the i 
presence and/or absence of coronary collateral I 
flow were examined in an experimental canine i 
model. In animals without coronary collaterals, 
construction of a bypass graft to the circumflex 
coronary artery produced no significant quan- 
titative or qualitative changes in distal or ad- 
jacent coronary hemodynamics. Proximal cor- 
onary inflow was decreased, however, and i 
functional occlusion occurred if the proximal 
segment had significant stenosis prior to bypass. 
In animals which underwent bypass six weeks j 
after ameroid constriction of the circumflex I 
coronary artery, significant collateral vessels ' 
were present. These were associated with an | 
elevation of peripheral circumflex pressure and I 
reduction of graft flow. Occlusion of the left i 
anterior descending artery in these animals in- | 
creased graft flow and reduced peripheral cir- ' 
cumflex artery pressure. Conversely, after graft 
occlusion, left anterior descending artery flow 
increased and peripheral pressure decreased. 
The data document an initial decrease in aorto- ' 
coronary graft flow in the presence of extensive 
collateral vessels, but demonstrate a reduction 
in collateral flow following graft insertion. 
REFERENCES 
1. Sghaper, W., Schaper, J., Xhonneux, R. and Van- 
DESTEENE, R. The Morphology of Intercoronary 
Anastomoses in Chronic Coronary Artery Occlusion 
Cardiovasc. Res. 3:315, 1969. 
2. Johnson, W. D., Flemma, R. J., Manley, J. C. and 
Lepley, D. The Physiologic Paramenters of Ven- 
tricular Function as Affected by Direct Coronary 
Surgery J. Thoracic Cardiovasc. Surg. 60:483, 1970. 
3. Khouri, E. M., Gregg, D. M. and McGranahan, 
Jr., G. M. Regression and Reappearance of Coronary 
Collaterals Am. J. Physiol. 220:655, 1971. 
4. Rees, G., Bristown, J. D., Dremkau, E. L., Green, 
G. S., Herr, R. H., Griswold, H. E. and Starr, A. 
Influence of Aortocoronary Bypass Surgery on Left 
Ventricular Function N. Engl. J. Med. 284:1116, 
1971. 
5. Wakabayashi, a., Beron, E., Lou, M. A., Mino, J. 
Y., DA Costa, I. A., and Connolly, J. E. Physio- 
logical Basis for the Systemic-To-Coronary Artery 
Bypass Graft. Arch. Surg. 100:17, 1970. 
