1 
W. B. HOOD, JR. AND J. C. NORMAN 
47 
hand, studies in anesthetized animals do not 
show marked alterations in heart rate, left ven- 
tricular filling pressures are seldom markedly 
elevated, and hypotension and cardiogenic 
shock appeared to be potentiated. It seems clear 
that further studies of myocardial ischemia 
which are designed to simulate clinical situa- 
tions should utilize unanesthetized animals 
whenever this is feasible. 
GRADED VENTRICULAR FAILURE FROM 
OBSTRUCTION OF MULTIPLE CORONARY 
VESSELS 
Whereas obstruction of a single major coro- 
nary vessel in the dog usually results in mild to 
moderate left ventricular failure, complete oc- 
clusion of both the left anterior descending and 
circumflex vessels leads to marked cardiac de- 
compensation (Figure 9). Such severe ischemia 
cannot be long maintained without the demise 
of the animal. Extensive studies carried out in 
18 dogs have shown, however, that it is possible 
to produce total obstruction of one major coro- 
nary vessel and a partial stenosis of another, re- 
sulting in stable states of left ventricular 
failure.'^ In the majority of these animals, an- 
terior wall myocardial infarction was produced 
by occlusion of the left anterior descending cor- 
onary artery, the animals were allowed to re- 
cover for one or more weeks, and then partial 
obstruction of the circumflex coronary vessel 
was carried out. The degree of obstruction of 
the circumflex vessel is highly critical, and it is 
difficult to obtain a stable state of left ventricu- 
lar decompensation from manual inflation of 
the circumflex balloon. 
Several methods have been tested in an at- 
tempt to stabilize the preparation. By monitor- 
ing the pressure in the circumflex balloon, and 
holding this pressure constant, it is possible to 
produce left ventricular failure which is stable 
for many minutes (Figure 10). Recent testing 
with a more sophisticated method has also been 
carried out in our laboratory in three dogs. In 
this method the left atrial pressure is monitored 
and utilized to drive a servo-controlled pump- 
motor combination, which infuses or withdraws 
minute amounts of fluid from the circumflex 
balloon to hold left atrial pressure constant at a 
preselected level. Using this method it has been 
possible to stabilize left atrial pressure at a de- 
sired value in a range of 20-30 mm Hg for 
many hours.-" 
Of the total of 18 dogs studied with severe 
coronary ischemia, four have developed acute 
pulmonary edema, indicating the severity of the 
left ventricular ischemic lesion. In the future, 
more studies should be directed toward severe 
failure preparations. Present studies by many 
investigators often deal with preparations in 
which the degree of ischemic ventricular dam- 
age is slight, thus failing to simulate the clinical 
situation in which interventions are most likely 
to be required. An ideal preparation of severe 
left ventricular failure does not yet exist, how- 
ever, the servo-controlled method described 
above appears to hold considerable promise. 
We have not carried out studies of multiple 
vessel coronary occlusions in intact unanesthe- 
tized calves or pigs. However, studies of tran- 
sient double-vessel coronary occlusion in eleven 
anesthetized calves suggest that results similar 
to those in dogs would be obtained. The ex- 
tensive studies of LaFarge and Bernhard and 
coworkers utilizing left main coronary artery 
occlusion in intact unanesthetized calves indi- 
FiGURE 9. — Left ventricular pressure in a dog during transient occlusion of both the left anterior descending and 
circumflex coronary arteries. There is severe and progressive deterioration in left ventricular performance, 
as shown by the marked fall in systolic and rise in diastolic pressures. (By permission.^) 
