W. B, HOOD, JR. AND J. C. NORMAN 
43 
Prior to permanent vessel occlusion, one or 
more "trial" occlusions, using an increasing vol- 
ume of fluid in the balloon, is employed to ascer- 
tain the volume required for ischemia to occur. 
Subsequently, permanent occlusion is carried 
out, resulting in myocardial infarction. In our 
initial studies, permanent inflation of a single 
coronary artery balloon cuff was performed 
over a period of one-half hour or more using a 
microinfusion pump." It was subsequently de- 
termined that occlusion may be safely carried 
out over a period of ten to fifteen minutes by 
manual inflation of the balloon cuff without an 
untoward incidence of ventricular fibrillation, 
and this method is now used exclusively. Onset 
of myocardial infarction may be determined by 
electrocardiographic and hemodynamic changes 
(vide infra), and subsequently by a rise in 
serum enzymes (Figure 2) . 
RESULTS OF STUDIES IN VARIOUS SPECIES 
Approximately two hundred studies in var- 
ious animal species have been carried out, the 
majority in dogs. 
I 000 
600 - 
Figure 2. — Serial serum glutamic oxaloacetic transa- 
minase (SGOT), lactic dehydrogenase (LDH) and 
creatine phosphokinase (CPK) levels in one dog. 
Following balloon implantation (operation) there 
was an initial increase in enzymes, which returned to 
normal over the next week. Subsequently a second 
higher enzyme rise resulted from balloon cuff coro- 
nary occlusion. (By permission.") 
LEFT ANTERIOR DESCENDING OCCLUSION 
ONSET 
2 Mm 1 1 Sec 
(left chest lead) 
IP . II 'l li. 'i Ijl 1,1 f•>^f^^*^f 
. 4|i|A^|||iU|a||u^|i 
! 
I50|- 
l-VP look 
(mmHg) 5o'~ 
r 
40r 
LVP , 
(mmHgl 2o|- 
CARDIAC OUTPUT 2.7 
(L /M'n) 
1 Sec I 
17 
Figure 3. — Electrocardiographic and hemodynamic 
measurements in a dog during left anterior descend- 
ing coronary artery occlusion. Above: At the onset 
of occlusion, there is initial peaking of T waves, fol- 
lowed within a few minutes by ST segment elevation. 
Below: High-gain left ventricular pressure (LVP) 
tracings show an increase in left ventricular end-dias- 
tolic pressure with occlusion. There is a decline in 
cardiac output, but little change in left ventricular 
systolic pressure. (By permission.^^) 
Canine Studies 
Approximately 180 studies have been carried 
out in intact conscious dogs. A large body of 
evidence has been gathered which shows that 
consistent electrocardiographic and hemodyn- 
amic changes occur in this species (Figure 3). 
Typically, with left anterior descending coro- 
nary occlusion, the electrocardiogram shows in- 
itial peaking of the T waves in the left anterior 
chest leads followed within several minutes by 
elevation of the S-T segment. The S-T segment 
often regresses toward normal over a one-hour 
period following myocardial infarction. From 5 
to 30 minutes after onset of coronary occlusion 
dogs often show ventricular irritability, and on 
occasion this degenerates into ventricular fibril- 
lation. However, the incidence of ventricular fib- 
rillation within the first few hours after my- 
ocardial infarction in this preparation is low, 
approximating 20%.!^ From 4-72 hours after 
myocardial infarction dogs typically develop a 
multifocal ventricular tachycardia, during 
which another small percentage of animals may 
succumb to ventricular fibrillation. Thereafter 
the animals return to normal sinus rhythm, and 
survival is virtually assured. 
