J. N. ROSS, JR., J. M. FUQUA, JR., B, S. RUARK AND J. H. KENNEDY 
421 
vessels. The epicardial vessels of the calf are 
easily accessible and of good size ; i.e., the main 
left coronary artery is suitable for the applica- 
tion of flow probes in the 5 to 7 mm range in a 
100 kg animal. Anatomic peculiarities of the 
calf include the presence of the hemiazygous 
vein which drains into the coronary sinus. The 
hemiazygous vein can be ligated without com- 
plication and is a useful route for catheterizing 
the coronary sinus to obtain blood samples. The 
aortic arch of the calf may present a problem 
since the ascending aorta is extremely short 
(about 1.2-2.5 cm in a 100 kg animal) giving 
rise to a single brachiocephalic trunk. How- 
ever, flow transducers can be placed around the 
ascending aorta and pulmonary artery without 
difficulty. We have found that 22 to 26 mm 
probes fit well on these vessels in the 100 kg 
calf. 
Electrical defibrillation of the heart is 
frequently not possible with commerically avail- 
able equipment because of the animals' ex- 
tremely large cardiac mass. However, a com- 
bination of pharmacological and electrical 
means has been successfully employed in a 
number of cases in our laboratory. When de- 
fibrillation is necessary, the heart is arrested 
by the rapid left intraventricular injection of 
potassium chloride (20-80 mEq) during man- 
ual massage until fibrillation ceases. Normal 
acid-base balance is restored by the intravenous 
injection of sodium bicarbonate in amounts 
necessary to correct the base deficit. While con- 
tinuing cardiac massage, an intravenous infu- 
sion of 1 g of calcium chloride is begun slowly 
and continued to effect. Full cardiac contraction 
is restored by these methods alone in approxi- 
mately 30 % of all cases. In others which return 
to fibrillation, electrical defibrillation has been 
occasionally successful. 
Postoperative Management 
Postoperative management of the calf neces- 
sarily varies with the experimental procedure. 
In general, the animals are placed in sternal 
recumbancy as soon as possible, preferably 
within 8 hours after the operation. The calf 
tolerates externalized leads, wires, catheters 
and cardiac assist devices relatively well for 
long periods of time. Chronic monitoring in the 
facility (Figure 3) has proven adequate for 
observing animals postoperatively for 3-5 
weeks. After this time, it is desirable to provide 
the animals with more freedom since their abil- 
ity to exercise in there quarters is extremely 
limited. This has been a problem in our lab- 
oratory, and when possible during long-term 
experiments, the animals are returned to the 
preoperative conditioning facility for exercise. 
DISCUSSION 
Considerations other than size when select- 
ing an experimental animal for any given car- 
diovascular surgical procedure include: ana- 
tomical and physiological peculiarities of the 
species; age and rate of growth; local avail- 
ability and cost; facilities and space required 
for husbandry and ease of handling; tolerance 
to anesthesia and surgical procedures; and 
spontaneous diseases frequently encountered in 
the species. While it is not the purpose of this 
paper to fully discuss each of these topics, cer- 
tain generalities are warranted regarding spe- 
cies selection for any given cardiovascular sur- 
gical procedure. 
In Table I, seven species are rated in 11 cate- 
gories relative to their comparative suitability 
for experimental cardiovascular surgery. It is 
based on the authors' experience with 380 
calves, 160 sheep, 30 pigs, 20 goats and hun- 
dreds of dogs and on the experience of others 
as indicated in the references under each 
species. 
Cost/availability is, of course, regional. The 
relative availability and the low cost of dogs 
and the relative high cost of primates of hu- 
man size, at least in our area, has limited our 
own use of the latter. However, the increasing 
cost of institutionally bred and reared canines 
has caused us to reconsider this matter. 
Husbandry refers to the relative ease of pro- 
duction, housing, and all phases of preoperative 
care and conditioning necessary to obtain a 
suitable animal for chronic experimental cardio- 
vascular surgery. Most laboratories have the fa- 
cilities to house and care for dogs and are 
familiar with their needs. Relatively few labora- 
tories are equipped to handle the requirements 
