30 
CARDIAC MODELS 
fate, 0.25 mgm per pound. The dogs were artifi- 
cially ventilated with room air by means of a 
Harvard animal respirator pump. The experi- 
ments were divided in general into 2 categories : 
acute, in which the planned survival was 4 
hours or less, and chronic, so-called, in which 
planned survival was 1 to 7 days. There were 49 
acute experiments and 27 chronic experiments 
attempted, totaling 76 dogs. The 4 remaining 
animals were excluded from further considera- 
tion because in 2 cases the coronary artery sys- 
tem could not be entered with a catheter, and in 
the remaining 2 cases technical problems neces- 
sitated termination of the experiments. 
General Techniques 
Certain general experimental methods, com- 
mon to all experiments, were followed in the 
course of preparing and carrying out these 
studies. In the acute experiments, catheters 
were passed into the great cardiac vein and into 
the coronary artery via the superficial jugular 
vein and common carotid artery, respectively. A 
third catheter was passed into the descending 
thoracic or abdominal aorta via the right fe- 
moral artery. The catheter in the coronary ar- 
tery was used to pass the electric current and 
cause thombosis. The catheters in the cardiac 
vein and aorta were used to obtain A-V differ- 
ences across the myocardium, to monitor ar- 
terial blood pressure and to administer drugs as 
required. In the chronic experiments, in which 
complete hemodynamic studies were performed, 
the locations of the catheter tips and their sites 
of entry were the coronary sinus and great car- 
diac vein via the left jugular vein, the pulmon- 
ary artery via the right jugular vein, the left 
ventricle via the left carotid artery, and later, 
replacement of the left ventricular catheter by 
the catheter into the left anterior descending 
coronary arery via the left carotid artery. A 
short catheter was also passed to the root of the 
aorta via the right carotid artery for determi- 
nation of ejection factions. All catheters were 
kept patent by slow infusion of normal saline. 
Heparin in a concentration of 20 mgms per liter 
was added to the saline which was used to in- 
fuse the cornary sinus catheter, since clotting 
was found to be a problem in this site. The first 
day in the chronic experimental animals re- 
quired between 12 and 14 hours, during which 
time continuous anesthesia was maintained. A 
total of between 2 and 2V2 liters of saline was 
infused during this time. Blood loss due to sam- 
pling totaled between 100 and 150 milliliters 
during the same period of time, and this blood 
loss was not replaced. 
All arteries and veins were ligated at the site 
of entrance of the catheter introduced into 
them, except for the femoral artery which was 
repaired after the catheter was removed. None 
of these ligatures were removed, including the 
ligatures around both common carotid arteries 
in the chronic experiments. Even with bilateral 
ligation of carotid arteries and jugular veins no 
neurological deficit was apparent up to the time 
of sacrifice in any dogs. 
Antiarrhythmic therapy with lidocaine was 
administered only as required to control or 
abolish arrhythmias after they appeared. Doses 
of 25-75 mgms of this drug were injected 
acutely intravenously when arrhythmias ap- 
peared, especially in the first hour following 
myocardial infarction. Since the surgical tech- 
niques involved clean but not sterile methods, 
dogs which were to survive in the chronic cate- 
gory were given 1 gm of ampicillin or penicillin 
G intravenously near the conclusion of the first 
day of experiment. This proved to be effective 
in preventing wound infections. 
Rectal temperature was monitored with 
a continuous indwelling thermocouple, and 
blankets were applied as necessary when deep 
body temperature tended to fall. 
Regional blood flow through the branch of the 
coronary artery system in which the catheter 
was located was estimated semiquantitatively 
by fluoroscopic observation of the rapidity with 
which Hypaque was washed out of the artery 
following its injection. 
Traumatic Interventions 
With regard to the traumatic interventions 
necessary to cause coronary thrombosis and 
myocardial infarction, the following 4 variables 
were studied in an attempt to gain insight into 
the optimal conditions necessary for causing 
this pathological sequence of events. 
1. The effect of anodal versus cathodal cur- 
rent. 
