86 
CARDIAC MODELS 
Table II. — Numerical data corresponding to Figure 6 
and amplifying Table I. HR = heart (and pump) 
rates. SV = LV stroke volume. COr.v = minute out- 
put of LV. PSV = pump stroke volume. COp = min- 
ute output of pump. CO.iTjt = minute output from 
atrium in addition to COi.v. CO — total cardiac output 
per minute: CO = COiv, non-pumping ; CO — COr.v 
+ COati! pumping. 
ANIMAL 
s 
PUMP 
STATUS 
HR 
•SV 
•PSV 
•COp 
•CO. 
PER NIN 
ML 
L/hin 
HL 
Umin 
l/hin 
L/min 
OFF 
76 
103 
7.8 
7.8 
ON 
75 
75 
5,6 
UO 
8.3 
2.7 
8.3 
OFF 
79 
59 
1.7 
1.7 
ON 
68 
68 
1.6 
90 
6.1 
1.5 
6.1 
* Indexed 
mia-free, stable failure (LVedp = 28 mmHg) ! 
Over inflation and rupture of the balloon, with 
return of normal coronary flow, provoked a 
fatal series of arrhythmias ending in ventric- 
ular fibrillation. 
The search for a closed-chest chronic failure 
model is still under way. Quebec beer-drinker's, 
cobalt cardiomyopathy, successfully used in rab- 
bits looked promising, but the cobaltous 
chloride proved so generally toxic (at any dos- 
age level in rats and dogs) that the promise for 
calves remained unfulfilled. Chaga's disease was 
considered, but found unappealing for vectorial 
reasons. 
The profound cardiomyopathy which accom- 
panies radiation therapy to the myocardium 
prompted an attempt to create specific myo- 
cardial lesions from within, using Strontium-90 
(beta-radiation) to the endomyocardium. No 
success was achieved with this catheter tech- 
nique. 
Of all of the substances which have been in- 
fused into the coronary arteries and myocar- 
dium to create obstruction to flow and distal 
ischemia, our experiences, from 1963 on, led us 
finally to select the microscopic latex micro- 
spheres (6-14 microns in diameter) which have 
proved so useful. Larger diameter micro- 
spheres are worse: in fact, the larger the 
diameter, the greater the frequency of disturb- 
ing arrhythmias. In the dog,-^ the small micro- 
spheres are best; in the calf, they have been 
nearly infallible, except for the animals with 
right coronary infusions. This latter fallibility 
is due, perhaps, to the significant influence 
which the beads must exert over the sino-atrial 
pacemaker. 
In the left coronary artery, the reproduci- 
bility of a desired end-point in LVedp (30-40 
mmHg), the freedom from immediate or late 
arrhythmias, and the prolonged state of slowly 
self-compensating failure have characterized an 
extremely desirable animal failure model. Even 
the method of compensation is desirable: ven- 
tricular hypertrophy with gradual return of 
LVedp toward — but rarely to — the normal 
range (0 to 16 mmHg). 
As the result of a personal communication 
with the author, the microsphere technique de- 
scribed was employed at the National Heart 
Lung Institute in two studies: baseline failure 
evaluation in control animals and adaptation 
of this technique and coronary-cuff balloon oc- 
clusion for evaluation of intra-aortic balloon 
pumping systems,-* both studies in calves. There 
are no essential differences between the results 
of those studies and those reported here and 
previously. However, in a bypass pump-assisted 
animal one can begin a prolonged period of 
chronic failure at a higher LVedp (non-pump- 
ing) than one can afford to do in an unassisted 
animal. This has proved useful in the perform- 
ance of late and repeated treadmill exercise 
studies in animals in failure, the subject of a 
future report from our laboratory. 
In the microsphere-induced failure state, the 
acute phase (first 1-3 hours), hemodynamic 
evaluation yields data which are exactly compar- 
able to that produced by the reversible, balloon- 
cuff coronary occluder. Hence, we have aban- 
doned the latter technique for the former, since 
the only remaining advantage of the occluder is 
the reversibility to the normal state. The only 
condition in which this capability would be use- 
ful is the serial study of the hemodynamic ef- 
fects of pump bypass, with and without LV 
failure, in the long-term reduction and mainte- 
