94 • Alternatives to Animal Use in Research, Testing, and Education 
Experimental Animals' Contribution 
to Coronary Artery Bypass 
Graft Surgery 
A second way to describe the role of animals 
in biomedical research is to review the ways in 
which a single advance in applied biomedical re- 
search came about. As an illustration of this proc- 
ess, the development of the coronary artery by- 
pass graft operation, recently recounted (9,46), 
is summarized here. 
Coronary or arteriosclerotic heart disease, often 
caused by a narrowing or blocking of the arteries 
supplying blood to the heart, is the number one 
cause of death in the United States. In 1982, it 
was responsible for approximately 500,000 deaths 
(59). Coronary artery bypass graft surgery was 
introduced in the early 1970s. In this procedure, 
which has become the primary surgical approach 
to treatment of coronary artery disease, a grafted 
vessel is attached to the coronary artery to cir- 
cumvent the constricted portion. The graft im- 
proves the blood and oxygen supply to the heart 
muscle. The growth of the procedure has been 
quite rapid: Approximately 70,000 operations 
were performed in 1977; 160,000 in 1981 (7); and 
191,000 in 1983 (38). 
Coronary artery bypass graft surgery is now 
the most commonly performed major operation 
in the United States (7). It is accepted as far more 
effective than medication in relieving the severe 
chest pain, or angina pectoris, associated with 
coronary heart disease (47). The long-term ben- 
efit of this procedure, in terms of mortality, varies 
among patient groups (60). 
The experimental steps leading to the success- 
ful coronary artery bypass graft operation are 
depicted in figure 5-1, in which the cardiac sur- 
geon stands at the summit of Mt. Coronary Ar- 
tery Bypass. In the early stages of research— that 
is, in the foothills of the mountain— there was a 
great deal of variability in the kinds of animals 
required. Studies in frogs, reptiles, horses, cats, 
dogs, sheep, and deer contributed to scientists' 
understanding of the fundamental principles of 
circulation, blood pressure, and temperature reg- 
ulation. As problems became more specialized, 
the choices of animal species became more re- 
stricted. Dogs, chimpanzees, and, ultimately, hu- 
mans contributed to the later stages of research 
leading to the coronary artery bypass. Virtually 
every step up Mt. Coronary Artery Bypass re- 
quired initial stages of study on living animal 
models of various species. 
Today, in retrospect, the experimental steps 
leading to this surgical procedure appear as a sim- 
ple and logical progression. In this sense, figure 
5-1 is deceptive. It is important to note that the 
first step was not predictive of the second step, 
the second not predictive of the third, and so on. 
The advance from each step involved uncertainty, 
missteps, and serendipity. All are inherent in the 
process of basic biomedical research. Moreover, 
only a poor understanding exists of the path lead- 
ing from basic to applied biomedical research. Al- 
though Mt. Coronary Artery Bypass stands as a 
bona fide illustration of the integration of data 
drawn from several species, it was formed with- 
out a blueprint. 
Use of Multiple Species in 
Biomedical Research 
The contributions of animals are an important 
part of the history of human health, disease, and 
medicine . It is noteworthy that animals have not 
only contributed to human welfare, but deterred 
from it as well. The benefits and detriments de- 
rived from animals involve numerous species. 
The number of animal diseases labeled zoo- 
noses— diseases transmissible from animals to 
humans— now stands at about 200. These exact 
a heavy toll of human morbidity and mortality 
on a worldwide scale. Research to combat zoo- 
noses logically focuses on the species that are the 
principal sources of the diseases. And the more 
species that are infected by a particular agent, 
the greater are the biological resources available 
for research to overcome it. Numerous animal 
vectors of an infectious agent provide increased 
opportunities for the study of variation among 
species in the incubation of, transmission of, and 
susceptibility to the infectious agent. Most of the 
threats to humans from animals— including ra- 
bies, tuberculosis, brucellosis, toxoplasmosis, an- 
thrax, and dengue fever— infect a sufficient va- 
