J. ROSENWEIG AND S. CHATTERJEE 
127 
flex artery were ligated. The marginal branch 
of the left circumflex artery was ligated ini- 
tially, then the major branches of the anterior 
descending artery. At least 15-30 minutes were 
allowed between ligations for stabilization of 
transient acute effects on coronary flow and 
hemodynamics. 
Criteria for cardiogenic shock were: 
1. Sustained elevation of mean left atrial 
pressure above 12 mm. Hg. 
2. Reduction of cardiac output by 40 percent 
or more, and 
3. Diminution in aortic systolic pressure by 
30 percent or more. 
The latter two criteria were invariably pres- 
ent when mean left atrial pressure remained 
above 12 mm. Hg. Time interval from ligation 
of the first coronary artery branch to the de- 
velopment of cardiogenic shock average 120 
minutes (70-160 minutes in Group I, 138 min- 
utes (116-170 minutes) in Group II, 137 min- 
utes (110-160 minutes) in Group III, and 140 
minutes (110-175 minutes) in Group IV. The 
time differences between the groups were not 
significant (t = 1.464, p = 0.25). 
TREATMENT PROCEDURES 
Group I 
Ten animals served as controls. Once cardio- 
genic shock was manifest, the dogs were moni- 
tored until death. 
Group II 
Ten animals were subjected to arterio-arterial 
counterpulsation for one hour using a SIMAS 
pump. Counterpulsation was effected through 
No. 14 Fr. cannulas inserted into both femoral 
arteries as in Study I (Figure lA). Because of 
