170 
CARDIAC MODELS 
relation of these observation with several expe- 
rimental preparations which we and others have 
utilized over the past several years will allow 
us to assess the present state of the art for 
experimental analogs. 
METHODS 
Clinical Data 
Selection of patients: Seventy-nine patients 
with ventricular dysfunction complicating acute 
myocardial infarction were admitted to the 
Myocardial Infarction Research Unit (January, 
1970 to January, 1972) and subsequently under- 
went hemodynamic evaluation. The diagnosis 
of acute myocardial infarction was established 
by an appropriate history and clinical picture 
in association with electrocardiographic evi- 
dence of either transmural or subendocardial in- 
farction. The development of diagnostic Q 
waves and evolutionary changes in the ST seg- 
ment and T waves and associated serial enzyme 
changes (CPK, SCOT and/or LDH) were re- 
quired. Left bundle branch block (LBBB) was 
observed in five patients and was considered 
separately. All patients were studied within 
several hours of the onset of their symptoms 
and within 16 hours after the development of 
shock or failure. Informed consent was obtained 
in all patients. Pertinent information relating 
to the presence and duration of angina, conges- 
tive heart failure, previous myocardial infarc- 
tion, and hypertension was obtained on each 
patient. The diagnosis of shock was made in 
45 patients (Group A, cases 1-22 previously 
reported)^ with a systolic blood pressure of 90 
mmHg or less (or 80 mmHg decline from basal 
levels in known hypertensives) and confirmed 
by intra-arterial catherization and not second- 
ary to arrhythmias, hypovolemia, pain or drug 
reactions. Clinical signs of shock (seen in 45 
patients) included depressed mentation, pe- 
ripheral vascular constriction (pallor, cool and 
clammy skin) and oliguria. The criteria for 
ventricular failure without shock included the 
presence of a ventricular gallop sound (S3) 
and/or pulmonary rales. Thirty-four patients 
were included here (Group B). 
Hemodynamics 
Right heart and arterial or left heart cathe- 
terization was accomplished under fluoroscopic 
control using an image intensifier. Phasic and 
mean pressures were monitored with Statham 
P23Db manometers and were amplified and dis- 
played on a multi-channel direct writing re- 
corder (Honeywell). The zero reference was 
marked at the mid-chest level. Pulmonary ar- 
terial and left ventricular or central aortic pres- 
sures were measured in the 79 patients in whom 
hemodynamic studies were performed. Left ven- 
tricular filling pressure (LVFP) was either 
measured directly using left ventricular end 
diastolic pressure (LVEDP) or indirectly using 
pulmonary arterial end diastolic pressure 
(PAEDP). Cardiac outputs were determined by 
indicator dilution technique (Indocyanine 
green) using central sampling. The measure- 
ments of cardiac output were obtained in dupli- 
cate and were reproducible within 15%. Sym- 
pathomimetic therapy for shock was not 
withheld prior to hemodynamic study when 
clinically indicated; however, none of the pa- 
tients studied were supported by these agents 
or digitalis at the time of the baseline studies. 
Patency of the arterial and venous catheters 
was maintained with constant or bolus heparin 
infusions. Catheters remained in position for 
24 to 48 hours for hemodynamic monitoring 
and cardiac output determinations. 
The following calculations were made: left 
ventricular stroke and minute work (gram 
meters'/meter- and kilogram meters/minute/ 
meter-, respectively) using mean ejection pres- 
sure, left ventricular filling pressure, stroke 
index and heart rate. Peripheral vascular re- 
sistance (PVR, in millimeters of mercury/liter/ 
minute/meter- or units) was derived from mean 
ejection pressure and cardiac index. 
Experimental Data 
Holstein, Hereford, Charolais and Angus 
calves, four to twelve weeks of age and weigh- 
ing 50 to 100 kg, were utilized for the experi- 
mental studies. The animals were maintained in 
metabolic cages or stalls with stanchions both 
pre- and postoperatively. The animals were 
