"PACING" LEFT VENTRICULAR FUNCTION 
CURVES IN CONSCIOUS DOGS 
F. Kraft-Hunter and E. W. Hawthorne* 
In seeking to determine the efficacy of using "pac- 
ing" ventricular function curves, obtained from con- 
scious instrumented animals, as one means of evaluat- 
ing ventricular performance changes that might occur 
in them as a result of some experimental intervention, 
observations have been made of the effects of atrial, 
ventricular, and sequential pacing in dogs. The left 
atrium and ventricle were paced for short periods at 2, 
2.5, 3, and 3.5 Hz using bipolar electrodes. Then se- 
quential pacing using an atrial systole-ventricular sys- 
tole of 95 milliseconds was used. The animals were in- 
strumented so as to permit simultaneous recordings of 
d InP/dt, dP/dt, aortic, left ventricular and atrial pres- 
sures, left ventricular internal diameter, and the left 
ventricular electrocardiogram. The recording of these 
primary variables permitted the calculation for each of 
a series of cardiac cycles, derived variables such as left 
ventricular volumes, stroke work, total peripheral re- 
sistance, stroke power, cycle lengths and a variety of 
other variables. A small digital computer and A to D 
converter was used for the on-line data acquisition and 
reduction. End-diastolic volume stroke work function 
curves were constructed using the data derived from 
the stepwise atrial pacing. It was observed that my- 
ocardial contractility, as evaluated by changes in peak 
dP/dt, developed left ventricular pressure (40 mm Hg), 
mean Vcf at the endocardial surface of the left ventri- 
cle, peak d InP/dt and peak dP/dt, increased system- 
atically with each increase in heart rate during atrial 
and sequential pacing. This was not seen with ventricu- 
lar pacing. These "pacing" ventricular function curves 
were shifted to the left during periods of norepine- 
phrine infusion and to the right after beta blockade 
using propranolol. Left ventricular pacing appears to 
provide usable left ventricular function curves in con- 
scious instrumented dogs. It is suggested that this type 
of "pacing ventricular function curve" is one way to 
evaluate ventricular performance in man. 
INTRODUCTION** 
Until recently the Frank-Starling ventricu- 
lar function curve^'2 clarified and popular- 
ized by the studies of Sarnoff and his 
^ssociates^-^ was viewed as the ultimate tool 
• Department of Physiology & Biophysics, College of Medicine 
Howard University, Washington, D.C. 
** This research was supported by Grant HE-01015-20. 
for evaluating ventricular performance. The 
difficulties with applying this approach to man 
are numerous. First there is the problem of the 
sensitivity of shift of these curves in demon- 
strating small changes in myocardial contractil- 
ity. There is the difficulty of holding constant 
heart rate, aortic pressure, and myocardial ca- 
techolamine concentration in conscious man and 
animals so as to study the heterometric autoreg- 
ulatory phenomenon through observing the 
effects of increasing venous return on the end- 
diastolic volume /stroke work relationship. 
Finally there is the matter of a reasonable, feasi- 
ble and reproducible means of changing end- 
diastolic volume, and measuring the latter 
simultaneously with stroke volume and pres- 
sures in conscious man. During recent times 
the popularity for using the "force-veloci- 
ty-volume relation""^ in characterizing the 
heart as a muscle, and in terms of basic me- 
chanics, has done much to deemphasize the use 
and the development of new and provacative 
approaches to the application of ventricular 
function curves in the routine analysis of car- 
diac performance in patients. Interestingly all 
during this period of renaissance atrial pacing 
has become commonplace for the cardiac pa- 
tient. It is used for the treatment of selected 
atrial and ventricular arrhythmias. Atrial pac- 
ing has become a valuable tool for clinical 
and experimental investigation of electrocar- 
diographic, metabolic and hemodynamic phe- 
nomena as they affect ventricular function. Re- 
cently, Desanctis" has discussed the diagnostic 
and therapeutic uses of atrial pacing as well as 
its safety. The concept of using "pacing" left 
ventricular function curves has thus emerged 
and served to revitalize, at least for a time, 
more intensive use of the ventricular function 
curve, and the concepts which must surround 
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