638 
PHYSIOLOGY 
VENTRICULAR PACING 
. „ „ i,.ii..i.., , • II. I I mi I miiiMiiii iiiMmiii i ii ii iii ii miii i iiii i N i i i i i i ii i iiii i i ii i mi i i iiiii ii i i ii n ii i i im i i ii i i M i i ii n l i i i l i ii ii iiii i ii i ii i li i iii l 
1 2 3 4 
HR/min 
-171 
-32 
DLNP/DT sec"' 
-116 
DP/DT mmhg/sec 
-3733 ^ 
LVID cm 
-5.7 
\ 
V V 
-2.7 
LAEG 
_i r-u_lL_ 
Figure 6. — Effect of ventricular, bipolar stimulation, at increasing pacing rates. Labels are same as in Figure 2. 
ume there is reduction in the amount of stroke 
work which the ventricle generated under the 
influence of propranolol. It is to be noted that 
the usual result seen with propranolol was no 
change in SW/EDV relation from that of the 
control curve. Table I shows the data on which 
the computer plots for ventricular pacing are 
based. In addition, these data show that with 
norepinephrine infusion there was a significant 
increase in peak dP/dt and an increase in mean 
VcF and average wall force. Propranolol injec- 
tion caused a marked decrease in peak dP/dt, 
and a decrease during ejection in mean Vcf and 
average wall force at the endocardial surface of 
the left ventricle. 
SUMMARY 
It is well known that increasing the rate of 
ventricular contraction by artificial stimulation 
