Abstracts of Papers*
16th Annual Scientific Session of American College
of Cardiology
Washington, D. C., February 15-19, 1767
Paradox of the Permanent Cardiac Pacemaker,
ROBERT J. ADOLPH, M.D., Cincinnati, Ohio.
The cardiac output of patients with chronic ac-
quired complete A-V block (CHB) is increased dur-
ing acute electronic ventricular pacing. It is generally
assumed that this improvement is maintained follow-
ing a permanent pacemaker.
Cardiac output was measured by indicator-dilution
technic in 17 adult patients (aged 46-79 yr.) with
CHB during supine rest, temporary pacing and
treadmill exercise to exhaustion. Studies were re-
peated during long term pacing for an average of 34
weeks after implantation of a fixed-rate ventricular
pacemaker (range, l-88 wk.).
The average resting control cardiac index was low
(2.1 L./min./M. *, rate 36) and rose significantly dur-
ing temporary pacing (2.8, rate 80). With long term
pacing, the resting cardiac index was unchanged
from control (2.1. rate 75). Before pacing. the in-
crease in cardiac output with exercise was low (302
ml./min./lOO ml. Oe consumption). The cardiac out-
put response to exercise was unimproved postopera-
tively (320 ml.), and the stroke volume was lower than
preoperative levels at rest or exercise.
How the heart resets its output following a perma-
nent pacemaker is obscure. In dogs, left ventricular
myocardial catecholamine concentrations were sig-
nificantly reduced (0.34 Fg./gm., normal 0.66) two
weeks after surgically induced CHB and were further
reduced after two weeks of electrical pacing (0.20
pg.:‘gm.). During acute short term pacing of dogs
with CHB, inotropic concentrations of catecholamines
were released from the adrenals and were taken up by
the left ventricle. Whether these observations apply to
man with CHB is uncertain at this time.
Enhancement of Coronary Vasodilator Action of
ATP and Adenosine After Lidoflazine (R 7904), S.
AKIXSO, M.D., G. S. O’BRIEN, M.D. and CHARLES W.
CRIJMPTOK, M.D., F.A.c.c., Madison, Wis.
There is a paucity of information on the combined
effects of coronary vasodilator agents. Supra-additive
combined coronary vasodilator effects of dipyrida-
mole and ATP or adenosine have been reported
(Bretschneider, 1959; and Afonso and O’Brien, 1966).
In the present study it was observed that lidoflazine.
1 - [4,4 - di - (4 - fluoro-phenyl) - butyl] - 4 - [(2:6 -
dimethyl-anilio - carbonyl) - methyl] - piperazine,
a newly reported coronary vasodilator, enhances
greatly and persistently the coronary vasodilator ac-
tion of both ATP and adenosine.
The study was performed on 10 mongrel dogs, anesthetized with morphine-Dial@-urethane-Nembu-
tal”. Cardiac output (dye-dilution technic). arterial
blood pressure, cardiac rate and coronary sinus blood
flow (thermodilution flowmeter) were measured. In
the first part of the experiment coronary sinus flow
was recorded at different effective doses of ATP (8
dogs) or adenosine (2 dogs) given as continuous intra-
venous infusions. Lidoflazine in a single intravenous
dose (1.5 mg./kg. to 8 dogs and 2.0 mg./kg. to 2
dogs) was then administered. Thereafter. doses of
ATP or adenosine which would produce increases in
coronary sinus flow similar to the increases obtained
in the first part of the experiment were tried every
hour for three hours. Results showed that in all dogs. after lidoflazine for similar coronary vasodilator
responses, the doses of ATP or adenosine were 30 to
150 times less than the doses used before lidoflazine.
This enhancement of ATP or adenosine action was
maintained during the three hour period.
Ten minutes after lidoflazine alone, coronary
sinus flow was increased significantly (f 120%) , also
cardiac rate and cardiac output (+16yG and +31%).
After 90 min.? rate and output were at resting levels
while coronary sinus flow was a little elevated
(+19%).
Experimental Muscular Subaortic Stenosis (Hyper-
trophic Obstructive Cardiomyopathy), EORS
BAJUSZ,M.D., F.A.c.c., Cambridge,Mass.
Myocardial pathologic change characterized by focal myolysis occurs regularly in a hamster strain
* Listed alphabetically according to fmt author.
VOLUME 19,JANUARY 1967 117