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