The Annals of Thoracic Surgery, Vol 40, 475-482, Copyright © 1985 by The Society of Thoracic Surgeons
Postoperative left ventricular contractility in the cardiac surgical patient: an evaluation of the force-interval relationship
JD Sink, PA Anderson and AS Wechsler
The force-interval relationship--the dependence of cardiac contractility on
the rate and pattern of stimulation--was evaluated for its potential use in
monitoring patients in the period immediately following heart surgery. Six
patients were studied for three days after coronary artery bypass grafting.
The monitoring instrumentation used during operation included a
catheter-tip micromanometer introduced into the left ventricle, a pair of
ultrasonic transducers placed on the left ventricular (LV) epicardium to
monitor minor-axis dimension, pacing electrodes placed on the right atrium,
and systemic arterial and venous catheters. During the experiments, heart
rate was controlled by atrial pacing. After every twentieth systole (the
control systole), a pause in the heart rate was introduced during which an
extrasystole (SE) and a postextrasystole (SPES) were elicited at test
intervals tE and tPES, respectively. The intervals between the control
systole and test systoles SE and SPES were experimentally manipulated. When
the test intervals were increased, the peak first derivative of LV pressure
(Pmax) of SE and of SPES increased monophasically. To eliminate the effects
of LV end-diastolic volume, we used only SPES and control systoles with the
same LV end-diastolic dimension in construction of PES ratio curves (Pmax
of SPES/Pmax of the control systole, as a function of tPES). The PES ratio
rose monophasically with an increase in tPES; these curves were well fitted
by an exponential relationship. The PES ratio exceeded unity at long tPES
intervals. This ratio, denoting postextrasystolic potentiation, was
inversely dependent on tE. The patients experienced no
complications.(ABSTRACT TRUNCATED AT 250 WORDS)
