Author + information
- Received December 10, 1985
- Revision received March 17, 1986
- Accepted May 8, 1986
- Published online November 1, 1986.
- Raymond G. McKay, MD*,1,
- Michael J. Miller, MD1,2,
- James J. Ferguson, MD1,
- Shin-Ichi Momomura, MD1,
- Peter Sahagian, BS1,
- William Grossman, MD, FACC1 and
- Richard C. Pasternak, MD, FACC1
- ↵*Address for reprints: Raymond G. McKay, MD, Cardiovascular Division, Beth Israel Hospital, 330 Brookline Avenue, Boston, Massachusetts 02215.
The end-systolic pressure-volume relation has been postulated as a load-independent measure of cardiac contractility, but has been difficult to measure because of technical problems associated with the serial measurement of intracardiac volume over a physiologic range of ventricular loading conditions. Utilizing a multielectrode impedance catheter to assess continuous, on-line left ventricular relative volume during transient inferior vena cava occlusion, a method is described for determining the end-systolic pressure-volume relation and for assessing changes in this relation secondary to inotropic modulation. In particular, using this method, the relative inotropic properties were determined of four drugs: dobutamine, milrinone, epinephrine and an experimental cardiotonic agent (Ro 13-6438, Posicor).
Left ventricular micromanometer pressure and impedance catheter volume were measured continuously in 10 open chest, anesthetized dogs and 14 pigs. Arterial pressure was altered over a range of 20 to 60 mm Hg by brief inferior vena cava constriction. A linear end-systolic pressure-volume relation was observed in pressure-volume diagrams constructed from on-line pressure and impedance catheter recordings. Administration of dobutamine, milrinone and epinephrine resulted in a leftward shift and an increase in the slope of the end-systolic pressure-volume relation as compared with baseline; Posicor did not alter the slope over a range of doses, despite an increase in the cardiac output secondary to arterial vasodilation. Volume changes as measured by the impedance method closely paralleled simultaneous changes in the ultrasonic crystal-determined segment length, and the impedance end-systolic pressure-volume relation slope was reproducible with repeated load-altering manuevers.
It is concluded that the end-systolic pressure-impedance volume relation can be determined on a beat to beat basis during acute decreases in ventricular preload induced by transient inferior vena cava occlusion. This method of determining relative changes in the end-systolic pressure-volume relation may be useful in the assessment of relative inotropic effects of experimental cardiotonic drugs.
- Received December 10, 1985.
- Revision received March 17, 1986.
- Accepted May 8, 1986.
- American College of Cardiology Foundation