End-systolic pressure/volume ratio: a new index of ventricular contractility.

A thesis recently developed from a series of experiments on the isolated canine left ventricle is described. It is claimed that the ventricular presure/volume ratio at end-systole is relatively insensitive to cardiac loading and varies greatly in response to changes in ventricular contractility. The clinical viability of this basic finding rests on the substitution of diameter for volume in this formulation. Diameter can be measured using a noninvasive ultrasonic technique in the clinic. Accordingly, end-systolic pressure/diameter ratio was studied in the isolated preparation and found to be similarly insensitive to loading conditions and sensitive to inotropic interventions. A further analysis of the pressure/diameter ratio in the ventricle of the conscious dog is in progress. In parallel with these studies, use of the pressure/diameter ratio to evaluate contractility in cardiac patients is being tested. The preliminary findings from conscious dogs and clinic patients are briefly discussed.