Use of right ventricular pressure increase rate to evaluate cardiac contractility in horses

OBJECTIVE: To establish reference values for right ventricular maximal rate of increase in pressure (dP/dt(max)) in horses and determine the usefulness of this variable to evaluate cardiac contractility. ANIMALS: 15 crossbred horses, 3 to 20 years old. PROCEDURE: Cardiac catheterization was performed, using a high-fidelity catheter tip micromanometer, to determine right ventricular dP/dt(max). The following mathematic corrections were made: for preload, (dP/dt(max))/instantaneous total pressure, (dP/dt(max))/instantaneous developed pressure, and (dP/dt(max))/end diastolic pressure; for afterload, (dP/dtCPIP)/common peak isovolumic pressure. Wedge pressure was measured simultaneously, using a Swan-Ganz catheter. A negative inotropic drug, detomidine hydrochloride, was administered to 6 horses to examine the effect of the negative inotropic drug on right ventricular dP/dt(max) and derived variables. RESULTS: The mean right ventricular dP/dt(max) was 477 (+/- 84.1) mm Hg/s in 15 horses. A 40% decrease in dP/dt(max) was found for 30 minutes after detomidine administration. Variables that correct for preload and afterload were influenced similarly. Detomidine administration also caused a 24% increase in mean wedge pressure, probably indicating reduced left-sided cardiac contractility. CONCLUSIONS AND CLINICAL RELEVANCE: Right ventricular dP/dt(max) may be a useful clinical variable for determining acute changes in cardiac contractility in horses.