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 cath eter tip micromanometer, to determine right ventricular dP/dt(max). The fol lowing mathematic corrections were made: for preload, (dP/dt(max))/instanta neous total pressure, (dP/dt(max))/instantaneous developed pressure, and (d P/dt(max))/end diastolic pressure; for afterload, (dP/dt(CPIP))/common peak isovolumic pressure. Wedge pressure was measured simultaneously, using a S wan-Ganz catheter. A negative inotropic drug, detomidine hydrochloride, was administered to 6 horses to examine the effect of the negative inotropic d rug 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 det omidine administration, Variables that correct for preload and afterload we re influenced similarly. Detomidine administration also caused a 24% increa se in mean wedge pressure, probably indicating reduced left-sided cardiac c ontractility. Conclusions and Clinical Relevance-Right ventricular dP/dt(max) may be a us eful clinical variable for determining acute changes in cardiac contractili ty in horses.