Left Ventricular Ejection Fraction in the Normal Horse Determined by First‐pass Nuclear Angiocardiography*

A method to perform first‐pass nuclear angiocardiography (FPNA) in the conscious, standing horse is proposed. Technetium −99m (0.75–1.0 mCi per 5 kg body weight) is injected as a bolus into the peripheral venous circulation. The passage of the radioactive bolus is recorded in listmode format using a dedicated nuclear medicine computer and a gamma camera. A semiautomatic equine cardiac computer program to calculate left ventricular ejection fraction (LVEF) is described. Effects of region‐of‐interest selection, background correction, portion of levophase analyzed, and sampling rate on ejection fraction values are discussed. Mean LVEF determined for a group of 13 normal horses using separate end‐systolic and end‐diastolic LV regions of interest for the middle three levophase beats and background correction was 71%±5%. Additional LV parameters recorded were LV ejection time, 429±78 milliseconds; LV ejection rate, −1.9±.5 midsytolic volumes per second; LV filling time, 238±33 milliseconds; and LV filling rate, 2.4±0.5 midfast filling volumes per second. LVEF determinations were repeated three times in four horses to determine reproducibility of the method. Results were independently determined for three horses by four persons to assess interobserver error in processing data. Paired FPNA and electrical conductivity (EC) studies were performed on four horses to determine correlation of the two methods (FPNA=1.16 EC+9.16, R=0.75). FPNA is a safe and reproducible method to measure LVEF in the horse. Additional valuable information regarding cardiac function can be easily obtained using this technique.