USE OF FIRST‐PASS NUCLEAR ANGIOCARDIOGRAPHY TO DETECT LEFT‐TO‐RIGHT CARDIAC SHUNTS IN THE HORSE

First-pass nuclear angiocardiography was performed on 13 normal horses and 5 horses with confirmed left-to-right ventricular septal defects. Two methods of analyzing the ensuing pulmonary time-activity histograms for shunt recirculation through the lungs were evaluated: (1) pulmonary-to-systemic blood flow ratio (QP:QS), based on gamma variate modeling of the lung histogram, and (2) a simple count-ratio method (C2:C1). Normal values were QP:QS=1.17±0.04 and C2:C1=0.40±0.07. Values for the five horses with left-to-right shunts were QP:QS=2.94±0.13 and C2:C1=0.76±0.11. Both parameters showed significant differences (unpaired t-test; p<0.005) between the two groups, although separation was better with QP:QS.