Comparison of regional myocardial blood flow measurements with 133Xe and radioactive microspheres in dogs with coronary artery constrictions

Paired measurements of regional and total left ventricular myocardial blood flow were performed using radioactive microspheres and 133Xe and a multiple-crystal scintillation camera. Measurements were carried out in nine control dogs and in 14 dogs with blood flow reductions distal to left anterior descending constrictions at rest and during isoprenaline infusion. In the control animals, the two measurements correlated well, r=0.97, P<0.01 (n = 14). The regression equation, y =0.90x+7.32, was not significantly different from the line of identity. In the dogs with partial left anterior descending constrictions, total left ventricular myocardial blood flow measured with 133Xe also correlated with microsphere determinations, r=0.95, P<0.01 (n = 17). The regression equation, y = 1.07x−0.18, was not significantly different from the line of identity or the regression line for the control animals. Regional blood flow was measured in an ischaemic region distal to the contriction and in the remainder of the left ventricle. In the ischaemic zone 133Xe overestimated blood flow as compared to the microspheres, 0.74±0.29 cm3·g−1·min−1, P<0.05. In the remainder of the left ventricle the measurements were not significantly different, 0.93 ±0.36 vs 0.91 ±0.31 cm3·g−1·min−1. The coefficient of variation of microsphere flow rates averaged 39% for the ischaemic region and 18 % for the control region. The overestimation of 133Xe blood flow in the ischaemic region correlated directly with the coefficient of variation of microsphere flow rates for that region, r=0.57, P <0.01. These data indicate that measurements of myocardial blood flow with 133Xe correspond closely to measurements made with radioactive microspheres. However, 133Xe blood flow measurements distal to constrictions may modestly overestimate the actual blood flow rate and this overestimation is a function of the degree of heterogeneity of flow within this region.