Pathophysiologic correlates of right ventricular thallium-201 uptake in a canine model.

We evaluated the pathophysiologic correlates of right ventricular (RV) thallium-201 (9°1Tl) visualization in three canine models: (1) acute RV pressure overload (RVPO) induced by acute constriction of the pulmonary artery; (2) acute RV volume overload (RVVO) induced by acute left-to-right atrial shunt; and (3) RV hypertrophy (RVH) induced by chronic constriction of the pulmonary artery. Thallium-201 myocardial images, RV and left ventricular (LV) 201T1 tissue accumulation and RV and LV myocardial blood flow (MBF) were compared with control measurements. In control dogs, the right ventricle was not visualized. In dogs with RVPO, RVVO and RVH, the right ventricle was clearly visualized. In RVPO, and to a lesser degree in RVVO, RV/LV 201T1 uptake per gram tissue and RV/LV MBF per gram tissue were increased significantly compared with control, whereas in RVH, these values were not significantly different from control. However, total RV/LV "1Tl tissue uptake and total RV/LV MBF (RV/LV MBF X RV/LV mass) were not significantly different in RVPO and RVH, consistent with the similar degree ofRV visualization on 201T1 images. Total RV/LV 201T1 tissue uptake correlated well with the degree of RVH (r = 0.91). However, quantitative analysis of computerized 20111T images correlated less well (r = 0.77) with the degree of RVH. We conclude that RV visualization at rest in 201T1 images does not necessarily indicate RVH, but may be due to acutely increased RV work load. In acute RVPO, RV visualization is predominantly due to a marked increase of RV MBF per unit tissue, whereas in RVH this is predominantly due to an increase of RV mass. Although total 20111T tissue accumulation correlates well with the degree of RVH, quantitative analysis in 20111T images appears to be of limited value.