Radionuclide left ventricular contractile indices and their relationship to heart size in dogs.

To identify possible mechanisms to explain differences between the maximum time-varying elastance (Emax) and end-systolic pressure-volume (Ees) slope values calculated with radionuclide angiography and to establish whether they have a relationship to heart size, we studied 16 dogs that were instrumented with micromanometer left ventricular catheters and had red blood cells tagged with technetium-99m for radionuclide angiography. Hemodynamics and radionuclide angiograms were obtained under control conditions and during six additional steady-state loading conditions. Isochronal Emax averaged 7.14 +/- 2.54 mm Hg/ml, while Ees averaged 5.68 +/- 1.88 mm Hg/ml (p less than 0.01), but they were highly correlated (r = 0.95, p less than 0.001). This observation was related to the assumption of linearity when curvilinearity was present and to the important influence of timing on these relationships. The Emax and Ees slope values were compared to dog weight; left ventricular weight, which ranged from 85 to 142 gm (mean 113 +/- 18 gm); and left ventricular end-diastolic volume, which ranged from 15 to 56 ml (mean 29 +/- 10 ml) using multiple regression analyses. The Emax and Ees slope values demonstrated a comparable inverse linear relationship with only left ventricular end-diastolic volume (r = 0.76 and -0.69, p less than 0.001 and p less than 0.01). We conclude that the differences between Emax and Ees slope values calculated with radionuclide angiography are related to the assumption of linearity when curvilinearity is present and to the importance of the timing of systolic events and that both Emax and Ees are comparably related to left ventricular end-diastolic volume.(ABSTRACT TRUNCATED AT 250 WORDS)