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 (E& 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 ceils tagged with technetium-99m for radionuclide angiography. Hemodynamics and radionuclide angiograms were obtained under control conditions and during six additional steady-state loading conditions. lsochronal E,,, averaged 7.14 k 2.54 mm Hg/ml, while E.. averaged 5.66 f 1.66 mm Hg/ml (p < O.Ol), but they were highly correlated (r = 0.95, p < 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 E max and Ege slope values were compared to dog weight; left ventricular weight, which ranged from 65 to 142 gm (mean 113 + 16 gm); and left ventricular end-diastolic volume, which ranged from 15 to 56 ml (mean 29 + 10 ml) using multiple regression analyses. The E,., and Eeo slope values demonstrated a comparable inverse linear relationship with only left ventricular end-diastolic volume (r = 0.76 and -0.69, p < 0.001 and p < 0.01). We conclude that the differences between E msx and Egs slope values calculated with radionuclide anglography 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 E,, are comparably related to left ventricular end-diastolic volume. Since the E,,, and E.s slope values are affected by similar influences, are highly correlated, and are comparably related to heart size, they both may be useful for assessing alterations in left ventricular contractility as long as they are applied consistently In animals or man. (AM HEART J 1989;118:325.)