Sources of variability in the radionuclide angiographic assessment of ejection fraction: a comparison of first-pass and gated equilibrium techniques.

Measurements of ejection fractions (EF) determined by first-pass and gated equilibrium radionuclide angiography are widely believed to be equivalent. To compare these measurements in a large group of patients over a wide range of EF values, left ventricular (LV) and right ventricular (RV) EFs at rest were measured in 135 consecutive patients who underwent the 2 methods of radionuclide angiography within 1 hour: first-pass upright with a multi-crystal camera in the anterior projection and gated equilibrium supine with a single-crystal camera in the left anterior oblique projection. The population included 18 normal patients and 117 patients with various cardiac and pulmonary disorders. First-pass and gated equilibrium LVEF correlated well (r = 0.83, p less than 0.001), but the slope of the regression line was different from unity, with the first-pass values lower than the gated equilibrium values (0.51 +/- 0.16 vs 0.56 +/- 0.15, p less than 0.05 [mean +/- standard deviation] ). Among the 45 patients with a gated equilibrium LVEF of less than or equal to 0.50, the correlation (r = 0.84) was better than that for the 90 patients with a LVEF greater than 0.50 (r = 0.44, p less than 0.05). However, in the latter group, the correlation remained good in the 15 patients with cardiomegaly due to aortic or mitral regurgitation (r = 0.80). Inter- and intraobserver error was similar for both methods. In contrast, there was a poor correlation between first-pass and gated equilibrium RVEF, with the first-pass values higher than the gated equilibrium values (0.51 +/- 0.11 vs 0.43 +/- 0.11, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)