Underestimation of the ejection fraction using the quantitative gated SPECT for patients with myocardial hypertrophy

The aim of the present study is to quantify the degree of the error as a function of the left ventricular (LV) wall thickness, in calculation of the ejection fraction (EF) using gated single-photon emission computed tomography (SPECT). The essential error of quantitative gated SPECT (QGS) software in patients with myocardial hypertrophy has not been quantitatively estimated.

Forty-six patients with known or suspected hypertrophic cardiomyopathy underwent gated myocardial perfusion SPECT and cardiac magnetic resonance (MR) imaging. The EF value was automatically calculated from gated SPECT using the QGS software. Twelve points of regional LV wall thickness and the EF value were estimated from MR images.

Only a fair correlation was found between the QGS-EF and the MR-EF values (r = 0.48, y = 0.49x + 26.80, p < 0.01), and the QGS-EF was underestimated (r = 0.25, y = 0.90x) in 30 patients with myocardial hypertrophy (mean wall thickness > 12 mm). The magnitude of the error of the EF quantification from gated SPECT showed a significant negative correlation with the mean 12-point LV wall thickness in all 46 patients (r = -0.67, y = -4.12x + 40.44, p < 0.0001). The degree of the error of the ESV and that of the EDV showed positive correlation with the mean LV wall thickness (r = 0.55, y = 5.46x - 56.13, p < 0.0001; r = 0.31, y = 4.20x - 55.28, p < 0.05, respectively).

The underestimation of EF increases with the degree of myocardial hypertrophy, because of the overestimation of the LV cavity especially in the end-systolic phase.