Relationship of gated SPECT ventricular function parameters to angiographic measurements

Left ventricular volumes and ejection fractions constitute important information in the diagnosis of cardiac disease. This investigation examined the relations of functional parameters computed with a recently published scintigraphic gated tomographic method with those from angiography, analyzing discrepancies arising from differences involved in modeling the left ventricle.

While left ventricular ejection fractions obtained from myocardial perfusion gated single-photon emission computed tomography (SPECT) have demonstrated accurate comparisons with other imaging modalities, validations of volumes have not been examined as extensively, and some recent studies have reported a wide range of angiographic correlation. It is important to know how volumes obtained by a new class of methods compare with those from older, well-established techniques in order to interpret individual patients' results, particularly when scintigraphic images are severely hypoperfused.

Tc-99m sestamibi myocardial perfusion gated SPECT data were processed retrospectively for 58 patients studied by single-plane angiography. Endocardial borders were generated automatically on paired vertical and horizontal long-axis Tc-99m sestamibi gated tomograms for computing ventricular volume using a Simpson's rule summation of elliptical slices. Linear regression and paired t tests were used to compare SPECT with angiographic parameters for all patients and for groups identified on the basis of tomogram visual examination as hypoperfused, ischemic or nonischemic, with the latter category further subgrouped as to fixed defects or normal perfusion. Linear regression analysis demonstrated Pearson correlation coefficients of 0.87 for end-diastolic volumes, 0.91 for end-systolic volumes, and 0.86 for ejection fraction; paired t test analysis showed end-systolic volumes to be nearly identical (p > 0.99) to angiographic values. However, paired t tests also revealed gated SPECT end-diastolic volumes and ejection fractions were significantly lower (p < 10(-4)) than angiography. Correlations and trends were essentially the same for all subgroups except for the small sample (n = 10) of patients with normal perfusion.

Gated SPECT provides ventricular volumes and ejection fractions that correlate well with angiography, even in hypoperfused and ischemic populations. However, gated SPECT end-diastolic volumes and ejection fractions are significantly lower than angiographic measurements, partly because of inclusion of greater outflow tract amounts in standard angiographic models. Because myocyte concentration decreases rapidly at the ventricular base, it is likely that most gated SPECT methods will produce endocardial borders encompassing less of the outflow tract than do angiographic outlines.