Direct measurement of cardiac output by gated equilibrium blood pool scintigraphy: Validation of scintigraphic volume measurements by a nongeometric technique

A nongeometric technique for the determination of left ventricular volumes from the count data derived from gated equilibrium blood pool scans was previously described and validated by the demonstration of an excellent correlation between the derived data and angiographically determined left ventricular volumes. To provide a further prospective evaluation of this method and to validate its ability to determine stroke volume and cardiac output by a technique that is itself independent of geometric assumptions, simultaneous measurements of cardiac output by the thermodilution technique and gated scintigraphy were performed in 21 patients without valve regurgitation or intracardiac shunts. To substantiate the reliability of scintigraphic measurements at high levels of cardiac output, seven patients had multiple measurements of cardiac output at rest and during an infusion of isoproterenol. There was an excellent correlation between thermodilution and scintigraphic values for cardiac output (scan cardiac output = 0.99 thermodilution cardiac output - 0.005 liters/min; n = 31, standard error of the estimate [SEE]= 0.175 liters/min, r = 0.97) as well as between thermodilution and scintigraphic stroke volumes (scan stroke volume = 1.03 thermodilution stroke volume - 2.8 ml; n = 31, SEE = 2.5 ml, r = 0.95). In addition, the relation between scintigraphic and angiographic measurements of left ventricular volumes continued to be excellent: In 15 patients with technically adequate angiograms, scintigraphic left ventricular volume = 0.90 angiographic left ventricular volume + 7 ml (n = 30, SEE = 10 ml, r = 0.91). Thus, this study further validates the nongeometric method of measuring left ventricular volumes with gated scintigraphy and demonstrates its ability to measure left ventricular stroke volume and cardiac output reliably.