First passage radionuclide cardiography for determination of cardiac output: a critical analysis

First-pass radiocardiography, by single probe or gamma camera, has the theoretic potential to be an attractive non-invasive indicator dilution method of measuring cardiac output. Registrations, once programmed, require little time to perform and entail hardly any risk for the subject. At the same time, they are to varying degrees inaccurate. As long as technology is not standardized, each institution that wishes to employ these measurements has to do its own critical validation before results can be accepted. As with any other indicator dilution technique, precision of radiocardiography is served by repetitive measurements. However, radiation dose and disturbing background radioactivity preclude taking multiple measurements within a short period. This holds particularly for the gamma camera. The speed and simplicity of the probe system make this device very suitable for serial evaluation of cardiac function at the bedside. Depending on collimation of the probe and extracardiac background activity, a correction factor has to be derived empirically to avoid overestimation of cardiac output. The major advantage of the gamma camera linked to a data system is that an infinite number of first-pass curves can be obtained from different parts of the heart. Provided that appropriate regions of interest are selected, first-pass studies can yield reasonably accurate and reproducible determinations of cardiac output. In addition, functional image analysis during the equilibrium phase enables calculation of other cardiac variables such as ejection fraction and chamber size. Nevertheless, standardization of 'hardware' and 'software' is imperative.