Should clinical cardiologists incorporate the proximal isovelocity surface area (PISA) method into their ever enlarging armamentarium?

Should clinical cardiologists incorporate the proximal isovelocity surface area (PISA) method into their ever enlarging armamentarium? This issue contains a paper comparing measurement of ventricular septal defect shunt ratio by a proximal iso-velocity surface area technique (usually abbreviated as PISA) method and by the Fick method.' The authors used some shortcuts in the PISA method, perhaps to make the measurements easier and more appealing to the cardiolo-gist, and demonstrated a reasonable correlation of shunt calculation by the two techniques. Measurement of flows Although the PISA technique and theory may be only minimally familiar to many cardiologists, non-invasive measurement of flow, forward or regurgitant, has long been a goal of physicians treating patients with cardiac malformations. Various techniques for flow computation have been reported and all have limitations. For the echocardiographer, the earliest methods used assumptions about ventricular shape.2 Such assumptions worked well for normal ventricles and somewhat less well for diseased or excessive volume loaded ventricles. Doppler computations provided the next major wave of enthusiasm for non-inva-sive measurement of cardiac output,' 4 but these methods required accurate measurements of flow area and velocity. The product of flow area (cm2) and velocity (cm/s) is flow (cm3/s); Although both flow area and velocity can be measured in many instances, examples in which one or both cannot be measured, particularly in hearts with malforma-tions, limited the usefulness of this technique. Furthermore , measurement of shunting or regurgitation require determination of the difference between two flows, thus increasing the opportunity for error. An excellent example of a difficult measurement is determining the shunt through a septal defect. Echocardiographic imaging of the size of the defect does not provide an estimate of the shunt volume that passes through the defect. Further, echocardiographic sizing of atrial defects for device closure has demonstrated the inadequacy of this method.5 Qualitative estimation of shunt size by colour Doppler may also be misleading. Accordingly, such two dimensional echocardiographic measurements of defect size and shunt magnitude provide a mere approximation of the actual situation. Proximal isovelocity surface area AN INTRODUCTION The search for the Holy Grail of accurate flow measurements led, at the beginning of the 1990s, to detailed investigation of the PISA technique.67 It has been long known that velocities accelerate and converge in radial streamlines before an obstruction. If the rate of isovelocities can be measured and if PISA can be determined accurately, application of the familiar flow formula …