VISUALLY DETERMINED LONG-AXIS AND SHORT-AXIS PARASTERNAL VIEWS AND 4-CHAMBER AND 2-CHAMBER APICAL ECHOCARDIOGRAPHIC VIEWS DO NOT CONSISTENTLY REPRESENT PAIRED ORTHOGONAL PROJECTIONS

The long-axis and short-axis two-dimensional (2-D) echocardiographic v iews from the parasternal window and the four- and two-chamber views f rom the apical window, respectively, are considered to be orthogonal t o each other. The validity of this was tested using custom-designed 3. 5-MHz transducers with an electric motor that rotated the transducer b y 2.9-degrees increments through 180-degrees about a central axis. Ima ges were acquired beginning at the best appearing long-axis parasterna l or apical four-chamber views and rotating, blinded to the degree of rotation, to the best appearing short-axis or apical two-chamber views . Imaging in 40 patients (age 15-89, mean 46) undergoing clinical echo cardiography yielded 35 parasternal and 27 apical rotations adequate f or analysis. The difference between 'orthogonal' views in degrees of r otation were: (mean, minimum and maximum, respectively) from the paras ternal window, 100 +/- 19-degrees, 64-degrees and 156-degrees, and fro m the apical window, 95 +/- 21-degrees, 30-degrees and 136-degrees. De viations from orthogonality exceeded 20-degrees in 12/35 (34%) paraste rnal rotations and in 7/27 (26%) from the apical window; deviation exc eeded 30-degrees in 4/35 (11%) and 5/27 (19%), respectively. Thus, on average, the assumption of orthogonality between parasternal long- and short-axis views and between the four- and two-chamber views is corre ct, but there is wide deviation from this expectation in individual pa tients. These deviations may affect the accuracy of 2-D echocardiograp hic measurements and calculation of derived variables by methods that assume orthogonality of projections.