Right ventricular volume measurement: can conductance do it better?

The measurement of right ventricular volume will be reviewed with special reference to the conductance catheter technique. The historical development of the intracavitary impedance technique will be described along with the theory of the multielectrode conductance method. The major potential advantage of this technique is its ability to measure dynamic volume change during the cardiac cycle. This enables a real time beat to beat assessment of ventricular volume in addition to providing continuous recordings during loading manoeuvres performed on the ventricle. However, the conductance catheter technique is based on the assumption that the electric field produced by the catheter is homogeneous and parallel to the long axis of the ventricle, and the current, created by the excitation electrodes of the catheter, is contained within the ventricular cavity. The measurement of these two calibration factors (known as parallel conductance volume (V(C)) and dimensionless slope factor (alpha)), along with the effects of changes in blood resistivity and the orientation of the catheter on the measurement of absolute volume, will be described. Furthermore, some of the clinical applications of the technique in adults and children with heart disease will be outlined.