Potential artifact in measurement of left ventricular filling pressure with flow-directed catheters.

Artifactual pulmonary wedge pressure measurements were encountered during bedside use of Swan-Ganz catheters. These values were higher than pulmonary artery end diastolic pressure and devoid of typical phasic contours. Utilizing fluoroscopy these artifacts were reproduced by advancing the catheter tip 2-4 cm beyond the site of initial wedging and reinflating the balloon. Spurious increases of pulmonary wedge pressure of up to 15 mm Hg were thus obtained. In vitro catheter testing demonstrated overlapping of the catheter tip by the deformed balloon when it was fully inflated in a channel too small to accomodate it. These measurement artifacts are thus attributed to distal migration of the catheter tip into relatively small pulmonary artery branches and to subsequent occlusion of the catheter lumen by the balloon when it is reinflated. This can readily be avoided by routinely inflating the balloon with the minimum volume of air sufficient to yield a pulmonary wedge pressure tracing.