Evaluation of Wall Motion and Dynamic Geometry of the Inferior Vena Cava Using Intravascular Ultrasound:Implications for Future Device Design

Abstract

To use intravascular ultrasound (IVUS) to define the wall motion of the inferior vena cava (IVC) during normal respiratory cycles and evaluate its dynamic geometry during Valsalva maneuvers. Between September 2005 and October 2006, 10 patients who were having IVC filters placed underwent IVUS prior to filter implantation. With the anesthetized patient in a supine position, a 10-second IVUS recording of IVC motion below the renal veins was made during both normal respiratory cycles and Valsalva maneuvers. Diameters (n = 100 measurements) were measured from the epicenter of the lumen in both a long and short axis. Changes in diameters were evaluated using a Student t test for paired data; variations in IVC wall motion circumference of the vessel were compared using an analysis of variance for repeated measurements. Intra-/interobserver variability was analyzed with Bland-Altman plots. The mean IVC diameter was 14.3+/-4.1 mm in the short axis and 23.2+/-3.5 mm in the long axis. There was significant variation in infrarenal IVC wall movement about the circumference, with 1.4+/-0.2 mm (range 0.6-1.8) displacement in the short axis and 1.0+/-0.2 mm (range 0.2-1.4) displacement in the long axis during the normal respiratory cycle (p = 0.04). In the short axis, the IVC diameter significantly increased with Valsalva from 14.3+/-4.1 to 19.6+/-1.2 mm (p = 0.0001); in the long axis, the diameter increased from 23.2+/-3.5 to 24+/-1.2 mm (p = 0.02). With Valsalva, there was a significantly greater change in the short axis (30.9%+/-4.8%) compared to the long axis (3.4%+/-2.2%; p = 0.0001). There were no significant differences in the interobserver and intraobserver measurements. In the supine position, the IVC is elliptical and deforms anisotropically during the normal respiratory cycle. The greatest displacement (36%) is in the short axis during a Valsalva maneuver. These profound changes within the venous system will require intracaval devices to have active fixation to prevent migration. Devices should be designed to accommodate these changes to prevent fatigue failure.