An expansible aortic ring for a physiological approach to conservative aortic valve surgery.

OBJECTIVE: Dystrophic aortic insufficiency is characterized by dilation of the aortic annular base and sinotubular junction diameters preventing coaptation of thin and pliable cusps amenable to valve repair. An expansible aortic ring was designed to reduce dilated aortic root diameters to increase valvular coaptation height while maintaining root dynamics. The properties of the device were tested in vitro and in vivo in an ovine model. METHODS: Expansible rings were composed of an elastomer core covered by polyester fabric. After in vitro analysis of their mechanical properties, the rings were implanted in 6 sheep at both the level of the annular base and sinotubular junction (double subvalvular and supravalvular external aortic annuloplasty). Root dynamics were assessed by using intracardiac ultrasonography before surgical intervention and at 6 months. Histologic, scanning electron microscopic, and mechanical studies were then performed on explanted samples. RESULTS: The expansible ring produced a significant reduction of the aortic annular base and sinotubular junction diameters. Coaptation height was increased from 2.5 +/- 0.7 mm to 6.2 +/- 1.1 mm (P < .001). Mechanical testing on 6-month explanted samples revealed no significant differences in elastic modulus. Dynamics of the root were well preserved. Histomorphologic studies showed incorporation of the material without degradation. CONCLUSIONS: Expansible aortic ring implantation produces a significant annuloplasty that increases coaptation height while preserving the dynamics of the aortic root. The effectiveness of the device in treating aortic insufficiency is currently being evaluated in the prospective Conservative Aortic Valve surgery for aortic Insufficiency and Aneurysm of the Aortic Root trial comparing conservative aortic valve surgery versus mechanical valve replacement.

Ipsative comparisons of WISC-IV index scores.

The Wechsler Intelligence Scale for Children-4th Edition (Wechsler, 2003a) yields standard scores for four indexes that can be compared when practitioners examine within-child variability. The test manual provides pairwise comparison tables that clinicians can use to examine the scale variability, but it does not adequately caution them about the statistical pitfalls of multiple pairwise comparisons (e.g., inflated error rate). An alternative to the pairwise comparison approach called an ipsative method can be used to compare the 4 WISC-IV standard scores to an individual child's mean of the 4 index scores with more control over the error rate. These values were computed at the .05 and .01 levels following the method used by Naglieri (1993) for the Wechsler Intelligence Scale for Children-3rd Edition (WISC-III; Wechsler, 1991) as originally suggested by Davis (1959) and modified by Silverstein (1982) for previous versions of Wechsler's scales and other multiscore intelligence tests. An example of the use of the technique is provided, as are interpretive cautions.