The Effect of Pulmonic and Aortic Constriction on Regional Left Ventricular Thickening Dynamics, Geometry and the Radius of Septal Curvature

Abstract

We evaluated the effects of aortic and pulmonic constriction on cross-sectional cardiac dynamics using prospectively gated computed transmission tomography (CT) in six dogs in order to evaluate 1) the effect of altering the end-diastolic trans-septal pressure gradient on the radius of septal curvature, and 2) the effect of right ventricular overload on regional left ventricular geometry and wall thickening dynamics. Cross-sectional CT data were obtained in a control state, at two incrementally higher levels of right ventricular end-diastolic pressure produced by constriction of the pulmonary artery (PA₁ and PA₂) and then at one higher level of left ventricular end-diastolic pressure resulting from acute aortic constriction (A_o). Using fluid-filled polyethylene catheters, we measured right and left ventricular pressures simultaneous with the image acquisition. The measured radius of septal curvature was then normalized by the calculated average radius derived from the left ventricular area at end-diastole. The end-diastolic radius of septal curvature ratio increased as Δ [LVEDP-RVEDP] declined (from 1.03 ± 0.13 at control; 1.20 ± 0.18 PA₂; 1.27 ± 0.14 PA₂ and 0.87 ± 0.11 A_o). As this LVEDP-RVEDP gradient declined (ie, RVEDP increased in proportion to LVEDP) septal wall thickening declined (P < 0.005), with significantly less change in left ventricular anterior or lateral wall thickening. With PA hypertension, LV end-diastolic volume and percent Δ volume significantly declined (P < 0.005) while RV end-diastolic volume increased. With PA pressure overload, septum-free wall distance declined (P < 0.01) as did percent shortening along this dimension (P < 0.01). We conclude that predictable changes in LV and RV dynamics occur when trans-septal pressure gradients change. In particular there is a marked change in the radius of septal wall curvature and in percent thickening of the septal wall. Combining all 24 points, the correlation between the normalized radius and the trans-septal pressure gradient was 0.76 (P < 0.005).