Septal geometry in the unloaded living human heart.

Abstract

Right ventricular loading leads to diastolic septal flattening in man without necessarily requiring right ventricular pressure to exceed left ventricular pressure. This observation suggested that the unstressed septal configuration is flat and that its normal concave shape is due to the left-to-right transseptal pressure gradient. To examine this hypothesis, we studied septal configuration by twodimensional echocardiography in nine patients with normal global and regional left ventricular function during surgery for coronary artery disease. (CA). There were no changes in any measurements between C and OP or between CPB and CA. Left ventricular end-diastolic cavity area decreased from 16.5 + 2.1 cm2 at C to 11.1 + 4.5 cm2 after CPB, and further decreased to 8.9 + 3.5 cm2 after CA (p < .001), yet the septum flattened, as shown by an increase in its radius of curvature from 1.7 0.5 cm during C to 2.5 0.7 cm after CPB, and to 2.9 + 1.0 cm after CA (p < .001), or from 0.4 0.1 to 0.8 0.4 to 1.1 0.5 U (p < .001) when normalized for cavity area. Diastolic transseptal pressure gradient was reduced from 4.1 ± 2.3 mm Hg during C to 1. 1 ± 1.8 mm Hg after CPB, and to 0.5 ± 1.4 mm Hg after CA (p < .01). Thus, in the unloaded human heart, the interventricular septum is more flat and occupies a neutral position between the left and right ventricle. Septal flattening due to a reduced but not reversed transseptal left-to-right gradient results from assumption of this unstressed shape as the right ventricular end-diastolic pressure approaches the left ventricular end-diastolic pressure. Circulation 74, No. 3, 463-468, 1986. OWING TO its anatomic position, the interventricular septum is postulated to be a mediator of ventricular interaction. 1-5 However, the mechanisms underlying the changes in septal position are still unclear. Previous work from our laboratory demonstrated leftward displacement of the interventricular septum with acute right ventricular loading during a Mueller maneuver in humans (a forced inspiration against a closed airway). 1 In an effort to determine whether these shifts occurred as a result of right ventricular diastolic pressure exceeding left ventricular diastolic pressures, we then measured the diastolic transseptal pressure gradient during the Mueller maneuver, and correlated these changes with alterations in septal geometry. This study (again in humans) showed that the septal flattening that occurs with acute right ventricular loading is accompanied by a decrease in the diastolic left-to-right transseptal pressure gradient, without requiring a reversal of this gradient.2 This raised the possibility that the reason why the interventricular septum shifts leftward during acute right ventricular loading is that the normal septal configuration in the unloaded heart is flat, and that in the working heart it is held in its usual position concave to the left ventricular cavity by the normal and persistent left-to-right positive transseptal pressure gradient. The goal of the current study was to de...

Regional contribution to ventricular stroke volume is affected on the left side, but not on the right in patients with pulmonary hypertension

“…The septal contribution differs from patients with volume loaded rV such as patients with pulmonary regurgitation or atrial septal defects where the septum moves towards the right side in systole [11,13,25,26]. The movement of septum towards the left in our study is in concordance with earlier studies with pressure loaded rV [16,[27][28][29]. SV long% was decreased on the left side in patients with PH compared to controls, but did not differ on the right side between patients and controls (Table 3; Fig.…”

Ventricular interaction during experimental acute pulmonary embolism.

“…These results are similar to those we previously reported1' in experiments during pulmonary artery constriction, are similar to the studies of others, 3,20,2' and are in general agreement with our current understanding of diastolic septal mechanics. [25][26][27] The importance of the contribution of pericardial constraint to the mechanism of the shift has been emphasized previously; opening the pericardium results in less septal shift than occurs while the pericardium is intact.1 7} 28 Our data differ from those in a recent report that concluded that septal shift was not an important factor in the reduction of LV volume in dogs with pulmonary vascular injury induced by glass beads." The degree of elevation of RV diastolic pressure in that study suggests that a septal shift was not observed because the increase in RV afterload was not as great as that produced by the repeated embolization in our study.…”

The value of tools to assess pulmonary arterial hypertension

“…3) is generally considered a noninvasive reference standard for evaluating biventricular dimensions, geometry and function [40,41]. The configuration and curvature of the septum is a function of transseptal pressure gradient [42,43], whereas transmural pressure gradient determines the left ventricular free wall curvature [44]. Patients with PH may have a substantially reduced trans-septal pressure gradient, which may lead to the frequently observed flattening (or bowing) of the intraventricular septum (IVS) [42].…”