Fluid dynamics of aortic stenosis: subvalvular gradients without subvalvular obstruction.

Abstract

SUMMARY Analysis of a tapering, pulsatile flow field predicts that substantial subvaivular pressure gradients exist in patients with valvular aortic stenosis (AS) without invoking a second anatomic site of obstruction. Using a catheter with two laterally mounted micromanometers, we examined the left ventricle in 11 patients with AS, mean age 64 ± 11 years (± SD); the mean valve area was 1.0 ± 0.3 cm2. Simultaneous measurements were made in (1) the left ventricular (LV) chamber and the LV outflow tract (LVOT) and (2) the LVOT and ascending aorta (AO). No patient had anatomic evidence of a subvalvular obstruction, but large subvalvular gradients were present in all. The average peak LV-LVOT and LV-AO gradients were 41 ± 17 mm Hg and 58 ± 23 mm Hg, respectively. Flow velocity was electromagnetically derived in two patients. The LV-LVOT gradient was associated with an increased flow velocity in the LVOT. This study suggests that large subvalvular gradients are present in AS and help overcome blood's inertia to convective and local accelerations in the tapering subvalvular flow field.SUBSTANTIAL intraventricular pressure differences and gradients* are traditionally considered to reflect an organic "outflow obstruction" in the region across which they are measured.1-9 It is commonly postulated that organic obstructions can be fixed or dynamic, and range from the collar type to the hypertrophic cardiomyopathy variants of subvalvular stenosis.'I--3 Aortic valvular stenosis can coexist with various types of subvalvular obstruction.2-14A9 These associated lesions cannot always be demonstrated angiographically, even by left ventriculography in several views. In such cases, obstructive lesions are best diagnosed from pressure gradients detected by catheter pullback from the ventricle to the proximal aorta.2 3, 10, 12, 19 Persistence or recurrence of intraventricular gradients shown by repeated or serial postoperative catheterization signals inadequate resection or regrowth of subvalvular obstructive lesions and possibly the need for further surgical resection.6 [20][21][22][23][24][25] Clinical investigation of normal ejection dynamics has shown that dynamic factors associated with flow contribute to physiologic transvalvular pressure gradients.26 Studies of flow dynamics in hypertrophic cardiomyopathy have cast strong doubt on the premise that large intraventricular pressure gradients are always a consequence of an anatomic obstruction of the outflow tract region.27 Improved instrumentation for measuring pressure28 33 has led to the frequent observation of subvalvular gradients in patients with valvular aortic stenosis without subvalvular pathology in our *The term gradients in this paper is used in the conventional hemodynamic sense, but in fluid dynamic terms represents a driving pressure difference evaluated across a finite distance in the direction of flow.

RV functional imaging: 3-D echo-derived dynamic geometry and flow field simulations

“…This reflects the strong convective deceleration ensuing as blood moves from the orifice to the periphery of the chamber. It is anal-ogous and exactly the converse of the strong convective acceleration of the intraventricular ejection flow in the immediate vicinity of the outflow orifice, which has previously been demonstrated in cardiac catheterization and CFD studies (3,(8)(9)(10)(18)(19)(20)(21).…”

“…With the use of the prism model with RT3D data, RV chamber dynamic geometry and boundary conditions (RV endocardial velocities) were obtained for solution of the Navier-Stokes equations (8-10, 18, 19) in CFD simulations of RV filling characteristics. Blood was assumed to be a Newtonian, incompressible fluid with a kinematic viscosity of 0.04 Stokes and mass density of 1.05 g/cm 3 . We used a combination of custom software and FIDAP (Fluid Dynamics International; Evanston, IL).…”

Subvalvular Gradients in Patients With Valvular Aortic Stenosis

“…At this point, proximal sensor recordings exhibited morphologies consistent with both aortic and ventricular origins (hybrid). However, in every instance, 2 distinctive features of the proximal sensor waveform suggested a predominantly ventricular (therefore subvalvular) origin: (1) virtual identity in the rate of pressure development (dP/dt) to that of the distal sensor recording and (2) appearance of a distinctive inscription on the pressure tracing corresponding in time to the peak velocity. The former consideration, of necessity, supports a ventricular source.…”

“…1 These authors subsequently 2 developed an elegant mathematical model that fully explained the presence of these resting gradients as a manifestation of significant inertial effects within a rapidly tapering flow field. In the present study, careful exploration revealed no evidence of a resting pressure gradient within the deep left ventricular cavity, a small gradient accompanied by an increase in local linear flow velocity with slight catheter withdrawal, and a larger and continuously increasing gradient (accompanied by progressive local velocity increase) up to the subvalvular region.…”

Complementarity and competitiveness of the intrinsic and extrinsic components of the total ventricular load: Demonstration after valve replacement in aortic stenosis

“…[17][18][19] In the presence of left (right) ventricular outflow tract obstruction, including aortic (pulmonic) valvular stenosis, intraventricular ejection gradients of large magnitude are typical. 2,3,20 The total systolic ejection load Through the above-mentioned endeavors, the view was developed 3,13 that total ventricular systolic load comprises both extrinsic (the aortic root ejection pressure waveform) and intrinsic (flow-associated intraventricular pressure gradients) components. Figure 1 provides a framework for understanding systolic loading dynamics.…”