Pressure gradient vs. flow relationships to characterize the physiology of a severely stenotic aortic valve before and after transcatheter valve implantation

Abstract

AimsEchocardiography and tomographic imaging have documented dynamic changes in aortic stenosis (AS) geometry and severity during both the cardiac cycle and stress-induced increases in cardiac output. However, corresponding pressure gradient vs. flow relationships have not been described.Methods and resultsWe recruited 16 routine transcatheter aortic valve implantations (TAVI’s) for graded dobutamine infusions both before and after implantation; 0.014″ pressure wires in the aorta and left ventricle (LV) continuously measured the transvalvular pressure gradient (ΔP) while a pulmonary artery catheter regularly assessed cardiac output by thermodilution. Before TAVI, ΔP did not display a consistent relationship with transvalvular flow (Q). Neither linear resistor (median R2 0.16) nor quadratic orifice (median R2 < 0.01) models at rest predicted stress observations; the severely stenotic valve behaved like a combination. The unitless ratio of aortic to left ventricular pressures during systolic ejection under stress conditions correlated best with post-TAVI flow improvement. After TAVI, a highly linear relationship (median R2 0.96) indicated a valid valve resistance.ConclusionPressure loss vs. flow curves offer a fundamental fluid dynamic synthesis for describing aortic valve pathophysiology. Severe AS does not consistently behave like an orifice (as suggested by Gorlin) or a resistor, whereas TAVI devices behave like a pure resistor. During peak dobutamine, the ratio of aortic to left ventricular pressures during systolic ejection provides a ‘fractional flow reserve’ of the aortic valve that closely approximates the complex, changing fluid dynamics. Because resting assessment cannot reliably predict stress haemodynamics, ‘valvular fractional flow’ warrants study to explain exertional symptoms in patients with only moderate AS at rest.

Hemodynamic exercise responses with a continuous-flow left ventricular assist device: Comparison of patients’ response and cardiorespiratory simulations

“…This permitted to mimic a better/poorer chronotropic, inotropic or peripheral circulatory response to exercise. Valvular pathologies, as observed in some LVAD patients, were also simulated such as aortic valve insufficiency (AI) and aortic valve stenosis (AS) [28,29]. The simulated cardiovascular parameters mentioned beforehand are reported in Table 1.…”

Phasic pressure measurements for coronary and valvular interventions using fluid‐filled catheters: Errors, automated correction, and clinical implications

“…Given that invasive physiology often acts as the final gatekeeper for coronary revascularization or valve implantation, a biased or faulty measurement can lead to adverse clinical consequences when accounting for the periprocedural risk of any device therapy. Ideally a second pressure wire would be inserted to measure aortic pressure, in addition to the existing pressure wire in the distal coronary artery or left ventricle. However, its added cost and logistical complexity remain prohibitive in daily practice.…”

“…For coronary stenosis, established fractional flow reserve (FFR) has been joined by nonhyperemic pressure ratios (NHPR) . For aortic stenosis, the mean transvalvular pressure gradient (Δ P ) remains classic, with emerging data for the stress aortic valve index (SAVI) …”

“…Hence historic 2F microcatheters and 0.015″ fluid‐filled wires gave way to modern, high‐fidelity 0.014″ piezoelectric or fiberoptic pressure wires for coronary physiology. While most aortic valve assessment uses single‐ or dual‐lumen pigtail catheters, high‐fidelity micromanometers have found limited clinical uptake, in contrast to repurposing coronary pressure wires for valvular assessment …”

LVAD speed increase during exercise, which patients would benefit the most? A simulation study

“…This permitted to mimic LVAD patients with a better/poorer chronotropic, inotropic, or peripheral circulatory response to exercise. Additionally, aortic insufficiency (AI) and aortic valve stenosis (AS) sometimes observed in LVAD patients were also simulated . A comprehensive overview of the cardiovascular parameters at BL and of their manual changes are reported in Table and in Supplementary Figure .…”