Possible Early Generation of Physiological Helical Flow Could Benefit the Triflo Trileaflet Heart Valve Prosthesis Compared to Bileaflet Valves

Abstract

Background—Physiological helical flow in the ascending aorta has been well documented in the last two decades, accompanied by discussions on possible physiological benefits of such axial swirl. Recent 4D-MRI studies on healthy volunteers have found indications of early generation of helical flow, early in the systole and close to the valve plane. Objectives—Firstly, the aim of the study is to investigate the hypothesis of premature swirl existence in the ventricular outflow tract leading to helical flow in the valve plane, and second to investigate the possible impact of two different mechanical valve designs on the preservation of this early helical flow and its subsequent hemodynamic consequences. Methods—We use a pulse duplicator with an aortic arch and High-Speed Particle Image Velocimetry to document the flow evolution in the systolic cycle. The pulse-duplicator is modified with a swirl-generating insert to generate early helical flow in the valve plane. Special focus is paid to the interaction of such helical flow with different designs of mechanical prosthetic heart valves, comparing a classical bileaflet mechanical heart valve, the St. Jude Medical Regent valve (SJM Regent BMHV), with the Triflo trileaflet mechanical heart valve T2B version (Triflo TMHV). Results—When the swirl-generator is inserted, a vortex is generated in the core flow, demonstrating early helical flow in the valve plane, similar to the observations reported in the recent 4D-MRI study taken for comparison. For the Triflo trileaflet valve, the early helical flow is not obstructed in the central orifice, similar as in the case of the natural valve. Conservation of angular momentum leads to radial expansion of the core flow and flattening of the axial flow profile downstream in the arch. Furthermore, the early helical flow helps to overcome separation at the outer and inner curvature. In contrast, the two parallel leaflets for the bileaflet valve impose a flow straightener effect, annihilating the angular momentum, which has a negative impact on kinetic energy of the flow. Conclusion—The results imply better hemodynamics for the Triflo trileaflet valve based on hydrodynamic arguments under the discussed hypothesis. In addition, it makes the Triflo valve a better candidate for valve replacements in patients with a pathological generation of nonaxial velocity in the ventricle outflow tract.

Trileaflet Mechanical Valves: What Is Already Known? A Systematic Review

“…The researchers conclude that the trileaflet valve preserves over 80% the swirling core flow and angular momentum compared to a biological valve [27]. Stronger retrograde flow was found in the sinuses of the trileaflet valve, supporting the early onset of leaflet closure.…”

“…In 2020, Bruecker et al investigated the effect of a bileaflet and trileaflet design on the preservation of early helical flow in the ventricular outflow tract [27]. Using a pulse duplicator, high speed particle image velocimetry and a 25mm aorta with comparable geometry, the effect of helical flow was studied over a SJM Regent valve and Triflo T2B trileaflet mechanical valve.…”

“…Conservation of this helical flow can be of importance to the distribution of microbubbles, generated by MHV due to degassing during the localized pressure drop at valve closure [27]. These microbubbles can be propagated in the ascending aorta and cause gas embolism.…”

In vivo performance of a tri-leaflet mechanical heart valve prosthesis in an ovine model

“…Currently used mechanical heart valves all consist of a cuffed ring housing 2 leaflets, mostly made from pyrolytic carbon. The parallel leaflets of On-X valves impose a flow straightener effect, converting the normal helical flow to axial flow [ 2 ]. This leads to a drop in kinetic energy and thus total pressure loss over the valve, meaning the left ventricle experiences a higher afterload to eject the same amount of fluid into the systolic pulse [ 3 ].…”

“…This leads to a drop in kinetic energy and thus total pressure loss over the valve, meaning the left ventricle experiences a higher afterload to eject the same amount of fluid into the systolic pulse [ 3 ]. This differs significantly from the Triflo valve, which conserves the physiological helical flow, angular momentum and kinetic energy [ 2 , 4 ]. This closely mimics the haemodynamic profile of a natural trileaflet valve.…”