Nonsymmetric leaflet motion of St. Jude Medical mitral valves simulated with a computer-controlled hydraulic mock circulator

Early Prosthetic Valve Malfunction Leading to Cardiogenic Shock and Emergency Redo Mitral Valve Replacement

Early onset prosthetic valve stenosis is an uncommon complication after valve replacement surgery and is often caused by thrombus formation. Frequently it can be diagnosed by echocardiography and managed with optimizing anticoagulation and/or thrombolysis. We review a unique case of early bi-leaflet mechanical heart valve (BMHV) dysfunction where the patient rapidly progressed to cardiogenic shock requiring emergent re-do mitral valve surgery. Intraoperatively, the valve leaflets were found to be almost completely immobile secondary to thrombus formation directly on the hinges of the valve. This case demonstrates how the leaflet orientation of a BMHV affects transmitral flow and fluid dynamics. Furthermore, we also discuss left atrial vortex formation in the setting of atrial fibrillation, kinetic energy transfer through an anatomically implanted mechanical mitral valve, and their roles in contributing to early prosthetic valve thrombosis despite adequate anticoagulation.

A compliant aortic model for in vitro simulations: Design and manufacturing process

We design and manufacture a silicone model of the human aorta, able to mimic both the geometrical and the mechanical properties of physiological individuals, with a specific focus on reproducing the compliance. In fact, while the models available in the literature exhibit an unrealistic compliant behavior, though they are detailed from the geometrical viewpoint, here the goal is to provide an accurate compliant tool for in vitro testing the devices that interface with the vascular system. A parametric design of the aortic model is obtained based on the available literature data, and the model is manufactured with a specific silicone mixture using rapid prototyping and molding techniques. The manufactured prototype has been tested by means of computed tomography scans for evaluating the matching of the mechanical properties with the desired ones. Results show a high degree of adherence between the imposed and the measured compliance values for each main aortic section. Thus, our work proves the feasibility of the approach, and the possibility to manufacture compliant models that reproduce the mechanical behavior of the aorta for in vitro studies.

The Effect of Vortex Formation on Left Ventricular Filling and Mitral Valve Efficiency

A new mechanism for quantifying the filling energetics in the left ventricle (LV) and past mechanical heart valves (MHV) is identified and presented. This mechanism is attributed to vortex formation dynamics past MHV leaflets. Recent studies support the conjecture that the natural healthy left ventricle (LV) performs in an optimum, energy-preserving manner by redirecting the flow with high efficiency. Yet to date, no quantitative proof has been presented. The present work provides quantitative results and validation of a theory based on the dynamics of vortex ring formation, which is governed by a critical formation number (FN) that corresponds to the dimensionless time at which the vortex ring has reached its maximum circulation content, in support of this hypothesis. Herein, several parameters (vortex ring circulation, vortex ring energy, critical FN, hydrodynamic efficiencies, vortex ring propagation speed) have been quantified and presented as a means of bridging the physics of vortex formation in the LV. In fact, the diastolic hydrodynamic efficiencies were found to be 60, 41, and 29%, respectively, for the porcine, anti-anatomical, and anatomical valve configurations. This assessment provides quantitative proof of vortex formation, which is dependent of valve design and orientation, being an important flow characteristic and associated to LV energetics. Time resolved digital particle image velocimetry with kilohertz sampling rate was used to study the ejection of fluid into the LV and resolve the spatiotemporal evolution of the flow. The clinical significance of this study is quantifying vortex formation and the critical FN that can potentially serve as a parameter to quantify the LV filling process and the performance of heart valves.

Time-resolved DPIV analysis of vortex dynamics in a left ventricular model through bileaflet mechanical and porcine heart valve prostheses

The performance of the heart after a mitral valve replacement operation greatly depends on the flow character downstream of the valve. The design and implanting orientation of valves may considerably affect the flow development. A study of the hemodynamics of two orientations, anatomical and anti-anatomical, of the St. Jude Medical (SJM) bileaflet valve are presented and compared with those of the SJM Biocor porcine valve, which served also to represent the natural valve. We document the velocity field in a flexible, transparent (LV) using time-resolved digital particle image velocimetry (TRDPIV). Vortex formation and vortex interaction are two important physical phenomena that dominate the filling and emptying of the ventricle. For the three configurations, the following effects were examined: mitral valve inlet jet asymmetry, survival of vortical structures upstream of the aortic valve, vortex-induced velocities and redirection of theflow in abidance of the Biot-Savart law, domain segmentation, resonant times of vortical structures, and regions of stagnantflow. The presence of three distinct flow patterns, for the three configurations, was identified by the location of vortical structures and level of coherence corresponding to a significant variation in the turbulence level distribution inside the LV. The adverse effect of these observations could potentially compromise the efficiency of the LV and result in flow patterns that deviate from those in the natural heart.

A new dual activation simulator of the left heart that reproduces physiological and pathological conditions

Heart valve replacements are often associated with cardiac pathologies, but valvular prostheses are still tested in vitro under the same physiological conditions as for a healthy young man. Therefore a new mock circulatory system of the left heart, the dual activation simulator (DAS), has been built. The DAS allows atrial and ventricular dynamics to be controlled with pumps that activate anatomically shaped silicon models of the cavities. The mitral flow is a two-peak waveform. The E/A ratio can be changed, and the A-wave can be suppressed to simulate, for instance, atrial fibrillation. The cardiac rhythm and the mean flow-rate can be changed at will. The ability of the DAS to reproduce physiological flow is assessed by computation of the aortic input impedance and by harmonic analysis of left ventricular and atrial pressures. It allows the behaviour of valve prostheses to be studied in various conditions of concern to clinicians and can be a useful tool for engineers to improve valve prostheses or validate diagnostic tools such as 3D colour Doppler. The DAS and its capacities are described.