Simultaneous Doppler and catheter transvalvular pressure gradients across St Jude bileaflet mitral valve prosthesis: in vivo study in a chronic animal model with pediatric valve sizes

Prognostic Implications of Left Ventricular Global Longitudinal Strain in Patients With Surgically Treated Mitral Valve Disease and Preserved Ejection Fraction

Background

This study investigated whether left ventricular (LV) global longitudinal strain (LV-GLS), as an LV function parameter less affected by mitral valve (MV) repair or prosthesis, is associated with clinical outcomes in patients with surgically treated MV disease.

Methods

Among 750 patients who underwent MV surgery, we assessed LV-GLS by speckle tracking echocardiography in 344 patients (148 men, mean age 58 ± 13 years) who showed preserved LV ejection fraction on echocardiography between 6 months and 2 years after MV surgery and who did not undergo aortic valve surgery. The assessed clinical events included admission for worsening of heart failure and cardiac death.

Results

During a period of 42.4 ± 26.0 months, 32 (9.3%) patients were hospitalized for worsening heart failure, and 3 (0.8%) died due to cardiac causes. The absolute value of LV-GLS (|LV-GLS|) was significantly lower in patients with clinical events than in those without (12.1 ± 3.1 vs. 15.0 ± 3.2%, p < 0.001) despite comparable LV ejection fraction between groups. |LV-GLS| showed predictive value for clinical events (cut-off 13.9%, area under the curve 0.744, p < 0.001). Patients with |LV-GLS| ≤14.0% had poorer outcomes than those with |LV-GLS| >14.0% (log-rank p < 0.001). Prognosis was worse in patients with |LV-GLS| ≤14.0% and pulmonary hypertension than among those who with |LV-GLS| ≤14.0% without pulmonary hypertension (log rank p < 0.001). In nested Cox proportional hazard regression models, reduced |LV-GLS| was independently associated with the occurrence of clinical events.

Conclusions

In patients with surgically treated MV and preserved LV ejection fraction, assessment of LV-GLS provides functional information associated with cardiovascular outcomes.

Comparison of the Hemodynamic and Thrombogenic Performance of Two Bileaflet Mechanical Heart Valves Using a CFD/FSI Model

The hemodynamic and the thrombogenic performance of two commercially available bileaflet mechanical heart valves (MHVs)—the ATS Open Pivot Valve (ATS) and the St. Jude Regent Valve (SJM), was compared using a state of the art computational fluid dynamics-fluid structure interaction (CFD-FSI) methodology. A transient simulation of the ATS and SJM valves was conducted in a three-dimensional model geometry of a straight conduit with sudden expansion distal the valves, including the valve housing and detailed hinge geometry. An aortic flow waveform (60 beats/min, cardiac output 4 l∕min) was applied at the inlet. The FSI formulation utilized a fully implicit coupling procedure using a separate solver for the fluid problem (FLUENT) and for the structural problem. Valve leaflet excursion and pressure differences were calculated, as well as shear stress on the leaflets and accumulated shear stress on particles released during both forward and backward flow phases through the open and closed valve, respectively. In contrast to the SJM, the ATS valve opened to less than maximal opening angle. Nevertheless, maximal and mean pressure gradients and velocity patterns through the valve orifices were comparable. Platelet stress accumulation during forward flow indicated that no platelets experienced a stress accumulation higher than 35 dyne×s/cm2, the threshold for platelet activation (Hellums criterion). However, during the regurgitation flow phase, 0.81% of the platelets in the SJM valve experienced a stress accumulation higher than 35 dyne×s/cm2, compared with 0.63% for the ATS valve. The numerical results indicate that the designs of the ATS and SJM valves, which differ mostly in their hinge mechanism, lead to different potential for platelet activation, especially during the regurgitation phase. This numerical methodology can be used to assess the effects of design parameters on the flow induced thrombogenic potential of blood recirculating devices.

Jet eccentricity: a misleading source of agreement between Doppler/catheter pressure gradients in aortic stenosis

Characterization of the severity of aortic stenosis relies on accurate measurement of the pressure gradient across the valve and the valve area. Pressure gradients measured by Doppler ultrasound based on the clinical form of the Bernoulli equation often overestimate pressure gradients by catheter as the result of pressure recovery. Doppler techniques measure the velocity of the vena contracta of the stenotic jet. This corresponds to the maximal pressure gradient and the minimal effective valve area. Pressure recovery can be characterized by analysis of the spread of the stenotic jet downstream of the valve as it fills the aorta and should be influenced by the shape of the velocity profile of the decaying jet. In this study, we addressed the hypothesis that the site of complete pressure recovery (the point at which the jet fully expands to the size of the aorta), the effective valve area, and the maximal pressure gradient are affected by jet eccentricity. To accomplish this, we developed a computational model of aortic stenosis that provides detailed velocity and pressure information in the vicinity of the valve. The results show that the width of the eccentric wall jet decreased and maximal velocity increased with greater jet eccentricity. Furthermore, for a constant anatomic area, the effective valve area decreased, the distance to complete pressure recovery increased, and the maximal pressure gradient increased with the degree of eccentricity. Failure to take this into account could fortuitously drive Doppler and catheter measurements toward agreement because the distal pressure sensor will not record the fully recovered pressure. Therefore the pressure gradient across a stenotic valve depends on jet eccentricity. The spread of the wall jet after attachment must be characterized to develop a robust method for the prediction of pressure recovery.

A method for determining the reference effective flow areas for mechanical heart valve prostheses: in vitro validation studies

BACKGROUND

The anatomic opening area (AOA) is usually reported as the primary index of mechanical heart valve function. Because flow contracts immediately distal to an orifice as a result of the vena contracta effect, AOA may not be a good measure of true effective flow area.

METHODS AND RESULTS

Laser flow imaging was used to visualize the contraction in the jet flow stream as it passed through bileaflet mechanical valves under steady and pulsatile conditions. Such visualization allowed clear measurement of the individual vena contracta areas (VCAs) of the 3 valve orifices. VCAs for side orifices were larger (94+/-2% of AOA) than those through the central orifice (34+/-8%). Formation of large radial vortices around the leaflet tips constricted the central orifice flow stream and appeared to be the main reason for smaller central VCA. Total VCA remained constant until approximately 0.5 orifice diameters ( approximately 1.0 cm) downstream, beyond which cross-sectional area increased as a result of entrainment of receiving chamber flow. Total VCA was larger for steady flow (89.6+/-2.7% of AOA) than for pulsatile flow (76.3+/-5.0% of AOA).

CONCLUSIONS

This study further clarifies flow dynamics through bileaflet mechanical valves and provides previously unavailable reference information on VCAs for these valves. Such information should aid clinicians in explaining Doppler-derived and catheter-measured pressure discrepancies, validating clinical techniques for quantifying effective flow areas, and optimizing valve size for implantation. The method should also be useful for comparative studies of different valve designs.