Larger Effective Orifice Area Research Articles

Impact of Prosthesis-Patient Mismatch on Survival After Mitral Valve Replacement

We recently reported that valve prosthesis-patient mismatch (PPM) is associated with persisting pulmonary hypertension after mitral valve replacement. Thus, the objective of this study was to evaluate the impact of PPM on mortality in patients undergoing mitral valve replacement. The indexed valve effective orifice area was estimated for each type and size of prosthesis being implanted in 929 consecutive patients and used to define PPM as not clinically significant if > 1.2 cm2/m2, as moderate if > 0.9 and < or = 1.2 cm2/m2, and as severe if < or = 0.9 cm2/m2. Moderate PPM was present in 69% of patients; severe PPM was seen in 9%. For patients with severe PPM, 6-year survival (74+/-5%) and 12-year survival (63+/-7%) were significantly less than for patients with moderate PPM (84+/-1% and 76+/-2%; P=0.027) or nonsignificant PPM (90+/-2% and 82+/-4%; P=0.002). On multivariate analysis, severe PPM was associated with higher mortality (hazard ratio, 3.2; 95% confidence interval, 1.5 to 6.8; P=0.003). Severe PPM is an independent predictor of mortality after mitral valve replacement. As opposed to other independent risk factors, PPM may be avoided or its severity may be reduced with the use of a prospective strategy at the time of operation. For patients identified as being at risk for severe PPM, every effort should be made to implant a prosthesis with a larger effective orifice area.

One year hemodynamic performance of the Perimount Magna pericardial xenograft and the Medtronic Mosaic bioprosthesis in the aortic position: a prospective randomized study

We compared the hemodynamic performance of the Edwards Perimount Magna (EPM) and the Medtronic Mosaic (MM) bioprostheses according to the patient aortic annulus diameter (AAD). Eighty-six patients undergoing aortic valve replacement were prospectively assigned to receive either an EPM-valve (n=43) or an MM-bioprosthesis (n=43). Randomization was performed after measuring the AAD and patients were grouped according to their AAD: <22 mm (n=12), 22-23 mm (n=31) and >23 mm (n=43). Echocardiographic assessment was performed one year postoperatively. The mean AAD (EPM 23.9+/-2.1 mm vs. MM 23.6+/-2.3 mm) and mean valve size implanted (EPM 22.6+/-2.1 mm vs. MM 23.3+/-2.1 mm) were comparable in both groups. The EPM-group showed significantly lower mean gradient (EPM 10.2+/-3.2 mmHg vs. MM 17.1+/-8.2 mmHg) and larger effective orifice area (EOA) (EPM 1.99+/-0.4 cm(2) vs. MM 1.69+/-0.4 cm(2), P<0.0001). The EPM-valve was superior with respect to mean pressure gradient and EOA in all AAD. This difference was statistically significant in AAD of 22-23 mm (EPM 9.6+/-3.0 mmHg vs. MM 18.2+/-8.6 mmHg; EPM 1.82+/-0.3 cm (2) vs. MM 1.51+/-0.2 cm (2)) and >23 mm (EPM 9.9+/-3.1 mmHg vs. MM 14.2+/-5.6 mmHg; EPM 2.18+/-0.4 cm(2) vs. MM 1.94+/-0.5 cm(2)). Patient-prosthesis mismatch was present in 26.8% (MM) vs. 6.9% (EPM) of the patients (P=0.01). When the same AAD is taken as a reference, the EPM-valve was hemodynamically superior to the MM-bioprosthesis. The EPM-prosthesis significantly reduced the incidence of PPM.

AN EXPERIMENTAL FLUID DYNAMIC STUDY OF A POLYMERIC TRILEAFLET HEART VALVE USING LDV

While mechanical heart valves (MHVs) remain the most widely implanted valves, polymeric valves have inherent advantages. These include both their larger effective orifice area and their lower leaflet closing velocities which minimize their cavitation, hemolysis, and platelet activation relative to MHVs. Currently, most polymeric valves are used as part of left ventricular assist devices and total artificial hearts. There is interest to use these valves as replacement valves, and characterizing their fluid dynamics will help achieve this goal. An in vitro laser Doppler velocimetry study was conducted on a 25 mm polymeric trileaflet heart valve (Abiomed Inc), in the aortic position. The valve is mounted in an acrylic conduit with aortic sinuses that allows for optical access upstream and downstream of the valve. A sodium/iodide/glycerin fluid that matches the kinematic viscosity of blood and the index of refraction of the model was used as a blood analog. Flow was driven using a ventricular assist device at a heart rate of 90 bpm, a flow rate of 4.5 l/min, and an aortic pressure of 130/90 mmHg. Mean velocity data was collected in four planes: one diameter upstream, one diameter downstream of the commissural plane, within the sinuses, and at the tip of the commissures. High velocity jets and high Reynolds stresses were measured near the orifice at the leaflet tips and between the leaflets. Recirculation occurs in the aortic sinuses, reducing the potential for thrombus formation.

Full-root versus subcoronary implantation of stentless bioprostheses: Which technique provides superior hemodynamics?

Objectives: The SJM Toronto Root stentless bioprosthesis is suitable for full-root replacement (FR) with coronary reimplantation, or subcoronary implantation (SC). It is presumed, that the FR technique results in lower gradients and larger effective orifice areas.

Impact of Prosthesis-Patient Mismatch on Long-Term Survival in Patients With Small St Jude Medical Mechanical Prostheses in the Aortic Position

The impact of aortic prosthesis-patient mismatch (P-PtM) on long-term survival is unclear. Between 1985 and 2000, 388 patients at Mayo Clinic in Rochester, Minn, underwent aortic valve replacement (AVR) with 19- or 21-mm St Jude Medical prostheses and had transthoracic echocardiography within 1 year after AVR. Mean age of patients was 62+/-13 years; 69% were female. Prosthesis effective orifice area (EOA) was derived from the continuity equation. P-PtM was classified as severe (indexed EOA < or =0.60 cm2/m2), moderate (0.60 cm2/m2<indexed EOA< or =0.85 cm2/m2), or not hemodynamically significant (indexed EOA >0.85 cm2/m2). P-PtM was severe in 66 patients (17%), moderate in 168 (43%), and not hemodynamically significant in 154 (40%). Patients with severe P-PtM had a significantly larger body surface area (P<0.0001), higher mean gradient (P<0.0001), lower preoperative (P<0.0001) and postoperative (P<0.0001) ejection fractions, and lower stroke volume (P<0.0001) and more often received a 19-mm prosthesis (P=0.0008) than patients with moderate or no hemodynamically significant mismatch. For patients with severe mismatch, 5-year survival rates (72+/-6%) and 8-year survival rates (41+/-8%) were significantly less than for patients with moderate mismatch (80+/-3% and 65+/-5%; P=0.026) or no hemodynamically significant mismatch (85+/-3% and 74+/-5%; P=0.002). On multivariate analysis after adjustment for other predictors of outcome, severe mismatch was associated with higher mortality (hazard ratio 2.18; 95% confidence interval 1.24 to 3.85; P=0.007) and higher incidence of congestive heart failure (hazard ratio 3.1; 95% confidence interval 1.3 to 7.4; P=0.009) than no hemodynamically significant mismatch. Severe P-PtM is an independent predictor of higher long-term mortality and congestive heart failure in patients with small St Jude Medical aortic valve prostheses. For patients undergoing AVR who are at risk of severe mismatch, every effort should be made to use a larger prosthesis or to consider a prosthesis with a larger EOA.

Flow in Prosthetic Heart Valves: State-of-the-Art and Future Directions

Since the first successful implantation of a prosthetic heart valve four decades ago, over 50 different designs have been developed including both mechanical and bioprosthetic valves. Today, the most widely implanted design is the mechanical bileaflet, with over 170,000 implants worldwide each year. Several different mechanical valves are currently available and many of them have good bulk forward flow hemodynamics, with lower transvalvular pressure drops, larger effective orifice areas, and fewer regions of forward flow stasis than their earlier-generation counterparts such as the ball-and-cage and tilting-disc valves. However, mechanical valve implants suffer from complications resulting from thrombus deposition and patients implanted with these valves need to be under long-term anti-coagulant therapy. In general, blood thinners are not needed with bioprosthetic implants, but tissue valves suffer from structural failure with, an average life-time of 10-12 years, before replacement is needed. Flow-induced stresses on the formed elements in blood have been implicated in thrombus initiation within the mechanical valve prostheses. Regions of stress concentration on the leaflets during the complex motion of the leaflets have been implicated with structural failure of the leaflets with bioprosthetic valves. In vivo and in vitro experimental studies have yielded valuable information on the relationship between hemodynamic stresses and the problems associated with the implants. More recently, Computational Fluid Dynamics (CFD) has emerged as a promising tool, which, alongside experimentation, can yield insights of unprecedented detail into the hemodynamics of prosthetic heart valves. For CFD to realize its full potential, however, it must rely on numerical techniques that can handle the enormous geometrical complexities of prosthetic devices with spatial and temporal resolution sufficiently high to accurately capture all hemodynamically relevant scales of motion. Such algorithms do not exist today and their development should be a major research priority. For CFD to further gain the confidence of valve designers and medical practitioners it must also undergo comprehensive validation with experimental data. Such validation requires the use of high-resolution flow measuring tools and techniques and the integration of experimental studies with CFD modeling.

Stentless Aortic Valves are Hemodynamically Superior to Stented Valves During Mid-Term Follow-Up: A Large Retrospective Study

Several studies have compared left venticular mass (LVM) regression and hemodynamic data for stentless versus stented aortic bioprostheses with conflicting results. The major limitations of these studies are their small sample size and short-term follow-up. We therefore compared midterm LVM regression, hemodynamic data, and survival in a large population of tissue aortic valve replacement (AVR) patients. All patients undergoing tissue AVR at our institution between 1998 and 2001 were included (n = 737). Patients were divided into two groups according to type of bioprosthetic implanted: stentless patients (total n = 310) (Toronto SPV [St Jude Medical, St Paul, MN], n = 146 and Freestyle [Medtronic, Minneapolis, MN], n = 164) and stented patients (total n = 427) (Perimount [Edwards Life Sciences Inc, Irvine, CA], n = 291 and Mosaic [Medtronic], n = 136). The two groups of patients had similar preoperative transvalvular gradients and LVM index (130 +/- 47 vs 130 +/- 42 g/m2 for stentless versus stented valves, respectively). Predischarge echos revealed that stentless patients had significantly lower mean transvalvular gradients (11 +/- 5 vs 15 +/- 6 mm Hg, p < 0.001) and larger effective orifice areas (1.32 +/- 0.52 vs 1.22 +/- 0.48 cm2, p = 0.01). Follow-up echocardiograms were obtained in 99% of surviving patients 28 +/- 22 (range, 0-79) months postoperatively. Stentless patients had significantly lower LVM index during follow-up (100 +/- 32 vs 107 +/- 32 g/m2, p = 0.005) and stentless valves were an independent predictor of LVM regression. Furthermore, a higher proportion of stented patients had residual LV hypertrophy during follow-up (28% vs 18%, p = 0.001). Stentless valves were associated with improved midterm survival by univariate analysis, but not by multivariable analysis. Midterm follow-up in a large number of patients reveals that stentless bioprostheses are hemodynamically superior to stented valves.

Early diastolic left ventricular inflow pressures in normal subjects and patients with dilated cardiomyopathy. Reconstruction from pulsed Doppler echocardiography.

To estimate early diastolic left ventricular inflow pressures in normal subjects and patients with dilated cardiomyopathy, and thus to assess the potential effect of restoring forces. Early diastolic left ventricular inflow pressures were reconstructed using the ventricular blood as an accelerometer, by measuring velocity at 1 cm intervals within the left ventricle from mitral ring to apex by pulsed Doppler echocardiography, and differentiating the records to obtain the acceleration. Aortic component of second heart sound (A2) was used to fix relative timings. The local pressure gradient was determined from the acceleration at each level, and the total pressure drop during the acceleration (+ peak PD) and deceleration (- peak PD) phases of the filling interval were determined by summing the local increments. The total stroke volume (SV) at the left ventricular outflow tract and the mitral stroke distances (MSD) were also determined, using the time-velocity integral at mitral ring level. Effective flow orifice area was thus SV/MSD. Inflow jet width across the mitral valve was estimated by cross sectional colour Doppler flow mapping. 32 patients with dilated cardiomyopathy with a dominant mitral E or summation wave, and 24 normal subjects of similar ages. Normal + peak PD was 3.9 (SD 0.7) v 7.4 (2.2) mm Hg in dilated cardiomyopathy (P < 0.01). Normal - peak PD was 2.5 (0.9) v 5.6 (2.8) mm Hg in cardiomyopathy (P < 0.01). Normal effective flow orifice area was 5.9 (1.3) v 1.9 (0.8) [range 0.9 approximately 3.7] cm2 in cardiomyopathy (P < 0.01). This corresponded to 71 (18)% of the end systolic cavity cross section in normals v 11 (6)% in dilated cardiomyopathy (P < 0.01). Normal cross sectional colour inflow jet width was 2.7 (0.3) v 1.5 (0.4) cm in cardiomyopathy (P < 0.01). The jet width correlated with flow width calculated from effective flow orifice area (r = 0.82, P < 0.01). (1) Total early diastolic positive and negative peak pressure drop are normally low, so that significant negative left ventricular pressures are not needed to explain normal resting early diastolic mitral flow velocities. (2) These low pressure drops are only possible with a large effective orifice area approaching end systolic left ventricular cavity area. (3) Atrioventricular pressure drops are much greater in dilated cardiomyopathy, where increased inflow accelerations are due to reduced effective flow orifice area. These disturbances will impair filling independently of any abnormality of relaxation or compliance.

In vitro pulsatile flow hemodynamics of five mechanical aortic heart valve prostheses

In vitro measurements of velocity, turbulent shear stress, effective orifice area (EOA), and regurgitant fraction were performed on five new-generation low-profile mechanical aortic heart valve designs under pulsatile flow conditions. These were: Medtronic-Hall tilting disc, St. Jude Medical bileaflet, Björk-Shiley Monostrut tilting disc, Omni-Carbon tilting disc, and Duromedics bileaflet. In general, bileaflet valves have larger EOAs than the tilting disc design, especially in the larger sizes, due to the larger opening angles and lack of obstructive struts. The regurgitant fractions range from 8% for 21-mm valves to 13% for the 29-mm sizes. This increase was largely due to an increase in leakage volume as opposed to closing volume. Furthermore, the leakage volumes increased as the mean aortic pressures increased. The tilting disc valves generally have better regurgitant characteristics compared to the bileaflet valve designs, due to lower leakage volumes and to the smaller opening angle of the occluder providing a more rapid closure of the valve. The velocity and shear stress measurements showed that none of the current valve designs are ideal: all designs create areas of stasis and/or regions of low-velocity reverse flow and regions of elevated turbulent shear stresses capable of causing sublethal and/or lethal damage to the formed elements of blood. It is therefore unlikely that these valve designs will eliminate the problems of hemolysis, thrombosis, and thromboembolic complications.