Pressure gradients across bileaflet aortic valves by direct measurement and echocardiography

A multilayered valve leaflet promotes cell-laden collagen type I production and aortic valve hemodynamics

Patients with aortic heart valve disease are limited to valve replacements that lack the ability to grow and remodel. This presents a major challenge for pediatric patients who require a valve capable of somatic growth and at a smaller size. A patient-specific heart valve capable of growth and remodeling while maintaining proper valve function would address this major issue. Here, we recreate the native valve leaflet structure composed of poly-ε-caprolactone (PCL) and cell-laden gelatin-methacrylate/poly (ethylene glycol) diacrylate (GelMA/PEGDA) hydrogels using 3D printing and molding, and then evaluate the ability of the multilayered scaffold to produce collagen matrix under physiological shear stress conditions. We also characterized the valve hemodynamics under aortic physiological flow conditions. The valve's fibrosa layer was replicated by 3D printing PCL in a circumferential direction similar to collagen alignment in the native leaflet, and GelMA/PEGDA sustained and promoted cell viability in the spongiosa/ventricularis layers. We found that collagen type I production can be increased in the multilayered scaffold when it is exposed to pulsatile shear stress conditions over static conditions. When the PCL component was mounted onto a valve ring and tested under physiological aortic valve conditions, the hemodynamics were comparable to commercially available valves. Our results demonstrate that a structurally representative valve leaflet can be generated using 3D printing and that the PCL layer of the leaflet can sustain proper valve function under physiological aortic valve conditions.

Evaluating the Performance of Cardiac Pulse Duplicators Through the Concept of Fidelity

INTRODUCTION

The advanced design techniques used in modern prosthetic heart valve (PHV) development require accurate replication of the entire cardiac cycle. While cardiac pulse duplicator (CPD) design has a direct impact on the PHV test data generated, no clear guidelines exist to evaluate the CPD's performance. In response to this, we present a method to quantitatively assess CPD performance.

MATERIALS AND METHODS

A method to establish the fidelity of CPDs was formulated based on the pressure/time relationship and the error related to this relationship's target. This method was applied to assess the performance of a custom-made CPD. The performance evaluation included the assessment of the motion control system and overall repeatability of pressure measurements using a St Jude Epic 21 mm aortic valve.

RESULTS

The CPD's motion control system had an average root mean square error (RMSE) beat-to-beat tracking accuracy of 0.046 ± 0.008 mm. Assessment of the pressure measurements yielded a repeatability of < 2.4 ± 0.9 mmHg RMSE beat-to-beat differential pressure. The combination of pressure and its location within a heartbeat (fidelity) was within 5.0% of the individual targets for at least 95% of heartbeats.

CONCLUSION

Fidelity can be used to objectively quantify the performance of various aspects of CPDs and to identify the cause of unexpected PHV or CPD behaviour. It also enables comparisons to be made among various CPDs in terms of overall performance. This approach may enable standardization of the assessment of CPD performance in the future.

Quantitative Study of Abdominal Blood Flow Patterns in Patients with Aortic Dissection by 4-Dimensional Flow MRI

The purpose of this study is to evaluate the hemodynamic characteristics of the true lumen (TL) and the false lumen (FL) in 16 patients with aortic dissection (AD) using 4D flow magnetic resonance imaging (MRI) and thoracic and abdominal computed tomography (CT) angiography. The quantitative parameters that were measured in the TL and FL included velocity and flow. The mean area and regurgitant fraction of the TL were significantly lesser at all four levels (p < 0.05); the average through-plane velocity, peak velocity magnitude, average net flow, peak flow, and net forward volume in the TL were considerably higher (p < 0.05). The intimal entry's size was negatively correlated with the blood flow velocity and flow rate in the TL (p < 0.05) and positively correlated with the average through-plane velocity, average net flow, and peak flow in the FL (p < 0.05); the blood flow indices in the TL were enhanced with an increase in the intimal entry numbers (p < 0.05) and the peak flow in the FL was lowered (p = 0.025); if FL thrombosis existed, the average through-plane velocity and peak velocity magnitude in the TL were substantially higher (p < 0.05). 4D flow MRI facilitates qualitative and quantitative analysis of the alterations in the abdominal aortic blood flow patterns.

The Ross Operation: Clinical Results and Echocardiographic Findings

Between November 2001 and September 2004, 80 patients aged 11 to 56 years (mean, 27.6 years) underwent the Ross operation. The mean preoperative New York Heart Association functional class was 2.37 ± 0.72, and the mean ejection fraction was 52.8% ± 16%. Aortic involvement included stenosis in 19 (24%) patients, regurgitation in 22 (28%), and both in 39 (49%). Root replacement was the technique used in all cases. The mean hospital stay was 5 days, and 74 patients (93%) were followed up for 4–48 months. Four-year actuarial survival rate was 96.25%. Postoperative echocardiography revealed no pulmonary autograft insufficiency in 50 patients (63%), trivial to mild insufficiency in 22 (28%), moderate insufficiency in 2 (3%), and severe insufficiency in one (1%). Two patients required autograft re-intervention. Postoperative echocardiography of the pulmonary homograft valve showed severe stenosis (peak gradient > 50 mm Hg) in 2 patients, and moderate stenosis (peak gradient 25–50 mm Hg) in one. The mean postoperative left ventricular ejection fraction was 51.4%. The Ross operation can be considered an elegant alternative to prosthetic valves in the treatment of aortic valve diseases in developing countries.

Non-invasive pressure difference estimation from PC-MRI using the work-energy equation

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A novel semi-automatic method for the estimation of pressure differences in cardiovascular compartments from dense velocity fields (4D flow MRI data).

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The approach relies on the work-energy principle, and removes the need for second order spatial derivatives.

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Pressure differences are evaluated directly from the 4D flow data, without the need of any computational mesh.

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The method shows good accuracy, robustness to noise and robustness to segmentation compared to existing methods.

Pressure difference is an accepted clinical biomarker for cardiovascular disease conditions such as aortic coarctation. Currently, measurements of pressure differences in the clinic rely on invasive techniques (catheterization), prompting development of non-invasive estimates based on blood flow. In this work, we propose a non-invasive estimation procedure deriving pressure difference from the work-energy equation for a Newtonian fluid. Spatial and temporal convergence is demonstrated on in silico Phase Contrast Magnetic Resonance Image (PC-MRI) phantoms with steady and transient flow fields. The method is also tested on an image dataset generated in silico from a 3D patient-specific Computational Fluid Dynamics (CFD) simulation and finally evaluated on a cohort of 9 subjects. The performance is compared to existing approaches based on steady and unsteady Bernoulli formulations as well as the pressure Poisson equation. The new technique shows good accuracy, robustness to noise, and robustness to the image segmentation process, illustrating the potential of this approach for non-invasive pressure difference estimation.

Combining numerical and clinical methods to assess aortic valve hemodynamics during exercise

Computational simulations have the potential to aid understanding of cardiovascular hemodynamics under physiological conditions, including exercise. Therefore, blood hemodynamic parameters during different heart rates, rest and exercise have been investigated, using a numerical method. A model was developed for a healthy subject. Using geometrical data acquired by echo-Doppler, a two-dimensional model of the chamber of aortic sinus valsalva and aortic root was created. Systolic ventricular and aortic pressures were applied as boundary conditions computationally. These pressures were the initial physical conditions applied to the model to predict valve deformation and changes in hemodynamics. They were the clinically measured brachial pressures plus differences between brachial, central and left ventricular pressures. Echocardiographic imaging was also used to acquire different ejection times, necessary for pressure waveform equations of blood flow during exercise. A fluid-structure interaction simulation was performed, using an arbitrary Lagrangian-Eulerian mesh. During exercise, peak vorticity increased by 14.8%, peak shear rate by 15.8%, peak cell Reynolds number by 20%, peak leaflet tip velocity increased by 47% and the blood velocity increased by 3% through the leaflets, whereas full opening time decreased by 11%. Our results show that numerical methods can be combined with clinical measurements to provide good estimates of patient-specific hemodynamics at different heart rates.

Estimation of maximum intraventricular pressure: a three-dimensional fluid-structure interaction model

Background

The aim of this study was to propose a method to estimate the maximum pressure in the left ventricle (MPLV) for a healthy subject, based on cardiac outputs measured by echo-Doppler (non-invasive) and catheterization (invasive) techniques at rest and during exercise.

Methods

Blood flow through aortic valve was measured by Doppler flow echocardiography. Aortic valve geometry was calculated by echocardiographic imaging. A Fluid–structure Interaction (FSI) simulation was performed, using an Arbitrary Lagrangian–Eulerian (ALE) mesh. Boundary conditions were defined as pressure loads on ventricular and aortic sides during ejection phase. The FSI simulation was used to determine a numerical relationship between the cardiac output to aortic diastolic and left ventricular pressures. This relationship enabled the prediction of pressure loads from cardiac outputs measured by invasive and non-invasive clinical methods.

Results

Ventricular systolic pressure peak was calculated from cardiac output of Doppler, Fick oximetric and Thermodilution methods leading to a 22%, 18% and 24% increment throughout exercise, respectively. The mean gradients obtained from curves of ventricular systolic pressure based on Doppler, Fick oximetric and Thermodilution methods were 0.48, 0.41 and 0.56 mmHg/heart rate, respectively. Predicted Fick-MPLV differed by 4.7%, Thermodilution-MPLV by 30% and Doppler-MPLV by 12%, when compared to clinical reports.

Conclusions

Preliminary results from one subject show results that are in the range of literature values. The method needs to be validated by further testing, including independent measurements of intraventricular pressure. Since flow depends on the pressure loads, measuring more accurate intraventricular pressures helps to understand the cardiac flow dynamics for better clinical diagnosis. Furthermore, the method is non-invasive, safe, cheap and more practical. As clinical Fick-measured values have been known to be more accurate, our Fick-based prediction could be the most applicable.

Effect of exercise on blood flow through the aortic valve: a combined clinical and numerical study

The aim of this study was to measure the cardiac output and stroke volume for a healthy subject by coupling an echocardiogram Doppler (echo-Doppler) method with a fluid-structure interaction (FSI) simulation at rest and during exercise. Blood flow through aortic valve was measured by Doppler flow echocardiography. Aortic valve geometry was calculated by echocardiographic imaging. An FSI simulation was performed, using an arbitrary Lagrangian-Eulerian mesh. Boundary conditions were defined by pressure loads on ventricular and aortic sides. Pressure loads applied brachial pressures with (stage 1) and without (stage 2) differences between brachial, central and left ventricular pressures. FSI results for cardiac output were 15.4% lower than Doppler results for stage 1 (r = 0.999). This difference increased to 22.3% for stage 2. FSI results for stroke volume were undervalued by 15.3% when compared to Doppler results at stage 1 and 26.2% at stage 2 (r = 0.94). The predicted mean backflow of blood was 4.6%. Our results show that numerical methods can be combined with clinical measurements to provide good estimates of patient-specific cardiac output and stroke volume at different heart rates.

Diagnostic evaluation of left-sided prosthetic heart valve dysfunction. Nat Rev Cardiol. 2011;8:466-478. [PMID: 21587215 DOI: 10.1038/nrcardio.2011.71]

Prosthetic heart valve (PHV) dysfunction is a rare, but potentially life-threatening, complication. In clinical practice, PHV dysfunction poses a diagnostic dilemma. Echocardiography and fluoroscopy are the imaging techniques of choice and are routinely used in daily practice. However, these techniques sometimes fail to determine the specific cause of PHV dysfunction, which is crucial to the selection of the appropriate treatment strategy. Multidetector-row CT (MDCT) can be of additional value in diagnosing the specific cause of PHV dysfunction and provides valuable complimentary information for surgical planning in case of reoperation. Cardiac magnetic resonance imaging (CMR) has limited value in the evaluation of biological PHV dysfunction. In this Review, we discuss the use of established imaging modalities for the detection of left-sided mechanical and biological PHV dysfunction and discuss the complementary role of MDCT in this context.

Prosthetic heart valves: Types and echocardiographic evaluation

In the last five decades multiple different models of prosthetic valves have been developed. The purpose of this article is to provide a comprehensive source of information for the types and the echocardiographic evaluation of the prosthetic heart valves.

Assessment of hemodynamics properties of a new-type artificial heart valve prosthesis using catheterization and echocardiography

OBJECTIVE

The objectives of this study were to assess the hemodynamic properties of the newly developed artificial heart valve prosthesis experimentally in laboratory simulation, in an animal model, and clinically in a human model and to compare the results measured by catheterization and echocardiography.

METHODS

(1) Laboratory simulation. The prosthesis was tested using a pulsatile flow simulator in the aortic position. Hydrodynamics parameters were automatically analyzed through a custom-designed data processing program. (2) Animal experiment. Six sheep subjected to mitral replacement with 21-mm-valve prosthesis were measured by open cardiac catheterization intraoperatively. Doppler echocardiography and open cardiac catheterization under dobutamine stress were performed in two sheep subjected to implantation 2.5 years ago. (3) Clinical patient observation. Observations were carried out on 14 patients with aortas replacement and 10 patients with bicuspid replacement using both doppler echocardiography and open cardiac catheterization.

RESULTS

(1) Laboratory simulation. The results showed that the value of the transvalvular gradient (DeltaP) decreased with the increase of heart rate, and the values were not greater that 10 mm Hg at any given tissue annulus diameter. (2) Animal experiment. The mean DeltaP value of the six sheep was 5.2 +/- 1.7 mm Hg intraoperatively, while the corresponding DeltaP value of the two sheep 2.5 years after implantation was 6.1 +/- 0.3 mm Hg measured by open cardiac catheterization. (3) Clinical patient observation. The mean DeltaP values in the aortic position measured by catheterization and echocardiography were 6.26 approximately 4.10 and 9.42 approximately 7.48 mm Hg, respectively. The gradients in the mitral position were 2.10 approximately 1.9 and 5.28 approximately 4.10 mm Hg, respectively.

CONCLUSIONS

The results demonstrate that the new-type bileaflet heart valve prosthesis only generates a relatively low transvalvar gradient and thus has good hemodynamic properties.

Comparative Evaluation of Small-Size Sorin Slimline and St. Jude HP Heart Valve Prostheses

BACKGROUND

The Sorin Slimline aortic valve prosthesis, a modification of the Sorin Bicarbon valve with increased internal orifice diameter and geometric orifice area, may show improved hemodynamic performance when compared with other previous prosthesis, but so far no comparison study has been reported.

METHODS

Between May 1999 and March 2002, 80 patients (31 to 81 years of age; mean, 65 years) with a small aortic annulus were randomized to undergo aortic valve replacement with either the Sorin Slimline (n = 40) or St. Jude High Performance (n = 40) valve prosthesis. Clinical and echocardiographic Doppler follow-up was performed at 3 to 4 weeks, and 6 and 12 months postoperatively.

RESULTS

One patient died of non-valve-related causes 9 months after operation. Mean and peak pressure gradients at 6 and 12 months in the Sorin Slimline valve were lower than in the St. Jude High Performance valve for both size 19 and 21 mm. Effective orifice area and effective orifice area index were not significantly different. There was a significant (p = 0.0001) reduction in left ventricular mass and left ventricular mass index between preoperative measurements and at 12 months after surgery for both valves, but there was no difference (p = 0.27) between the Sorin Slimline and St. Jude High Performance valve prosthesis at any other follow-up period. Clinical results showed similarly good results with both valves.

CONCLUSIONS

No clinically significant difference in the hemodynamics of both valves was appreciated; patients with a Sorin Slimline valve exhibited statistically significantly lower pressure gradients, but the small differences in effective orifice area and effective orifice area index did not reach significance. A significant left ventricular mass regression was observed with both valve models. Both prostheses provided a satisfactory clinical outcome.

Net pressure gradients in aortic prosthetic valves can be estimated by Doppler

BACKGROUND

In aortic prosthetic valves, both the Doppler-estimated gradients and orifice areas are misleading in the assessment of hemodynamic performance. The parameter of major interest is the net pressure gradient after pressure recovery (PR). We, therefore, investigated, in vitro, our ability to predict the net pressure gradient and applied the formulas in a representative patient population with 2 different valve designs.

METHODS

We studied the St Jude Medical (SJM) standard valve (size 19-27) and SJM Biocor (size 21-27) in an in vitro steady-flow model with simultaneous Doppler-estimated pressure and catheter pressure measurements. Using echocardiography, we also studied patients who received the SJM (n = 66) and SJM Biocor (n = 45).

RESULTS

In the SJM, we observed PR both within the prosthesis and aorta, whereas in the SJM Biocor, PR was only present in the aorta. We estimated the PR within the valve and within the aorta separately from echocardiographic in vitro data, combining a regression equation (valve) with an equation on the basis of fluid mechanics theory (aorta). The difference between estimated and catheter-obtained net gradients (mean +/- SD) was 0.6 +/- 1.6 mm Hg in the SJM and -0.2 +/- 1.9 mm Hg in the SJM Biocor. When these equations were applied in vivo, we found that PR had an overall value of 57 +/- 7% of the peak Doppler gradient in the SJM and 33 +/- 9% in the SJM Biocor.

CONCLUSIONS

The in vitro results indicate that it is possible to predict the net pressure gradient by Doppler in bileaflet and stented biologic valves. Our data indicate that important PR is also present in stented biologic valves.

Left ventricular mass regression after implantation of St. Jude Medical cardiac valves in small aortic roots

In this study, we analyzed the extent of regression of left ventricular hypertrophy in patients who received small St. Jude Medical (SJM) aortic valves and compared the results with those of another group receiving larger valves. Eighty-eight patients received either 19 or 21 mm valves (Group 1, 25 patients) or either 23 or 25 mm valves (Group 2, 53 patients). Echocardiographic studies were done before the operation and 5 years postoperatively. At follow-up a significant reduction in the left ventricular mass was found for both patient groups (p < 0.0001). Doppler echocardiography derived pressure gradients for both groups were obtained during the follow-up period. As expected, the patients in Group 1 had higher peak pressure gradients than did those in Group 2. However, there was no significant difference between the 2 groups or any significant correlations between peak pressure gradients and body surface area (BSA). Actuarial survival was 84.7% at 15 years for Group 1 and 85.9% at 17 years for Group 2. Actuarial freedom from valve related events was 91.4% at 15 years for Group 1 and 82.7% at 17 years for Group 2. There was no significant difference in survival or valve related event free curves between the 2 groups. After implantations of SJM valves in small aortic roots, significant left ventricular mass regression was obtained, and the results were comparable to those for valves of other sizes. The long-term performance of aortic valve replacement with small valves was satisfactory as judged by improvement in the functional class of patients and survival statistics, the durability of the prosthesis, and valve related morbidity comparable to that of valves of other sizes.

Reference Doppler echocardiographic values for St. Jude Medical, Omnicarbon, and Biocor prosthetic valves in the aortic position

The objectives of the present investigation were (1) to describe Doppler echocardiographic findings for mechanical and biologic aortic valves at an early stage after operation and later in a stable phase and (2) to study the changes occurring between these investigations. Patients (n = 213) who received a mechanical (St. Jude Medical, Omnicarbon) or a biologic (Biocor) valve were studied by Doppler echocardiography within the first week (baseline, n = 203) and after 2 years (late, n = 172). The comparison of baseline with late investigation (mean +/- SD) showed an increase in systolic blood pressure (137 +/- 18.5 to 154 +/- 20.6 mm Hg, p = 0.0001, n = 112), reduction of heart rate (85 +/- 15.3 to 74 +/- 12.0 beats/min, p = 0.0001, n = 141) and increase in stroke volume (59 +/- 20.6 to 77 +/- 19.8 ml, p = 0.0001, n = 132). Prosthetic Doppler echocardiographic findings demonstrated a reduction in blood flow velocity in the left ventricular outflow tract (VLVOT, 1.10 +/- 0.25 to 0.96 +/- 0.23 m/sec, p = 0.0001, n = 146) reduction in peak velocity (Vmax 2.72 +/- 0.53 to 2.59 +/- 0.54 m/sec, p = 0.02, n = 150), reduction in mean pressure gradient (deltaPmean, 18.4 +/- 7.2 to 16.3 +/- 7.3 mm Hg, p = 0.004) and an increase in velocity index (Vmax/VLVOT, 2.56 +/- 0.62 to 2.67 +/- 0.60, p = 0.003, n = 144). The standard deviations of difference between baseline and late investigation expressed as percentage of mean were 25% for VLVOT, 20% for Vmax, 44% for deltaPmean, and 25% for velocity index. In conclusion, this large reference base provides data that should be useful for the clinician evaluating patients with prosthetic valves early after valve replacement as well as at a later stage. When valve dysfunction is suspected a previous investigation for comparison is helpful, and our data describe the changes that normally may be seen between an early baseline and a late investigation.

Clinical use of CarboMedics and St. Jude Medical valves

Three hundred and twenty-six patients underwent CarboMedics valve implantation (CM) in the aortic (119 patients), mitral (148 patients) or aortic and mitral (59 patients) positions while 371 patients underwent St. Jude Medical valve implantation (SJ) in the aortic (113 patients), mitral (184 patient), or aortic and mitral (74 patients) positions at National Taiwan University Hospital from August 1991 through 1995. All patients received warfarin (Coumadin) anticoagulation with the target international normalized ratio around 1.5. The hospital mortality was 3.7% in the CM group and 4.3% in the SJ group. In the CM group at 5 years, the actuarial freedom from thromboembolism, valve thrombosis, and anticoagulant-related hemorrhage was 89.91 +/- 2.66%, 95. 23 +/- 1.50%, and 99.62 +/- 0.37%, respectively, and the actuarial survival rate was 90.4 +/- 1.6%. In the SJ group at 5 years, the actuarial freedom from thromboembolism, valve thrombosis, and anticoagulant-related hemorrhage was 94.79% +/- 1.70%, 98.80 +/- 0.72%, and 99.68 +/- 0.31%, respectively, and the actuarial survival rate was 91.3 +/- 1.7%. We therefore concluded that a similar survival rate was noted in the CM and SJ groups. With low dose anticoagulation, the complications of thromboembolism, valve thrombosis, and anticoagulant-related hemorrhage were low in the SJ group.