Effect of prosthetic valve malfunction on the Doppler-catheter gradient relation for bileaflet aortic valve prostheses

Echocardiographic Versus Invasive Aortic Valve Gradients in Different Clinical Scenarios

BACKGROUND

The role of echocardiography in deriving transvalvular mean gradients from transaortic velocities in aortic stenosis (AS) and in structural valve degeneration (SVD) is well established. However, reports following surgical aortic valve replacement, post-transcatheter aortic valve replacement (TAVR), and valve-in-valve-TAVR (ViV-TAVR) have cautioned against the use of echocardiography-derived mean gradients to assess normal functioning bioprosthesis due to discrepancy compared with invasive measures in a phenomenon called discordance.

METHODS

In a multicenter study, intraprocedural echocardiographic and invasive mean gradients in AS, SVD, post-native TAVR, and post-ViV-TAVR were compared, when obtained concomitantly, and discharge echocardiographic gradients were recorded. Absolute discordance (intraprocedural echocardiographic - invasive mean gradient) and percent discordance (intraprocedural echocardiographic - invasive mean gradient/echocardiographic mean gradient) were calculated. Multivariable regression analysis was performed to determine variables independently associated with elevated postprocedure invasive gradients ≥20 mm Hg, absolute discordance >10 mm Hg, and discharge echocardiographic mean gradient ≥20 mm Hg.

RESULTS

A total of 5,027 patients were included in the registry: 4,725 native TAVR and 302 ViV-TAVR. Intraprocedural concomitant echocardiographic and invasive mean gradients were obtained pre-TAVR in AS (n = 2,418), pre-ViV-TAVR in SVD (n = 101), in post-ViV-TAVR (n = 77), and in post-TAVR (n = 823). Echocardiographic and invasive mean gradients demonstrated strong correlation (r = 0.69) and agreement (bias, 0.11; 95% CI, -0.4-0.62) in AS, moderate correlation (r = 0.56) and agreement (bias, 1.08; 95% CI, -2.53 to 4.59) in SVD, moderate correlation (r = 0.61) and weak agreement (bias, 6.47; 95% CI, 5.08-7.85) post-ViV-TAVR, and weak correlation (r = 0.18) and agreement (bias, 3.41; 95% CI, 3.16-3.65) post-TAVR. Absolute discordance occurs primarily in ViV-TVR and is not explained by sinotubular junction size and increases with increasing echocardiographic mean gradient. Percent discordance in AS and SVD (1.3% and 4%, respectively) was lower compared with post-TAVR/ViV-TAVR (66.7% and 100%, respectively). Compared with self-expanding valves, balloon expanding valves were independently associated with elevated discharge echocardiographic but lower invasive mean gradient (odds ratio = 3.411, 95% CI, 1.482-7.852, P = .004; vs odds ratio = 0.308, 95% CI, 0.130-0.731, P = .008, respectively).

CONCLUSIONS

Post-TAVR/ViV-TAVR, echocardiography is discordant from invasive mean gradients, and absolute discordance increases with increasing echocardiographic mean gradient and is not explained by sinotubular junction size. Percent discordance is significantly higher post-TAVR/ViV-TAVR than in AS and SVD. Post-TAVR/ViV-TAVR, poor correlation and wide limits of agreement suggest echocardiographic and invasive mean gradients may not be used interchangeably and a high residual echocardiographic mean gradient should be confirmed invasively before considering any additional procedure to "correct" the gradient. Transcatheter aortic valve replacement valve types have variable impact on echocardiographic and invasive mean gradients.

Simulation of Mechanical Heart Valve Dysfunction and the Non-Newtonian Blood Model Approach

The mechanical heart valve (MHV) is commonly used for the treatment of cardiovascular diseases. Nonphysiological hemodynamic in the MHV may cause hemolysis, platelet activation, and an increased risk of thromboembolism. Thromboembolism may cause severe complications and valve dysfunction. This paper thoroughly reviewed the simulation of physical quantities (velocity distribution, vortex formation, and shear stress) in healthy and dysfunctional MHV and reviewed the non-Newtonian blood flow characteristics in MHV. In the MHV numerical study, the dysfunction will affect the simulation results, increase the pressure gradient and shear stress, and change the blood flow patterns, increasing the risks of hemolysis and platelet activation. The blood flow passes downstream and has obvious recirculation and stagnation region with the increased dysfunction severity. Due to the complex structure of the MHV, the non-Newtonian shear-thinning viscosity blood characteristics become apparent in MHV simulations. The comparative study between Newtonian and non-Newtonian always shows the difference. The shear-thinning blood viscosity model is the basics to build the blood, also the blood exhibiting viscoelastic properties. More details are needed to establish a complete and more realistic simulation.

Comparison of Transvalvular Aortic Mean Gradients Obtained by Intraprocedural Echocardiography and Invasive Measurement in Balloon and Self-Expanding Transcatheter Valves

Background Concerns about discordance between echocardiographic and invasive mean gradients after transcatheter aortic valve replacement (TAVR) with balloon-expandable valves (BEVs) versus self-expanding valves (SEVs) exist. Methods and Results In a multicenter study, direct-invasive and echocardiography-derived transvalvular mean gradients obtained before and after TAVR were compared as well as post-TAVR and discharge echocardiographic mean gradients in BEVs versus SEVs in 808 patients. Pre-TAVR, there was good correlation (R=0.614; P<0.0001) between direct-invasive and echocardiography-derived mean gradients and weak correlation (R=0.138; P<0.0001) post-TAVR. Compared with post-TAVR echocardiographic mean gradients, both valves exhibit lower invasive and higher discharge echocardiographic mean gradients. Despite similar invasive mean gradients, a small BEV exhibits higher post-TAVR and discharge echocardiographic mean gradients than a large BEV, whereas small and large SEVs exhibit similar post-TAVR and discharge mean gradients. An ejection fraction <50% (P=0.028) and higher Society of Thoracic Surgeons predicted risk of mortality score (P=0.007), but not invasive or echocardiographic mean gradient ≥10 mm Hg (P=0.378 and P=0.341, respectively), nor discharge echocardiographic mean gradient ≥20 mm Hg (P=0.393), were associated with increased 2-year mortality. Conclusions Invasively measured and echocardiography-derived transvalvular mean gradients correlate well in aortic stenosis but weakly post-TAVR. Post-TAVR, echocardiography overestimates transvalvular mean gradients compared with invasive measurements, and poor correlation suggests these modalities cannot be used interchangeably. Moreover, echocardiographic mean gradients are higher on discharge than post-TAVR in all valves. Despite similar invasive mean gradients, a small BEV exhibits higher post-TAVR and discharge echocardiographic mean gradients than a large BEV, whereas small and large SEVs exhibit similar post-TAVR and discharge mean gradients. Immediately post-TAVR, elevated echocardiographic-derived mean gradients should be assessed with caution and compared with direct-invasive mean gradients. A low ejection fraction and higher Society of Thoracic Surgeons score, but not elevated mean gradients, are associated with increased 2-year mortality.

Invasive versus echocardiographic gradients in degenerated surgical aortic valve prostheses: A multicenter study

Objectives

To compare echocardiographic and invasive mean gradients obtained concomitantly in degenerated bioprosthetic surgical aortic valves (SAVRs).

Methods

In a multicenter study, we compared concomitant echocardiographic and invasive mean gradients of SAVR, obtained before valve-in-valve transcatheter aortic valve replacement in all patients, patients with primary stenosis (AS), primary aortic regurgitation (AR), and mixed aortic valve disease (MAVD), and in small versus large valves (≤ or >23 mm). Dimensionless index (DI) was calculated in all groups.

Results

In total, 74 patients were included and data presented as median (interquartile range). Echocardiography-catheterization mean gradient discordance was observed in all patients (invasive = 22 mm Hg [11-34] vs echocardiographic = 32 mm Hg [21-42], P = .013), small valves (invasive = 15 mm Hg [8-34] vs echocardiographic = 28 mm Hg [21-41], P = .013), and large valves (invasive = 20 mm Hg [8.5-27.13] vs echocardiographic = 32 mm Hg [25.5 – 41.5], P < .0001), with a bias of 8 ± 15 mm Hg and wide limits of agreement (–22 to 39 mm Hg) on Bland–Altman plots, indicating these modalities may not be interchangeable. Discordance occurred in AR (invasive = 3 mm Hg [1-6] vs echocardiographic = 12 mm Hg [7-22], P = .017) and in MAVD (invasive = 19 mm Hg [12-29] vs echocardiographic = 31 mm Hg [23-39], P < .0001) but not in AS (invasive = 35 mm Hg [24-45] vs echocardiographic = 41 mm Hg [30-50], P = .45). A lower DI (0.21 [0.14-0.25]) occurred in AS compared with MAVD (0.31 [0.19-0.39]) and AR (0.55 [0.51-0.69]), P < .0001.

Conclusions

Discordance between echocardiography and invasive mean gradients exists in degenerated SAVR, regardless of valve size, but depends on mechanism of failure and DI helps stratify these patients. With a discrepancy between echocardiographic mean gradients AND the patient's symptoms OR the valve leaflet structure and/or mobility on imaging, especially before redo-SAVR or valve-in-valve transcatheter aortic valve replacement, invasive gradients may adjudicate the true valvular hemodynamics.

Evaluation of shear stress accumulation on blood components in normal and dysfunctional bileaflet mechanical heart valves using smoothed particle hydrodynamics

Evaluating shear induced hemodynamic complications is one of the major concerns in design of the mechanical heart valves (MHVs). The monitoring of these events relies on both numerical simulations and experimental measurements. Currently, numerical approaches are mainly based on a combined Eulerian-Lagrangian approach. A more straightforward evaluation can be based on the Lagrangian analysis of the whole blood. As a consequence, Lagrangian meshfree methods are more adapted to such evaluation. In this study, smoothed particle hydrodynamics (SPH), a fully meshfree particle method originated to simulate compressible astrophysical flows, is applied to study the flow through a normal and a dysfunctional bileaflet mechanical heart valves (BMHVs). The SPH results are compared with the reference data. The accumulation of shear stress patterns on blood components illustrates the important role played by non-physiological flow patterns and mainly vortical structures in this issue. The statistical distribution of particles with respect to shear stress loading history provides important information regarding the relative number of blood components that can be damaged. This can be used as a measure of the response of blood components to the presence of the valve implant or any implantable medical device. This work presents the first attempt to simulate pulsatile flow through BMHVs using SPH method.

Flow through a defective mechanical heart valve: a steady flow analysis

Approximately 250,000 valve replacement operations occur annually around the world and more than two thirds of these operations use mechanical heart valves (MHV). These valves are subject to complications such: pannus and/or thrombus formation. Another potential complication is a malfunction in one of the valve leaflets. Although the occurrence of such malfunctions is low, they are life-threatening events that require emergency surgery. It is, therefore, important to develop parameters that will allow an early non-invasive diagnosis of such valve malfunction. In the present study, we performed numerical simulations of the flow through a defective mechanical valve under several flow and malfunction severity conditions. Our results show that the flow upstream and downstream of the defective valve is highly influenced by malfunction severity and this resulted in a misleading improvement in the correlation between simulated Doppler echocardiographic and catheter transvalvular pressure gradients. In this study, we were also able to propose and test two potential non-invasive parameters, using Doppler echocardiography and phase contrast magnetic resonance imaging, for an early detection of mechanical heart valve malfunction. Finally, we showed that valve malfunction has a significant impact on platelet activation and therefore on thrombus formation.

Role of cine-fluoroscopy, transthoracic, and transesophageal echocardiography in patients with suspected prosthetic heart valve thrombosis

Prosthetic heart valve thrombosis (PVT) is a rare but potentially life-threatening complication of heart valve replacement. An effective, quick, and easy diagnostic method is highly desirable. We evaluated the diagnostic efficacy of cine-fluoroscopy (CF), transthoracic (TTE), and transesophageal (TEE) echocardiography in 82 consecutive patients with mechanical valves and suspected PVT. Criteria for PVT were: leaflet(s) motion restriction at CF, increased Doppler gradients at TTE, and evidence of thrombi at TEE. Patients were divided in 4 groups (A, B, C, and D) according to results of CF and TTE. Group A was composed of 24 patients with positive CF and TTE. Thrombi were detected by TEE in all cases, suggesting that when both are positive, CF and TTE correctly identified PVT in all patients so that TEE may be deferred. Group B was composed of 12 patients with positive CF and negative TTE; TEE showed PVT in 4 patients (33%). These patients had very slight leaflet motion restriction as in the case of initial PVT. This suggests that CF compared with Doppler may identify patients with "hemodynamically significant" PVT. The remaining 8 patients in this group had monocuspid prostheses with negative TEE, suggesting that abnormal leaflet motion at CF may be due to functional changes. Therefore, TEE should always be performed in case of monocuspid prostheses with isolated CF abnormalities. Group C was composed of 18 asymptomatic patients with small-sized aortic prostheses and very high Doppler gradients on routine TTE. CF showed normal leaflet motion and TEE ruled out PVT in all cases outlining the diagnostic role of CF in this particular subset. Finally, group D was composed of 28 patients with negative CF and TTE. TEE did not show thrombi in 24 of 28 patients (86%), confirming that, when both yield negative results, CF and TTE are reliable methods to rule out valve thrombosis in most cases. However, in 4 of 28 patients (14%) TEE showed "nonobstructive" prosthetic thrombosis: these patients had mitral prostheses, chronic atrial fibrillation, and 3 of 4 had systemic embolisms. Thus, TEE should be performed in selected patients despite negative CF and TTE results. Sensitivity, specificity, and positive and negative predictive values were 87%, 78%, 80%, and 91% for CF and 75%, 64%, 57%, and 78% for TTE, respectively. CF and TTE correctly identified PVT in 70 of 82 patients (85%). TEE was actually required in 15% of the cases. Thus, CF and TTE are quick, effective, and complementary diagnostic tools to diagnose PVT in most patients. TEE still remains the gold standard technique in selected cases.

Evaluation of prosthetic valve function and associated complications

Significant advances in imaging modalities have occurred to evaluate prosthetic valve function and associated complications. These developments involve predominantly the introduction of Doppler technology for the non-invasive determination of gradients and valve areas and TEE for an improved assessment of valve structure, function, and associated complications. The current role of cinefluoroscopy is mostly to complement TEE in the evaluation of motion of mechanical prosthetic valves in the aortic position. Cardiac catheterization is now rarely needed to assess valve function. Diagnosis of prosthetic valve obstruction can be performed in the majority of cases with transthoracic Doppler echocardiography. Differentiation of valve obstruction from normal valve function in small valves with high flow conditions, however, may be difficult. Because of this and the variability in normal valves among different prostheses, knowledge of the type and size of the implanted valve is essential. Patients and ultrasound laboratories are encouraged to seek and provide this information on a routine basis. Although transthoracic echocardiography is the main diagnostic modality for the serial evaluation of prosthetic valve function, it is important to recognize its limitations in assessing prosthetic mitral regurgitation and evaluating structural abnormalities of prosthetic valves. These are the situations in which TEE has the most impact. A summary of general indications of TEE in prosthetic valves is provided in Table 6. Finally, a baseline transthoracic Doppler study is essential in the overall follow-up and serial evaluation of valve function. For future comparisons, the best indices of valve functions are those obtained for patients as their own control, from a baseline Doppler echocardiographic study performed early after the operation.

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.

Extent and pattern of regression of left ventricular hypertrophy in patients with small size CarboMedics aortic valves

OBJECTIVE

To assess the extent and pattern of regression of left ventricular hypertrophy after valve replacement for aortic stenosis, we studied 26 patients receiving either 19 or 21 mm CarboMedics valves (group I, 13 patients) or either 23 or 25 mm CarboMedics valves (group II, 13 patients). The studies were done before the operation and after 3 years, and results were compared with those of 10 control patients.

METHODS

Left ventricular end-diastolic and end-systolic diameters and volumes, ejection fraction and fractional shortening, and interventricular septum and posterior wall thickness were measured. The ratio between interventricular septum and posterior wall thickness, the ratio between left ventricular wall thickness and left ventricular chamber radius, and the left ventricular mass were then calculated.

RESULTS

At follow-up there was a significant reduction in the left ventricular mass, interventricular septum, and posterior wall thickness for both patient groups (p < 0.01). However, only the posterior wall thickness reached normal values; the interventricular septum and the left ventricular mass indices were still significantly greater than in the control group (p < 0.01). Because of the incomplete regression of interventricular septal hypertrophy, the ratio between interventricular septum and posterior wall thickness was similar between both patient groups but it was significantly higher than in control subjects (p < 0.01). The ratio between wall thickness and chamber radius did not decrease significantly in group II patients, in whom it remained above the control values.

CONCLUSION

Having a bileaflet aortic prosthesis of one size larger did not seem to significantly influence the pattern and the extent of regression of left ventricular hypertrophy after an intermediate period of follow-up.

Doppler Hemodynamics of CarboMedics Prosthetic Valves in Aortic Position at Rest and Exercise

To evaluate the size adequacy of CarboMedics prosthetic heart valves, Doppler pressure gradients after aortic valve replacement were determined at rest and immediately after exercise in 83 patients, at a mean time of 18.8 days after aortic valve replacement with CarboMedics prosthetic heart valves (31 standard and 52 R-series). There were 54 males and 29 females, average age 55 years; 12 had pure aortic stenosis, 47 had aortic regurgitation, and 24 had combined lesions. Exercise significantly increased (p < 0.01) the peak velocity (from 2.50 to 2.88 m/sec), the peak pressure gradient (from 25.9 to 34.6 mm Hg), and the mean pressure gradient (from 13.9 to 18.4 mm Hg). Significant differences were observed even in patients with seemingly large valve sizes. Significant correlation (p < 0.0001) was observed between pressure gradients at rest and immediately after exercise, as well as between pressure gradients and theoretical performance index. A theoretical performance index larger than 1.0 cm2/m2 was needed to obtain a postexercise Doppler peak pressure gradient of less than 60 mm Hg early after aortic valve replacement using either the Carbomedics standard or R-series prosthetic heart valves.

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