In Vitro Mitral Valve Model with Unrestricted Ventricular Access: Using Vacuum to Close the Valve and Enable Static Trans-Mitral Pressure

Current in vitro models of the left heart establish the pressure difference required to close the mitral valve by sealing and pressurizing the ventricular side of the valve, limiting important access to the subvalvular apparatus. This paper describes and evaluates a system that establishes physiological pressure differences across the valve using vacuum on the atrial side. The subvalvular apparatus is open to atmospheric pressure and accessible by tools and sensors, establishing a novel technique for experimentation on atrioventricular valves. Porcine mitral valves were excised and closed by vacuum within the atrial chamber. Images were used to document and analyze closure of the leaflets. Papillary muscle force and regurgitant flow rate were measured to be 4.07 N at 120 mmHg and approximately 12.1 ml/s respectively, both of which are within clinically relevant ranges. The relative ease of these measurements demonstrates the usefulness of improved ventricular access at peak pressure/force closure. Graphical abstract

Computational analysis of quantitative echocardiographic assessments of functional mitral regurgitation: Proximal Isovelocity Surface Area (PISA) methods

While proximal isovelocity surface area (PISA) method is one of the most common echocardiographic methods for quantitative mitral regurgitation (MR) assessment, accurate MR quantification remains challenging. This study examined the theoretical background of PISA, performed virtual echocardiography on computer models of functional MR, and quantified different sources of errors in PISA. For regurgitant flow rate measurement, the conventional 2D hemispherical PISA caused significant underestimation due to underestimation of PISA area, the multiplane 2D hemiellipsoidal and hemicylindrical PISA provided improved accuracy with better assumptions on PISA contour shape. With the direct capture of PISA area, the 3D-PISA was found to be the most accurate. However, it should be noted that PISA method is subject to systematic underestimation due to the Doppler angle effect, and systematic overestimation due to the “flow direction angle” between the regurgitant flow direction and the PISA contour normal direction. For regurgitant volume quantification, integrated PISA, when performed properly, was able to capture the dynamic MR and therefore was more accurate than peak PISA. In specific, integrated PISA using the sum of regurgitant flow rates is recommended.ObjectivesThe aim of this study was to evaluate the accuracy of different proximal isovelocity surface area (PISA) methods, examine their theoretical background, and quantify multiple sources of error in functional mitral regurgitation (MR) assessment.BackgroundWhile PISA method is one of the most common echocardiographic methods for MR severity assessment, it is associated with multiple sources of errors, and accurate MR quantification remains challenging.MethodsFive functional MR (FMR) computer models were created, validated and treated as phantom models. The phantom models have fully resolved and detailed flow fields in the left atrium (LA), left ventricle (LV) and cross the mitral valve, from which the reference values of mitral regurgitant flow rate and regurgitant volume can be obtained. The virtual PISA measurements (i.e., 3D and 2D PISA) were performed on the phantom models assuming optimal echo probe angulation and positioning. The results of different PISA methods were compared with the reference values.ResultsFor regurgitant flow rate measurements, compared to the reference values, excellent correlations were observed for 3D-PISA (R = 0.97, bias -24.4 ± 55.5 ml/s), followed by multiplane 2D hemicylindrical (HC)-PISA (R = 0.88, bias -24.1 ± 85.4 ml/s) and hemiellipsoidal (HE)-PISA (R = 0.91, bias -55.7 ± 96.6 ml/s), while weaker correlations were observed for single plane 2D hemispherical (HS)-PISA with large underestimation (PLAX view: R = 0.71, bias -77.6 ± 124.5 ml/s; A2Ch view: R = 0.69, bias -52.0 ± 122.0 ml/s; A4Ch view: R = 0.82, bias -65.5 ± 107.3 ml/s). For regurgitant volume (RV) quantification, integrated PISA presented improved accuracy over peak PISA for all PISA methods. For 3D-PISA, the bias in RV improved from -12.7 ± 7.8 ml (peak PISA) to -2.1 ± 5.3 ml (integrated PISA).ConclusionsIn FMR, conventional single plane 2D HS-PISA significantly underestimated MR, multiplane 2D PISA (HE-PISA and HC-PISA) improved the accuracy, and 3D-PISA is the most accurate. To better capture the dynamic feature of MR, integrated PISA using the sum of regurgitant flow rates is recommended.

Patient-Specific Computational Analysis of Hemodynamics and Wall Mechanics and Their Interactions in Pulmonary Arterial Hypertension

Vascular wall stiffness and hemodynamic parameters are potential biomechanical markers for detecting pulmonary arterial hypertension (PAH). Previous computational analyses, however, have not considered the interaction between blood flow and wall deformation. Here, we applied an established computational framework that utilizes patient-specific measurements of hemodynamics and wall deformation to analyze the coupled fluid–vessel wall interaction in the proximal pulmonary arteries (PA) of six PAH patients and five control subjects. Specifically, we quantified the linearized stiffness (E), relative area change (RAC), diastolic diameter (D), regurgitant flow, and time-averaged wall shear stress (TAWSS) of the proximal PA, as well as the total arterial resistance (Rt) and compliance (Ct) at the distal pulmonary vasculature. Results found that the average proximal PA was stiffer [median: 297 kPa, interquartile range (IQR): 202 kPa vs. median: 75 kPa, IQR: 5 kPa; P = 0.007] with a larger diameter (median: 32 mm, IQR: 5.25 mm vs. median: 25 mm, IQR: 2 mm; P = 0.015) and a reduced RAC (median: 0.22, IQR: 0.10 vs. median: 0.42, IQR: 0.04; P = 0.004) in PAH compared to our control group. Also, higher total resistance (Rt; median: 6.89 mmHg × min/l, IQR: 2.16 mmHg × min/l vs. median: 3.99 mmHg × min/l, IQR: 1.15 mmHg × min/l; P = 0.002) and lower total compliance (Ct; median: 0.13 ml/mmHg, IQR: 0.15 ml/mmHg vs. median: 0.85 ml/mmHg, IQR: 0.51 ml/mmHg; P = 0.041) were observed in the PAH group. Furthermore, lower TAWSS values were seen at the main PA arteries (MPAs) of PAH patients (median: 0.81 Pa, IQR: 0.47 Pa vs. median: 1.56 Pa, IQR: 0.89 Pa; P = 0.026) compared to controls. Correlation analysis within the PAH group found that E was directly correlated to the PA regurgitant flow (r = 0.84, P = 0.018) and inversely related to TAWSS (r = −0.72, P = 0.051). Results suggest that the estimated elastic modulus E may be closely related to PAH hemodynamic changes in pulmonary arteries.

Abstract 16662: Central Lymphatic Dysfunction is a Contributing Cause of Tissue Congestion in Heart Failure

Introduction: Symptomatic Heart failure (HF) is a leading cause of morbidity and mortality in the world. HF with right sided symptoms may result in fluid overload including edema and ascites. The pathophysiology of fluid overload is poorly understood with no clear association between symptoms and hemodynamic parameters. Hypothesis: In animals with RHF and elevated CVP, the presence of ascites correlates with changes in lymphatic function and is independent of myocardial function and hemodynamic parameters. Methods: RHF was induced in fifteen swine animals by creating severe tricuspid regurgitation. Hemodynamics and anatomic changes were characterized using fluoroscopy, echocardiogram, and MRI. Measurements of the thoracic duct (TD) were made in the abdomen and thorax and the cross-sectional area was calculated. TD regurgitant flow was identified with ethiodized oil injection into the TD and was noted to be present or absent. Data is reported as median (IQR). Results: All 15 animals developed RHF with a dilated right atrium (RA) and right ventricle (RV). Nine animals developed ascites. Comparing animals with and without ascites, there were no differences in IVC pressure(mmHg) 11.5 (7.7-13.4) vs. 11.9 (10.2-17.4) (p= 0.364), SVC pressure 12.8 (11.3-16.8) vs. 12 (8.3-14.9) (p=0.343). Other hemodynamics parameters including pulmonary artery (PA), RV, and RA pressure were also not significantly different. In addition, left ventricular (LV) ejection fraction was normal in both groups (68.7% (57.9-74.8) vs. 55% (53.1-69.4) (p=0.135)). However, animals in the ascites group had larger relative liver volume (mL/Kg) 59.1 (65.1-51.9) vs. 34.85 (42.3-24.1) (p = 0.003), larger dimension of the minimal TD size (mm) 3.2 (5.8-2.7) vs. 2.2 (2.6-2.0) (p=0.04), and more animals had TD regurgitant flow 89% vs. 16% (p=0.01). Conclusion: In animal model with RV failure, there is no association between hemodynamic parameters and occurrence of ascites, consistent with observations in humans. In contrast, parameters of lymphatic congestion differ significantly between the two groups supporting the notion that lymphatic dysfunction is a contributing cause of tissue congestion in patients with HF and elevated CVP.

Clinical use of 4D flow MRI for quantification of aortic regurgitation

ObjectiveThe main objective of the present study was to compare the use of four-dimensional (4D) flow MRI with the habitual sequence (two-dimensional phase-contrast (2DPC) MRI) for the assessment of aortic regurgitation (AR) in the clinical routine.MethodsThis was a retrospective, observational cohort study of patients with varying grades of AR. For the purposes of the present study, we selected all the cases with a regurgitant fraction (RF)>5% as determined by 2DPC MRI (n=34). In all cases, both sequences (2DPC and 4D flow MRI) were acquired in a single session to ensure comparability. We compared the results of the two techniques by evaluating forward flow, regurgitant flow and regurgitation fraction. Then, the patients were divided into subgroups to determine if these factors had any influence on the measurements: aortic diameter (≤ vs >38 mm), valve anatomy (tricuspid vs bicuspid/quadricuspid), stenosis (gradient ≥15 vs <15) and region of interest location (aortic valve vs sinotubular junction).ResultsNo statistically significant differences were observed between the two techniques with Pearson’s correlation coefficients (r) of forward flow (r=0.826/p value<0001), regurgitant flow (r=0.866/p value<0001) and RF (r=0.761/p value<0001).ConclusionsThe findings of this study confirm the value of 4D flow MRI for grading AR in clinical practice with an excellent correlation with the standard technique (2DPC MRI).

P1254 Gerbode defect makes sense after 20 years of a prosthetic mitral valve

60 year old female has been checked for routine prosthetic mitral valve control for the first time in our outpatient clinic. She was also complaining about severe dyspnea for several months. Mitral valve replacement has been done 20 years ago, without tricuspide ring or any other repair.Transthoracic echocardiography showed high normal mitral prosthetic gradients and dilated right heart chambers with severe tricuspid regurgitation. Close to the tricuspid regurgitant flow; there was an additional left to right shunt from left ventricle to right atrium. As she had denied of having a congenital defect before surgery and as there should not have been a possibility of such a missed diagnosis by many echocardiographers for years; we suspected that it had become as a complication of mitral valve surgery, rather than being a congenital defect. Surgical closure of the defect and tricuspide ring annuloplasty repair have been planned. Abstract P1254 Figure.

Secondary mitral regurgitation (part 2): deliberations on mitral surgery and transcatheter repair

Secondary mitral regurgitation (MR) develops as a consequence of postinfarction remodelling of the ventricle or other causes of left ventricular (LV) dilatation and dysfunction. The presence of MR amplifies the poor prognosis of the failing ventricle, but it has not been established whether the adverse outcomes stem from the MR or whether the MR is simply a marker of progressive LV dysfunction. In this article, an attempt will be made to clarify the clinical impact of mitral surgery and transcatheter repair in patients with secondary MR. Observational studies indicate symptomatic improvement, but the results of randomised trials are mixed. Furthermore, neither mitral surgery nor transcatheter repair consistently leads to reversal of the adverse LV remodelling. There is, however, general agreement that these procedures do not have a salutary effect on survival. Certainly mitral surgery and transcatheter repair can substantially reduce the mitral regurgitant flow, but inconsistencies and uncertainties regarding clinical outcomes persist in the published literature. Some such problems could be resolved by utilisation of more accurate and reproducible imaging modalities in randomised studies of patients who are most likely to benefit from a reduction in the regurgitant volume—namely those with the most severe MR.