The Critical Biomechanics of Aortomitral Angle and Systolic Anterior Motion: Engineering Native Ex Vivo Simulation

Systolic anterior motion (SAM) of the mitral valve (MV) is a complex pathological phenomenon often occurring as an iatrogenic effect of surgical and transcatheter intervention. While the aortomitral angle has long been linked to SAM, the mechanistic relationship is not well understood. We developed the first ex vivo heart simulator capable of recreating native aortomitral biomechanics, and to generate models of SAM, we performed anterior leaflet augmentation and sequential undersized annuloplasty procedures on porcine aortomitral junctions (n = 6). Hemodynamics and echocardiograms were recorded, and echocardiographic analysis revealed significantly reduced coaptation-septal distances confirming SAM (p = 0.003) and effective manipulation of the aortomitral angle (p < 0.001). Upon increasing the angle in our pathological models, we recorded significant increases (p < 0.05) in both coaptation-septal distance and multiple hemodynamic metrics, such as aortic peak flow and effective orifice area. These results indicate that an increased aortomitral angle is correlated with more efficient hemodynamic performance of the valvular system, presenting a potential, clinically translatable treatment opportunity for reducing the risk and adverse effects of SAM. As the standard of care shifts towards surgical and transcatheter interventions, it is increasingly important to better understand SAM biomechanics, and our advances represent a significant step towards that goal.

Ex vivo biomechanical analysis of the Ross procedure using the modified inclusion technique in a 3-dimensionally printed left heart simulator

OBJECTIVE

The inclusion technique was developed to reinforce the pulmonary autograft to prevent dilation after the Ross procedure. Anticommissural plication (ACP), a modification technique, can reduce graft size and create neosinuses. The objective was to evaluate pulmonary valve biomechanics using the inclusion technique in the Ross procedure with and without ACP.

METHODS

Seven porcine and 5 human pulmonary autografts were harvested from hearts obtained from a meat abattoir and from heart transplant recipients and donors, respectively. Five additional porcine autografts without reinforcement were used as controls. The Ross procedure was performed using the inclusion technique with a straight polyethylene terephthalate graft. The same specimens were tested both with and without ACP. Hemodynamic parameter data, echocardiography, and high-speed videography were collected via the ex vivo heart simulator.

RESULTS

Porcine autograft regurgitation was significantly lower after the use of inclusion technique compared with controls (P < .01). ACP compared with non-ACP in both porcine and human pulmonary autografts was associated with lower leaflet rapid opening velocity (3.9 ± 2.4 cm/sec vs 5.9 ± 2.4 cm/sec; P = .03; 3.5 ± 0.9 cm/sec vs 4.4 ± 1.0 cm/sec; P = .01), rapid closing velocity (1.9 ± 1.6 cm/sec vs 3.1 ± 2.0 cm/sec; P = .01; 1.8 ± 0.7 cm/sec vs 2.2 ± 0.3 cm/sec; P = .13), relative rapid opening force (4.6 ± 3.0 vs 7.7 ± 5.2; P = .03; 3.0 ± 0.6 vs 4.0 ± 2.1; P = .30), and relative rapid closing force (2.5 ± 3.4 vs 5.9 ± 2.3; P = .17; 1.4 ± 1.3 vs 2.3 ± 0.6; P = .25).

CONCLUSIONS

The Ross procedure using the inclusion technique demonstrated excellent hemodynamic parameter results. The ACP technique was associated with more favorable leaflet biomechanics. In vivo validation should be performed to allow direct translation to clinical practice.

A Novel Rheumatic Mitral Valve Disease Model with Ex Vivo Hemodynamic and Biomechanical Validation

PURPOSE

Rheumatic heart disease is a major cause of mitral valve (MV) dysfunction, particularly in disadvantaged areas and developing countries. There lacks a critical understanding of the disease biomechanics, and as such, the purpose of this study was to generate the first ex vivo porcine model of rheumatic MV disease by simulating the human pathophysiology and hemodynamics.

METHODS

Healthy porcine valves were altered with heat treatment, commissural suturing, and cyanoacrylate tissue coating, all of which approximate the pathology of leaflet stiffening and thickening as well as commissural fusion. Hemodynamic data, echocardiography, and high-speed videography were collected in a paired manner for control and model valves (n = 4) in an ex vivo left heart simulator. Valve leaflets were characterized in an Instron tensile testing machine to understand the mechanical changes of the model (n = 18).

RESULTS

The model showed significant differences indicative of rheumatic disease: increased regurgitant fractions (p < 0.001), reduced effective orifice areas (p < 0.001), augmented transmitral mean gradients (p < 0.001), and increased leaflet stiffness (p = 0.025).

CONCLUSION

This work represents the creation of the first ex vivo model of rheumatic MV disease, bearing close similarity to the human pathophysiology and hemodynamics, and it will be used to extensively study both established and new treatment techniques, benefitting the millions of affected victims.

Biomechanical Engineering Analysis of Pulmonary Valve Leaflet Hemodynamics and Kinematics in the Ross Procedure

The Ross procedure using the inclusion technique with anticommissural plication (ACP) is associated with excellent valve hemodynamics and favorable leaflet kinematics. The objective was to evaluate individual pulmonary cusp's biomechanics and fluttering by including coronary flow in the Ross procedure using an ex vivo three-dimensional-printed heart simulator. Ten porcine and five human pulmonary autografts were harvested from a meat abattoir and heart transplant patients. Five porcine autografts without reinforcement served as controls. The other autografts were prepared using the inclusion technique with and without ACP (ACP and NACP). Hemodynamic and high-speed videography data were measured using the ex vivo heart simulator. Although porcine autografts showed similar leaflet rapid opening and closing mean velocities, human ACP compared to NACP autografts demonstrated lower leaflet rapid opening mean velocity in the right (p = 0.02) and left coronary cusps (p = 0.003). The porcine and human autograft leaflet rapid opening and closing mean velocities were similar in all three cusps. Porcine autografts showed similar leaflet flutter frequencies in the left (p = 0.3) and noncoronary cusps (p = 0.4), but porcine NACP autografts versus controls demonstrated higher leaflet flutter frequency in the right coronary cusp (p = 0.05). The human NACP versus ACP autografts showed higher flutter frequency in the noncoronary cusp (p = 0.02). The leaflet flutter amplitudes were similar in all three cusps in both porcine and human autografts. The ACP compared to NACP autografts in the Ross procedure was associated with more favorable leaflet kinematics. These results may translate to the improved long-term durability of the pulmonary autografts.

DynaRing: A Patient-Specific Mitral Annuloplasty Ring With Selective Stiffness Segments

Annuloplasty ring choice and design are critical to the long-term efficacy of mitral valve (MV) repair. DynaRing is a selectively compliant annuloplasty ring composed of varying stiffness elastomer segments, a shape-set nitinol core, and a cross diameter filament. The ring provides sufficient stiffness to stabilize a diseased annulus while allowing physiological annular dynamics. Moreover, adjusting elastomer properties provides a mechanism for effectively tuning key MV metrics to specific patients. We evaluate the ring embedded in porcine valves with an ex-vivo left heart simulator and perform a 150 million cycle fatigue test via a custom oscillatory system. We present a patient-specific design approach for determining ring parameters using a finite element model optimization and patient MRI data. Ex-vivo experiment results demonstrate that motion of DynaRing closely matches literature values for healthy annuli. Findings from the patient-specific optimization establish DynaRing's ability to adjust the anterior-posterior and intercommissural diameters and saddle height by up to 8.8%, 5.6%, 19.8%, respectively, and match a wide range of patient data.

Biomechanical engineering analysis of an acute papillary muscle rupture disease model using an innovative 3D-printed left heart simulator

OBJECTIVES

The severity of acute papillary muscle (PM) rupture varies according to the extent and site of the rupture. However, the haemodynamic effects of different rupture variations are still poorly understood. Using a novel ex vivo model, we sought to study acute PM rupture to improve clinical management.

METHODS

Using porcine mitral valves (n = 32) mounted within an ex vivo left heart simulator, PM rupture was simulated. The mitral valve was divided into quadrants for analysis according to the PM heads. Acute PM rupture was simulated by incrementally cutting from 1/3 to the total number of chordae arising from 1 PM head of interest. Haemodynamic parameters were measured.

RESULTS

Rupture >2/3 of the chordae from 1 given PM head or regurgitation fraction >60% led to markedly deteriorated haemodynamics. Rupture at the anterolateral PM had a stronger negative effect on haemodynamics than rupture at the posteromedial PM. Rupture occurring at the anterior head of the anterolateral PM led to more marked haemodynamic instability than rupture occurring at the other PM heads.

CONCLUSIONS

The haemodynamic effects of acute PM rupture vary considerably according to the site and extent of the rupture. Rupture of ≤2/3 of chordae from 1 PM head or rupture at the posteromedial PM lead to less marked haemodynamics effects, suggesting a higher likelihood of tolerating surgery. Rupture at the anterolateral PM, specifically the anterior head, rupture of >2/3 of chordae from 1 PM head or regurgitation fraction >60% led to marked haemodynamic instability, suggesting the potential benefit from bridging strategies prior to surgery.

Quantitative Biomechanical Optimization of Neochordal Implantation Location on Mitral Leaflets during Valve Repair

Objective

Methods

Results

Conclusions

Ex vivo biomechanical analysis of flexible versus rigid annuloplasty rings in mitral valves using a novel annular dilation system

Background

Mitral annuloplasty rings restore annular dimensions to increase leaflet coaptation, serving a fundamental component in mitral valve repair. However, biomechanical evaluations of annuloplasty rings are lacking. We aim to biomechanically analyze flexible and rigid annuloplasty rings using an ex vivo mitral annular dilation model.

Methods

Juvenile porcine mitral valves (n = 4) with intercommissural distance of 28 mm were dilated to intercommissural distances of 40 mm using a 3D-printed dilator and were sewn to an elastic mount. Fiber bragg grating sensors were anchored to native chordae to measure chordal forces. The valves were repaired using size 28 rigid and flexible annuloplasty rings in a random order. Hemodynamic data, echocardiography, and chordal force measurements were collected.

Results

Mitral annular dilation resulted in decreased leaflet coaptation height and increased mitral regurgitation fraction. Both the flexible and rigid annuloplasty rings effectively increased leaflet coaptation height compared to that post dilation. Rigid ring annuloplasty repair significantly decreased the mitral regurgitation fraction. Flexible annuloplasty ring repair reduced the chordal rate of change of force (7.1 ± 4.4 N/s versus 8.6 ± 5.9 N/s, p = 0.02) and peak force (0.6 ± 0.5 N versus 0.7 ± 0.6 N, p = 0.01) compared to that from post dilation. Rigid annuloplasty ring repair was associated with higher chordal rate of change of force (9.8 ± 5.8 N/s, p = 0.0001) and peak force (0.7 ± 0.5 N, p = 0.01) compared to that after flexible ring annuloplasty repair.

Conclusions

Both rigid and flexible annuloplasty rings are effective in increasing mitral leaflet coaptation height. Although the rigid annuloplasty ring was associated with slightly higher chordal stress compared to that of the flexible annuloplasty ring, it was more effective in mitral regurgitation reduction. This study may help direct the design of an optimal annuloplasty ring to further improve patient outcomes.

A Novel Device for Intraoperative Direct Visualization of a Pressurized Root in Aortic Valve Repair

PURPOSE

One major challenge in generating reproducible aortic valve (AV) repair results is the inability to assess AV morphology under physiologic pressure. A transparent intraoperative aortic valve visualization device was designed and manufactured.

DESCRIPTION

This device is comprised of an open proximal end, a cantilevered edge to allow attachment of the device to the aorta or graft, a distal viewing surface, and two side ports for fluid delivery and air removal.

EVALUATION

The performance of the device was evaluated ex vivo using normal porcine AV in situ (n=3), AV after valve-sparing aortic root replacement (VSARR, n=3), and porcine pulmonary valve in Ross procedure (n=3), and in 3 patients who underwent VSARR. AV morphology was clearly visualized using the device in all experiments. In human, the use of this device successfully illustrated cusp prolapse after the initial VSARR and effectively guided additional cusp repair.

CONCLUSIONS

This device successfully allows for direct visual assessment of the AV apparatus under physiologic pressure. The use of this device can potentially increase the adoptability of AV repair in clinical practice.

Novel bicuspid aortic valve model with aortic regurgitation for hemodynamic status analysis using an ex vivo simulator

OBJECTIVE

The objective was to design and evaluate a clinically relevant, novel ex vivo bicuspid aortic valve model that mimics the most common human phenotype with associated aortic regurgitation.

METHODS

Three bovine aortic valves were mounted asymmetrically in a previously validated 3-dimensional-printed left heart simulator. The non-right commissure and the non-left commissure were both shifted slightly toward the left-right commissure, and the left and right coronary cusps were sewn together. The left-right commissure was then detached and reimplanted 10 mm lower than its native height. Free margin shortening was used for valve repair. Hemodynamic status, high-speed videography, and echocardiography data were collected before and after the repair.

RESULTS

The bicuspid aortic valve model was successfully produced and repaired. High-speed videography confirmed prolapse of the fused cusp of the baseline bicuspid aortic valve models in diastole. Hemodynamic and pressure data confirmed accurate simulation of diseased conditions with aortic regurgitation and the subsequent repair. Regurgitant fraction postrepair was significantly reduced compared with that at baseline (14.5 ± 4.4% vs 28.6% ± 3.4%; P = .037). There was no change in peak velocity, peak gradient, or mean gradient across the valve pre- versus postrepair: 293.3 ± 18.3 cm/sec versus 325.3 ± 58.2 cm/sec (P = .29), 34.3 ± 4.2 mm Hg versus 43.3 ± 15.4 mm Hg (P = .30), and 11 ± 1 mm Hg versus 9.3 ± 2.5 mm Hg (P = .34), respectively.

CONCLUSIONS

An ex vivo bicuspid aortic valve model was designed that recapitulated the most common human phenotype with aortic regurgitation. These valves were successfully repaired, validating its potential for evaluating valve hemodynamics and optimizing surgical repair for bicuspid aortic valves.

Natural cardiac regeneration conserves native biaxial left ventricular biomechanics after myocardial infarction in neonatal rats

After myocardial infarction (MI), adult mammals exhibit scar formation, adverse left ventricular (LV) remodeling, LV stiffening, and impaired contractility, ultimately resulting in heart failure. Neonatal mammals, however, are capable of natural heart regeneration after MI. We hypothesized that neonatal cardiac regeneration conserves native biaxial LV mechanics after MI. Wistar rat neonates (1 day old, n = 46) and adults (8-10 weeks old, n = 20) underwent sham surgery or permanent left anterior descending coronary artery ligation. At 6 weeks after neonatal MI, Masson's trichrome staining revealed negligible fibrosis. Echocardiography for the neonatal MI (n = 15) and sham rats (n = 14) revealed no differences in LV wall thickness or chamber diameter, and both groups had normal ejection fraction (72.7% vs 77.5%, respectively, p = 0.1946). Biaxial tensile testing revealed similar stress-strain curves along both the circumferential and longitudinal axes across a full range of physiologic stresses and strains. The circumferential modulus (267.9 kPa vs 274.2 kPa, p = 0.7847), longitudinal modulus (269.3 kPa vs 277.1 kPa, p = 0.7435), and maximum shear stress (3.30 kPa vs 3.95 kPa, p = 0.5418) did not differ significantly between the neonatal MI and sham groups, respectively. In contrast, transmural scars were observed at 4 weeks after adult MI. Adult MI hearts (n = 7) exhibited profound LV wall thinning (p < 0.0001), chamber dilation (p = 0.0246), and LV dysfunction (ejection fraction 45.4% vs 79.7%, p < 0.0001) compared to adult sham hearts (n = 7). Adult MI hearts were significantly stiffer than adult sham hearts in both the circumferential (321.5 kPa vs 180.0 kPa, p = 0.0111) and longitudinal axes (315.4 kPa vs 172.3 kPa, p = 0.0173), and also exhibited greater maximum shear stress (14.87 kPa vs 3.23 kPa, p = 0.0162). Our study is the first to show that native biaxial LV mechanics are conserved after neonatal heart regeneration following MI, thus adding biomechanical support for the therapeutic potential of cardiac regeneration in the treatment of ischemic heart disease.

Biomechanical Analysis of Neochordal Repair Error from Diastolic Phase Inversion of Static Left Ventricular Pressurization

Objective

Neochordal implantation is a common form of surgical mitral valve (MV) repair. However, neochord length is assessed using static left ventricular pressurization, leading surgeons to evaluate leaflet coaptation and valve competency when the left ventricle is dilating instead of contracting physiologically, referred to as diastolic phase inversion (DPI). We hypothesize that the difference in papillary muscle (PM) positioning between DPI and physiologic systole results in miscalculated neochord lengths, which might affect repair performance.

Methods

Porcine MVs (n = 6) were mounted in an ex vivo heart simulator and PMs were affixed to robots that accurately simulate PM motion. Baseline hemodynamic and chordal strain data were collected, after which P2 chordae were severed to simulate posterior leaflet prolapse from chordal rupture and subsequent mitral regurgitation. Neochord implantation was performed in the physiologic and DPI static configurations.

Results

Although both repairs successfully reduced mitral regurgitation, the DPI repair resulted in longer neochordae (2.19 ± 0.4 mm; P < .01). Furthermore, the hemodynamic performance was reduced for the DPI repair resulting in higher leakage volume (P = .01) and regurgitant fraction (P < .01). Peak chordal forces were reduced in the physiologic repair (0.57 ± 0.11 N) versus the DPI repair (0.68 ± 0.12 N; P < .01).

Conclusions

By leveraging advanced ex vivo technologies, we were able to quantify the effects of static pressurization on neochordal length determination. Our findings suggest that this post-repair assessment might slightly overestimate the neochordal length and that additional marginal shortening of neochordae might positively affect MV repair performance and durability by reducing load on surrounding native chordae.

Biomechanical engineering analysis of commonly utilized mitral neochordae

Objective

To evaluate the suture rupture forces of commonly clinically utilized neochord repair techniques to identify the most biomechanically resistant most biomechanically resistant technique.

Methods

Several types of neochord techniques (standard interrupted neochordae, continuous running neochordae, and loop technique), numbers of neochordae, and suture calibers (polytetrafluoroethylene CV-3 to CV-6) were compared. To perform the tests, both ends of the neochordae were loaded in a tensile force analysis machine. During the test, the machine applied tension to the neochord until rupture was achieved. The tests were performed 3 times for each variation, and the rupture forces were averaged for statistical analysis.

Results

Rupture force was significantly higher for running neochordae relative to interrupted neochordae (P < .01). However, a single rupture in the running technique resulted in failure of the complete neochord system. For both running and interrupted neochordae, a greater number of neochordae as well as a thicker suture caliber significantly increased the neochord rupture force (P < .01). The loop technique ruptured at significantly lower forces compared with the other 2 techniques (P < .01). A greater number of loops did not significantly increase the rupture force of loop neochordae. Observed rupture forces for all techniques were higher than those normally observed in physiologic conditions.

Conclusions

Under experimental conditions, the running neochord technique has the best mechanical performance due to an increased rupture force. If using running neochordae, more than 1 independent set of multiple running neochordae are advised (ie, >2 independent sets of multiple running neochordae in each set).

Ex Vivo Model of Ischemic Mitral Regurgitation and Analysis of Adjunctive Papillary Muscle Repair

Ischemic mitral regurgitation (IMR) is particularly challenging to repair with lasting durability due to the complex valvular and subvalvular pathologies resulting from left ventricular dysfunction. Ex vivo simulation is uniquely suited to quantitatively analyze the repair biomechanics, but advancements are needed to model the nuanced IMR disease state. Here we present a novel IMR model featuring a dilation device with precise dilatation control that preserves annular elasticity to enable accurate ex vivo analysis of surgical repair. Coupled with augmented papillary muscle head positioning, the enhanced heart simulator system successfully modeled IMR pre- and post-surgical intervention and enabled the analysis of adjunctive subvalvular papillary muscle repair to alleviate regurgitation recurrence. The model resulted in an increase in regurgitant fraction: 11.6 ± 1.7% to 36.1 ± 4.4% (p < 0.001). Adjunctive papillary muscle head fusion was analyzed relative to a simple restrictive ring annuloplasty repair and, while both repairs successfully eliminated regurgitation initially, the addition of the adjunctive subvalvular repair reduced regurgitation recurrence: 30.4 ± 5.7% vs. 12.5 ± 2.6% (p = 0.002). Ultimately, this system demonstrates the success of adjunctive papillary muscle head fusion in repairing IMR as well as provides a platform to optimize surgical techniques for increased repair durability.

Heart Valve Biomechanics: The Frontiers of Modeling Modalities and the Expansive Capabilities of Ex Vivo Heart Simulation

The field of heart valve biomechanics is a rapidly expanding, highly clinically relevant area of research. While most valvular pathologies are rooted in biomechanical changes, the technologies for studying these pathologies and identifying treatments have largely been limited. Nonetheless, significant advancements are underway to better understand the biomechanics of heart valves, pathologies, and interventional therapeutics, and these advancements have largely been driven by crucial in silico, ex vivo, and in vivo modeling technologies. These modalities represent cutting-edge abilities for generating novel insights regarding native, disease, and repair physiologies, and each has unique advantages and limitations for advancing study in this field. In particular, novel ex vivo modeling technologies represent an especially promising class of translatable research that leverages the advantages from both in silico and in vivo modeling to provide deep quantitative and qualitative insights on valvular biomechanics. The frontiers of this work are being discovered by innovative research groups that have used creative, interdisciplinary approaches toward recapitulating in vivo physiology, changing the landscape of clinical understanding and practice for cardiovascular surgery and medicine.

Mitral chordae tendineae force profile characterization using a posterior ventricular anchoring neochordal repair model for mitral regurgitation in a three-dimensional-printed ex vivo left heart simulator

OBJECTIVES

Posterior ventricular anchoring neochordal (PVAN) repair is a non-resectional technique for correcting mitral regurgitation (MR) due to posterior leaflet prolapse, utilizing a single suture anchored in the myocardium behind the leaflet. This technique has demonstrated clinical efficacy, although a theoretical limitation is stability of the anchoring suture. We hypothesize that the PVAN suture positions the leaflet for coaptation, after which forces are distributed evenly with low repair suture forces.

METHODS

Porcine mitral valves were mounted in a 3-dimensional-printed heart simulator and chordal forces, haemodynamics and echocardiography were collected at baseline, after inducing MR by severing chordae, and after PVAN repair. Repair suture forces were measured with a force-sensing post positioned to mimic in vivo suture placement. Forces required to pull the myocardial suture free were also determined.

RESULTS

Relative primary and secondary chordae forces on both leaflets were elevated during prolapse (P < 0.05). PVAN repair eliminated MR in all valves and normalized chordae forces to baseline levels on anterior primary (0.37 ± 0.23 to 0.22 ± 0.09 N, P < 0.05), posterior primary (0.62 ± 0.37 to 0.14 ± 0.05 N, P = 0.001), anterior secondary (1.48 ± 0.52 to 0.85 ± 0.43 N, P < 0.001) and posterior secondary chordae (1.42 ± 0.69 to 0.59 ± 0.17 N, P = 0.005). Repair suture forces were minimal, even compared to normal primary chordae forces (0.08 ± 0.04 vs 0.19 ± 0.08 N, P = 0.002), and were 90 times smaller than maximum forces tolerated by the myocardium (0.08 ± 0.04 vs 6.9 ± 1.3 N, P < 0.001).

DISCUSSION

PVAN repair eliminates MR by positioning the posterior leaflet for coaptation, distributing forces throughout the valve. Given extremely low measured forces, the strength of the repair suture and the myocardium is not a limitation.

Biomimetic six-axis robots replicate human cardiac papillary muscle motion: pioneering the next generation of biomechanical heart simulator technology

Papillary muscles serve as attachment points for chordae tendineae which anchor and position mitral valve leaflets for proper coaptation. As the ventricle contracts, the papillary muscles translate and rotate, impacting chordae and leaflet kinematics; this motion can be significantly affected in a diseased heart. In ex vivo heart simulation, an explanted valve is subjected to physiologic conditions and can be adapted to mimic a disease state, thus providing a valuable tool to quantitatively analyse biomechanics and optimize surgical valve repair. However, without the inclusion of papillary muscle motion, current simulators are limited in their ability to accurately replicate cardiac biomechanics. We developed and implemented image-guided papillary muscle (IPM) robots to mimic the precise motion of papillary muscles. The IPM robotic system was designed with six degrees of freedom to fully capture the native motion. Mathematical analysis was used to avoid singularity conditions, and a supercomputing cluster enabled the calculation of the system's reachable workspace. The IPM robots were implemented in our heart simulator with motion prescribed by high-resolution human computed tomography images, revealing that papillary muscle motion significantly impacts the chordae force profile. Our IPM robotic system represents a significant advancement for ex vivo simulation, enabling more reliable cardiac simulations and repair optimizations.

Artificial papillary muscle device for off-pump transapical mitral valve repair

OBJECTIVE

New transapical minimally invasive artificial chordae implantation devices are a promising alternative to traditional open-heart repair, with the potential for decreased postoperative morbidity and reduced recovery time. However, these devices can place increased stress on the artificial chordae. We designed an artificial papillary muscle to alleviate artificial chordae stresses and thus increase repair durability.

METHODS

The artificial papillary muscle device is a narrow elastic column with an inner core that can be implanted during the minimally invasive transapical procedure via the same ventricular incision site. The device was 3-dimensionally printed in biocompatible silicone for this study. To test efficacy, porcine mitral valves (n = 6) were mounted in a heart simulator, and isolated regurgitation was induced. Each valve was repaired with a polytetrafluoroethylene suture with apical anchoring followed by artificial papillary muscle anchoring. In each case, a high-resolution Fiber Bragg Grating sensor recorded forces on the suture.

RESULTS

Hemodynamic data confirmed that both repairs-with and without the artificial papillary muscle device-were successful in eliminating mitral regurgitation. Both the peak artificial chordae force and the rate of change of force at the onset of systole were significantly lower with the device compared with apical anchoring without the device (P < .001 and P < .001, respectively).

CONCLUSIONS

Our novel artificial papillary muscle could integrate with minimally invasive repairs to shorten the artificial chordae and behave as an elastic damper, thus reducing sharp increases in force. With our device, we have the potential to improve the durability of off-pump transapical mitral valve repair procedures.

Comprehensive Ex Vivo Comparison of 5 Clinically Used Conduit Configurations for Valve-Sparing Aortic Root Replacement Using a 3-Dimensional-Printed Heart Simulator

Supplemental Digital Content is available in the text.

Background:

Many graft configurations are clinically used for valve-sparing aortic root replacement, some specifically focused on recapitulating neosinus geometry. However, the specific impact of such neosinuses on valvular and root biomechanics and the potential influence on long-term durability are unknown.

Methods:

Using a custom 3-dimenstional–printed heart simulator with porcine aortic roots (n=5), the anticommissural plication, Stanford modification, straight graft (SG), Uni-Graft, and Valsalva graft configurations were tested in series using an incomplete counterbalanced measures design, with the native root as a control, to mitigate ordering effects. Hemodynamic and videometric data were analyzed using linear models with conduit as the fixed effect of interest and valve as a fixed nuisance effect with post hoc pairwise testing using Tukey’s correction.

Results:

Hemodynamics were clinically similar between grafts and control aortic roots. Regurgitant fraction varied between grafts, with SG and Uni-Graft groups having the lowest regurgitant fractions and anticommissural plication having the highest. Root distensibility was significantly lower in SG versus both control roots and all other grafts aside from the Stanford modification (P≤0.01 for each). All grafts except SG had significantly higher cusp opening velocities versus native roots (P<0.01 for each). Relative cusp opening forces were similar between SG, Uni-Graft, and control groups, whereas anticommissural plication, Stanford modification, and Valsalva grafts had significantly higher opening forces versus controls (P<0.01). Cusp closing velocities were similar between native roots and the SG group, and were significantly lower than observed in the other conduits (P≤0.01 for each). Only SG and Uni-Graft groups experienced relative cusp closing forces approaching that of the native root, whereas relative forces were >5-fold higher in the anticommissural plication, Stanford modification, and Valsalva graft groups.

Conclusions:

In this ex vivo modeling system, clinically used valve-sparing aortic root replacement conduit configurations have comparable hemodynamics but differ in biomechanical performance, with the straight graft most closely recapitulating native aortic root biomechanics.

Collagen-Supplemented Incubation Rapidly Augments Mechanical Property of Fibroblast Cell Sheets

Cell sheet technology using UpCell™ (Thermo Fisher Scientific, Roskilde, Denmark) plates is a modern tool that enables the rapid creation of single-layered cells without using extracellular matrix (ECM) enzymatic digestion. Although this technique has the advantage of maintaining a sheet of cells without needing artificial scaffolds, these cell sheets remain extremely fragile. Collagen, the most abundant ECM component, is an attractive candidate for modulating tissue mechanical properties given its tunable property. In this study, we demonstrated rapid mechanical property augmentation of human dermal fibroblast cell sheets after incubation with bovine type I collagen for 24 h on UpCell plates. We showed that treatment with collagen resulted in increased collagen I incorporation within the cell sheet without affecting cell morphology, cell type, or cell sheet quality. Atomic force microscopy measurements for controls, and cell sheets that received 50 and 100 μg/mL collagen I treatments revealed an average Young's modulus of their respective intercellular regions: 6.6 ± 1.0, 14.4 ± 6.6, and 19.8 ± 3.8 kPa during the loading condition, and 10.3 ± 4.7, 11.7 ± 2.2, and 18.1 ± 3.4 kPa during the unloading condition. This methodology of rapid mechanical property augmentation of a cell sheet has a potential impact on cell sheet technology by improving the ease of construct manipulation, enabling new translational tissue engineering applications.

Quadrupling the N95 Supply during the COVID-19 Crisis with an Innovative 3D-Printed Mask Adaptor

The need for personal protective equipment during the COVID-19 pandemic is far outstripping our ability to manufacture and distribute these supplies to hospitals. In particular, the medical N95 mask shortage is resulting in healthcare providers reusing masks or utilizing masks with filtration properties that do not meet medical N95 standards. We developed a solution for immediate use: a mask adaptor, outfitted with a quarter section of an N95 respirator that maintains the N95 seal standard, thereby quadrupling the N95 supply. A variety of designs were 3D-printed and optimized based on the following criteria: seal efficacy, filter surface area and N95 respirator multiplicity. The final design is reusable and features a 3D-printed soft silicone base as well as a rigid 3D-printed cartridge to seal one-quarter of a 3M 1860 N95 mask. Our mask passed the computerized N95 fit test for six individuals. All files are publicly available with this publication. Our design can provide immediate support for healthcare professionals in dire need of medical N95 masks by extending the current supply by a factor of four.

Ex Vivo Analysis of a Porcine Bicuspid Aortic Valve and Aneurysm Disease Model

We identified an extremely rare congenital porcine type 0 lateral bicuspid aortic valve from a fresh porcine heart. Using a 3-dimensionally printed ex vivo left heart simulator, we analyzed valvular hemodynamics at baseline, in an aortic aneurysm disease model, and after valve-sparing root replacement. We showed that bicuspid aortic valve regurgitation due to aortic aneurysm can be successfully repaired without significant hemodynamic impairment using the valve-sparing root replacement technique in an individualized approach. Our results provide direct hemodynamic evidence supporting the use of valve-sparing root replacement for patients with bicuspid aortic valve regurgitation.

In Vivo Validation of Restored Chordal Biomechanics After Mitral Ring Annuloplasty in a Rare Ovine Case of Natural Chronic Functional Mitral Regurgitation

Mitral valve chordae tendineae forces are elevated in the setting of mitral regurgitation (MR). Ring annuloplasty is an essential component of surgical repair for MR, but whether chordal forces are reduced after mitral annuloplasty has never been validated in vivo. Here, we present an extremely rare ovine case of natural, severe chronic functional MR, in which we used force-sensing fiber Bragg grating neochordae to directly measure chordal forces in the baseline setting of severe MR, as well as after successful mitral ring annuloplasty repair. Overall, our report is the first to confirm in vivo that mitral ring annuloplasty reduces elevated chordae tendineae forces associated with chronic functional MR.

Multiaxial Lenticular Stress-Strain Relationship of Native Myocardium is Preserved by Infarct-Induced Natural Heart Regeneration in Neonatal Mice

Neonatal mice exhibit natural heart regeneration after myocardial infarction (MI) on postnatal day 1 (P1), but this ability is lost by postnatal day 7 (P7). Cardiac biomechanics intricately affect long-term heart function, but whether regenerated cardiac muscle is biomechanically similar to native myocardium remains unknown. We hypothesized that neonatal heart regeneration preserves native left ventricular (LV) biomechanical properties after MI. C57BL/6J mice underwent sham surgery or left anterior descending coronary artery ligation at age P1 or P7. Echocardiography performed 4 weeks post-MI showed that P1 MI and sham mice (n = 22, each) had similar LV wall thickness, diameter, and ejection fraction (59.6% vs 60.7%, p = 0.6514). Compared to P7 shams (n = 20), P7 MI mice (n = 20) had significant LV wall thinning, chamber enlargement, and depressed ejection fraction (32.6% vs 61.8%, p < 0.0001). Afterward, the LV was explanted and pressurized ex vivo, and the multiaxial lenticular stress-strain relationship was tracked. While LV tissue modulus for P1 MI and sham mice were similar (341.9 kPa vs 363.4 kPa, p = 0.6140), the modulus for P7 MI mice was significantly greater than that for P7 shams (691.6 kPa vs 429.2 kPa, p = 0.0194). We conclude that, in neonatal mice, regenerated LV muscle has similar biomechanical properties as native LV myocardium.

A novel cross-species model of Barlow's disease to biomechanically analyze repair techniques in an ex vivo left heart simulator

OBJECTIVE

Barlow's disease remains challenging to repair, given the complex valvular morphology and lack of quantitative data to compare techniques. Although there have been recent strides in ex vivo evaluation of cardiac mechanics, to our knowledge, there is no disease model that accurately simulates the morphology and pathophysiology of Barlow's disease. The purpose of this study was to design such a model.

METHODS

To simulate Barlow's disease, a cross-species ex vivo model was developed. Bovine mitral valves (n = 4) were sewn into a porcine annulus mount to create excess leaflet tissue and elongated chordae. A heart simulator generated physiologic conditions while hemodynamic data, high-speed videography, and chordal force measurements were collected. The regurgitant valves were repaired using nonresectional repair techniques such as neochord placement.

RESULTS

The model successfully imitated the complexities of Barlow's disease, including redundant, billowing bileaflet tissues with notable regurgitation. After repair, hemodynamic data confirmed reduction of mitral leakage volume (25.9 ± 2.9 vs 2.1 ± 1.8 mL, P < .001) and strain gauge analysis revealed lower primary chordae forces (0.51 ± 0.17 vs 0.10 ± 0.05 N, P < .001). In addition, the maximum rate of change of force was significantly lower postrepair for both primary (30.80 ± 11.38 vs 8.59 ± 4.83 N/s, P < .001) and secondary chordae (33.52 ± 10.59 vs 19.07 ± 7.00 N/s, P = .006).

CONCLUSIONS

This study provides insight into the biomechanics of Barlow's disease, including sharply fluctuating force profiles experienced by elongated chordae prerepair, as well as restoration of primary chordae forces postrepair. Our disease model facilitates further in-depth analyses to optimize the repair of Barlow's disease.

Development and Ex Vivo Validation of Novel Force-Sensing Neochordae for Measuring Chordae Tendineae Tension in the Mitral Valve Apparatus Using Optical Fibers With Embedded Bragg Gratings

Few technologies exist that can provide quantitative data on forces within the mitral valve apparatus. Marker-based strain measurements can be performed, but chordal geometry and restricted optical access are limitations. Foil-based strain sensors have been described and work well, but the sensor footprint limits the number of chordae that can be measured. We instead utilized fiber Bragg grating (FBG) sensors—optical strain gauges made of 125 μm diameter silica fibers—to overcome some limitations of previous methods of measuring chordae tendineae forces. Using FBG sensors, we created a force-sensing neochord (FSN) that mimics the natural shape and movement of native chordae. FBG sensors reflect a specific wavelength of light depending on the spatial period of gratings. When force is applied, the gratings move relative to one another, shifting the wavelength of reflected light. This shift is directly proportional to force applied. The FBG sensors were housed in a protective sheath fashioned from a 0.025 in. flat coil, and attached to the chordae using polytetrafluoroethylene suture. The function of the force-sensing neochordae was validated in a three-dimensional (3D)-printed left heart simulator, which demonstrated that FBG sensors provide highly sensitive force measurements of mitral valve chordae at a temporal resolution of 1000 Hz. As ventricular pressures increased, such as in hypertension, chordae forces also increased. Overall, FBG sensors are a viable, durable, and high-fidelity sensing technology that can be effectively used to measure mitral valve chordae forces and overcome some limitations of other such technologies.

Ex Vivo Biomechanical Study of Apical Versus Papillary Neochord Anchoring for Mitral Regurgitation

BACKGROUND

Neochordoplasty is an important repair technique, but optimal anchoring position is unknown. Although typically anchored at papillary muscles, new percutaneous devices anchor the neochordae at or near the ventricular apex, which may have an effect on chordal forces and the long-term durability of the repair.

METHODS

Porcine mitral valves (n = 6) were mounted in a left heart simulator that generates physiologic pressure and flow through the valves, and chordal forces were measured with Fiber Bragg Grating strain gauge sensors. Isolated mitral regurgitation was induced by cutting P2 primary chordae, and the regurgitant valve was repaired with polytetrafluoroethylene neochord with apical anchoring, followed by papillary muscle fixation for comparison. In both situations, the neochord was anchored to a customized force-sensing post positioned to mimic the relevant in vivo placement.

RESULTS

Echocardiographic and hemodynamic data confirmed that the repairs restored physiologic hemodynamics. Forces on the chordae and neochord were lower for papillary fixation than for the apical fixation (p = 0.003). In addition, the maximum rate of change of force on the chordae and neochordae was higher for apical fixation than for papillary fixation (p = 0.028).

CONCLUSIONS

Apical neochord anchoring results in effective repair of mitral regurgitation, albeit with somewhat higher forces on the chordae and neochord suture, as well as an increased rate of loading on the neochord compared with the papillary muscle fixation. These results may guide strategies to reduce stresses on neochordae as well as aid optimal patient selection.