A novel passive left heart platform for device testing and research

Soft robotic artificial left ventricle simulator capable of reproducing myocardial biomechanics

The heart's intricate myocardial architecture has been called the Gordian knot of anatomy, an impossible tangle of intricate muscle fibers. This complexity dictates equally complex cardiac motions that are difficult to mimic in physical systems. If these motions could be generated by a robotic system, then cardiac device testing, cardiovascular disease studies, and surgical procedure training could reduce their reliance on animal models, saving time, costs, and lives. This work introduces a bioinspired soft robotic left ventricle simulator capable of reproducing the minutiae of cardiac motion while providing physiological pressures. This device uses thin-filament artificial muscles to mimic the multilayered myocardial architecture. To demonstrate the device's ability to follow the cardiac motions observed in the literature, we used canine myocardial strain data as input signals that were subsequently applied to each artificial myocardial layer. The device's ability to reproduce physiological volume and pressure under healthy and heart failure conditions, as well as effective simulation of a cardiac support device, were experimentally demonstrated in a left-sided mock circulation loop. This work also has the potential to deliver faithful simulated cardiac motion for preclinical device and surgical procedure testing, with the potential to simulate patient-specific myocardial architecture and motion.

Design and Analysis of a Polymeric Left Ventricular Simulator via Computational Modelling

Preclinical testing of medical devices is an essential step in the product life cycle, whereas testing of cardiovascular implants requires specialised testbeds or numerical simulations using computer software Ansys 2016. Existing test setups used to evaluate physiological scenarios and test cardiac implants such as mock circulatory systems or isolated beating heart platforms are driven by sophisticated hardware which comes at a high cost or raises ethical concerns. On the other hand, computational methods used to simulate blood flow in the cardiovascular system may be simplified or computationally expensive. Therefore, there is a need for low-cost, relatively simple and efficient test beds that can provide realistic conditions to simulate physiological scenarios and evaluate cardiovascular devices. In this study, the concept design of a novel left ventricular simulator made of latex rubber and actuated by pneumatic artificial muscles is presented. The designed left ventricular simulator is geometrically similar to a native left ventricle, whereas the basal diameter and long axis length are within an anatomical range. Finite element simulations evaluating left ventricular twisting and shortening predicted that the designed left ventricular simulator rotates approximately 17 degrees at the apex and the long axis shortens around 11 mm. Experimental results showed that the twist angle is 18 degrees and the left ventricular simulator shortens 5 mm. Twist angles and long axis shortening as in a native left ventricle show it is capable of functioning like a native left ventricle and simulating a variety of scenarios, and therefore has the potential to be used as a test platform.

Investigating the importance of left atrial compliance on fluid dynamics in a novel mock circulatory loop

The left atrium (LA) hemodynamic indices hold prognostic value in various cardiac diseases and disorders. To understand the mechanisms of these conditions and to assess the performance of cardiac devices and interventions, in vitro models can be used to replicate the complex physiological interplay between the pulmonary veins, LA, and left ventricle. In this study, a comprehensive and adaptable in vitro model was created. The model includes a flexible LA made from silicone and allows distinct control over the systolic and diastolic functions of both the LA and left ventricle. The LA was mechanically matched with porcine LAs through expansion tests. Fluid dynamic measures were validated against the literature and pulmonary venous flows recorded on five healthy individuals using magnetic resonance flow imaging. Furthermore, the fluid dynamic measures were also used to construct LA pressure-volume loops. The in vitro pressure and flow recordings expressed a high resemblance to physiological waveforms. By decreasing the compliance of the LA, the model behaved realistically, elevating the a- and v-wave peaks of the LA pressure from 12 to 19 mmHg and 22 to 26 mmHg, respectively, while reducing the S/D ratio of the pulmonary venous flowrate from 1.5 to 0.3. This model provides a realistic platform and framework for developing and evaluating left heart procedures and interventions.

Biorobotic hybrid heart as a benchtop cardiac mitral valve simulator

In this work, we developed a high-fidelity beating heart simulator that provides accurate mitral valve pathophysiology. The benchtop platform is based on a biorobotic hybrid heart that combines preserved intracardiac tissue with soft robotic cardiac muscle providing dynamic left ventricular motion and precise anatomical features designed for testing intracardiac devices, particularly for mitral valve repair. The heart model is integrated into a mock circulatory loop, and the active myocardium drives fluid circulation producing physiological hemodynamics without an external pulsatile pump. Using biomimetic soft robotic technology, the heart can replicate both ventricular and septal wall motion, as well as intraventricular pressure-volume relationships. This enables the system to recreate the natural motion and function of the mitral valve, which allows us to demonstrate various surgical and interventional techniques. The biorobotic cardiovascular simulator allows for real-time hemodynamic data collection, direct visualization of the intracardiac procedure, and compatibility with clinical imaging modalities.

Robotic right ventricle is a biohybrid platform that simulates right ventricular function in (patho)physiological conditions and intervention

The increasing recognition of the right ventricle (RV) necessitates the development of RV-focused interventions, devices and testbeds. In this study, we developed a soft robotic model of the right heart that accurately mimics RV biomechanics and hemodynamics, including free wall, septal and valve motion. This model uses a biohybrid approach, combining a chemically treated endocardial scaffold with a soft robotic synthetic myocardium. When connected to a circulatory flow loop, the robotic right ventricle (RRV) replicates real-time hemodynamic changes in healthy and pathological conditions, including volume overload, RV systolic failure and pressure overload. The RRV also mimics clinical markers of RV dysfunction and is validated using an in vivo porcine model. Additionally, the RRV recreates chordae tension, simulating papillary muscle motion, and shows the potential for tricuspid valve repair and replacement in vitro. This work aims to provide a platform for developing tools for research and treatment for RV pathophysiology.

Morphometric Characterization of an Ex Vivo Porcine Model of Functional Tricuspid Regurgitation

Emerging treatments for tricuspid valve (TV) regurgitation require realistic TV pathological models for preclinical testing. The aim of this work was to investigate structural features of fresh and defrosted porcine right-heart samples as models of mild and severe functional tricuspid regurgitation (FTR) condition in ex-vivo pulsatile flow platform. Ten fresh hearts were tested ex-vivo under steady and pulsatile flow in typical right-heart loading conditions. Hemodynamics and 3D echocardiographic imaging of TV and right ventricle (RV) were acquired. Hearts were then kept frozen for 14 days, defrosted, and tested again with the same protocol. Morphometric parameters of TV and RV were derived from 3D reconstructions based on echo data. Fresh samples showed a slightly dilated TV morphology, with coaptation gaps among the leaflets. Sample freezing induced worsening of TV insufficiency, with significant (p < 0.05) increases in annulus size (annulus area and perimeter 7.7-3.1% respectively) and dilation of RV (9.5%), which led to an increase in tenting volume (123.7%). These morphologic alterations reflected into a significant increment of regurgitation fraction (27%). Together, such results suggest that fresh porcine heart samples may be a reliable ex-vivo model of mild FTR condition, which can be enhanced through freezing/thawing treatment to model a severe pathological condition.

In Vitro Model for the Evaluation of Innovative Transcatheter Debridement Device (TDD): Pericardium-Based Scaffold and Stem Cells to Reproduce Calcificated Valves

Aortic valve stenosis has become the most common valvular disease in elderly patients. Several treatments are available such as surgical aortic valve replacement and transcatheter aortic valve implantation. To date, however, there is a need to discover alternative treatments that can delay the disease progression and, therefore, the implant of a prosthetic valve. In this regard, a decalcification procedure based on the use of ultrasonic waves could represent an innovative solution in transcatheter cardiovascular therapies. In this article, we describe an innovative transcatheter debridement device (TDD) that uses low-intensity ultrasound shock waves for calcium ablation from the native aortic valve and bioprosthetic valve. Mesenchymal stem cells were seeded onto pericardium-based scaffolds and committed into an osteogenic phenotype. After treatment with TDD, cell proliferation was analyzed, as well as lactate dehydrogenase release and cell morphology. The release of calcium and inflammation events were detected. The results confirmed that the TDD was able to induce a safe decalcification without any adverse inflammatory events.

In vitro benchtop mock circulatory loop for heart failure with preserved ejection fraction emulation

In this work, a novel mock circulatory loop (MCL) is presented that is capable of simulating both healthy cardiac function and Heart Failure with preserved Ejection Fraction (HFpEF). This MCL differs from others presented in the literature as it features two independently actuated heart chambers, representing the left atrium and the left ventricle. This is an important improvement over other designs as it allows for potential HFpEF treatments to be examined, not just in relation to their effect on the left ventricle but also on the left atrium. The aim of this work was to show that novel MCL designs could be developed to allow for testing of new mechanical circulatory support devices for the treatment of HFpEF. Two loop configurations are presented, one featuring hard PVC cylindrical chambers and one that features soft silicone chambers which are anatomically analogous to the native heart. We show that both MCLs are capable of simulating the onset of HFpEF with a sustained increase in diastolic pressure of 62.03% and a sustained decrease in end diastolic volume (EDV) of 14.24%.

Validation of Virtual Imaging of a Dynamic, Functioning Aortic Valve Using an Ex-vivo Porcine Heart

PURPOSE

To investigate a virtual reality imaging system in terms of visualization accuracy and appropriate orientation when displaying cardiac anatomy, we used an ex-vivo model enabling direct comparison between reconstructed three-dimensional visualization of intracardiac structures and real-time visual images.

DESCRIPTION

We established a systole-diastole platform using a swine heart activated by an external mechanical pump and reservoir, allowing simultaneous acquisition of endoscopic visual and computed tomography (CT) images of the aortic valve. Virtual images were processed from CT data using Vesalius 3D software and compared with visual images seen through a fiberoptic scope.

EVALUATION

An endoscope gave a fine view of the aortic valve, while the virtual images elucidated the valve structures. Superimposition of the images from those two different modalities showed the virtual reality images precisely matching the visual images in both systole and diastole, confirming the validity of this virtual reality application.

CONCLUSION

In view of this demonstrated fidelity of virtual imaging, this technology may be of sufficiently high quality to be considered a gold standard for cardiac anatomy.

A Single-opening&closing Valve Tester for Direct Measurement of Closing Volume of the Heart Valve

PURPOSE

The objective of this study was to develop a novel single opening&closing pulsatile flow in-vitro valve tester for direct measurement of closing volume of the heart valve.

METHODS

A single opening&closing valve tester was composed of a piston pump, valve mounting chamber, reservoir, measurement and control system. The piston pump was used to drive a valve to open and close with dictated flow which comprised three phases of accelerated, constant, and decelerated flow with six slopes. A high speed camera was used to record valve opening and closing images. Two pressure transducers across the tested valve were used to capture the ending time of valve closing which was verified by the high-speed photography. The closing time was measured and closing volume was calculated with a piston displacement volume during valve closing. A tilting disc valve and porcine mitral valve were tested.

RESULTS

There was a big difference in flowrate between the Transonic flowmeter and piston pump. The heart valve opened and closed under the dictated flow driven by the piston pump. The transvalvular pressure was minor during valve opening and then increased sharply during valve closing. The closing time varied approximately linearly with the slope of the decelerated flow and was comparable between the two methods by the transvalvular pressure and high-speed photography. The closing volumes did not change much with the slope of the decelerated flow and were 7.0 ± 1.0 and 14.0 ± 1.5 mL for the tilting disc valve and mitral valve, respectively.

CONCLUSION

Pulsatile flow is challenging to the flowmeter. A novel single opening&closing pulsatile flow in-vitro valve tester for the heart valve has successfully been developed and can be used to simulate and evaluate the opening and closing hemodynamics of the heart valve. The tester can be used to measure valve closing volume and time accurately with a standardized testing protocol free from effect of other components such as the resistance, compliance units and auxiliary valve in the continuous pulsatile flow valve tester.

Leaflet kinematics after the Yacoub and Florida-sleeve operations: results of an in vitro study

OBJECTIVES

The Florida-sleeve is a valve-sparing technique that causes minimal interference to leaflet kinematics and aortic root dynamism. The aim of this in vitro study was to evaluate the effects of the Florida-sleeve and Yacoub techniques on aortic leaflet kinematics.

METHODS

Two groups of 6 whole porcine hearts were treated with either the Florida-sleeve technique or the Yacoub technique and tested in a pulsatile loop. Valve fluid dynamics, coronary flow analysis and valve echocardiograms were performed both before and after the procedures.

RESULTS

Both procedures showed no difference in rapid valve opening time as compared with their respective baseline values. The Florida-sleeve procedure showed a shorter slow closing time (192 ± 19 ms vs baseline 244 ± 14 ms, P = 0.016) and increased slow closing velocity (-1.5 ± 0.4 cm/s vs baseline -0.8 ± 0.4 cm/s, P = 0.038). In the rapid valve closing phase, the Yacoub procedure showed a trend towards slower closing valve velocity (-16 ± 9 cm/s vs baseline -25 ± 9 cm/s, P = 0.07). The Yacoub procedure showed larger leaflet displacement at the end of the slow valve closing time that was 2.0 ± 0.5 cm vs baseline 1.5 ± 0.3 cm, P = 0.044. When comparing the Florida-sleeve and Yacoub procedures, the former showed statistically significant shorter slow valve closing time (P = 0.017).

CONCLUSIONS

This study showed that the Florida-sleeve technique alters the slow closing phase of the aortic valve leaflet kinematics when compared with both the normal baseline and Yacoub procedure, while the latter showed a larger leaflet displacement before the rapid closing valve phase.

Ex Vivo Model of Functional Mitral Regurgitation Using Deer Hearts

Transcatheter therapies are emerging for functional mitral regurgitation (FMR) treatment, however there is lack of pathological models for their preclinical assessment. We investigated the applicability of deer hearts for this purpose.

8 whole deer hearts were housed in a pulsatile flow bench. At baseline, all mitral valves featured normal coaptation. The pathological state was induced by 60-minutes intraventricular constant pressurization. It caused mitral annulus dilation (antero-posterior diameter increase from 31.8 ± 5.6 mm to 39.5 ± 4.9 mm, p = 0.001), leaflets tethering (maximal tenting height increase from 7.3 ± 2.5 mm to 12.7 ± 3.4 mm, p < 0.001) and left ventricular diameter increase (from 67.8 ± 7.5 mm to 79.4 ± 6.5 mm, p = 0.004). These geometrical reconfigurations led to restricted mitral valve leaflets motion and leaflet coaptation loss. Preliminary feasibility assessment of two FMR treatments was performed in the developed model.

Deer hearts showed ability to dilate under constant pressurization and have potential to be used for realistic preclinical research of novel FMR therapies.

Mechanical and Structural Evaluation of Tricuspid Bicuspidization in a Porcine Model

INTRODUCTION

Tricuspid regurgitation (TR) affects approximately 1.6 million Americans and is associated with just a 63.9% 1-year survival rate in its moderate to severe forms due to its asymptomatic nature and late diagnosis and surgical referral. As a result, industrial fervor has begun to broach this topic, with several percutaneous treatment devices currently under development. As much remains unknown about the tricuspid apparatus, the mechanics of these procedures remain unquantified. In this study, a testing apparatus and technique for the evaluation of percutaneous tricuspid valve (TV) bicuspidization were developed for the evaluation of these parameters in twelve porcine hearts.

METHODS

The passive relaxed myocardial state and the active contracted state were each induced in six porcine hearts and the bicuspidization experiment was run twice, the second time after induction of TR. TV annular area, cinching force, static leakage through the TV annulus, and annular ellipticity were quantified and compared among the groups.

RESULTS

The use of phenol was effective to induce functional TR by increased annular area. Cinching force was not found to differ between any of the testing states, but the bicuspidization experiment was able to reduce the TR annular area to that of its healthy counterpart in addition to reducing static leakage through the TV annulus. Despite appropriately reducing the area, bicuspidization was found to induce a more circular TV annular shape.

CONCLUSION

Taken together, these results provide a first mechanical analysis of the TV bicuspidization mechanism and may serve as a point of reference for future clinical animal studies.

Feasibility of a Mitral Annuloplasty With the Capability for Peri- and Postoperative Adjustment

Surgical repair with implantation of a mitral annuloplasty ring is the gold standard treatment for mitral regurgitation. However, outcomes are variable and recurrent mitral regurgitation is not uncommon. A REshapeable Mitral Annuloplasty DevIce (REMADI) is proposed, which consists of a fully encapsulated low melting temperature alloy. The alloy is solid and rigid at body temperature and provides traction force to shape the annulus. When heated using a noncontact method, the alloy melts and the REMADI becomes malleable. The REMADI is engaged with the mitral valve annulus using anchors which automatically deploy upon contact. A passive beating porcine heart model was used to demonstrate the feasibility of the REMADI device, which was deployed, engaged, and used to reduce the diameter of the mitral valve annulus.

Ultrasound-based estimation of remaining cardiac function in LVAD-supported ex vivo hearts

Left ventricular assist devices (LVAD) provide cardiac support to patients with advanced heart failure. Methods that can directly measure remaining LV function following device implantation do not currently exist. Previous studies have shown that a combination of loading (LV pressure) and deformation (strain) measurements enables quantitation of myocardial work. We investigated the use of ultrasound (US) strain imaging and pressure–strain loop analysis in LVAD‐supported hearts under different hemodynamic and pump unloading conditions, with the aim of determining LV function with and without LVAD support. Ex vivo porcine hearts (n = 4) were implanted with LVADs and attached to a mock circulatory loop. Measurements were performed at hemodynamically defined “heart conditions” as the hearts deteriorated from baseline. Hemodynamic (including LV pressure) and radio‐frequency US data were acquired during a pump‐ramp protocol at speeds from 0 (with no pump outflow) to 10 000 revolutions per minute (rpm). Regional circumferential (ε_circ) and radial (ε_rad) strains were estimated over each heart cycle. Regional ventricular dyssynchrony was quantitated through time‐to‐peak strain. Mean change in LV pulse pressure and ε_circ between 0 and 10 krpm were −21.8 mm Hg and −7.24% in the first condition; in the final condition −46.8 mm Hg and −19.2%, respectively. ε_rad was not indicative of changes in pump speed or heart condition. Pressure–strain loops showed a degradation in the LV function and an increased influence of LV unloading: loop area reduced by 90% between 0 krpm in the first heart condition and 10 krpm in the last condition. High pump speeds and degraded condition led to increased dyssynchrony between the septal and lateral LV walls. Functional measurement of the LV while undergoing LVAD support is possible by using US strain imaging and pressure–strain loops. This can provide important information about remaining pump function. Use of novel LV pressure estimation or measurement techniques would be required for any future use in LVAD patients.

An organosynthetic dynamic heart model with enhanced biomimicry guided by cardiac diffusion tensor imaging

The complex motion of the beating heart is accomplished by the spatial arrangement of contracting cardiomyocytes with varying orientation across the transmural layers, which is difficult to imitate in organic or synthetic models. High-fidelity testing of intracardiac devices requires anthropomorphic, dynamic cardiac models that represent this complex motion while maintaining the intricate anatomical structures inside the heart. In this work, we introduce a biorobotic hybrid heart that preserves organic intracardiac structures and mimics cardiac motion by replicating the cardiac myofiber architecture of the left ventricle. The heart model is composed of organic endocardial tissue from a preserved explanted heart with intact intracardiac structures and an active synthetic myocardium that drives the motion of the heart. Inspired by the helical ventricular myocardial band theory, we used diffusion tensor magnetic resonance imaging and tractography of an unraveled organic myocardial band to guide the design of individual soft robotic actuators in a synthetic myocardial band. The active soft tissue mimic was adhered to the organic endocardial tissue in a helical fashion using a custom-designed adhesive to form a flexible, conformable, and watertight organosynthetic interface. The resulting biorobotic hybrid heart simulates the contractile motion of the native heart, compared with in vivo and in silico heart models. In summary, we demonstrate a unique approach fabricating a biomimetic heart model with faithful representation of cardiac motion and endocardial tissue anatomy. These innovations represent important advances toward the unmet need for a high-fidelity in vitro cardiac simulator for preclinical testing of intracardiac devices.

Measurement of in vitro cardiac deformation by means of 3D digital image correlation and ultrasound 2D speckle-tracking echocardiography

Ultrasound-based 2D speckle-tracking echocardiography (US-2D-STE) is increasingly used to assess the functionality of the heart. In particular, the analysis of cardiac strain plays an important role in the identification of several cardiovascular diseases. However, this imaging technique presents some limitations associated with its operating principle that result in low accuracy and reproducibility of the measurement. In this study, an experimental framework for multimodal strain imaging in an in vitro porcine heart was developed. Specifically, the aim of this work was to analyse displacement and strain in the heart by means of 3D digital image correlation (3D-DIC) and US-2D-STE. Over a single cardiac cycle, displacement values obtained from the two techniques were in strong correlation, although systematically larger displacements were observed with 3D-DIC. Notwithstanding an absolute comparison of the strain measurements was not possible to achieve between the two methods, maximum principal strain directions computed with 3D-DIC were consistent with the longitudinal and circumferential strain distribution measured with US-2D-STE. 3D-DIC confirmed its high repeatability in quantifying displacement and strain over multiple cardiac cycles, unlike US-2D-STE which is affected by accumulated errors over time (i.e. drift). To conclude, this study demonstrates the potential of 3D-DIC to perform dynamic measurement of displacement and strain during heart deformations and supports future applications of this method in ex vivo beating heart platforms, which replicate more fully the complex contraction of the heart.

Design, simulation, and fabrication of a three-dimensional printed pump mimicking the left ventricle motion

The development of accurate replicas of the circulatory and cardiac system is fundamental for a deeper understanding of cardiovascular diseases and the testing of new devices. Although numerous works concerning mock circulatory loops are present in the current state of the art, still some limitations are present. In particular, a pumping system able to reproduce the left ventricle motion and completely compatible with the magnetic resonance environment to permit the four-dimensional flow monitoring is still missing. The aim of this work was to evaluate the feasibility of an actuator suitable for cardiovascular mock circuits. Particular attention was given to the ability to mimic the left ventricle dynamics including both compression and twisting with the magnetic resonance compatibility. In our study, a left ventricle model to be actuated through vacuum was designed. The realization of the system was evaluated with finite element analysis of different design solutions. After the in silico evaluation phase, the most suitable design in terms of physiological values reproduction was fabricated through three-dimensional printing for in vitro validation. A pneumatic experimental setup was developed to evaluate the pump performances in terms of actuation, in particular ventricle radial and longitudinal displacement, twist rotation, and ejection fraction. The study demonstrated the feasibility of a custom pneumatic pump for mock circulatory loops able to reproduce the physiological ventricle movement and completely suitable for the magnetic resonance environment.

Novel In Vitro Test Systems and Insights for Transcatheter Mitral Valve Design, Part I: Paravalvular Leakage

While transcatheter mitral valve (TMV) replacement technology has great clinical potential for surgically inoperable patients suffering from mitral regurgitation, no TMV has yet achieved regulatory approval. The diversity of devices currently under development reflects a lack of consensus regarding optimal design approaches. In Part I of this two-part study, a test system was developed for the quantification of paravalvular leakage (PVL) following deployment of a TMV or TMV-like device in pressurized, explanted porcine hearts (N = 7). Using this system, PVL rate was investigated as a function of steady trans-mitral pressure (ΔP), TMV shape, and TMV-annular oversizing, using a series of "mock TMV plug" devices. Across all devices, PVL was found to approximately trend with the square of ΔP. PVL rates were approximately 0-15 mL/s under hypotensive pressure, 10-40 mL/s under normotension, and 30-85 mL/s under severe hypertension. D-shaped devices significantly reduced PVL vs. circular devices; however, this effect was diminished upon oversizing to the annulus by 6 mm inter-trigonal distance. In conclusion, this steady pressure, in vitro test system was effective to compare PVL performance across TMV-like designs. PVL exhibited complex dynamics in terms of its response to transvalvular pressure and TMV profile.

Cardiovascular tissue engineering: From basic science to clinical application

Valvular heart disease is an increasing population health problem and, especially in the elderly, a significant cause of morbidity and mortality. The current treatment options, such as mechanical and bioprosthetic heart valve replacements, have significant restrictions and limitations. Considering the increased life expectancy of our aging population, there is an urgent need for novel heart valve concepts that remain functional throughout life to prevent the need for reoperation. Heart valve tissue engineering aims to overcome these constraints by creating regenerative, self-repairing valve substitutes with life-long durability. In this review, we give an overview of advances in the development of tissue engineered heart valves, and describe the steps required to design and validate a novel valve prosthesis before reaching first-in-men clinical trials. In-silico and in-vitro models are proposed as tools for the assessment of valve design, functionality and compatibility, while in-vivo preclinical models are required to confirm the remodeling and growth potential of the tissue engineered heart valves. An overview of the tissue engineered heart valve studies that have reached clinical translation is also presented. Final remarks highlight the possibilities as well as the obstacles to overcome in translating heart valve prostheses into clinical application.

Functional Tricuspid Regurgitation Model in a Beating Heart Platform

Currently, clinicians are seeking new, minimally invasive treatment options for functional tricuspid regurgitation (FTR). Challenging tricuspid complexity requires the evaluation of the treatment techniques in adequate and realistic preclinical scenario. The purpose of this article is to describe the design and functional assessment of a novel passive beating heart model of the pulmonary circulation with the possibility to tightly control FTR. The model housed porcine hearts actuated by a volumetric pump that cyclically pressurized the right ventricle. The in-vitro FTR model exploited the tendency of the ventricle to dilate under pressure. The dilation entailed papillary muscles displacement and valve annulus enlargement, thus inducing tricuspid valve insufficiency. Employment of constraint bands allowed to restore valve competency. The system provided consistent replication of the main determinants of the pulmonary hemodynamics in a wide range of working conditions. The experimental model of FTR was reliable, easily controllable, and showed good stability-over-time. Echocardiography and fiberscope imaging provided a unique opportunity to investigate valve dynamics. These features make the platform suitable for realistic training purposes and testing of the upcoming FTR therapies.

Ultrasound functional imaging in an ex vivo beating porcine heart platform

In recent years, novel ultrasound functional imaging (UFI) techniques have been introduced to assess cardiac function by measuring, e.g. cardiac output (CO) and/or myocardial strain. Verification and reproducibility assessment in a realistic setting remain major issues. Simulations and phantoms are often unrealistic, whereas in vivo measurements often lack crucial hemodynamic parameters or ground truth data, or suffer from the large physiological and clinical variation between patients when attempting clinical validation. Controlled validation in certain pathologies is cumbersome and often requires the use of lab animals. In this study, an isolated beating pig heart setup was adapted and used for performance assessment of UFI techniques such as volume assessment and ultrasound strain imaging. The potential of performing verification and reproducibility studies was demonstrated. For proof-of-principle, validation of UFI in pathological hearts was examined. Ex vivo porcine hearts (n  =  6, slaughterhouse waste) were resuscitated and attached to a mock circulatory system. Radio frequency ultrasound data of the left ventricle were acquired in five short axis views and one long axis view. Based on these slices, the CO was measured, where verification was performed using flow sensor measurements in the aorta. Strain imaging was performed providing radial, circumferential and longitudinal strain to assess reproducibility and inter-subject variability under steady conditions. Finally, strains in healthy hearts were compared to a heart with an implanted left ventricular assist device, simulating a failing, supported heart. Good agreement between ultrasound and flow sensor based CO measurements was found. Strains were highly reproducible (intraclass correlation coefficients  >0.8). Differences were found due to biological variation and condition of the hearts. Strain magnitude and patterns in the assisted heart were available for different pump action, revealing large changes compared to the normal condition. The setup provides a valuable benchmarking platform for UFI techniques. Future studies will include work on different pathologies and other means of measurement verification.

The dynamic cardiac biosimulator: A method for training physicians in beating-heart mitral valve repair procedures

OBJECTIVE

Previously, cardiac surgeons and cardiologists learned to operate new clinical devices for the first time in the operating room or catheterization laboratory. We describe a biosimulator that recapitulates normal heart valve physiology with associated real-time hemodynamic performance.

METHODS

To highlight the advantages of this simulation platform, transventricular extruded polytetrafluoroethylene artificial chordae were attached to repair flail or prolapsing mitral valve leaflets. Guidance for key repair steps was by 2-dimensional/3-dimensional echocardiography and simultaneous intracardiac videoscopy.

RESULTS

Multiple surgeons have assessed the use of this biosimulator during artificial chordae implantations. This simulation platform recapitulates normal and pathologic mitral valve function with associated hemodynamic changes. Clinical situations were replicated in the simulator and echocardiography was used for navigation, followed by videoscopic confirmation.

CONCLUSIONS

This beating heart biosimulator reproduces prolapsing mitral leaflet pathology. It may be the ideal platform for surgeon and cardiologist training on many transcatheter and beating heart procedures.

Interaction of a Transapical Miniaturized Ventricular Assist Device With the Left Ventricle: Hemodynamic Evaluation and Visualization in an Isolated Heart Setup

New left ventricular assist devices (LVADs) offer both important advantages and potential hazards. VAD development requires better and expeditious ways to identify these advantages and hazards. We validated in an isolated working heart the hemodynamic performance of an intraventricular LVAD and investigated how its outflow cannula interacted with the aortic valve. Hearts from six pigs were explanted and connected to an isolated working heart setup. A miniaturized LVAD was implanted within the left ventricle (tMVAD, HeartWare Inc., Miami Lakes, FL, USA). In four experiments blood was used to investigate hemodynamics under various loading conditions. In two experiments crystalloid perfusate was used, allowing visualization of the outflow cannula within the aortic valve. In all hearts the transapical miniaturized ventricular assist device (tMVAD) implantation was successful. In the blood experiments hemodynamics similar to those observed clinically were achieved. Pump speeds ranged from 9 to 22 krpm with a maximum of 7.6 L/min against a pressure difference between ventricle and aorta of ∼50 mm Hg. With crystalloid perfusate, central positioning of the outflow cannula in the aortic root was observed during full and partial support. With decreasing aortic pressures the cannula tended to drift toward the aortic root wall. The tMVAD could unload the ventricle similarly to LVADs under conventional cannulation. Aortic pressure influenced central positioning of the outflow cannula in the aortic root. The isolated heart is a simple, accessible evaluation platform unaffected by complex reactions within a whole, living animal. This platform allowed detection and visualization of potential hazards.

In vitro assessment of mitral valve function in cyclically pressurized porcine hearts

Recent approaches to the in vitro experimental study of cardiac fluid mechanics involve the use of whole biological structures to investigate in the lab novel therapeutic approaches for the treatment of heart pathologies. To enhance reliability and repeatability, the influence of the actuation strategy of the experimental apparatuses on the biomechanics of biological structures needs to be assessed. Using echography and intracardiac high-speed imaging, we compared the mitral valve (MV) anatomo-functional features (coaptation areas/lengths, papillary muscles-valvular plane distances) in two passive-beating-heart mock loops with internal (IPML) or external (EPML) pressurization of the ventricular chamber. Both apparatuses showed fluid dynamic conditions that closely resembled the physiology. The MVs analyzed in the EPML presented coaptation areas and lengths that were systematically higher, and exhibited greater variability from early-to peak-systole, as compared to those in the IPML. Moreover, in the EPML, the MV leaflets exhibited a convexity with high curvature toward the atrium. With the IPML, MV coaptation lengths ranged similar to available clinical data and the papillary muscles-valve plane distances were more stable throughout systole. In conclusion, both the apparatuses allow for reproducing in vitro the left heart hemodynamics, in terms of flow rates and pressures, with proper mitral valve continence. Results suggest that the IPML is more suitable for replicating the physiological MV functioning, while the EPML may have more potential as a model for the study of MV pathologies.