Human Fitting Studies of Cleveland Clinic Continuous-Flow Total Artificial Heart

Cleveland Clinic Continuous-Flow Total Artificial Heart: Progress Report and Technology Update

Cleveland Clinic's continuous-flow total artificial heart (CFTAH) is being developed at our institution and has demonstrated system reliability and optimal performance. Based on the results from recent chronic in vivo experiments, CFTAH has been revised, especially to improve biocompatibility. The purpose of this article is to report our progress in developing CFTAH. To improve biocompatibility, the right impeller, the pump housing, and the motor were reviewed for design revision. Updated design features were based on computational fluid dynamics analysis and observations from in vitro and in vivo studies. A new version of CFTAH was created, manufactured, and tested. All hemodynamic and pump-related parameters were observed and found to be within the intended ranges, and the new CFTAH yielded acceptable biocompatibility. Cleveland Clinic's continuous-flow total artificial heart has demonstrated reliable performance, and has shown satisfactory progress in its development.

Human fitting of pediatric and infant continuous-flow total artificial heart: visual and virtual assessment

Background

This study aimed to determine the fit of two small-sized (pediatric and infant) continuous-flow total artificial heart pumps (CFTAHs) in congenital heart surgery patients.

Methods

This study was approved by Cleveland Clinic Institutional Review Board. Pediatric cardiac surgery patients (n = 40) were evaluated for anatomical and virtual device fitting (3D-printed models of pediatric [P-CFTAH] and infant [I-CFTAH] models). The virtual sub-study consisted of analysis of preoperative thoracic radiographs and computed tomography (n = 3; 4.2, 5.3, and 10.2 kg) imaging data.

Results

P-CFTAH pump fit in 21 out of 40 patients (fit group, 52.5%) but did not fit in 19 patients (non-fit group, 47.5%). I-CFTAH pump fit all of the 33 patients evaluated. There were critical differences due to dimensional variation (p < 0.0001) for the P-CFTAH, such as body weight (BW), height (Ht), and body surface area (BSA). The cutoff values were: BW: 5.71 kg, Ht: 59.0 cm, BSA: 0.31 m². These cutoff values were additionally confirmed to be optimal by CT imaging.

Conclusions

This study demonstrated the range of proper fit for the P-CFTAH and I-CFTAH in congenital heart disease patients. These data suggest the feasibility of both devices for fit in the small-patient population.

Patient-specific, echocardiography compatible flow loop model of aortic valve regurgitation in the setting of a mechanical assist device

Background

Aortic regurgitation (AR) occurs commonly in patients with continuous-flow left ventricular assist devices (LVAD). No gold standard is available to assess AR severity in this setting. Aim of this study was to create a patient-specific model of AR-LVAD with tailored AR flow assessed by Doppler echocardiography.

Methods

An echo-compatible flow loop incorporating a 3D printed left heart of a Heart Mate II (HMII) recipient with known significant AR was created. Forward flow and LVAD flow at different LVAD speed were directly measured and AR regurgitant volume (RegVol) obtained by subtraction. Doppler parameters of AR were simultaneously measured at each LVAD speed.

Results

We reproduced hemodynamics in a LVAD recipient with AR. AR in the model replicated accurately the AR in the index patient by comparable Color Doppler assessment. Forward flow increased from 4.09 to 5.61 L/min with LVAD speed increasing from 8,800 to 11,000 RPM while RegVol increased by 0.5 L/min (2.01 to 2.5 L/min).

Conclusions

Our circulatory flow loop was able to accurately replicate AR severity and flow hemodynamics in an LVAD recipient. This model can be reliably used to study echo parameters and aid clinical management of patients with LVAD.

Anatomical human fitting of the BiVACOR total artificial heart

BACKGROUND

BiVACOR is a novel total artificial heart (TAH) utilizing a single centrifugal magnetically levitated rotor with the ability to modulate pulsatile flow. The device has been successfully tested in a bovine model. We undertook a multicenter anatomical and virtual fitting study of the BiVACOR in patients undergoing heart transplantation.

METHODS

10 patients were recruited across two heart transplant centers. A sterilized 1:1 titanium model of the device was inserted into the patient's chest post heart explant, prior to implantation of the donor heart. Measurements were recorded in situ. The device was then removed. Following this, retrospective 3D reconstructions were created from computed tomography chest scans to simulate a virtual fitting.

RESULTS

Mean age was 53 years (range 38-67). Mean BMI was 28 (range 20-37). Heart failure etiology was varied-with ischemic cardiomyopathy being the most common. Mean spine-to-sternum distance at the tenth thoracic vertebrae (T10) was 14 cm (range 11-18). Mean aorta to aortic Port distance was 0.2 cm (range 0-0.5). Mean pulmonary artery to pulmonary artery port distance was 4.2 cm (range 1-7). The device fitted suitably in all patients without gross distortion to the geometry between native vessel/chamber and port.

CONCLUSIONS

This study described the anatomical and virtual fitting of the BiVACOR TAH. The device fit well within the chest cavities of all 10 patients, who represented a variety of body morphologies and heart failure etiology.

Three-dimensional printing in adult cardiovascular medicine for surgical and transcatheter procedural planning, teaching and technological innovation

Three-dimensional (3D)-printing technologies in cardiovascular surgery have provided a new way to tailor surgical and percutaneous treatments. Digital information from standard cardiac imaging is integrated into physical 3D models for an accurate spatial visualization of anatomical details. We reviewed the available literature and analysed the different printing technologies, the required procedural steps for 3D prototyping, the used cardiac imaging, the available materials and the clinical implications. We have highlighted different materials used to replicate aortic and mitral valves, vessels and myocardial properties. 3D printing allows a heuristic approach to investigate complex cardiovascular diseases, and it is a unique patient-specific technology providing enhanced understanding and tactile representation of cardiovascular anatomies for the procedural planning and decision-making process. 3D printing may also be used for medical education and surgical/transcatheter training. Communication between doctors and patients can also benefit from 3D models by improving the patient understanding of pathologies. Furthermore, medical device development and testing can be performed with rapid 3D prototyping. Additionally, widespread application of 3D printing in the cardiovascular field combined with tissue engineering will pave the way to 3D-bioprinted tissues for regenerative medicinal applications and 3D-printed organs.

Virtual implantations to transition from porcine to bovine animal models for a total artificial heart

Realheart total artificial heart (TAH) is a novel, pulsatile, four-chamber total artificial heart which had been successfully tested acutely in a porcine animal model. However, the bovine model is better suited for long-term testing and thus an evaluation of how the design would fit the bovine anatomy was required. Virtual implantation is a method that enables a computer simulated implantation based on anatomical 3D-models created from computer tomography images. This method is used clinically, but not yet adopted for animal studies. Herein, we evaluated its suitability in the redesign of the outer dimensions and vessel connections of Realheart TAH to transition from the porcine to the bovine animal model. Virtual implantations in combination with bovine cadaver studies enabled a series of successful acute bovine implantations. Virtual implantations are a useful tool to replace the use of animals in early device development and refine subsequent necessary in vivo experiments. The next steps are to carry out human virtual implantations and cadaver studies to ensure the design is optimized for all stages of testing as well as the final recipient.

Evaluation of the novel total artificial heart Realheart in a pilot human fitting study

Heart failure affects >26 million patients worldwide. Current cardiac devices save lives, but patients suffer complications. Hence, improved devices are needed. Realheart TAH is a novel total artificial heart which has shown promising results in acute pig studies. However, the device design needed to be evaluated in humans. Virtual implantations demonstrated the device fits in two of three patients, but that there was some interference with the left lung. Herein, we used an innovative 3D-printed model with swivelling device components to test the device in human cadavers. Our new method demonstrated how to optimize design to improve the surgical fit.

Current and Future Considerations in the Use of Mechanical Circulatory Support Devices: An Update, 2008–2018

Our review in the 2008 volume of this journal detailed the use of mechanical circulatory support (MCS) for treatment of heart failure (HF). MCS initially utilized bladder-based blood pumps generating pulsatile flow; these pulsatile flow pumps have been supplanted by rotary blood pumps, in which cardiac support is generated via the high-speed rotation of computationally designed blading. Different rotary pump designs have been evaluated for their safety, performance, and efficacy in clinical trials both in the United States and internationally. The reduced size of the rotary pump designs has prompted research and development toward the design of MCS suitable for infants and children. The past decade has witnessed efforts focused on tissue engineering–based therapies for the treatment of HF. This review explores the current state and future opportunities of cardiac support therapies within our larger understanding of the treatment options for HF.

Innovative Modeling Techniques and 3D Printing in Patients with Left Ventricular Assist Devices: A Bridge from Bench to Clinical Practice

Left ventricular assist devices (LVAD) cause altered flow dynamics that may result in complications such as stroke, pump thrombosis, bleeding, or aortic regurgitation. Understanding altered flow dynamics is important in order to develop more efficient and durable pump configurations. In patients with LVAD, hemodynamic assessment is limited to imaging techniques such as echocardiography which precludes detailed assessment of fluid dynamics. In this review article, we present some innovative modeling techniques that are often used in device development or for research purposes, but have not been utilized clinically. Computational fluid dynamic (CFD) modeling is based on computer simulations and particle image velocimetry (PIV) employs ex vivo models that helps study fluid characteristics such as pressure, shear stress, and velocity. Both techniques may help elaborate our understanding of complications that occur with LVAD and could be potentially used in the future to troubleshoot LVAD-related alarms. These techniques coupled with 3D printing may also allow for patient-specific device implants, lowering the risk of complications increasing device durability.

3D Printing and Heart Failure: The Present and the Future

Advanced imaging modalities provide essential anatomic and spatial information in patients with complex heart disease. Two-dimensional imaging can be limited in the extent to which true 3-dimensional (3D) relationships are represented. The application of 3D printing technology has increased the creation of physical models that overcomes the limitations of a 2D screen. Many groups have reported the use of 3D printing for preprocedural planning in patients with different causes of heart failure. This paper reviews the innovative applications of this technique to provide patient-specific models to improve patient care.

Mechanism of Self-Regulation and In Vivo Performance of the Cleveland Clinic Continuous-Flow Total Artificial Heart

Cleveland Clinic's continuous-flow total artificial heart (CFTAH) provides systemic and pulmonary circulations using one assembly (one motor, two impellers). The right pump hydraulic output to the pulmonary circulation is self-regulated by the rotating assembly's passive axial movement in response to atrial differential pressure to balance itself to the left pump output. This combination of features integrates a biocompatible, pressure-balancing regulator with a double-ended pump. The CFTAH requires no flow or pressure sensors. The only control parameter is pump speed, modulated at programmable rates (60-120 beats/min) and amplitudes (0 to ±25%) to provide flow pulses. In bench studies, passive self-regulation (range: -5 mm Hg ≤ [left atrial pressure - right atrial pressure] ≤ 10 mm Hg) was demonstrated over a systemic/vascular resistance ratio range of 2.0-20 and a flow range of 3-9 L/min. Performance of the most recent pump configuration was demonstrated in chronic studies, including three consecutive long-term experiments (30, 90, and 90 days). These experiments were performed at a constant postoperative mean speed with a ±15% speed modulation, demonstrating a totally self-regulating mode of operation, from 3 days after implant to explant, despite a weight gain of up to 40%. The mechanism of self-regulation functioned properly, continuously throughout the chronic in vivo experiments, demonstrating the performance goals.

Future Prospects for the Total Artificial Heart

A total artificial heart (TAH) is the sole remaining option for patients with biventricular failure who cannot be rescued by left ventricular assist devices (LVADs) alone. However, the pulsatile TAH in clinical use today has limitations: large pump size, unknown durability, required complex anticoagulation regimen, and association with significant postsurgical complications. That pump is noisy; its large pneumatic driving lines traverse the body, with bulky external components for its drivers. Continuous-flow pumps, which caused a paradigm shift in the LVAD field, have already contributed to the rapidly evolving development of TAHs. Novel continuous-flow TAHs are only in preclinical testing or developmental stages. We here review the current state of TAHs, with recommended requirements for the TAH of the future.

The total artificial heart

The total artificial heart (TAH) is a form of mechanical circulatory support in which the patient's native ventricles and valves are explanted and replaced by a pneumatically powered artificial heart. Currently, the TAH is approved for use in end-stage biventricular heart failure as a bridge to heart transplantation. However, with an increasing global burden of cardiovascular disease and congestive heart failure, the number of patients with end-stage heart failure awaiting heart transplantation now far exceeds the number of available hearts. As a result, the use of mechanical circulatory support, including the TAH and left ventricular assist device (LVAD), is growing exponentially. The LVAD is already widely used as destination therapy, and destination therapy for the TAH is under investigation. While most patients requiring mechanical circulatory support are effectively treated with LVADs, there is a subset of patients with concurrent right ventricular failure or major structural barriers to LVAD placement in whom TAH may be more appropriate. The history, indications, surgical implantation, post device management, outcomes, complications, and future direction of the TAH are discussed in this review.