Critical anatomic dimensions for intrathoracic circulatory assist devices

Multi-Purpose Mechanical Circulatory Device

A mechanical circulatory assist device for long term use outside the hospital setting has been developed. The device can be used for left, right or bi-ventricular support, and several of the developed technologies are applicable for total artificial hearts and non-pulsatile flow systems. The totally implantable device is principally designed for left ventricular support with implantation in the left hemithorax. The system utilizes transcutaneous energy and information transfer sub-systems, and has no percutaneous connections. In vitro durability testing has been conducted for periods from 1-4 years. Bovine experiments have been conducted with sustained circulation for periods form 1.5 to 96 hours. The in vitro and in vivo evaluation to date has demonstrated that the system can function effectively as a totally implantable ventricular assist device. The transcutaneous energy and information transfer sub-systems provided the ability to power, monitor and control the device, without the need for percutaneous connections. Design optimization and chronic in vivo evaluation is planned

A Preclinical Cadaver Fitting Study of Implantable Biventricular Assist Device - AnyHeart™

A multifunctional, Korean-made artificial heart (AnyHeart™) was developed, and prior to its clinical application, a cadaver-fitting study was performed. The study proposed to determine the optimal cannulation approach, implantation technique and route of the cannula to minimize the organ compression of AnyHeart™. The anatomical feasibility and a variety of surgical techniques were evaluated using ten preserved, human cadavers. Implanting AnyHeart™ with ease is possible using various approaches, including a median sternotomy, and a right or left lateral thoracotomy. The lateral thoracotomy approach is shown to be safe and reproducible, especially in patients who have already undergone an operation that used a median sternotomy. The results of this study will guide improvements in the designs of cannulae and AnyHeart™ for future clinical applications.

Virtual Anatomical Three-Dimensional Fit Trial for Intra-Thoracically Implanted Medical Devices

Our purpose is to develop a system that converts computed tomography (CT) scans into an interactive three-dimensional (3-D) model of the thoracic cavity. This study will allow for the preoperative determination of optimal anatomical fit of intra-thoracically implanted medical equipment such as circulatory support devices. From the radiology data bank, we consecutively selected 34 cardiac and 42 noncardiac patients who had CT scans of the chest. Anatomical structures of the electronic CT scans were manually extracted using software. These structures included the thoracic cage, lungs, heart, and the great vessels. The information was converted into a 3-D surface mesh model, which was imported into a 3-D viewer to acquire direct anatomical measurements. The thoracic cage and intra-thoracic organs were measured for data analysis. A methodology was successfully developed to convert a patient's thoracic CT scans into interactive 3-D models, permitting the collection of key anatomical measurements to assess intra-thoracic device fit feasibility. Extensive measurements of the reconstructed thoracic cavity were recorded in a database format and analyzed. This study demonstrated the feasibility of implementing a rapid preoperative screening method based on anatomical fit for the selection or rejection of patients who are candidates for an intra-thoracic mechanical device. This new method will allow for the virtual preoperative implantation of such devices within a patient's chest cavity.

The HeartSaver left ventricular assist device: an update

BACKGROUND

Ventricular assist devices have been shown to be effective as bridges to transplantation and recovery for patients with end-stage heart failure. Current technology has been limited because of the need for percutaneous connections with controllers. The HeartSaver ventricular assist device (VAD) (World Heart Corporation, Ottawa, Ontario, Canada) was developed with the intention of having a completely implantable, portable VAD system. The system consists of an electrohydraulic blood pump, internal and external battery power, and a transcutaneous energy transfer and telemetry unit that allows for power transmission through the skin. Control of the device may be achieved locally or remotely through a variety of communication systems.

METHODS

The device has been modified with the Series II preclinical version being available for in vitro (mock loop) and in vivo (bovine model) testing.

RESULTS

Seventeen Series II devices have been functional on mock loops or other testing trials for an accumulated 900 days of operation. There have been eight acute experiments using a bovine model to test various components as they have become available from manufacturing. Mean pump output was 10.4 +/- 1.1 L/min in full-fill/full-eject mode. Changes in the last 24 months include (1) cannula redesign for better port alignment and integration of tissue valves; (2) battery redesign to convert to new lithium-ion cells; (3) optimized infrared information and electromagnetic inductance energy transmission through various skin thicknesses and pigmentation; and (4) improved reliability of internal and external controller hardware and software.

CONCLUSIONS

Modifications have been required to optimize the HeartSaver VAD's performance. The final HeartSaver VAD design will be produced in the near future to allow for formal in vitro and in vivo testing before clinical implantation.

Progress with the HeartSaver Ventricular Assist Device

BACKGROUND

Ventricular assist devices (VADs) have been shown to be effective for short- or long-term circulatory support. Devices are either being adapted or newly designed for longer term or permanent support, with the goal to provide patients with improved quality of life. Since 1990, a program has been in place to develop a totally implantable, permanent VAD.

METHODS

A multidisciplinary team is developing this VAD with specific goals in mind: (1) that it have an intrathoracic position, (2) that it be a totally implantable device without any percutaneous connections, and (3) that it be possible to communicate with the device from remote locations. These goals would allow for complete patient mobility and flexibility for follow-up.

RESULTS

The electrohydraulically actuated VAD combines the blood pump, volume displacement chamber, energy converter, and internal electronic module into a single compact unit. The device called the HeartSaver VAD is powered by a transcutaneous energy transfer system and can be remotely monitored and controlled. Prototypes of different versions of the device have been tested in vitro and in vivo with satisfactory performance.

CONCLUSIONS

The prototypes of the HeartSaver VAD have functioned well under test conditions and fulfilled the outlined goals. Further development and testing of the design are being conducted before clinical availability.

Development of a ventricular assist device for out-of-hospital use

BACKGROUND

Success with temporary ventricular assist devices, has prompted interest in devices developed for long term use outside of the hospital setting.

METHODS

A totally implantable intrathoracic electro-hydraulic ventricular assist device has been developed. Design focused on providing the recipient with a near normal quality of life. To meet this goal the system utilizes transcutaneous energy transfer and biotelemetry to eliminate percutaneous drive-lines/cables as well as a displacement chamber capable of pressure equalization to atmospheric pressures, so as to eliminate the need for percutaneous venting. An implanted battery provides backup power to allow the recipient the ability to bathe, shower, or swim without connection to an external power source. An integrated telemedicine capability allows the device to be monitored/controlled remotely, using telephone lines.

RESULTS

The system has been tested in vitro with early prototypes running for up to 5 1/2 years. The system was studied in calves (n = 25) with durations of support of up to 30 days, demonstrating the ability of the device to function as a totally implantable device without percutaneous connections.

CONCLUSIONS

The various in vitro and in vivo studies have demonstrated the feasibility of the totally implantable device. Chronic in vivo experiments will follow in preparation for regulatory submissions for human use.

A remotely controlled and powered artificial heart pump

An intrathoracic pulsatile artificial heart pump has been developed. Transcutaneous energy transfer and biotelemetry systems provide continuous power and remote monitoring and control, with no percutaneous connections required. The electrohydraulic system can be used either as a ventricular assist device or with modifications as a total artificial heart. The device uses a unidirectional axial flow pump coupled with a pressure activated one-way valve to allow hydraulic fluid to passively return to the volume displacement chamber during diastole. The transcutaneous energy transfer system provides power to the device and recharges the implantable battery pack. A wearable external controller and external battery pack provide the patient enhanced mobility and thus an improved quality of life. The biotelemetry system allows control and monitoring of the device after implantation, as well as an added capability to monitor and control the device remotely over public communication lines. Early prototypes have functioned failure free for up to 3 years in vitro. The device has sustained circulation in vivo for up to 4 days. Design optimization is continuing, and chronic in vivo evaluation is planned.

Totally implantable intrathoracic ventricular assist device

BACKGROUND

A totally implantable, intrathoracic electrohydraulic ventricular assist device (EVAD) is being developed for permanent use or as a bridge to transplantation.

METHODS

The blood pump with 70-mL nominal stroke volume, volume displacement chamber, reversible turbine, internal electronics and infrared diaphragm position sensor are combined in one compact unit (unified system). The size and geometry are based on human anatomic measurements and fluid dynamic studies. A transcutaneous energy transfer powers the system and recharges the implantable nickel-cadmium battery pack. Autotuning circuitry optimizes energy transfer efficiency over a range of transcutaneous energy transfer coil spacings and misalignments. An infrared diaphragm position sensor detects end-systole and diastole points.

RESULTS

In vitro and acute in vivo tests have demonstrated flow rates greater than 6 L/min. The transcutaneous energy transfer system demonstrated power transfer efficiencies of 60% to 80% for power demands from 5 to 60 W. Thirteen systems are currently undergoing durability testing; one has run for more than 750 days failure-free. The system recently sustained circulation in an acute calf implantation for 96 hours.

CONCLUSIONS

Results of the in vitro and in vivo testing to date have demonstrated that the developed system can function effectively as a totally implantable ventricular assist device. Chronic in vivo evaluation is planned.