Ventricular Assist Device System Research Articles

Left heart bypass using the oscillated blood flow with totally implantable vibrating flow pump.

Aiming at a totally implantable ventricular assist device (VAD), a vibrating flow pump (VFP) was developed in Tohoku University. A transcutaneous energy transmission system (TETS) using an amorphous fiber was developed for the totally implantable VAD system. The VFP works with a higher frequency than the natural heart of a biological system, a frequency of 10-50 Hz. In this research, animal experiments on left heart bypass were performed with healthy goats. Blood from the apex of the left ventricle was received and was sent to the aorta so that an adequate supporting effect of the left heart was provided. In particular, the depression effect of the left ventricle was obvious. As a result, sufficient artificial heart flow was provided. For a totally implantable type VAD, left heart bypass of almost 100% may become necessary in some situations. Therefore, apex approaches of left heart bypass may be desirable. From an anatomical consideration, an apex of the heart is suitable for the VFP of this totally implantable type. In the left heart bypass for which the apex of the heart was used, an almost 100% bypass was possible. This is a requirement that is important when waiting for recovery of sufficient cardiac function. It is also important that left heart circulation is maintained fully by an artificial heart of the complete implantation type. The VFP was considered to be useful as a totally implantable type artificial heart from the results.

Double chamber ventricular assist device with a roller screw linear actuator driven by left and right latissimus dorsi muscles.

A double chamber ventricular assist device (VAD) with a roller screw linear muscle actuator (RSLMA) driven by the left and right latissimus dorsi muscles was developed. The inflow port of each chamber was connected to form the compound inflow port, and the outflow ports were connected to form the compound outflow port. The advantages of this system include 1) the contraction of each muscle contributes to ejection from each ventricle into the common outflow port, thus doubling the net outflow; 2) through proper adjustment of muscle length, the preload to each muscle can be optimized to yield the maximum muscle force; 3) muscle can be stimulated at a lower rate to reduce fatigue and to optimize muscle performance; and 4) the compliance chamber needed in the implantable VAD system is not required with this system. In vitro evaluation in the mock loop with the human arm actuating the RSLMA revealed that the double chamber VAD can provide pump flows of 2-4 L/min against an afterload of 100 mmHg at a stimulation rate of 35-50 beats per minute. The power requirement for each muscle ranged from 2.5 to 3 W at a muscle stroke length of 4 cm. These results verify that the double chamber VAD with the RSLMA driven by the left and right latissimus dorsi muscles can meet the design requirements of a muscle driven VAD to assist the left heart.

Characterization and work optimization of skeletal muscle as a VAD power source.

Powering a ventricular assist device (VAD) with skeletal muscle in a linear configuration will require the understanding of basic muscle mechanics and efficient use of available power. Accordingly, a mathematical model incorporating aspects of the Hill equation has been developed. This model relates whole muscle length, force, velocity, and time during cyclic contraction to investigate coupling with a hydraulically actuated VAD. Parameters of the model have been determined from in vivo isometric and isotonic measurements of electrically stimulated pig latissimus dorsi with the humerus insertion reattached to a hydraulic loading system. The in vivo results show an exponential passive force-length relationship and active isometric forces increasing from 2 to 8 kgf over a 5 cm change in length. The maximum shortening velocity extrapolated from isotonic data in 85 cm/sec. With the experimentally determined parameters, the model system of differential equations was optimized computationally. Predicted maximum cycle work and corresponding muscle force are nonlinear functions of contraction duration; an increase in duration yields little improvement in work output for longer contraction times. The model helps clarify VAD system design parameters for optimal muscle coupling; for example, the model predicts that operating at maximum instantaneous power does not optimize stroke work.

Univentricular and biventricular thoratec VAD support as a bridge to transplantation

As of October 1991, the Thoratec ventricular assist device (VAD) system has been used in 154 transplant candidates who were in imminent risk of dying before donor heart procurement at 39 medical centers in 10 countries. The VAD system consists of a prosthetic ventricle with a 65-mL pumping chamber made from Thoratec's BPS-215M polyurethane, cannulas for atrial or ventricular inflow and arterial outflow connections, and a pneumatic drive console. The devices can be used for partial or complete support of the pulmonary, systemic, or both circulations. In all patients (average age, 42 years; range, 11 to 64 years), the pumps were placed in a paracorporeal position on the anterior abdominal wall and connected to the heart and great vessels by cannulas crossing the chest wall. Biventricular support was used in 120 patients (78%) and isolated left VADs were used in 34. Average flow rate was 5.0 ± 0.9 L/min for the left VAD and 4.3 ± 0.8 L/min for the right VAD. The most frequent complications were bleeding (42% incidence, 7% mortality) and infection (36% incidence, 8% mortality). Ninety-eight patients (65%) recovered sufficiently to undergo heart transplantation after 8 hours to 226 days of support (average, 17.5 days), and 3 are waiting on VADs for transplantation. Eighty-two patients who received transplants have been discharged. This is an 84% early posttransplantation survival and a 54% overall survival. The actuarial survival 1 year after transplantation is 82%, comparable with that of conventional heart transplantation. We conclude that these heterotopic prosthetic devices provide an effective method of maintaining blood flow to vital organs until a donor heart can be procured.

Clinical Choices for Circulatory Assist Devices

Approximately 1.0% of open heart surgery patients become unweanable from cardiac bypass during the surgical procedure. In addition, nearly 20% of patients accepted for cardiac transplantation die while waiting for a donor heart. Pulsatile pneumatic ventricular assist devices (VADs) provide a realistic solution to these dilemmas. Currently, there are five manufacturers who are competing for the major market share in the clinical use of these devices. Novacor, Thermetics, Thoratec, Symbion, and Abiomed all have competitive VAD systems. Because no one system is optimal for all patients, the limitations, similarities, and strengths of each system should be known to enhance the patient's outcome when using these devices. Successful use of VAD systems, either as a bridge to transplantation or to ventricular recovery, is best approached by adherence to strict patient selection. Once instituted, VAD management centers on detailed attention to anticoagulation and prompt diagnosis and treatment of various complications.

Clinical Choices for Circulatory Assist Devices

Approximately 1.0% of open heart surgery patients become unweanable from cardiac bypass during the surgical procedure. In addition, nearly 20% of patients accepted for cardiac transplantation die while waiting for a donor heart. Pulsatile pneumatic ventricular assist devices (VADs) provide a realistic solution to these dilemmas. Currently, there are five manufacturers who are competing for the major market share in the clinical use of these devices. Novacor, Thermetics, Thoratec, Symbion, and Abiomed all have competitive VAD systems. Because no one system is optimal for all patients, the limitations, similarities, and strengths of each system should be known to enhance the patient's outcome when using these devices. Successful use of VAD systems, either as a bridge to transplantation or to ventricular recovery, is best approached by adherence to strict patient selection. Once instituted, VAD management centers on detailed attention to anticoagulation and prompt diagnosis and treatment of various complications.

Experimental evaluation and clinical application of a pediatric ventricular assist device.

A pneumatic pediatric ventricular assist device (VAD) with a stroke volume of 20 ml has been developed to treat post-operative heart failure (HF), and maintain transplant candidates. The polyurethane VAD has two #21 Bjork-Shiley valves and the internal diameter of the cannula is either 6 or 8 mm. Hemodynamic effects of a left ventricular assist device (LVAD) on a HF after Fontan's procedure model, and those of a right ventricular assist device (RVAD) on right HF with pulmonary hypertension model, were investigated in acute experiments with four and five dogs, respectively. In the former, the pressure gradient across the lung and cardiac output (CO) increased with an LVAD; right atrial pressure decreased and CO increased with an RVAD in the latter. The pump was implanted as an LVAD in 8 young goats, 9-22 kg in weight, for 4-10 weeks and favorable in vivo performance was demonstrated. The VAD system was applied as an LVAD to two postcardiotomy patients, a 12 kg boy with a ventricular septal defect, and a 13 kg boy with an endocardial cushion defect. In these cases, CO was well maintained at the level of 2.5-4.1 L/min/m2 for three and seven days, respectively, and the pump was removed. In conclusion, this VAD will become a promising circulatory support system for pediatric uses.

Extracorporeal pulsatile biventricular support after cardiac transplantation

A donor heart failed to adequately sustain hemodynamic function after cardiac transplantation. The cause of the donor heart dysfunction was unknown, and there were no definite risk factors identified to suggest the heart would not recover. A Symbion Acute Ventricular Assist Device System was used to support both ventricles. The heart gradually recovered and the system was explanted after 1 week of support. The patient recuperated and has been discharged from the hospital.

A pusher plate pump for totally implantable left ventricular assist device systems

A pusher plate pump for totally implantable left ventricular assist device systems