Biventricular assist using a portable driver in combination with implanted devices: preliminary experience

A durability study of a paracorporeal pulsatile electro-mechanical pneumatic biventricular assist device

In 2002, the paracorporeal pulsatile electro-mechanical pneumatic ventricular assist device (VAD) began to be developed by the Korea Artificial Organ Center at Korea University under a Health & Medical Technology Research and Development program which finished in 2008. In vitro durability testing was conducted on the paracorporeal pulsatile pneumatic VAD to determine device durability and to evaluate device failures. The 1- and 2-year reliability of the paracorporeal pulsatile pneumatic VAD was shown to be 91.2% and 54.9%, respectively, with an 80% confidence level. Failure modes were analyzed using fault tree analysis, with customized software continuously acquiring data during the test period. After this period, 21 in vivo animal tests were done, with 14 cases of left atrium to left ventricle (LV) inflow cannulation (36Fr)/outflow grafting to descending aorta, and seven cases of apex cannulation of LV to descending aorta (12 mm). The longest postoperative day (182 days) in Korea was recently recorded in in vivo animal testing (bovine, 90 kg, male, 3.5-4.0 L/min flow rate, and 55 bpm).

A versatile intracorporeal ventricular assist device based on the thoratec VAD system

BACKGROUND

As patients are supported for longer durations with paracorporeal Thoratec left ventricular and biventricular assist devices (longest durations: 515 and 457 days, respectively), there is a need for implantable options.

METHODS

We are developing a small, simple, and versatile intracorporeal ventricular assist device (IVAD) for left, right, or biventricular support as an alternative to the large, implantable, pulsatile left ventricular assist device (LVAD) systems available today. The new device is based on the Thoratec paracorporeal VAD that has been used in more than 1,400 patients weighing from 17 to 144 kg and for durations exceeding 1 year including patient discharge (using the portable driver).

RESULTS

The IVAD has the same blood flow path and Thoralon polyurethane blood pumping sac as the paracorporeal VAD, but the housing is a smooth contoured, polished titanium alloy. The IVAD has a new sensor to detect when the pump is full and empty, and is controlled with the Thoratec TLC-II portable VAD driver, which is a small, briefcase-sized, battery-powered, pneumatic control unit. A small flexible (9 mm OD) percutaneous pneumatic driveline for each VAD is tunneled out of the body from the LVAD or right VAD in a pre- or intraperitoneal position. Small size and simplicity are the major advantages of the new device. The IVAD weight (339 g) and implanted volume (252 mL) are approximately one-half that of the current implantable pulsatile electromechanical LVAD systems.

CONCLUSIONS

The small size of the IVAD should not only allow support of a large range of patient sizes and body habitus, but also provide options for implantable left, right, or biventricular support. By implanting only the mechanically simple blood pump, the more complex control unit is external, where it can be serviced and replaced without surgery. The IVAD with the portable driver will be a viable alternative to large implanted electromechanical systems and should address a larger segment of the physically diverse patient population.

Clinically available extracorporeal assist devices

Mechanical circulatory support has been shown to be of benefit to allow recovery after conventional heart surgery and as a successful bridge to heart transplantation. Recent clinical trials with implantable left ventricular assist devices (LVADs) have been completed with these devices showing restoration of normal hemodynamics and successful bridge to transplantation. A major advantage of the implantable devices is the ability for the patient to be discharged and followed up at an outpatient setting. However, multiple advantages to extracorporeal devices still remain, which are the focus of this review. One advantage of the extracorporeal devices is that they can be placed in much smaller patients than currently available implantable LVADs. Also, because of differences in design of the assist devices, the extracorporeal devices can be placed without the need for the cardiopulmonary bypass and with decreased operative time and dissection. Perhaps the biggest advantage of the extracorporeal devices is that they can provide a support for both the right and left side of the heart as opposed to the implantable LVADs, which are only used as left ventricular assist devices. This article describes in detail the advantages and disadvantages of the extracorporeal devices as well as the operative techniques used to implant them. As the number of patients with heart failure continues to rise, so will the need for mechanical circulatory support. Though the majority of these patients will be served by a long-term implantable device, there will remain a subset of patients that will be best suited for treatment with extracorporeal devices.

Development of an intracorporeal Thoratec ventricular assist device for univentricular or biventricular support

There is a need for a small, simple, and versatile intracorporeal ventricular assist device (IVAD) as an alternative to the large implantable electromechanical LVAD systems in current use. Because the basic design of the Thoratec paracorporeal VAD has been demonstrated in over 1,000 patients, weighing from 17 to 144 kg, and for durations up to 515 days including patient discharge (by using the portable driver), we are developing a new intracorporeal version of our VAD. This IVAD has a smooth contoured, polished titanium housing, and maintains the same blood flow path and Thoralon polyurethane blood pumping sac as the paracorporeal VAD. The IVAD is controlled with the Thoratec TLC-II Portable VAD Driver, which is a small briefcase sized, battery powered, pneumatic control unit. Intracorporeal LVADs and/or RVADs are implanted in a preperitoneal position, with a single small (9 mm OD) percutaneous pneumatic driveline for each VAD. The major advantages of the new IVAD design are size and simplicity. The IVAD weight (339 g) and implanted volume (252 ml) are substantially smaller than current implantable electromechanical LVAD systems. Only the small blood pump is implanted, leaving the more complex control unit external, where it can be serviced and replaced. The versatile design is intended for left and/or right heart support in large or small patients. The IVAD in combination with the TLC-II portable driver will be a viable and attractive alternative to large, implanted electromechanical systems.

Single-center experience with the thoratec ventricular assist device

OBJECTIVE

The Thoratec ventricular assist device (Thoratec Laboratories, Pleasanton, Calif) is widely accepted for univentricular and biventricular support in patients with various indications. The aim of this study is to describe our experience with implantation of the Thoratec ventricular assist device in more than 100 patients.

METHODS

From March 1992 to June 1998, 114 patients (98 men and 16 women; mean age, 47.9 years) received the Thoratec ventricular assist device for a mean duration of 44.9 days. The patients were divided into 3 groups. Group 1 included 84 patients in whom the system was applied as a bridge-to-transplant procedure. Group 2 included 17 patients with postcardiotomy cardiogenic shock, and group 3 included 13 patients with cardiogenic shock of other causes.

RESULTS

Sixty-eight percent of patients in group 1 survived to transplantation with a posttransplant survival of 88%. The only independent risk factor affecting survival was age more than 60 years. Survivals in groups 2 and 3 were 47% and 31%, respectively. Main complications in all groups were bleeding, multiple organ failure, liver failure, sepsis, and neurologic disorders.

CONCLUSIONS

The Thoratec ventricular assist device has proved to be a reliable device for bridge to transplantation and postcardiotomy support. Further studies are required on patient selection and on patient and device management to reduce the incidence of complications in these patient populations.