Long-term Circulatory Support - The Left Ventricular Assist System for Advanced Heart Failure

Long-term Circulatory Support - The Left Ventricular Assist System for Advanced Heart Failure

Murali Srinivas
US Cardiology 2004
Published: August 2004
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Introduction Nearly five million Americans suffer from heart failure, with 550,000 new cases diagnosed with this disease each year. Heart failure is responsible for 11 million office visits and over 3.5 million hospitalizations per year in the US, with a total bill of US$23 billion spent annually on treatment. About 250,000 people in the US suffer from severe, end-stage heart failure (NYHA Class IV). For this patient population, annual mortality on medical therapy approaches 50%, and heart transplantation is often the only treatment option. However, limited donor availability has resulted in only 2,400 transplants per year in the US,with about 4,000 patients populating the heart transplant waiting list at any given time. It is estimated that up to 50,000 patients per year in the US could benefit from heart transplantation if organs were available.

Implantable, wearable left ventricular assist devices (LVADs) have emerged in the past decade as safe and effective treatment measures, improving survival and quality of life, for patients with end-stage heart failure awaiting heart transplantation.1 The implantable LVAD, which includes pulsatile devices as well as axial flow pumps, allows the patient greater mobility compared with external pumps and longer-term support. The typical, implantable LVAD comprises three primary components: a pump,which receives blood through an inflow cannula and outputs blood through an outflow cannula; a drive console, which powers the pump and features system controls to adjust its operation; and a power source, which typically involves a combination option of direct electricity and a rechargeable battery pack. Despite the implantable feature of these devices, all current US Food and Drug Administration (FDA)-approved LVADs feature external power sources requiring percutaneous driveline connections. A number of fully implantable systems are under development that will eliminate the need for the percutaneous driveline connection in the future and feature implantable and external coils that transfer energy through the skin.

The Novacor® LVAS (WorldHeart Corporation) is an electrically powered, pulsatile flow LVAD with more than 20 years of clinical use, and the first ventricular assist device to provide more than four years of continuous circulatory support without pump replacement.To date, more than 1,500 patients have been supported with the Novacor LVAS, with almost 600 patient-years of experience, and no deaths attributable to device failure. Twenty-five patients have been supported close to, or over, three years on a single device with the Novacor LVAS. Furthermore, a heart failure patient in Italy has been supported for over six years with the Novacor device (elective replacement of the initial device after four years) before successfully receiving a heart transplant.

Device Description
The Novacor LVAS is a fully autonomous system capable of supporting the entire circulation and substantially unloading the left ventricle.2 The implanted pump drive unit is an integrated pulsatile pump with an electromagnetic driver (solenoid) coupled via springs to the pusher plates of the blood pump. The cyclical, high pulsatile flow mimics the natural function of the heart and takes over the function of the left ventricle. Internal sensors allow the system to recognize native LV function and pump timing. Bioprosthetic valves at the pump inlet and outlet maintain forward flow through a seamless polyurethane blood sac. An external controller provides electrical energy via the percutaneous lead to actuate the driver during the eject cycle.A pair of portable, wearable batteries or an LVAS monitor provides power. 3

Bridge-to-Transplant Experience
‘Bridging to transplant’ with an LVAD has become a standard of care for patients with end-stage heart failure who continue to decompensate on optimal medical therapy. The number of bridge-to-transplant LVAD implants have increased over the years due to the everwidening gap between the number of potential cardiac transplant recipients and the number of available donor organs.4 Between March 1996 and June 1998, a total of 191 patients were enrolled in the Novacor LVAS Bridgeto- Transplantation INTrEPID Trial (156 device and 35 control). Implant duration ranged from one to 657 days with mean support duration being 80 days. Survival to transplantation was a remarkable 78%.5 Therefore, in November 1998, the FDA approved the Novacor LVAS for bridge-to-cardiac transplantation. There are three other commercially-available devices approved by the FDA for this indication. These include HeartMate® LVAD (Thoratec Corporation),Thoratec LVAD and the CardioWest total artificial heart.

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