Identification of device malfunction in patients supported with the HeartMate XVE left ventricular assist system.

Predicting end-of-life for left ventricular assist devices is important to determine timing of device removal. A retrospective analysis was performed on 46 patients undergoing implantation of the latest HeartMate XVE from July 1, 2003, through March 31, 2006. Devices were assessed by analysis of motor current waveforms and quantification of the titanium or copper particles within dust localized to the driveline vent filter by optical, polarized light, scanning electron microscopy, and energy dispersive x-ray spectroscopy. Assessments were performed monthly for patients supported > or =330 days or for unexpected device alarms. Thirty-one (67%) patients were supported for <330 days and 15 (33%) were supported for > or =330 days. No malfunctions occurred in patients supported <330 days. For patients supported > or =330 days, five had abnormal current waveforms or copper and titanium dust localized to the vent filter. One underwent urgent transplantation, three underwent device replacement (one death; two ongoing), and one is with ongoing support. Of the remaining 10 patients, seven underwent transplantation; two remain on device; and one died while on left ventricular assist device support. There were no unexpected device failures. Bearing wear of the HeartMate XVE is predictable by analysis of current waveforms or titanium and copper dust within the vent filter.

Design features, developmental status, and experimental results with the Heartmate III centrifugal left ventricular assist system with a magnetically levitated rotor.

A long-term left ventricular assist system for permanent use in advanced heart failure is being developed on the basis of a compact centrifugal pump with a magnetically levitated rotor and single-fault-tolerant electronics. Key features include its "bearingless" (magnetic levitation) design, textured surfaces similar to the HeartMate XVE left ventricular assist device (LVAD) to reduce anticoagulation requirements and thromboembolism, a sensorless flow estimator, and an induced pulse mode for achieving an increased level of pulsatility with continuous flow assistance. In vitro design verification testing is underway. Preclinical testing has been performed in calves demonstrating good in vivo performance at an average flow rate of 6 L/min (maximum: >11 L/min) and normal end-organ function and host response. Induced pulse mode demonstrated the ability to produce a physiological pulse pressure in vivo. Thirteen LVADs have achieved between 16 to 40 months of long-term in vitro reliability testing and will be continued until failure. Both percutaneous and fully implanted systems are in development, with a modular connection for upgrading without replacing the LVAD.

In vivo assessment of a rotary left ventricular assist device-induced artificial pulse in the proximal and distal aorta.

The increasing clinical use of rotary left ventricular assist devices (LVADs) suggests that chronic attenuation of arterial pulse pressure has no clinically significant detrimental effects. However, it remains possible that modulating LVAD rotor speed to produce an artificial pulse may be of temporary or occasional benefit. We sought to evaluate a pulse produced by a continuous-flow, centrifugal pump in an ovine thoracic and abdominal aorta. Both ventricles of an adult sheep were resected to eliminate all native cardiac contributions to pulsatility, each replaced by a continuous-flow Thoratec HeartMate III blood pump (Burlington, MA, USA). An LVAD-induced pulsatile flow was achieved by sharply alternating the speed of the magnetically levitated rotor of the left pump between 1,500 rpm (artificial diastole) and 5,500 rpm (artificial systole) at a rate of 60 bpm at a "systolic" interval of 30%. A catheter was advanced from the ascending aorta to the iliac bifurcation via the ventricular assist device outflow graft for pressure measurement and data acquisition. The mean LVAD-induced pulse pressures were 34, 29, 27, and 26 mm Hg in the ascending, thoracic, and abdominal aorta, and the iliac bifurcation, respectively. The maximum rate of pressure rise (deltap/deltat) was between 189 and 238 mm Hg/s, approaching that of the native pulse, although the energy equivalent pressure did not exceed the mean arterial pressure. The HeartMate III's relatively stiff speed control, low rotor mass, and robust magnetic rotor suspension result in a responsive system, enabling very rapid speed changes that can be used to simulate physiologic pulse pressure and deltap/deltat.

Left ventricular assist device performance with long-term circulatory support: lessons from the REMATCH trial.

BACKGROUND: Left ventricular assist device (LVAD) failure and malfunction rates are critical gauges for establishing LVADs as a long-term therapy for end-stage heart failure patients. These device performance measures, however, have been inadequately characterized in the bridge-to-transplantation literature. METHODS: REMATCH is a randomized trial that compares optimal medical management with LVAD implantation for patients with end-stage heart failure. An independent committee adjudicated patient outcomes. The primary endpoint--survival--was analyzed by intention to treat using the log-rank statistic. Frequency of event occurrence was analyzed by Poisson regression. The time to first event was analyzed by the product limit method. Device performance was disaggregated into confirmed malfunctions and system failures. The latter were events in which patients could not be rescued with backup circulatory support measures. RESULTS: The 1-year survival rate was 52% (95% confidence limit [CL]; 40%-63%) for LVAD patients versus 28% (95% CL; 17%-39%) for medical patients and the 2-year survival rate was 29% (95% CL; 19%-40%) for LVAD patients versus 13% (95% CL; 5%-22%) for medical patients. System failure was 0.13 per patient per year and the confirmed LVAD malfunction rate was 0.90. Freedom from device replacement was 87% at 1 year and 37% at 2 years. CONCLUSIONS: Despite the observed rates of device malfunction and replacement, LVAD implantation confers clinically significant improvement with regard to survival as compared with medical management. Device modifications and innovations for infection management exhibit great promise of improving device performance in the near future.

Computational fluid dynamics analysis of a maglev centrifugal left ventricular assist device.

The fluid dynamics of the Thoratec HeartMate III (Thoratec Corp., Pleasanton, CA, U.S.A.) left ventricular assist device are analyzed over a range of physiological operating conditions. The HeartMate III is a centrifugal flow pump with a magnetically suspended rotor. The complete pump was analyzed using computational fluid dynamics (CFD) analysis and experimental particle imaging flow visualization (PIFV). A comparison of CFD predictions to experimental imaging shows good agreement. Both CFD and experimental PIFV confirmed well-behaved flow fields in the main components of the HeartMate III pump: inlet, volute, and outlet. The HeartMate III is shown to exhibit clean flow features and good surface washing across its entire operating range.

Incorporation of electronics within a compact, fully implanted left ventricular assist device.

The promise of expanded indications for left ventricular assist devices in the future for very long-term applications (10+ years) prompts sealed (i.e. fully implanted) systems and less-obtrusive and more reliable implanted components than their external counterparts in percutaneous configurations. Furthermore, sealed systems increase the fraction of total power losses dissipated intracorporeally, a disadvantage that must be carefully managed. We set out to incorporate the motor drive and levitation control electronics within the HeartMate III blood pump without substantially increasing the pump's size. Electronics based on a rigid-flex satellite printed circuit board (PCB) arrangement that could be folded into a very compact, dense package were designed, fabricated, and tested. The pump's lower housing was redesigned to accommodate these PCBs without increasing any dimension of the pump except the height, and that by only 5 mm. The interconnect cable was reduced from 22 wires to 10 (two fully redundant sets of 5). An ongoing test of the assembled pump in vitro has demonstrated no problems in 5 months. In addition, a 20-day in vivo test showed only 1 degrees C temperature rises, equivalent to pumps without incorporated electronics at similar operating conditions.

Can We Develop a Permanent Pulsatile Rotary Blood Pump? Yes, We Can.

Active U.S. participation in the development of artificial heart technology began in 1966 with the award of six contracts. Since that beginning, and continuing to this day, we have been asking the same question, "Can we develop a system to take the place of a natural heart?" There are four formidable barriers that must be overcome before success can be achieved: technological development (Can the system perform as designed?); economic challenges (Can we finance the development?); regulatory hurdles (Can we get it approved for general use?); and acceptance (Will it be used, and will society accept it for what it is?). After 30 years, all but the last barrier has been overcome.

PREFABRICATION DESIGN CONSIDERATIONS FOR A LONG-TERM ELECTRICALLY-ACTUATED ABDOMINAL LEFT VENTRICULAR ASSIST DEVICE (E-TYPE ALVAD).

The conceptual design and development of a long-term, low-profile intracorporeal left ventricular assist device is a multifaceted project involving a series of technical, anatomic and physiologic considerations. Patients with severe left ventricular failure refractory to all other forms of therapy could benefit from such a device. Prior to fabrication of such a blood pump, consideration must be given to physiologic parameters of the projected patient population. The pump must be designed to meet physiologic demands and yet conform to the anatomic constraints posed by the patient population. We measured the body surface area (BSA) of a group of patients (n=50) and found the mean BSA for this group to be 1.804 +/- 0.161 m(2). Using 25 ml/m(2) as a stroke volume index indicative of left ventricular failure and a stroke volume index of 45 ml/m(2) as normal, distributions of stroke volumes (normal and in left ventricular failure) were plotted for a potential population and demonstrated that 63% of the projected population can be returned to normal by a pump with a stroke volume >/= 83 ml. Cadaver fitting studies established that 73% of the potential population can accommodate an ALVAD 10.8 cm in diameter. In-vitro tests demonstrated that a pump stroke volume >/= 83 ml could be achieved by the proposed pump with a 15 mmHg filling pressure at rates up to 125 B/min. A pusher-plate stroke of 0.56 inches would be necessary to provide a stroke volume >/= 83 ml. The percent of the patient population that could be served was determined by excluding those in whom the pump would not fit or in whom it would provide less than a normal resting stroke volume. Approximately 73% of the projected patient population would accommodate this pump and be returned to normal circulatory dynamics.