Improving outcomes in patients with ventricular assist devices transferred from outlying to tertiary care hospitals.

In this retrospective study, the implant course and outcome of patients with ventricular assist devices (VADs) transferred from outlying "spoke" hospitals and converted nonsurgically to a device designed for ambulation at tertiary care "hub" hospitals are evaluated. Factors affecting the crucial decision to transfer and to convert devices have not previously been characterized. Data from 50 patients at 26 US hub institutions were voluntarily submitted to a VAD data registry at ABIOMED, between December 2003 and December 2005. The patients were transferred from 40 spokes on the BVS 5000 Blood Pump and converted to the AB5000 Ventricle (both ABIOMED) at hubs. Comparisons were made on implant indications, time-course, and end-organ function at the time of conversion between surviving patients and patients that had died. Patients who were transferred and converted had a survival to recovery or to next therapy rate of 42%. Eighteen of the surviving patients were still alive 30 days after the explant: 61% were weaned, 33% were transplanted, and 5.6% received a destination device. Average implant-to-transfer time was 1.5 vs. 2.0 days for 30-day survivors and expired patients, respectively, whereas support time from transfer to conversion was 4.8 vs. 4 days, respectively. At the time of device conversion, a total bilirubin below a threshold level of 3.5 mg/dL was predictive of 30-day survival (n = 26, p = .03, odds ratio = 2.73, 95% confidence interval: 1.22-6.16). Patients who survived 30 days were supported longer than those who died (35 vs. 21.1 days, p = .026). At least 18 patients recovered sufficiently on the AB5000 Ventricle to tolerate extubation and 11 patients were able to ambulate. Liver function after implant both at the spoke and before conversion at the hub may be a good indicator of patient survivability. Patients transferred from the BVS 5000 Blood Pump benefited from easy, safe conversion to the AB5000 Ventricle, which provided them with additional support time and afforded the opportunity to recover native heart function.

Vascular tone estimation in patients implanted with the AbioCor implantable replacement heart.

The AbioCor implantable replacement heart provides continuous hydraulic pressure data that are used for control purposes. The magnitude of the end systolic pressure spikes are compared to a preset threshold and used for controlling motor speeds to maintain a full stroke on every beat. Portions of the diastolic pressures of the left and the right side are averaged and can be used for left-right balance control. The mean right diastolic pressure may be used for beat rate (cardiac output) control. The systolic and diastolic hydraulic pressures of the left and right side are correlatable to the respective afterload and preload pressures. More importantly, with known hydraulic pump pressure-flow characteristics, cardiac output is derived. The slopes of the hydraulic pressure traces as a function of time are not used for control or monitoring purposes. However, the magnitudes and shapes of these slopes can provide information on the tones of a patient's vasculature. The ratio of the slope of the systolic pressure to that of the stroke volume yields the vascular tone given in mm Hg/cc. Due to pre-existing pulmonary complications, some AbioCor patients have pulmonary vascular tones that are substantially higher than their respective aortic tones by as much as a factor of four. Pulmonary tones as high as 2 mm Hg/cc, or approximately ten times the normal tone, are recorded. The ratio of averages of the aortic to the pulmonary tone range between 2.2 and 0.25 in patients implanted with the AbioCor compared with a normal value of 5 in subjects without pre-existing pulmonary diseases. The AbioCor implantable replacement heart's hydraulic drive system is capable of providing valuable physiological information, including estimates of physiological pressures, cardiac outputs, and vascular tones.

Improved microvessel repair: laser welding with an anti-thrombotic solder.

BACKGROUND AND OBJECTIVES: Concentrated protein solutions can be used as thermally polymerized solders in laser welding. Solders supplemented with biologically active chemicals may provide in situ drug delivery for localized therapeutics. These studies characterize a serum albumin (SA) solder containing heparin, designed to reduce microvascular thrombosis rates. STUDY DESIGN/MATERIALS AND METHODS: Samples of heparin added to 30% SA to obtain heparin-to-albumin molar ratios (HAMR) of 4:1 and 2:1 were thermally polymerized, and heparin release into saline was measured. Using a rat thrombosis model, patency was determined for suture, and 0 U/ml (control), 2.5 U/ml, 50 U/ml heparin solder repairs. RESULTS: Heparin release was five times higher for 4:1 than 2:1 HAMR solder acutely, but was equivalent after 2 days. Animal patency rates were: 50% suture, 0% control, 50% low heparin, 66% high heparin (P < 0.05 vs. control). CONCLUSIONS: Solders incorporating heparin should provide in situ anti-thrombotic therapy reducing the risk of microvascular thromboses.

Therapeutic potential of implantable replacement hearts.

In patients hospitalized with decompensated life-threatening heart failure, the impact of newer pharmacologic therapies and mechanical circulatory support has not yet been realized, except for those who are bridged to cardiac transplantation. For long-term support of transplant-ineligible patients who have severe biventricular failure that is refractory to optimized pharmacologic therapy, replacement of the natural heart with a totally implantable mechanical replacement heart, capable of producing blood flow of up to 8 to 10 L/min, may become the most well tolerated and effective treatment. This article summarizes the current status of the first generation implantable replacement heart (AbioCor trade mark, ABIOMED. Inc., Danvers, MA). With regard to optimizing the further enhancement of treatment options for end-stage heart failure and other life-threatening illnesses, the pharmacodynamics-like principle of therapeutic efficiency should play a role in the development of both drugs and devices. In keeping with that principle, we recommend that adjusting a product's design input requirements to maximize the therapeutic effect per exposure and;to separate the cumulative therapeutic effects of the product from the cumulative adverse effects (of the product, and of the comorbid disease processes in the patients treated) should be part of the good product development process for any therapeutic product.

A Magnetically Suspended and Hydrostatically Stabilized Centrifugal Blood Pump.

A magnetically suspended centrifugal blood pump intended for application as a long-term implantable ventricular assist device has been built and tested. The rotor is freely suspended in the blood by magnetic and hydrostatic restoring forces. This design obviates the need for bearings and shaft seals, and eliminates the problems of reliability and thrombogenicity associated with them. The positional stability and hydrodynamic performance of the pump has been characterized in vitro at flows of up to 10 L/min at physiologic pressures. Radial position control is realized by an analog electronic feedback control system. The pressure distribution in the fluid surrounding the rotor provides dynamic control in the axial direction with no active feedback. Rotor excursion is less than 50 microns (µ) when the housing receives an impulse peaking at an acceleration of 40 g or upon sudden blockage of the flow. In vitro blood measurements indicate an acceptable level of hemolysis compared with that of a standard centrifugal pump.