Bridge to transplantation with the DeBakey VAD axial pump: a single center report

Flow dynamics of a novel counterpulsation device characterized by CFD and PIV modeling

BACKGROUND

Historically, single port valveless pneumatic blood pumps have had a high incidence of thrombus formation due to areas of blood stagnation and hemolysis due to areas of high shear stress.

METHODS

To ensure minimal hemolysis and favorable blood washing characteristics, particle image velocimetry (PIV) and computational fluid dynamics (CFD) were used to evaluate the design of a new single port, valveless counterpulsation device (Symphony). The Symphony design was tested in 6-h acute (n=8), 5-day (n=8) and 30-day (n=2) chronic experiments in a calf model (Jersey, 76 kg). Venous blood samples were collected during acute (hourly) and chronic (weekly) time courses to analyze for temporal changes in biochemical markers and quantify plasma free hemoglobin. At the end of the study, animals were euthanized and the Symphony and end-organs (brain, liver, kidney, lungs, heart, and spleen) were examined for thrombus formations.

RESULTS

Both the PIV and the CFD showed the development of a strong moving vortex during filling phase and that blood exited the Symphony uniformly from all areas during ejection phase. The laminar shear stresses estimated by CFD remained well below the hemolysis threshold of 400 Pa inside the Symphony throughout filling and ejection phases. No areas of persistent blood stagnation or flow separation were observed. The maximum plasma free hemoglobin (<10mg/dl), average platelet count (pre-implant = 473 ± 56 K/μl and post-implant = 331 ± 62 K/μl), and average hematocrit (pre-implant = 31 ± 2% and post-implant = 29 ± 2%) were normal at all measured time-points for each test animal in acute and chronic experiments. There were no changes in measures of hepatic function (ALP, ALT) or renal function (creatinine) from pre-Symphony implantation values. The necropsy examination showed no signs of thrombus formation in the Symphony or end organs.

CONCLUSIONS

These data suggest that the designed Symphony has good washing characteristics without persistent areas of blood stagnation sites during the entire pump cycle, and has a low risk of hemolysis and thrombus formations.

[The results of the artificial heart]

The artificial heart is no more a dream but a reality. Over the last 40 years, many circulatory assist devices have been developed. First were the pneumatic devices, external or implantable, providing uni- or biventricular support; next were the partially implantable electromecanical devices. We went from the first generation of devices with all components (pump, energy power, control system) outside of the body to the second generation of devices with the pump and the motor implanted inside the body. Recently, the third generation of artificial hearts appeared with all components implanted inside the body allowing better mobility and quality of life. Results depend on the indication and on the kind of artificial heart implanted: partial (native heart still in place) or total (native heart removed). Essentially developped as a bridge to transplant, the artificial heart is now allowed as destination therapy.

[Clinical experiences with the new electromagnetic ventricular assist devices]

Recently, the third generation of partial electromagnetic artificial hearts appeared, which are a real technological advancement. These new ventricular assist devices are small, implantable, silent and increase the patients' quality of life in comparison with the electromechanical pump of second generation. Their clinical efficiency is at least as good as the second generation in light of the first experiences reported on animals and human beings. Their use as a bridge to transplant and especially as a destination therapy should increase in the coming years as they represent an answer to the health problem, which is the increasing population of patients in heart failure.

Histoire de l'assistance circulatoire mécanique et du cœur artificiel

The impact of heart failure on patients and economical burden on health insurance resources is increasing. Cardiac transplantation is still the primary treatment for patients who are in end stage heart failure. The development of artificial hearts (total and partial) was implemented by the discrepancy between the scarcity of available donors and the importance of waiting lists for cardiac transplantation. The technical progresses achieved since the first works of Kolff in 1957 now allow these patients to have their circulation restored and go home to wait for their transplantation. The encouraging results of the artificial heart and the miniaturization of these devices allow them to be considered as a possible destination therapy for patients not eligible for cardiac transplantation.

Human leukocyte antigen sensitization in ventricular assist device recipients: a lesser risk with the DeBakey axial pump

BACKGROUND

Previous reports, all concerning pulsatile devices, have indicated an increased risk of development of circulating antileukocyte antigen (HLA; human leukocyte antigen) antibodies during ventricular assist device (VAD) support. We investigated sensitization in patients implanted with the DeBakey VAD (MicroMed Technology, Inc, Houston, TX) axial flow pump as a bridge to heart transplantation.

METHODS

Inclusion criteria for this prospective study were the following. Patients implanted with the DeBakey VAD axial flow pump, without HLA antibodies prior to implantation, with a duration of support of at least one month. The HLA antibody testing for IgG and IgM class I and II antibodies was performed weekly during support, using both a complement dependant cytotoxicity assay and an enzyme-linked immunosorbent assay (ELISA). Retrospective cross match was performed for all patients transplanted. The occurrence of graft rejection was determined by regular endomyocardial biopsies after heart transplantation, graded according to the International Society for Heart and Lung Transplantation (ISHLT) guidelines. Additionally, the transfusion history was reviewed for all patients.

RESULTS

Fourteen patients were included representing 1,220 cumulative patient-days of support (mean duration time on support, 87 days). No patient developed detectable IgG antibodies to class I or II. One patient had a positive ELISA, corresponding to nonsignificant (6/30) class I IgM antibodies at 3 weeks postimplantation. Ten patients underwent successful heart transplantation, representing 156 cumulative months. No retrospective cross match was positive. The percentage of significant acute rejection episodes (ISHLT grade 3A or more) was 6% and 4.3% in the first 6 months and from 6 to 12 months, respectively. No vascular rejection was noted. The posttransplantation survival rate was 87% at 6 months and 75% at 1 year, respectively.

CONCLUSIONS

Patients implanted with the DeBakey VAD axial flow pump as a bridge to heart transplantation do not appear to be exposed to an increased risk of sensitization.

Bridge to transplantation with the MicroMed DeBakey ventricular assist device axial pump: a single centre report

OBJECTIVE

Left ventricular assist devices (VADs) are an accepted therapy to bridge patients with end-stage heart failure to heart transplantation. The DeBakey VAD, a continuous axial flow pump weighing 93 g, has been introduced into clinical practice as a bridge to transplant.

METHODS

Starting from April 2000,17 patients (12 males, five females, mean age 44.3 +/- 12.8 years; 11 dilated idiopathic cardiomyopathy, five ischaemic cardiomyopathy, one pulsatile device failure) with end-stage heart failure were implanted with a DeBakey VAD as a bridge to transplantation at our institution. Before implant, all patients suffered from severe heart failure (New York Heart Association functional class IV) despite optimal medical therapy and were put on the waiting list for heart transplantation. Mean cardiac index was 1.59 +/- 0.51 l/min/m2.

RESULTS

Fourteen patients were successfully transplanted after 99 +/- 117 days of assistance (range 11-443 days). Two patients died during assistance of multiorgan failure, one patient is still on VAD. No patient needed additional right ventricular mechanical support. Left ventricular/left VAD thrombosis occurred in one patient who was successfully treated conservatively. No clinical elevation of plasma free haemoglobin was detected. Neither device, driveline, abdominal pocket infection nor device failure occurred.

CONCLUSIONS

In our experience with the continuous axial flow DeBakey VAD, a high success rate was obtained associated with a low risk of complications. All the patients tolerated continuous blood flow for extended periods that makes this device a valuable alternative to pulsatile VADs as a bridge to transplantation.

Left ventricular support by axial flow pump: the echocardiographic approach to device malfunction

Axial flow pumps have gained increased acceptance in recent years as a bridge to heart transplantation and, more recently, as destination therapy. As left ventricular (LV) assist device dysfunction will be increasingly prevalent, the aim of our work was to introduce an echocardiographic management protocol as a guide to recognize the causes of pump failure. In this article we describe the echocardiographic approach to 5 episodes of malfunction of an axial flow pump (DeBakey, MicroMed Technology Inc, Houston, Tex) in 4 patients: 4 episodes caused by thrombosis of LV assist device and one caused by abnormal increase of systemic vascular resistance. In our experience, echocardiography played a pivotal role in clinical management of LV assist device failure. It allowed us to: assess patency and position of inflow and outflow cannulae; research the source of thromboembolic material; assess adequate LV filling and unloading; and optimize right ventricular function, volume replacement therapy, and pharmacologic support.

Bridge to Transplant Using the MicroMed DeBakey Ventricular Assist Device in a Child with Idiopathic Dilated Cardiomyopathy

We report the implantation of the MicroMed DeBakey left ventricular assist device (MDBVAD) in a 10-year-old girl with cardiogenic shock secondary to an idiopathic dilated cardiomyopathy. This was the first pediatric implant of the MDBVAD in the United States and the youngest patient worldwide. The patient recovered well and subsequently underwent successful heart transplantation after 84 days of support.

Long-term support of 9 patients with the DeBakey VAD for more than 200 days

OBJECTIVE

Pulsatile left ventricular assist devices serving as mechanical circulatory support for patients with end-stage heart failure are associated with complications, including bleeding, thromboembolism, and infection. Axial-flow pumps might overcome some of these shortcomings. Here we report our experience with long-term application of the DeBakey VAD (MicroMed Technology, Inc, Houston, Tex).

METHODS

Nine male transplant candidates (37 +/- 14 years) with severe hemodynamic compromise (cardiac index, 1.6 +/- 0.5 L . min(-1) x m(-2); pulmonary capillary wedge pressure, 27 +/- 6 mm Hg) and beginning end-organ failure despite inotropic and intra-aortic balloon pump support received the DeBakey VAD. Clinical outcome was evaluated.

RESULTS

Cumulative support was 7.8 years, and the mean duration of support was 314 +/- 75 days (range, 229-438 days). Eight patients were transplanted, and one died from intracerebral bleeding. Peripheral circulation and end-organ function recovered rapidly after implantation. Continuous flow was able to maintain adequate organ perfusion over the long term. Eight patients were discharged during support, with good quality of life. There were no early bleedings, but there were late bleedings in 3 patients caused by excessive anticoagulation and platelet inhibition. Neurologic events occurred in 4 patients. Three patients recovered completely from symptoms, and one had lethal intracerebral bleeding. Because of thrombus formation, the device was exchanged in 4 patients. With increasing experience, thrombolysis was performed in similar situations. All such patients underwent successful transplantation. Hemolysis occurred, with events indicating thrombus formation. Device-related infection was found in one patient.

CONCLUSIONS

The DeBakey VAD demonstrated its potential for long-term bridge to transplantation. The risk for thrombus formation needs to be addressed by improvement of pump technology and new strategies for platelet inhibition.

Rotary Blood Pumps for Cardiac Assistance: A "Must"?

Ventricular Assist Devices (VADs) were developed following the observation that most end-stage heart failure patients only required left heart support for survival. The trend toward left VAD implantation instead of a TAH has actually contributed to the development of nonpulsatile rotational devices. This article intends to evaluate the current and future technology of continuous flow pumps. Various issues pertaining to the long-term effects of continuous blood flow, biocompatibility of axial flow pumps, and the safety and reliability of such devices need to be addressed. Some of the advantages of rotary blood pumps include their small size, ease of implantation, and encouraging low infection rates. Certain issues such as automatic flow control, device components durability, and hemocompatibility remain unresolved. The quest for an ideal device combining optimal efficiency, ease of anatomical fit, and perfect bioacceptance, continues. Rotary blood pumps are not yet a "must."