MicroMed DeBakey Research Articles

Long-term heart transplant outcomes after lowering fixed pulmonary hypertension using left ventricular assist devices.

Fixed pulmonary hypertension (fPH) is a contraindication for heart transplantation (HTX). Left ventricular assist device (LVAD) implantation as a bridge to candidacy can reverse fPH in patients with terminal heart failure by chronic left ventricular unloading. We report our institutional experience with terminal heart failure patients and fPH that were successfully bridged to candidacy and underwent subsequent HTX. We retrospectively reviewed the data of 79 patients with terminal heart failure and fPH who were successfully bridged to candidacy for HTX with 6 different LVAD devices at our centre from October 1998 to September 2016 (Novacor n = 4, MicroMed DeBakey n = 29, DuraHeart n = 2, HeartMate II n = 14, HVAD n = 29 and MVAD n = 1). Median duration of LVAD support was 288 days (range 45-2279 days). Within the same timeframe, a control group of 48 patients underwent HTX after bridge-to-transplant LVAD therapy for reasons other than PH. Study end points were (i) development of fPH after LVAD implantation, (ii) post-transplant outcomes and (iii) incidence of severe adverse events. Pulmonary vascular resistance, assessed by vasodynamic catheterization, was 4.3 ± 1.8 WU before LVAD implantation. After a median support period of 89 days (interquartile range 4-156 days), pulmonary vascular resistance decreased to 2.0 ± 0.9 WU (P ≤ 0.001), and patients were listed for HTX. Median duration of LVAD support in the study group was 288 days (45-2279 days). We observed 2 patients (2.5%) with acute right heart failure who required extracorporeal mechanical support after HTX in the study group. Long-term post-transplant survival between the study group (3 years: 83.5%, 5 years: 81.0%) and the control group (3 years: 87.5%, 5 years: 85.4%) was comparable (log-rank: P = 0.585). LVAD implantation as a bridge to candidacy reverses fPH in patients with terminal heart failure. Post-HTX survival is excellent and comparable to results obtained in patients without fPH at the time of HTX listing.

Enhancement of Arterial Pressure Pulsatility by Controlling Continuous-Flow Left Ventricular Assist Device Flow Rate in Mock Circulatory System.

Continuous-flow left ventricular assist devices (CF-LVADs) generally operate at a constant speed, which reduces pulsatility in the arteries and may lead to complications such as functional changes in the vascular system, gastrointestinal bleeding, or both. The purpose of this study is to increase the arterial pulse pressure and pulsatility by controlling the CF-LVAD flow rate. A MicroMed DeBakey pump was used as the CF-LVAD. A model simulating the flow rate through the aortic valve was used as a reference model to drive the pump. A mock circulation containing two synchronized servomotor-operated piston pumps acting as left and right ventricles was used as a circulatory system. Proportional-integral control was used as the control method. First, the CF-LVAD was operated at a constant speed. With pulsatile-speed CF-LVAD assistance, the pump was driven such that the same mean pump output was generated. Continuous and pulsatile-speed CF-LVAD assistance provided the same mean arterial pressure and flow rate, while the index of pulsatility increased significantly for both arterial pressure and pump flow rate signals under pulsatile speed pump support. This study shows the possibility of improving the pulsatility of CF-LVAD support by regulating pump speed over a cardiac cycle without reducing the overall level of support.

Rotary Blood Pumps as Long-Term Mechanical Circulatory Support: A Review of a 15-Year Berlin Experience

This article reports our 15-year single-center experience with rotary blood pumps (RBPs) as long-term mechanical circulatory support (MCS) with emphasis on outcomes. For more than 15-year period, we have used various RBPs as bridge to transplantation or to myocardial recovery. Our group performed the first human implantation worldwide of RBCs, the MicroMed DeBakey ventricular assist device in November 1998 in a patient with end-stage heart failure who was supported for 47 days until his death. Based on this initial experience, we recognized the feasibility of providing long-term support and since then it has been our primary armamentarium in treating patients with heart failure. Between 1987 and September 2013, we have implanted 2208 ventricular assist devices ranging from pulsatile to continuous-flow systems, as short-term, long-term, or permanent support in patients with end-stage heart failure. In total, 1009 RBPs were implanted on 908 patients, and their outcomes are reported here. We have shared some milestones in MCS including the first implantation of Jarvik 2000 on the oldest patient (81-year old) in 2008 and the first worldwide implantation of a biventricular HeartWare. Over time, implantation techniques, anticoagulation, and postoperative care have been modified and individualized. A relevant aspect of our experience has been the incidence of pump thrombosis. This is particularly frustrating because the problem has occurred in the setting of full anticoagulation and antiplatelet therapy, guided by strict anticoagulation monitoring. It has become clear to us that the devices are still not perfect. Technical pump failures such as cable breaks also occur, prompting urgent pump exchange, and infection. A 15-year cumulative mortality rate is 46.9%. This report emphasizes that MCS with RBPs has evolved into a routine treatment in heart failure and is a highly feasible option for permanent therapy particularly for elderly patients.

Estimation of left ventricular pressure with the pump as "sensor" in patients with a continuous flow LVAD.

In long-term ventricular support of patients with LVADs, left ventricular pressure (p(lv)) is relevant for indicating the unloading level of the heart. Monitoring of p(lv) over time might give more insight into the increase or decrease in native ventricular function. In this study, we aim to assess dynamic p(lv) noninvasively, using the LVAD as a pressure sensor. Pressure head (dp(lvad)) was estimated from pump flow with a dynamic pump model (1). Estimated dp(lvad) and measured aortic pressure were used to calculate left ventricular pressure. Moreover, parameters dp/dtmax and mean, minimum, and maximum p(lv) were derived.The method was validated with a porcine ex vivo beating heart model by measurements conducted in 4 hearts supported with a Micromed DeBakey VAD and 3 hearts with a Heartmate II VAD. During each measurement, aortic and left ventricular pressure, pump flow, and pressure head were recorded for 30 s with a sampling frequency of 1 kHz. The estimation of left ventricular pressure appeared to be accurate for both pumps. The parameters mean and minimum pressure were estimated with high accuracy. The degree of accuracy of the estimated p(lv) was proportional to the degree of accuracy of the dynamic pump model. We proved that the LVAD model described in this paper can be used as a pressure indicator to determine LV pressure at any time based on noninvasive measurements of pump flow, aortic pressure, and the properties of the outlet graft.

Aortic Valve Function Under Support of a Left Ventricular Assist Device: Continuous vs. Dynamic Speed Support.

Continuous flow left ventricular devices (CF-LVADs) support the failing heart at a constant speed and alters the loads on the aortic valve. This may cause insufficiency in the aortic valve under long-term CF-LVAD support. The aim of this study is to assess the aortic valve function under varying speed CF-LVAD support. A Medtronic freestyle valve and a Micromed DeBakey CF-LVAD were tested in a mock circulatory system. First, the CF-LVAD was operated at constant speeds between 7500 and 11,500 rpm with 1000 rpm intervals. The mean pump outputs obtained from these tests were applied in varying speed CF-LVAD support mode using a reference model for the pump flow. The peak of the instantaneous pump flow was applied at peak systole and mid-diastole, respectively. Ejection durations and in the aortic valve were the longest when the peak pump flow was applied at mid-diastole among the CF-LVAD operating modes. Furthermore, mean aortic valve area over a cardiac cycle was highest when the peak pump flow was applied at mid-diastole. The results show that changing phase of the reference flow rate signal may reduce the effects of the CF-LVADs on altered aortic valve closing behavior, without compromising the overall pump support level.

Improving arterial pulsatility by feedback control of a continuous flow left ventricular assist device via in silico modeling.

Continuous flow left ventricular assist devices (CF-LVADs) generally operate at a constant speed, which causes a decrease in pulse pressure and pulsatility in the arteries and allegedly may lead to late complications such as aortic insufficiency and gastrointestinal bleeding. The purpose of this study is to increase the arterial pulse pressure and pulsatility while obtaining more physiological hemodynamic signals, by controlling the CF-LVAD flow rate. A lumped parameter model was used to simulate the cardiovascular system including the heart chambers, heart valves, systemic and pulmonary arteries and veins. A baroreflex model was used to regulate the heart rate and a model of the Micromed DeBakey CF-LVAD (Micromed Technology, Houston, TX, USA) to simulate the pump dynamics at different operating speeds. A model simulating the flow rate through the aortic valve served as reference model. CF-LVAD operating speed was regulated by applying proportional-integral (PI) control to the pump flow rate. For comparison, the CF-LVAD was also operated at a constant speed, equaling the mean CF-LVAD speed as applied in pulsatile mode. In different operating modes, at the same mean operating speeds, mean pump output, mean arterial pressure, end-systolic and end-diastolic volume and heart rate were the same over the cardiac cycle. However, the arterial pulse pressure and index of pulsatility increased by 50% in the pulsatile CF-LVAD support mode with respect to constant speed pump support. This study shows the possibility of obtaining more physiological pulsatile hemodynamics in the arteries by applying output-driven varying speed control to a CF-LVAD.

Thromboresistance Comparison of the HeartMate II Ventricular Assist Device With the Device Thrombogenicity Emulation-Optimized HeartAssist 5 VAD

Approximately 7.5 × 106 patients in the US currently suffer from end-stage heart failure. The FDA has recently approved the designations of the Thoratec HeartMate II ventricular assist device (VAD) for both bridge-to-transplant and destination therapy (DT) due to its mechanical durability and improved hemodynamics. However, incidence of pump thrombosis and thromboembolic events remains high, and the life-long complex pharmacological regimens are mandatory in its VAD recipients. We have previously successfully applied our device thrombogenicity emulation (DTE) methodology for optimizing device thromboresistance to the Micromed Debakey VAD, and demonstrated that optimizing device features implicated in exposing blood to elevated shear stresses and exposure times significantly reduces shear-induced platelet activation and significantly improves the device thromboresistance. In the present study, we compared the thrombogenicity of the FDA-approved HeartMate II VAD with the DTE-optimized Debakey VAD (now labeled HeartAssist 5). With quantitative probability density functions of the stress accumulation along large number of platelet trajectories within each device which were extracted from numerical flow simulations in each device, and through measurements of platelet activation rates in recirculation flow loops, we specifically show that: (a) Platelets flowing through the HeartAssist 5 are exposed to significantly lower stress accumulation that lead to platelet activation than the HeartMate II, especially at the impeller-shroud gap regions (b) Thrombus formation patterns observed in the HeartMate II are absent in the HeartAssist 5 (c) Platelet activation rates (PAR) measured in vitro with the VADs mounted in recirculation flow-loops show a 2.5-fold significantly higher PAR value for the HeartMate II. This head to head thrombogenic performance comparative study of the two VADs, one optimized with the DTE methodology and one FDA-approved, demonstrates the efficacy of the DTE methodology for drastically reducing the device thrombogenic potential, validating the need for a robust in silico/in vitro optimization methodology for improving cardiovascular devices thromboresistance.

Optimization of axial-pump pressure sensitivity for a continuous-flow total artificial heart

In this study, we describe the potential advantages of a continuous-flow total artificial heart (CFTAH) comprising two small, non-pulsatile pumps with optimized responsiveness to the pressure gradient. We modified a MicroMed DeBakey axial-flow pump by increasing its inducer-impeller inlet angle, thereby increasing its pressure responsivity. We obtained the in vitro pressure gradient response and compared it with those of the clinically used, unmodified MicroMed DeBakey pump, Jarvik 2000 FlowMaker and HeartMate II. The modified pump showed an increased response to changes in the pressure gradient at pump flow rates of between 2 and 4 liters/min. The maximum pressure responsivity of the modified pump was 2.5 liters/min/mm Hg; the corresponding maximum responsivities of the Jarvik 2000, HeartMate II and MicroMed DeBakey ventricular assist devices (VADs) were 0.12, 0.09 and 0.38 liters/min/mm Hg, respectively. Because of the inherent properties of non-pulsatile pumps, the CFTAH may potentially respond to changes in inflow and outflow pressures while maintaining physiologic flow rates sufficient for normal daily activity. In addition, the hemodynamic interplay between the two optimized pumps should allow a physiologic response to normal flow imbalances between the pulmonary and systemic circulations. Improved responsiveness to inflow pressure may further simplify and improve the CFTAH and affect its potential clinical use as a meaningful therapy for terminal heart failure.

Use of CoSeal in a Patient With a Left Ventricular Assist Device

A 45-year-old man with end-stage idiopathic dilatated cardiomyopathy had previously undergone two left anterolateral thoracotomies for implantation and explantation of a left ventricular epicardial lead for biventricular pacing. Because of worsening heart failure and a predicted long delay to heart transplantation, a left-ventricular assist device was implanted, with application of CoSeal surgical sealant (Baxter Healthcare Corp, Fremont, CA) on the cardiac surface. At re-sternotomy for heart transplantation, surgical dissection of the left-ventricular assist device was greatly facilitated by the presence of avascular, very loose adhesions. CoSeal (Baxter Healthcare Corp) seems to be useful for the inhibition of adhesion formation after left-ventricular assist device implantation, although further clinical experience with this approach is required.

Interactive Blood Damage Analysis for Ventricular Assist Devices

Ventricular Assist Devices (VADs) support the heart in its vital task of maintaining circulation in the human body when the heart alone is not able to maintain a sufficient flow rate due to illness or degenerative diseases. However, the engineering of these devices is a highly demanding task. Advanced modeling methods and computer simulations allow the investigation of the fluid flow inside such a device and in particular of potential blood damage. In this paper we present a set of visualization methods which have been designed to specifically support the analysis of a tensor-based blood damage prediction model. This model is based on the tracing of particles through the VAD, for each of which the cumulative blood damage can be computed. The model's tensor output approximates a single blood cell's deformation in the flow field. The tensor and derived scalar data are subsequently visualized using techniques based on icons, particle visualization, and function plotting. All these techniques are accessible through a Virtual Reality-based user interface, which features not only stereoscopic rendering but also natural interaction with the complex three-dimensional data. To illustrate the effectiveness of these visualization methods, we present the results of an analysis session that was performed by domain experts for a specific data set for the MicroMed DeBakey VAD.

Off-pump Exchange of Short-term Percutaneous Ventricular Assist Device (VAD) to Long-term Implantable VAD in Severe Coagulopathy and Multi-organ Failure

Ventricular support in patients with end-stage heart failure can be achieved using intracorporeal left ventricular assist device (LVAD) or percutaneous ventricular assist device (pVAD) systems. Multiple efforts have been made to minimize procedure-associated complications. We present a case report of an off-pump insertion of a MicroMed DeBakey VAD after Tandem Heart support using a previous sternotomy incision. A 47-year-old woman with end-stage heart failure after coronary artery bypass graft revascularization was admitted for pharmacologic treatment. She developed multi-organ failure and a severe coagulopathy with thromboembolic complications. Heparin-induced thrombocytopenia (HIT) was suspected. A percutaneous Tandem Heart was placed, the patient's condition stabilized, and finally a MicroMed DeBakey Child VAD was implanted off-pump, re-opening a previous sternotomy incision. To avoid the need for heparinization in the light of HIT and severe coagulopathy, the LVAD implantation was performed under Tandem Heart support without cardiopulmonary bypass. The patient has been anti-coagulated with angiomax ever since. Critically ill patients with end-stage heart disease, multi-organ failure, severe coagulopathy and a previous median sternotomy can be bridged from a Tandem Heart to MicroMed DeBakey VAD without cardiopulmonary bypass using the previous incision, provided there are few adhesions and stable hemodynamic conditions.

Choroidal Microcirculation in Patients With Rotary Cardiac Assist Device

In recent years, fully implanted rotary blood pumps have been used for long-term cardiac assist in patients with end-stage heart failure. With these pumps, the pulsatility of arterial blood flow and arterial pressure pulse is considerably reduced. Effects on end-organ perfusion, particularly microcirculation, have been assessed. The ocular choroid offers a unique opportunity to study the pulsatile component of blood flow by measurement of fundus pulsation amplitude (FPA) as well as the microcirculation by laser Doppler flowmetry. Both techniques were applied in three male patients with rotary pumps (MicroMed DeBakey VAD), in whom pump velocity was adjusted to four levels of flow between individual minimal need and maximal support. In addition, blood flow velocities in the ophthalmic artery (peak, end-diastolic and mean flow velocity--PSV, EDV and MFV, respectively) were measured using color Doppler imaging. Systolic blood pressure increased by 6 to 22 mm Hg with increasing support. At maximal support FPA was reduced by -60% to -52% as compared with minimal pump support. Blood flow in the choroidal microvasculature, however, did not show relevant changes. A reduction in PSV (-31%, range -47% to -21%) and a pronounced rise in EDV (+93%, range +28% to +147%) was observed, whereas MFV was independent of pump flow. Our data indicate that mean choroidal blood flow is maintained when pump support is varied within therapeutic values, whereas the ratio of pulsatile to non-pulsatile choroidal flow changes. This study shows that, in patients with ventricular assist devices, a normal perfusion rate in the ocular microcirculation is maintained over a wide range of support conditions.

Left ventricular assist devices decrease fixed pulmonary hypertension in cardiac transplant candidates

Fixed pulmonary hypertension is a contraindication for cardiac transplantation because of the increased risk of donor heart failure. We sought to determine whether left ventricular assist devices improve fixed pulmonary hypertension in cardiac transplant candidates to enable safe cardiac transplantation. Thirty-five consecutive cardiac transplant candidates (age 56 +/- 6 years, 88.5% were men) with fixed pulmonary hypertension (5.1 +/- 2.6 Wood units) resistant to medical treatment received a left ventricular assist device as a bridge to transplantation. Three left ventricular assist device systems were used (pulsatile blood flow: Novacor [World Heart Inc, Oakland, Calif] n = 8; continuous blood flow: MicroMed DeBakey [MicroMed Technology Inc, Houston, Tex] n = 24, DuraHeart [Terumo Heart Inc, Ann Arbor, Mich] n = 3). Right-sided heart catheter data were obtained before left ventricular assist device implantation at 3-day and 6-week follow-ups. Clinical data and complications were recorded. Before left ventricular assist device implantation, the pulmonary vascular resistance was 5.1 +/- 2.8 Wood units. Values were comparable in patients receiving pulsatile (5.1 +/- 3.4 Wood units) or continuous blood flow left ventricular assist devices (5.1 +/- 2.7 Wood units, P = .976). Left ventricular assist device implantation decreased pulmonary vascular resistance at 3-day (2.9 +/- 1.3 Wood units, P < .0001) and 6-week (2.0 +/- 0.8 Wood units, P < .0001) follow-ups compared with before implantation. This effect was independent of the type of left ventricular assist device system used (3-day follow-up: pulsatile flow: 3.2 +/- 1.3 Wood units vs continuous flow: 2.7 +/- 1.2 Wood units; P = .310 and 6-week follow-up: pulsatile flow: 1.9 +/- 0.9 Wood units vs continuous flow: 2.1 +/- 0.8 Wood units; P = .905). Twenty-four patients had successful bridges to transplantation (69%, mean time on left ventricular assist device 210 +/- 83 days), and 11 patients died before transplantation (31%, mean time on left ventricular assist device 67 +/- 30 days). The 1-year survival after transplantation was 95%. Left ventricular assist devices decrease fixed pulmonary hypertension in cardiac transplant candidates and allow patients to overcome a contraindication for cardiac transplantation. Therefore, left ventricular assist devices should be considered in all cardiac transplant candidates with fixed pulmonary hypertension.

126: Left ventricular assist device exchange – indications and outcomes

Purpose: In patients with end-stage heart failure the survival benefit of mechanical circulatory support with LVAD exceeds outcomes of any known medical therapy. With improved outcomes of LVAD implantation, increasing number of patients outlive the life-span of the LVAD, rendering the need for repeated surgeries which is challenging both for the LVAD team as well as the patient. Methods and Materials: We retrospectively reviewed indications and outcomes of device exchange among 188 pts with end-stage heart failure who received LVADs as a bridge-to-transplant (BTT, n 167) or destination therapy (DT, n 21) at the University of Minnesota between 1995 and 2006. One-way repeated measures ANOVA and Kaplan Meier estimates were employed for statistical analysis. Results: 17 pts (9.6%) required device replacement after a median device support time of 19 months. A total number of 44 permanent LVADs were placed in these patients; 7 patients received 3 devices. Indication for device exchange included pump failure (Heartmate, n 22), infected LVAD (Heartmate, n 2), refractory pump thrombosis (MicroMed DeBakey, n 3). Recipients of DT were most likely to undergo VAD exchange; 90% of them required at least one VAD replacement within 2 years (RR 3.5, p 0.01). There was no difference seen between the type of the first device inserted and the likelihood of VAD exchange: HM-IP (0/20 replacements), HM-VE (7/44 replacements), HM-XVE (7/82 replacements), HMII (0/25), and Micromed (3/8). Actuarial survival by Kaplan Meier analysis from the time of 1 implantation was 85.1% and 70.1% at 1 and 2 years respectively. Conclusions: With increasing reliability and durability of newer LVADs the need for LVAD pump exchanges may reduce in frequency. However, there will always be a select group of patients that will present with indications for and may benefit from LVAD pump exchange. Our study shows that with careful patient selection, peri-operative optimization and excellent surgical techniques, LVAD pump exchange is not only feasible, but also associated with good mid-term survival.

104: CCR4, CCR5, CCR6 and CCR7 expression on BAL lymphocytes and macrophages of patients with bronchiolitis obliterans syndrome (BOS)

of the most recent changes to the MicroMed DeBakey VAD design. Methods and Materials: The design-changes to the MicroMed DeBakey VAD included 1) increased distance between the impeller and diffuser along with a change to the diffuser blade inlet angle and 2) improved pump bearings through a modification of the manufacturing process. Patient management remained unchanged compared to previous pump design. Results: Modified DeBakey VADs were implanted in 21 patients as bridge to transplant. Duration of support was close to 6 patient years with a mean of 102 days and 9 patients still ongoing. The mean BSA of the patients was 1.94 (1.48 – 2.20), their mean age was 49 years (20 – 66). The observed adverse event rates per 100 days are: systemic infection: 0.09 per 100 days; suspected pump thrombus: 0.09; neurologic events: 0.0; peripheral thromboembolic events: 0.0 Conclusions: These changes in device design show promising early clinical results. A significant reduction in adverse event rates compared with the initial pump design was found. Furthermore, no thrombembolic or neurologic events were observed. Improved pump design substantially adds to the safety and reliability of second generation blood pumps. Consultant MicroMed Inc; MicroMed Inc.

103: Improved clinical results with the redesigned MicroMed DeBakey VAD

103: Improved clinical results with the redesigned MicroMed DeBakey VAD

Recurrent Device Thrombi During Mechanical Circulatory Support With an Axial-flow Pump Is a Treatable Condition and Does Not Preclude Successful Long-term Support

The formation of pump thrombus after implantation of axial-flow ventricular assist devices has been described previously. We report a case of recurrent pump thrombus formation in a 63-year-old man who was bridged to heart transplantation with a MicroMed DeBakey ventricular assist device. He was treated with a low, dose-adjusted thrombolytic treatment protocol, and was subsequently successfully bridged to transplantation. Transient pump thrombus formation does not preclude safe long-term support with an axial-flow pump when diagnosed and treated appropriately.

Endocrine function is not impaired in patients with a continuous MicroMed–DeBakey axial flow pump

Pulsatile blood flow has been regarded to be of importance for the regulation of endocrine organs. A new generation of continuous flow mechanical blood pumps is now available for clinical application. Patients with implanted MicroMed-DeBakey axial pumps show nonphysiologic low-pulsatile blood flow profiles, and therefore it appeared to be of interest to evaluate their possible effect on the endocrine system. Eight male patients and 1 female patients (mean age, 51 +/- 10 years) with end-stage left-sided heart failure were implanted with a MicroMed-DeBakey axial pump. After a mean period of 67 +/- 19 days, basal pituitary hormone concentrations and their responses to a bolus injection of hypothalamic releasing hormones were tested. In addition, thyroid hormones, testosterone, and plasma and urinary catecholamine levels were measured at baseline. Administration of the hypothalamic releasing hormones revealed normal responses of all pituitary hormones (adrenocorticotropic hormone, thyroid-stimulating hormone, luteinizing hormone, and prolactin), except for growth hormone, the response of which was slightly impaired (10.2 +/- 6.8 vs 19.9 +/- 6.5 ng/L, P < .05). Also, the cortisol response to the corticotropin-releasing hormone-stimulated adrenocorticotropic hormone release was normal, as were basal concentrations of thyroid hormones (triiodothyronine, thyroxine, free triiodothyronine, and free thyroxine), testosterone, and urinary catecholamines. Implantation of a continuous flow axial pump with low-pulsatile blood flow profile appears to have no major effect on the hypothalamic-pituitary-endorgan system and sympathoadrenal functions. This finding is reassuring for the growing number of patients treated with this convenient new pump and could contribute considerably to their prognosis and quality of life.

PRELOAD SENSITIVITY OF CONTINUOUS FLOW VENTRICULAR ASSIST DEVICES: APPLICATION TO THE TOTAL ARTIFICIAL HEART

Purpose: Pump design can affect pump sensitivity to preload. The effect of preload on the output of 3 axial flow ventricular assist devices (VADs) was studied in vitro. We hypothesize that slight changes in the design of axial flow pumps will alter the response to preload. Methods: The VADs studied included the HeartMate II, Jarvik 2000, and MicroMed DeBakey. The pump inflow cannulas of the HeartMate II and MicroMed DeBakey were removed so the pumps had direct interface with the testing fluid. The outlet of each pump was attached via a short tubing segment to a vertical PVC pipe with negligible flow resistance. Water column height in the PVC pipe determined pump afterload. Pump inlet and outlet pressures and flow rate were measured. To vary pump preload, the fluid in the preload cylinder was gradually drained while keeping water level in the afterload piping constant at 50, 70, or 90 mm Hg. Pressure and flow data were continuously measured at different pump speeds. Results: The flow-preload curves of the HeartMate II were nearly linear at all speeds. The Jarvik 2000 demonstrated increased sensitivity to preload at 11 and 12 krpm, with a maximum sensitivity of 0.35 L/min/mm Hg. The maximum sensitivity of the modified DeBakey pump was 2 L/min/mm Hg. Conclusions: Increasing preload sensitivity enhances the Starling-type autoregulatory mechanism of continuous flow pumps. We offer additional experimental evidence concerning this mechanism by using pumps with inherently different preload sensitivities.

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.