Pulsatile Ventricular Assist Device Research Articles

Numerical Investigation of Three Patterns of Motion in an Electromagnetic Pulsatile VAD

Hemolysis and thrombus formation which are critical concerns in designing a long-term implantable ventricular assist device (VAD) have impeded the widespread use of VADs. In this study, thus, the three-dimensional fluid domain of blood flow in a small bichamber positive displacement VAD (25 ml) with a magnetically levitated moving pusher plate was simulated by the means of a finite element package called ADINA. To optimize the function of the pump for minimizing shear stress induced blood damage, three different driver patterns (linear, sinusoidal, and Guyton's pulse) were investigated. The first pattern produced a constant flow, whereas the two others created pulsatile flows. The flow pattern and the distribution of shear stress of each pattern were observed for comparison. It was revealed that the three types of motions may induce less than 0.06% red blood cell damage. Moreover, in comparison to the other patterns not only did the sinusoidal motion of the pusher plate cause less risk of hemolysis, but in comparison to the linear pattern, it produced a pulsatile flow which reduced the stagnation areas in chambers, lowering the probability of thrombosis. In addition, this motion eliminates the probability of cavitations as compared with the Guyton's pulse pattern.

The Use of Fluid Mechanics to Predict Regions of Microscopic Thrombus Formation in Pulsatile VADs

We compare the velocity and shear obtained from particle image velocimetry (PIV) and computational fluid dynamics (CFD) in a pulsatile ventricular assist device (VAD) to further test our thrombus predictive methodology using microscopy data from an explanted VAD. To mimic physiological conditions in vitro, a mock circulatory loop is used with a blood analog that matched blood's viscoelastic behavior at 40% hematocrit. Under normal physiologic pressures and for a heart rate of 75 bpm, PIV data is acquired and wall shear maps are produced. The resolution of the PIV shear rate calculations are tested using the CFD and found to be in the same range. A bovine study, using a model of the 50 cc Penn State V-2 VAD, for 30 days at a constant beat rate of 75 beats per minute (bpm) provides the microscopic data whereby after the 30 days, the device is explanted and the sac surface analyzed using scanning electron microscopy (SEM) and, after immunofluorescent labeling for platelets and fibrin, confocal microscopy. Areas are examined based on PIV measurements and CFD, with special attention to low shear regions where platelet and fibrin deposition are most likely to occur. Data collected within the outlet port in a direction normal to the front wall of the VAD shows that some regions experience wall shear rates less than 500 s-1, which increases the likelihood of platelet and fibrin deposition. Despite only one animal study, correlations between PIV, CFD, and in vivo data show promise. Deposition probability is quantified by the thrombus susceptibility potential, a calculation to correlate low shear and time of shear with deposition.

Mechanical Cardiac Support with Berlin Heart EXCOR Pulsatile Ventricular Assist Device in Infants and Children: 23-Year Single Center Experience

Object: We present outcome of infants and children undergoing mechanical cardiac support with Berlin Heart EXCOR ventricular assist device (BH-VAD) over a period of 23 years.

Computation of residence time in the simulation of pulsatile ventricular assist devices

A continuum-based model of particle residence time for moving-domain fluid mechanics and fluid---structure interaction (FSI) computations is proposed, analyzed, and applied to the simulation of an adult pulsatile ventricular assist device (PVAD). Residence time is a quantity of clinical interest for blood pumps because it correlates with thrombotic risk. The proposed technique may be easily implemented in any flow or FSI solver. In the context of PVADs the results of the model may be used to assess how efficiently the pump moves the blood through its interior. Three scalar measures of particle residence time are also proposed. These scalar quantities may be used in the PVAD design with the goal of reducing thrombotic risk.

Rotary Pumps and Diminished Pulsatility

Ventricular assist devices (VADs) have been successfully used as a bridge to heart transplant and destination therapy (DT) for congestive heart failure (HF) patients. Recently, continuous flow VAD (CVAD) has emerged as an attractive clinical option for long-term mechanical support of HF patients, with bridge-to-transplant outcomes comparable with pulsatile flow VAD (PVAD). Continuous flow VADs are smaller, more reliable, and less complex than the first-generation PVAD. Despite the widespread clinical use, CVAD support has been associated with gastrointestinal bleeding, hemorrhagic strokes, and aortic valve insufficiency. Speculation that diminished arterial pressure pulsatility associated with continuous flow devices may be contributing to these complications has sparked much debate over CVAD support. Studies comparing pulsatile flow and continuous flow (CF) support have presented conflicting findings, and the relevance to CVAD as DT is uncertain due to variations in device operation, support duration, and the criteria used to quantify pulsatility. Currently, there is interest in developing control algorithms for CVAD to increase the delivered pulsatility as a strategy to mitigate adverse event risks associated with CVAD therapy. There may also be the added benefit of specific control strategies for managing CVAD therapy, potentially improving the rate of myocardial recovery and successful weaning of mechanical circulatory support.

Improved Survival in Patients with Continuous-Flow Ventricular Assist Device for Bridge to Heart Transplantation

BackgroundContemporary continuous-flow ventricular assist devices (CFVADs) have greatly improved patient survival for indications of bridge to transplantation (BTT) and destination therapy. In Japan, CFVAD is limited for BTT use. The waiting period for heart transplantation (HT) is long owing to donor shortage. We examined the results of CFVAD for BTT indication. MethodsEighty-nine VAD treatments were performed among subjects whose preimplantation condition was profile 1 (n = 49) or profile 2 or 3 (n = 40). The device was the paracorporeal pulsatile Nipro VAD (n = 67) or CFVAD (n = 22). All CFVAD patients were profile 2 or 3. ResultsThe median assist period was 529 days (Nipro VAD, 530; CFVAD, 528). Twenty-six patients were on the device for >2 years. Actuarial survival was 81.6%, 69.5%, and 61.1% at 1, 3, and 5 years. Survival in profile 1 was significantly worse than in profile 2 or 3. Survival of CFVAD patients was superior to that of paracorporeal VAD. Six-month mortality rate of 20% in cases before 2009 (n = 60) was dramatically improved to 3% among those after 2010 (n = 29). All patients with CFVAD were alive and discharged home. 26 patients were transplanted, 7 had been weaned from VAD and 27 were on a device. The rate of events requiring hospital admission was 0.98 per patient-year in CFVAD patients. ConclusionsContemporary CFVADs have enabled advanced heart failure patients to await HT safely with an improved quality of life. The advent of CFVAD has also shifted their preimplantation condition to a less sick status. CFVADs were the safest, most reliable circulatory support devices for long-term waiting periods for the BTT indications.

Fluid–structure interaction simulation of pulsatile ventricular assist devices

In this paper we present a collection of fluid---structure interaction (FSI) computational techniques that enable realistic simulation of pulsatile Ventricular Assist Devices (VADs). The simulations involve dynamic interaction of air, blood, and a thin membrane separating the two fluids. The computational challenges addressed in this work include large, buckling motions of the membrane, the need for periodic remeshing of the fluid mechanics domain, and the necessity to employ tightly coupled FSI solution strategies due to the very strong added mass effect present in the problem. FSI simulation of a pulsatile VAD at realistic operating conditions is presented for the first time. The FSI methods prove to be robust, and may be employed in the assessment of current, and the development of future, pulsatile VAD designs.

Abstract No. 252 - Single center interventional radiology experience in the management of gastrointestinal bleeding in patients with ventricular assist devices

Purpose Gastrointestinal (GI) bleeding is a well-recognized complication in patients with ventricular assist devices (VADs). Possible mechanisms include use of anticoagulation and development of GI angiodysplasia. Treatment of GI bleeding in this patient population is not well-defined. We aim to study VAD patients with GI bleeding, including an in depth analysis of those patients referred to interventional radiology (IR) for further management. Materials and Methods A single center retrospective review of VAD patients between 2005 and 2011 was conducted. Patients who subsequently developed GI bleeding were identified. Covariates such as gender, age, days on support prior to first episode of bleed, and management of GI bleeding was analyzed. Patients referred to IR were analyzed in detail and the outcomes associated with intervention recorded. Results GI bleeding was common, seen in 23/154 (15%) of VAD patients. Of these, none required surgery for the treatment of recurrent bleeding, and all episodes were managed with supportive, endoscopic or endovascular management. Bleeding was more common with continuous versus pulsatile VADs (21% vs. 4%, p Conclusion GI bleeding is common in VAD patients. When the bleed is localized to the duodenum or stomach, empiric embolization of the GDA or left gastric artery may be of benefit in obtaining hemostasis. If the bleed is localized with angiography, targeted embolization can be performed. In this fragile population, appropriate management is critical to minimize interventions and prevent further recurrence. A management algorithm involving IR could be of great benefit to these patients.

Thrombosis and Bleeding Complications in Pediatric Patients with Ventricular Assist Devices

Purpose Bleeding and embolic complications are common after pediatric ventricular assist device (VAD) implantation. Little is known about associated non-VAD thrombosis and risk factors for the development of thrombosis or bleeding. Methods and Materials All pediatric patients on a pulsatile VAD as a bridge to heart transplantation (HTx) from 2004–2012 at our institution were reviewed. Anticoagulation on the VAD consisted of heparin, transitioned to enoxaparin or warfarin and 2 anti-platelet agents. Thrombotic, embolic and bleeding events were determined from the time of VAD implantation to discharge from hospital after HTx or death (whichever was 1st). Factors associated with thrombotic or bleeding complications were assessed by univariable logistic regression. Results A total of 26 patients (46% males, 96% cardiomyopathy) were reviewed. Median age at VAD implant was 11 yrs (IQR:2.5-13.8 yrs) with 6 (25%) 10 yrs old. Median time on VAD was 21d (IQR: 8-34, max 109d). Biventricular VAD was used in 16/25 (64%); remaining patients had LVAD support. Five patients (19%) were on ECMO prior to VAD and 3 (12%) patients required ECMO after HTx. Thrombosis and bleeding were frequent: 12 patients (46%) were diagnosed with thrombosis, only 4 of these due to clot in the VAD; 7 (27%) patients had major bleeding; 4 (15%) had stroke/pulmonary embolism. Four patients (3 before, 1 after HTx) died. VAD insertion later in this series (OR:1.95,95% CI:1.08-3.52, p=0.02) and use of LVAD support only (OR:5.13,95% CI:0.92-28.57, p=0.06) were associated with increased risk of thrombosis. No factors associated with increased bleeding risk could be identified. Conclusions Non-VAD related thromboses are frequent in patients bridged with a VAD to HTx; bleeding and embolic issues are less common. No risk factors for bleeding could be identified from this study but both implantation later in the series and the use of LVAD alone increased the risk of thrombosis. These may reflect our low threshold for investigating patients with suspected thrombosis in recent years.

Impact of Different Indications for HU Listing of VAD Patients on Survival after Heart Transplantation

Purpose German allocation system prioritizes (“HU”) patients with complications (compl.) during VAD-support. The impact of “HU” indications on survival was evaluated. Methods and Materials We performed a retrospective chart analysis of all pts. Transplanted in “HU”-status. Results 01/2000-10/2012 932 HU-pts. (305 VAD/627 no VAD) received a HTx. Used were Syncardia TAH (60/19,7%), Thoratec BVAD (36/11,8%), DuraHeart LVAD (34/11,1%), Thoratec LVAD (28/9,2%), Novacor LVAD (26/8,5%), HeartMate II LVAD (25/8,2%), HeartWare LVAD (21/6,9%), Ventrassist (15/4,9%), TCI LVAD (14/4,6%) and others (46/15,1%). In the VAD infection group, reasons for death were rejection (7/10.8%), abdominal compl. (4/6.25), sepsis (4/6.2%) and MOF (2/3.1%), in the neurological compl. group rejection (3/8.3%), abdominal compl. (2/5,6%) and technical compl. (2/5,6%). In the technical failure group MOF (5/9.1%), neurological compl. (3/5.5%) and rejection (3/5.5%) occurred. Within the VAD-related compl.group MOF (5/13.5%) was predominant. In the right heart failure group reasons for death included MOF, tumor, sepsis and abdominal compl. (all 1/6.3%). The main causes of death for HU patients without MCS were sepsis (24/6.2%), graft rejection (16/4.1%), malignant tumors (10/2.6%), neurological compl. and MOF (both 8/2.1%). Worst outcomes occurred in the infection and neurological compl.group (p=0,026), especially in 2000-2006 with more frequent use of pulsatile VAD (p Conclusions VAD-infection and neurological compl.group had significantly higher mortality. In infection, neurological and technical compl.group mortality steadily increased until 5 years. Results improved with a lower rate of pulsatile VAD use. Mortality stratified for HU reason HU group 3 months (%) 1 year (%) 5 years (%) VAD infection (n=65) 6,2 14,3 38,8 VAD neurological compl. (n=36) 8,3 33,3 43,9 VAD technical problem (n=56) 17,9 19,6 30,2 VAD-related compl. (n=37) 13,5 27,7 27,7 VAD right heart failure (n=17) 12,5 27,3 27,3 VAD various indications (n=25) 8,3 27,8 27,8 no VAD (n=697) 1,6 18,8 27,0

Superior Survival in Patients with Continuous Flow Ventricular Assist Device for Bridge to Transplantation

Background: Contemporary continuous flow ventricular assist devices (CFVAD) have greatly improved patient survival for indications of bridge to transplantation (BTT) and destination therapy. In Japan, CFVAD is limited for BTT use, and waiting period of heart transplantation (HTx) is very long due to severe donor shortage (about 880 days as of December 2011). We examined the results of CFVAD for BTT indication in this particular situation. Patients: Eighty-nine VAD treatments were performed in our Hospital since October 2002. Pre-implant patient condition was profile-1 in 49 and profile-2 or 3 in 40. The device used was paracorporeal pulsatile Nipro VAD in 67 and CFVADs (DuraHeart, EVAHEART, Jarvik 2000 and HeartMate II) in 22. All CFVAD patients were in profile 2 or 3. Recent two patients, who were in profile 1 in the first admission to our hospital, underwent conversion to DuraHeart from Nipro VAD. This clinical study was carried out in accordance with the principles of the Declaration of Istanbul and executed prisoners were not the source of organs in HTx. Results: Assist periods were 529 days in average (Nipro VAD: 530 ± 439, CFVADs: 528 ± 518). Twenty-six patients (29%) were on device more than 2 years. Actuarial survival was 81.6%, 69.5% and 61.1% at 1, 3 and 5 years in whole cases. Survival in profile-1 was significantly worse than in profile-2 or 3 (73.3%, 61.6% and 48.2% v.s. 91.9%, 79.4% and 79.4%). Survival of CFVAD patients was superior to that of paracorporeal VAD (95.0%, 95.0% and 95.0% v.s. 77.6%, 63.8% and 54.2%). Six-month mortality rate of 20% in cases before 2009 (n = 60) was dramatically improved to 3% in those after 2010 (n = 29). There was no in-hospital death in CFVAD patients. And all patients with CFVAD were discharged home. In general 26 patients were transplanted, seven weaned from VAD, and 27 on device. Event-rate requiring hospital admission was 0.98 per patient-year in CFVAD patients. Conclusion: Contemporary CFVADs enabled advanced heart failure patients to wait HTx safely and with improved quality of life. An advent of CFVAD has also urged a shift of pre-implant condition to less sick. CFVADs are the safest and most reliable circulatory support devices for long-term waiting period (more than 2 years in Japan) as BTT indication.

Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS)

The Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) is a North American national registry for mechanical circulatory support devices (MCSDs) that are used to treat advanced heart failure. Durable MCSDs that have been approved by the US Food and Drug Administration (FDA) are included in this registry; however, MCSDs that remain in FDA trials pending initial approval (ie, investigational device exemption [IDE] trials) and devices intended for short-term use (eg, Abiomed BVS 5000 ventricular assist device [Abiomed, Danvers, MA]) are not included. The purposes of this article are to present a developmental history of INTERMACS, to outline the collaboration of INTERMACS with various constituencies (eg, FDA, National Institutes of Health, Center for Medicare & Medicaid Services, industry, and physicians), to present a summary of information generated to date by INTERMACS, and to describe the future directions of INTERMACS. The concept of using mechanical circulatory assistance for more than a brief time after a cardiac operation dates to the early 1960s with the development of MCSDs that fit the definitions of counterpulsation devices (eg, the intra-aortic balloon pump), ventricular assist devices (VADs), and total artificial hearts.1–5 The development and initial clinical evaluation of these devices were regulated by individual academic medical center review groups that evolved into institutional review boards. The FDA entered this arena in 1976 with the advent of the FDA section for device regulation based on passage of the 1976 Medical Device Amendments.6 By 1991, groups including the Institute of Medicine foresaw the need for a detailed longitudinal database for patients receiving MCSDs, stating in an Institute of Medicine report that “patients should be followed through a registry for the remainder of their lives….”7 The committee further recommended that the National Heart, Lung, and Blood Institute support long-term follow-up studies. Eventually, a …

539 Higher Incidence of Class II Human Leukocyte Antigen (HLA)-Allosensitization in Patients Supported with Pulsatile Ventricular Assist Devices (VAD)

Higher Incidence of Class II Human Leukocyte Antigen (HLA)Allosensitization in Patients Supported with Pulsatile Ventricular Assist Devices (VAD) M. Askar, A. Zhang, L. Klingman, M. Mastroianni, A. Nowacki, P. Reville, J. Gatto, S. Bakdash, N. Smedira, R. Starling, G. Gonzalez-Stawinski. Allogen Laboratoires, Cleveland Clinic; Doisey College of Health Sciences, St. Louis University; Department of Quantitative Health Sciences, Cleveland Clinic; College of Arts and Sciences, The Ohio State University; Clinical Pathology, Cleveland Clinic; Cardiothoracic Surgery, Cleveland Clinic; Cardiovascular Medicine, Cleveland Clinic.

관형의 구조적 특징을 갖춘 박동형 관형 심실보조장치의 혈류, 혈압 평가

심실보조장치는 말기 심부전환자에게 심장이식수술 없이 1 년 생존율을 25%에서 52%까지 증가시킬 수 있는 유일한 장치이다. 하지만 심실보조장치 이식 후 1 년이 이내에 사망하는 원인 중 기기의 고장으로 인한 사망률이 6%를 차지하기 때문에 심실보조장치의 고장이 환자의 심장 움직임과 혈류 역학적인 상태에 영향을 주지 않는 새로운 방법이 필요하다. 기존의 심실보조장치는 원심형, 축심형으로 혈액을 박출해 주는 방식이어서 동맥압 보다 박출하는 압력이 낮을 때 혈액의 역류가 일어나는 문제점이 있다. 본 논문에서는 박출 압력이 약할 때, 2 개의 밸브에 의하여 혈액의 역류를 방지하고 관 형태의 구조에 의해 혈액의 정체량을 줄일 수 있는 새로운 박동형 관형 심실보조장치를 개발하였으며, 체외실험과 동물실험으로 박출량과 펌프의 압력을 측정하여 그 특성을 평가하였다.

Mechanisms of Bleeding and Approach to Patients With Axial-Flow Left Ventricular Assist Devices

Axial-flow LVADs have become an integral tool in the management of end-stage heart failure. Consequently, nonsurgical bleeding has emerged as a major source of morbidity and mortality in this fragile population. The mechanisms responsible for these adverse events include acquired von Willebrand disease, GI tract angiodysplasia formation, impaired platelet aggregation, and overuse of anticoagulation therapy. Because of ongoing concerns for pump thrombosis and thromboembolic events, the thrombotic/bleeding paradigm has led to a difficult clinical dilemma for those managing patients treated with axial flow LVADs. As the field progresses, advances in the understanding of the pathological mechanisms underlying bleeding/thrombosis risk, careful risk stratification, and potential use of novel anticoagulants will all play a role in the management of the LVAD patient.

The Effect of Fluid Viscosity on the Hemodynamic Energy Changes During Operation of the Pulsatile Ventricular Assist Device

Blood viscosity during operation of ventricular assist device (VAD) can be changed by various conditions such as anemia. It is known generally that the blood viscosity can affect vascular resistance and lead to change of blood flow. In this study, the effect of fluid viscosity variation on hemodynamic energy was evaluated with a pulsatile blood pump in a mock system. Six solutions were used for experiments, which were composed of water and glycerin and had different viscosities of 2, 2.5, 3, 3.5, 4, and 4.5 cP. The hemodynamic energy at the outlet cannula was measured. Experimental results showed that mean pressure was increased in accordance with the viscosity increase. When the viscosity increased, the mean pressure was also increased. However, the flow was decreased according to the viscosity increase. Energy equivalent pressure value was increased according to the viscosity-induced pressure rise; however, surplus hemodynamic energy value did not show any apparent changing trend. The hemodynamic energy made by the pulsatile VAD was affected by the viscosity of the circulating fluid.

Powering a Ventricular Assist Device over Meter Distances Wirelessly: The Free-Range Resonant Electrical Energy Delivery (FREE-D) System

Technological innovation of smaller, frictionless, single moving part has an advantage over earlier large pulsatile Ventricular Assist Devices (VAD) prone to mechanical failure. Drivelines limits the potential of newer pumps and act as source for infection, increased morbidity, and re-hospitalizations. Older TETS based technologies are hampered by power delivery over few millimeters, mis-alignment and poor efficiency. The Free-range Resonant Electrical Energy Delivery (FREE-D) wireless power system uses magnetically coupled resonators to efficiently transfer power.

Physiological control of an in-series connected pulsatile VAD: numerical simulation study

This paper investigates ventricular assist device (VAD)-assisted cardiovascular dynamics under proportion–integration–differentiation (PID) feedback control. Previously, we have studied the cardiovascular responses under the support of an in-series connected reciprocating-valve VAD through numerical simulation, and no feedback control was applied in the VAD. In this research, we explore the contribution of the VAD control on the circulatory dynamics assisted by the reciprocating-valve VAD, in response to the changing physiological conditions. The classical PID control algorithm is implemented to regulate the VAD stroke beat-to-beat, based on the error signal between the expected and the realistic mean aortic pressures. Simulation results show that under the PID VAD control, physiological variables such as left atrial, ventricular and systemic arterial pressures, cardiac output and ventricular volumes are satisfactorily maintained in the physiological ranges. With the online PID feedback control, operation of the reciprocating-valve VAD can be satisfactorily regulated to accommodate metabolic requirements under various physiological conditions including normal resting and exercise situations.

A Durability Study of a Paracorporeal Pulsatile Electro‐Mechanical Pneumatic Biventricular Assist Device

In 2002, the paracorporeal pulsatile electro-mechanical pneumatic ventricular assist device (VAD) began to be developed by the Korea Artificial Organ Center at Korea University under a Health & Medical Technology Research and Development program which finished in 2008. In vitro durability testing was conducted on the paracorporeal pulsatile pneumatic VAD to determine device durability and to evaluate device failures. The 1- and 2-year reliability of the paracorporeal pulsatile pneumatic VAD was shown to be 91.2% and 54.9%, respectively, with an 80% confidence level. Failure modes were analyzed using fault tree analysis, with customized software continuously acquiring data during the test period. After this period, 21 in vivo animal tests were done, with 14 cases of left atrium to left ventricle (LV) inflow cannulation (36Fr)/outflow grafting to descending aorta, and seven cases of apex cannulation of LV to descending aorta (12 mm). The longest postoperative day (182 days) in Korea was recently recorded in in vivo animal testing (bovine, 90 kg, male, 3.5-4.0 L/min flow rate, and 55 bpm).

Cardiovascular Simulator Improvement: Pressure Versus Volume Loop Assessment

This article presents improvement on a physical cardiovascular simulator (PCS) system. Intraventricular pressure versus intraventricular volume (PxV) loop was obtained to evaluate performance of a pulsatile chamber mimicking the human left ventricle. PxV loop shows heart contractility and is normally used to evaluate heart performance. In many heart diseases, the stroke volume decreases because of low heart contractility. This pathological situation must be simulated by the PCS in order to evaluate the assistance provided by a ventricular assist device (VAD). The PCS system is automatically controlled by a computer and is an auxiliary tool for VAD control strategies development. This PCS system is according to a Windkessel model where lumped parameters are used for cardiovascular system analysis. Peripheral resistance, arteries compliance, and fluid inertance are simulated. The simulator has an actuator with a roller screw and brushless direct current motor, and the stroke volume is regulated by the actuator displacement. Internal pressure and volume measurements are monitored to obtain the PxV loop. Left chamber internal pressure is directly obtained by pressure transducer; however, internal volume has been obtained indirectly by using a linear variable differential transformer, which senses the diaphragm displacement. Correlations between the internal volume and diaphragm position are made. LabVIEW integrates these signals and shows the pressure versus internal volume loop. The results that have been obtained from the PCS system show PxV loops at different ventricle elastances, making possible the simulation of pathological situations. A preliminary test with a pulsatile VAD attached to PCS system was made.