Resilience-Oriented Approach to the Control of Ventricular Assist Devices

Context: Advanced heart failure (AHF) poses a global challenge, where heart transplantation is a treatment option but limited by donor scarcity. Proposal: This study aims to enhance the performance of ventricular assist devices (VADs) in the face of adverse events (AEs) using a resilience-based approach. The objective is to develop a method for integrating resilience attributes into VAD control systems, employing dynamic risk analysis and control strategies. Results: The outcomes include a resilient control architecture enabling anticipatory, regenerative, and degenerative actions in response to AEs. A method of applied resilience (MAR) based on dynamic risk management and resilience attribute analysis was proposed. Conclusion: Dynamic integration between medical and technical teams allows continuous adaptation of control systems to meet patient needs over time, improving reliability, safety, and effectiveness of VADs, with potential positive impact on the health of heart failure patients.

Short and long term outcomes of 200 patients supported by continuous-flow left ventricular assist devices

AIM: To study the institutional experience over 8 years with 200 continuous-flow(CF)- left ventricular assist devices(LVAD).METHODS: We evaluated our institution's LVAD database and analyzed all patients who received a CF LVAD as a bridge to transplant(BTT) or destination therapy from March 2006 until June 2014. We identified 200 patients, of which 179 were implanted with a Heart Mate II device(Thoratec Corp., Pleasanton, CA) and 21 received a Heartware HVAD(Heart Ware Inc., Framingham, MA).RESULTS: The mean age of our LVAD recipients was 59.3 years(range 17-81), 76%(152/200) were males, and 49% were implanted for the indication of BTT. The survival rate for our LVAD patients at 30 d, 6 mo, 12 mo, 2 years, 3 years, and 4 years was 94%, 86%, 78%, 71%, 62% and 45% respectively. The mean duration of LVAD support was 581 d(range 2-2595 d). Gastrointestinal bleeding(was the most common adverse event(43/200, 21%), followed by right ventricular failure(38/200, 19%), stroke(31/200, 15%), re exploration for bleeding(31/200, 15%),ventilator dependent respiratory failure(19/200, 9%) and pneumonia(15/200, 7%). Our driveline infection rate was 7%. Pump thrombosis occurred in 6% of patients. Device exchanged was needed in 6% of patients. On multivariate analysis, preoperative liver dysfunction, ventilator dependent respiratory failure, tracheostomy and right ventricular failure requiring right ventricular assist device support were significant predictors of post LVAD survival.CONCLUSION: Short and long term survival for patients on LVAD support are excellent, although outcomes still remain inferior compared to heart transplantation. The incidence of driveline infections, pump thrombosis and pump exchange have declined significantly in recent years.

Left ventricular assist devices as destination therapy in stage D heart failure

1 Introduction? Mechanical circulatory support (MCS) has increasingly become an important management opportunity for patients with stage D heart failure (HF) with remarkable impact on patient survival and quality of life. Early clinical trials have demonstrated improved outcomes of durable left ventricular assist device (LVAD) support compared with optimal medical management.[1] As technology advanced, continuous flow LVADs outperformed pulsatile flow devices in clinical trials and the field migrated to HeartMate (Abbott Laboratories, Abbott Park, IL) and HeartWare (Medtronic, Minneapolis, MN) devices due to their clinical superiority. Among the continuous flow devices.

Treatment of gastrointestinal bleeding in left ventricular assist devices:A comprehensive review

Left ventricular assist devices(LVAD)are increasingly become common as life prolonging therapy in patients with advanced heart failure.Current devices are now used as definitive treatment in some patients given the improved durability of continuous flow pumps.Unfortunately,continuous flow LVADs are fraught with complications such as gastrointestinal(GI)bleeding that are primarily attributed to the formation of arteriovenous malformations.With frequent GI bleeding,antiplatelet and anticoagulation therapies are usually discontinued increasing the risk of life-threatening events.Small bowel bleeds account for 15%as the source and patients often undergo multiple endoscopic procedures.Treatment strategies include resuscitative measures and endoscopic therapies.Medical treatment is with octreotide.Novel treatment options include thalidomide,angiotensin converting enzyme inhibitors/angiotensinⅡreceptor blockers,estrogen-based hormonal therapies,doxycycline,desmopressin and bevacizumab.Current research has explored the mechanism of frequent GI bleeds in this population,including destruction of von Willebrand factor,upregulation of tissue factor,vascular endothelial growth factor,tumor necrosis factor-α,tumor growth factor-β,and angiopoetin-2,and downregulation of angiopoetin-1.In addition,healthcare resource utilization is only increasing in this patient population with higher admissions,readmissions,blood product utilization,and endoscopy.While some of the novel endoscopic and medical therapies for LVAD bleeds are still in their development stages,these tools will yet be crucial as the number of LVAD placements will likely only increase in the coming years.

Evolvement of left ventricular assist device： the implications on heart failure management

Heart failure （HF） is a potentially fatal disease that affects increasing number of people worldwide. Although heart transplant is the ＂gold standard＂ therapy for HF, due to the limited availability of organs, many patients died when waiting for the transplant. Left ventricular assist device （LVAD）, as a mechanical circulatory support, has become a new light for patients with HF. With the technical advancements, LVADs work not only as a bridge to transplant, but also assist heart recovery and even as a destination therapy in long-term treatment. This observation paper reviewed the development of LVAD and its clinical roles. The challenges and possible solutions in nursing care for pa- tients with LVAD at different stage of implantation were discussed. The healthcare professionals could obtain a better understanding about the LVAD treatment for HF patients.

Comprehensive review of hemolysis in ventricular assist devices

Ventricular assist devices(VADs)have played an important role in altering the natural history of end-stage heart failure.Low-grade hemolysis has been traditionally described in patients with VADs,indicating effective device functionality.However,clinically significant hemolysis could be crucial in terms of prognosis,calling for prompt therapeutic actions.The absence of solid and widely approved diagnostic criteria for clinically significant hemolysis,render the utilization of hemolysis laboratory markers challenging.Hemolysis incidence varies(5%-18%)depending on definition and among different VAD generations,being slightly higher in continuous-flow devices than in pulsatile devices.Increased shear stress of red blood cells and underlying device thrombosis appear to be the main pathogenetic pathways.No certain algorithm is available for the management of hemolysis in patients with VADs,while close clinical and laboratory monitoring remains the cornerstone of management.Imaging examinations such as echocardiography ramp test or computed tomography scan could play a role in revealing the underlying cause.Treatment should be strictly personalized,including either pharmacological(antithrombotic treatment)or surgical interventions.

Optimal timing of same-admission orthotopic heart transplantation after left ventricular assist device implantation

AIM To investigate the impact of timing of same-admission orthotopic heart transplant(OHT) after left ventricular assist device(LVAD) implantation on in-hospital mortality and post-transplant length of stay.METHODS Using data from the Nationwide Inpatient Sample from 1998 to 2011, we identified patients 18 years of age or older who underwent implantation of a LVAD and for whom the procedure date was available. We calculated in-hospital mortality for those patients who underwent OHT during the same admission as a function of time from LVAD to OHT, adjusting for age, sex, race, household income, and number of comorbid diagnoses. Finally, we analyzed the effect of time to OHT after LVAD implantation on the length of hospital stay post-transplant.RESULTS Two thousand and two hundred patients underwent implantation of a LVAD in this cohort. One hundred and sixty-four(7.5%) patients also underwent OHT duringthe same admission, which occurred on average 32 d(IQR 7.75-66 d) after LVAD implantation. Of patients who underwent OHT, patients who underwent transplantation within 7 d of LVAD implantation("early") experienced increased in-hospital mortality(26.8% vs 12.2%, P = 0.0483) compared to patients who underwent transplant after 8 d("late"). There was no statistically significant difference in age, sex, race, household income, or number of comorbid diagnoses between the early and late groups. Post-transplant length of stay after LVAD implantation was also not significantly different between patients who underwent early vs late OHT. CONCLUSION In this cohort of patients who received LVADs, the rate of in-hospital mortality after OHT was lower for patients who underwent late OHT(at least 8 d after LVAD implantation) compared to patients who underwent early OHT. Delayed timing of OHT after LVAD implantation did not correlate with longer hospital stays post-transplant.

Left ventricular assist device hemolysis leading to dysphagia

A 41-year-old man with a continuous- flow left ventricular assist device presented for evaluation of dysphagia and dark urine. He was found to have a significantly elevated L-lactate dehydrogenaseand an elevated plasma free hemoglobin consistent with intravascular hemolysis.After the hemolysis ceased,both the black urine and dysphagia resolved spontaneously.Transient esophageal dysfunction,as a manifestation of gastrointestinal dysmotility,is known to occur in the setting of hemolysis.Paroxysmal nocturnal hemoglobinuria is another recognized cause of massive hemolysis with gastrointestinal dysmotility occurring in25%-35%of patients during a paroxysm.Intravascular hemolysis increases plasma free hemoglobin,which scavenges nitric oxide(NO),an important second messenger for smooth muscle cell relaxation.The decrease in NO can lead to esophageal spasm and resultant dysphagia.In our patient the resolution of hemolysis resulted in resolution of dysphagia.

Resolution of hemolysis from pump thrombus during left ventricular assist device exchange

A 50-year-old male who underwent a Heart Mate Ⅱ left ventricular assist device placement for ischemic cardiomyopathy presented with discolored urine and hemolysis 3 mo after the operation. His hemolysis was thought to be due to thrombosis within the pump. Imaging studies were not able to visualize a left ventricular thrombus. Medical management with anticoagulation failed and he underwent surgery for a pump exchange. Intraoperatively, a firm thrombus was found within the pump of the Heart Mate Ⅱ, and the color of the urine changed dramatically from cola-colored to yellow which enabled us to confirm the diagnosis.

Gastrointestinal bleeding in a patient with a continuous-flow biventricular assist device

The association between continuous-flow left ventricular assist devices(CF-LVADs)and gastrointestinal(GI)bleeding from angiodysplasia is well recognized.However,the association between continuous-flow biventricular assist devices(CF-BIVADs)and bleeding angiodysplasia is less understood.We report a case of GI bleeding from a patient with a CF-BIVAD.The location of GI bleeding was identified by nuclear red blood cell bleeding scan.The vascular malformation leading to the bleed was identified and localized on angiography and then by pathology.The intensity of bleeding,reflected by number of units of packed red blood cells needed for normalization of hemoglobin,as well as the time to onset of bleeding after transplantation,are similar to that seen in the literature for CF-LVADs and pulsatile BIVADs.While angiography only detected a dilated late draining vein,pathology demonstrated the presence of both arterial and venous dilation in the submucosa,vascular abnormalities characteristic of a late arteriovenous malformation.

Computational fluid dynamics of left ventricular assist device under unsteady flow

Left ventricular assist device( LVAD) in this study is a mechanical tool that is used to support blood flow in the patient with heart disease. It supports left ventricle by building up the pressure to the pump outlet connected to the aorta. This pump was designed based on the magnetic driven centrifugal pump with a unique small washout hole constructed inside the impeller to generate the washout flow passage to prevent the stagnation at the region underneath and around the rotor. Computational fluid dynamics( CFD) was adopted in this study to assess the performance and optimize the design to avoid recirculation and high shear stress which is the main cause of stagnation and blood damage. Transient simulation was used for this study due to the asymmetric design of the washout hole and the complication of the bottom support of the impeller that has a risk of thrombosis,also,it was used to predict the variation of hydraulic performance caused by the rotation of the impeller and pulsed flow at the pump inlet. The simulation results show no excessive stress and no recirculation observed within the computational domain; in addition,the research result also provides information for further optimization and development to the pump.

Utility and correlation of known anticoagulation parameters in the management of pediatric ventricular assist devices

AIM To assess utility and correlation of known anticoagulation parameters in the management of pediatric ventricular assist device(VAD). METHODS Retrospective study of pediatric patients supported with a Berlin EXCOR VAD at a single pediatric tertiary care center during a single year.RESULTS We demonstrated associations between activated thro-mboplastin time(a PTT) and R-thromboelastography(R-TEG) values(rs = 0.65, P < 0.001) and between anti-Xa assay and R-TEG values(rs = 0.54, P < 0.001). The strongest correlation was seen between a PTT and anti-Xa assays(rs = 0.71, P < 0.001). There was also a statistically significant correlation between platelet counts and the maximum amplitude of TEG(rs = 0.71, P < 0.001). Importantly, there was no association between dose of unfractionated heparin and either measure of anticoagulation(a PTT, anti-Xa or R-TEG value). CONCLUSION This study suggests that while there is strong correlation between a PTT, anti-Xa assay and R-TEG values for patients requiring VAD support, there is a lack of relevant correlation between heparin dose and degree of effect. This raises concern as various guidelines continue to recommend using these parameters to titrate heparin therapy.

Continuous Flow Left Ventricular Assist Device Therapy:A Focused Review on Optimal Patient Selection and Long-Term Follow-up Using Echocardiography

Despite widespread awareness and use of scientifi cally proven life-prolonging medical and device-based therapies over the last two decades,heart failure remains a leading cause of morbidity,mortality,and health care expenditure in the United States.Mechanical circulatory support with a continuous-fl ow left ventricular assist device(CF-LVAD),either as a bridge to heart transplantation or as destination therapy,is an increasingly used treatment modality for patients with advanced heart failure syndromes that worsen despite their receiving standard therapies.CF-LVAD support creates unique hemodynamic alterations that must be understood to provide appropriate care for these patients before and after implantation.Echocardiography is essential in the evaluation of patients who are being considered for or are mechanically supported by CF-LVADs.Here we provide a focused clinical review on the use of echocardiography in two main aspects of the evaluation of these patients:(a)optimal patient selection for CF-LVAD support and(b)followup assessment of optimal pump function.

OBSERVATION AND ANALYSIS OF BLOOD CONTACTING SURFACE OF LEFT VENTRICULAR ASSIST DEVICE WITH SCANNING ELECTRON MICROSCOPY

Thrombus formation in the artificial heart blood pump is a complex problem. The most important factor of thrombosis in the blood pump is the quality of blood contacting surface which is related to hemocompatibility of materials and micromorphololgy or roughness of the surface. So it is necessary to understand the morphology of the surface inside of blood pump in order to develop and improve a good quality blood pump. The authors observed and analysed the inner surface of blood pumps (both preimplanted and postimplanted) with scanning electron microscopy (SEM) providing a means for evaluating the blood pumps and for developing good quality of blood pumps. It was observed that there were four kinds of surface defects on the inner surface of the blood pumps: air bubble domes, open bubble craters, contaminated dust and gel particles. Microcrakes had also been found on the diaphragm of the postimplanted pump. But in the newly improved blood pump that had been imlanted for 16 days, there were few defects on the blood contacting surface, and only a little fibrinous layer observed. It could be considered that the current design and modifications are reasonable. Since some problems associated with the surface defects and thrombosis still existed, further improvement in fabrication process and quality control procedures with SEM are under way.

Subacute gastric perforation caused by a left ventricular assist device

This case report describes a rare complication of a left ventricular assist device (LVAD). A patient with ischemic cardiomyopathy had an LVAD placed due to intractable congestive heart failure following a large anterior myocardial infarction. The patient developed chronic bacteremia and multiple septic episodes. A gastric endoscopy revealed perforation of the anterior wall of the stomach by the LVAD. Gastric acid related erosions were present on the metallic surface suggesting prolonged exposure. This is the second case report of this rare complication and the first case report of a subacute course.

To ventricular assist devices or not:When is implantation of a ventricular assist device appropriate in advanced ambulatory heart failure?

Advanced heart failure has been traditionally treated via either heart transplantation,continuous inotropes,consideration for hospice and more recently via left ventricular assist devices(LVAD).Heart transplantation has been limited by organ availability and the futility of other options has thrust LVAD therapy into the mainstream of therapy for end stage heart failure.Improvements in technology and survival combined with improvements in the quality of life have made LVADs a viable option for many patients suffering from heart failure.The question of when to implant these devices in those patients with advanced,yet still ambulatory heart failure remains a controversial topic.We discuss the current state of LVAD therapy and the risk vs benefit of these devices in the treatment of heart failure.

Effects of left ventricular assist device on pulmonary functions and pulmonary hemodynamics:A meta-analysis

BACKGROUND Given current evidence,the effect of left ventricular assist device(LVAD)implantation on pulmonary function tests remains controversial.AIM To better understand the factors contributing to the changes seen on pulmonary function testing and the correlation with pulmonary hemodynamics after LVAD implantation.METHODS Electronic databases were queried to identify relevant articles.The summary effect size was estimated as a difference of overall means and standard deviation on a random-effects model.RESULTS A total of four studies comprising 219 patients were included.The overall mean forced expiratory volume in one second(FEV1),forced vital capacity(FVC)and diffusion lung capacity of carbon monoxide(DLCO)after LVAD implantation were significantly lower by 0.23 L(95%CI:0.11-0.34,P=00002),0.18 L(95%CI:0.03-0.34,P=0.02),and 3.16 mmol/min(95%CI:2.17-4.14,P<0.00001),respectively.The net post-LVAD mean value of the cardiac index was significantly higher by 0.49 L/min/m2(95%CI:0.31-0.66,P<0.00001)compared to pre-LVAD value.The pulmonary capillary wedge pressure and pulmonary vascular resistance were significantly reduced after LVAD implantation by 8.56 mmHg(95%CI:3.78-13.35,P=0.0004),and 0.83 Woods U(95%CI:0.11-1.55,P=0.02),respectively.There was no significant difference observed in the right atrial pressure after LVAD implantation(0.61 mmHg,95%CI:-2.00 to 3.32,P=0.65).Overall findings appear to be driven by studies using HeartMateII devices.CONCLUSION LVAD implantation might be associated with a significant reduction of the spirometric measures,including FEV1,FVC,and DLCO,and an overall improvement of pulmonary hemodynamics.

Simultaneous ramp right heart catheterization and echocardiography in a Reliant Heart left ventricular assist device

Many clinicians caring for patients with continuous flow left ventricular assist devices(CF-LVAD) use ramp right heart catheterization(RHC) studies to optimize pump speed and also to troubleshoot CF-LVAD malfunction. An investigational device,the Reliant Heart Heart Assist 5(Houston,TX),provides the added benefit of an ultrasonic flow probe on the outflow graft that directly measures flow through the CF-LVAD. We performed a simultaneous ramp RHC and echocardiogram on a patient who received the above CF-LVAD to optimize pump parameters and investigate elevated flow through the CF-LVAD as measured by the flow probe. We found that the patient's hemodynamics were optimized at their baseline pump speed,and that the measured cardiac output via the Fick principle was lower than that measured by the flow probe. Right heart catheterization may be useful to investigate discrepancies between flow measured by a CF-LVAD and a patient's clinical presentation,particularly in investigational devices where little clinical experience exists. More data is needed to elucidate the correlation between the flow measured by an ultrasonic probe and cardiac output as measured by RHC.

Impact of Ventricular Assist Device Implantation on Clinical and Economic Outcomes of Heart Transplantation in the United States from 2003-2007

The use of ventricular assist devices (VADs) as a bridge to transplantation (BTT) has evolved considerably as clinical experience has grown and newer generation devices have become available. This study investigated the impact of VAD implantation on the clinical and economic outcomes of patients undergoing heart transplantation in the United States(US) from 2003-2007. A retrospective study was carried out using the Nationwide Inpatient Sample, to track the characteristics and outcomes of an estimated 7859 patients undergoing heart transplantation in the United States from 2003-2007. Patients were divided based on whether they were bridged to transplant with a VAD and whether they were outpatient (VAD Outpt) or inpatient (VAD Inpt). Multivariate analysis was performed to identify risk factors for inhospital mortality following heart transplantation. Hospital costs were also measured. A VAD was used as a BTT in 20.8% of patients undergoing heart transplantation during the study period. Early in the series the frequency of VAD Outpts and Inpts was similar but in later years patients were more commonly bridged as outpatients. Hospital mortality for the entire population was 6.2%. Multivariate analysis identified several risk factors for mortality, including advanced age, history of congenital heart disease, and VAD Inpt status. VAD Inpt status was the strongest predictor of mortality. The hospital cost of patients bridged as inpatients was more than double the cost of outpatients. Median hospital cost declined by 11% over the study period, from $115,868 to $103,578. Much of this cost reduction was related to the shift in VAD status from Inpt to Outpt. Heart transplant recipients are increasingly bridged to transplantation with VADs as outpatients. Those bridged as inpatients have substantially higher hospital mortality and cost. These findings have important clinical implications and should inform policy development, resource utilization and donor allocation.

A Comparison Study of Cavitating Flow in a Ventricular Assist Device Using Laminar and Turbulent Model

The two-dimensional cavitating flow phenomena due to the valve closure in a ventricular assist device were computationally studied. This is a simplification of three-dimensional viscous effects in a ventricular valve. Both laminar flow and turbulent flow were computed and compared with each other. For computations, a dynamic mesh strategy to cope with the movement of the valve was developed. The simulation of cavitation was conducted with a model which took considerations of the first-order effect of the formation and transport of vapor bubbles, the turbulent fluctuations of pressure and velocity, and the magnitude of non-condensable gases. The turbulent flow was computed by using thek-wmodel. The results show that the local turbulence is one of the vital effects on the development of the cavitating flow. The maximum velocity at the moments of valve closure was significantly reduced in the turbulent flow modeling. Turbulence also reduces the jet intensity at the valve closure and, hence, the cavitating region on the valve. Furthermore, the results show that the turbulent flow model has a better capability for prediction of cavitation duration.