Pulsatile Ventricular Assist Device Research Articles

Windkessel model of hemodynamic state supported by a pulsatile ventricular assist device in premature ventricle contraction

BackgroundCounter-pulsation control (CPC) by ventricular assist devices (VADs) is believed to reduce cardiac load and increase coronary perfusion. However, patients with VADs have a higher risk of arrhythmia, which may cause the CPC to fail. Consequently, CPC has not been applied by VADs in clinical practice. The phase-locked loop (PLL) algorithm for CPC is readily implemented in VADs; however, it requires a normal, consistent heartbeat for adequate performance. When an arrhythmia occurs, the algorithm maintains a constant pumping rate despite the unstable heartbeat. Therefore, to apply the PLL algorithm to CPC, the hemodynamic effects of abnormal heartbeats must be analyzed.ObjectivesThis study sought to predict the hemodynamic effects in patients undergoing CPC using VADs, based on electrocardiogram (ECG) data, including a wide range of heart rate (HR) changes caused by premature ventricular contraction (PVC) or other reasons.MethodsA four-element Windkessel hemodynamic model was used to reproduce the patient’s aortic blood pressure in this study. ECG data from 15 patients with severe congestive heart failure were used to assess the effect of the CPC on the patients’ hemodynamic state. The input and output flow characteristics of the pulsatile VAD (LibraHeart I, Cervika, Korea) were measured using an ultrasound blood flow meter (TS410, Transonic, USA), with the aortic pressure maintained at 80–120 mmHg. All other patient conditions were also reproduced.ResultsIn patients with PVCs or normal heartbeats, CPC controlled by a VAD reduced the cardiac load by 20 and 40%, respectively. When the HR was greater for other reasons, such as sinus tachycardia, simultaneous ejection from the heart and VAD was observed; however, the cardiac load was not increased by rapid cardiac contractions resulting from decreased left ventricle volume. These data suggest that the PLL algorithm reduces the cardiac load and maintains consistent hemodynamic changes.

Acute and Long-Term Effects of LVAD Support on Right Ventricular Function in Children with Pediatric Pulsatile Ventricular Assist Devices.

Right ventricular failure (RVF) is a significant issue when considering left ventricular assist device (LVAD) implantation in pediatrics. The aim of this study was to evaluate the effects of LVAD on right ventricular (RV) function in children. We retrospectively reviewed clinical and echocardiographic data of children who underwent Berlin Heart EXCOR LVAD focusing on RV function before and after implantation (1, 3, and 6 month follow-up). An isolated LVAD was used in 27 patients. Median age was 11 months (interquartile range [IQR]: 5-24 months), with a median weight of 6.3 kg (IQR: 5-9 kg). Median time on ventricular assist device (VAD) support was 147 days (IQR: 86-210 days). Twenty patients were successfully bridged to orthotopic heart transplantation (OHT) (74%), six patients died (22%), and also heart function recovered in one patient (4%). Before LVAD implantation, nine patients (33%) showed a RV fractional area change (RVFAC) less than or equal to 30%. After implantation, mean RVFAC increased up until the 3 month follow-up (43.13%; p = 0.033) and then slightly decreased. In a subgroup of 18 patients, the average strain value increased after the 1 month follow-up (p = 0.022). Right ventricular failure developed in 33% of patients before the 1 month follow-up, and 7.4% experienced RVF at the 6 month follow-up. No patient required biventricular assist device (BiVAD). In our population, pulsatile-flow LVAD in children allows optimal RV decompression and function post-LVAD as measured by improvement in RV function at echo particularly at 1 and 3 month follow-up. At long-term follow-up, the beneficial effects of LVAD on RV function seem to be reduced as signs and symptoms of late RVF may develop in some patients despite LVAD support.

Management of Hemostasis for Pediatric Patients on Ventricular-Assist Devices.

Ventricular-assist devices (VADs) have seen increased utilization in the pediatric population. Formerly, this therapeutic modality was limited to only the pulsatile VAD, EXCOR (Berlin Heart GmbH). However, the continuous flow VAD devices, HeartMate II (Abbott Inc.) and HeartWare (Medtronic Inc.), are now increasingly used in this population. Postoperatively, VAD patients are acutely anticoagulated using unfractionated heparin, often beginning 24 to 48 hours after VAD placement. Once the patient is stabilized and ready to transition to a lower acuity or outpatient setting, low-molecular-weight heparin or warfarin therapy may be instituted. Also, because of the risk for thrombotic and thromboembolic complications, antiplatelet strategies are employed using medications such as aspirin, clopidogrel, or dipyridamole. Platelet-rich plasma or whole blood platelet aggregation studies, platelet function analyzer-100 (Siemens), VerifyNow (Accriva Diagnostics), or thromboelastography platelet mapping (Haemonetics) may be used to help monitor antiplatelet effects, though the interpretation of the strength of the antiplatelet effect remains difficult. Care must be taken to monitor the hematologic complications of VAD, including acquired von Willebrand syndrome, which increases the risk for bleeding, and intravascular hemolysis, which increases the risk of thrombosis. Appropriate device placement and anticoagulation management are imperative to help avoid neurological dysfunction and ischemic stroke, the most devastating potential complications of VAD therapy. As our experience grows, we continue to gain an increased understanding of the management of anticoagulation, need for antiplatelet medication, and appropriate monitoring for these critical patients.

Improved identification of the electrocardio-signal for pulsatile ventricular assist devices

We introduce and investigate a method to identify the feature point of an electrocardiogram (ECG) to provide real-time and accurate trigger signals for pulsatile ventricular assist devices (PVADs). An important part of this method is an improved data processing algorithm, in which a differential calculator and another a low-pass filtering were added to avoid drift in the original signal and systematically delay caused by physical devices. The method was systematically illustrated in this article and a test-setup was built based on the LabVIEW program development environment. Both simulations and experiments were carried out to demonstrate the merits of the method. Simulated results based on four typical pathological ECG signals confirm the robustness and adaptability of this method. Experimental results verified the benefits of this method with regard to increased accuracy that can pick up the interested signal accurately in a degree of larger than 99%. This improved technology proposed in this research will be greatly beneficial to simultaneous triggering in VADs and eventually to the heart failure recovery.

Systematic Design of a Magnetically Levitated Brushless DC Motor for a Reversible Rotary Intra-Aortic Blood Pump.

The IntraVAD is a miniature intra-aortic ventricular assist device (VAD) designed to work in series with the compromised left ventricle. A reverse-rotation control (RRc) mode has been developed to increase myocardial perfusion and reduce ventricular volume. The RRc mode includes forward rotation in systole and reverse rotation in diastole, which requires the IntraVAD to periodically reverse its rotational direction in synchrony with the cardiac cycle. This periodic reversal leads to changes in pressure force over the impeller, which makes the entire system less stable. To eliminate the mechanical wear of a contact bearing and provide active control over the axial position of the rotor, a miniature magnetically levitated bearing (i.e., the PM-Coil module) composed of two concentric permanent magnetic (PM) rings and a pair of coils-one on each side-was proposed to provide passive radial and active axial rotor stabilization. In the early design stage, the numerical finite element method (FEM) was used to optimize the geometry of the brushless DC (BLDC) motor and the maglev module, but constructing a new model each time certain design parameters were adjusted required substantial computation time. Because the design criteria for the module had to be modified to account for the magnetic force produced by the motor and for the hemodynamic changes associated with pump operation, a simplified analytic expression was derived for the expected magnetic forces. Suitable bearings could then be designed capable of overcoming these forces without repeating the complicated FEM simulation for the motor. Using this method at the initial design stage can inform the design of the miniature maglev BLDC motor for the proposed pulsatile axial-flow VAD.

Pneumatic paracorporeal ventricular assist device as bridge to transplant in children ≤ 20 kg: Krakow experience

Pulsatile mechanical ventricular assist devices (VADs) of various designs and functional principles have been in use in adult patients for long-term support of the failing heart. Despite the remarkable advances with the use of VAD, its support in children is still limited. We report on our experience in the paediatric population. The aim is either recovery of the heart or, more often, to keep the patient alive until later transplantation. We retrospectively study of children ≤ 20 kg, who were mechanically bridged to heart transplantation using the Berlin Heart (BH) Excor VAD at our hospital. The period of review was from November 2009 to March 2017. A total eight patients were included in this analysis, with these patients weighing < 20 kg. The study included three boys and five girls, with a mean weight of 10.55 kg (5.30–20 kg) and mean age of 20.69 months (4.5 to 60 months). Eight patients were supported with the Berlin Excor VAD, and six patients were supported with a left-sided ventricular assist device (LVAD) and two patients were supported with biventricular assist device (BVAD). Three of eight patients (38%) have been successfully bridged to heart transplant. Insertion of pulsatile paracorporeal VADs in children with end-stage heart failure is an effective strategy as a bridge to heart transplantation. This study demonstrates VAD support had serious ceribrovascular complications, and implantation BVAD support results were not satisfactory.

Experience With a Long-term Pulsatile Ventricular Assist Device as a Bridge to Heart Transplant in Adults

Introduction and objectivesMost long-term ventricular assist devices (VADs) that are currently implanted are intracorporeal continuous-flow devices. Their main limitations include their high cost and inability to provide biventricular support. The aim of this study was to describe the results of using paracorporeal pulsatile-flow VADs as a bridge to transplant (BTT) in adult patients. MethodsRetrospective analysis of the characteristics, complications, and outcomes of a single-center case series of consecutive patients treated with the EXCOR VAD as BTT between 2009 and 2015. ResultsDuring the study period, 25 VADs were implanted, 6 of them biventricular. Ventricular assist devices were indicated directly as a BTT in 12 patients and as a bridge to decision in 13 due to the presence of potentially reversible contraindications or chance of heart function recovery. Twenty patients (80%) were successfully bridged to heart transplant after a median of 112 days (range, 8-239). The main complications included infectious (52% of patients), neurological events (32%, half of them fatal), bleeding (28%), and VAD malfunction requiring component replacement (28%). ConclusionsEighty percent of patients with the EXCOR VAD as BTT achieved the goal after an average of almost 4 months of support. The most frequent complications were infectious, and the most severe were neurological. In our enivonment, the use of these pulsatile-flow VAD as BTT is a feasible strategy that obtains similar outcomes to those of intracorporeal continuous-flow devices.

Cardiac prosthesis as an advanced surgical therapy for end-stage cardiac patients: current status and future perspectives.

This paper reviews the current status and future perspectives of the artificial heart research that was started in 1957 by Akutsu and Kolff. During the 1960's, although not much progress was made in increasing animal survival time with artificial hearts, clinical applications were already made for both a ventricular assist device in 1962 and total artificial heart (TAH) in 1969 followed by a second TAH application in 1981. Both TAH applications were done as bridges to heart transplantation. Meanwhile, the animal survival time improved during the 1970's because of the availability of better biomaterials, better understanding of the circulatory system, and improvement in surgical techniques. Continuous flow pumps were also investigated during the 1970's, which demonstrated feasibility for chronically supporting circulation in healthy animals. Four permanent cases of TAH application were done early 1980's for patients who could not be the candidates for heart transplantation. Although the patients were tethered to the external drive-console, one of them survived for nearly two years. Complications due to thromboembolism and infection were the major causes of death in these patients. The patients' quality of life was questionable and the permanent application of the TAH was then stopped to make improvements in the system in terms of implantability and biocompatibility. During the 1980's, efforts were then switcthed to development of totally implantable VAD and TAH systems, which led to the first discharge of a VAD patient from the hospital in 1992. In the early 1990's, implantable electric VADs, Novacor and ThermoCardio System (TCI), became available to support the circulation of end-stage cardiac patients until a donor heart could be found. The transplantation rate of the VAD patients ranged around 70% with the average waiting time of 80 to 100 days. The number of patients transplanted with VADs are more than 5000 and those with the pneumatic TAH exceed 200. Because of the larger size, requirement of heart valves, and complicated control mechanism of the pulsatile VADs, continuous flow pumps have been gaining popularity among clinicians. The clinical applications of the continuous flow devices have just begun, demonstrating remarkable performance in bridging to heart transplantation. In, the 21st century, we will see prevalent clinical applications of various circulatory support devices from pulsatile VAD, pulsatile TAH to continuous flow VAD. These devices will be combined with genetic treatment to re-generate the myocardium and recover the failing heart. Complete recovery of the myocardium may become possible through therapy combining circulatory assist devices and biotechnology.

High-frequency operation of a pulsatile VAD - a simulation study.

Ventricular assist devices (VADs) are mechanical blood pumps that are clinically used to treat severe heart failure. Pulsatile VADs (pVADs) were initially used, but are today in most cases replaced by turbodynamic VADs (tVADs). The major concern with the pVADs is their size, which prohibits full pump body implantation for a majority of patients. A reduction of the necessary stroke volume can be achieved by increasing the stroke frequency, while maintaining the same level of support capability. This reduction in stroke volume in turn offers the possibility to reduce the pump's overall dimensions. We simulated a human cardiovascular system (CVS) supported by a pVAD with three different stroke rates that were equal, two- or threefold the heart rate (HR). The pVAD was additionally synchronized to the HR for better control over the hemodynamics and the ventricular unloading. The simulation results with a HR of 90 bpm showed that a pVAD stroke volume can be reduced by 71%, while maintaining an aortic pulse pressure (PP) of 30 mm Hg, avoiding suction events, reducing the ventricular stroke work (SW) and allowing the aortic valve to open. A reduction by 67% offers the additional possibility to tune the interaction between the pVAD and the CVS. These findings allow a major reduction of the pVAD's body size, while allowing the physician to tune the pVAD according to the patient's needs.

Superior performance of continuous over pulsatile flow ventricular assist devices in the single ventricle circulation: A computational study

This study compares the physiological responses of systemic-to-pulmonary shunted single ventricle patients to pulsatile and continuous flow ventricular assist devices (VADs). Performance differences between pulsatile and continuous flow VADs have been clinically observed, but the underlying mechanism remains poorly understood. Six systemic-to-pulmonary shunted single ventricle patients (mean BSA=0.30m2) were computationally simulated using a lumped-parameter network tuned to match patient specific clinical data. A first set of simulations compared current clinical implementation of VADs in single ventricle patients. A second set modified pulsatile flow VAD settings with the goal to optimize cardiac output (CO). For all patients, the best-case continuous flow VAD CO was at least 0.99L/min greater than the optimized pulsatile flow VAD CO (p=0.001). The 25 and 50mL pulsatile flow VADs exhibited incomplete filling at higher heart rates that reduced CO as much as 9.7% and 37.3% below expectations respectively. Optimization of pulsatile flow VAD settings did not achieve statistically significant (p<0.05) improvement to CO. Results corroborate clinical experience that continuous flow VADs produce higher CO and superior ventricular unloading in single ventricle patients. Impaired filling leads to performance degradation of pulsatile flow VADs in the single ventricle circulation.

Adverse events in children implanted with ventricular assist devices in the United States: Data from the Pediatric Interagency Registry for Mechanical Circulatory Support (PediMACS)

Ventricular assist devices (VADs) have been used in children on an increasing basis in recent years. One-year survival rates are now >80% in multiple reports. In this report we describe adverse events experienced by children with durable ventricular assist devices, using a national-level registry (PediMACS, a component of INTERMACS) METHODS: PediMACS is a national registry that contains clinical data on patients who are <19 years of age at the time of VAD implantation. Data collection concludes at the time of VAD explantation. All FDA-approved devices are included. PediMACS was launched on September 1, 2012, and this report includes all data from launch until August 2014. Adverse events were coded with a uniform, pre-specified set of definitions. This report comprises data from 200 patients with a median age of 11 years (range 11 days to 18 years), and total follow-up of 783 patient-months. The diagnoses were cardiomyopathy (n = 146, 73%), myocarditis (n = 17, 9%), congenital heart disease (n = 35, 18%) and other (n = 2, 1%). Pulsatile-flow devices were used in 91 patients (45%) and continuous-flow devices in 109 patients (55%). Actuarial survival was 81% at 6 months. There were 418 adverse events reported. The most frequent events were device malfunction (n = 79), infection (n = 78), neurologic dysfunction (n = 52) and bleeding (n = 68). Together, these accounted for 277 events, 66% of the total. Although 38% of patients had no reported adverse event and 16% of patients had ≥5 adverse events. Adverse events occurred at all time-points after implantation, but were most likely to occur in the first 30 days. For continuous-flow devices, there were broad similarities in adverse event rates between this cohort and historic rates from the INTERMACS population. In this study cohort, the overall rate of early adverse events (within 90 days of implantation) was 86.3 events per 100 patient-months, and of late adverse events it was 20.4 events per 100 patient-months. The most common adverse events in recipients of pulsatile VADs were device malfunction, neurologic dysfunction, bleeding and infection. For continuous-flow VADs, the most common adverse events were infection, bleeding, cardiac arrhythmia, neurologic dysfunction and respiratory failure. Compared with an adult INTERMACS cohort, the overall rate and distribution of adverse events appears similar.

The Influence of Different Operating Conditions on the Blood Damage of a Pulsatile Ventricular Assist Device.

Because of pulsatile blood flow's benefit for myocardial recovery, perfusion of coronary arteries and end organs, pulsatile ventricular assist devices (VADs) are still widely used as paracorporeal mechanical circulatory support devices in clinical applications, especially in pediatric heart failure patients. However, severe blood damage limits the VAD's service period. Besides optimizing the VAD geometry to reduce blood damage, the blood damage may also be decreased by changing the operating conditions. In this article, a pulsatile VAD was used to investigate the influence of operating conditions on its blood damage, including hemolysis, platelet activation, and platelet deposition. Three motion profiles of pusher plate (sine, cosine, and polynomial), three stroke volumes (ejection fractions) (56 ml [70%], 42 ml [52.5%], and 28 ml [35%]), three pulsatile rates (75, 100, and 150 bpm), and two assist modes (copulsation and counterpulsation) were implemented respectively in VAD fluid-structure interaction simulations to calculate blood damage. The blood damage indices indicate that cosine motion profile, higher ejection fraction, higher pulsatile rate, and counterpulsation can decrease platelet deposition whereas increase hemolysis and platelet activation, and vice versa. The results suggest that different operating conditions have different effects on pulsatile VAD's blood damage and may be beneficial to choose suitable operating condition to reduce blood damage in clinical applications.

Vascular Reactivity Analysis in Patients with Continuous Flow Left Ventricular Assist Devices (CF-LVADs) - the Role of Endothelial Function in Continuous Flow Physiology

Endothelial dysfunction associated with heart failure should improve after a CF-LVAD placement due to correction of the heart failure environment. Yet, a loss of pulsatility could counteract such improvement as endothelial cells need a pulse pressure for normal function. Mixed results of endothelial dysfunction in CF-LVAD when compared to pulsatile VAD have been reported utilizing both brachial reactivity and EndoPAT® machines. Both these tests rely on physical pulse volume and might be impacted by the mere loss of pulsatility. Hence, we set out to analyze endothelial function utilizing thermal digital monitoring (VENDYS) in patients with CF-LVADs. We recruited stable patients during their routine visits and performed the VENDYS test in a soothing environment. Aortic valve opening was determined with a portable echo (GE V-scan) and graded as per previously described classification. Rest of the data was collected from the patient charts. Patients were classified into three groups based on parameters of vascular reactivity index (VRI) described in normal population: poor (<1) intermediate (1 - 2) and good VRI (2 - 3) with higher VRI correlated with better endothelial function, hence better outcomes. Pearsons correlation and T-test were performed, P-values < 0.05 were considered significant. 40 patients had Heartmate II and 2 had Heartware devices. Table 1 describes the characteristics of the 3 cohorts of endothelial function. Overall 81% had aortic valve opening consistently at the time of endothelial function assessment. Only 19% had a poor VRI, while majority had an intermediate VRI. Older patients had worse endothelial function while rest of the baseline characteristics including aortic valve opening and flow were not different between the groups. Correlation between VRI and VAD flow (r= -0.2766 P value= 0.08) and high Doppler blood pressure (r= -0.2656 P value=0.09) showed no significance. However, 50% of the patients with a poor VRI had adverse events while only 23% of those with good endothelial function did (Table 1). The 2 patients with poor VRI who had a GI bleed had 5 episodes while the 3 patients with good VRI had 4 episodes. In a cohort of CF-LVAD patients where the majority had their aortic valve open, endothelial function, as reflected by DTM was poor in only a few. It is not clear if endothelial dysfunction contributes to any of adverse events for CF-LVAD patients but there seem to be a higher recurrence of GI bleeding in patients who had a poor endothelial function.Table 1Total<11 to 22 to 3p valueN42 (100%)8 (19%)21 (50%)13 (31%)VENDYS score1.71±0.780.45±0.351.69±0.282.5±0.35Age57±12.860.3±7.559.6±10.150.2±16.70.073Male34 (81%)5 (62.5%)19 (90%)10 (77%)0.2082Caucasian17(40%)2 (25%)9 (43%)6 (46%)0.6009DT31 (74%)6 (75%)17 (81%)8 (61%)0.45AV opened34 (81%)7 (87%)17 (81%)10 (77%)0.835Days under support585±567244±276672±586497±5820.17BUN275.47±282.425.25±16.4724.8±7.2320.6±7.540.41Hgb11.06±2.229.77±1.4711.56±2.4511.04±2.010.15Flow5.49±1.346.4±1.475.21±1.515.37±0.510.098Patients with events17(100%)4 (23%)10 (59%)3 (18%)0.3GIB10 (58%)2530.99Infections4 (23%)1300.36Arrhythmia1 (6%)0100.59ADHF3 (18%)0300.19Death3 (14%)1200.46VENDYS score: Endothelial function based thermal vascular reactivity. DT: Destination Therapy. AV: Aortic valve. GIB: Gastrointestinal bleeding. ADHF: Acute decompensated heart failure. Open table in a new tab

Multi-objective optimization of pulsatile ventricular assist device hemocompatibility based on neural networks and a genetic algorithm.

Given the benefit of pulsatile blood flow for perfusion of coronary arteries and end organs, pulsatile ventricular assist devices (VADs) are still widely used as paracorporeal mechanical circulatory support devices in clinical applications. However, poor hemocompatibility limits the service period of the VADs. Most previous improvements on VAD hemocompatibility were conducted by trial-and-error CFD analysis, which does not easily arrive at the best solution. In this paper, a multi-objective optimization method integrating neural networks and NSGA-II (Non-dominated Sorted Genetic Algorithm-II) based on FSI simulation was developed and applied to a pulsatile VAD to optimize its hemocompatibility. First, the VAD blood chamber was parameterized with the principal geometrical parameters. Three hemocompatibility indices including hemolysis, platelet activation, and platelet deposition were chosen as goal functions. The neural networks were built to fit the nonlinear relationship between goal functions and geometrical parameters. Next, a multi-objective optimization algorithm (NSGA-II) was used to search out the Pareto optimal solutions in the built neural networks. Finally, the best compromise solution was selected from the Pareto optimal solutions by a fuzzy membership approach and validated by FSI simulation. The best compromise solution simultaneously possesses an acceptable hemolysis index, platelet activation index, and platelet deposition index, and the corresponding relative errors between the indices predicted by optimization algorithm and the one calculated by FSI simulations are all less than 5%. The results suggest that the proposed multi-objective optimization method has the potential for application in optimizing pulsatile VAD hemocompatibility, and may also be applied to other blood-wetted devices.

공압식 박동형 심실보조장치에서 공압관 내 공기압에 따른 박출량 추정

심실보조장치는 심장질환자에게 심장이식까지의 가교로서 사용된다. 공압식 박동형 심실보조장치를 체내에 이식했을 때, 심실보조장치를 통과하는 혈류가 느려질 경우 혈전이 발생할 수 있기 때문에 박출량을 측정하는 것이 중요하다. 심실보조장치의 박출량을 측정하기 위해 각종 센서를 함께 이식할 경우, 감염의 위험성이 커지기 때문에 본 연구에서는 체외에서 측정할 수 있는 공압관 내 압력을 통해 심실보조장치의 상태를 추정하고자 한다. 체외실험을 통해 공압식 박동형 심실보조장치의 공압관 내 차동압력과 심실보조장치 박출량의 상관관계를 계산하였다. Pearson correlation coefficient r=0.623 으로 두 값의 상관관계가 높으며, 박출량 추정값과 측정값에서 오차가 있었지만 공기 분자의 이동에 따른 식을 개발하여 박출량 추정의 정확성을 높일 수 있을 것으로 보인다.

공압식 박동형 심실보조장치의 공압관 내 압력 측정을 통한 박출량 추정

Abstract: A Ventricular assist device (VAD) is one of the most efficient treatments to raise the survivability of theend stage heart failure patient. However, some of LVAD patients have died for the failures and improper control ofLVAD. To detect critical dangers in LVAD, the monitoring methods of LVAD outflow have been requested, becauseit can be affected by patient’s hemodynamic states and abnormal conditions of LVAD. In the case of an external pul-satile LVAD, the air movement through the air line can be used to estimate LVAD outflow. In this study, the air move-ment in the air-line of the extracorporeal pulsatile LVAD was measured with a differential pressure sensor betweendifferent points. The precise estimation of air movement could be achieved by additional measurement of air pres-sure. In a series of in-vitro experiments, the LVAD outflow were changed according to the afterload of LVAD andthe differential pressure of LVAD didn’t have close correlation with the LVAD outflow that were measured with anultrasonic flowmeter at the same time. However, new precise estimation with the data from differential pressure andone point pressure in the air-line showed higher correlations with LVAD outflow.Key words: Pneumatic Pulsatile Ventricular Assist Device, VAD Pump Outflow, Air Pressure, Air Flow

Modified TandemHeart Ventricular Assist Device for Infant and Pediatric Circulatory Support

The development of pediatric ventricular assist device (VAD) circuits with lower flow ranges for infants and small children is ongoing. We present our results with modifying a readily available adult VAD to support the pediatric population. The TandemHeart VAD (CardiacAssist, Pittsburgh, PA) circuit was modified to include a variable restrictive recirculation shunt to permit lower flow ranges in small pediatric patients. Initial benchtop flow rates and pressures were studied. Hemolysis trials were performed using whole bovine blood to compare plasma-free hemoglobin levels between modified and unmodified VAD circuits. The modified VAD was surgically implanted in 7 piglets (6 to 14 kg) and which supported them for 4 hours. Levels of hemolysis did not increase and full hemodynamic support was achieved. The modified TandemHeart VAD with a recirculation shunt was subsequently implanted in 2 pediatric patients who were bridged to transplant successfully. Because of its simplicity, availability, low prime volume, greater patient flow range, and lower cost, the modified TandemHeart VAD with a recirculation shunt should be considered as an alternative to extracorporeal membrane oxygenation and other pulsatile VADs in children.

Effects of Thoratec pulsatile ventricular assist device timing on the abdominal aortic wave intensity pattern.

Arterial waves are seen as possible independent mediators of cardiovascular risks, and the wave intensity analysis (WIA) has therefore been proposed as a method for patient selection for ventricular assist device (VAD) implantation. Interpreting measured wave intensity (WI) is challenging, and complexity is increased by the implantation of a VAD. The waves generated by the VAD interact with the waves generated by the native heart, and this interaction varies with changing VAD settings. Eight sheep were implanted with a pulsatile VAD (PVAD) through ventriculoaortic cannulation. The start of PVAD ejection was synchronized to the native R wave and delayed between 0 and 90% of the cardiac cycle in 10% steps or phase shifts (PS). Pressure and velocity signals were registered, with the use of a combined Doppler and pressure wire positioned in the abdominal aorta, and used to calculate the WI. Depending on the PS, different wave interference phenomena occurred. Maximum unloading of the left ventricle (LV) coincided with constructive interference and maximum blood flow pulsatility, and maximum loading of the LV coincided with destructive interference and minimum blood flow pulsatility. We believe that noninvasive WIA could potentially be used clinically to assess the mechanical load of the LV and to monitor the peripheral hemodynamics such as blood flow pulsatility and risk of intestinal bleeding.

ST and ALE-VMS methods for patient-specific cardiovascular fluid mechanics modeling

This paper provides a review of the space–time (ST) and Arbitrary Lagrangian–Eulerian (ALE) techniques developed by the first three authors' research teams for patient-specific cardiovascular fluid mechanics modeling, including fluid–structure interaction (FSI). The core methods are the ALE-based variational multiscale (ALE-VMS) method, the Deforming-Spatial-Domain/Stabilized ST formulation, and the stabilized ST FSI technique. A good number of special techniques targeting cardiovascular fluid mechanics have been developed to be used with the core methods. These include: (i) arterial-surface extraction and boundary condition techniques, (ii) techniques for using variable arterial wall thickness, (iii) methods for calculating an estimated zero-pressure arterial geometry, (iv) techniques for prestressing of the blood vessel wall, (v) mesh generation techniques for building layers of refined fluid mechanics mesh near the arterial walls, (vi) a special mapping technique for specifying the velocity profile at an inflow boundary with non-circular shape, (vii) a scaling technique for specifying a more realistic volumetric flow rate, (viii) techniques for the projection of fluid–structure interface stresses, (ix) a recipe for pre-FSI computations that improve the convergence of the FSI computations, (x) the Sequentially-Coupled Arterial FSI technique and its multiscale versions, (xi) techniques for calculation of the wall shear stress (WSS) and oscillatory shear index (OSI), (xii) methods for stent modeling and mesh generation, (xiii) methods for calculation of the particle residence time, and (xiv) methods for an estimated element-based zero-stress state for the artery. Here we provide an overview of the special techniques for WSS and OSI calculations, stent modeling and mesh generation, and calculation of the residence time with application to pulsatile ventricular assist device (PVAD). We provide references for some of the other special techniques. With results from earlier computations, we show how these core and special techniques work.

Right Ventricular Assist Device Support After Continuous Flow Left Ventricular Assist Device Implantation: Predicting a Poor Predictor.

Purpose: Demographic, perioperative and late clinical outcomes in patients who require right ventricular assist device (RVAD) support after left ventricular assist device (LVAD) implantation, has not been well described. Predictive tools of RVAD after LVAD are based on univariate models from combined pulsatile and continuous flow (CF) VAD patients. Multivariable models have been inconsistent in predictors elucidated. We aimed to review contemporary CF LVADs with long term follow-up, to determine the predictors of RVAD need after CF LVAD, and the impact on mid and long term survival. Methods: A retrospective review of a single center was done. All HeartMate II CF LVADs (2003-2012) were identified. Patients were stratified by whether they received a RVAD after LVAD implant. Descriptive univariate statistics, multivariate regression and survival analysis were performed. Results: We identified 294 patients; 26 (8.8%) required a RVAD. Mean follow up was 2.5 years (maximum 8 years). Late survival was worse in those who received a RVAD (15% vs 76%, p<0.001). Receiving an RVAD was an independent predictor of mortality (HR 2.4, 95% CI 3.7-40, p<0.001). Patients who required a RVAD had similar demographics and preoperative characteristics, however more likely to be: bridge to transplant (69% vs 46%, p=0.03), intubated pre-operatively (31% vs 12%, p=0.008), on temporary circulatory support preop (27% vs 8%, p=0.09) and had higher preoperative bilirubin and AST. RVAD patients more often required redo sternotomy (69% vs 39%, p=0.003). In-hospital outcomes included longer ventilator support (30+50 vs 9+17 days, p<0.001). Multivariable regression analysis found significant independent predictors of getting a RVAD after LVAD implant to be redo sternotomy (HR 1.5, 95% CI 1.3-9.3, p=0.002) and pre-operative temporary circulatory support (HR 1.3, 95% CI 1.2-9.6, p=0.01). Conclusion: This is the largest series of patients with contemporary CF LVADs and long term follow-up. RVAD requirement after LVAD purports very poor early, mid and long term survival. Redo sternotomy and pre-operative temporary circulatory support were independent predictors of RVAD requirement, which along with univariate variables identified above, may be used to identify and stratify this high risk cohort.