Pulsatile Flow Ventricular Assist Devices Research Articles

Bivalirudin or Unfractionated Heparin for Anticoagulation in Pediatric Patients on Continuous Flow Ventricular Assist Device Support: Single-Center Retrospective Cohort Study

Bivalirudin is a direct thrombin inhibitor that is being increasingly used for anticoagulation in children after ventricular assist device (VAD) implantation. While the data on bivalirudin use in pulsatile flow VADs are growing, reports on its use in patients on continuous flow (CF) VAD as well as comparisons of associated outcomes with unfractionated heparin (UFH) remain limited. Retrospective cohort study. Single tertiary-quaternary referral center. All patients less than 21 years old on CF-VAD support who received bivalirudin or UFH for anticoagulation between the years 2016 and 2020. Not applicable. Clinical characteristics compared between the cohorts included time to target range of anticoagulation, markers of hemolysis, and prevalence of hemocompatibility-related adverse events such as major hemorrhagic complications, ischemic stroke, and pump thrombosis. In 42 unique patients (41 HeartWare HVAD [Medtronic, Minneapolis, MN], one HeartMate 3 LVAD [Abbott Laboratories, Abbott Park, IL]) during the study period, a total of 67 encounters of IV anticoagulation infusions (29 UFH and 38 bivalirudin) were retrospectively reviewed. In comparison with use of UFH, bivalirudin was associated with lesser odds of major bleeding complications (odds ratio [OR], 0.29; 95% CI, 0.09-0.97; p = 0.038). We failed to identify any difference in odds of major thrombotic complications (OR, 2.53; 95% CI, 0.47-13.59; p = 0.450). Eight of the patients (28%) on UFH were switched to bivalirudin due to hemorrhagic or thrombotic complications or inability to achieve therapeutic anticoagulation, while two of the patients (5%) on bivalirudin were switched to UFH due to hemorrhagic complications. Bivalirudin was used for a "washout" in eight cases with concern for pump thrombosis-six had resolution of the pump thrombosis, while two needed pump exchange. Use of bivalirudin for anticoagulation in patients on CF-VAD support was associated with lesser odds of hemorrhagic complications compared with use of UFH. Bivalirudin "washout" was successful in medical management of six of eight cases of possible pump thrombosis.

The use of serotonin reuptake inhibitors increases the risk of bleeding in patients with assist devices

BackgroundBleedings are frequent and dreaded complications in heart failure patients with ventricular assist devices (VAD). Serotonin reuptake inhibitor (SRI) antidepressants are widely used to treat depression in these patients, though they are attributed an increased risk of bleeding due to their modification of hemostasis. Evidence on bleeding risk of VAD patients under SRI medication is scarce and limited. We therefore aimed to assess if SRI use is associated with an elevated bleeding risk in this particularly vulnerable population.MethodsWe analyzed the medical records of 92 VAD patients at the University Heart Center Zurich between September 2004 and April 2018 for the occurrence of bleedings and the concomitant use of an SRI. Bleeding was defined as any type of post-implantation bleeding requiring medical treatment. We performed univariate analyses and linear mixed-effects models, adjusting for baseline clinical characteristics as potential predictors to identify differences in bleeding rates in patients with vs. without SRI intake.ResultsThe cohort comprised 60.9% of patients with a continuous-flow VAD and 39.1% with a pulsatile-flow VAD. A total of 77.2% of patients experienced at least one bleeding incident. Overall, 28.6% of bleedings occurred under SRI therapy. A generalized linear mixed model showed a predictive effect of SRI medication on bleeding rate, independent of VAD type (z = 2.091, p = 0.037).ConclusionsBleeding events in heart failure patients occur frequently after VAD implantation. Patients with SRI medication were at increased risk of bleeding. The indication and use of SRI, therefore, should be considered carefully.

Investigating the cause of hemolysis in patients supported by a pulsatile ventricular assist device.

A survey conducted by Abiomed, Inc. revealed that 10 of 60 patients who received ventricular assistance via the AB5000 ventricular assist device (VAD) experienced hemolysis. The present study was conducted to investigate which factors influence hemolysis under pulsatile-flow VADs such as the AB5000. We compared the specificity of the AB5000 and its driving console with those of the NIPRO-VAD and VCT50χ under severe heart failure conditions using a mock circulatory system with a glycerol water solution. We used the mock circuit with bovine blood to confirm which pump conditions were most likely to cause hemolysis. In addition, we measured the shear velocity using particle image velocimetry by analyzing the seeding particle motion for both the AB5000 and NIPRO-VAD under the same conditions as those indicated in the initial experiment. Finally, we analyzed the correlation between negative pressure, exposure time, and hemolysis by continuously exposing fixed vacuum pressures for fixed times in a sealed device injected with bovine blood. Applying higher vacuum pressure to the AB5000 pump yielded a larger minimum inlet pressure and a longer exposure time when the negative pressure was under - 10mmHg. The plasma-free hemoglobin increased as more negative pressure was driven into the AB5000 pump. Moreover, the negative pressure interacted with the exposure time, inducing hemolysis. This study revealed that negative pressure and exposure time were both associated with hemolysis.

Hemodynamic effects of the human aorta arch with different inflow rate waveforms from the ascending aorta inlet: A numerical study.

Heart failure (HF) is a common disease globally. Ventricular assist devices (VADs) are widely used to treat HF. In contrast to the natural heart, different VADs generate different blood flow waves in the aorta. To explore whether the different inflow rate waveforms from the ascending aorta generate far-reaching hemodynamic influences on the human aortic arch. An aortic geometric model was reconstructed based on computed tomography data of a patient with HF. A total of five numerical simulations were conducted, including a case with the inflow rate waveforms from the ascending aorta with normal physiological conditions, two HF, and two with typical VAD support. The hemodynamic parameters, wall shear stress (WSS), oscillatory shear index (OSI), relative residence time (RRT), and the strength of the helical flow, were calculated. In contrast to the natural heart, numerical simulations showed that HF decreased WSS and induced higher OSI and RRT. Moreover, HF weakened helical flow strength. Pulsatile flow VADs that elevated the WSS, induced some helical flow, while continuous flow VADs could not. HF leads to an adverse hemodynamic environment by decreasing WSS and reducing the helical flow strength. Based upon hemodynamic effects, pulsatile flow VADs may be more advantageous than continuous flow VADs. Thus, pulsatile flow VADs may be a better option for patients with HF.

Right heart failure with left ventricular assist device implantation in children: An analysis of the Pedimacs registry database

The use of ventricular assist device (VAD) in children has increased, but the decision of left VAD (LVAD) vs biventricular support remains a challenge. Children who undergo LVAD placement are at risk for right ventricular failure (RHF), but the incidence has not been described. Analysis was performed for patients <18 years old who underwent durable LVAD placement within the Pedimacs registry (September 19, 2012-February 28, 2017), excluding single ventricle morphology and temporary devices. RHF was defined as the need for right ventriculalr assist device (RVAD) or prolonged inotrope use between 1 week to 1 month and 1 to 3 months. End-points included death, heart transplant (HT), and recovery. A total of 272 durable LVAD were placed of which 37 died on device over 24 month follow-up, primarily from multiorgan failure and neurologic dysfunction. RVAD occurred in 12 children at median 8.5 days, with 9 undergoing HT and 3 dying on device. In patients with only LVAD, RHF was present in 111/207 (55%) between 1 week to 1 month and 28/116 (25%) between 1 and 3 months. Younger age, smaller weight, Intermacs profile 1, chemical paralysis, and pulsatile flow VAD were associated with RHF. RHF was associated with increased risk of death on device at both >1 month (hazard ratio 3.2, 95% CI 1.4-7.7, p = 0.007) and >3 month (hazard ratio 6.9, 95% CI 2-23.1, p = 0.002). In children, RHF is common after durable LVAD implantation, but subsequent RVAD is relatively rare. RHF in children, as indicated by prolonged inotrope support, was associated with an increased risk of death on the device. Whether early RVAD support and higher waitlist status may improve the outcome remains unknown.

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.

Experiencia con una asistencia ventricular pulsátil de larga duración como puente al trasplante cardiaco en adultos

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.Full English text available from:www.revespcardiol.org/en

Concurrent use of continuous and pulsatile flow Ventricular Assist Device on a fontan patient: A simulation study.

The aim of this work is to develop and test a lumped parameter model of the cardiovascular system to simulate the concurrent use of pulsatile (PVAD) and continuous flow (CVAD) ventricular assist device (VAD) on Fontan patients. Echocardiographic and hemodynamic data of five Fontan patients were retrospectively collected and used to simulate the patients' baseline hemodynamics. Then, for each patient, the following assistance modality was simulated for the cavopulmonary and the single ventricle (SV): (a) CVAD for cavopulmonary assistance (RCF) and PVAD assisting the SV (LCF) (RPF + LCF), (b) CVAD assisting SV and PVAD for cavopulmonary assistance (LPF + RCF). The numerical model can well reproduce patients' baseline. The cardiac output increases more importantly in the LCF + RPF configuration (35 vs. 8%). Ventricular volume decreases more evidently in the configuration LCF + RPF (28 vs. 6%), atrial pressure decreases in the LCF + RPF modality (10%), while it slightly increases in the RCF + LPF modality. The pulmonary arterial pressure slightly decreases (increases) in the configuration RCF + LPF (LCF + RPF). Ventricular external work increases in both configurations because of the total increment of the cardiac output. However, artero-ventricular coupling improves in both configurations: RCF + LPF-14%, LCF + RPF-41%. The pulsatility index decreases (increases) by 8% (13.8%) in the configuration LCF + RPF (RCF + LPF). A model could permit us to simulate extreme physiological conditions of the implantation of both CF and PF VAD on the Fontan patient and could permit to choose the proper VAD on the base of patients' condition. The configuration LCF + RPF seems to maximize the hemodynamic benefits.

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.

Outcomes of pediatric patients supported with continuous-flow ventricular assist devices: A report from the Pediatric Interagency Registry for Mechanical Circulatory Support (PediMACS)

Continuous-flow (CF) ventricular assist devices (VADs) have largely replaced pulsatile-flow VADs in adult patients. However, there are few data on CF VADs among pediatric patients. In this study we aimed to describe the overall use, patients' characteristics and outcomes of CF VADs in this population. The Pediatric Interagency Registry for Mechanical Circulatory Support (PediMACS) is a national registry for U.S. Food and Drug Adminstration (FDA)-approved VADs in patients <19 years of age. Patients undergoing placement of durable CF VADs between September 2012 and June 2015 were included and outcomes were compared with those of adults from the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS). CF VADs were implanted in 109 patients at 35 hospitals. The median age at implantation was 15 years (2.8 to 18.9 years) and median weight was 62 kg (range 16 to 141 kg). The underlying disease was cardiomyopathy in 89 (82%) patients. The INTERMACS level at time of implant was Level 1 in 20 (19%), Level 2 in 64 (61%) and Levels 3 to 7 in 21 (20%) patients. Most were implanted as LVADs (n = 102, 94%). Median duration of support was 2.3 months (range <1 day to 28 months). Serious adverse event rates were low, including neurologic dysfunction (early event rate 4.1 per 100 patient-months with 2 late events). Competing outcomes analysis at 6 months post-implant indicated 61% transplanted, 31% alive with device in place and 8% death before transplant. These outcomes compared favorably with the 3,894 adults supported with CF VADs as a bridge to transplant. CF VADs are commonly utilized in older children and adolescents, with excellent survival rates. Further study is needed to understand impact of patient and device characteristics on outcomes in pediatric patients.

Implantation of HeartWare Left Ventricular Assist Device in Pediatric Population

The new-generation continuous-flow left ventricular assist devices (VAD) have dramatically improved clinical outcomes of adult patients with end-stage heart failure in the current era. 1 In the adult population, multiple devices are available as a long-term bridge to transplantation 2 and as destination therapy 1 with low device-related morbidity and mortality. On the contrary, long-term mechanical circulatory support options in the pediatric population have been extremely limited. Pediatric patients with end-stage heart failure have traditionally been supported with extracorporeal membrane oxygenation with dismal success rate for bridge to transplantation owing to extracorporeal membrane oxygenation–related complications. 3 Recent clinical application of the EXCOR pediatric assist device (Berlin Heart), a paracorporeal pulsatile-flow VAD, has substantially improved the survival of the patients who were bridged to transplantation with VAD. 4 Nonetheless, approximately one-third of the patients who are supported with the Berlin Heart have embolic stroke and other major complications. 4 Adult-sized VADs have been used in adolescents and some selected patients with a high rate of bridge to transplantation 5 ; however, the mismatch between device and body sizes precludes routine use of adult-sized VADs in the pediatric population. The HeartWare ventricular assist system (HVAD) (HeartWare, Framingham, MA) is a new-generation, small, centrifugal, continuous-flow pump. This device is designed to be implanted directly into the left ventricle and positioned within the pericardial space without requiring a subdiaphragmatic pocket. The initial clinical trial using HVAD showed 90.7% success rate (transplanted or alive) with reasonable incidence of stroke (12%) in patients who were supported with HVAD, which was equivalent to that of the commercially available devices. 6 HVAD is particularly attractive for the pediatric population because of the small pump size and integrated short inflow cannula, which allows complete intrapericardial implantation. In Canada, HVAD has been implanted since 2010, and the first HVAD implantation was performed in 2011 in The Hospital for Sick Children. Herein, the surgical principles and techniques of HVAD implantation in the pediatric population are discussed.

Paracorporeal ventricular assist device as a bridge to transplant candidacy in the era of implantable continuous-flow ventricular assist device

Ventricular assist devices (VADs) have long been used as bridge to transplant therapy (BTT). Nipro-Toyobo paracorporeal pulsatile-flow VAD (nt-VAD) was the only device available until April 2011, when implantable continuous-flow VADs (cf-VADs) became available. Although cf-VADs are central to BTT, nt-VAD remains a necessary option. We aimed to clarify the role of nt-VAD in an era of increasing cf-VAD use. We retrospectively reviewed patients who underwent VAD implantation at the National Cerebral and Cardiovascular Center from May 2011 to March 2013. Characteristics were compared between the nt-VAD and cf-VAD groups. Twenty-nine patients (mean age 37.7 ± 11.1 years, 23 males) underwent VAD implantation. Fifteen patients initially received nt-VADs, although 4 were converted to cf-VADs. Of these 15 patients, 3 were too small for cf-VADs and 2 needed bilateral ventricular support. The remaining 10 patients received nt-VADs (7 patients at INTERMACS level 1 and 3 at level 2). The nt-VAD group patients had significantly more preoperative mechanical circulatory support and were in a more critical condition before VAD implantation than the cf-VAD group. The 2-year survival rate was not significantly different. Despite the critical conditions of nt-VAD patients, their overall survival is not statistically inferior to that of cf-VAD patients. nt-VAD is a good option as a BTC for the patient with urgent and critical condition.

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.

243 Comparison of Outcomes for Heart Transplantation Following Continuous Versus Pulsatile Flow Ventricular Assist Device Bridging

the treatment of chronic heart failure(CHF) is worldwide tremendously increasing. Therefore, we analyzed the outcome of patients suffering from end-stage-CHF in whom a LVAD(HeartWare-HVAD) was implanted with a newly developed surgical technique. Methods and Materials: Between April,2011 and November,2011 we retrospectively analyzed the data of 19 patients who were operated at our institution with a novel, minimized approach:first, using cardiopulmonary bypass, LVAD pump was inserted through anterolateral thoracotomy and secondly, LVAD-outflowgraft was anastomosed end-to-side to the ascending-aorta through upper-hemisternotomy. Results: In 19 patients a novel, minimized approach for LVAD implantation was used. Mean age of the patient population (17men/2women) was 51.1 13years(range:19-74years). Etiology of heart failure was widely distributed (DCM-10,ICM-6,toxic-CM-1,postpartal-CM-1,Myocarditis-1). One patient died within the first 30days(1/13),none of the patients revealed wound infections(0/19),only one patient right ventricular assist device implantation(RVAD) became necessary to treat the occurrence of perioperative right heart failure(1/19). Finally,all surviving patients(100%) were successfully discharged to rehabilitation-centre. Conclusions: Surgical implantation of centrifugal pumps through this novel, minimized approach is proven to be feasible and associated with several positive effects. Surgical trauma is minimized which leads to reduced complication rates; the pericardium remains closed which protects the RV against over-dilation. In summary, 30-day-mortality for this high risk patient collection remains very low.

257: Determinants of Survival in Patients Bridged to Heart Transplantation with Continuous-Flow Versus Pulsatile-Flow Ventricular Assist Devices

257: Determinants of Survival in Patients Bridged to Heart Transplantation with Continuous-Flow Versus Pulsatile-Flow Ventricular Assist Devices

Development of mechanical circulatory support devices at the University of Tokyo

The development of mechanical circulatory support devices at the University of Tokyo has focused on developing a small total artificial heart (TAH) since achieving 532 days of survival of an animal with a paracorporial pneumatically driven TAH. The undulation pump was invented to meet this purpose. The undulation pump total artificial heart (UPTAH) is an implantable TAH that uses an undulation pump. To date, the UPTAH has been implanted in 71 goats weighting from 39 to 72 kg. The control methods are very important in animal experiments, and sucking control was developed to prevent atrial sucking. Rapid left-right balance control was performed by monitoring left atrial pressure to prevent acute lung edema caused by the rapid increase in both arterial pressure and venous return associated with the animal becoming agitated. Additionally, 1/R control was applied to stabilize the right atrial pressure. By applying these control methods, seven goats survived more than 1 month. The maximum survival period was 63 days. We are expecting to carry out longer term animal experiments with a recent model of TAH. In addition to the TAH, an undulation pump ventricular assist device (UPVAD), which is an implantable ventricular assist device (VAD), has been in development since 2002, based on the technology of the UPTAH. The UPVAD was implanted in six goats; three goats survived for more than 1 month. While further research and development is required to complete the the UPVAD system, the UPVAD has good potential to be realized as an implantable pulsatile-flow VAD.

Quantification of Pulsatility as a Function of Vascular Input Impedance: An In Vitro Study

The physiological benefits of pulsatility generated by ventricular assist device (VAD) support continue to be heavily debated as application of VAD support has been expanded to include destination and recovery therapies. In this study, the relationship between input impedance (Zart) and vascular pulsatility during continuous flow (CF) or pulsatile flow (PF) VAD support was investigated. Hemodynamic waveforms were recorded at baseline failure and with 50%, 75%, and 100% CF or PF VAD support for nine different Zart test conditions (combination of three different resistance and compliance settings) in a mock circulatory system simulating left ventricular failure. High-fidelity hemodynamic pressure and flow waveforms were recorded to calculate mean arterial pressure (MAP), Zart, energy equivalent pressure (EEP), and surplus hemodynamic energy (SHE) as metrics for quantifying vascular pulsatility. MAP and EEP were elevated with increasing resistance whereas SHE was reduced with increasing compliance. Vascular pulsatility was restored with increasing PF VAD support, but diminished by up to 90% with increasing CF VAD support. The nonpulsatile energy component (MAP) of the pressure waveform is dependent on resistance whereas the pulsatile energy component (SHE) is dependent on compliance. The impact of Zart and vascular pulsatility on patient recovery with VAD support warrants further investigation.

A Computer Model of the Pediatric Circulatory System for Testing Pediatric Assist Devices

Lumped parameter computer models of the pediatric circulatory systems for 1- and 4-year-olds were developed to predict hemodynamic responses to mechanical circulatory support devices. Model parameters, including resistance, compliance and volume, were adjusted to match hemodynamic pressure and flow waveforms, pressure-volume loops, percent systole, and heart rate of pediatric patients (n = 6) with normal ventricles. Left ventricular failure was modeled by adjusting the time-varying compliance curve of the left heart to produce aortic pressures and cardiac outputs consistent with those observed clinically. Models of pediatric continuous flow (CF) and pulsatile flow (PF) ventricular assist devices (VAD) and intraaortic balloon pump (IABP) were developed and integrated into the heart failure pediatric circulatory system models. Computer simulations were conducted to predict acute hemodynamic responses to PF and CF VAD operating at 50%, 75% and 100% support and 2.5 and 5 ml IABP operating at 1:1 and 1:2 support modes. The computer model of the pediatric circulation matched the human pediatric hemodynamic waveform morphology to within 90% and cardiac function parameters with 95% accuracy. The computer model predicted PF VAD and IABP restore aortic pressure pulsatility and variation in end-systolic and end-diastolic volume, but diminish with increasing CF VAD support.

ACUTE HEMODYNAMIC AND PRESSURE-VOLUME RESPONSES TO CONTINUOUS AND PULSATILE ASSIST IN DIMINISHED CARDIAC FUNCTION CALF MODEL

Acute hemodynamic and left ventricular pressure-volume responses to continuous flow (CF) and pulsatile flow (PF) ventricular assist devices (VAD) at 50%, 75%, and 100% bypass flow rates were investigated in calves (n=8) with diminished cardiac function (DCF). A clinically relevant DCF model (MAP = 65–75 mmHg, CO = 6–8 L/m, and LAP = 12–15 mmHg) was induced by a single oral dose of Monensin. CF and PF VAD were implanted via ventricular apical and brachiocephallic cannulae. Calves were instrumented with catheters for simultaneous measurement of aortic root pressure (AoP), left ventricular pressure (LVP) and volume (LVV), and aortic, brachiocephallic artery, coronary artery (CoF), and VAD flow probes. PF and CF VAD increased cardiac output, mean AoP, and mean CoF and reduced left ventricular work with increasing levels of VAD support. CF VAD decreased AoP pulsatility with increasing levels of support while PF VAD maintained physiologic pulsatility. Although both CF and PF VAD reduced LVV toward normal, the variation in end-systolic and end-diastolic volume (ΔV) for CF is less with increasing levels of VAD support compared to PF VAD which maintains a normal physiologic ΔV. Though both CF VAD and PF VAD increased diastolic CoF, the augmentation of the diastolic CoF with PF VAD was higher in comparison to CF VAD. The differences in vascular pulsatility, ventricular volume, and myocardial perfusion between VAD type (CF and PF) and level of VAD support may impact device selection, operation, and the potential for myocardial recovery.

A COMPUTER MODEL OF THE PEDIATRIC CIRCULATORY SYSTEM FOR TESTING PEDIATRIC ASSIST DEVICES

To predict hemodynamic responses of mechanical circulatory support devices in the pediatric circulation, computer models of the circulatory systems for one and four year olds were developed. Model parameters were adjusted to match the hemodynamic pressure and flow waveforms, percent systole, and heart rate from 6 pediatric patients with normal ventricles. Left ventricular failure was modeled by adjusting the time-varying compliance curve of the left heart to produce aortic pressures (AoP) and cardiac outputs (CO) consistent with clinical observations. Models of a continuous flow (CF) and pulsatile flow (PF) pediatric ventricular assist device (VAD) and intra aortic balloon pump (IABP) were developed and integrated to the model. Simulations were conducted to predict acute hemodynamic responses to PF and CF VAD operating at 50%, 75% and 100% support and 2.5 and 5 ml IABP. PF VAD, CF VAD, and IABP increased CO, mean AoP and mean coronary flow (CoF) and reduced left ventricular work (LVEW) with increasing levels of support. CF VAD decreased aortic pressure pulsatility with increasing levels of support while PF VAD and IABP maintained physiologic aortic pulse pressures. Although both CF and PF VAD reduce ventricular volume toward the normal range, the variation in end-systolic and end-diastolic volume (ΔV) for CF diminishes with increasing levels of VAD support compared to PF VAD which maintains a normal physiologic ΔV. Computer simulation may aid in development of pediatric devices and control strategies.