Ventricular Assist Device Speed Research Articles

Remote Monitoring of Pediatric VAD Patients: Early Recognition for Improved Management

<h3>Purpose</h3> Over 50% of pediatric durable, discharge-eligible ventricular assist device (VAD) patients are discharged thereby transitioning high-risk patients to outpatient clinics. To enhance management of these patients, our center developed VAD specific content for a home monitoring iPad application (App). We hypothesized that remote monitoring via App + CardioMems Pulmonary Artery Pressure (CMEMS) could reduce risk among outpatient pediatric VAD patients. <h3>Methods</h3> VAD App parameters were developed by our VAD APRN and App company with existing technology for cardiac transplant patients. Manual data entry including VAD speed, output, power, driveline exit site (DLES) picture, residual heart failure symptoms, bleeding, and fluid status, is performed by the patient. The VAD team contacts patient and family if data has not been entered in 2+ days as these platforms are intended for daily trending to enhance remote monitoring. Continuous refinements have been made to the content based on utilization assessment by VAD team and patients. <h3>Results</h3> 13 patients have utilized the VAD App since 2019 for a total of 2519 VAD support days. Median age was 14 years (range 5-16), 7/13 had cardiomyopathy, 10 were supported on HeartMate3 and 3 with HeartWare. Of the 13 patients monitored, 7 were transplanted, 3 are alive and supported, and 2 have died (both destination therapy patients). AE's in this group represent 6 driveline related infections, 2 right heart failures, 4 arrhythmias. We have used CMEMS on 3/13 patients for 457 days of CMEMS monitoring. CMEMS remote monitoring helped recognize two separate episodes of ventricular tachycardia in a patient, allowing for early intervention. Frequent review of App data and CMEMS measurements allows for medical optimization, including diuretic and fluid management without additional clinic and inpatient encounters. Serial image monitoring of DLES directed care for early outpatient intervention of infection. <h3>Conclusion</h3> Remote monitoring in pediatric VAD patients provides more data collection, which augments care of these high-risk patients. Combined use of the App and CMEMS allows for improved optimization of heart failure medications and early recognition of high-risk events. Future study will investigate the impact on hospital admissions and acute heart failure exacerbations.

Does Cardiac Catheterization Facilitate Hemodynamic Optimization of Pediatric Patients on Continuous-Flow Ventricular Assist Devices?

Understanding optimal ventricular assist device (VAD) parameters for pediatric patients is valuable given the inherent issue of patient-device size mismatch and heterogeneous cardiac anatomy in children. We evaluated our center's experience of continuous-flow VAD (CF-VAD) optimization using cardiac catheterization. We performed a retrospective analysis of all patients on CF-VAD support who underwent hemodynamic heart catheterization from 2013 to 2018. Fifteen patients had 16 hemodynamic catheterizations performed. The indications for hemodynamic optimization by catheterization included clinical signs of heart failure while on CF-VAD (9 of 16, 56%), pretransplant evaluation of pulmonary hypertension (2 of 16, 13%), or assessment of myocardial recovery (5 of 16, 31%). The median age at catheterization was 12 years (interquartile range: 8-16). Median baseline speed of device was 2333 ± 253 rotations per minute. The goal was to find the speed at which optimal hemodynamics were achieved, defined by low wedge pressure with an acceptable central venous pressure. Of the 16 catheterizations, there were 9 (56%) speed increases to achieve optimal hemodynamics and 5 (33%) speed decreases for hemodynamic optimization or for potential explant. The speed was not changed in 2 (13%) catheterizations as the patients were determined to be at an optimal hemodynamic state. Overall, VAD settings were optimized in 75% (14 of 16) of hemodynamic catheterizations. There were no adverse events related to catheterization. Thus, we conclude that catheterization-based hemodynamic assessment is safe and effective for optimizing VAD speed and provides guidance on medical management in children supported on CF-VAD.

Rotary Ventricular Assist Device Control With a Fiber Bragg Grating Pressure Sensor

Current ventricular assist devices (VADs) are rotary blood pumps used to treat end-stage heart failure. VADs are operated at a constant speed that is manually adjusted by a clinician based on the patient's cardiac demand during routine medical examinations. VADs operated at a constant speed have inadequate passive flow regulation due to the inherent mechanical pressure-flow characteristics of the pump; this can lead to harmful situations where the VAD is overpumping or underpumping. Typically, patients on long-term VAD support are discharged to an outpatient setting where the VAD speed can remain the same for weeks or months at a time, impacting patient safety and quality of life. Previously, physiological controllers for VADs have been proposed, which automatically adjust VAD speed to meet patient cardiac demand. Clinical implementation of physiological control is currently hindered by the lack of clinically available, implantable, and continuous hemodynamic sensors. This study describes the physiological control of a VAD using a fiber Bragg grating (FBG) sensor previously developed for measuring VAD inlet pressure. The FBG sensor was used as a feedback to a Starling-like physiological controller, and the control quality was compared against the same controller with feedback from a nonimplantable industrial pressure sensor (Omega sensor). Experiments were conducted in a bench-top cardiovascular simulator under various simulated patient scenarios. The average steady-state difference in VAD flow across all experiments was 0.1 L/min with a maximum difference of -0.4 L/min. Similarly, the average steady-state difference in left ventricular end-diastolic pressure was 0.02 mmHg with a maximum difference of -0.2 mmHg. The clinically insignificant differences found between the two feedback methods indicate that the FBG pressure sensor is viable for the physiological control of VADs.

Designing an Active Valvulated Outflow Conduit for a Continuous-Flow Left Ventricular Assist Device to Increase Pulsatility: A Simulation Study.

The purpose of this work was to investigate, using a lumped parameter model, the feasibility of increasing the pulsatility of a continuous-flow ventricular assist device (VAD) by implanting an active valvulated outflow cannula. A lumped parameter model was adopted for this study. VAD was modeled, starting from its pressure-flow characteristics. The valvulated outflow conduit was modeled as an active resistance described by a square function. Starting from pathologic condition, the following simulations were performed: VAD, VAD and valvulated outflow conduit in copulsation and counterpulsation with different ratios between the VAD valve opening rate and the heart rate, and asynchrony work with the heart with different VAD valve opening intervals. The copulsation 1:1 configuration and the asynchrony 0.3s-close-0.7s-open configurations permit to maximize the hemodynamic benefits provided by the presence of the active VAD outflow valvulated conduit providing an increase of arterial pulsatility from 1.86% to 14.98% without the presence of left ventricular output. The presence of the active VAD valve in the outflow conduit causes a decrement of the left ventricular unloading and of VAD flow and, that can be counteracted by increasing the VAD speed without affecting arterial pulsatility. The valvulated outflow tube provides an increase in arterial pulsatility; it can be driven in different working modality and can be potentially applicable to all types of VADs. However, the valvulated outflow conduit causes a decrement of left ventricular unloading and of the VAD flow that can be counteracted, increasing the VAD speed.

In vitro evaluation of an adaptive Starling-like controller for dual rotary ventricular assist devices.

Rotary ventricular assist devices (VADs) operated clinically under constant speed control (CSC) cannot respond adequately to changes in patient cardiac demand, resulting in sub-optimal VAD flow regulation. Starling-like control (SLC) of VADs mimics the healthy ventricular flow regulation and automatically adjusts VAD speed to meet varying patient cardiac demand. The use of a fixed control line (CL - the relationship between ventricular preload and VAD flow) limits the flow regulating capability of the controller, especially in the case of exercise. Adaptive SLC (ASLC) overcomes this limitation by allowing the controller to adapt the CL to meet a diverse range of circulatory conditions. This study evaluated ASLC, SLC and CSC in a biventricular supported mock circulation loop under the simulated conditions of exercise, sleep, fluid loading and systemic hypertension. Each controller was evaluated on its ability to remain within predefined limits of VAD flow, preload, and afterload. The ASLC produced superior cardiac output (CO) during exercise (10.1 L/min) compared to SLC (7.3 L/min) and CSC (6.3 L/min). The ASLC produced favourable haemodynamics during sleep, fluid loading and systemic hypertension and could remain within a predefined haemodynamic range in three out of four simulations, suggesting improved haemodynamic performance over SLC and CSC.

Stop the Leak! Transcatheter Aortic Valve Replacement in Pediatric VAD Patient

Introduction Recognition of ventricular assist device (VAD) complications such as aortic insufficiency (AI) are important to optimize long-term management. We highlight a case of the treatment of severe AI in a pediatric continuous flow (CF) VAD patient using transcatheter aortic valve replacement (TAVR). Case Report A 9-year-old male with congenitally corrected transposition of the great arteries and pulmonary atresia underwent staged surgical palliation including a Mustard and Rastelli operation. He developed severe left ventricular (LV) dysfunction with refractory heart failure and underwent implant of a HeartWare (Medtronic, Minneapolis MN) in the morphologic LV on the right side at almost 5 years of age (weight 13.7 kg, BSA 0.64 m2). His waitlist time was prolonged due to significant allosensitization. After 4 years on support, clinical signs of congestive heart failure (CHF) developed and BNP rose (1000 pg/mL) despite optimal VAD performance. Cardiac catheterization showed severe AI and pulmonary hypertension. Mean pulmonary arterial pressure was 40 mmHg with pulmonary vascular resistance of 8.5 WUm2 that was responsive to pulmonary vasodilators. The pulmonary hypertension was attributed to the AI. To avoid a difficult redo sternotomy, TAVR was deemed the optimal way to replace his aortic valve. He underwent catheterization and a 29 mm Edwards SAPIEN 3 valve (Edwards Lifesciences, Irvine CA) was placed in the aortic valve position via right carotid artery cut down using a 21 French sheath. The VAD speed was reduced to 1800 RPM and rapid ventricular pacing allowed for stabilization during valve deployment. Post TAVR, angiography showed resolution of AI with only mild perivalvar leak around the aortic valve. After discharge, he was noted to have a transient rise in lactate dehydrogenase from baseline and increased bruising due to unclear etiology. Within 5 months of his TAVR, his diuretics were weaned with marked improvement in his BNP and resolution of his CHF. Summary AI is a significant complication of long-term CF VAD support that can lead to detrimental hemodynamics and worsening CHF. TAVR may be a reasonable therapy to mitigate AI in high-risk children.

Small Left Ventricular Size Is an Independent Risk Factor for Ventricular Assist Device Thrombosis.

The prevalence of ventricular assist device (VAD) therapy has continued to increase due to a stagnant donor supply and growing advanced heart failure (HF) population. We hypothesize that left ventricular (LV) size strongly influences biocompatibility and risk of thrombosis. Unsteady computational fluid dynamics (CFD) was used in conjunction with patient-derived computational modeling and virtual surgery with a standard, apically implanted inflow cannula. A dual-focus approach of evaluating thrombogenicity was employed: platelet-based metrics to characterize the platelet environment and flow-based metrics to investigate hemodynamics. Left ventricular end-diastolic dimensions (LVEDds) ranging from 4.5 to 6.5 cm were studied and ranked according to relative thrombogenic potential. Over 150,000 platelets were individually tracked in each LV model over 15 cardiac cycles. As LV size decreased, platelets experienced markedly increased shear stress histories (SHs), whereas platelet residence time (RT) in the LV increased with size. The complex interplay between increased SH and longer RT has profound implications on thrombogenicity, with a significantly higher proportion of platelets in small LVs having long RT times and being subjected to high SH, contributing to thrombus formation. Our data suggest that small LV size, rather than decreased VAD speed, is the primary pathologic mechanism responsible for the increased incidence of thrombosis observed in VAD patients with small LVs.

Exercise physiology with a left ventricular assist device: Analysis of heart-pump interaction with a computational simulator.

Patients with a Ventricular Assist Device (VAD) are hemodynamically stable but show an impaired exercise capacity. Aim of this work is to identify and to describe the limiting factors of exercise physiology with a VAD. We searched for data concerning exercise in heart failure condition and after VAD implantation from the literature. Data were analyzed by using a cardiorespiratory simulator that worked as a collector of inputs coming from different papers. As a preliminary step the simulator was used to reproduce the evolution of hemodynamics from rest to peak exercise (ergometer cycling) in heart failure condition. Results evidence an increase of cardiac output of +2.8 l/min and a heart rate increase to 67% of the expected value. Then, we simulated the effect of a continuous-flow VAD at both rest and exercise. Total cardiac output increases of +3.0 l/min (+0.9 l/min due to the VAD and +2.1 l/min to the native ventricle). Since the left ventricle works in a non-linear portion of the diastolic stiffness line, we observed a consistent increase of pulmonary capillary wedge pressure (from 14 to 20 mmHg) for a relatively small increase of end-diastolic volume (from 182 to 189 cm3). We finally increased VAD speed during exercise to the maximum possible value and we observed a reduction of wedge pressure (-4.5 mmHg), a slight improvement of cardiac output (8.0 l/min) and a complete unloading of the native ventricle. The VAD can assure a proper hemodynamics at rest, but provides an insufficient unloading of the left ventricle and does not prevent wedge pressure from rising during exercise. Neither the VAD provides major benefits during exercise in terms of total cardiac output, which increases to a similar extend to an unassisted heart failure condition. VAD speed modulation can contribute to better unload the ventricle but the maximal flow reachable with the current devices is below the cardiac output observed in a healthy heart.

Exercise capacity in ventricular assist device patients: clinical relevance of pump speed and power.

Patients with ventricular assist device (VAD) show a limited exercise capacity. The aim of this work is to investigate whether VAD speed increase has an effect on exercise performance in the upright position. Fourteen patients implanted with a HeartMate II underwent two cardiopulmonary maximal exercise tests on an upright bicycle ergometer the same day. During one test, VAD speed was set as constant (CONST) and during the other test, VAD speed was increased by 200 rpm each minute (INCR). No statistical differences were found between the two tests in terms of maximum heart rate, peak oxygen uptake, peak minute ventilation, ventilation efficiency slope and arterial blood pressure. Patients' fatigue perception, measured with a Borg scale, was similar between the two tests over the entire group (15 ± 1 for both CONST and INCR). VAD flow increased from 4.5 ± 0.7 to 6.0 ± 1.0 l/min during CONST and to 7.6 ± 1.4 l/min during INCR. Four patients experienced an easier cycling during INCR, and the other patients noticed no difference. One patient had a suction event during INCR and another had non-sustained ventricular tachycardia at peak exercise. A negative correlation was found between the rate of increase in VAD power during exercise and peak oxygen uptake. Although VAD speed increase provided an additional pump flow of 1.6 l/min at peak exercise, no significant objective and subjective benefits on patients' exercise performance were observed. Finally, VAD power could be a useful parameter to monitor patients during exercise.

In Vivo Evaluation of Active and Passive Physiological Control Systems for Rotary Left and Right Ventricular Assist Devices.

Preventing ventricular suction and venous congestion through balancing flow rates and circulatory volumes with dual rotary ventricular assist devices (VADs) configured for biventricular support is clinically challenging due to their low preload and high afterload sensitivities relative to the natural heart. This study presents the in vivo evaluation of several physiological control systems, which aim to prevent ventricular suction and venous congestion. The control systems included a sensor-based, master/slave (MS) controller that altered left and right VAD speed based on pressure and flow; a sensor-less compliant inflow cannula (IC), which altered inlet resistance and, therefore, pump flow based on preload; a sensor-less compliant outflow cannula (OC) on the right VAD, which altered outlet resistance and thus pump flow based on afterload; and a combined controller, which incorporated the MS controller, compliant IC, and compliant OC. Each control system was evaluated in vivo under step increases in systemic (SVR ∼1400-2400 dyne/s/cm(5) ) and pulmonary (PVR ∼200-1000 dyne/s/cm(5) ) vascular resistances in four sheep supported by dual rotary VADs in a biventricular assist configuration. Constant speed support was also evaluated for comparison and resulted in suction events during all resistance increases and pulmonary congestion during SVR increases. The MS controller reduced suction events and prevented congestion through an initial sharp reduction in pump flow followed by a gradual return to baseline (5.0 L/min). The compliant IC prevented suction events; however, reduced pump flows and pulmonary congestion were noted during the SVR increase. The compliant OC maintained pump flow close to baseline (5.0 L/min) and prevented suction and congestion during PVR increases. The combined controller responded similarly to the MS controller to prevent suction and congestion events in all cases while providing a backup system in the event of single controller failure.

Use of Ventricular Assist Device in Univentricular Physiology: The Role of Lumped Parameter Models.

Failing single-ventricle (SV) patients might benefit from ventricular assist devices (VADs) as a bridge to heart transplantation. Considering the complex physiopathology of SV patients and the lack of established experience, the aim of this work was to realize and test a lumped parameter model of the cardiovascular system, able to simulate SV hemodynamics and VAD implantation effects. Data of 30 SV patients (10 Norwood, 10 Glenn, and 10 Fontan) were retrospectively collected and used to simulate patients' baseline. Then, the effects of VAD implantation were simulated. Additionally, both the effects of ventricular assistance and cavopulmonary assistance were simulated in different pathologic conditions on Fontan patients, including systolic dysfunction, diastolic dysfunction, and pulmonary vascular resistance increment. The model can reproduce patients' baseline well. Simulation results suggest that the implantation of VAD: (i) increases the cardiac output (CO) in all the three palliation conditions (Norwood 77.2%, Glenn 38.6%, and Fontan 17.2%); (ii) decreases the SV external work (SVEW) (Norwood 55%, Glenn 35.6%, and Fontan 41%); (iii) increases the mean pulmonary arterial pressure (Pap) (Norwood 39.7%, Glenn 12.1%, and Fontan 3%). In Fontan circulation, with systolic dysfunction, the left VAD (LVAD) increases CO (35%), while the right VAD (RVAD) determines a decrement of inferior vena cava pressure (Pvci) (39%) with 34% increment of CO. With diastolic dysfunction, the LVAD increases CO (42%) and the RVAD decreases the Pvci. With pulmonary vascular resistance increment, the RVAD allows the highest CO (50%) increment with the highest decrement of Pvci (53%). The single ventricular external work (SVEW) increases (decreases) increasing the VAD speed in cavopulmonary (ventricular) assistance. Numeric models could be helpful in this challenging and innovative field to support patients and VAD selection to optimize the clinical outcome and personalize the therapy.

246 * A MONITORING AND PHYSIOLOGICAL CONTROL SYSTEM FOR DETERMINING AORTIC VALVE CLOSING

Objectives: Accurate monitoring and assessment of the residual cardiac function of a patient supported by a ventricular assist device (VAD) is critical for better patient management and potential weaning. Information regarding the VAD speed at which the aortic valve remains closed can assist clinicians to maintain appropriate unloading, reduce the risk of aortic insufficiency and potentially reduce the risk of aortic leaflet fusion. Methods: A pressure sensor implanted in the inlet cannula determines the left ventricular (LV) pressure. The area of the LV pressure and motor power is calculated for each heart beat. A feedback signal is monitored at high speed and low speed to determine the change in the system. Small amplitude (<300 rpm) and low frequency (<0.1 Hz) square wave changes to the VAD speed are made. Results: Ten ovine trials have been completed with the DP3 pump (LV to aortic cannulation). The feedback variable (pressure power area) proved to have a peak at the speed of aortic valve closure The gradient (Δ pressure power area) could be measured by using the square wave speed modulation. In both the baseline and beta blocked heart the zero-crossing of gradient occurred at the aortic closure speed. Conclusions: Feedback gives a definite peak around aortic valve closure point and uses pump speed modulation for more accuracy; there is no sensitivity to sensor drift or haematocrit changes, and it provides noninvasive, continuous measurement.

B-Type Natriuretic Peptide Guided Therapy Reduces Length of Hospital Stay Post Left Ventricular Assist Device Implantation

B-Type Natriuretic Peptide Guided Therapy Reduces Length of Hospital Stay Post Left Ventricular Assist Device Implantation

Left Ventricle Afterload Impedance Control by an Axial Flow Ventricular Assist Device: A Potential Tool for Ventricular Recovery

Ventricular assist devices (VADs) are increasingly used for supporting blood circulation in heart failure patients. To protect or even to restore the myocardial function, a defined loading of the ventricle for training would be important. Therefore, a VAD control strategy was developed that provides an explicitly definable loading condition for the failing ventricle. A mathematical model of the cardiovascular system with an axial flow VAD was used to test the control strategy in the presence of a failing left ventricle, slight physical activity, and a recovering scenario. Furthermore, the proposed control strategy was compared to a conventional constant speed mode during hemodynamic changes (reduced venous return and arterial vasoconstriction). The physiological benefit of the control strategy was manifested by a large increase in the ventricular Frank-Starling reserve and by restoration of normal hemodynamics (5.1 L/min cardiac output at a left atrial pressure of 10 mmHg vs. 4.2 L/min at 21 mmHg in the unassisted case). The control strategy automatically reduced the pump speed in response to reduced venous return and kept the pump flow independent of the vasoconstriction condition. Most importantly, the ventricular load was kept stable within 1%, compared to a change of 75% for the constant speed. As a key feature, the proposed control strategy provides a defined and adjustable load to the failing ventricle by an automatic regulation of the VAD speed and allows a controlled training of the myocardium. This, in turn, may represent a potential additional tool to increase the number of patients showing recovery.

Total Heart Replacement with Dual Centrifugal Ventricular Assist Devices

In an ovine feasibility study, we implanted two HeartMate-III centrifugal ventricular assist devices (VADs) for total heart replacement. With cardiopulmonary bypass support, both ventricles were transected at the atrioventricular groove, preserving a rim of ventricular tissue. The atrioventricular valves were excised, and the aorta and pulmonary artery were transected above the ventriculoarterial valves. An interatrial septal window was created by excising the foramen ovale. The VADs' sewing rings were attached to the left and right ventricular remnants, respectively. Outflow grafts were anastomosed to the aorta and pulmonary artery. The left VAD operated continuously at 4,500 rpm. Right VAD speed increased from 2,000 to 4,500 rpm in 500 rpm increments. Outflow graft flow, pressure, oxygen saturation, and shunt direction were recorded. The pulmonary artery to aortic ratio of flow and pressure increased from 0.26 and 0.15 (at 2,000 rpm) to 1.21 and 0.53, respectively (at 4,500 rpm). The interatrial shunt, which was right to left at lower right VAD speeds, progressed to bidirectional, then to left dominant as right VAD speed increased. Outflow-graft oxygen saturation was reflective of the shunt direction. In this acute experiment, total heart replacement with continuous flow VADs satisfactorily balanced left and right ventricular flows and preserved the physiologic circulatory response.