HeartWare Left Ventricular Assist Device Exercise Hemodynamics With Speed Adjustment Based on Left Ventricular Filling Pressures

Functional capacity remains limited in heart failure patients with left ventricular assist devices (LVADs) due to fixed pump speed and inability to offload the left ventricle adequately. We hypothesized that manually adjusting LVAD speed during exercise based on pulmonary capillary wedge pressures would increase total cardiac output and maximal oxygen consumption. Two participants with a HeartWare LVAD underwent an invasive ramp study at rest followed by an invasive cardiopulmonary stress test exercising in two randomized phases: fixed speed and adjusted speed. In the latter phase, speed was adjusted every 1 minute during exercise at ±20 rpm/1 mm Hg change from baseline pulmonary capillary wedge pressure. There was no difference in maximal oxygen consumption between the two phases, with a modest increase in total cardiac output during speed adjustment. Filling pressures were initially controlled during speed adjustment until speed was capped at 4,000 rpm, at which point filling pressures increased. Blood pressure was variable. The pressure across the head of the pump (ΔP) was higher with speed adjustment. Contrary to our hypothesis, LVAD speed adjustment during exercise did not improve total cardiac output and functional capacity. This variable response may be attributed to the native cardiac reserve and baroreceptor response; however, additional studies are needed.

In-silico hemodynamic ramp testing of ventricular assist device implanted patients using acausal cardiovascular-VAD modeling

BACKGROUND

While cardiovascular system and mechanical circulatory support devices are efficiently model the effect of disease and assistance, they can also lend valuable insights into clinical procedures. This study demonstrates the use of a CVS-VAD model for an invasive procedure; hemodynamic ramp testing, in-silico.

METHODS

The CVS model is developed using validated models in literature, using Simscape™. An analytically derived pump model is calibrated for the HeartWare VAD. Dilated cardiomyopathy is used as an illustrative example of heart failure, and heart failure patients are created virtually by calibrating the model with requisite disease parameters obtained from published patient data. A clinically applied ramp study protocol is adopted whereby speed optimization is performed following clinically accepted hemodynamic normalization criteria. Trends in hemodynamic variables in response to pump speed increments are obtained. Optimal speed ranges are obtained for the three virtual patients based on target values of central venous pressure (CVP), pulmonary capillary wedge pressure (PCWP), cardiac output (CO), and mean arterial pressure (MAP) for hemodynamic stabilization.

RESULTS

Appreciable speed changes in the mild case (300 rpm), slight changes in the moderate case (100 rpm), and no changes in the simulated severe case are possible.

CONCLUSION

The study demonstrates a novel application of cardiovascular modeling using an open-source acausal model, which can be potentially beneficial for medical education and research.

Exercise Performance and Quality of Life of Left Ventricular Assist Device Patients After Long-Term Outpatient Cardiac Rehabilitation

PURPOSE

Exercise performance and quality of life (QoL) of left ventricular assist device (LVAD) patients improve after early cardiac rehabilitation (CR). The purpose of this study was to examine the efficacy of multiprofessional long term phase 3 outpatient CR, and whether cardiopulmonary exercise testing (CPX) and 6-min walk testing (6MWT) post-LVAD implantation predict hospital readmission.

METHODS

This retrospective observational cohort study included 29 LVAD patients (58.6 ± 7.7 yr, female: 13.8%, body mass index: 29.4 ± 3.3 kg/m 2 ). Functional performance tests (CPX, 6MWT, sit-to-stand test), QoL, and psychological surveys (Kansas City Cardiomyopathy Questionnaire, hospital anxiety and depression scale, and Control Convictions about Disease and Health [KKG]) were performed at baseline and at the end of CR.

RESULTS

The CR was initiated at a median (IQR) of 159 (130-260) d after LVAD implantation for a duration of 340 (180-363) d with 46.8 ± 23.2 trainings. The 6MWT (408.4 ± 113.3 vs 455.4 ± 115.5 m, P = .003) and sit-to-stand test (16.7 ± 6.9 vs 19.0 ± 5.3 repetitions, P = .033) improved, but relative peak oxygen uptake (V˙ o2peak : 9.4 [8.2-14.4] vs 9.3 [7.8-13.4] mL/min/kg, P = .57) did not change. Using receiver operating characteristic curve analysis, baseline V˙ o2peak values were associated with readmission 1-yr after CR onset (C-statistic = 0.88) with a cutoff value of V˙ o2peak < 9.15 mL/min/kg (100% sensitivity, 78% specificity, P < .001). The Kansas City Cardiomyopathy Questionnaire self-efficacy and knowledge (+6.3 points), QoL (+5.0 points), and social limitation (+7.1 points) demonstrated clinically important changes. In addition, the hospital anxiety and depression scale showed a significant reduction in anxiety (4.6 ± 3.2 vs 2.6 ± 2.4, P = .03).

CONCLUSIONS

Long-term CR is safe and LVAD outpatients showed improvement of QoL, anxiety, and submaximal exercise performance. In addition, V˙ o2peak and 6MWT have prognostic value for readmission.

Echo-guided left ventricular assist device speed optimisation for exercise maximisation

Objective

Current generation left ventricular assist devices (LVADs) operate with a fixed rotation speed and no automated speed adjustment function. This study evaluates the concept of physiological pump speed optimisation based on aortic valve opening (AVO) imaging during a cardiopulmonary exercise test (CPET).

Methods

This prospective crossover study (NCT05063006) enrolled patients with implanted third-generation LVADs with hydrodynamic bearing. After resting speed optimisation, patients were randomised to a fixed-modified speed or modified-fixed speed CPET sequence. Fixed speed CPET maintained baseline pump settings. During the modified speed CPET, the LVAD speed was continuously altered to preserve periodic AVO.

Results

We included 22 patients, the mean age was 58.4±7 years, 4.5% were women and 54.5% had ischaemic cardiomyopathy. Exertional AVO assessment was feasible in all subjects. Maintaining periodic AVO allowed to safely raise the pump speed from 2900 (IQR 2640–3000) to 3440 revolutions per minute (RPM) (IQR 3100–3700; p<0.001). As a result, peak oxygen consumption increased from 11.1±2.4 to 12.8±2.8 mL/kg/min (p<0.001) and maximum workload from 1.1 (IQR 0.9–1.5) to 1.2 W/kg (IQR 0.9–1.7; p=0.028). The Borg scale exertion level decreased from 15.2±1.5 to 13.5±1.2 (p=0.005).

Conclusions

Transthoracic AVO imaging is possible during CPETs in patients with LVAD. Dynamic echo-guided pump speed adjustment based on the AVO improves exercise tolerance and augments peak oxygen consumption and maximum workload.

Patient-Specific Modelling and Parameter Optimisation to Simulate Dilated Cardiomyopathy in Children

PURPOSE

Lumped parameter modelling has been widely used to simulate cardiac function and physiological scenarios in cardiovascular research. Whereas several patient-specific lumped parameter models have been reported for adults, there is a limited number of studies aiming to simulate cardiac function in children. The aim of this study is to simulate patient-specific cardiovascular dynamics in children diagnosed with dilated cardiomyopathy, using a lumped parameter model.

METHODS

Patient data including age, gender, heart rate, left and right ventricular end-systolic and end-diastolic volumes, cardiac output, systolic and diastolic aortic pressures were collected from 3 patients at Great Ormond Street Hospital for Children, London, UK. Ventricular geometrical data were additionally retrieved from cardiovascular magnetic resonance images. 23 parameters in the lumped parameter model were optimised to simulate systolic and diastolic pressures, end-systolic and end-diastolic volumes, cardiac output and left and right ventricular diameters in the patients using a direct search optimisation method.

RESULTS

Difference between the haemodynamic parameters in the optimised cardiovascular system models and clinical data was less than 10%.

CONCLUSION

The simulation results show the potential of patient-specific lumped parameter modelling to simulate clinical cases. Modelling patient specific cardiac function and blood flow in the paediatric patients would allow us to evaluate a variety of physiological scenarios and treatment options.

Exercise capacity following ventricular assist device implantation via thoracotomy with outflow cannula anastomosis to the descending aorta

Left ventricular assist device (LVAD) implantation via left lateral thoracotomy with outflow cannula anastomosis to the descending aorta is an alternative technique that avoids anterior mediastinal planes and requires a single incision. This study compares changes in exercise capacity following LVAD implantation with outflow cannula anastomosis to the descending aorta versus ascending aorta. Adult patients who received a continuous flow centrifugal LVAD implantation and completed both pre- and postimplantation cardiopulmonary exercise tests (CPETs) and or 6-minute walk tests (6MWT) were included. Change in CPET parameters (maximum oxygen intake: vO₂ max, oxygen uptake efficiency ratio: OUES, ventilatory efficiency ratio: vE/vCO₂ Slope) and 6MWT distance were compared between ascending and descending aorta anastomosis groups. Ascending and descending aorta anastomosis cohorts included 59 and 14 patients, respectively. Pre- and postimplantation CPETs were performed 63 ± 12 days before and 216 ± 17 days following implantation. The improvement in CPET parameters (vO₂ max, OUES, vE/vCO₂ Slope) or 6MWT distance was not significantly different between the ascending and descending aorta anastomosis groups. This study found no significant difference in the improvement of CPET parameters or 6MWT distance between LVAD implantation via thoracotomy with outflow cannula anastomosis to descending aorta and standard implantation via sternotomy with outflow cannula anastomosis to ascending aorta.

Exercise Tolerance in Patients Treated With a Durable Left Ventricular Assist Device: Importance of Myocardial Recovery

The number of patients supported with left ventricular assist devices (LVADs) is growing and support times are increasing. This has led to a greater focus on functional capacity of these patients. LVADs greatly improve heart failure symptoms, but surprisingly, improvement in peak oxygen uptake (pVO₂) is small and remains decreased at approximately 50% of normal values. Inadequate increase in cardiac output during exercise is the main responsible factor for the low pVO₂ in LVAD recipients. Some patients experience LV recovery during mechanical unloading and these patients have a higher pVO₂. Here we review the various components determining exercise cardiac output in LVAD recipients and discuss the potential impact of cardiac recovery on these components. LV recovery may affect several components, leading to improved hemodynamics during exercise and, in turn, physical capacity in patients with advanced heart failure undergoing LVAD implantation.

Changes in Resting and Exercise Hemodynamics Early After Heart Transplantation: A Simulation Perspective

Introduction: During heart transplantation (HTx), cardiac denervation is inevitable, thus typically resulting in chronic resting tachycardia and chronotropic incompetence with possible consequences in patient quality of life and clinical outcomes. To this date, knowledge of hemodynamic changes early after HTx is still incomplete. This study aims at providing a model-based description of the complex hemodynamic changes at rest and during exercise in HTx recipients (HTxRs). Materials and Methods: A numerical model of early HTxRs is developed that integrates intrinsic and autonomic heart rate (HR) control into a lumped-parameter cardiovascular system model. Intrinsic HR control is realized by a single-cell sinoatrial (SA) node model. Autonomic HR control is governed by aortic baroreflex and pulmonary stretch reflex and modulates SA node activity through neurotransmitter release. The model is tuned based on published clinical data of 15 studies. Simulations of rest and exercise are performed to study hemodynamic changes associated with HTxRs. Results: Simulations of HTxRs at rest predict a substantially increased HR [93.8 vs. 69.5 beats/min (bpm)] due to vagal denervation while maintaining normal cardiac output (CO) (5.2 vs. 5.6 L/min) through a reduction in stroke volume (SV) (55.4 vs. 82 mL). Simulations of exercise predict markedly reduced peak CO (13 vs. 19.8 L/min) primarily resulting from diminished peak HRs (133.9 vs. 169 bpm) and reduced ventricular contractility. Yet, the model results show that HTxRs can maintain normal CO for low- to medium-intensity exercise by increased SV augmentation through the Frank-Starling mechanism. Conclusion: Relevant hemodynamic changes occur after HTx. Simulations suggest that (1) increased resting HRs solely result from the absence of vagal tone; (2) chronotropic incompetence is the main limiting factor of exercise capacity whereby peripheral factors play a secondary role; and (3) despite the diminished exercise capacity, HTxRs can compensate chronotropic incompetence by a preload-mediated increase in SV augmentation and thus maintain normal CO in low- to medium-intensity exercise.

Hemodynamic exercise responses with a continuous-flow left ventricular assist device: Comparison of patients' response and cardiorespiratory simulations

Background

Left ventricular assist devices (LVADs) are an established treatment for end stage heart failure patients. As LVADs do not currently respond to exercise demands, attention is also directed towards improvements in exercise capacity and resulting quality of life. The aim of this study was to explore hemodynamic responses observed during maximal exercise tests to infer underlying patient status and therefore investigate possible diagnostics from LVAD derived data and advance the development of physiologically adaptive LVAD controllers.

Methods

High resolution continuous LVAD flow waveforms were recorded from 14 LVAD patients and evaluated at rest and during maximum bicycle exercise tests (n = 24). Responses to exercise were analyzed in terms of an increase (↑) or decrease (↓) in minimum (Q_MIN), mean (Q_MEAN), maximum flow (Q_MAX) and flow pulsatility (Q_P2P). To interpret clinical data, a cardiorespiratory numerical simulator was used that reproduced patients’ hemodynamics at rest and exercise. Different cardiovascular scenarios including chronotropic and inotropic responses, peripheral vasodilation, and aortic valve pathologies were simulated systematically and compared to the patients’ responses.

Results

Different patients’ responses to exercise were observed. The most common response was a positive change of ΔQ_MIN↑ and ΔQ_P2P↑ from rest to exercise (70% of exercise tests). Two responses, which were never reported in patients so far, were distinguished by Q_MIN↑ and Q_P2P↓ (observed in 17%) and by Q_MIN↓ and Q_P2P↑ (observed in 13%). The simulations indicated that the Q_P2P↓ can result from a reduced left ventricular contractility and that the Q_MIN↓ can occur with a better left ventricular contractility and/or aortic insufficiency.

Conclusion

LVAD flow waveforms determine a patients’ hemodynamic “fingerprint” from rest to exercise. Different waveform responses to exercise, including previously unobserved ones, were reported. The simulations indicated the left ventricular contractility as a major determinant for the different responses, thus improving patient stratification to identify how patient groups would benefit from exercise-responsive LVAD control.