Exercise physiology, testing, and training in patients supported by a left ventricular assist device

Exercise and weight loss with a left ventricular assist device: A case report and review of the literature

With changes in the heart transplant allocation system in the United States, the use of left ventricular device therapy (LVAD) as a bridge to transplant has decreased. Currently, one of the primary reasons to implant a device is for patient support until they can lose weight to qualify for transplant. This paper reviews the outcomes of various weight loss strategies for patients with LVADs including weight reduction surgery and cardiac rehab. Additionally, results of the use of GLP1 agonists on weight loss in general and in heart failure patients is reviewed. Finally, because of the unique issues involving exercise for patients with LVADs, we review safe exercise techniques with instructions for patients.

Development of in vitro microfluidic models to study endothelial responses to pulsatility with different mechanical circulatory support devices

Continuous-flow ventricular assist devices (CFVAD) and counterpulsation devices (CPD) are used to treat heart failure (HF). CFVAD can diminish pulsatility, but pulsatile modes have been implemented to increase vascular pulsatility. The effects of CFVAD in a pulsatile mode and CPD support on the function of endothelial cells (ECs) are yet to be investigated. In this study, two in vitro microfluidic models for culturing ECs are proposed to reproduce blood pressure (BP) and wall shear stress (WSS) on the arterial endothelium while using these medical devices. The layout and parameters of the two microfluidic systems were optimized based on the principle of hemodynamic similarity to efficiently simulate physiological conditions. Moreover, the unique design of the double-pump and double afterload systems could successfully reproduce the working mode of CPDs in an in vitro microfluidic system. The performance of the two systems was verified by numerical simulations and in vitro experiments. BP and WSS under HF, CFVAD in pulsatile modes, and CPD were reproduced accurately in the systems, and these induced signals improved the expression of Ca2+, NO, and reactive oxygen species in ECs, proving that CPD may be effective in normalizing endothelial function and replacing CFVAD to a certain extent to treat non-severe HF. This method offers an important tool for the study of cell mechanobiology and a key experimental basis for exploring the potential value of mechanical circulatory support devices in reducing adverse events and improving outcomes in the treatment of HF in the future.

Study on the hemodynamic effects of different pulsatile working modes of a rotary blood pump using a microfluidic platform that realizes in vitro cell culture effectively

Rotary blood pumps (RBPs) operating at a constant speed generate non-physiologic blood pressure and flow rate, which can cause endothelial dysfunction, leading to adverse clinical events in peripheral blood vessels and other organs. Notably, pulsatile working modes of the RBP can increase vascular pulsatility to improve arterial endothelial function. However, the laws and related mechanisms of differentially regulating arterial endothelial function under different pulsatile working modes are still unclear. This knowledge gap hinders the optimal selection of the RBP working modes. To address these issues, this study developed a multi-element in vitro endothelial cell culture system (ECCS), which could realize in vitro cell culture effectively and accurately reproduce blood pressure, shear stress, and circumferential strain in the arterial endothelial microenvironment. Performance of this proposed ECCS was validated with numerical simulation and flow experiments. Subsequently, this study investigated the effects of four different pulsation frequency modes that change once every 1-4-fold cardiac cycles (80, 40, 80/3, and 20 cycles per min, respectively) of the RBP on the expression of nitric oxide (NO) and reactive oxygen species (ROS) in endothelial cells. Results indicated that the 2-fold and 3-fold cardiac cycles significantly increased the production of NO and prevented the excessive generation of ROS, potentially minimizing the occurrence of endothelial dysfunction and related adverse events during the RBP support, and were consistent with animal study findings. In general, this study may provide a scientific basis for the optimal selection of the RBP working modes and potential treatment options for heart failure.

The Effects of Exercise on Cardiogenic Shock with an Intra-Aortic Balloon Pump: A Case Report

This case report describes the exercise program on a hospitalized 54-year-old male patient with cardiogenic shock waiting for a heart transplant assisted by an intra-aortic balloon pump, a temporary mechanical circulatory support device. The temporary mechanical circulatory support device, an intra-aortic balloon pump, was placed in the left subclavian artery, enabling the exercise protocol. Measurements and values from Swan-Ganz catheter, blood sample, brain natriuretic peptide (NT-proBNP), and high-sensitivity C-reactive protein (hs-CRP), as well as the six-minute walk test (6MWT) and venous oxygen saturation (SvO2) were obtained before and after an exercise protocol. The exercise training protocol involved the use of an unloaded bed cycle ergometer once a day, for a maximum of 30 minutes, to the tolerance limit. No adverse events or events related to the dislocation of the intra-aortic balloon pump were observed during the exercise protocol. The exercise program resulted in higher SvO2 levels, with an increased 6MWT with lower Borg dyspnea scores (312 meters vs. 488 meters and five points vs. three points, respectively). After completing the ten-day exercise protocol, the patient underwent a non-complicated heart transplant surgery and a full recovery in the ICU. This study showed that exercise is a feasible option for patients with cardiogenic shock who are using an intra-aortic balloon pump and that it is well-tolerated with no reported adverse events.

Hemodynamic parameters at rest predicting exercise capacity in patients supported with left ventricular assist device

Left ventricular assist devices improve prognosis and quality of life, but exercise capacity remains limited in most patients after device implantation. Left ventricular assist device optimization through right heart catheterization reduces device-related complications. However, hemodynamic parameters associated with exercise capacity under optimized conditions. The aim of this study was to elucidate the predictors of exercise capacity from hemodynamic parameters at rest after left ventricular assist device optimization. We retrospectively reviewed 24 patients who underwent a ramp test with right heart catheterization, echocardiography and cardiopulmonary exercise testing more than 6 months after left ventricular assist device implantation. Pump speed was optimized to a lower setting that achieved right atrial pressure < 12 mmHg, pulmonary capillary wedge pressure < 18 mmHg, and cardiac index > 2.2 L/min/m2, then exercise capacity was assessed by cardiopulmonary exercise testing. After left ventricular assist device optimization, the mean right atrial pressure, pulmonary capillary wedge pressure, cardiac index, and peak oxygen consumption were 7 ± 5 mmHg, 10 ± 7 mmHg, 2.7 ± 0.5 L/min/m2, and 13.2 ± 3.0 mL/min/kg, respectively. Pulse pressure, stroke volume, right atrial pressure, mean pulmonary artery pressure, and pulmonary capillary wedge pressure were significantly associated with peak oxygen consumption. Multivariate linear regression analysis of factors predicting peak oxygen consumption revealed that pulse pressure, right atrial pressure, and aortic insufficiency remained independent predictors (β = 0.401, p = 0.007; β = - 0.558, p < 0.001; β = - 0.369, p = 0.010, respectively). Our findings suggests that cardiac reserve, volume status, right ventricular function, and aortic insufficiency predict exercise capacity in patients with a left ventricular assist device.

Preoperative and mid-term right ventricular systolic function assessment, at rest and during exercise, with speckle-tracking echocardiography after left ventricular assist device implantation

OBJECTIVES

The study aimed to compare pre- and postoperative resting as well as postprocedural resting and exertional right ventricular speckle-tracking echocardiographic parameters at a mid-term follow-up after left ventricular assist device (LVAD) implantation.

METHODS

Patients with implanted third-generation LVADs with hydrodynamic bearings were prospectively enrolled (NCT05063006). Myocardial deformation was evaluated before pump implantation and at least three months after the procedure, both at rest and during exercise.

RESULTS

We included 22 patients, 7.3 months (IQR, 4.7-10.2) after the surgery. The mean age was 58.4 ± 7 years, 95.5% were men, and 45.5% had dilated cardiomyopathy. The RV strain analysis was feasible in all subjects both at rest and during exercise. The RV free wall strain (RVFWS) worsened from -13% (IQR, -17.3 to -10.9) to -11.3% (IQR, -12.9 to -6; p = 0.033) after LVAD implantation with a particular decline in the apical RV segment [-11.3% (IQR, -16.4 to -6.2) vs -7.8% (IQR, -11.7 to -3.9; p = 0.012)]. The RV four-chamber longitudinal strain (RV4CSL) remained unchanged [-8.5% (IQR, -10.8 to -6.9) vs -7.3% (IQR, -9.8 to -4.7; p = 0.184)]. Neither RVFWS (-11.3% (IQR, -12.9 to -6) vs -9.9% (IQR, -13.5 to -7.5; p = 0.077) nor RV4CSL [-7.3% (IQR, -9.8 to -4.7) vs -7.9% (IQR, -9.8 to -6.3; p = 0.548)] changed during the exercise test.

CONCLUSIONS

In patients who are pump-supported, the right ventricular free wall strain tends to worsen after LVAD implantation and remains unchanged during a cycle ergometer stress test.

Numerical simulation analysis of multi-scale computational fluid dynamics on hemodynamic parameters modulated by pulsatile working modes for the centrifugal and axial left ventricular assist devices

Continuous flow (CF) left ventricular assist devices (LVAD) operate at a constant speed mode, which could result in increased risk of adverse events due to reduced vascular pulsatility. Consequently, pump speed modulation algorithms have been proposed to augment vascular pulsatility. However, the quantitative local hemodynamic effects on the aorta when the pump is operating with speed modulation using different types of CF-LVADs are still under investigation. The computational fluid dynamics (CFD) study was conducted to quantitatively elucidate the hemodynamic effects on a clinical patient-specific aortic model under different speed patterns of CF-LVADs. Pressure distribution, wall shear stress (WSS), time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), and velocity were calculated to compare their differences at constant and pulsatile speeds under centrifugal and axial LVAD support. Results showed that pulse pressure on the aorta was significantly larger under pulsatile speed mode than that under constant speed mode for both CF-LVADs, indicating enhanced aorta pulsatility, as well as the higher peak blood flow velocity on some representative slices of aorta. Pulsatile speed modulation enhanced peak WSS compared to constant speed; high TAWSS region appeared near the branch of left common carotid artery and distal aorta regardless of speed modes and CF-LVADs but these regions also had low OSI; RRT was almost the same for all the cases. This study may provide a basis for the scientific and reasonable selection of the pulsatile speed patterns of CF-LVADs for treating heart failure patients.

Determinants of exercise performance in heart failure patients with extremely reduced cardiac output and left ventricular assist device

The evaluation of exercise capacity and cardiac output (QC) is fundamental in the management of patients with advanced heart failure (AdHF). QC and peak oxygen uptake (VO2) have a pivotal role in the prognostic stratification and in the definition of therapeutic interventions, including medical therapies and devices, but also specific treatments such as heart transplantation and left ventricular assist device (LVAD) implantation. Due to the intertwined relationship between exercise capacity and daily activities, exercise intolerance dramatically has impact on the quality of life of patients. It is a multifactorial process that includes alterations in central and peripheral haemodynamic regulation, anaemia and iron deficiency, pulmonary congestion, pulmonary hypertension, and peripheral O2 extraction. This paper aims to review the pathophysiological background of exercise limitations in HF patients and to examine the complex physiology of exercise in LVAD recipients, analysing the interactions between the cardiopulmonary system, the musculoskeletal system, the autonomic nervous system, and the pump. We performed a literature review to highlight the current knowledge on this topic and possible interventions that can be implemented to increase exercise capacity in AdHF patients-including administration of levosimendan, rehabilitation, and the intriguing field of LVAD speed changes. The present paper confirms the role of CPET in the follow-up of this peculiar population and the impact of exercise capacity on the quality of life of AdHF patients.

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.

Increased Dead Space Ventilation as a Contributing Factor to Persistent Exercise Limitation in Patients with a Left Ventricular Assist Device

(1) Background: The exercise capacity of patients with a left ventricular assist device (LVAD) remains limited despite mechanical support. Higher dead space ventilation (VD/VT) may be a surrogate for right ventricular to pulmonary artery uncoupling (RV-PA) during cardiopulmonary exercise testing (CPET) to explain persistent exercise limitations. (2) Methods: We investigated 197 patients with heart failure and reduced ejection fraction with (n = 89) and without (HFrEF, n = 108) LVAD. As a primary outcome NTproBNP, CPET, and echocardiographic variables were analyzed for their potential to discriminate between HFrEF and LVAD. As a secondary outcome CPET variables were evaluated for a composite of hospitalization due to worsening heart failure and overall mortality over 22 months. (3) Results: NTproBNP (OR 0.6315, 0.5037-0.7647) and RV function (OR 0.45, 0.34-0.56) discriminated between LVAD and HFrEF. The rise of endtidal CO2 (OR 4.25, 1.31-15.81) and VD/VT (OR 1.23, 1.10-1.40) were higher in LVAD patients. Group (OR 2.01, 1.07-3.85), VE/VCO2 (OR 1.04, 1.00-1.08), and ventilatory power (OR 0.74, 0.55-0.98) were best associated with rehospitalization and mortality. (4) Conclusions: LVAD patients displayed higher VD/VT compared to HFrEF. Higher VD/VT as a surrogate for RV-PA uncoupling could be another marker of persistent exercise limitations in LVAD patients.

[Cardiac rehabilitation in LVAD patients : Aspects regarding exercise and rhythm]

After implantation of a left ventricular assist device (LVAD), it is strongly recommended that patients participate in an inpatient cardiac rehabilitation program (CR). Relevant topics during CR include sports and exercise therapy as well as aspects of cardiac rhythm control. Over time, LVAD patients usually regain a good quality of life and an adequate functional capacity can be observed. However, maximum performance values remain markedly reduced, in part due to the fixed LVAD pump speed and the limited total cardiac output. Therefore, structured long-term exercise training programs (even beyond CR phase II) are of particular importance in order to optimize neuromuscular control and muscle metabolism. Limitations to physical performance values may also be caused by the occurrence of supraventricular and/or ventricular arrhythmias. In both cases, the cause is an increasing hemodynamic impairment of the right heart, which may also lead to a reduced LVAD pump flow. In addition, inadequate setting of other cardiac implantable electronic devices (e.g., implantable cardioverter-defibrillator [ICD] or cardiac resynchronization therapy with defibrillator [CRT-D]) may also have a crucial impact on hemodynamics after LVAD implantation. In this article, we will discuss specific aspects of LVAD therapy related to exercise and rhythm control, particularly in the context of CR programs.

Impact of right ventricular reserve on exercise capacity and quality of life in patients with left ventricular assist device

Although measuring right ventricular (RV) function during exercise is more informative than assessing it at rest, the relationship between RV reserve function, exercise capacity, and health-related quality of life (HRQoL) in patients with left ventricular assist devices (LVAD) remains unresolved. We aimed to investigate whether RV reserve assessed by the change in RV stroke work index (RVSWI) during exercise is correlated with exercise capacity and HRQoL in patients with LVAD. We prospectively assessed 24 consecutive patients with LVAD who underwent invasive right heart catheterization in the supine position. Exercise capacity and HRQoL were assessed using the 6-min walk distance (6 MWD) and peak oxygen consumption (V̇o₂) in cardiopulmonary exercise testing, and the EuroQol visual analog scale (EQ-VAS), respectively. The patients were divided into two groups according to the median ΔRVSWI (change from rest to peak exercise). Patients with lower ΔRVSWI had significantly lower changes in cardiac index and absolute value of RV dP/dt than those with higher ΔRVSWI. The ΔRVSWI was positively correlated with 6 MWD (r = 0.59, P = 0.003) and peak V̇o₂ (r = 0.56, P = 0.006). In addition, ΔRVSWI was positively correlated with the EQ-VAS (r = 0.44, P = 0.030). In contrast, there was no significant correlation between RVSWI at rest and 6 MWD (r = -0.34, P = 0.88), peak V̇o₂ (r = 0.074, P = 0.74), or EQ-VAS (r = 0.127, P = 0.56). Our findings suggest that the assessment of RV reserve function is useful for risk stratification in patients with LVAD.NEW & NOTEWORTHY The change in right ventricular stroke work index (RVSWI) during exercise, not RVSWI at rest, was associated with exercise capacity and HRQoL. Our findings suggest that the assessment of change in RVSWI during exercise as a surrogate of RV reserve function may aid in risk stratification of patients with LVAD.

In Vivo Evaluation of a Novel Control Algorithm for Left Ventricular Assist Devices Based Upon Ventricular Stroke Work

The physical fitness of patients with terminal heart failure and an implanted left ventricular assist device (LVAD) might be improved by load-adaptive control of the LVAD. In this study, three control strategies for LVAD were compared in eight pigs: (1) a constant stroke work (CSW) control strategy that ensures a constant ventricular load using ventricular stroke work as the control variable; (2) a work ratio (WR) controller that maintains a constant ratio of ventricular work to hydraulic pump work; and (3) a controller that maintains the pump pace at a constant speed (CS). Biventricular heart insufficiency was induced by increased isoflurane application, and preload, afterload, and contractility alterations were performed. LVAD speed changes were significantly more pronounced in all load interventions with the CSW control strategy (preload: P < 0.001 vs. CS and P = 0.004 vs. WR; afterload: P < 0.001 vs. CS and P < 0.001 vs. WR; contractility: P < 0.001 vs. CS and P < 0.001 vs. WR). However, a significant difference in systemic flow only became evident in the experiments upon afterload increase ( P < 0.001 vs. CS and P = 0.004 vs. WR). An implementation of an evolved version of the CSW control strategy that dispenses with invasively measured parameters might be feasible for clinical use.

Exercise oscillatory ventilation in patients with advanced heart failure with and without left ventricular assist device

BACKGROUND

Exercise oscillatory ventilation (EOV), indicating pathological fluctuations on pulmonary arterial pressure, is associated with mortality in patients with heart failure (HF). Whether left ventricular assist device (LVAD)-induced ventricular unloading can reverse EOV and may prevent short-term rehospitalization has not been investigated.

METHODS

We performed a retrospective single-center in- and outpatient analysis of patients with (n = 20, LVAD) and without (n = 27, HF) circulatory support and reduced ejection fraction (EF, 22.8 ± 7.9%). The association of cardiopulmonary exercise testing (CPET) variables and 3 months-rehospitalization (3MR) as a primary outcome was analyzed. Furthermore, CPET variables were compared regarding the presence of EOV (+/-).

RESULTS

Lower VO_2peak (11.6 ± 4.9 ml/kg/min vs. 14.4 ± 4.3 ml/kg/min, p = 0.039), lower increase of PETCO₂ (CI = 0.049-1.127; p = 0.068), and higher VE/VCO₂ (43.8 ± 9.5 vs. 38.3 ± 10.6; p = 0.069) were associated with 3MR. Flattening of O₂ pulse (CI = 0.139-2.379; p = 0.487) had no impact on 3MR. EOV was present in 59.5% (n = 28/47) of patients, without a significant difference between LVAD and HF patients (p = 0.959). Patients with HF/EOV+ demonstrated significantly lower VO_2peak compared with HF/EOV- (p = 0.039). LVAD/EOV+ displayed significantly lower EF (p = 0.004) and fewer aortic valve opening than LVAD/EOV- (p = 0.027).

CONCLUSIONS

Lower VO_2peak , but not EOV, was associated with 3MR. EOV occurred at a similar rate in LVAD and HF patients, which may illustrate insufficient unloading during exercise in chronic LVAD therapy and may contribute to the limited exercise capacity following LVAD implantation. Simultaneous CPET and right heart catheterization studies are needed to elucidate whether EOV may serve as a non-invasive predictor of insufficient LV unloading necessitating LVAD reprograming.

Initial clinical validation of a hybrid in silico—in vitro cardiorespiratory simulator for comprehensive testing of mechanical circulatory support systems

Simulators are expected to assume a prominent role in the process of design—development and testing of cardiovascular medical devices. For this purpose, simulators should capture the complexity of human cardiorespiratory physiology in a realistic way. High fidelity simulations of pathophysiology do not only allow to test the medical device itself, but also to advance practically relevant monitoring and control features while the device acts under realistic conditions. We propose a physiologically controlled cardiorespiratory simulator developed in a mixed in silico-in vitro simulation environment. As inherent to this approach, most of the physiological model complexity is implemented in silico while the in vitro system acts as an interface to connect a medical device. As case scenarios, severe heart failure was modeled, at rest and at exercise and as medical device a left ventricular assist device (LVAD) was connected to the simulator. As initial validation, the simulator output was compared against clinical data from chronic heart failure patients supported by an LVAD, that underwent different levels of exercise tests with concomitant increase in LVAD speed. Simulations were conducted reproducing the same protocol as applied in patients, in terms of exercise intensity and related LVAD speed titration. Results show that the simulator allows to capture the principal parameters of the main adaptative cardiovascular and respiratory processes within the human body occurring from rest to exercise. The simulated functional interaction with the LVAD is comparable to the one clinically observed concerning ventricular unloading, cardiac output, and pump flow. Overall, the proposed simulation system offers a high fidelity in silico-in vitro representation of the human cardiorespiratory pathophysiology. It can be used as a test bench to comprehensively analyze the performance of physically connected medical devices simulating clinically realistic, critical scenarios, thus aiding in the future the development of physiologically responding, patient-adjustable medical devices. Further validation studies will be conducted to assess the performance of the simulator in other pathophysiological conditions.

Prognostic Value of Cardiopulmonary Exercise Test Parameters in Ventricular Assist Device Therapy

Cardiopulmonary exercise test (CPET) parameters are established prognosticators in heart failure. However, the prognostic value of preimplantation and postimplantation CPET parameters in left ventricular assist device (LVAD) therapy is unclear and it is evaluated in this study. Adult patients who were implanted with an LVAD and underwent CPET during the preimplantation or postimplantation period were retrospectively analyzed. Five CPET parameters were calculated: vO2 max, oxygen uptake efficiency slope (OUES), VE/vCO2 Slope, VE/vCO2 min, and VE/vCO2 max. The relationship between CPET parameters and postimplantation outcomes was evaluated with multivariable analysis. Pre and postimplantation CPET cohorts included 191 and 122 patients, respectively. Among preimplantation CPET parameters: vO2 max and OUES were associated with 1, 3, and 5 year mortality, VE/vCO2 min was associated with 3 and 5 year mortality, whereas VE/vCO2 Slope was associated with 5 year mortality. From postimplantation CPET parameters: vO2 max was an independent predictor of 3 and 5 year mortality, whereas VE/vCO2 max was an independent predictor of 3 year mortality following LVAD implantation. Preimplantation CPET parameters have a prognostic value for long-term survival following LVAD implantation, whereas their association with early postimplantation outcomes appears to be weaker. Postimplantation vO2 max and VE/vCO2 max values are associated with survival on device support and may provide a second chance for prognostication in patients without preimplantation CPET data.

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.

Relationship between spleen size and exercise tolerance in advanced heart failure patients with a left ventricular assist device

OBJECTIVE

Spleen volume increases in patients with advanced heart failure (HF) after left ventricular assist device (LVAD) implantation. However, the relationship between spleen volume and exercise tolerance (peak oxygen consumption [VO₂]) in these patients remains unknown. In this exploratory study, we enrolled 27 patients with HF using a LVAD (median age: 46 years). Patients underwent blood testing, echocardiography, right heart catheterization, computed tomography (CT), and cardiopulmonary exercise testing. Spleen size was measured using CT volumetry, and the correlations/causal relationships of factors affecting peak VO₂ were identified using structural equation modeling.

RESULTS

The median spleen volume was 190.0 mL, and peak VO₂ was 13.2 mL/kg/min. The factors affecting peak VO₂ were peak heart rate (HR; β = 0.402, P = .015), pulmonary capillary wedge pressure (PCWP; β =  - 0.698, P = .014), right ventricular stroke work index (β = 0.533, P = .001), blood hemoglobin concentration (β = 0.359, P = .007), and spleen volume (β = 0.215, P = .041). Spleen volume correlated with peak HR, PCWP, and hemoglobin concentration, reflecting sympathetic activity, cardiac preload, and oxygen-carrying capacity, respectively, and was thus related to peak VO₂. These results suggest an association between spleen volume and exercise tolerance in advanced HF.

Short- and long-term effects of a cardiac rehabilitation program in patients implanted with a left ventricular assist device

The efficacy of cardiac rehabilitation in heart-failure patients who received a left-ventricular assist device (LVAD) instead of heart transplantation (HTx) is still unclear. This study aims to evaluate whether cardiac rehabilitation is beneficial in LVAD as HTx patients in the short term and whether its effects in LVAD patients persist over time. Twenty-five LVAD patients were evaluated by functional and psychological tests at admission (T0) and discharge (T1) of a 4-week inpatient structured rehabilitation program, and follow-ups 3 (T2), 6 (T3), and 12 months (T4) after discharge. Twenty-five matched HTx patients were also studied from T0 to T1 to compare the improvements in the six-minute walk test (6MWT). The quality-of-life scores substantially improved in LVAD patients and the 6MWT showed the same functional recovery as in HTx patients from T0 to T1. After T1, numerous LVAD patients withdrew from the study. However, the 6MWT outcome increased further from T1 to T3, with a positive trend during the follow-ups. Hemoglobin and the ventilatory performance increased, and the psychological perception of heart-failure symptoms and pain further improved at T2. In conclusion, exercise-based rehabilitation programs provide similar beneficial effects in LVAD and HTx patients, without deterioration in LVAD patients up to 12 months after discharge.

Contrast-Enhanced Ultrasound of Muscle Perfusion May Indicate Patient Response to Left Ventricular Assist Device Therapy

PURPOSE

Left ventricular assist device (LVAD) support is associated with peripheral vascular abnormalities beyond those associated with heart failure (HF). These abnormalities are associated with persistent functional impairments that adversely impact quality of life (QoL). Methods for measuring peripheral vascular function in this population are needed.

METHODS

This pilot study investigated the use of contrast-enhanced ultrasound (CEUS) using standardized protocols to estimate changes in peripheral (quadriceps) muscle perfusion among patients with HF (INTERMACS profile 3) undergoing LVAD implantation (n = 7). Patients were then stratified by those who did ("responders", n = 4) and did not ("nonresponders", n = 3) report QoL improvement with LVAD support.

RESULTS

Serial measurements obtained preoperatively and 3 months following LVAD implantation showed no significant change (P > .23) in muscle perfusion by all CEUS-based measures at rest or with an exercise stimulus for the overall population. Responders exhibited improved muscle perfusion at rest (P = .043) and decreased time to peak contrast enhancement (P = .010) at 3 months compared with baseline, suggesting improved delivery of blood to the extremities post-LVAD. Nonresponders showed unchanged resting muscle perfusion (P > .99), time to peak contrast enhancement (P = .59), and response to exercise stimulus (P > .99) following LVAD therapy.

CONCLUSION

Our findings suggest that CEUS evaluation is a promising noninvasive, quantitative modality for real-time assessment of peripheral vasculature and muscle perfusion as an indication of treatment response in LVAD recipients and that this modality may capture perfusion measures important to QoL following LVAD implantation.

Cardiac Rehabilitation in German Speaking Countries of Europe-Evidence-Based Guidelines from Germany, Austria and Switzerland LLKardReha-DACH-Part 2

Background: Scientific guidelines have been developed to update and harmonize exercise based cardiac rehabilitation (ebCR) in German speaking countries. Key recommendations for ebCR indications have recently been published in part 1 of this journal. The present part 2 updates the evidence with respect to contents and delivery of ebCR in clinical practice, focusing on exercise training (ET), psychological interventions (PI), patient education (PE). In addition, special patients’ groups and new developments, such as telemedical (Tele) or home-based ebCR, are discussed as well. Methods: Generation of evidence and search of literature have been described in part 1. Results: Well documented evidence confirms the prognostic significance of ET in patients with coronary artery disease. Positive clinical effects of ET are described in patients with congestive heart failure, heart valve surgery or intervention, adults with congenital heart disease, and peripheral arterial disease. Specific recommendations for risk stratification and adequate exercise prescription for continuous-, interval-, and strength training are given in detail. PI when added to ebCR did not show significant positive effects in general. There was a positive trend towards reduction in depressive symptoms for “distress management” and “lifestyle changes”. PE is able to increase patients’ knowledge and motivation, as well as behavior changes, regarding physical activity, dietary habits, and smoking cessation. The evidence for distinct ebCR programs in special patients’ groups is less clear. Studies on Tele-CR predominantly included low-risk patients. Hence, it is questionable, whether clinical results derived from studies in conventional ebCR may be transferred to Tele-CR. Conclusions: ET is the cornerstone of ebCR. Additional PI should be included, adjusted to the needs of the individual patient. PE is able to promote patients self-management, empowerment, and motivation. Diversity-sensitive structures should be established to interact with the needs of special patient groups and gender issues. Tele-CR should be further investigated as a valuable tool to implement ebCR more widely and effectively.

Exercise physiology in left ventricular assist device patients: insights from hemodynamic simulations

Left ventricular assist devices (LVADs) assure longer survival to patients, but exercise capacity is limited compared to normal values. Overall, LVAD patients show high wedge pressure and low cardiac output during maximal exercise, a phenomenon hinting at the need for increased LVAD support. Clinical studies investigating the hemodynamic benefits of an LVAD speed increase during exercise, ended in inhomogeneous and sometimes contradictory results. The native ventricle-LVAD interaction changes between rest and exercise, and this evolution is complex, multifactorial and patient-specific. The aim of this paper is to provide a comprehensive overview on the patient-LVAD interaction during exercise and to delineate possible therapeutic strategies for the future. A computational cardiorespiratory model was used to simulate the hemodynamics of peak bicycle exercise in LVAD patients. The simulator included the main cardiovascular and respiratory impairments commonly observed in LVAD patients, so as to represent an average hemodynamic response to exercise. In addition, other exercise responses were simulated, by tuning the chronotropic, inotropic and vascular functions, and implementing aortic regurgitation and stenosis in the simulator. These profiles were tested under different LVAD speeds and LVAD pressure-flow characteristics. Simulations output showed consistency with clinical data from the literature. The simulator allowed the working condition of the assisted ventricle at exercise to be investigated, clarifying the reasons behind the high wedge pressure and poor cardiac output observed in the clinics. Patients with poorer inotropic, chronotropic and vascular functions, are likely to benefit more from an LVAD speed increase during exercise. Similarly, for these patients, a flatter LVAD pressure-flow characteristic can assure better hemodynamic support under physical exertion. Overall, the study evidenced the need for a patient-specific approach on supporting exercise hemodynamics. In this frame, a complex simulator can constitute a valuable tool to define and test personalized speed control algorithms and strategies.

One year improvement of exercise capacity in patients with mechanical circulatory support as bridge to transplantation

AIMS

Mechanical circulatory support (MCS) results in substantial improvement of prognosis and functional capacity. Currently, duration of MCS as a bridge to transplantation (BTT) is often prolonged due to shortage of donor hearts. Because long-term results of exercise capacity after MCS are largely unknown, we studied serial cardiopulmonary exercise tests (CPETs) during the first year after MCS implantation.

METHODS AND RESULTS

Cardiopulmonary exercise tests at 6 and 12 months after MCS implantation in BTT patients were retrospectively analysed, including clinical factors related to exercise capacity. A total of 105 MCS patients (67% male, 50 ± 12 years) underwent serial CPET at 6 and 12 months after implantation. Power (105 ± 35 to 114 ± 40 W; P ≤ 0.001) and peak VO2 per kilogram (pVO2/kg) improved significantly (16.5 ± 5.0 to 17.2 ± 5.5 mL/kg/min (P = 0.008)). Improvement in pVO2 between 6 and 12 months after LVAD implantation was not related to heart failure aetiology or haemodynamic severity prior to MCS. We identified maximal heart rate at exercise as an important factor for pVO2. Younger age and lower BMI were related to further improvement. At 12 months, 25 (24%) patients had a normal exercise capacity (Weber classification A, pVO2 > 20 mL/kg/min).

CONCLUSIONS

Exercise capacity (power and pVO2) increased significantly between 6 and 12 months after MCS independent of Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) profile or heart failure aetiology. Heart rate at exercise importantly relates to exercise capacity. This long-term improvement in exercise capacity is important information for the growing group of long-term MCS patients as this is critical for the quality of life of patients.

Markers of Right Ventricular Dysfunction Predict Maximal Exercise Capacity After Left Ventricular Assist Device Implantation

Although left ventricular assist device (LVAD) improves functional capacity, on average LVAD patients are unable to achieve the aerobic capacity of normal healthy subjects or mild heart failure patients. The aim of this study was to examine if markers of right ventricular (RV) function influence maximal exercise capacity. This was a single-center prospective study that enrolled 20 consecutive HeartWare ventricular assist device patients who were admitted at the Freeman Hospital (Newcastle upon Tyne, United Kingdom) for a heart transplant assessment from August 2017 to October 2018. Mean peak oxygen consumption (Peak VO2) was 14.0 ± 5.0 ml/kg/min, and mean peak age and gender-adjusted percent predicted oxygen consumption (%VO2) was 40.0% ± 11.5%. Patients were subdivided into two groups based on the median peak VO2, so each group consisted of 10 patients (50%). Right-sided and pulmonary pressures were consistently higher in the group with poorer exercise tolerance. Patients with poor exercise tolerance (peak VO2 below the median) had higher right atrial pressures at rest (10.6 ± 6.4 vs. 4.3 mmHg ± 3.2; p = 0.02) and the increase with passive leg raising was significantly greater than those with preserved exercise tolerance (peak VO2 above the median). Patients with poor functional capacity also had greater RV dimensions (4.4 cm ± 0.5 vs. 3.7 cm ± 0.5; p = 0.02) and a higher incidence of significant tricuspid regurgitation (moderate or severe tricuspid regurgitation in five patients in the poor exercise capacity group vs. none in the preserved exercise capacity group; p = 0.03). In conclusion, echocardiographic and hemodynamic markers of RV dysfunction discriminate between preserved and nonpreserved exercise capacity in HeartWare ventricular assist device patients.

Role of Cardiac Rehabilitation After Ventricular Assist Device Implantation

Patients with heart failure suffered by a complex syndrome, where the filling of the ventricle or ejection of the blood is impaired. In this setting, the exercise capacity decreases for many reasons, one of them being the insufficient oxygen transfer due to reduced cardiac output and anemia. Ventricular assist device has emerged as a durable and safe therapy for patients with end-stage heart failure. The benefits of cardiac rehabilitation in ventricular assist device patients are enormous: the first aim is to progressively reduce the physical and functional impairments of these patients, so that they will be able to resume meaningful daily activities.

Feasibility of high-intensity interval training in patients with left ventricular assist devices: a pilot study

Aims

Patients with left ventricular assist device (LVAD) suffer from persistent exercise limitation despite improvement of their heart failure syndrome. Exercise training (ET) programmes to improve aerobic capacity have shown modest efficacy. High‐intensity interval training (HIIT), as an alternative to moderate continuous training, has not been systematically tested in this population. We examine the feasibility of a short, personalized HIIT programme in patients with LVAD and describe its effects on aerobic capacity and left ventricular remodelling.

Methods and results

Patients on durable LVAD support were prospectively enrolled in a 15‐session, 5 week HIIT programme. Turndown echocardiogram, Kansas City Cardiomyopathy Questionnaire, and cardiopulmonary exercise test were performed before and after HIIT. Training workloads for each subject were based on pretraining peak cardiopulmonary exercise test work rate (W). Percentage of prescribed training workload completed and adverse events were recorded for each subject. Fifteen subjects were enrolled [10 men, age = 51 (29–71) years, HeartMate II = 12, HeartMate 3 = 3, and time on LVAD = 18 (3–64) months]. Twelve completed post‐training testing. HIIT was well tolerated, and 90% (inter‐quartile range: 78, 99%) of the prescribed workload (W) was completed with no major adverse events. Improvements were seen in aV̇O₂ at ventilatory threshold [7.1 (6.5, 9.1) to 8.5 (7.7, 9.3) mL/kg/min, P = 0.04], work rate at ventilatory threshold [44 (14, 54) to 55 (21, 66) W, P = 0.05], and left ventricular end‐diastolic volume [168 (144, 216) to 159 (124, 212) mL, n = 7, P = 0.02]. HIIT had no effect on maximal oxygen consumption (V̇O_2peak) or Kansas City Cardiomyopathy Questionnaire score.

Conclusions

Cardiopulmonary exercise test‐guided HIIT is feasible and can improve submaximal aerobic capacity in stable patients with chronic LVAD support. Further studies are needed on its effects on the myocardium and its potential role in cardiac rehabilitation programmes.

Prospective evaluation of ventricular assist device risk scores' capacity to predict cardiopulmonary exercise parameters

OBJECTIVES

Risk scores for left ventricular assist device (LVAD) therapy are known to predict morbidity and adverse events in addition to mortality. This study evaluates the capacity of popular LVAD risk scores to predict cardiopulmonary exercise parameters.

METHODS

Adult patients undergoing continuous flow LVAD implantation were prospectively followed. Five risk scores were calculated before implantation: Model for End-stage Liver Disease (MELD), MELD excluding international normalized ratio (MELD-XI), MELD including sodium (MELD-Na), HeartMate2 Risk Score (HMRS) and Destination Therapy Risk Score (DTRS). Cardiopulmonary exercise tests (CPETs) were performed before and after implantation; peak oxygen consumption (vO2max), the lowest ventilation to carbon dioxide output ratio (vE/vCO2) and exercise time were measured.

RESULTS

Ninety-two patients were implanted during the study period; of these, 30 patients completed preimplantation and postimplantation CPETs (CPET cohort). The mean preimplantation and postimplantation CPET dates were 29 ± 10 days before and 109 ± 5 days following implantation. CPET parameters significantly improved after implantation (P < 0.05). In multivariate analysis, MELD, MELD-XI, MELD-Na and HMRS independently predicted both preimplantation and postimplantation vE/vCO2, while MELD-Na and HMRS were also independent predictors of preimplantation and postimplantation vO2max, respectively.

CONCLUSIONS

Four preimplantation LVAD risk scores (HMRS, MELD, MELD-Na and MELD-XI) independently predict important cardiopulmonary exercise parameters such as vE/vCO2 and vO2 max in LVAD therapy. Out of these 4 risk scores, MELD-Na and HMRS appear to be the best predictors of preimplantation and postimplantation CPET parameters, respectively.

Association Between Neurohormone Levels and Exercise Testing Measures in Patients with Mechanical Circulatory Supports

Continuous-flow left ventricular assist device (CF-LVAD) recipients exhibit impaired exercise capacity. Long-term continuous blood flow also elevates norepinephrine (NE) and aldosterone (Aldo) levels. However, the relationship between exercise capacity and neurohormonal activation has not been elucidated. Our study objective was to assess the association between cardiopulmonary exercise testing (CPT) measures and neurohormonal levels in CF-LVAD recipients. Symptom-limited CPT on a treadmill, using the modified Bruce protocol was performed in 15 CF-LVAD recipients. Norepinephrine and Aldo levels were measured, and the association between their levels and CPT measures were assessed. Peak VO2 (13.6 ml/kg/min) and percent age, sex predicted VO2 max (49.4%), and oxygen pulse (O2 pulse) (9.0 ± 4.0 ml/beat) were low, whereas minute ventilation/carbon dioxide output (VE/VCO2) slope (35) was elevated. In addition, VO2 at anaerobic threshold (VO2 AT), and O2 pulse values negatively correlated with NE levels. Norepinephrine levels positively correlated with chronotropic responses and heart rate (HR) recovery. Aldo levels in CF-LVAD recipients were not related to any CPT measures. Continuous-flow left ventricular assist device recipients exhibited impaired exercise capacity and chronotropic incompetence (CI). Despite the association of NE levels with chronotropic responses at peak exercise, neither NE levels nor chronotropic responses predicted peak VO2. This suggests that CI may not be the primary factor responsible for the low peak VO2. O2 pulse, which is a combined measure for stroke volume and peripheral oxygen extraction during exercise, was an independent predictor of peak VO2. Future studies should examine the contribution of peripheral factors to exercise capacity limitations.

Limiting factors of peak and submaximal exercise capacity in LVAD patients

AIMS

Although patients supported with a Continuous-Flow Left Ventricular Assist Device (CF-LVAD) are hemodynamically stable, their exercise capacity is limited. Hence, the aim of this work was to investigate the underlying factors that lead to peak and submaximal exercise intolerance of CF-LVAD supported patients.

METHODS

Seven months after CF-LVAD implantation, eighty three patients performed a maximal cardiopulmonary exercise test and a six minute walk test. Peak oxygen uptake and the distance walked were measured and expressed as a percentage of the predicted value (%VO2p and %6MWD, respectively). Preoperative conditions, echocardiography, laboratory results and pharmacological therapy data were collected and a correlation analysis against %VO2p and %6MWD was performed.

RESULTS

CF-LVAD patients showed a relatively higher submaximal exercise capacity (%6MWD = 64±16%) compared to their peak exertion (%VO2p = 51±14%). The variables that correlated with %VO2p were CF-LVAD parameters, chronotropic response, opening of the aortic valve at rest, tricuspid insufficiency, NT-proBNP and the presence of a cardiac implantable electronic device. On the other hand, the variables that correlated with %6MWD were diabetes, creatinine, urea, ventilation efficiency and CF-LVAD pulsatility index. Additionally, both %6MWD and %VO2p were influenced by the CF-LVAD implantation timing, calculated from the occurrence of the cardiac disease.

CONCLUSION

Overall, both %6MWD and %VO2p depend on the duration of heart failure prior to CF-LVAD implantation. %6MWD is primarily determined by parameters underlying the patient's general condition, while %VO2p mostly relies on the residual function and chronotropic response of the heart. Moreover, since %VO2p was relatively lower compared to %6MWD, we might infer that CF-LVAD can support submaximal exercise but is not sufficient during peak exertion. Hence concluding that the contribution of the ventricle is crucial in sustaining hemodynamics at peak exercise.

Characteristics, Therapeutic Needs, and Scope of Patients With a Continuous-Flow Left Ventricular Device Entering Cardiac Rehabilitation: A RETROSPECTIVE ANALYSIS

BACKGROUND

With an increasing number of left ventricular assist devices (LVADs) being implanted, the need for adequate cardiac rehabilitation (CR) regimens meeting the special needs of these patients arises. Only a few studies have reported experience gained on this topic. Structured CR strategies are poorly implemented. The aim was to evaluate the characteristics, therapeutic needs, and scope of LVAD patients at admission to CR within a greater cohort in order to identify their special CR needs.

METHODS

Retrospective single-center study; 69 LVAD patients (50.7 ± 13.6 y; 59 male; 48 HVAD; 21 HeartMate II) who completed first inpatient CR were included. Patient records were used to document relevant medical information (including the results of a 6-min walk test and a maximal isometric strength test for quadriceps femoral muscles in both legs) and the International Classification of Functioning, Disability and Health for classification of health and health-related domains.

RESULTS

Patient characteristics demonstrated a heterogeneous group: CR was started 44 ± 38.6 d after implantation; CR duration was 28 ± 9.7 d. Despite similar etiology, physical and psychological condition was diverse, although, overall a high degree of impairment was present, especially in the body function (79.7%) and activity and participation (95.7%) domains. The results demonstrated the need for a highly individualized approach in the somatic and also in the education, psychosocial, and social therapeutic regimes.

CONCLUSION

The results demonstrate a heterogeneous group with a high level of impairment and special needs in many CR domains. The development and evaluation of a special highly individualized approach of CR, which meets the special needs of these patients, is needed.

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.

Patients with left ventricle assist devices presenting for thoracic surgery and lung resection: tips, tricks and evidence

PURPOSE OF REVIEW

Over a thousand left ventricular-assist device (LVAD) implants were performed for heart failure destination therapy in 2017. With increasing survival, we are seeing increasing numbers of patients present for noncardiac surgery, including resections for cancer. This article will review the relevant literature and guidelines for patients with LVADs undergoing thoracic surgery, including lung resection.

RECENT FINDINGS

The International Society for Heart and Lung Transplant Mechanically Assisted Circulatory Support Registry has received data on more than 16 000 patients with LVADs. Four-year survival is more than 60% for centrifugal devices. There are increasing case reports, summaries and recommendations for patients with LVADs undergoing noncardiac surgery. However, data on thoracic surgery is restricted to case reports.

SUMMARY

Successful thoracic surgery requires understanding of the LVAD physiology. Modern devices are preload dependent and afterload sensitive. The effects of one-lung ventilation, including hypoxia and hypercapnia, may increase pulmonary vascular resistance and impair the right ventricle. Successful surgery necessitates a multidisciplinary approach, including thorough preoperative assessment; optimization and planning of intraoperative management strategies; and approaches to anticoagulation, right ventricular failure and LVAD flow optimization. This article discusses recent evidence on these topics.

Hemodynamic Response to Exercise in Patients Supported by Continuous Flow Left Ventricular Assist Devices

OBJECTIVES

This study sought to characterize the hemodynamic response to exercise in LVAD-supported patients and identify parameters most strongly associated with peak oxygen consumption (VO₂).

BACKGROUND

Despite improved survival for heart failure patients afforded by continuous flow left ventricular assist devices (LVADs), peak exercise capacity remains impaired. Mechanisms underlying this reduced functional capacity remain poorly understood.

METHODS

Patients referred for post-VAD hemodynamic optimization from December 2017 through June 2019 were enrolled. Swan Ganz catheters were inserted and upright incremental bicycle ergometry with respiratory gas analysis was performed. Hemodynamic measurements, mixed venous saturation, and arterial blood pressure were recorded every 3 min during exercise. Linear correlations were performed between peak VO₂ (ml/min) and peak Fick cardiac output (CO), peak device flow, the assumed intrinsic CO derived as Fick CO-device flow, peak pressure differential across the LVAD (mean arterial pressure-pulmonary capillary wedge pressure), peak pressure differential across right ventricle (mean pulmonary artery pressure - right atrial pressure) and systemic vascular resistance.

RESULTS

Forty-five patients supported by axial flow pumps (n = 12) and centrifugal flow pumps (n = 33) were studied. There were 34 men and 11 women. Age averaged 60 ± 10 years. Peak VO₂ averaged 10.6 ± 3.1 ml/kg/min. Fick CO had the greatest correlation with peak VO₂ with r = 0.73 (p < 0.0001) followed by intrinsic CO (r = 0.67; p < 0.0001). Multivariate model that best predicted peak VO₂ included Fick CO and peak arterial venous oxygen (AVO₂) difference.

CONCLUSIONS

LVAD supported patients have severely impaired peak exercise capacity. The peak Fick cardiac output was the best correlate of peak exercise performance.

Exercise-induced hypoxemia predicts heart failure hospitalization and death in patients supported with left ventricular assist devices

Following implantation of continuous-flow left ventricular assist devices, mechanical off-loading results in improved resting hemodynamics; however, peak exercise capacity generally does not increase substantially. This study evaluated patients supported by continuous-flow left ventricular assist devices who were invasively monitored during exercise to define parameters that underpin exercise capacity and outcomes. A review of all patients supported by continuous-flow left ventricular assist devices who underwent supine bicycle ergometry exercise testing with measurement of pulmonary gas exchange during right heart catheterization for evaluation of dyspnea at one institution between 2007 and 2018 was performed (n = 22). The primary outcome of this investigation was death or heart failure hospitalization. Although resting filling pressures were relatively preserved, resting cardiac index (Fick) was low (2.1 ± 0.5 mL/kg/min). An impaired cardiac output reserve was present in 75% of patients. On univariate modeling, patients with supine exercise-induced hypoxemia (O₂ saturation <90%) experienced significantly diminished hospitalization-free survival (unadjusted hazard ratio = 11.0, confidence interval = 2.4-57.2, p = 0.003), which persisted despite adjustment for right heart catheterization peak VO₂ and peak cardiac output (adjusted hazard ratio = 25, confidence interval = 3.6-322, p = 0.001). Our findings suggest that supine exercise testing provides additional prognostic utility in the continuous-flow left ventricular assist device population.

Approaches to improving exercise capacity in patients with left ventricular assist devices: an area requiring further investigation

Introduction: Left ventricular assist device (LVAD) implantation has become a well-established treatment option for patients with end stage heart failure (HF) who are refractory to medical therapy. While LVADs implantation does effectively improve hemodynamic performance many patients still possess peripheral pathological adaptations often present in end-stage HF. Therefore, increased attention has been placed on investigating the effects of exercise training for patients with LVADs to improve clinical outcomes. However, the available evidence on exercise training for patients with LVADs is limited. Areas covered: The purpose of this narrative review is to summarize: 1) The evolution of LVAD technology and usage; 2) The physiological responses to exercise in patients with LVADs; 3) The available evidence regarding exercise training; 4) Potential strategies to implement exercise training programs for this patient population. Expert opinion: The available evidence for exercise training to improve physical function and clinical outcomes for patients with LVADs is promising but limited. Future research is needed to further elucidate the ideal exercise training parameters, method of delivery for exercise training, and unique barriers and facilitators to exercise training for patients receiving LVAD implantation.

Clinical outcomes of inpatient cardiac rehabilitation for patients with treated left ventricular assist device in Korea: 1-year follow-up

In Korea, the first patient with a left ventricular assist device (LVAD) for destination therapy had successful implantation of a continuous-flow model in 2012. We investigated the safety and efficacy of exercise therapy with LVAD implantation 15 Korean patients. We retrospectively reviewed 15 patients (mean age, 67.4±11.6 years; 10 males, 5 female, left ventricular ejection fraction 23.6%±7.1%), including 4 with implanted continuous-flow and 11 an axial-flow LVAD. The New York Heart Association functional classification, ejection fraction, and quality of life were obtained. Survival rate, adverse events, admission rates, and enrollment rates in cardiac rehabilitation were investigated. Survival at 6 and 12 months was 100% and 89%, respectively. The New York Heart Association functional classification improved from 3.4±0.5 to 2.3±0.05 at 12 months postoperatively (P<0.0001). The ejection fraction significantly increased from 23.6%±7.2% on the preoperative day to 35.4%±14.2% at 1 year (P<0.0018). The quality of life was also improved at 1 year (P<0.0001). The most common adverse events were bleeding (56%) and dyspnea (44%). The number of admissions was 3.2 per patient-year. LVAD therapy is a safe and effective treatment option with exercise intervention for Korean patients waiting for heart transplantation or those who were ineligible for heart transplantation. A larger study with longer follow-up is needed to determine details clinical outcomes after LVAD.

Influence of left ventricular assist device pressure-flow characteristic on exercise physiology: Assessment with a verified numerical model

Current left ventricular assist devices are designed to reestablish patient's hemodynamics at rest but they lack the suitability to sustain the heart adequately during physical exercise. Aim of this work is to assess the performance during exercise of a left ventricular assist device with flatter pump pressure-flow characteristic and increased pressure sensitivity (left ventricular assist device 1) and to compare it to the performance of a left ventricular assist device with a steeper characteristic (left ventricular assist device 2). The two left ventricular assist devices were tested at constant rotational speed with a verified computational cardiorespiratory simulator reproducing an average left ventricular assist device patient response to exercise (EXE↑) and a left ventricular assist device patient with no chronotropic and inotropic response (EXE→). According to the results, left ventricular assist device 1 pumps a higher flow than left ventricular assist device 2 both at EXE↑ (6.3 vs 5.6 L/min) and at EXE→ (6.7 vs 6.1 L/min), thus it better unloads the left ventricle. Left ventricular assist device 1 increases the power delivered to the circulation from 0.63 W at rest to 0.67 W at EXE↑ and 0.82 W at EXE→, while left ventricular assist device 2 power shows even a minimal decrease. Left ventricular assist device 1 better sustains exercise hemodynamics and can provide benefits in terms of exercise performance, especially for patients with a poor residual left ventricular function, for whom the heart can hardly accommodate an increase of cardiac output.

The Rehabilitation of Patients With Advanced Heart Failure After Left Ventricular Assist Device Placement: A Narrative Review

Because more patients with advanced heart failure are receiving a left ventricular assist device (LVAD) as destination therapy or a bridge to transplantation, there is increasing attention on functional outcomes and quality of life after LVAD implantation. Rehabilitation providers in the acute inpatient rehabilitation setting increasingly will treat patients with an LVAD and should understand the exercise physiology, medical management, rehabilitation considerations, and outcomes after rehabilitation for patients with an LVAD. The purpose of this article is to provide the physiatrist with a comprehensive understanding of the rehabilitation of patients with advanced heart failure and LVAD implantation. Changes in relevant organ system physiology and exercise physiology after LVAD are summarized. Safety of rehabilitation and program considerations for acute inpatient rehabilitation are reviewed. Recommendations for medical management and prevention of secondary complications seen in patients with an LVAD are outlined. A discussion of outcomes after acute inpatient rehabilitation, the dual diagnosis of stroke and LVAD placement, and long-term cognitive, functional, and quality-of-life outcomes after LVAD placement is presented.

LVAD Pump Flow Does Not Adequately Increase With Exercise

Left ventricular assist devices (LVADs) restore cardiovascular circulatory demand at rest with a spontaneous increase in pump flow to exercise. The relevant contribution of cardiac output provided by the LVAD and ejected through the aortic valve for exercises of different intensities has been barely investigated in patients. The hypothesis of this study was that different responses in continuous recorded pump parameters occur for maximal and submaximal intensity exercises and that the pump flow change has an impact on the oxygen uptake at peak exercise (pVO₂ ). Cardiac and pump parameters such as LVAD flow rate (Q_LVAD ), heart rate (HR), and aortic valve (AV) opening were analyzed from continuously recorded LVAD data during physical exercises of maximal (bicycle ergometer test) and submaximal intensities (6-min walk test and regular trainings). During all exercise sessions, the LVAD speed was kept constant. Cardiac and pump parameter responses of 16 patients for maximal and submaximal intensity exercises were similar for Q_LVAD : +0.89 ± 0.52 versus +0.59 ± 0.38 L/min (P = 0.07) and different for HR: +20.4 ± 15.4 versus +7.7 ± 5.8 bpm (P < 0.0001) and AV-opening with 71% versus 23% of patients (P < 0.0001). Multi-regression analysis with pVO₂ (R²  = 0.77) showed relation to workload normalized by bodyweight (P = 0.0002), HR response (P = 0.001), AV-opening (P = 0.02), and age (P = 0.06) whereas the change in Q_LVAD was irrelevant. Constant speed LVADs provide inadequate support for maximum intensity exercises. AV-opening and improvements in HR show an important role for higher exercise capacities and reflect exercise intensities. Changes in pump flow do not impact pVO₂ and are independent of AV-opening and response in HR. An LVAD speed control may lead to adequate left ventricular support during strenuous physical activities.

Exercise gas exchange in continuous-flow left ventricular assist device recipients

Exercise ventilation/perfusion matching in continuous-flow left ventricular assist device recipients (LVAD) has not been studied systematically. Twenty-five LVAD and two groups of 15 reduced ejection fraction chronic heart failure (HFrEF) patients with peak VO₂ matched to that of LVAD (HFrEF-matched) and ≥14 ml/kg/min (HFrEF≥14), respectively, underwent cardiopulmonary exercise testing with arterial blood gas analysis, echocardiogram and venous blood sampling for renal function evaluation. Arterial-end-tidal PCO₂ difference (P(a-ET)CO₂) and physiological dead space-tidal volume ratio (VD/VT) were used as descriptors of alveolar and total wasted ventilation, respectively. Tricuspid annular plane systolic excursion/pulmonary artery systolic pressure ratio (TAPSE/PASP) and blood urea nitrogen/creatinine ratio were calculated in all patients and used as surrogates of right ventriculo-arterial coupling and circulating effective volume, respectively. LVAD and HFrEF-matched showed no rest-to-peak change of P(a-ET)CO₂ (4.5±2.4 vs. 4.3±2.2 mm Hg and 4.1±1.4 vs. 3.8±2.5 mm Hg, respectively, both p >0.40), whereas a decrease was observed in HFrEF≥14 (6.5±3.6 vs. 2.8±2.0 mm Hg, p <0.0001). Rest-to-peak changes of P(a-ET)CO₂ correlated to those of VD/VT (r = 0.70, p <0.0001). Multiple regression indicated TAPSE/PASP and blood urea nitrogen/creatinine ratio as independent predictors of peak P(a-ET)CO₂. LVAD exercise gas exchange is characterized by alveolar wasted ventilation, i.e. hypoperfusion of ventilated alveoli, similar to that of advanced HFrEF patients and related to surrogates of right ventriculo-arterial coupling and circulating effective volume.

Effects of pump speed changes on exercise capacity in patients supported with a left ventricular assist device-an overview

The implantation of left ventricular assist devices (LVAD) has been established as a successful treatment for terminal heart failure (HF) for many years. Patient benefits include significantly improved survival, as well as improved quality of life. However, peak exercise capacity following LVAD implantation remains considerably restricted. This could be due to the predominate use of continuous-flow pumps, which operate at a fixed rotational speed and do not adapt to exercise conditions. Therefore, current research is focused on whether, and to what extent, adaptations in pump speed can influence and improve patient exercise capacity. We performed a systematic PubMed literature search on this topic, and found 11 relevant studies with 161 patients. Exercise time, peak work load, total cardiac output (TCO), peak oxygen consumption (peak VO₂) and, if available, values at the anaerobic threshold (AT) were all taken into consideration. Possible complications were documented. This paper aims to compare the results from these studies in order to discuss the effects of pump speed adaptations on exercise capacity.