Counterpulsation Mode Research Articles

The hemodynamics and blood trauma in axial blood pump under different operating models.

Speed modulation of blood pumps has been proved to help restore vascular pulsatility and implemented clinically during treatment for cardiac failure. However, its effect on blood trauma has not been studied thoroughly. In this paper, we study the flow field of an axial pump FW-X under the modes of co-pulse, counter pulse, and constant speed to evaluate the blood trauma. Based on the coupling model of cardiovascular systems and axial blood pump, aortic pressure and the pump flow were obtained and applied as the boundary conditions at the pump outlet and inlet. The level of shear stress and hemolysis index were derived from computational fluid dynamics (CFD) simulation. Results showed that the constant speed mode had the lowest shear stress level and hemolytic index at the expense of diminished pulsatility. Compared with the constant speed mode, the hemolysis index of co-pulse and counter pulse mode was higher, but it was helpful to restore vascular pulsatility. This method can be easily incorporated in the in vitro testing phase to analyze and decrease a pump's trauma before animal experimentation, thereby reducing the cost of blood pump development.

Model-based evaluation of local hemodynamic effects of enhanced external counterpulsation

Background and ObjectivesThe treatment benefits of enhanced external counterpulsation (EECP) heavily depends on hemodynamics. Global hemodynamics of EECP can cause blood flow redistribution in the circulatory system whereas local hemodynamic effects act on vascular endothelial cells (VECs). Local hemodynamic effects of EECP on VECs are important in the treatment of atherosclerosis, but currently cannot be not evaluated. Herein we aim to establish evaluation models of local hemodynamic effects based on the global hemodynamic indicators. MethodsWe established 0D/3D geometric multi-scale hemodynamic models of the coronary and cerebral artery of two healthy individuals to calculate the global hemodynamic indicators and the local hemodynamic effects. Clinical EECP trials were performed to verify the accuracy of the multi-scale hemodynamic model. The global hemodynamic indicators included diastolic blood pressure/systolic blood pressure (Q = D/S), mean arterial pressure (MAP), internal carotid artery flow (ICAF) and cerebral blood flow (CBF), whereas local hemodynamic effects focused on time-averaged wall shear stress (TAWSS). The correlation between these indicators was analyzed via Pearson correlation coefficient. Significantly related indicators were selected for curve-fitting to establish evaluation models of the coronary and cerebral artery. Moreover, clinical data of a coronary heart disease patient and a cerebral ischemic stroke patient were collected to verify the effectiveness of the application of the established evaluation models to real patients. ResultsFor coronary artery, TAWSS was correlated to Q = D/S and ICAF (P < 0.05), whereas for cerebral artery, TAWSS was correlated to MAP and CBF (P < 0.05). The mean square error (MSE) between the evaluated values using evaluation model and the calculated values using 0D/3D model of TAWSS of the coronary and cerebral artery were 5.4% and 1.0%, respectively. The MSE of evaluation model applied to real patients was greater than that applied to healthy individuals, but within an acceptable range. ConclusionsThe presented error demonstrated validity and accuracy of the evaluation models in clinical patients. Based on the evaluation models, global hemodynamic indicators could be used to evaluate the local hemodynamic effects under the current counterpulsation mode. With TAWSS range of 4–7 Pa as the target range, EECP strategies can further be optimized.

A Numerical Model for Simulating the Hemodynamic Effects of Enhanced External Counterpulsation on Coronary Arteries.

Traditional enhanced external counterpulsation (EECP) used for the clinical treatment of patients with coronary heart disease only assesses diastolic/systolic blood pressure (Q = D/S > 1.2). However, improvement of the hemodynamic environment surrounding vascular endothelial cells of coronary arteries after long-term application of EECP is the basis of the treatment. Currently, the quantitative hemodynamic mechanism is not well understood. In this study, a standard 0D/3D geometric multi-scale model of the coronary artery was established to simulate the hemodynamic effects of different counterpulsation modes on the vascular endothelium. In this model, the neural regulation caused by counterpulsation was thoroughly considered. Two clinical trials were carried out to verify the numerical calculation model. The results demonstrated that the increase in counterpulsation pressure amplitude and pressurization duration increased coronary blood perfusion and wall shear stress (WSS) and reduced the oscillatory shear index (OSI) of the vascular wall. However, the impact of pressurization duration was the predominant factor. The results of the standard model and the two real individual models indicated that a long pressurization duration would cause more hemodynamic risk areas by resulting in excessive WSS, which could not be reflected by the change in the Q value. Therefore, long-term pressurization during each cardiac cycle therapy is not recommended for patients with coronary heart disease and clinical treatment should not just pay attention to the change in the Q value. Additional physiological indicators can be used to evaluate the effects of counterpulsation treatment.

Study on the synchronization of biventricular beats with the control mode of left ventricular assist device

Right ventricular (RV) failure has become a deadly complication of left ventricular assist device (LVAD) implantation, for which desynchrony in bi-ventricular pulse resulting from a LVAD is among the important factor. This paper investigated how different control modes affect the synchronization of pulse between LV (left ventricular) and RV by numerical method. The numerical results showed that the systolic duration between LV and RV did not significantly differ at baseline (LVAD off and cannula clamped) (48.52% vs. 51.77%, respectively). The systolic period was significantly shorter than the RV systolic period in the continuous-flow mode (LV vs. RV: 24.38% vs. 49.16%) and the LV systolic period at baseline. The LV systolic duration was significantly shorter than the RV systolic duration in the pulse mode (LV vs. RV: 28.38% vs. 50.41%), but longer than the LV systolic duration in the continuous-flow mode. There was no significant difference between the LV and RV systolic periods in the counter-pulse mode (LV vs. RV: 43.13% vs. 49.23%). However, the LV systolic periods was shorter than the no-pump mode and much longer than the continuous-flow mode. Compared with continuous-flow and pulse mode, the reduction in rotational speed (RS) brought out by counter-pulse mode significantly corrected the duration of LV systolic phase. The shortened duration of systolic phase in the continuous-flow mode was corrected as re-synchronization in the counter-pulse mode between LV and RV. Hence, we postulated that the beneficial effects on RV function were due to re-synchronizing of RV and LV contraction. In conclusion, decreased RS delivered during the systolic phase using the counter-pulse mode holds promise for the clinical correction of desynchrony in bi-ventricular pulse resulting from a LVAD and confers a benefit on RV function.

Effects of Pulsatile Frequency of Left Ventricular Assist Device (LVAD) on Coronary Perfusion: A Numerical Simulation Study

BackgroundLeft ventricular assist devices (LVADs) with counter-pulsation mode have been widely used to support left ventricular function and improve coronary circulation. However, the frequency characteristics of the coronary system have not been considered. The aim of this study was to investigate the effects of pulsatile frequency of LVADs on coronary perfusion.Material/MethodsFirst, a lumped parameter (LP) model incorporating coronary circulation, systemic circulation, left heart, and LVAD was established to simulate the cardiovascular system. Then, the frequency characteristics of the coronary system were analyzed and the calculation results showed that the pulsatile frequency of the LVAD has a substantial effect on coronary blood flow. To verify the accuracy of the theoretical analysis, the hemodynamic effects of the LVAD on the coronary artery were compared under 4 support modes: co-pulsation mode, and counter-pulsation modes in synchronization ratios of 1: 1, 2: 1, and 3: 1.ResultsWe found that the coronary flow increased by 5% when the working mode changed from co-pulsation to counter-pulsation in a synchronization ratio of 1: 1, and by an additional 6% when the working mode changed from counter-pulsation in a synchronization ratio of 1: 1 to counter-pulsation in a synchronization ratio of 3: 1.ConclusionsThis work provides a useful method to increase coronary perfusion and may be beneficial for improving myocardial function in patients with end-stage heart failure, especially those with ischemic cardiomyopathy (ICM).

Biomechanical effects of the working modes of LVADs on the aortic valve: A primary numerical study

Aortic valve diseases caused by the support from left ventricular assist devices (LVADs) have attracted increasing attention due to the wide application of the LVADs. However, the biomechanical effects of the working modes of LVADs on the aortic valve are still poorly understood. Hence, in this study, these biomechanical effects are investigated using a novel fluid–structure interaction method, which combines the lattice Boltzmann and the finite element methods. On the basis of the clinical practice, three working modes of LVADs, namely, the constant flow, co-pulse, and counter pulse modes, are chosen. Results demonstrate that the working mode of LVADs is an important factor as it can change the biomechanical states of the aortic valve and the hemodynamic environment in the aortic root directly. Compared with the constant flow mode, the two other working modes can provide better biomechanical effects on the aortic valve. However, the advantages of the co-pulse and the counter pulse modes on the aortic valve are not the same. The LVADs in the co-pulse mode can remarkable reduce the pressure load of the leaflets during the diastolic phase (maximum stress: co-pulse mode, 0.85 MPa; constant flow mode, 1.23 MPa; counter pulse mode, 1.50 MPa). By contrast, the LVADs in the counter pulse mode can achieve the highest effective orifice area of the aortic valve (co-pulse mode: 0.12 cm2, constant flow mode: 0.17 cm2, counter pulse mode: 0.25 cm2). In sum, the co-pulse mode is suitable for patients with certain cardiac function, because this mode keeps the valve open intermittently and reduces the pressure load on the aortic leaflets during the diastolic phase to prevent valve remodeling. By contrast, the counter pulse mode is suitable for patients with severely impaired cardiac function, because this mode keeps the valve open as much as possible and provides high blood perfusion.

Left Ventricular Assist Device Shear Stress Quantification Utilizing Computational Fluid Dynamics: Using Physics and Physiology to Optimize Programmable Flow Algorithms

Our current understanding of left ventricular assist device (LVAD) flow algorithms and their impact on shear stress and platelet activation remains incompletely understood. Computational fluid dynamics (CFD) allows for analysis of flow in the cardiovascular system. CFD simulations were carried out on a patient with a HeartMate II. Simulations were also done substituting for HVAD with or without Lavare cycle, HeartMate 3 in continuous mode or with Artificial Pulse as well as novel flow algorithms including copulsation and counterpulsation modes. LVAD flow was calculated using a lumped-parameter-model (LPM) of the systemic circulation, which was calibrated with patient-specific ventricular volume changes from 4 dimensional CT and hemodynamic tracings. The LVADs were implemented in the LPM via published H-Q curves. Shear stress and platelet activation were quantified for each flow algorithm and pump type. Wall shear stress was greater with the HVAD when compared to the HMII or HM3 (Figure Top). In the aortic arch and carotid arteries, a 42% increase in shear stress was noted with the HVAD compared to the HM3 in continuous mode (1.86 vs. 1.31 Pa) with little impact from the addition of the Lavare Cycle (Figure Bottom). Platelet activation was similarly greatest with the HVAD in the carotid arteries. The addition of the artificial pulse to the HM3 flow algorithm led to a 168% increase in shear stress (0.363 vs 0.139 Pa) throughout the ascending aorta (Figure Bottom). CFD analysis reveals that the artificial pulse increases wall shear stress in the ascending aorta and may represent a plausible mechanism to explain the high observed rates of aortic insufficiency seen with the HM3. Similarly, the higher shear stress rates in the carotid arteries seen with the HVAD might partly explain the higher residual rates of stroke with this pump. These hypothesis generating questions need to be prospective explored.

Hemodynamic effects of enhanced external counterpulsation on cerebral arteries: a multiscale study

BackgroundEnhanced external counterpulsation (EECP) is an effective method for treating patients with cerebral ischemic stroke, while hemodynamics is the major contributing factor in the treatment of EECP. Different counterpulsation modes have the potential to lead to different acute and long-term hemodynamic changes, resulting in different treatment effects. However, various questions about appropriate counterpulsation modes for optimizing hemodynamic effects remain unanswered in clinical treatment.MethodsA zero-dimensional/three-dimensional (0D/3D) geometric multiscale model of the cerebral artery was established to obtain acute hemodynamic indicators, including mean arterial pressure (MAP) and cerebral blood flow (CBF), as well as localized hemodynamic details for the cerebral artery, which includes wall shear stress (WSS) and oscillatory shear index (OSI). Counterpulsation was achieved by applying pressure on calf, thigh and buttock modules in the 0D model. Different counterpulsation modes including various pressure amplitudes and pressurization durations were applied to investigate hemodynamic responses, which impact acute and long-term treatment effects. Both vascular collapse and cerebral autoregulation were considered during counterpulsation.ResultsVariations of pressure amplitude and pressurization duration have different impacts on hemodynamic effects during EECP treatment. There were small differences in the hemodynamics when similar or different pressure amplitudes were applied to calves, thighs and buttocks. When increasing pressure amplitude was applied to the three body parts, MAP and CBF improved slightly. When pressure amplitude exceeded 200 mmHg, hemodynamic indicators almost never changed, demonstrating consistency with clinical data. However, hemodynamic indicators improved significantly with increasing pressurization duration. For pressurization durations of 0.5, 0.6 and 0.7 s, percentage increases for MAP during counterpulsation were 1.5%, 23.5% and 39.0%, for CBF were 1.2%, 23.4% and 41.6% and for time-averaged WSS were 0.2%, 43.5% and 85.0%, respectively.ConclusionsWhen EECP was applied to patients with cerebral ischemic stroke, pressure amplitude applied to the three parts may remain the same. Patients may not gain much more benefit from EECP treatment by excessively increasing pressure amplitude above 200 mmHg. However, during clinical procedures, pressurization duration could be increased to 0.7 s during the cardiac circle to optimize the hemodynamics for possible superior treatment outcomes.

The assessment bioenergy of cardiac contraction in the conditions of mechanical support circulation

Aim: to develop a new modified index for the assessment of bioenergy heart in conditions of heart failure. To assess the energy of the heart when using systems to bypass the left ventricle of the heart using non-pulsed flow pumps. To consider the fundamental advantage of non-pulsating flow pumps with the generation of a pulsating flow in the cardio-synchronized copulsation mode over the counterpulsation mode.

The Influence of Rotary Blood Pump Speed Modulation on the Risk of Intraventricular Thrombosis.

Rotary left ventricular assist devices (LVADs) are commonly operated at a constant speed, attenuating blood flow pulsatility. Speed modulation of rotary LVADs has been demonstrated to improve vascular pulsatility and pump washout. The effect of LVAD speed modulation on intraventricular flow dynamics is not well understood, which may have an influence on thromboembolic events. This study aimed to numerically evaluate intraventricular flow characteristics with a speed modulated LVAD. A severely dilated anatomical left ventricle was supported by a HeartWare HVAD in a three-dimensional multiscale computational fluid dynamics model. Three LVAD operating scenarios were evaluated: constant speed and sinusoidal co- and counter-pulsation. In all operating scenarios, the mean pump speed was set to restore the cardiac output to 5.0L/min. Co- and counter-pulsation was speed modulated with an amplitude of 750rpm. The risk of thrombosis was evaluated based on blood residence time, ventricular washout, kinetic energy densities, and a pulsatility index map. Blood residence time for co-pulsation was on average 1.8 and 3.7% lower than constant speed and counter-pulsation mode, respectively. After introducing fresh blood to displace preexisting blood for 10 cardiac cycles, co-pulsation had 1.5% less old blood in comparison to counter-pulsation. Apical energy densities were 84 and 27% higher for co-pulsation in comparison to counter-pulsation and constant speed mode, respectively. Co-pulsation had an increased pulsatility index around the left ventricular outflow tract and mid-ventricle. Improved flow dynamics with co-pulsation was caused by increased E-wave velocities which minimized blood stasis. In the studied scenario and from the perspective of intraventricular flow dynamics, co-pulsation of rotary LVADs could minimize the risk of intraventricular thrombosis.

The numerical study on specialized treatment strategies of enhanced external counterpulsation for cardiovascular and cerebrovascular disease

Traditional clinical mode of enhanced external counterpulsation is not targeted for different diseases. Specialized strategies in the treatment of enhanced external counterpulsation for coronary heart disease and cerebral ischemic stroke are supposed to be distinguished. The goal of treatment for coronary heart disease is diastolic blood pressure/systolic blood pressure = Q ≥ 1.2 after counterpulsation, while the goal of treatment for cerebral ischemic stroke is the improvement of mean arterial pressure. A computational lumped parameter model was established for the simulation of hemodynamic effect of enhanced external counterpulsation on two diseases. Vessel collapse was considered during the simulation of counterpulsation. Based on different pressurized and decompressed rate, pressurized moment, pressure duration, and pressure amplitude, different counterpulsation modes were applied to the model and the immediate hemodynamic effects were compared. Results showed that the pressure duration and pressure amplitude had most influence on two diseases. For cerebral ischemic stroke, the longer pressure duration and the higher pressure amplitude of thighs, the higher mean arterial pressure; while for coronary heart disease, the value of Q was highest when the pressure end moment was 0.6s during a 0.88-s cardiac cycle, and Q had a linear increase in the pressure amplitude of buttocks, but little change with the increase of calves and thighs pressure amplitude. For patients with coronary heart disease, the pressure duration was not supposed to be too long to avoid the increase of systolic blood pressure, and the improvement of pressure amplitude of buttocks could promise a positive treatment effect for coronary heart disease. While for patients with cerebral ischemic stroke, both the long pressure duration of each part and the high pressure amplitude of thighs could result in the systolic blood pressure and diastolic blood pressure have a certain increase, thus promoting the maximum mean arterial pressure and a best treatment. Graphical abstract The specialized treatment strategies of EECP for cardiovascular and cerebrovascular disease.

Pulsatile operation of a continuous-flow right ventricular assist device (RVAD) to improve vascular pulsatility.

Despite the widespread acceptance of rotary blood pump (RBP) in clinical use over the past decades, the diminished flow pulsatility generated by a fixed speed RBP has been regarded as a potential factor that may lead to adverse events such as vasculature stiffening and hemorrhagic strokes. In this study, we investigate the feasibility of generating physiological pulse pressure in the pulmonary circulation by modulating the speed of a right ventricular assist device (RVAD) in a mock circulation loop. A rectangular pulse profile with predetermined pulse width has been implemented as the pump speed pattern with two different phase shifts (0% and 50%) with respect to the ventricular contraction. In addition, the performance of the speed modulation strategy has been assessed under different cardiovascular states, including variation in ventricular contractility and pulmonary arterial compliance. Our results indicated that the proposed pulse profile with optimised parameters (Apulse = 10000 rpm and ωmin = 3000 rpm) was able to generate pulmonary arterial pulse pressure within the physiological range (9–15 mmHg) while avoiding undesirable pump backflow under both co- and counter-pulsation modes. As compared to co-pulsation, stroke work was reduced by over 44% under counter-pulsation, suggesting that mechanical workload of the right ventricle can be efficiently mitigated through counter-pulsing the pump speed. Furthermore, our results showed that improved ventricular contractility could potentially lead to higher risk of ventricular suction and pump backflow, while stiffening of the pulmonary artery resulted in increased pulse pressure. In conclusion, the proposed speed modulation strategy produces pulsatile hemodynamics, which is more physiologic than continuous blood flow. The findings also provide valuable insight into the interaction between RVAD speed modulation and the pulmonary circulation under various cardiovascular states.

Rotational speed modulation used with continuous-flow left ventricular assist device provides good pulsatility.

Continuous-flow left ventricular assist devices (CF-LVADs) are widely used to treat patients with end-stage heart failure. Although continuous flow is different from physiological flow, patients show improved outcomes after CF-LVAD implantation. A novel rotational speed (RS) modulation system used with CF-LVAD (EVAHEART) has been developed, which can change RS in synchronization with the native cardiac cycle. We conducted the present study to investigate the influence of the system on pulsatility in peripheral perfusion. We implanted EVAHEART devices at the left ventricular apex drainage and the descending aortic perfusion via a left thoracotomy in 7 adult goats (56.8 ± 8.1 kg). Cardiogenic shock was induced by a beta-adrenergic antagonist. We evaluated the pulsatility index and maximal time derivative of flow rate (max dQ/dt) of the carotid, mesenteric and renal arteries. These data were collected with a bypass rate of 100% under 4 conditions: circuit clamp, continuous mode, co-pulse mode (increased RS during systole) and counter-pulse mode (increased RS during diastole). The pulsatility indexes of the carotid and renal artery in the co-pulse mode were significantly higher than in the other modes. Max dQ/dt of the carotid and mesenteric arteries were significantly higher in the co-pulse mode than in the counter-pulse mode. The co-pulse mode of this novel RS modulation system may provide better pulsatility not only in the large vessels but also in the peripheral vasculature.

Novel Rotational Speed Modulation System Used With Venoarterial Extracorporeal Membrane Oxygenation

Femoral venoarterial extracorporeal membrane oxygenation (VA-ECMO) is widely used to maintain blood flow in patients with cardiogenic shock. However, retrograde blood flow increases left ventricular (LV) afterload during femoral VA-ECMO. Additional support by means of an intraaortic balloon pump (IABP) alleviates LV afterload but is associated with significant adverse events. We previously developed a system for rotational speed modulation in synchrony with the native cardiac cycle, for use with implantable continuous-flow LV assist devices. Here, we aimed to evaluate whether our novel rotation speed modulation system can improve coronary artery flow and reduce LV during femoral VA-ECMO. VA-ECMO was installed by means of right atrial drainage and distal abdominal aortic perfusion in six adult goats. Cardiogenic shock was induced with β-adrenergic antagonist infusion. An IABP was placed in the descending aorta. LV stroke work, LV end-systolic pressure, and coronary arterial flow were evaluated. Data were collected under five conditions (modes): baseline, circuit-clamp (cardiogenic shock), continuous mode (constant rotational speed), counterpulse mode (increasing rotational speed during diastole), and continuous mode with IABP support. LV stroke work and LV end-systolic pressure tended to be lower in the counterpulse mode, indicating decreased LV work load and afterload in this mode. Furthermore, coronary arterial flow tended to be higher in the counterpulse mode. Our system enabled an increase in coronary arterial flow and a decrease in LV work load and afterload during VA-ECMO. The system offers the effects of VA-ECMO and an IABP in a single device.

Abstract 12771: A Novel Rotational Speed Modulation System Used With an Implantable Continuous-flow Left Ventricular Assist Device Provides Good Pulsatility on Peripheral Organ Perfusion

Introduction: Continuous-flow left ventricular assist devices (CFLVAD) is widely used to treat patients with end-stage heart failure. Even though the continuous flow is not physiologic, outcomes of CFLVAD have been improved. We have developed a novel rotational speed (RS) modulation system used with CFLVAD (EVAHEART), which can change RS in synchronization with the native cardiac cycle. We have reported that the system can change cardiac load and optimize coronary artery flow. We conducted the present study to investigate the influence of our system on peripheral perfusion. Methods: We implanted EVAHEART devices by the left ventricular apex drainage and the descending aortic perfusion via left thoracotomy in seven adult goats (56.8 ± 8.1 kg). Cardiogenic shock was induced by a beta adrenergic antagonist and coronary artery ligations. We evaluated blood flow, pulsatility index (PI), and maximum time derivative of flow rate (max dQ/dt) of carotid artery (CA), mesenteric artery (MA), renal artery (RA), respectively, using ultrasonic flow meters directly placed on the arteries. Mean tissue blood flow (TBF) of the heart and omentum and PIs of TBF were measured using the TBF meter. Venous lactate level, cerebral oxygen extraction rate (ExO2) and regional saturation of oxygen (rSO2) of brain, kidney, and leg muscle were also evaluated. Those data were collected with a bypass rate of 100% under four conditions: circuit clamp, continuous mode (constant RS), co-pulse mode (increase RS during systole), and counter-pulse mode (increase RS during diastole). Results: PIs of CA and RA in the copulse mode were significantly higher than those in the other modes. Max dq/dt of CA and MA were significantly higher in the copulse mode than those in the counter-pulse mode. Max dq/dt of the three arteries in the copulse mode tended to be higher than those in the other modes. PIs of TBF of the heart and the omentum in the copulse mode tended to be higher than those in the other modes. As for the metabolic changes in each mode, there were no significant differences in levels of lactate, cerebral ExO2, or rSO2. Conclusions: The copulse mode of our novel RS modulation system may provide better pulsatility not only in the large vessels but also in the peripheral perfusion.

Hemodynamic analysis of outflow grafting positions of a ventricular assist device using closed-loop multiscale CFD simulations: Preliminary results

Subclavian arteries are a possible alternate location for left ventricular assist device (LVAD) outflow grafts due to easier surgical access and application in high risk patients. As vascular blood flow mechanics strongly influence the clinical outcome, insights into the hemodynamics during LVAD support can be used to evaluate different grafting locations. In this study, the feasibility of left and right subclavian artery (SA) grafting was investigated for the HeartWare HVAD with a numerical multiscale model. A 3-D CFD model of the aortic arch was coupled to a lumped parameter model of the cardiovascular system under LVAD support. Grafts in the left and right SA were placed at three different anastomoses angles (90°, 60° and 30°). Additionally, standard grafting of the ascending and descending aorta was modelled. Full support LVAD (5l/min) and partial support LVAD (3l/min) in co-pulsation and counter-pulsation mode were analysed. The grafting positions were investigated regarding coronary and cerebral perfusion. Furthermore, the influence of the anastomosis angle on wall shear stress (WSS) was evaluated. Grafting of left or right subclavian arteries has similar hemodynamic performance in comparison to standard cannula positions. Angularity change of the graft anastomosis from 90° to 30° slightly increases the coronary and cerebral blood flow by 6–9% while significantly reduces the WSS by 35%. Cannulation of the SA is a feasible anastomosis location for the HVAD in the investigated vessel geometry.

What Is the Optimal Setting for a Continuous-Flow Left Ventricular Assist Device in Severe Mitral Regurgitation?

Excessive left ventricular (LV) volume unloading can affect right ventricular (RV) function by causing a leftward shift of the interventricular septum in patients with mitral regurgitation (MR) receiving left ventricular assist device (LVAD) support. Optimal settings for the LVAD should be chosen to appropriately control the MR without causing RV dysfunction. In this study, we assessed the utility of our electrocardiogram-synchronized rotational speed (RS) modulation system along with a continuous-flow LVAD in a goat model of MR. We implanted EVAHEART devices after left thoracotomy in six adult goats weighing 66.4 ± 10.7 kg. Severe MR was induced through inflation of a temporary inferior vena cava filter placed within the mitral valve. We evaluated total flow (TF; the sum of aortic flow and pump flow [PF]), RV fractional area change (RVFAC) calculated by echocardiography, left atrial pressure (LAP), LV end-diastolic pressure (LVEDP), LV end-diastolic volume (LVEDV), and LV stroke work (LVSW) with a bypass rate (PF divided by TF) of 100% under four conditions: circuit-clamp, continuous mode, co-pulse mode (increased RS during systole), and counter-pulse mode (increased RS during diastole). TF tended to be higher in the counter-pulse mode. Moreover, RVFAC was significantly higher in the counter-pulse mode than in the co-pulse mode, whereas LAP was significantly lower in all driving modes than in the circuit-clamp condition. Furthermore, LVEDP, LVEDV, and LVSW were significantly lower in the counter-pulse mode than in the circuit-clamp condition. The counter-pulse mode of our RS modulation system used with a continuous-flow LVAD may offer favorable control of MR while minimizing RV dysfunction.

Shifting the pulsatility by increasing the change in rotational speed for a rotary LVAD using a native heart load control system.

We have previously developed a native heart load control system for a continuous-flow left ventricular assist device (LVAD) ((EVAHEART®; Sun Medical) and demonstrated that the rotational speed (RS) in synchronization with the cardiac cycle can alter pulsatility and left ventricular (LV) load under general anesthesia. In this study, we assessed the effects of different levels of increase in RS on pulsatility and LV load in the chronic awake phase. We implanted the EVAHEART via left thoracotomy in 7 normal goats (59.3±4.6kg). Two weeks after implantation, we examined the effects of co-pulse mode (increased RS in the systolic phase) and counter-pulse mode (increased RS in the diastolic phase), as well as shifting the change in RS from 250 to 500rpm, and 750rpm in both modes on pulsatility and LV load. Pulsatility was assessed using pulse pressure and mean dP/dt max of aortic pressure. LV load was assessed using stroke work and left ventricle end-diastolic volume determined from LV pressure-volume loops. In the co-pulse mode, pulsatility values increased as the change in RS increased. By contrast, in the counter-pulse mode, these values decreased as the change in RS increased. LV load increased significantly in the co-pulse mode compared with the counter-pulse mode, but there were no significant differences among the three levels of RS increase in either mode. Increasing RS to varying degrees with our newly developed system could contribute to pulsatility. However, it appeared to have little effect on LV load in normal hearts.

Abstract 10766: What is an Optimal Setting of Continuous-flow Left Ventricular Assist Device for Severe Mitral Regurgitation?

Introduction: Excessive volume unloading of the left ventricle (LV) affects the right ventricular (RV) function by causing shift of the ventricular septum during left ventricular assist device (LVAD) support in patients with mitral regurgitation (MR). Optimal settings of LVAD that control MR without RV dysfunction are required. We developed a novel cardiac-cycle synchronized rotational speed (RS) modulation system for a continuous-flow LVAD and assessed the system in a goat model of MR. Methods: We implanted EVAHEART (Sun Medical Technology Research Corp.) through left thoracotomy in six adult goats weighing 66.4 ± 10.7 kg. After implantation of the device, severe MR was induced with inflation of a temporary inferior vena cava filter that was placed in the mitral valve. The severity of MR was defined by left ventriculography and echocardiography. We evaluated total flow (TF: the sum of aortic flow and pump flow), RV fractional area change (RVFAC) calculated by echocardiography, left atrial pressure (LAP), LV end-diastolic pressure (LVEDP), LV end-diastolic volume (LVEDV), and LV stroke work (LVSW) with a bypass rate (pump flow divided by TF) of 100% under four conditions: circuit-clamp, continuous mode, co-pulse mode (increase RS in systole) and counter-pulse mode (increase RS in diastole). Results: TF tended to be higher in counter-pulse mode (3.27 ± 1.09, 3.51 ± 2.14, 3.45 ± 2.58, and 3.75 ± 2.39 L/min, in circuit-clamp, continuous mode, co-pulse mode, and counter-pulse mode, respectively; p &gt; 0.05). RVFAC was significantly higher in counter-pulse mode than in co-pulse mode (0.68 ± 0.05 vs 0.51 ± 0.08 , p &lt; 0.05). LAP was significantly lower in all the driving modes than in circuit-clamp. LVEDP, LVEDV and LVSW, shown as percentages of those in circuit-clamp (= 100%), were significantly lower in counter-pulse mode than in circuit-clamp (54.43 ± 32.05, 89.6 0 ± 4.23, and 60.30 ± 28.41 %, respectively; p &lt; 0.05). Conclusions: Good control of MR in counter-pulse mode could be achieved with enough LV volume unloading during diastole not to leave blood that regurgitates during systole. Given higher TF and RVFAC in counter-pulse mode, the mode has less adverse effects on the RV function. In conclusion, the mode may offer a favorable control of MR with minimizing RV dysfunction.

Abstract 15064: Control of Left Ventricular Load and Pulsatility by a Continuous-flow Left Ventricular Assist Device With a Native Heart Load Control System in Chronic Awake Phase

Introduction: We have previously developed a Native Heart Load Control System for a continuous-flow left ventricular assist device (EVAHEART) and demonstrated that the rotational speed (RS) in synchronization with the cardiac cycle can alter left ventricular (LV) load and pulsatility under general anesthesia. In this study, we assessed this system in chronic awake phase. Methods: We implanted EVAHEART in five goats (59.4±5.6kg) with a normal heart. Two weeks after the implantation, we examined the effects of the continuous mode (constant RS), counter-pulse mode (increase RS in diastolic phase) and co-pulse mode (increase RS in systolic phase) of this system on LV load and pulsatility in 100%, 75% and 50% bypass. We used two parameters to evaluate LV load, including stroke work (SW) and end-diastolic volume (LVEDV) determined from LV pressure-volume loops. About pulsatility, we used pulse pressure (PP) and mean dP/dt max of aortic pressure. Results: The co-pulse mode created greater LV load and pulsatility than the continuous mode in all bypass rates. In contrast, LV load and pulsatility in the counter-pulse mode were smaller than those in the continuous mode. There were statistically significant differences between values about LV load and pulsatility in counter-pulse and co-pulse mode; continuous/counter-pulse/co-pulse SW (ml·mmHg); 2601.71±2208.50/2127.88±1745.11/2845.54±2230.82 (100%): 2968.05±2265.75/2485.79±1714.07/3133.92±2203.64 (75%): 3134.42±2319.75/2927.76±2111.76/3313.13±2350.49 (50%), LVEDV (ml); 52.79±26.43/46.95±20.31/56.32±25.43 (100%): 57.22±28.19/51.38±21.83/59.06±26.63 (75%), 59.59±28.24/56.02±25.40/61.88±28.61 (50%), PP (mmHg); 30.09±10.01/22.63±8.09/36.79±9.32 (100%): 32.88±9.88/26.66±10.80/40.69±7.83 (75%): 37.30±10.86/32.76±12.43/41.97±9.59 (50%), mean dP/dt max of aortic pressure (mmHg/s); 979.89±369.20/687.98±230.12/1165.67±391.36 (100%): 1321.25±446.14/1047.78±393.29/1474.99±474.53 (75%): 1511.06±519.18/1332.6±471.91/1666.59±511.55 (50%). Conclusions: Our newly developed system could control LV load and pulsatility in the chronic awake phase. This system may provide the most favorable LV loading conditions for the recovery of the native heart.