Aortic insufficiency (AI) is an intractable complication during long term left ventricular assist device (LVAD) support. Conventional evaluation of AI depends on ultrasound evaluation, which is ...mainly a qualitative, not a quantitative method. The pathophysiology of AI during LVAD is shunt formation. Conversely, the methods to quantify the shunt of congenital heart disease are already established, and among these is the thermodilution technique. To develop an accurate quantification method for AI (namely, a shunt), we have adopted this conventional thermodilution technique. The purpose of this study was to determine whether this technique could calculate the shunt magnitude accurately in a simulated cardiac circuit. The magnitude of AI was represented by the recirculation rate (RR), defined by regurgitant flow (RF) divided by pump flow (PF). A mock circulatory system for an LVAD endurance test (Laboheart NCVC; Iwaki & Co., Ltd, Tokyo, Japan) was used. A centrifugal LVAD was equipped in the Laboheart in parallel from the left ventricle to the aorta. A parallel shunt circuit was created across the aortic valve to mimic AI. To control the magnitude of AI, the resistance of the AI circuit was changed. Heart failure was simulated by controlling the parameters of the Laboheart. The LVAD was driven in full bypass condition, confirming that the heart did not eject forward flow via the aortic valve. PF, RF, and the temperatures of two points of the outflow graft measured with two thermistors were monitored. Analyses were started after confirming that circuit water temperature was the same as room temperature. Hot water was injected from a port between the two thermistors of the outflow conduit. The time–temperature curves of both thermistors were recorded, and RR was calculated. Two values of RR calculated in two different ways (by analyzing thermistors and by calculating from flowmeter values) were compared. Multiple measurements were done by changing the magnitude of AI. The existence of AI could be easily confirmed by analyzing the temperature data. There was a good correlation between RR by thermistor and RR by flowmeter data (r = 0.984). Furthermore, the two RR values were almost the same. This novel technique could provide an accurate method for quantifying AI during LVAD support. This method can be clinically applied by left‐sided cardiac catheterization if a dedicated catheter with two thermistors and an injection hole is developed.
The effect of rotary left ventricular assist devices (LVADs) on myocardial perfusion has yet to be clearly elucidated, and several studies have shown decreased coronary flow under rotary LVAD ...support. We have developed a novel pump controller that can change its rotational speed (RS) in synchronization with the native cardiac cycle. The aim of our study was to evaluate the effect of counterpulse mode, which increases the RS in diastole, during coronary perfusion. Experiments were performed on ten adult goats. The EVAHEART LVAD was installed by the left ventricular uptake and the descending aortic return. Ascending aortic flow, pump flow, and coronary flow of the left main trunk were monitored. Coronary flow was compared under four conditions: circuit-clamp, continuous mode (constant pump speed), counterpulse mode (increased pump speed in diastole), and copulse mode (increased pump speed in systole). There were no significant baseline changes between these groups. In counterpulse mode, coronary flow increased significantly compared with that in continuous mode. The waveform analysis clearly revealed that counterpulse mode mainly resulted in increased diastolic coronary flow. In conclusion, counterpulse mode of rotary LVADs can enhance myocardial perfusion. This novel drive mode can provide great benefits to the patients with end-stage heart failure, especially those with ischemic etiology.
The purpose of this study was to observe and clarify the interventricular dysscynchrony caused by continuous-flow left ventricular assist device (CF-LVAD) support using the conductance method. During ...CF-LVAD support, the systolic phase of the left ventricle (LV) becomes shorter than that of the right ventricle (RV). Accordingly, timing of the systole and diastole during the cardiac cycle is not synchronous between the LV and RV. In this study, we evaluated this phenomenon in a normal heart model using the adult goat (
n
= 5, body weight 44.5 ± 2.9 kg). A centrifugal LVAD was implanted under general anesthesia. We inserted the conductance catheter into the RV and LV to obtain the pressure–volume relationship of the two ventricles simultaneously. We defined the dyssynchronous status as the sign (plus or minus) of the LV volume-change opposite to that of RV volume-change. Dyssynchronous phase of the cardiac cycle was observed in 5.6 ± 0.65% of hearts under LVAD pump-off and 25.3 ± 3.3% under LVAD full bypass, respectively (
p
< 0.05). To the best of our knowledge, this is the first experimental report clarifying interventricular dyssynchrony during CF-LVAD support using the conductance method. Quantification of this phenomenon under various support conditions and assessment of influences on the right ventricular function will be studied in future studies.
In the development of a new device for extracorporeal circulation, long‐term durability and biocompatibility are required. The CAPIOX SL Pump (SL pump, Terumo Corporation, Tokyo, Japan), which is a ...centrifugal pump using a two‐pivot bearing, was developed with the hope of suppressing pump thrombus formation around the bearings. This study aimed to evaluate the in vivo performance of the SL pump in the condition assumed severe clinical situation for long‐term extracorporeal membrane oxygenation (ECMO) support. Extracorporeal circulation using the SL pump was installed in three goats, with drainage from the inferior vena cava and infusion into the right jugular artery. The animals were maintained with target pump flow of 2.0–3.0 L/min for 3 or 7 days. Anticoagulation was performed by continuous infusion of heparin with a target activated coagulation time (ACT) of 200 ± 50 s. Blood tests were performed regularly. After 3 or 7 days, autopsies were performed on all animals. The pumps were disassembled and observed for thrombus formation. The results were compared with those of our previous study of the current model of the centrifugal pump (SP pump). All animals were successfully managed within target pump flows and ACT values during the scheduled period, with no adverse events. No thrombus formation was found around the bearing of the SL pump. The blood tests showed normal major organ functions, and platelet consumption and hemolysis were significantly lower in this study compared to the previous study of the SP pump. The CAPIOX SL Pump showed excellent durability and biocompatibility in a large animal experiment.
A left ventricular assist device (LVAD) is also used for right ventricular assist because a right ventricular assist device (RVAD) does not exist. In that case, the LVAD is operated at off-design ...point and can damage the blood. Therefore, our research group has been working on the development of the RVAD in recent years. In the present study, we investigated the effects of the clearance of dynamic pressure bearings and the mass of the impeller on the motion of the impeller of the RVAD under development. Performance tests of the RVAD were carried out and the motion of the impeller was analyzed by two laser displacement sensors and a high-speed video camera. The time-averaged motion of the impeller was a revolution on a circular orbit centered on a position eccentric to the outlet direction of the casing. The predominant frequency of the impeller motion was about the half of the rotational frequency, which was thought to be due to the so-called oil whirl observed in general journal bearings. The impeller rotated without mechanical contact when the clearance of the bearing was 60, 70, and 80 mm for a titanium impeller and 80 mm for a stainless steel impeller. From this fact, it was found that the optimum value exists in the clearance of the bearing, and the lighter the impeller, the wider its range.
Continuous-flow left ventricular assist devices (LVADs) have improved the prognosis of end-stage heart failure. However, continuous-flow LVADs diminish pulsatility, which possibly result in bleeding, ...aortic insufficiency, and other adverse effects. We previously developed a novel control system for a continuous-flow LVAD (EVAHEART
®
; Sun Medical), and demonstrated that we could create sufficient pulsatility by increasing its rotational speed (RS) in the systolic phase (Pulsatile Mode) in the normal heart model. Here, we aimed to evaluate differences between systolic assist with advanced and delayed loads by shifting the timing of increased RS. We implanted EVAHEART in six goats (55.3 ± 4.3 kg) with normal hearts. We reduced their heart rates to <60 bpm using propranolol and controlled the heart rates at 80 and 120 bpm using ventricular pacing. We shifted the timing of increasing RS from −60 to +60 ms in the systolic phase. We found significant increases in all the following parameters when assessments of delayed timing (+60 ms) were compared with assessments of advanced timing (−60 ms): pulse pressure, mean d
P
/d
t
max of aortic pressure, and energy-equivalent pulse pressure. During continuous-flow LVAD support, pulsatility can be controlled using a rotary pump. In particular, pulsatility can be shifted by delaying increased RS.
We developed a novel miniaturized extracorporeal centrifugal pump “BIOFLOAT NCVC (Nipro Corporation Osaka, Japan) as a ventricular assist device (VAD) and performed a preclinical study that is part ...of the process for its approval as a bridge to decision by the pharmaceutical and medical device agencies. The aim of this study was to assess the postoperative performance, hemocompatibility, and anticoagulative status during an extended period of its use. A VAD system, consisting of a hydrodynamically levitated pump, measuring 64 mm by 131 mm in size and weighing 635 g, was used. We installed this assist system in 9 adult calves (body weight, 90 ± 13 kg): as left ventricular assist device (LVAD) in 6 calves and right ventricular assist device (RVAD) in 3 calves, for over 30 days. Perioperative hemodynamic, hematologic, and blood chemistry measurements were obtained and end‐organ effects on necropsy were investigated. All calves survived for over 30 days, with a good general condition. The blood pump was operated at a mean rotational speed and a mean pump flow of 3482 ± 192 rpm and 4.08 ± 0.15 L/min, respectively, for the LVAD and 3902 ± 210 rpm and 4.24 ± 0.3 L/min, respectively, for the RVAD. Major adverse events, including neurological or respiratory complications, bleeding events, and infection were not observed. This novel VAD enabled a long‐term support with consistent and satisfactory hemodynamic performance and hemocompatibility in the calf model. The hemodynamic performance, hemocompatibility, and anticoagulative status of this VAD system were reviewed.
Continuous‐flow left ventricular assist devices (LVADs) have greatly improved the prognosis of patients with end‐stage heart failure, even if continuous flow is different from physiological flow in ...that it has less pulsatility. A novel pump controller of continuous‐flow LVADs has been developed, which can change its rotational speed (RS) in synchronization with the native cardiac cycle, and we speculated that pulsatile mode, which increases RS just in the systolic phase, can create more pulsatility than the current system with constant RS does. The purpose of the present study is to evaluate the effect of this pulsatile mode of continuous‐flow LVADs on pulsatility in in vivo settings. Experiments were performed on eight adult goats (61.7 ± 7.5 kg). A centrifugal pump, EVAHEART (Sun Medical Technology Research Corporation, Nagano, Japan), was installed by the apex drainage and the descending aortic perfusion. A pacing lead for the detection of ventricular electrocardiogram was sutured on the anterior wall of the right ventricle. In the present study, we compared pulse pressure or other parameters in the following three conditions, including Circuit‐Clamp (i.e., no pump support), Continuous mode (constant RS), and Pulsatile mode (increase RS in systole). Assist rate was calculated by dividing pump flow (PF) by the sum of PF and ascending aortic flow (AoF). In continuous and pulsatile modes, these assist rates were adjusted around 80–90%. The following three parameters were used to evaluate pulsatility, including pulse pressure, dp/dt of aortic pressure (AoP), and energy equivalent pulse pressure (EEP = (∫PF*AoP dt)/(∫PF dt), mm Hg). The percent difference between EEP and mean AoP is used as an indicator of pulsatility, and normally it is around 10% of mean AoP in physiological pulse. Both pulse pressure and mean dp/dt max were decreased in continuous mode compared with clamp condition, while those were regained by pulsatile mode nearly to clamp condition (pulse pressure, clamp/continuous/pulsatile, 25.0 ± 7.6/11.7 ± 6.4/22.6 ± 9.8 mm Hg, mean dp/dt max, 481.9 ± 207.6/75.6 ± 36.2/351.1 ± 137.8 mm Hg/s, respectively). In clamp condition, %EEP was 10% higher than mean AoP (P = 0.0078), while in continuous mode, %EEP was nearly equivalent to mean AoP (N.S.). In pulsatile mode, %EEP was 9% higher than mean AoP (P = 0.038). Our newly developed pulsatile mode of continuous‐flow LVADs can produce pulsatility comparable to physiological pulsatile flow. Further investigation on the effect of this novel drive mode on organ perfusion is currently ongoing.
OBJECTIVES
Right ventricular failure after left ventricular assist device (LVAD) implantation is associated with high mortality. This study was designed to evaluate the effectiveness of an atrial ...septostomy with a membrane oxygenator incorporated in an LVAD as a novel approach for right ventricular failure after LVAD implantation.
METHODS
The outflow and inflow cannulae were placed in the carotid artery and left ventricular apex, respectively. A centrifugal pump and an oxygenator were sequentially placed between the inflow and outflow cannulae in seven anesthetized goats. While right ventricular failure was induced by pulmonary artery banding, a balloon atrial septostomy was performed using a 19-mm balloon catheter under echocardiographic guidance. We investigated the effects of the interatrial shunt on LVAD flow and haemodynamics.
RESULTS
Development of right ventricular failure decreased LVAD flow (2.7 ± 0.6–0.9 ± 0.6 l/min), causing a state of shock mean arterial pressure (MAP) of 41 ± 12 mmHg. Following a balloon atrial septostomy, LVAD flow and MAP were significantly improved to 2.7 ± 0.4 l/min (P < 0.001) and 53 ± 18 mmHg (P = 0.006), respectively, while right atrial pressure decreased from 18 ± 5 to 15 ± 5 mmHg (P = 0.001). Furthermore, arterial blood oxygenation was maintained by the membrane oxygenator incorporated in the LVAD.
CONCLUSIONS
In the present model of right ventricular failure after LVAD implantation, LVAD flow was significantly increased and haemodynamics improved without compromising systemic oxygenation by the use of an interatrial shunt and a membrane oxygenator incorporated in the LVAD. Our results indicate that this novel approach may be less invasive for a right ventricular failure after LVAD implantation.
In the exploratory R&D phase of mechanical circulatory support (MCS) devices, mock circulation tests are useful in reducing the cost of animal experiments. In this presentation, we will first show ...the mechanism by which our mock circulation system can generate fluid loads simulated different cardiac conditions, and its application to MCS devices evaluation. On the other hand, many in silico hemodynamic simulators have been reported including applications to the field of artificial organs. They are expected to be further utilized in the development of MCS devices with the recent advances in computer technology. In this report, we present the results of a basic study on the control of a ventricular assist device using a PC-based real-time biventricular hemodynamic simulator constructed with a simple electrical circuit model. We will also report on our efforts to apply the same simulation method to the improvement of a mock circulation system.
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