Centrifugal Left Ventricular Assist Device Research Articles

Impact of Implantable Cardioverter Defibrillators on Survival of Patients with Centrifugal Left Ventricular Assist Devices.

Both implantable cardioverter defibrillators (ICDs) and left ventricular assist devices (LVADs) have a positive impact on survival in the heart failure population. We sought to determine whether these positive effects on survival are additive or whether LVAD therapy supersedes ICD therapy. We analyzed survival data of patients implanted with nonpulsatile LVADs between October 2004 and March 2013. Survival in patients with ICDs (n = 64) was compared to those without ICDs (n = 36). Patients exited the study at the time of heart transplantation or death. A total of 100 patients underwent LVAD implantation during this time. Patients had a mean follow-up time of 364 ± 295 days. Death occurred in 15 (38%) patients in the no ICD group versus 18 (30%) in the ICD group. Univariate analysis demonstrated a marginal early survival benefit at up to 1 year post-LVAD implant in the ICD cohort; however, at time points greater than 1 year there was no statistically significant benefit in ICD therapy in LVAD patients (P = 0.56). Multivariate analysis did not show any significant predictor of survival. There were no patients who died of sudden cardiac death. There was no significant difference in the time to heart transplantation (443 days ± 251 no ICD vs 372 days ± 277 ICD, P = 0.37). The benefit of ICD therapy in the setting of continuous flow LVAD therapy is uncertain. Although prolonged ventricular arrhythmias (VAs) may potentially impact on patient survival, LVAD therapy is beneficial in prevention of sudden cardiac death due to VAs.

Left ventricular volume unloading with axial and centrifugal rotary blood pumps.

Axial (AX) and centrifugal (CFG) rotary blood pumps have gained clinical acceptance for the treatment of advanced heart failure. Differences between AX and CFG designs and mechanism of blood flow delivery may offer clinical advantages. In this study, pump characteristics, and acute physiologic responses during support with AX (HeartMate II) and CFG (HVAD) left ventricular assist devices (LVAD) were investigated in mock loop and chronic ischemic heart failure bovine models. In the mock loop model, pump performance was characterized over a range of pump speeds (HeartMate II: 7,000-11,000 rpm, HVAD: 2,000-3,600 rpm) and fluid viscosities (2.7 cP, 3.2 cP, 3.7 cP). In the ischemic heart failure bovine model, hemodynamics, echocardiography, and end-organ perfusion were investigated. CFG LVAD had a flatter HQ curve, required less power, and had a more linear flow estimation relation than AX LVAD. The flow estimation error for the AX LVAD (±0.9 L/min at 2.7 cP, ±0.7 L/min at 3.2 cP, ±0.8 L/min at 3.7 cP) was higher than the CFG LVAD (±0.5 L/min at 2.7 cP, ±0.2 L/min at 3.2 cP, ±0.5 L/min at 3.7 cP). No differences in acute hemodynamics, echocardiography, or end-organ perfusion between AX and CFG LVAD over a wide range of support were statistically discernible. These findings suggest no pronounced acute differences in LV volume unloading between AX and CFG LVAD.

Hemodynamic changes and retrograde flow in LVAD failure.

In the event of left ventricular assist device (LVAD) failure, we hypothesized that rotary blood pumps will experience significant retrograde flow and induce adverse physiologic responses. Catastrophic LVAD failure was investigated in computer simulation with pulsatile, axial, and centrifugal LVAD, mock flow loop with pulsatile (PVAD) and centrifugal (ROTAFLOW), and healthy and chronic ischemic heart failure bovine models with pulsatile (PVAD), axial (HeartMate II), and centrifugal (HVAD) pumps. Simulated conditions were LVAD "off" with outflow graft clamped (baseline), LVAD "off" with outflow graft unclamped (LVAD failure), and LVAD "on" (5 L/min). Hemodynamics (aortic and ventricular blood pressures, LVAD flow, and left ventricular volume), echocardiography (cardiac volumes), and end-organ perfusion (regional blood flow microspheres) were measured and analyzed. Retrograde flow was observed with axial and centrifugal rotary pumps during LVAD failure in computer simulation (axial = -3.4 L/min, centrifugal = -2.8 L/min), mock circulation (pulsatile = -0.1 L/min, centrifugal = -2.7 L/min), healthy (pulsatile = -1.2 ± 0.3 L/min, axial = -2.2 ± 0.2 L/min, centrifugal = -1.9 ± 0.3 L/min), and ischemic heart failure (centrifugal = 2.2 ± 0.7 L/min) bovine models for all test conditions (p < 0.05). Differences between axial and centrifugal LVAD were statistically indiscernible. Retrograde flow increased ventricular end-systolic and end-diastolic volumes and workload, and decreased myocardial and end-organ perfusion during LVAD failure compared with baseline, LVAD support, and pulsatile LVAD failure.

Macrovascular and microvascular function after implantation of left ventricular assist devices in end-stage heart failure: Role of microparticles

The hemodynamic vascular consequences of implanting left ventricular assist devices (LVADs) have not been studied in detail. We investigated the effect of LVAD implantation compared with heart transplant (HTx) on microvascular and macrovascular function in patients with end-stage heart failure and evaluated whether microparticles may play a role in LVAD-related endothelial dysfunction. Vascular function was assessed in patients with end-stage heart failure awaiting HTx, patients who had undergone implantation of a continuous-flow centrifugal LVAD, and patients who had already received a HTx. Macrovascular function was measured by flow-mediated vasodilation (FMD) using high-resolution ultrasound of the brachial artery. Microvascular function was assessed in the forearm during reactive hyperemia using laser Doppler perfusion imaging and pulsed wave Doppler. Age-matched patients without heart failure and without coronary artery disease (CAD) (healthy control subjects) and patients with stable CAD served as control subjects. Circulating red blood cell (CD253(+)), leukocyte (CD45(+)), platelet (CD31(+)/CD41(+)), and endothelial cell (CD31(+)/CD41(-), CD62e(+), CD144(+)) microparticles were determined by flow cytometry and free hemoglobin by enzyme-linked immunosorbent assay. FMD and microvascular function were significantly impaired in patients with end-stage heart failure compared with healthy control subjects and patients with stable CAD. LVAD implantation led to recovery of microvascular function, but not FMD. In parallel, increased free hemoglobin was observed along with red and white cell microparticles and endothelial and platelet microparticles. This finding indicates destruction of blood cells with release of hemoglobin and activation of endothelial cells. HTx and LVAD implantation led to similar improvements in microvascular function. FMD increased and microparticle levels decreased in patients with HTx, whereas shear stress during reactive hyperemia was similar in patients with LVADs and patients with HTx. Our data suggest that LVAD support leads to significant improvements in microvascular perfusion and hemodynamics. However, destruction of blood cells may contribute to residual endothelial dysfunction potentially by increasing nitric oxide scavenging capacity.

Rotary blood pump control strategy for preventing left ventricular suction.

The risk for left ventricular (LV) suction while maintaining adequate perfusion over a range of physiologic conditions during continuous flow LV assist device (LVAD) support is a significant clinical concern. To address this challenge, we developed a suction prevention and physiologic control (SPPC) algorithm for use with axial and centrifugal LVADs. The SPPC algorithm uses two gain-scheduled, proportional-integral controllers that maintain a differential pump speed (ΔRPM) above a user-defined threshold to prevent LV suction, while maintaining an average reference differential pressure (ΔP) between the LV and aorta to provide physiologic perfusion. Efficacy and robustness of the proposed algorithm were evaluated in silico during simulated rest and exercise test conditions for (1) ΔP/ΔRPM excessive setpoint (ES); (2) rapid eightfold increase in pulmonary vascular resistance (PVR); and (3) ES and PVR. Hemodynamic waveforms (LV pressure and volume; aortic pressure and flow) were simulated and analyzed to identify suction event(s), quantify total flow output (pump + cardiac output), and characterize the performance of the SPPC algorithm. The results demonstrated that the proposed SPPC algorithm prevented LV suction while maintaining physiologic perfusion for all simulated test conditions, and warrants further investigation in vivo.

Normalisation of Haemodynamics in Patients with End-stage Heart Failure with Continuous-flow Left Ventricular Assist Device Therapy

New generation continuous-flow left ventricular assist devices (LVADs) utilise centrifugal pumps. Data concerning their effect on patient haemodynamics, ventricular function and tissue perfusion is limited. We aimed to document these parameters following HeartWare centrifugal continuous-flow LVAD (HVAD) implantation and to assess the impact of post-operative right heart failure (RHF). We reviewed 53 consecutive patients (mean age 49.5 ± 14.1 yrs) with HVAD implanted in the left ventricle, at St. Vincent's Hospital, Sydney, between January 2007 and August 2012. Available paired right heart catheterisation (n=35) and echocardiography (n=39) data was reviewed to assess response of invasive haemodynamics and ventricular function to LVAD support. A total of 28 patients (53%) were implanted from interim mechanical circulatory support. Seventeen patients (32%) required short-term post-implant veno-pulmonary artery extracorporeal membrane oxygenation. At 100 ± 61 days post-implant, mean pulmonary artery pressure and mean pulmonary capillary wedge pressure decreased from 38.8 ± 7.7 to 22.9 ± 7.7 mmHg and 28.3 ± 6.4 to 13.4 ± 5.4 mmHg respectively (p<0.001). LV end diastolic diameter decreased from 71.3 ± 12.7 to 61.1 ± 13.7 mm and LV end-systolic diameter from 62.7 ± 12.3 to 53.9 ± 14.4mm (p<0.001). Aortic regurgitation remained trivial. Serum sodium increased from 133.3 ± 5.7 to 139.3 ± 2.8 mmol/L and creatinine decreased from 109.1 ± 42.5 to 74.3 ± 26.2 μmol/L (p<0.001). Across the entire cohort, the six-month survival/transplant rate was significantly lower for RHF patients (72.2%, n=18) compared to those without (96.9%, n=35, p=0.01). HVAD support improves haemodynamics, LV dimensions and renal function. Following implantation with a centrifugal continuous-flow LVAD, RHF remains a significant risk with a tendency to worse outcomes in the short to medium term.

(472) - Comparison of Heart Transplant Outcomes in Patients Who Received an Axial Versus Centrifugal Flow LVAD as Bridge to Transplant

PurposeContinuous flow left ventricular assist devices (LVAD) are frequently used as a bridge to transplant (BTT) in patients with stage D heart failure. There is conflicting data regarding post transplant survival in patients bridged to transplant with a LVAD compared to those who proceed directly to transplant. We assessed post transplant outcomes at our institution among patients who received an axial or centrifugal flow LVAD as compared to those who went directly to transplant.MethodsNinety-seven patients underwent orthotopic heart transplant between January 2008 and October 2013. We performed a retrospective analysis of post transplant outcomes in patients with and without an isolated continuous flow LVAD as BTT. Patients with a permanent RVAD, pulsatile LVAD, re-transplant or dual-organ transplants were excluded. Eighty four patients were included in this analysis.ResultsThere was no statistically significant difference in baseline characteristics and post transplant outcomes between the groups.ConclusionThere was no difference in post transplant outcomes in patients bridged to transplant with an LVAD compared to those who went directly to transplant. There appeared to be a trend toward improved survival in the axial flow group and increased incidence of rejection in the centrifugal flow LVAD group. These findings should be further evaluated in future studies. PurposeContinuous flow left ventricular assist devices (LVAD) are frequently used as a bridge to transplant (BTT) in patients with stage D heart failure. There is conflicting data regarding post transplant survival in patients bridged to transplant with a LVAD compared to those who proceed directly to transplant. We assessed post transplant outcomes at our institution among patients who received an axial or centrifugal flow LVAD as compared to those who went directly to transplant. Continuous flow left ventricular assist devices (LVAD) are frequently used as a bridge to transplant (BTT) in patients with stage D heart failure. There is conflicting data regarding post transplant survival in patients bridged to transplant with a LVAD compared to those who proceed directly to transplant. We assessed post transplant outcomes at our institution among patients who received an axial or centrifugal flow LVAD as compared to those who went directly to transplant. MethodsNinety-seven patients underwent orthotopic heart transplant between January 2008 and October 2013. We performed a retrospective analysis of post transplant outcomes in patients with and without an isolated continuous flow LVAD as BTT. Patients with a permanent RVAD, pulsatile LVAD, re-transplant or dual-organ transplants were excluded. Eighty four patients were included in this analysis. Ninety-seven patients underwent orthotopic heart transplant between January 2008 and October 2013. We performed a retrospective analysis of post transplant outcomes in patients with and without an isolated continuous flow LVAD as BTT. Patients with a permanent RVAD, pulsatile LVAD, re-transplant or dual-organ transplants were excluded. Eighty four patients were included in this analysis. ResultsThere was no statistically significant difference in baseline characteristics and post transplant outcomes between the groups. There was no statistically significant difference in baseline characteristics and post transplant outcomes between the groups. ConclusionThere was no difference in post transplant outcomes in patients bridged to transplant with an LVAD compared to those who went directly to transplant. There appeared to be a trend toward improved survival in the axial flow group and increased incidence of rejection in the centrifugal flow LVAD group. These findings should be further evaluated in future studies. There was no difference in post transplant outcomes in patients bridged to transplant with an LVAD compared to those who went directly to transplant. There appeared to be a trend toward improved survival in the axial flow group and increased incidence of rejection in the centrifugal flow LVAD group. These findings should be further evaluated in future studies.

(224) - Impact of vWF Activity in the Long-term Management of Centrifugal Type Continuous-flow LVAD Patients

Lack of high-molecular-weight (HMW) von Willebrand factor (vWF) multimers is one of the most critical causes of bleeding complication in long-term management of continuous-flow (CF) left ventricular assist device (LVAD) patients. EVAHEART (SunMedical Technology Research Co., Japan) LVAD is an implantable centrifugal blood pump which has characterized by relatively low share stress pump. Aim of this study was to investigate the vWF activities in our new pump.

Abstract 18819: Clinical Outcomes Following Implantation of a Centrifugal Flow Left-Ventricular Assist Device and Concomitant Cardiac Valve Procedures

Purpose: Patients undergoing implantation of left ventricular assist devices (LVAD) often undergo concomitant cardiac valve procedures, but the added procedural risk has not been studied in detail. We reviewed patients receiving a centrifugal flow LVAD system in the ADVANCE Bridge to Transplant Trial (BTT) and Continued Access Protocol (CAP) to evaluate the impact of concomitant valve procedures on early outcomes. Methods: The ADVANCE BTT and CAP trial enrolled 381 patients (pts) through November 2012. This group was divided into two subgroups: pts who underwent a concomitant valve procedure in addition to LVAD implant (VP) and those who did not undergo a concomitant valve procedure (no VP). Preop characteristics, adverse events and Kaplan-Meier survival were compared for the two groups. Results: A total of 19.7% (75/381) of pts underwent VP at the time of LVAD implantation. The most frequent procedure was tricuspid valve repair or replacement, performed in 14.7% of pts, followed by aortic (3.4%), and mitral (2.1%) valve procedures. Patients undergoing a VP were younger and had more recent onset of heart failure. Other pre-implant variables were similar for the two groups. Length of time on cardiopulmonary bypass was increased for VP pts, but mean length of hospital stay did not differ. Proportions of pts having perioperative tamponade, bleeding, arrhythmias, or strokes were similar. VP pts had more right heart failure (RHF) requiring inotropic therapy (37.3% vs. 22.9%, P =0.01); however, there was no difference in RHF requiring RVAD support (2.7% vs. 2.6%, P =1.00). Overall Kaplan Meier survival for the two groups was similar, 97.3% VP vs. 98.0% No VP at 30 days and 88.2% VP vs. 90.5% No VP at 6 months ( P =0.57). Survival was also similar for aortic (N=13) versus tricuspid (N=56) procedures, with 6 month survival 90.0% and 88.5%, respectively ( P =0.75). Conclusion: Tricuspid repair was the most common VP. Increased post-op RHF may have reflected more pre-op right heart dysfunction in this patient subgroup. Overall, the concomitant valve group experienced very good survival, suggesting that VP can be performed at the time of LVAD implant with minimal additional risk.

Increased Incidence of Angiodysplasia of the Gastrointestinal Tract and Bleeding in Patients with Continuous Flow Left Ventricular Assist Devices (LVADs)

Continuous flow left ventricular assist devices (cfLVADs) are used in clinical practice for the management of end-stage heart failure. Axial flow cfLVADS have been associated with increased rates of adverse gastrointestinal events such as bleeding angiodysplasia. The purpose of this study was to determine the incidence of bleeding gastrointestinal tract angiodysplasia and the profile of patients supported with the centrifugal cfLVAD, referred for endoscopy. A retrospective analysis of 66 patients implanted with Ventrassist (n = 33) and Heartware (n = 33) centrifugal continuous flow LVADs was performed. All patients were on warfarin, aspirin and/or clopidogrel. Endoscopy was performed in all patients with either active gastrointestinal bleeding (n = 6) or anemia with positive fecal occult blood (n = 6). Bleeding gastrointestinal angiodysplasia was demonstrated in 5 out of the 12 (41.6%) patients who underwent endoscopy from the cohort of 66 cfLVAD supported patients (7.6%). The incidence of bleeding angiodysplasia was higher than the age-standardized rate of andiodysplasia from literature (0.8%). Active gastrointestinal bleeding in one other patient was due to diverticulosis. The five patients with bleeding angiodysplasia tended to be older than the remaining 61 patients (58.8 ± 10.3 vs 49.6 ± 15.7 years, p = 0.2). We found excess bleeding angiodysplasia in patients on centrifugal cfLVAD support. It may be appropriate to screen for angiodysplasia particularly in older patients prior to support by centrifugal cf LVADs. Reasons for the higher rate of bleeding angiodysplasia in cfLVAD patients warrant further study.

Interaction Between Physical Activity and Continuous-Flow Left Ventricular Assist Device Function in Outpatients

ObjectiveStudies have shown that pump output by continuous-flow left ventricular assist devices (LVADs) increases with graded exercise testing. However, data on pump behavior during activities of daily living and sleep, where cardiac output requirements vary markedly, are lacking. We sought to determine pump parameters and activity levels in stable patients receiving outpatient LVAD therapy. Methods and ResultsEleven outpatients (mean age 51 ± 14 years, 9 male) with centrifugal continuous-flow LVADs underwent monitoring of LVAD flow, heart rate (HR), energy expenditure, and physical activity over 1 week in an outpatient setting. Physical activity was recorded with the use of a combined pedometer, accelerometer, and calorimeter Sensewear armband. Pump, HR, and physical activity parameters were time matched for correlation analysis. Outpatients had an average pump flow of 5.67 ± 1.27 L/min and engaged predominately in low levels of physical activity (mean daily step count 3,249/day). Across the entire cohort, pump flow exhibited strong univariate relationships with patients’ energy expenditure (r = 0.73), step count (r = 0.69), HR (r = 0.73), sleep (r = −0.89), and skin temperature (r = −0.85; P < .0001 for all). Multivariate analysis suggested that pump output was predominantly affected by recumbent position, energy expenditure and skin temperature (r2 = 0.84; P < .0001). Pump flow and power consumption were significantly lower during sleep than during wake periods (5.48 ± 1.31 L/min vs 5.80 ± 1.26 L/min; P < .001). ConclusionsPump output from continuous-flow LVADs is adaptive to changes in activities of daily living. Circadian variation in pump flow is mostly explained by recumbency and activity levels. Despite adequate pump flow, many LVAD patients continue to live sedentary lifestyles.

Thrombolysis for Suspected Intrapump Thrombosis in Patients With Continuous Flow Centrifugal Left Ventricular Assist Device

The current recommended anticoagulation regimen during continuous flow centrifugal left ventricular device support is a combination of antiplatelet therapy as well as oral anticoagulation. Despite this, pump thrombosis occurs in rare situations. We report the risk factors and nonsurgical management and outcomes of five patients implanted with continuous flow centrifugal left ventricular assist devices who displayed clinical, hemodynamic, and laboratory features of intrapump thrombosis. This information may support the use of intravenous thrombolytics for suspected pump thrombus in these newer generation devices.

Development of a novel drive mode to prevent aortic insufficiency during continuous-flow LVAD support by synchronizing rotational speed with heartbeat

Aortic insufficiency (AI) is a serious complication for patients on long-term support with left ventricular assist devices (LVAD). Postoperative aortic valve opening is an important predictor of AI. A system is presently available that can promote native aortic flow by reducing rotational speed (RS) for defined intervals. However, this system can cause a reduction in pump flow and lead to insufficient support. We therefore developed a novel "delayed copulse mode" to prevent AI by providing both minimal support for early systole and maximal support shortly after aortic valve opening by changing the RS in synchronization with heartbeat. To evaluate whether our drive mode could open the aortic valve while maintaining a high total flow (sum of pump flow and native aortic flow), we installed a centrifugal LVAD (EVAHEART(®); Sun Medical) in seven goats each with normal hearts and acute LV dysfunction created by micro-embolization of the coronary artery. We intermittently switched the drive mode from continuous (constant RS) with 100% bypass to delayed copulse mode with 90% bypass. Total flow did not significantly change between the two modes. The aortic valve opened when the delayed copulse mode was activated. The delayed copulse mode allowed the aortic valve to open while maintaining a high total flow. This novel drive mode may considerably benefit patients with severe heart failure on long-term LVAD support by preventing AI.

Use of centrifugal left ventricular assist device as a bridge to candidacy in severe heart failure with secondary pulmonary hypertension

Raised pulmonary artery pressure (PAP), trans-pulmonary gradient (TPG) and pulmonary vascular resistance (PVR) are risk factors for poor outcomes after heart transplant in patients with secondary pulmonary hypertension (PH) and may contraindicate transplant. Unloading of the left ventricle with an implantable left ventricular assist device (LVAD) may reverse these pulmonary vascular changes. We studied the effect of implanting centrifugal LVADs in a cohort of patients with secondary PH as a bridge to candidacy. Pulmonary haemodynamics on patients implanted with centrifugal LVADs at a single unit between May 2005 and December 2010 were retrospectively reviewed. Twenty-nine patients were implanted with centrifugal LVADs (eight HeartWare ventricular assist device (HVAD), HeartWare International, USA and 21 VentrAssist, Ventracor Ltd., Australia). Seventeen were ineligible for transplant by virtue of high TPG/PVR. All the patients were optimized with inotrope/balloon pump followed by LVAD insertion. Four required temporary right VAD support. Thirty-day mortality post-LVAD was 3.4% (1 of 29) with a 1-year survival of 85.7% (24 of 28). Thirteen patients have been transplanted to date: 30-day mortality was 7.7% (1 of 13) and 1-year survival was 91% (10 of 11). Baseline and post-VAD pulmonary haemodynamics were significantly improved: systolic PAP (mmHg), mean PAP, TPG (mmHg) of 57 ± 9.5, 42 ± 4.4 and 14 ± 3.9 reduced to 32 ± 7.5, 18 ± 5.5 and 9 ± 3.3, respectively. PVR reduced from 5 ± 1.5 to 2.1 ± 0.5 Wood units (P < 0.05). In selected heart failure patients with secondary PH, use of centrifugal LVAD results in significant reductions in PAP, TPG and PVR, which are observed within 1 month, reaching a nadir by 3 months. Such patients bridged to candidacy have post-transplant survival comparable with those having a heart transplant as primary treatment.

Impact of Implantable Cardioverter Defibrillators on Survival of Patients with Centrifugal Left Ventricular Assist Devices

Background: Both Implantable Cardioverter Defibrillators (ICD) and Left Ventricular Assist Devices (LVAD) have a positive impact on survival in the heart failure population. We sought to determine whether these effects on survival are additive or whether LVAD therapy supersedes ICD therapy. Method: We analysed survival data of patients implanted with non-pulsatile, centrifugal LVADs between October 2004 and March 2013. Outcomes in patients with ICDs (n = 61) were compared to those without ICDs (n = 39). Patients exited the study at the time of heart transplantation or death. Results: 100 patients underwent LVAD implantation during the specified dates (92 Bridge-to-transplant, eight Destination-therapy). Mean follow up time was 364 ± 295 days. Death occurred in 15 (38%) patients in the No ICD group vs. 18 (30%) in the ICD group (p = 0.55). At day 500 post LVAD implant, there was no significant difference in Kaplan–Meier survival curves between the two groups (p = 0.21). The two most common causes of death were sepsis, which occurred in nine (27%) patients, and intracranial haemorrhage in seven (21%). There were no patients that died of sudden cardiac death. One patient died whilst in sustained (1 h) ventricular fibrillation in the context of progressive multi-organ failure and sepsis. There was no significant difference in the time to heart transplantation (443 ± 251 days no ICD vs. 372 ± 277 days ICD, p = 0.37). Conclusion: Whilst ICD therapy has an established role in heart failure, there is no long term benefit from ICD therapy in the setting of non-pulsatile LVAD therapy for end-stage heart failure.

Intracranial Haemorrhagic Events with Continuous-Flow Centrifugal Left Ventricular Assist Devices: A Tertiary Centre Experience

Conclusion: Increasing nitrogen gas flow lead to an increase in nitrogen incorporation in the deposited polymer. Compared to SS improved biocompatibility with lower thrombogenicity (static/flowmodels) and enhanced HCAEC attachment was seen with N10 samples. This novel high nitrogen polymer shows promise as a biocompatible coating for coronary stents. http://dx.doi.org/10.1016/j.hlc.2013.05.486

Computational Fluid Dynamics Analysis to Determine Shear Stresses and Rates in a Centrifugal Left Ventricular Assist Device

Axial flow left ventricular assist devices (LVADs) are a significant improvement in mechanical circulatory support. However, patients with these devices experience degradation of large von Willebrand factor (vWF) multimers, which is associated with bleeding and may be caused by high shear stresses within the LVAD. In this study, we used computational fluid mechanics to determine the wall shear stresses, shear rates, and residence times in a centrifugal LVAD and assess the impact on these variables caused by changing impeller speed and changing from a shrouded to a semi-open impeller. In both LVAD types, shear rates were well over 10,000/s in several regions. This is high enough to degrade vWF, but it is unclear if residence times, which were below 5ms in high-shear regions, are long enough to allow vWF cleavage. Additionally, wall shear stresses were below the threshold stress of 10Pa only in the outlet tube so it is feasible to endothelialize this region to enhance its biocompatibility.

Alteration of LV end-diastolic volume by controlling the power of the continuous-flow LVAD, so it is synchronized with cardiac beat: development of a native heart load control system (NHLCS)

There are many reports comparing pulsatile and continuous-flow left ventricular assist devices (LVAD). But continuous-flow LVAD with the pulsatile driving technique had not been tried or discussed before our group's report. We have previously developed and introduced a power-control unit for a centrifugal LVAD (EVAHEART®; Sun Medical), which can change the speed of rotation so it is synchronized with the heart beat. By use of this unit we analyzed the end-diastolic volume (EDV) to determine whether it is possible to change the native heart load. We studied 5 goats with normal hearts and 5 goats with acute LV dysfunction because of micro-embolization of the coronary artery. We used 4 modes, "circuit-clamp", "continuous", "counter-pulse", and "co-pulse", with the bypass rate (BR) 100%. We raised the speed of rotation of the LVAD in the diastolic phase with the counter-pulse mode, and raised it in the systolic phase with the co-pulse mode. As a result, the EDV decreased in the counter-pulse mode and increased in the co-pulse mode, compared with the continuous mode (p<0.05), in both the normal and acute-heart-failure models. This result means it may be possible to achieve favorable EDV and native heart load by controlling the rotation of continuous-flow LVAD, so it is synchronized with the cardiac beat. This novel driving system may be of great benefit to patients with end-stage heart failure, especially those with ischemic etiology.

Neointima-inducing inflow cannula with titanium mesh for left ventricular assist device

The formation of wedge thrombus is a crucial problem in any left ventricular assist device (LVAD) with a left ventricle apical inflow cannula. We therefore developed a new titanium mesh wrapped inflow cannula expecting to induce autologous neointima to avoid such wedge thrombus formation. We performed animal experiments to evaluate the feasibility of this newly developed inflow cannula with titanium mesh for the induction of autologous neointima. Four calves were implanted with the inflow cannula as well as an EVAHEART centrifugal pump LVAD (Sun Medical Technology Research Corp., Nagano, Japan) for a duration of about 2 months. The titanium mesh was enveloped with neointimal tissue grown from the ventricular endocardium. There was no thrombus formation in any of the blood pumps or around the outside of the inflow cannulas. The histological findings showed that the neointimal tissue consisted of a layer of endothelial cells and fibroblasts. The newly developed inflow cannula using a titanium mesh induces autologous neointima formation, avoiding wedge thrombus formation.

What is the ideal off-test trial for continuous-flow ventricular-assist-device explantation? Intracircuit back-flow analysis in a mock circulation model

Bridge to recovery has become a major goal after left-ventricular-assist-device (LVAD) implantation thanks to recent development in adjunctive therapies. Precise assessment of native heart function under minimum LVAD support is the key for successful LVAD explantation. However, weaning of centrifugal LVADs normally generates diastolic intracircuit backward flow. This retrograde flow may become excessive load for the native heart during off-pump test. The flow itself is an inevitable characteristic of centrifugal pumps. Therefore, evaluating this retrograde flow in vitro is of considerable significance, even if its amount is different from that in clinical settings. The purpose of this study was to assess diastolic backflow of continuous-flow centrifugal LVADs in a mock circulation model. A centrifugal LVAD (EVAHEART, Sun Medical Technology) was installed in a mock circulation model by the left ventricle uptake and the ascending aortic return. Pump flow was measured at the pump rotational speed of 1000, 1500, 2000, and 2500 rpm, and pulse rate of the virtual native heart was varied to 60, 90, and 120 beats/min. After data collection, pump flow was integrated, and forward and backward intracircuit flow were calculated. As a result, nonphysiological reverse flow of approximately 2.0 L/min exists at the rotational speed, providing 0 L/min mean pump flow. An ideal off-test trial condition should be realizing both ± 0 L/min pump flow and no intracircuit backward flow at the same time. We are developing a novel EVAHEART drive mode that can change its rotational speed in synchronization with cardiac cycle with the aim of controlling this retrograde flow with the new drive mode and creating an ideal off-test condition.