Inflow Cannula Research Articles

Left Ventricular Assist Device Inflow Cannula Position May Contribute to the Development of HeartMate II Left Ventricular Assist Device Pump Thrombosis.

Pump thrombosis (PT) is a dreaded complication after left ventricular assist device (LVAD) implantation. Problems with inflow cannula (IC) position may precipitate thrombus development. We sought to determine if IC position contributes to the development of PT. We conducted a retrospective review of 76 HeartMate II LVAD implants. The angle of the IC (AIC) to the horizontal plane was measured on chest x-rays. Patients who developed PT (PT group) were compared to the remaining patients (control group). The mean age at implantation was 56 ± 14 years, and 82% of the patients were male. Ten patients (13%) developed PT. Six (60%) required device exchange, and 4 (40%) were managed with anticoagulation and/or thrombolysis. The median AIC for all patients at implantation was 59° (range, 38°-98°; 25th-75th interquartile range, 50°-75°). In the PT group, the median AIC was larger at the time of PT diagnosis compared to implantation (70° vs 60°, P = 0.005). In the control group, the median AIC was also larger at follow-up compared to implantation (61° vs 58°, P < 0.001) although to a lesser degree than in the PT group. No difference was seen in the median AIC between the PT group and the control group at implantation (60° vs 58°, respectively; P = 0.668) or at follow-up (70° vs 61°, respectively; P = 0.309). However, the median AIC at follow-up in the PT group was significantly larger than the median AIC at implantation in the control group (70° vs 58°, respectively; P = 0.014). The HeartMate II LVAD IC position contributes to the development of PT. Regular monitoring of cannula position may help identify patients at risk for this problem.

Melt Electrospun Bilayered Scaffolds for Tissue Integration of a Suture-Less Inflow Cannula for Rotary Blood Pumps.

Implantation of left ventricular assist devices typically requires cardiopulmonary bypass support, which is associated with postoperative complications. A novel suture-less inflow cannula, which can be implanted without bypass, uses mild myocardial compression to seal the interface, however, this may lead to necrosis of the myocardium. To circumvent this issue, a bilayered scaffold has been developed to promote tissue growth at the interface between cannula and myocardium. The bilayered scaffold consists of a silicone base layer, which mimics the seal, and a melt electrospun polycaprolactone scaffold to serve as a tissue integration layer. Biocompatibility of the bilayered scaffolds was assessed by analyzing cell viability, morphology, and metabolic activity of human foreskin fibroblasts cultured on the scaffolds for up to 14 days. There was no evidence of cytotoxicity and the cells adhered readily to the bilayered scaffolds, revealing a cell morphology characteristic of fibroblasts, in contrast to the low cell adhesion observed on flat silicone sheets. The rate of cell proliferation on the bilayered scaffolds rose over the 14-day period and was significantly greater than cells seeded on the silicone sheets. This study suggests that melt electrospun bilayered scaffolds have the potential to support tissue integration of a suture-less inflow cannula for cardiovascular applications. Furthermore, the method of fabrication described here and the application of bilayered scaffolds could also have potential uses in a diverse range of biomedical applications.

Novel temporary left ventricular assist system with hydrodynamically levitated bearing pump for bridge to decision: initial preclinical assessment in a goat model.

The management of heart failure patients presenting in a moribund state remains challenging, despite significant advances in the field of ventricular assist systems. Bridge to decision involves using temporary devices to stabilize the hemodynamic state of such patients while further assessment is performed and a decision can be made regarding patient management. We developed a new temporary left ventricular assist system employing a disposable centrifugal pump with a hydrodynamically levitated bearing. We used three adult goats (body weight, 58-68kg) to investigate the 30-day performance and hemocompatibility of the newly developed left ventricular assist system, which included the pump, inflow and outflow cannulas, the extracorporeal circuit, and connectors. Hemodynamic, hematologic, and blood chemistry measurements were investigated as well as end-organ effect on necropsy. All goats survived for 30days in good general condition. The blood pump was operated at a rotational speed of 3000-4500rpm and a mean pump flow of 3.2 ± 0.6L min. Excess hemolysis, observed in one goat, was due to the inadequate increase in pump rotational speed in response to drainage insufficiency caused by continuous contact of the inflow cannula tip with the left ventricular septal wall in the early days after surgery. At necropsy, no thrombus was noted in the pump, and no damage caused by mechanical contact was found on the bearing. The newly developed temporary left ventricular assist system using a disposable centrifugal pump with hydrodynamic bearing demonstrated consistent and satisfactory hemodynamic performance and hemocompatibility in the goat model.

The Effect of Inflow Cannula Length on the Intraventricular Flow Field: An In Vitro Flow Visualization Study Using the Evaheart Left Ventricular Assist Device.

Left ventricular assist device (LVAD) inflow cannula malposition is a significant risk for pump thrombosis. Thrombus development is influenced by altered flow dynamics, such as stasis or high shear that promote coagulation. The goal of this study was to measure the intraventricular flow field surrounding the apical inflow cannula of the Evaheart centrifugal LVAD, and assess flow stasis, vortex structures, and pulsatility for a range of cannula insertion depths and support conditions. Experimental studies were performed using a mock loop with a customized silicone left ventricle (LV) and the Evaheart LVAD. A transparent inflow cannula was positioned at 1, 2, or 3 cm insertion depth into the LV and the velocity field in the LV midplane was measured for 2 levels of LVAD support: 1800 and 2300 rpm. The LV velocity field exhibits a diastolic vortex ring whose size, path, and strength are affected by the flow conditions and cannula position. During diastole, the large clockwise midplane vortex grows, but its circulation and kinetic energy are reduced with cannula insertion depth. The counterclockwise vortex is smaller and exhibits more complex behavior, reflecting a flow split at 3 cm. Overall, the 1 cm cannula insertion depth produces the flow pattern that exhibits the least apical flow stasis and greatest pulsatility and should correlate to a lower risk of thrombus formation.

CT Imaging of Complications Associated with Continuous-Flow Left Ventricular Assist Devices (LVADs)

Heart failure is becoming increasingly prevalent, and more patients are being treated with left ventricular assist devices (LVADs), either as a bridge to transplant or as destination therapy. The use of continuous-flow LVADs is on the rise. LVAD therapy is associated with several classes of complications, including bleeding, thrombosis, and infection. CT imaging can be used effectively to diagnose LVAD complications, including mediastinal hematomas and pericardial, abdominal wall, and retroperitoneal hemorrhage, inflow and outflow graft and aortic thrombi, and driveline and pump pocket infections. CT can also be helpful in cases of device malfunction and can detect outflow graft kinking and inflow cannula misalignment. When interpreting CT scans in patients with LVADs, accessory materials implanted with the device should not be mistaken for hemorrhage or calcification. With training in recognizing LVAD complications, radiologists can play an important role in the evaluation of patients with heart failure.

Characterization of Ventricular Tachycardia After Left Ventricular Assist Device Implantation as DestinationTherapy: A Single-Center Ablation Experience.

This study sought to report mechanisms of ventricular tachycardia (VT) and outcomes of VT ablationinpatients with a left ventricular assist device (LVAD) as destination therapy. Continuous flow LVAD implantation plays a growing role in the management of end-stage heart failure, and VT is common. There are limited reports of VT ablation in patients with a destination LVAD. Patients with a continuous-flow LVAD referred for VT ablation from 2010 to 2016 were analyzed retrospectively. Baseline patient characteristics, procedural data, and clinical follow-up were evaluated. Arrhythmia-free survival was assessed. Twenty-one patients (90% male, 62 ± 10 years) underwent catheter ablation of VT at a median of 191 days (interquartile range: 55 to 403 days) after LVAD implantation (15 HeartMate II, 6 HeartWare HVAD). Five patients (24%) had termination (n= 4) or slowing (n= 1) of VT with ablation near the apical inflow cannula, and 3 (14%) had bundle-branch re-entry. Freedom from recurrent VT among surviving patients was 64% at 1 year, with overall survival 67% at 1 year for patients without arrhythmia recurrence and 29% for patients with recurrence (p= 0.049). One patient had suspected pump thrombosis within 30 days of the ablation procedure, with no other major acute complications. In this relatively large, single-center experience of VT ablation in destination LVAD, freedom from recurrent VT and implantable cardioverter-defibrillator shocks was associated with improved 1-year survival. Bundlebranch re-entry was more prevalent than anticipated, and cannula-adjacent VT was less common. This challenging population remains at risk for late pump thrombosis and mortality.

A modified explant technique of HeartWare ventricular assist device for bridge to recovery.

The HeartWare left ventricular assist device is a miniaturized, continuous centrifugal-flow pump. The implantation technique is well described and relatively standardized across different institutions. However, there still exists a technical concern about handling the inflow cannula at the time of device explant. Specifically, the removal of the sewing ring and plicating the apical defect en masse may distort the geometry of the left ventricle and impart myocardial dysfunction. Additionally, a prefabricated repair mechanism by the manufacturer is not readily available in all countries (i.e. USA). Here, we describe a technique to address the apical core defect, using a tailor-made plug and leaving the sewing ring in situ, at the time of the HeartWare left ventricular assist device explant.

Left Ventricular Assist Device is a Viable Therapy in End Stage Hypertrophic Cardiomyopathy

&#x0D; &#x0D; &#x0D; Left Ventricular Assist Device (LVAD) therapy use is increasing rapidly in advanced heart failure (HF). Little data exists on the application of this therapy in patients with advanced HF due to hypertrophic cardiomyopathy (HCM). Altered ventricular geometry, thickened septum and reduced LV end-diastolic diameter (LVEDD) in HCM may lead to increased suction events, arrhythmias and inflow cannula malfunction. We hypothesized that patients with end stage HCM benefit from LVAD therapy and have a similar rate of complications to those with ischemic or dilated CM. Between 2009 and 2014, 5 patients with end stage HCM (HCM and EF &lt;50%), were implanted with either a HeartMate II ® (80%) or HVAD® (20%) device, as a bridge-to-transplant (BTT) (80%) or destination therapy (DT) (20%). We compared baseline characteristics, surgical, and long-term clinical outcomes between these patients and those receiving an LVAD for end stage dilated and ischemic CM (n=214) during that time frame. The HCM cohort had a smaller LVEDD (5.2 versus 6.9 cm, p=0.001) and a higher LVEF (28% v 18%, p=0.002). Cardiopulmonary bypass time was similar between the groups (72min vs 69min). Post-operative length of stay was also similar at 21 days. Operative mortality for HCM patients was 0. All 4 BTT patients survived to transplant. LVAD therapy resulted in improved LVEDD (5.2 cm to 3.9 cm), PASP (58.8 mmHg to 30.8 mmHg), and cardiac index (1.5 to 2.82L/min/m2) in patients with HCM, without an increased incidence of postoperative complications. Median duration of LVAD support in the HCM group was 14 months and 10 months for the control.&#x0D; &#x0D; &#x0D; &#x0D; We conclude that select patients with end stage HCM may benefit from LVAD therapy with a similar rate of complications compared to traditional candidates. Additional study is warranted to further evaluate durable mechanical support in this population.&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D;

Impact of LVAD Implantation Site on Ventricular Blood Stagnation.

Treatment of end-stage heart failure includes cardiac transplantation or ventricular assist device (VAD) therapy. Although increasingly prevalent, current VAD therapy has inherent complications, including thrombosis. Studies have demonstrated that VAD implantation alters intracardiac blood flow, creating areas of stagnation that predispose to thrombus formation. Two potential surgical configurations exist for VAD implantation: through the apical or diaphragmatic surfaces of the heart. We hypothesized that diaphragmatic implantation causes more stagnation than apical implantation. We also hypothesized that intermittent aortic valve (AV) opening reduces stagnation of blood inside the left ventricle (LV) when compared with a closed AV. To test these hypotheses, a human LV geometry was recreated in silico and a VAD inflow cannula was virtually implanted in each configuration. A computational indicator-dilution study was conducted where "virtually dyed blood" was washed out of the LV by injecting blood with no dye. Simulations demonstrated a substantial reduction in stagnation with intermittent AV opening. In addition, virtual dye was cleared slightly faster in the apical configuration. Simulations from our study demonstrate the clinical importance of VAD management to allow intermittent opening of the AV to prevent subvalvular stagnation, and also suggests that apical configuration might be more hemodynamically favorable.

The Effect of Compliant Inflow Cannulae on the Hemocompatibility of Rotary Blood Pump Circuits in an In Vitro Model.

Rotary blood pumps (RBPs) are used for mechanical circulatory support in heart failure patients but exhibit a reduced response to preload changes, which can lead to ventricular suction events. A passive control system, in the form of a compliant inflow cannula (IC), has been developed to mitigate suction, although this device may cause significant hemolysis. This study compared the incidence of mechanically induced hemolysis of two compliant IC designs (strutted and nonstrutted) with a rigid IC (control) in a blood circulation loop over 90min. The nonstrutted compliant IC introduced high frequency and high amplitude oscillations in RBP inlet pressure and RBP IC resistance. These oscillations were correlated with a significant increase in plasma-free hemoglobin (pfHb) and hemolysis: pfHb increased to 2.005±0.665g/L, while normalized index of hemolysis (NIH) and modified index of hemolysis (MIH) increased to 0.04945±0.01276g/100L and 4.0505±0.6589 after 90min (P<0.05). In contrast, the strutted compliant IC performed similar to the clinically utilized rigid IC and did not increase pfHb (0.300±0.090 and 0.320±0.171g/L, respectively) andrate of hemolysis (NIH 0.00435±0.00155 and 0.00543±0.00371g/100L; MIH 0.3896±0.1749 and 0.4261±0.2792, respectively) within the RBP circuit. These data indicated that strutted, compliant ICs meet the hemocompatibility of clinically used rigid ICs while also offering a potential solution to prevent ventricular suction events.

Refractory ventricular tachycardia caused by inflow cannula mechanical injury in a patient with left ventricular assist device: Catheter ablation and pathological findings

In patients with left ventricular assist device (LVAD), a minority of post-operative ventricular tachycardias (VTs) is caused by contact between the inflow cannula and the endocardium. Currently, electrophysiologic characteristics and pathologic features of this condition are lacking. We report on a case of a successfully ablated mechanical VT. After VT recurrence, heart transplantation took place. Pathologic observations were consistent with direct tissue injury and inflammation, eventually contributing to persisting arrhythmias. Radiofrequency catheter ablation can be a safe and effective option to treat arrhythmias caused by inflow cannula interference in the short term, although a high recurrence rate is expected.

Ventricular Assist Device Implantation Configurations Impact Overall Mechanical Circulatory Support System Thrombogenic Potential

Ventricular assist devices (VADs) became in recent years the standard of care therapy for advanced heart failure with hemodynamic compromise. With the steadily growing population of device recipients, various postimplant complications have been reported, mostly associated with the hypershear generated by VADs that enhance their thrombogenicity by activating platelets. Although VAD design optimization can significantly improve its thromboresistance, the implanted VAD need to be evaluated as part of a system. Several clinical studies indicated that variability in implantation configurations may contribute to the overall system thrombogenicity. Numerical simulations were conducted in the HeartAssist 5 (HA5) and HeartMate II (HMII) VADs in the following implantation configurations: 1) inflow cannula angles: 115° and 140° (HA5); 2) three VAD circumferential orientations: 0°, 30°, and 60° (HA5 and HMII); and 3) 60° and 90° outflow graft anastomotic angles with respect to the ascending aorta (HA5). The stress accumulation of the platelets was calculated along flow trajectories and collapsed into a probability density function, representing the "thrombogenic footprint" of each configuration-a proxy to its thrombogenic potential (TP). The 140° HA5 cannula generated lower TP independent of the circumferential orientation of the VAD. Sixty-degree orientation generated the lowest TP for the HA5 versus 0° for the HMII. An anastomotic angle of 60° resulted in lower TP for HA5. These results demonstrate that optimizing the implantation configuration reduces the overall system TP. Thromboresistance can be enhanced by combining VAD design optimization with the surgical implantation configurations for achieving better clinical outcomes of implanted VADs.

Optical Dynamic Analysis of Thrombus Inside a Centrifugal Blood Pump During Extracorporeal Mechanical Circulatory Support in a Porcine Model

Complications due to pump thrombus remain the weak point of mechanical circulatory support (MCS), such as the use of a left ventricular assist device (LVAD) or extracorporeal membrane oxygenation, leading to poor outcomes. Hyperspectral imaging (HSI) is an effective imaging method using a hyperspectral (HS) camera, which comprises a spectrophotometer and a charge-coupled device camera to discriminate thrombus from whole blood. Animal experiments were conducted to analyze dynamic imaging of thrombus inside a prototype of a hydrodynamically levitated centrifugal blood pump using an HSI system. Six pigs were divided into a venous circulation group (n = 3) and an arterial circulation group (n = 3). Inflow and outflow cannulae were inserted into the jugular veins in the venous circulation group. The latter simulated an LVAD application. To create thrombogenic conditions, pump flow was maintained at 1 L/min without anticoagulation. An image of the bottom surface of the pump was captured by the HS camera every 4 nm over the wavelength range of 608-752 nm. Real-time dynamic images of the inside of the pump were displayed on the monitor. Appearance of an area displaying thrombus was detected within 24 h after the start of the circulation in every experiment. This imaging system also succeeded in determining the origins of pump thrombus: from inside the pump in two cases, and from outside in four cases. Two main possible sources of pump thrombus originating outside the pump were identified on autopsy: wedge thrombus around the inflow cannula; and string-like thrombus at the junction between the pump inlet and circuit tube. The results of this study from close observation of the changing appearance of pump thrombus may contribute to improvements in the safety of extracorporeal MCS.

LEFT VENTRICULAR ASSIST DEVICE EVALUATION USING CARDIAC CT: INITIAL EXPERIENCE AT A HIGH VOLUME CENTER

Background: Left ventricular assist devices (LVAD), while lifesaving, are also often associated with their own problems and complications including malposition of the inflow cannula, ventricular tachycardia (VT), cannula obstruction, and/or pump thrombosis. There may be a role for cardiac CT to

Device-specific evaluation of intraventricular left ventricular assist device position by quantitative coaxiality analysis

BackgroundPatient-specific anatomy may influence the final intraventricular positioning of inflow cannula in left ventricular assist device (LVAD) recipients. An association exists between such positioning and clinical outcomes (specifically, orientation toward the interventricular septum has negative prognostic implications). Alternative commercially available LVADs are characterized by markedly different design, with potential consequences on intrathoracic fitting among individual patients. Material and methodsA cohort of 13 LVAD recipients (either HeartMate II–group A or Jarvik 2000 Flowmaker–group B) was evaluated. On postoperative computed tomography scans, we reconstructed the implanted LVAD (semiautomatic segmentation), defined the target mitral orifice (3D Slicer software), and built a coordinate system to quantify the coaxiality of the cannula with the mitral valve axis (angles φ and θ, expressed as percentage variation from the ideal value φ = θ = 0°). ResultsGroup A presented significantly greater average percentage variation of the φ angle (significantly greater orientation of the intraventricular cannula toward the interventricular septum; 33.2% ± 32.1% versus 1.9% ± 0.9%, P = 0.001). Group A presented significantly greater average percentage variation of the θ angle (52.7% ± 23.6% versus 14.5% ± 6.3%, P = 0.013). ConclusionsThe device assessed in group B showed in the present series better average coaxiality with the mitral orifice. Such finding is related with its design (total intraventricular placement) and interaction with thoracic structures. The present method is being integrated in the development of LVAD virtual implantation tools and may help physicians in patient-specific selection among alternative devices.

Role of contrast CT for the diagnosis and the prognosis of suspected LVAD thrombosis.

There is an urgent need for further studies evaluating the role of imaging modalities in the management of left ventricular assist device (LVAD) thrombosis. This study reviews the role of computed tomography (CT) in the diagnosis of suspected LVAD thrombosis. All contrast chest CTs performed in patients with suspected LVAD thrombosis at the University of Minnesota between January 2008 and April 2014 were reviewed. Significant CT findings were identified, operative notes were reviewed, and patient outcomes were reported. A total of 32 contrast chest CT examinations were performed in 24 patients with suspected LVAD thrombosis. LVAD thrombus was identified on CT in two patients (one in the outflow graft and one in the inflow cannula), and complications were found in two patients (one with inflow cannula malposition and one with outflow graft stenosis at aortic anastomosis site). Thirteen patients (67%) underwent LVAD explantation for clinically presumed LVAD thrombosis (LVAD exchange in seven, orthotopic heart transplant in six). LVAD thrombus was confirmed at the time of surgery in eight patients (62%; six in the motor, two in the outflow graft). CT has a low sensitivity but high specificity for detecting LVAD thrombus. The sensitivity is higher, but still modest for the detection of thrombus in the outflow cannula.

Post-Operative Anticoagulation and the Incidence of Left Ventricular Assist Device Thrombosis

IntroductionAnticoagulation is critical for patients with durable left ventricular assist devices (LVADs) in order to protect against life threatening thromboembolic events. An increase in the incidence of pump thrombosis between 2009 and 2014 prompted examination of our anticoagulation practices following device implants. As the majority of pump thromboses occurred within six months of implant, we hypothesized that anticoagulation strategies employed immediately after implant might play a role. We describe the initial post-operative anticoagulation management of 105 patients implanted with a Heart Mate II (HM II) LVAD by a single surgeon at our academic center. Although patients with more severe clinical compromise were more likely to be bridged, we found no difference in overall pump thrombosis incidence based on the use of a post-operative parenteral anticoagulation bridge compared to unopposed warfarin.MethodsWe performed a retrospective review of 105 patients undergoing primary implant of a HM II LVAD at our center from 2009 through 2014 with follow up through May 31, 2015. Data included demographics, clinical status at time of implant, intra-operative practices, and initial post-operative anticoagulation management. A parenteral bridge was defined as initiation of a parenteral anticoagulant prior to achieving an INR ≥2.0. A parenteral bridge was further defined as early if initiated within ≤3 days of device implant and therapeutic if a goal PTT was achieved during each of the first 0-24, 24-48, and 48-72 hours of the bridge duration. A parenteral bridge was considered sub-therapeutic if at least one but not all PTT measurements were at goal and non-therapeutic if no PTT measurements were at goal. Unopposed warfarin was defined as initiation to reach a therapeutic INR without the use of parenteral anticoagulants. Pump thrombosis was defined as detection within the device, inflow cannula, or outflow conduit at the time of pump replacement, pump explantation, heart transplantation, or autopsy. Pump thrombosis within 186 days of implant was defined as early. Fisher’s exact test and the Wilcoxon rank-sum test were used to compare categorical and continuous variables between groups. Cumulative incidence of pump thrombosis was compared using the Gray test with reimplantation, explantation, transplantation, or death as a competing risk.ResultsAmong 105 HM II implants, 73 (70%) were treated with any parenteral bridge, 50 (48%) with an early bridge, and 29 (28%) with an early therapeutic bridge. Median time to bridge initiation was 3 days (range 1 to 7) and median bridge duration was 6 days (range 1 to 45). A total of 32 patients (30%) received unopposed warfarin. Time to warfarin initiation and therapeutic INR were shorter in patients who received unopposed warfarin compared to a parenteral bridge, with median values of 1 vs. 2 days and 5 vs. 8 days, respectively (p<0.001 for both). Patients who received a parenteral bridge had more severe preoperative clinical compromise (p=0.039) and longer intensive care unit length of stay (p=0.005).Pump thrombosis occurred in 25 patients (24%) and 14 (13%) were early. Hypertension was the only clinical variable that differed by group (p=0.012) and was more prevalent in patients with pump thrombosis.Cumulative incidence analyses showed no significant difference in the incidence of pump thrombosis between patients who did and did not receive a parenteral bridge (p = 0.25), an early parenteral bridge (p=0.37), or a therapeutic parenteral bridge (p=0.87) (Figure 1). At 6 months the cumulative incidence (95% confidence interval) of pump thrombosis was 7.9% (2.0, 19.3) for those who received a therapeutic bridge and 16.4% (8.7, 26.3) for those who did not. At 24 months these values were 22.7% (9.4, 39.5) and 24.3% (14.6, 35.3), respectively.Among patients who did not receive a parenteral bridge, there was no difference in the time to initiation of warfarin (p=0.23) or therapeutic INR (p=0.13) according to the outcome of pump thrombosis.ConclusionsPost-operative parenteral bridging was more common than initiation of unopposed warfarin. Indices of more severe clinical compromise were associated with the use of a parenteral bridge. Our data suggest that post-implant bridging does not affect overall incidence of LVAD thrombosis. Further analysis will be performed to determine if parenteral bridging prevents early pump thrombosis. [Display omitted] DisclosuresConnors:Thoratec (St Jude's): Other: Consultant; Bristoml Meyer Squibb: Consultancy, Other: Scientific Ad Boards/Consultant; Boehringer Ingelheim: Consultancy, Other: Scientifc Ad Boards.

Numerical prediction of thrombus risk in an anatomically dilated left ventricle: the effect of inflow cannula designs.

BackgroundImplantation of a rotary blood pump (RBP) can cause non-physiological flow fields in the left ventricle (LV) which may trigger thrombosis. Different inflow cannula geometry can affect LV flow fields. The aim of this study was to determine the effect of inflow cannula geometry on intraventricular flow under full LV support in a patient specific model.MethodsComputed tomography angiography imaging of the LV was performed on a RBP candidate to develop a patient-specific model. Five inflow cannulae were evaluated, which were modelled on those used clinically or under development. The inflow cannulae are described as a crown like tip, thin walled tubular tip, large filleted tip, trumpet like tip and an inferiorly flared cannula. Placement of the inflow cannula was at the LV apex with the central axis intersecting the centre of the mitral valve. Full support was simulated by prescribing 5 l/min across the mitral valve. Thrombus risk was evaluated by identifying regions of stagnation. Rate of LV washout was assessed using a volume of fluid model. Relative haemolysis index and blood residence time was calculated using an Eulerian approach.ResultsThe inferiorly flared inflow cannula had the lowest thrombus risk due to low stagnation volumes. All cannulae had similar rates of LV washout and blood residence time. The crown like tip and thin walled tubular tip resulted in relatively higher blood damage indices within the LV.ConclusionChanges in intraventricular flow due to variances in cannula geometry resulted in different stagnation volumes. Cannula geometry does not appreciably affect LV washout rates and blood residence time. The patient specific, full support computational fluid dynamic model provided a repeatable platform to investigate the effects of inflow cannula geometry on intraventricular flow.

Left Ventricular Assist Device Thrombosis Is Associated With an Increase in the Systolic-to-Diastolic Velocity Ratio Measured at the Inflow and Outflow Cannulae

To determine whether the ratio of peak systolic-to-nadir diastolic velocity (S/D ratio) measured using Doppler at the left ventricular assist device (LVAD) inflow and outflow cannulae is associated with pump thrombosis and to determine whether there is an absolute decrease in the diastolic cannula velocities in LVAD thrombosis. Retrospective chart review. University hospital. Patients who underwent LVAD exchange. None. Transesophageal echocardiograms were reviewed from all patients with the HeartMate II device (Thoratec Corporation, Pleasanton, CA) over a 6-year period and who underwent LVAD exchange for pump thrombosis. The following 3 time points were evaluated: (1) initial LVAD placement (prethrombosis), (2) thrombosis, and (3) exchanged LVAD placement (postthrombosis). Systolic and diastolic flow velocities were examined using pulse-wave spectral Doppler at the inflow and outflow cannulae, and the S/D ratio for each was determined. Statistical analysis was performed with SAS, version 9.4 (SAS Institute, Cary, NC), using 2-tailed tests and alpha = 0.05. Thirteen patients were included in the study. Significant differences were observed in S/D ratios among the 3 phases at both the inflow (p = 0.0234) and outflow (p = 0.0047) cannulae. Pairwise tests of the inflow cannulae showed that the mean S/D ratio at the time of thrombosis (mean ± standard deviation [SD], 4.29 ± 1.74) was significantly greater than the prethrombosis ratio (2.49 ± 0.65; p = 0.0069). Among outflow measurements, the mean S/D ratio at thrombosis (3.94 ± 1.34) was significantly higher than both the prethrombosis (2.63 ± 0.56; p = 0.0025) and postthrombosis (2.74 ± 0.83) (p = 0.0093) ratios. Decreases in diastolic velocities were not statistically significant at the inflow cannula. At the outflow cannula, there was a significant difference in diastolic velocity among the phases (p = 0.0233). Specifically, the postthrombosis diastolic measurements (41.50 ± 9.94) were significantly higher than both the prethrombosis (26.85 ± 10.13; p = 0.0140) and thrombosis (26.7 ± 15.35; p = 0.0151) values. An increased S/D ratio measured with Doppler at the LVAD inflow and outflow cannulas may be associated with pump thrombosis. Decreased diastolic cannula velocities were not observed in LVAD thrombosis.

Effect of Ventricular Arrhythmia Ablation in Patients With Heart Mate II Left Ventricular Assist Devices: An Evaluation of Ablation Therapy.

Patients with advanced heart failure (HF) are predisposed to ventricular arrhythmias (VAs), particularly following implantation of a left ventricular assist device (LVAD). There is minimal evidence for appropriate management strategies. This study aimed to compare the burden of VA and response to ablation performed either before or following LVAD implantation. We created a retrospective cohort of patients who underwent both VA ablation and Heart Mate II (Thoratec, Pleasanton, CA, USA) LVAD implantation at Mayo Clinic (Rochester, MN, USA). Patients were stratified based on whether they underwent VA ablation before (pre-LVAD) or after LVAD (post-LVAD) implantation. Descriptive analyses assessed 6-month arrhythmia burden in relation to LVAD implantation and VA ablation. A total of 9 patients underwent both LVAD implantation and VA ablation. There were 3 and 6 patients, respectively, in the pre-LVAD and post-LVAD cohorts. Among patients in the pre-LVAD cohort, the median number of VAs tended to increase after ablation (9 vs. 72) and decreased after LVAD implantation (72 vs. 63). Similarly among patients in the post-LVAD cohort, the median burden of VAs increased after LVAD implantation (1 vs. 22) and the median burden decreased after ablation (22 vs. 13). Two of 6 patients had substrate related to the LVAD inflow cannula site, while other substrate was not related directly to the cannula. In patients with progressive HF and LVAD implantation, ablation is associated with reduced VA rates. In LVAD patients, most VAs arise from substrate unrelated to the inflow cannula site.