Inflow Cannula Research Articles

Hemodynamic Compromise Due to Left Atrium “Suction Event” in a Patient With HeartMate II Ventricular Assist Device Implantation

The implantation of a continuous flow left ventricular assist device (LVAD) for destination therapy or bridge to transplantation has become a standard therapeutic option. A “suction event” is a phenomenon whereby the walls of the ventricular cavity collapse and contact the inflow cannula causing obstruction and hemodynamic compromise. In rare cases, the complete collapse and inversion of the left atrium (LA) can occur before the collapse of the left ventricular (LV) cavity. We present a case of a “suction event” of the LA, leading to transmitral inflow obstruction during LVAD implantation.

Cable design improvements and sintering of the inflow cannula in continuous flow LVADs reduce the occurrence of life-threatening pump stops

Cable design improvements and sintering of the inflow cannula in continuous flow LVADs reduce the occurrence of life-threatening pump stops

CircuLite Synergy ventricular assist device: a new approach to end-stage congestive heart failure

The Synergy system, a miniature partial circulatory support device, is implanted by an off-pump, minimally invasive surgical approach. The system has been optimized to improve performance in an EU clinical trial for chronic ambulatory heart failure. This therefore offers the possibility of treating elderly chronic heart failure patients who might not usually be considered for long-term circulatory support. From June 2007 to December 2012, 63 patients were implanted with the Synergy system (12 patients ≥70 years) using four different releases of the device. Briefly, the system draws blood through the inflow cannula from the left atrium into the micro-pump (placed in a right subclavicular pocket) and pumps it through an outflow graft to the right subclavian artery. In this paper, we present an intermediate analysis of the clinical trial as performed on April 30, 2013, leading to the placing of the CE mark. Mean duration of support is ongoing at 230 days (range 23-1387). Follow-up showed improved hemodynamic response, with additional improvements in 6-min walk distance (299 ± 144 to 420 ± 119 m) and Minnesota Living with Heart Failure Questionnaire (69.5 ± 20.4 to 49.2 ± 24.3). Older patients had longer mean durations of support (337 vs 188 days). On average, elderly and younger patients showed similar improvements in hemodynamics and 6-min walk distance (107 ± 120 vs 130 ± 121 m). Major adverse cardiac events included bleeding (n=4) with one bleeding related to renal failure resulting in death. Clinical use of the Synergy device was associated with a significant functional improvement. Very low adverse event rates were reported with the latest device release. Older patients had smaller body sizes and worse renal function than younger patients. Both groups experienced similar hemodynamic benefits and functional improvements. The risk of bleeding and renal dysfunction appears to be increased in the elderly, though still within acceptable ranges compared to other full support devices. Minimally invasive long-term circulatory support devices, like Synergy, offer a new treatment option that might be available even for the elderly chronic heart failure population.

2C22 新規In vitro血栓性評価法による補助人工心臓の平滑及びメッシュ脱血管周囲に形成される血栓の飛散リスク比較評価(OS11-2:医療機器レギュラトリーサイエンス(2))

2C22 新規In vitro血栓性評価法による補助人工心臓の平滑及びメッシュ脱血管周囲に形成される血栓の飛散リスク比較評価(OS11-2:医療機器レギュラトリーサイエンス(2))

Left Ventricular Assist Device Management in the ICU

To review left ventricular assist device physiology, initial postoperative management, common complications, trouble shooting and management of hypotension, and other common ICU problems. Narrative review of relevant medical literature. Left ventricular assist devices prolong the lives of patients with end-stage heart failure, and their use is increasing. Continuous-flow left ventricular assist devices have replaced first-generation pulsatile devices. These patients present unique management concerns. In the immediate postimplant period, care must be taken to support the unassisted right ventricle. Invasive monitors for blood pressure, pulmonary artery catheterization, and echocardiography are essential to optimize left ventricular assist device settings and cardiac performance. Anticoagulation is necessary to prevent devastating thrombotic and embolic complications, but bleeding is a major source of morbidity due to inherent bleeding diatheses and prescribed anticoagulants. Infection of the device can be life threatening, and all infections must be aggressively treated to avoid seeding the device. Patients are at risk of ventricular arrhythmias because of their underlying disease, as well as the placement and position of the inflow cannula. Aortic valve stenosis and insufficiency develop over time and can lead to thrombosis or heart failure. Cardiopulmonary resuscitation with chest compressions must be performed with care or not at all due to risk of dislodging the device. Intensivists are increasingly likely to encounter patients requiring mechanical circulatory support with left ventricular assist devices at various points in the trajectory of their disease, from the immediate postimplant period to subsequent admissions for complications, and at end of life. A basic understanding of left ventricular assist device physiology is essential to the safe and effective care of these patients.

Implantation of HeartWare Left Ventricular Assist Device in Pediatric Population

The new-generation continuous-flow left ventricular assist devices (VAD) have dramatically improved clinical outcomes of adult patients with end-stage heart failure in the current era. 1 In the adult population, multiple devices are available as a long-term bridge to transplantation 2 and as destination therapy 1 with low device-related morbidity and mortality. On the contrary, long-term mechanical circulatory support options in the pediatric population have been extremely limited. Pediatric patients with end-stage heart failure have traditionally been supported with extracorporeal membrane oxygenation with dismal success rate for bridge to transplantation owing to extracorporeal membrane oxygenation–related complications. 3 Recent clinical application of the EXCOR pediatric assist device (Berlin Heart), a paracorporeal pulsatile-flow VAD, has substantially improved the survival of the patients who were bridged to transplantation with VAD. 4 Nonetheless, approximately one-third of the patients who are supported with the Berlin Heart have embolic stroke and other major complications. 4 Adult-sized VADs have been used in adolescents and some selected patients with a high rate of bridge to transplantation 5 ; however, the mismatch between device and body sizes precludes routine use of adult-sized VADs in the pediatric population. The HeartWare ventricular assist system (HVAD) (HeartWare, Framingham, MA) is a new-generation, small, centrifugal, continuous-flow pump. This device is designed to be implanted directly into the left ventricle and positioned within the pericardial space without requiring a subdiaphragmatic pocket. The initial clinical trial using HVAD showed 90.7% success rate (transplanted or alive) with reasonable incidence of stroke (12%) in patients who were supported with HVAD, which was equivalent to that of the commercially available devices. 6 HVAD is particularly attractive for the pediatric population because of the small pump size and integrated short inflow cannula, which allows complete intrapericardial implantation. In Canada, HVAD has been implanted since 2010, and the first HVAD implantation was performed in 2011 in The Hospital for Sick Children. Herein, the surgical principles and techniques of HVAD implantation in the pediatric population are discussed.

Device thrombosis in HeartMate II continuous-flow left ventricular assist devices: A multifactorial phenomenon

Continuous-flow left ventricular assist devices (CF-LVADs) are increasingly used to support patients with advanced heart failure (HF). Device thrombosis is a serious complication of CF-LVADs, but its precise prevalence and etiology remains uncertain. Root-cause analysis was performed in all cases with device thrombosis confirmed upon explant among patients implanted with a HeartMate II (HM II) from January 1, 2009 to November 15, 2012. Cannula position and bend relief integrity were assessed and charts were reviewed with particular attention to anti-coagulation and infection profiles. Nineteen of 177 patients (11%) were found to have device thrombosis of various etiologies after a mean of 351 ± 311 days, representing 0.12 event/patient-year. Of the 5 mechanically induced thromboses, proximate etiology was severely abnormal inflow cannula position in 3 patients and bend relief disconnect with deformed outflow graft in 2 patients. One patient had a hypercoagulable disorder with prior arterial embolism. In the remaining 13 patients (age 61 ± 14 years, 77% male, 69% Caucasian), "non-mechanical" device thrombosis occurred after 357 ± 383 days; INR at the time of diagnosis was 1.81 (1.62 to 2.07); and mean device speed was 8,855 ± 359 rpm. Five of 13 patients (38%) had an infection during the month leading up to device thrombosis. Of note, lactate dehydrogenase (LDH) was already elevated at the time of discharge in patients who would later develop non-mechanical device thrombosis (423 [354 to 766] vs 352 [272 to 373] U/liter, p < 0.01). Device thrombosis is a multifactorial phenomenon, and differentiation of mechanical and non-mechanical causes is an essential step for individual diagnosis and treatment plans. Larger studies excluding patients with obvious mechanical etiology are needed to investigate biologic and/or management-related risk factors for device thrombosis. Our findings suggest that LDH may be an early risk marker. Due to the difficulty in treating late-stage device thrombosis, we suggest early use of simple tests to rule out both causes of thrombosis, such as X-rays and closer LDH monitoring (bi-weekly).

Explantation of a CircuLite left ventricular assist device without removal of the inflow cannula: how to do it?

As the incidence of heart failure rises and given the shortage of donor organs, left ventricular assist device implantation offers a viable therapy in patients with end-stage heart disease. The CircuLite Synergy™ device is a less invasive support device for Intermacs class 4 heart failure patients. We report the first case of successful weaning from the CircuLite Synergy™ pump and propose our surgical technique to explant the device while leaving the inflow cannula in situ.

VADoscopy

With HeartMate II (HMII) implants increasing so has the frequency of device exchange. However, identifying inflow cannula obstruction, pump thrombosis, or outflow obstruction as the mechanism of pump dysfunction can be difficult. Echocardiography, CT angiogram, and cardiac catheterization are not definitive in determining the location of pump failure. Therefore, intraoperative examination is often necessary to confirm a diagnosis, requiring extensive dissection to visualize the entire system. We hypothesized a novel intraoperative technique, VADoscopy, can evaluate the inflow cannula for thrombus or pannus formation, and can help guide decision on which portion(s) of the HMII require replacement. Visualization of the inflow cannula can determine if either the pump itself or the pump along with the inflow cannula requires replacement, potentially limiting unnecessary dissection around the left ventricular apex and inflow cannula. A subxiphoid or subcostal incision exposes the pump. Patients are placed on cardiopulmonary bypass using the femoral vein and artery, after the outflow cannula is clamped. Once the pump is removed from the pocket, a 22 French 80 cm(Edwards Life Science, Irvine, CA) Fogarty balloon is advanced through the inflow cannula into the left ventricle and inflated to limit blood flow from the heart. A 5 French 30 cm flexible endoscope (Karl Starz Flex-X, Germany) is then placed into the inflow cannula and left ventricle to evaluate for the presence of thrombus, pannus, or debris. Six patients had HMII exchange with VADoscopy. In all patients, VADoscopy demonstrated no inflow cannula pannus or thrombus as the cause of pump dysfunction. Postoperatively there were no embolic events or evidence of reoccurring pump dysfunction suggesting an inflow cannula obstruction was not missed. VADoscopy is a novel and effective operative diagnostic modality to evaluate the inflow cannula within the HMII left ventricular assist device, limiting the amount of dissection, and potentially reducing the morbidity associated with HMII pump exchange.

Postimplant Left Ventricular Assist Device Fit Analysis Using Three-Dimensional Reconstruction

Left ventricular assist devices (LVADs) are blood pumps that augment the function of the failing heart to improve perfusion, resulting in improved survival. For LVADs to effectively unload the left ventricle, the inflow cannula (IC) should be unobstructed and ideally aligned with the heart's mitral valve (MV). We examined IC orientation deviation from a hypothesized conventional angle (45° right-posterior) and the approximate angle for direct IC-MV alignment in many patients. Three-dimensional anatomic models were created from computed tomography scans for 24 LVAD-implanted patients, and angles were measured between the IC and the apical z-axis in both the coronal and the sagittal planes. Common surgical IC angulation was found to be 22 ± 15° rightward and 21 ± 12° posterior from the apical z-axis; 38% (n = 9) of patients fell in this range. Direct IC-MV angulation was found to be 34 ± 8° rightward and 15 ± 7° posterior; only 8% (n = 2) of patients fell in this range. Rightward deviation toward ventricular septal wall and anterior deviation toward LV anterior freewall are associated with mortalities more so than leftward and posterior deviation. In conclusion, anatomic reconstruction may be a useful preoperative tool to obtain general population and patient-specific alignment for optimal LVAD implantation.

Left Ventricular Assist Device Inflow Cannula Thrombus

Thrombotic complications are inherent to current generation nonpulsatile left ventricular assist devices. The clinical expression of device thrombosis ranges from catastrophic failure to protracted and indolent. We report the case of a 79-year-old patient who received a left ventricular assist device as destination therapy and presented only with vague clinical symptoms. He was found to have a large thrombus in close proximity with the inflow cannula at the left ventricular apex, raising the question of mechanical obstruction. We describe the step-by-step contrast-enhanced two-dimensional transthoracic echocardiographic examination which allowed to obtain diagnostic acoustic tomograms of the inflow cannula and obviated the need for any additional imaging modalities. Transthoracic echocardiography (TTE) is the most common imaging modality used in the clinical follow-up of left ventricular assist device recipients. A frequent clinical indication for TTE is to exclude left ventricular apical thrombus near the inflow cannula. Imaging of the inflow cannula at the left ventricular apex in the traditional apical 4 chamber, apical 2 chamber, and parasternal long axis views is challenging by TTE mainly because of poor acoustic windows, image artifacts, large body habitus, and operator experience.

Extended in vivo evaluation of a miniaturized axial flow pump with a novel inflow cannula for a minimal invasive implantation procedure

Minimally invasive techniques are desirable to minimize surgical trauma during left ventricular assist device (LVAD) implantation. This is particularly challenging for full-flow support. In this study, a minimally invasive implantation technique was developed for a microaxial rotary pump. The system was evaluated in a chronic sheep model. A HeartWare MVAD (HeartWare, Miami Lakes, FL) pump (length, 50 mm; diameter, 21 mm; maximum flow, 7-8 liters/min) was combined with a novel inflow cannula, including a new flow-optimized tip. The device was implanted into sheep (range, 60-80 kg, mean, 71.6 ± 6.8 kg) through a right-sided minithoracotomy. The inflow cannula was inserted through the superior pulmonary vein, passing through the left atrium into the left ventricle. Scheduled implant period was 30 days for 8 sheep and 100 days for 3 sheep. Mean support flow was set to half of the nominal cardiac output. Six of 8 sheep finished the scheduled 30-day investigation period (one failed due to early non-pump-related post-operative bleeding and one due to prototype controller failure). The 3 sheep scheduled for 100 days reached the study end point. Peak pump flows of up to 6.9 liters/min were achieved. At necropsy, no signs of mitral valve lesions or thrombus formation around the cannula, the tip, or the insertion site were observed, except for valve leaflet erosion in 1 animal, where the cannula had been entangled in the sub-valvular chords due to lack of ultrasound monitoring. The minimally invasive implantation technique using the HeartWare MVAD pump, together with a new cannula, provided excellent results in a chronic animal model.

In vivo evaluation of the HeartWare MVAD Pump

The current design trend for left ventricular assist devices (LVADs) is miniaturization, which aims to increase the treatable patient population and enable new treatment indications by reducing surgical trauma and the complications associated with device implantation. The MVAD Pump (HeartWare Inc, Framingham, MA) is a small, axial VAD that uses magnetic and hydrodynamic impeller technology and incorporates wide helical flow channels to minimize shear stress. In this study, we implanted the MVAD Pump in an ovine model to evaluate device hemocomaptiblity, biocompatibility, performance, and safety. The MVAD Pump was implanted in an ovine model (n = 9) for 90 days. The pump was implanted through a thoracotomy and secured to the LV apex with a gimbaled sewing ring, which allowed for intraoperative adjustment of the insertion depth and angle of the inflow cannula. Serum analytes and coagulation parameters were analyzed at specific intervals throughout the study period. Pump flow, speed, and power were recorded daily to monitor device performance. Sheep were electively euthanized at 90 days for pathologic and histologic analysis. In this study, results demonstrated the safety, reliability, hemocompatability, and biocompatibility of the MVAD Pump. Nine animals were implanted for 90 ± 5 days. No complications occurred during surgical implantation. Seven of the 9 animals survived until elective sacrifice. Each sheep that survived to the scheduled explant appeared physically normal, with no signs of cardiovascular or other organ compromise. The 2 sheep that were euthanized early showed no evidence of device-related issues. The MVAD Pump was successfully implanted through a thoracotomy and demonstrated excellent hemodynamic support with no device malfunctions throughout the study period.

Role of Echocardiography in Patients With Intravascular Hemolysis Due to Suspected Continuous-Flow LVAD Thrombosis

This study sought to characterize the echocardiographic findings of patients presenting with intravascular hemolysis (IVH) due to suspected continuous-flow left ventricular assist device (LVAD) pump thrombosis. LVAD patients who develop pump thrombosis often present with IVH. Echocardiography may be able to detect device dysfunction in this setting. Continuous-flow LVAD patients presenting with IVH due to suspected pump thrombosis were identified. Patients underwent echocardiography with cannula Doppler flow velocity interrogation. Findings were compared with baseline and follow-up studies, and with 49 stable LVAD control patients. Of 145 patients, 14 (10%) had IVH due to suspected pump thrombosis. The mean age was 55 ± 15 years, 93% were men, and 50% received LVAD as destination therapy. Mean duration between implantation and IVH was 231 ± 218 days. Eleven (79%) patients presented with hemoglobinuria, 9 (64%) with jaundice, and 5 (36%) with acute heart failure. Reduced cannula diastolic flow velocity and increased systolic/diastolic (S/D) flow velocity ratio were the only echocardiographic parameters significantly different from controls (outflow cannula 0.3 ± 0.2 m/s vs. 0.8 ± 0.3 m/s, p = 0.03, and 5.9 ± 2.8 vs. 1.7 ± 0.7, p < 0.01, respectively), and were worse for IVH patients with acute heart failure compared with those without (outflow cannula 0.2 ± 0.1 m/s vs. 0.5 ± 0.2 m/s, p = 0.04, and 7.2 ± 3.3 vs. 5.3 ± 2.0, p = 0.02, respectively). Outflow cannula diastolic flow velocity and S/D flow velocity ratio changed significantly from baseline (p = 0.01 and p < 0.01, respectively) in IVH patients, whereas systolic flow velocity did not change (p = 0.59). Odds ratios for outflow cannula diastolic flow velocity and S/D flow velocity ratio for predicting IVH were 0.60 (95% confidence interval [CI]: 0.51 to 0.73), p = 0.02, and 2.45 (95% CI: 2.37 to 2.52) p < 0.01, respectively. Corresponding inflow cannula values were similarly significant. Pump thrombosis was confirmed in 7 (50%) patients after LVAD retrieval. Reduced cannula diastolic flow velocity and increased S/D flow velocity ratio identified continuous-flow LVAD dysfunction in patients with IVH due to suspected pump thrombosis better than other echocardiographic parameters.

Atypical fungal obstruction of the left ventricular assist device outflow cannula

Background Even if better clinical outcomes have been achieved with the implantation of newer generation continuous-flow left ventricular assist devices (LVADs), infection complications are still a major risk for these patients in longterm follow-up. We present a case of a 56-year-old male with dilated cardiomyopathy who was urgently implanted with left ventricular assist device HeartMate II. During the entire postoperative period, we observed repeated life-threatening septic complications. Clinical signs of infection disappeared after prolonged treatment with broad-spectrum antibiotics and patient was discharged to outpatient monitoring. During the entire duration of circulatory support, no LVAD suction events were detected, pump power consumption remained in the normal range and the patient was listed for heart transplantation. Patient was two month rehospitalized due to worsening of his status. Hemoglobinuria, an increase of inflammatory markers, and alteration in hepatic and renal function were detected. TEE imaging showed no obstructive formation in inflow or outflow cannulas; only velocities were decreased. The LV was severely dilated and the aortic valve was opening at each contraction. Patient was initially considered for systemic thrombolysis, but this urgent status was finally solved with explantation of the LVAD and subsequent heart transplantation. Massive obstruction with thrombuslike formation was found in the outflow cannula. Histopathologic examination and microbiologic culturing of the mass showed extensive fungal growth (Aspergillus species). During the postoperative period, patient was aggressively treated with antifungal therapy. He was discharged 8 weeks after the transplantation. Conclusion We believe that clinical decision-making in patients with signs of ongoing sepsis and end-organ dysfunction together with any signs of LVAD malfunction should be very straightforward in terms of device exchange or explantation.

Surgical Technique Influences HeartMate II Left Ventricular Assist Device Thrombosis

Thrombosis of the HeartMate II (HM2 [Thoratec Corporation, Pleasanton, CA]) is a potentially devastating complication. While attention has been focused on anticoagulation strategies to prevent this complication, the impact of surgical technique has not been assessed. Patients undergoing HM2 implantation at two institutions were reviewed. Pump thrombosis (PT) was defined as a clinical syndrome that included more than 30% elevation in pump power, more than 30% elevation in lactate dehydrogenase, and greater than 20% decrease in hemoglobin with the presence of thrombus in the HM2 stator or rotor, or both, at explant or autopsy. A blinded clinician reviewed dimensions and angles of the HM2 obtained from chest x-ray films. Patients demonstrating PT were compared with patients having normal function. Of the 49 patients reviewed, 11 (22.4%) displayed evidence of PT at a median of 42 days after HM2 implantation. Patient with PT had greater acute angulation of the HM2 inflow cannula immediately postoperatively (48.2 ± 6.8 versus 65.4 ± 9.2 degrees, p < 0.001) and after 30 days (50.1 ± 8.0 versus 65.1 ± 9.9 degrees, p < 0.001). Pump pocket depth was lower in the PT group immediately after HM2 implantation (107.0 ± 41.9 versus 144.3 ± 20.3 cm, p < 0.001) and after 30 days (86.0 ± 39.1 versus 113.1 ± 25.4 cm, p= 0.02). Patients with evidence of PT did not have a decrease in end-diastolic diameter (76 ± 9 versus 70 ± 15 mm, p= 0.24) whereas patients in the normal function group had effective remodeling of the left ventricle (70 ± 10 versus 56 ± 12 mm, p= 0.01). Meticulous surgical technique, which necessitates creating an adequately sized pump pocket and appropriately directing the inflow cannula at the time of operation, may reduce the risk of PT.

Continuous-flow left ventricular assist device implantation in the presence of a hostile ventricular apex

Management of a patient with a hostile ventricular apex at the time of continuous flow left ventricular assist device (LVAD) implantation is a challenging problem. Patients with ventricular apical aneurysm, calcified left ventricular apex, large mural thrombus burden, or massive apical myocardial infarction with friable myocardium may be unsuited to traditional LVAD implant techniques. The survival of these patients relies on the implantation of the LVAD with good inflow cannula positioning in the left ventricle. We describe a novel implant technique for a HeartMate II LVAD (Thoratec Corp, Pleasanton, Calif) in a patient with a heavily calcified left ventricular apex.

Right Ventricular Outflow Tract Cannulation for Right Ventricular Assist Device Implantation

A need persists for implantable devices that provide support for the failing right ventricle. The anatomy of the right ventricle presents unique challenges at the time of right ventricular assist device implant. We describe a technique for right ventricular outflow tract cannulation that minimizes the risk of right ventricular assist device inflow cannula obstruction and right ventricular compression.

Mitral commissurotomy through the left ventricle apical orifice with Heart Ware left ventricular assist device implantation

Diseased, replaced or repaired mitral valve can lead to restricted blood flow to left ventricle and inadequate flow in left ventricular assist device (LVAD). A middle age woman with ‘burnt out’ hypertrophic cardiomyopathy had mitral valve repair for mitral regurgitation. She needed LVAD to support severe decompensating heart failure. Repaired mitral valve posed a risk of restricted flow through the device. Mitral commissurotomy was performed on beating heart through the left ventricular apical hole created for insertion of inflow cannula of LVAD.

Safety and feasibility of percutaneous delivery of a novel circulatory assist device (CircuLite® SYNERGY®) in the swine model

To demonstrate the feasibility and safety of percutaneous delivery of the novel inflow cannula of the CircuLite® SYNERGY® pocket Micro-pump via transseptal access in the swine model. After transseptal puncture, the inflow cannula system was advanced into the left atrium (LA) via the right external jugular vein and anchored onto the atrial septum under fluoroscopic and intracardiac echo guidance in 14 acute animals. Subsequently, chronic studies were performed to examine the long-term healing response to the cannula implantation with an artery-LA shunt (n=10) and overall safety of the Micro-pump components (n=6). Acute studies proved the concept of transcatheter delivery of the inflow cannula via superior venous access. The cannula tips were securely anchored in all chronic animals and appropriately endothelialised as early as two weeks. No thrombi or septal damage was observed. For the chronic pump group, device speed of 22,000 rpm (~2.0 L/min) was maintained without any adverse cardiac events. Plasma free haemoglobin assays confirmed the absence of clinically significant haemolysis. The transcatheter delivery of the inflow cannula via superior venous access to the LA is feasible and safe. This percutaneous delivery presents a significantly less invasive alternative to deliver partial circulatory support devices.