Inflow Cannula Research Articles

Estimation of Early‐Stage Malfunction Using Implantable Artificial Heart Sound in Animal Experiments

We have developed an automatic diagnosis system of an artificial heart in order to ensure the safety of the patient implanted with the artificial heart. The automatic diagnosis system is composed of an electro-stethoscope system, adaptive noise canceller (ANC), and artificial neural network (ANN). The ANC effectively eliminates ambient noise from the sound signal of the artificial heart detected by the electro-stethoscope, and a filtered sound signal is separated into each frequency components by fast Fourier transformation. Each frequency component of an artificial heart's acoustic signal is fed into the ANN in order to make a diagnosis of pump condition. The automatic diagnosis system was evaluated in mock circulatory tests and a long-term animal experiment using a goat implanted with an undulation pump ventricular assist device (UPVAD). In mock circulatory tests, the ANN was able to detect pump failing conditions, which were occlusion of inflow and outflow cannula and deterioration of the ball bearing. In a long-term animal experiment, after training the ANN using UPVAD's sound signal in normal condition, the diagnosis system continuously monitored UPVAD's sound signal detected by the electro-stethoscope placed on the surface of the left thoracic cavity of the goat. The UPVAD was stopped by rupture of a diaphragm in the pump on the ninth day of operation. We were able to identify initial signs of malfunction of the pump on the eighth day, while the UPVAD was able to operate normally. In conclusion, the automatic diagnosis system for malfunction of the artificial heart has enough performance to detect early stages of malfunction of the artificial heart, and it contributes to ensure the patient's safety.

A STUDY OF HEARTBEAT SYNCHRONIZATION FOR THE UNDULATION PUMP VENTRICULAR ASSIST DEVICE USING THE INFLOW PRESSURE

The undulation pump ventricular assist device (UPVAD) is a small implantable ventricular assist device using an undulation pump. The UPVAD can produce arbitrary flow patterns: continuous flow, pulsatile flow, based on continuous flow and complete pulsatile flow, by changing the motor rotational speed of the UPVAD. The undulation pump is a volume displacement type pump in which the inflow action and outflow action both start at the same phase. A unique character of the UPVAD demands to synchronize with the natural heartbeat to prevent the sucking of inflow cannula. The purpose of this study is to develop heartbeat synchronization for the UPVAD. The inflow cannula of the UPVAD is implanted in the ventricular. Therefore, pressure fluctuation that synchronizes with the natural heartbeat is observed in the inflow cannula. The flow pattern of the UPVAD rapidly responds changes in the motor rotational speed. By changing the motor rotational speed that responds to the inflow pressure, the UPVAD can synchronize with the natural heartbeat.

FEASIBILITY OF THE RABBIT MODEL IN TESTING NEONATAL/PEDIATRIC CARDIAC ASSIST SYSTEMS

Purpose: To evaluate the feasibility of the rabbit model in testing neonatal/pediatric cardiac assist systems. Methods: Three New Zealand white rabbits (average weight, 4.5 kg) were used. After heparinization, an inflow cannula (10 Fr) was inserted into the left ventricular apex. An outflow cannula (12 Fr) was inserted into the left ventricle and advanced transaortically into the descending aorta while the heart was beating. The Levitronix UltraMag, an extracorporeal centrifugal pump, was used for mechanical circulatory support. Arterial pressure was continuously monitored throughout the study. Results: The pump’s rotation was maintained between 1600 rpm and 1800 rpm, with a flow range of 250–300 mL/min. All animals were successfully supported for 4 hours, at which time, the studies were electively terminated. Conclusion: The rabbit is an accurate, acute neonate model for studying cardiac assist systems. Further studies are being conducted to evaluate the rabbit as a chronic neonate/pediatric model.

PRELOAD SENSITIVITY OF CONTINUOUS FLOW VENTRICULAR ASSIST DEVICES: APPLICATION TO THE TOTAL ARTIFICIAL HEART

Purpose: Pump design can affect pump sensitivity to preload. The effect of preload on the output of 3 axial flow ventricular assist devices (VADs) was studied in vitro. We hypothesize that slight changes in the design of axial flow pumps will alter the response to preload. Methods: The VADs studied included the HeartMate II, Jarvik 2000, and MicroMed DeBakey. The pump inflow cannulas of the HeartMate II and MicroMed DeBakey were removed so the pumps had direct interface with the testing fluid. The outlet of each pump was attached via a short tubing segment to a vertical PVC pipe with negligible flow resistance. Water column height in the PVC pipe determined pump afterload. Pump inlet and outlet pressures and flow rate were measured. To vary pump preload, the fluid in the preload cylinder was gradually drained while keeping water level in the afterload piping constant at 50, 70, or 90 mm Hg. Pressure and flow data were continuously measured at different pump speeds. Results: The flow-preload curves of the HeartMate II were nearly linear at all speeds. The Jarvik 2000 demonstrated increased sensitivity to preload at 11 and 12 krpm, with a maximum sensitivity of 0.35 L/min/mm Hg. The maximum sensitivity of the modified DeBakey pump was 2 L/min/mm Hg. Conclusions: Increasing preload sensitivity enhances the Starling-type autoregulatory mechanism of continuous flow pumps. We offer additional experimental evidence concerning this mechanism by using pumps with inherently different preload sensitivities.

A LARGE SCALE RETROSPECTIVE ANALYSIS OF PRE-CLINICAL VENTRICULAR ASSIST DEVICE TESTING

Ventricular assist devices (VADs) have been in development for over 40 years. Data from preclinical animal trials provide important information about device efficacy, biocompatibility, and function of the devices. While significant effort is put into development of the VAD, it represents only one facet of a more complex system that can include cannulae, connectors, and controllers. This retrospective analysis was done to analyze explant findings associated with VADs during the animal phase of testing. Data was collected from 141 animal VAD studies done by the author and represent 11 different devices. A total of 268 explant findings were documented. Inflow cannula issues were the most commonly cited problem (26.1%), followed by connector/junction issues (18.7%). Taken together, inflow and outflow cannulae accounted for 40% of all findings. Findings associated with cannulae were primarily kinks, obstruction, and thrombus development. Those associated with connectors were primarily thrombus formation. Pump findings (i.e. thrombus, failure) represented 18% of the issues. Findings due to the animal (i.e. bleeding, chewed cables) only represented 6% of this series. This study represents an extensive retrospective analysis of preclinical VAD testing. The large number and type of devices examined lend credence to the conclusion that preclinical testing needs to place emphasis on the entire VAD system. In support of these results, human clinical data seem to indicate that actual VAD failure is rarely a cause for premature device removal. Rather, issues with the other parts of the circuit are most commonly responsible.

The DuraHeart VAD, a Magnetically Levitated Centrifugal Pump The University of Vienna Bridge-to-Transplant Experience

The clinical application of the DuraHeart (Terumo Heart Inc, USA) has begun in Europe as a clinical trial of a third-generation implantable centrifugal blood pump. Four successful clinical implants are presented. Four male patients had end-stage left heart failure and received a DuraHeart VAD as a left ventricular assist device for bridge-to-transplantation. The pump showed good performance with flow rates of 4.9+/-0.5 L/min after gradual weaning of extracorporeal circulation. The pump flow was then maintained at 6.1+/-0.5, 5.5+/-0.3, 5.5+/-0.1, 5.7+/-0.1, 5.5, 6.4 and 6.5 L/min at the 1st, 4th, 8th, 12th, 16th, 20th and 24th postoperative week, respectively. No significant elevation of mean plasma-free hemoglobin was detected. The patients were discharged on the 18th, 42nd, 41st and 31st postoperative day, respectively, and all were successfully transplanted on the 202nd, 84th, 128th and 96th postoperative day, respectively. At the time of transplant surfaces of the removed pumps were free from thrombus formation, although intraventricular pannus growth was observed around the inflow cannulae in all patients. The DuraHeart VAD showed stable and sufficient circulatory support for the bridge-to-transplant procedure in this cohort of 4 patients.

Respiratory failure of two sp gastric bypass patients and subsequent rescue with extracorporeal membrane oxygenation

Severe obesity is a chronic condition that is difficult to treat through diet and exercise alone. Gastrointestinal surgery for obesity (bariatric surgery) alters the digestive process by either restrictive surgical alterations or malabsorptive operations. Some 10-20% of patients who have weight-loss surgery require follow-up operations to correct complications. Hypoxemia after gastric bypass surgery for morbid obesity, a reported complication, can occur as early as 24 h post surgery. Two patients presented with severe hypoxia and were placed on veno-venous extracorporeal membrane oxygenation (ECMO). Patient No. 1 had an obstruction of the alimentary limb of the gastric bypass due to suture adhesions, and patient No. 2 had an incarcerated diaphragmatic hernia. While on ECMO, ventilation using a protective strategy (60% FiO2, pressure-controlled ventilation inspiratory pressure (PCV) IP 25-27, positive end-expiratory pressure (PEEP) 10-14, permissive hypercapnia) was employed. An inflow cannula to the level of the right atrium served as arterial outflow from the circuit to the patient, while the femoral vein served as venous inflow to the ECMO circuit. Although ECMO in adult respiratory failure is often used as the last resort due to serious associated adverse events, we report two patients with life-threatening complications from gastric bypass who were rescued, resuscitated to day 7, and uneventfully discharged from the hospital to home.

Left Ventricular Support by Axial Flow Pump: The Echocardiographic Approach to Device Malfunction

Axial flow pumps have gained increased acceptance in recent years as a bridge to heart transplantation and, more recently, as destination therapy. As left ventricular (LV) assist device dysfunction will be increasingly prevalent, the aim of our work was to introduce an echocardiographic management protocol as a guide to recognize the causes of pump failure. In this article we describe the echocardiographic approach to 5 episodes of malfunction of an axial flow pump (DeBakey, MicroMed Technology Inc, Houston, Tex) in 4 patients: 4 episodes caused by thrombosis of LV assist device and one caused by abnormal increase of systemic vascular resistance. In our experience, echocardiography played a pivotal role in clinical management of LV assist device failure. It allowed us to: assess patency and position of inflow and outflow cannulae; research the source of thromboembolic material; assess adequate LV filling and unloading; and optimize right ventricular function, volume replacement therapy, and pharmacologic support.

Continuous Aortic Flow Augmentation

Diminished aortic flow may induce adverse downstream vascular and renal signals. Investigations in a heart failure animal model have shown that continuous aortic flow augmentation (CAFA) achieves hemodynamic improvement and ventricular unloading, which suggests a novel therapeutic approach to patients with heart failure exacerbation that is inadequately responsive to medical therapy. We studied 24 patients (12 in Europe and 12 in the United States) with heart failure exacerbation and persistent hemodynamic derangement despite intravenous diuretic and inotropic and/or vasodilator treatment. CAFA (mean+/-SD 1.34+/-0.12 L/min) was achieved through percutaneous (n=19) or surgical (n=5) insertion of the Cancion system, which consists of inflow and outflow cannulas and a magnetically levitated and driven centrifugal pump. Hemodynamic improvement was observed within 1 hour. Systemic vascular resistance decreased from 1413+/-453 to 1136+/-381 dyne.s.cm(-5) at 72 hours (P=0.0008). Pulmonary capillary wedge pressure decreased from 28.5+/-4.9 to 19.8+/-7.0 mm Hg (P<0.0001), and cardiac index (excluding augmented aortic flow) increased from 1.97+/-0.44 to 2.27+/-0.43 L.min(-1).m(-2) (P=0.0013). Serum creatinine trended downward during treatment (overall P=0.095). There were 8 complications during treatment, 7 of which were self-limited. Hemodynamics remained improved 24 hours after CAFA discontinuation. In patients with heart failure and persistent hemodynamic derangement despite intravenous inotropic and/or vasodilator therapy, CAFA improved hemodynamics, with a reduction in serum creatinine. CAFA represents a promising, novel mode of treatment for patients who are inadequately responsive to medical therapy. The clinical impact of the observed hemodynamic improvement is currently being explored in a prospective, randomized, controlled trial.

Rupture of Inlet Graft of the HeartMate System: A Case Report

As the implantation of left ventricular assist devices (LVADs) as destination therapy for patients with heart failure increases in frequency, device durability and malfunction present an increasing concern. Complications such as inflow valve regurgitation, outflow valve distortion, and problems with power cable or pump motors place the LVAD recipient at increased risk for morbidity and mortality. To offset the risk of complications related to the inflow cannula, modifications to the valve conduit were made to the SNAP VE device in November 2002. These modifications were intended to improve durability with cycle performance of up to 6 times longer than the old inflow valve during in vitro testing. We describe here a patient who sustained disruption of the Dacron inlet graft after implantation of the Heart-Mate XVE System as a destination therapy.

Assessment of Recurrent Heart Failure Associated with Left Ventricular Assist Device Dysfunction

Patients with advanced heart failure may require long-term support with an intracorporeal left ventricular assist device (LVAD) before cardiac transplant, while awaiting myocardial recovery, or during destination therapy. Compared with the diagnosis of native heart dysfunction, there is less experience with the assessment of recurrent heart failure after LVAD placement. Ten patients (9 men, 1 woman; age, 58 +/- 11 years) were studied after LVAD placement. Six patients were studied because of recurrent heart failure; the remaining 4 had other indications for study and are reported here as controls. Cardiac catheterization, including LVAD and cannulae catheterization, and angiography were performed. Inflow cannula valve regurgitation by LVAD angiography was found in 3 cases. Patients with regurgitation had a mean increased resting LVAD rate of 105 beats/min (range, 90-120); LVAD output exceeded forward cardiac output (LVAD - thermodilution cardiac output = +3.7 liters/min [0.6-6.4]). Inflow cannula obstruction identified with a filling phase pressure gradient between the left ventricle and the LVAD was found in 3 additional patients. Patients with obstruction had decreased resting LVAD rates (50 beats/min, all patients); LVAD output was less than the forward cardiac output (LVAD - thermodilution cardiac output = -2.3 liters/min [-0.8 to -3.5]). Compared with those with inflow valve regurgitation, patients with cannula obstruction had higher pulmonary capillary wedge pressures; phasic left ventricular pressure variation was reduced. Patients with cannula dysfunction underwent surgical intervention, and 4 of 6 were long-term survivors. When heart failure recurs after LVAD placement, abnormalities of the inflow cannula are common. Cardiac catheterization can confirm the diagnosis before surgical intervention. Hemodynamic coupling between the left ventricle and the LVAD is increased with inflow valve regurgitation and reduced with cannula obstruction.

Mechanical support of total cavopulmonary connection with an axial flow pump

Even under optimal circumstances, total cavopulmonary connection is associated with a continuous late risk of death. Hemodynamics are distinctly abnormal, with increased systemic venous pressures and frequent low cardiac output. Our study uses a sheep model of total cavopulmonary connection to test the response to axial flow pump (Thoratec HeartMate II; Thoratec Corporation (Pleasanton, Calif)) support of total cavopulmonary connection, which might be suitable to treat patients with failing Fontan circulation. Eight sheep (42-48 kg) were studied. After pilot studies in 3 animals, 5 underwent both pump-supported and nonsupported total cavopulmonary connection in alternating sequence for up to 2 hours. This was achieved with a 12-mm polytetrafluoroethylene graft from the (distally ligated) superior vena cava to the main pulmonary artery and a cannula placed in the inferior vena cava with an attached 16-mm Dacron graft to the main pulmonary artery. Pressures (arterial, inferior vena cava, left atrium, and pulmonary artery) and flows (ascending aorta and inferior vena cava) were recorded over 1 hour both with unsupported total cavopulmonary connection and after placing an axial flow pump (Thoratec HeartMate II) between the inferior vena caval inflow cannula and the main pulmonary artery. Under nonsupported total cavopulmonary connection circulation, inferior vena caval and aortic blood flow decreased by nearly 50%. Inferior vena caval pressure nearly doubled, whereas arterial pressure decreased by one third. Pulmonary artery pressure became nonpulsatile; however, mean pulmonary artery pressure and left atrial pressure did not change significantly. With pump-supported Fontan circulation, cardiac output, inferior vena caval flow, and arterial pressure returned to baseline. Inferior vena caval pressure decreased to below baseline levels. Mean pulmonary artery pressure and left atrial pressure again remained unchanged. Axial flow pump support from the inferior vena cava to the pulmonary artery can prevent the substantial decrease of aortic flow and pressure associated with total cavopulmonary connection and can reverse its poor hemodynamics. This is a simple model that can be used to further evaluate the potential of mechanical support as a treatment option in failing Fontan circulation.

Initial Experience With the Abiomed AB5000 Ventricular Assist Device System

We describe our initial experience with the Abiomed AB5000 ventricular assist device (VAD). The Abiomed AB5000 VAD is a system recently approved by the Food and Drug Administration that consists of a fully automatic, vacuum-assisted console and a paracorporeal, pneumatically driven blood pump. The VAD is designed for short or intermediate term use. The console is designed to support the BVS5000 or AB5000 blood pumps. The cannulas and implantation are similar to the BVS5000 system. Four cases are described in which two AB5000 systems were placed de novo and two were transitioned from previously placed BVS5000 units. Hemolysis was observed in 2 cases. The AB5000 VAD flows were generally 4.0 to 4.5 L/min, approximately 0.5 L/min less than the BVS5000. Echocardiography demonstrated high-velocity jets from the inflow cannula in the 2 hemolysis cases. One patient died of multiorgan system failure while on support, 2 were successfully weaned from support and transferred to long-term care facilities, and 1 was weaned from support and successfully discharged to home. The AB5000 VAD is a versatile paracorporeal pneumatic VAD that can be placed de novo or transitioned from a previously placed BVS5000 unit without the need for additional surgery. Lower outputs, high-velocity jets, and hemolysis were observed in 2 of 4 cases. Modifications in cannulas design and placement as well as console reconfigurations may be necessary to optimize performance.

Comparison of Pulsatile With Nonpulsatile Mechanical Support in a Porcine Model of Profound Cardiogenic Shock

The aim of this study was to examine whether pulsatility by intraaortic balloon counterpulsation (IABP) is an important adjunct to the treatment of profound cardiogenic shock (CS) with a widely used, nonpulsatile centrifugal pump (CP). In each of 18 anesthetized, open chest pigs, the outflow cannula of the CP was inserted in the aortic arch through the right external carotid artery, and the inflow cannula of the CP was placed in the left atrium. A 40 cc IABP was subsequently placed in the descending aorta through the left external carotid artery. CS was induced by occlusion of coronary arteries and the infusion of propranolol and crystalloid fluid. Mean aortic pressure, pulse pressure, aortic end diastolic pressure, left ventricular end diastolic pressure, right atrial pressure, and heart rate were monitored. Cardiac output and left anterior descending artery flow were measured with a transit time ultrasound flowmeter. During profound CS, life sustaining hemodynamics were maintained only with the support of the assist devices. Hemodynamic support with the CP was associated with a nearly nonpulsatile flow and a pulse pressure of 7 +/- 4 mm Hg, which increased to 33 +/- 10 mm Hg (p = 0.000) after combining the CP with the IABP. Compared with the hemodynamic support offered by the CP alone, addition of the IABP increased mean aortic pressure from 40 +/- 15 to 50 +/- 16 mm Hg (p = 0.000), cardiac output from 810 +/- 194 to 1,200 +/- 234 ml/min (p = 0.003), and left anterior descending artery flow from 26 +/- 10 to 39 +/- 14 ml/min (p = 0.001). In profound CS, mechanical support provided by a continuous flow CP is enhanced by the added pulsatility of the IABP.

Pressure criterion for placement of distal perfusion catheter to prevent limb ischemia during adult extracorporeal life support

Pressure criterion for placement of distal perfusion catheter to prevent limb ischemia during adult extracorporeal life support

Performance analysis of ventricular assist devices using finite element flow simulation

AbstractNumerical simulation plays an increasingly important role in the design of medical devices in general, and ventricular assist devices in particular. Modelling of flow in blood pumps has the potential to shorten the design cycle and give the designers important insights into causes of blood damage and suboptimal performance. We present a set of flow simulations designed to reproduce previously obtained experimental data relating flow volume generated by the pump to the pressure head imposed between the outflow and inflow cannulas. These performance curves are obtained using a stabilized space–time finite element formulation of the Navier–Stokes equations, with a shear‐slip mesh update used to accommodate the movement of the impeller with respect to non‐axisymmetric housing. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Effects of Left Ventricular Assist Device Support and Outflow Graft Location Upon Aortic Blood Flow

Although continuous flow (CFVAD) and pulsatile (PVAD) ventricular assist devices (VADs) are being clinically used, their effects upon aortic blood flow as a measure of overall blood distribution remain unclear. The objective of this study was to compare the effects of CFVAD and PVAD support for ascending (AscA) and descending (DA) aorta outflow cannulation upon mean aortic blood flow and waveform morphology. Six experiments were conducted in a normal, acute calf model, in which an inflow cannula was implanted in the left ventricle apex and outflow cannulae were anastomosed to both the AscA and DA. Flow probes were placed around the pulmonary artery, pump outflow, brachiocephalic trunk, and aorta proximal and distal to the DA outflow. For each acute experiment, calves received randomly selected levels of VAD support (0-100% of cardiac output) and pump failure (VAD off and outflow cannula unclamped) for each of four randomly selected test conditions: (1) PVAD and AscA, (2) PVAD and DA, (3) CFVAD and AscA, and (4) CFVAD and DA. Regardless of pump type or support level, proximal and distal aorta mean flows were lower (p < 0.05) for DA compared with the AscA. No differences in mean aortic flows between pump types at either outflow graft location were discerned. Differences in morphologic features of blood flow waveforms between PVAD and CFVAD were observed. During simulated pump failure, retrograde aortic blood flow in both the aortic arch and DA was observed. Partial ventricular suction was also observed during the greatest levels of CFVAD support and suggested pronounced effects upon both the right and left ventricle. Collectively, these findings imply that VAD outflow location may have an important role in patient response and recovery. Investigation of the long-term pathophysiologic responses to pump type and outflow location is ongoing.

Transient and Quasi-Steady Computational Fluid Dynamics Study of a Left Ventricular Assist Device

The HeartQuest continuous flow left ventricle assist device (LVAD) with a magnetically levitated impeller operates under highly transient flow conditions. Due to insertion of the in-flow cannula into the apex of the left ventricle, the inlet flow rate is transient because of ventricular contraction, and the pump's asymmetric circumferential configuration with five rotating blades forces blood intermittently through the pump to the great arteries. These two transient conditions correspond to time varying boundary conditions and transient rotational sliding interfaces in computational fluid dynamics (CFD). CFD was used to investigate the pump's performance under these dynamic flow conditions. A quasi-steady analysis was also conducted to evaluate the difference between the steady and transient analyses and demonstrate the significance of transient analysis, especially for transient rotational sliding interfaces transient simulations. This transient flow analysis can be applied generally in the design process of LVADs; it provides more reliable fluid forces and moments on the impeller for successful design of the magnetic suspension system and motor.

Anatomic reconstruction of recurrent aortic arch obstruction in children.

Anatomical reconstruction of the aortic arch following aortic arch surgery is challenging. The placement of an extra-anatomical aortic bypass has been proposed for these difficult cases. This approach is not ideal in children due to possible long-term complications. This study presents the results of our policy to reconstruct the aortic arch in recurrent obstruction in children, which are not amenable to balloon dilatation. Seven children with a median age of 8 years (range 1 month-15 years) were operated for aortic arch obstruction following correction of an aortic coarctation. Six children presented another intra-cardial lesion (2 subaortic membranes; 2 VSDs, 1 ostium stenosis of the left main coronary artery, and 1 mitral valve insufficiency). The surgical approach involved a sternotomy, cardiopulmonary support using two arterial inflow cannulas (one above and one below the aortic arch), and moderate hypothermia. Enlargement of the aortic arch was performed by a sliding plasty in four patients and by a patch plasty in three patients. Associated cardiac defects were corrected as well. It was technically possible to perform the planned operation in all patients. All patients survived and none presented significant postoperative complications. There were no residual gradients in six patients and a gradient of 10 mmHg in one patient postoperatively. One patient showed transient recurrent nerve palsy which recovered within 6 weeks. Follow-up echocardiographic and MRI studies revealed a normal appearing aortic arch with laminar flow. Although more demanding, an anatomical reconstruction of the aortic arch can be performed in infants and children with recurrent obstruction of the aortic arch with excellent initial results. This approach may prove superior to an extra-anatomic bypass in the long-term.

One-lung ventilation, partial bypass and totally endoscopic CABG

One-lung ventilation, partial bypass and totally endoscopic CABG