Specification of supervisory control systems for ventricular assist devices

One of the most important recent improvements in cardiology is the use of ventricular assist devices (VADs) to help patients with severe heart diseases, especially when they are indicated to heart transplantation. The Institute Dante Pazzanese of Cardiology has been developing an implantable centrifugal blood pump that will be able to help a sick human heart to keep blood flow and pressure at physiological levels. This device will be used as a totally or partially implantable VAD. Therefore, an improvement on device performance is important for the betterment of the level of interaction with patient's behavior or conditions. But some failures may occur if the device's pumping control does not follow the changes in patient's behavior or conditions. The VAD control system must consider tolerance to faults and have a dynamic adaptation according to patient's cardiovascular system changes, and also must attend to changes in patient conditions, behavior, or comportments. This work proposes an application of the mechatronic approach to this class of devices based on advanced techniques for control, instrumentation, and automation to define a method for developing a hierarchical supervisory control system that is able to perform VAD control dynamically, automatically, and securely. For this methodology, we used concepts based on Bayesian network for patients' diagnoses, Petri nets to generate a VAD control algorithm, and Safety Instrumented Systems to ensure VAD system security. Applying these concepts, a VAD control system is being built for method effectiveness confirmation.     

Preliminary in vivo study of an intra-aortic impeller pump driven by an extracorporeal whirling magnet

To achieve the aim of long-term heart-assist with a simple implantable device, we have been trying to develop a minimal intra-aortic impeller blood pump driven by an extracorporeal magnetic device. The purpose of the current study was to evaluate its feasibility by acute in vivo animal tests. The minimal intra-aortic pump was a cage-supported rotor-impeller, 17 mm in diameter with a total length of 30 mm. The driving magnet, mounted extracorporeally, was 55 mm in diameter and 50 mm in length. Seventeen dogs weighing from 28-34 kg were used in the study. After thoracic incision, heparin (50 U/kg) was infused. The impeller pump was inserted into the aortic chamber via a prosthetic vessel and fastened. Thin tubes were inserted into the left ventricular apex and the femoral artery to monitor the left ventricular (LV) and the aortic pressure. After closing the thoracic cavity, the extracorporeal whirling magnet, turned by an electric motor, was placed tightly against the thoracic wall parallel to the intra-aortic pump. The experiments, each lasting for about 40 min, were successful in 7 animals; the other 10 animals died of bleeding during pump implantation and were excluded from the experiment. The peak systolic pressure of the left ventricle could be considerably decreased by the pump and was reduced to as low as 28 mm Hg at a rotational speed of 9,000 rpm, showing that the simple intra-aortic impeller was effective in unloading the natural heart. The novel left ventricular assist device (LVAD) concept of an intra-aortic impeller pump, driven by an extracorporeal magnetic device, is feasible.     

Totally implantable ventricular assist system that can increase brain blood flow

In the clinical usage of the ventricular assist device (VAD), multiple organ failure becomes an important problem. To improve the clinical record of the VAD, another organ function may be vitally important. For that reason, we have been developing a VAD system aiming at improving another organ's function. Development of the vibrating flow pump (VFP), which can generate a very unique flow pattern from 10 Hz to 50 Hz, was ongoing in our Institute. In order to evaluate brain blood flow and oxygen consumption, HbO2 was measured with a NIRO monitoring device in healthy adult goats. Four goats were anesthetized with halothane inhalation; then left thoracotomy was performed for the left heart bypass. HbO2 of the brain was measured by recording of the hemodynamic variables during left heart assistance with the VFP system. During left heart bypass with the VFP system, hemodynamic parameters stayed within normal range, and satisfactory pump output was easily obtained. Pump output stayed within 20-40% bypass to evaluate the effect of high frequency oscillated assist flow on brain blood flow during the same cardiac output. Interesting results were observed during the experiments. During 30 Hz drive of the VFP left heart assistance, HbO2 suggested that brain blood flow significantly increased compared with another drive frequency assistance during the same total cardiac output. These results suggest that we can control the brain blood flow with a totally implantable VAD system such as the VFP system.     

Bridge to transplantation with the DeBakey VAD axial pump: a single center report

Aims: To report our experience with a left ventricular assist device axial pump as a bridge to transplantation: the DeBakey Ventricular Assist Device (VAD). Methods: From February 1999 to February 2002, nine patients (among which eight males), with a mean age of 47 years, all in NYHA functional class IV, were proposed for a bridge to transplantation with the DeBakey VAD. Five patients had primary dilated cardiomyopathy, four had ischemic cardiomyopathy. All the patients had inotropic support prior to the intervention (dobutamine with a mean dose of 12 mcg/kg per min), six had an intra-aortic counterpulsation, four presented ventricular rhythm disorders. Interventions were performed through sternotomy alone (no need for an abdominal pocket) under extra-corporeal circulation on beating heart (except in one patient suffering from an apical thrombosis for which cardioplegic arrest was performed) as followed: implantation of the apical inflow cannula, tunneling of the percutaneous cable, implantation of the outflow graft under aortic side clamping, starting of the DeBakey VAD during CPB weaning-off. Results: Mean support duration was 81±62 days (16–224 days). Eight reoperations were required (three for bleeding or cardiac tamponade, one for haemoperitoneum, one for aortic bifurcation thrombectomy, one for right ventricular assist device implantation, two for iterative replacements of the DeBakey VAD). A significant hemolysis was observed in two patients. No device infection or dysfunction were observed. Secondary recovery of a pulsed flow was observed either clinically or by Echo-Doppler in six patients. Five patients were transplanted, four died prior to transplantation (three from multi-organ failure on post-operative day 35, 16 and 50, respectively, and the last patient was found disconnected at day 109). Conclusions: The DeBakey VAD is at the origin of renewed interest for continuous flow assist devices. Still under evaluation, the advantages of miniaturization and facility of implantation of this new device seem to be promising.     

End-stage heart failure

The ultimate treatment for end-stage heart failure patients is cardiac transplantation. However, many Japanese candidates have not received its benefits due to the extreme scarcity of donor hearts. The heart transplant waiting period in Japan is prolonged, particularly after the revision of the Organ Transplantation Law in 2010 which meant that patients must wait more than 900 days because of the increase in candidates. According to the Japanese Transplant Registry, almost 90% of candidates require bridge transplantation therapy (BTT) with a ventricular assist device (VAD), and the average duration of BTT is around 800 to 900 days. The excellent outcome of heart transplant surgery in Japan even with such a prolonged BTT duration with VADs is confirmation of the excellent clinical results of VAD support. Until April 2011, only the paracorporeal Nipro VAD for BTT was covered by Japanese national health insurance. Analysis of the clinical outcome of 303 patients who received a Nipro VAD (for left ventricular [LV] drainage) as BTT showed that the longest support duration was 1,673 days (average 427 days), 72 patients (24%) received a heart transplant, and 68 patients (22%) required ongoing VAD support. Thus the Nipro VAD is an excellent paracorporeal device. The 6-year survival rate of 36 patients in clinical trials of four types of implantable rotary blood pump LVADs (Evaheart, DuraHeart, Jarvik 200, HeartMate II) was about 70%, which is an outstanding result of BTT using implantable LVADs. Only 36 patients in seven Japanese heart centers have received implantable LVADs, and this small number corresponds to the initial learning curve. Therefore, the clinical results will improve greatly after the use of commercially available implantable LVADs becomes more widespread. The long waiting period for heart transplantation has contributed to the excellent clinical outcomes of VAD therapy in Japan.     

Ultracompact, completely implantable permanent use electromechanical ventricular assist device and total artificial heart

An ultracompact, completely implantable permanent use electromechanical ventricular assist device (VAD) and total artificial heart (TAH) intended for 50-60 kg size patients have been developed. The TAH and VAD share a miniature electromechanical actuator that comprises a DC brushless motor and a planetary roller screw. The rotational force of the motor is converted into the rectilinear force of the roller screw to actuate the blood pump. The TAH is a one piece design with left and right pusher plate type blood pumps sandwiching an electromechanical actuator. The VAD is one half of the TAH with the same actuator but a different pump housing and a backplate. The blood contacting surfaces, including those of the flexing diaphragm and pump housing, of both the VAD and TAH were made of biocompatible polyurethane. The diameter, thickness, volume, and weight of the VAD are 90 mm, 56 mm, 285 cc, and 380 g, respectively, while those of the TAH are 90 mm, 73 mm, 400 cc, and 440 g, respectively. The design stroke volume of both the VAD and TAH is 60 cc with the stroke length being 12 mm. The stroke length and motor speed are controlled solely based on the commutation signals of the motor. An in vitro study revealed that a maximum pump flow of 7.5 L/min can be obtained with a pump rate of 140 bpm against a mean afterload of 100 mm Hg. The power requirement ranged from 4 to 6 W to deliver a 4-5 L/min flow against a 100 mm Hg afterload with the electrical-to-hydraulic efficiency being 19-20%. Our VAD and TAH are the smallest of the currently available devices and suitable for bridge to transplant application as well as for permanent circulatory support of 50-60 kg size patients.     

Concomitant abdominal exploration with durable left ventricular assist device implantation

A 45-year-old male presented in decompensated heart failure from nonischemic cardiomyopathy and was implanted with a right transaxillary intra-aortic balloon pump. He was listed for heart transplantation but after 9 days, he developed abdominal pain with evidence of embolization on computed tomography scan despite a well-positioned balloon pump. He underwent concomitant abdominal exploration with small bowel resection and durable left ventricular assist device implantation. He recovered well and was discharged home. This case highlights the challenges of decision-making in the current era where intra-aortic balloon pumps are being utilized more frequently as a bridge to heart transplantation.     

Multiple splenic infarctions due to septic embolization in a patient supported with Berlin Heart-EXCOR biventricular assist device

Patients awaiting cardiac transplantation often require ventricular assist devices (VADs) due to instable circulatory condition. Device-related infections remain the 'Achilles heel' of mechanical circulatory support and wound complications after VAD placement are a formidable challenge to surgeons. Up to 25% of deaths in VAD patients are due to systemic sepsis, which occurs in 11-26% of patients and bacteria that are common pathogens including Staphylococcus, Pseudomonas, Enterococcus, and Candida. Sepsis, infection of implanted pump components, and infections of percutaneous drivelines continue to limit survival. The Berlin Heart-EXCOR VAD is a para-corporeal pulsatile system that has been successful in patients with severe biventricular dysfunction. We report a case of a 35-year-old male suffering from a postischemic cardiomyopathy who received an EXCOR biventricular assist device as a bridge to transplant. During the assistance the patient developed concomitant methicillin-resistant Staphylococcus aureus infection of implanted pump components which was resistant to conventional therapy. The patient developed sepsis with splenic infarctions due to septic embolization which was successfully treated with a heart transplant. In some extreme cases of VAD infections, such as this, the only therapeutic option is transplantation or device replacement.     

First Clinical Application of the DuraHeart Centrifugal Ventricular Assist Device for a Japanese Patient

The DuraHeart ventricular assist device (VAD) is a third-generation implantable centrifugal pump with a magnetically levitated impeller. Since February 2007, the device has been clinically applied with excellent results as a bridge to heart transplantation in Europe. As of this writing, however, the device has yet to be approved by the Ministry of Health, Labour and Welfare for clinical use in Japan. We herein report the first clinical application of this device for a Japanese patient. A 31-year-old man with dilated cardiomyopathy was transferred to the Heart and Diabetes Center NRW (HDZ-NRW) in Bad Oeynhausen, Germany, where he was to await heart transplantation. The transfer was safely completed under management with low-dose dopamine. His condition gradually deteriorated at HDZ-NRW, and the DuraHeart left ventricular assist device was implanted for the left ventricle at 7 weeks after admission. Shortly thereafter, however, on POD 7, a Thoratec VAD had to be inserted on the right side due to refractory right heart failure. The right ventricular assist device could be explanted after a 3-month assist, and the patient is now waiting for heart transplantation at home in Germany.     

Progress with the HeartSaver Ventricular Assist Device.

BACKGROUND: Ventricular assist devices (VADs) have been shown to be effective for short- or long-term circulatory support. Devices are either being adapted or newly designed for longer term or permanent support, with the goal to provide patients with improved quality of life. Since 1990, a program has been in place to develop a totally implantable, permanent VAD. METHODS: A multidisciplinary team is developing this VAD with specific goals in mind: (1) that it have an intrathoracic position, (2) that it be a totally implantable device without any percutaneous connections, and (3) that it be possible to communicate with the device from remote locations. These goals would allow for complete patient mobility and flexibility for follow-up. RESULTS: The electrohydraulically actuated VAD combines the blood pump, volume displacement chamber, energy converter, and internal electronic module into a single compact unit. The device called the HeartSaver VAD is powered by a transcutaneous energy transfer system and can be remotely monitored and controlled. Prototypes of different versions of the device have been tested in vitro and in vivo with satisfactory performance. CONCLUSIONS: The prototypes of the HeartSaver VAD have functioned well under test conditions and fulfilled the outlined goals. Further development and testing of the design are being conducted before clinical availability.     

Prevention of left ventricular thrombus formation during pneumatic pump assist

A postcardiotomy patient with a pneumatic pulsatile pump for left ventricular assist showed a smoke-like swirling echo within the left ventricle during pump assist. The image disappeared partially during intra-aortic balloon pumping, which was performed as usual. Subsequently, three pumps (native left ventricle, pneumatic and intra-aortic balloon) were driven synchronously: that is, the ventricular assist pump ejected the blood in the first half of the diastole of the native heart beat, and the intra-aortic balloon was inflated during the second half. With this bisected diastolic driving, the abnormal echo disappeared completely. The patient died 52 days after operation, but no thromboembolic episode was observed during the course, and no fresh thrombus was found within the left ventricle at autopsy. The bisected diastolic driving method served as an aid to prevent stagnation of blood and thrombus formation within the native left ventricle in this patient with a left ventricular assist device.     

Ruptured intra-aortic balloon pump. A case report

The intra-aortic balloon pump (IABP) is the gold standard for the mechanical assistance of failing heart. Balloon rupture is a potential complication that may result in a retained device. The operative removal by direct exposure of the femoral vessels has previously been described. We report the case of a retained IABP requiring laparotomy and direct aortic exposure for removal of the device.     

How does successful bridging with ventricular assist device affect cardiac transplantation outcome?

A best evidence topic in cardiac surgery was written according to a structured protocol. The issue was to determine the impact of bridge-to-transplant ventricular assist device support on survival after cardiac transplantation. Altogether 428 papers were found using the reported search, of which 12 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. The treatment options for patients with advanced heart failure or those with deteriorating end-organ function on maximal medical therapy are limited to intravenous inotropes and mechanical assistance with intra-aortic balloon pump (IABP) or ventricular assist device (VAD). Studies exploring the effect of VADs on post-transplant mortality have yielded conflicting results. The Registry of the International Society for Heart and Lung Transplantation continues to identify mechanical support as a risk factor for decreased survival after transplantation. A limitation of this report is that the multivariable adjustment uses variables recorded not at the time of device implant but at the time of transplant. Some of the recipient characteristics thus may be altered by the device implant. Compared with the previous reports the latest data show improvement in post-transplant survival in the recent era. In addition, the excess risk appears to be limited to the early post-transplant period. Experienced centers consistently report outstanding post-transplant results with left ventricular assist device (LVAD) bridging. Of the 12 papers seven showed no difference in survival, and five showed a reduced survival. In the papers showing no difference, one year survival averaged from 85% in supported patients to 87% in non-supported patients. In papers reporting a difference in outcome, one year averaged survival was 74% in LVAD recipients compared to 90% in non-bridged patients. Decreased survival is associated with patients suffering from dilated cardiomyopathy, transplanted within two weeks of LVAD implantation and bridged to transplantation before 2003 as opposed to patients transplanted more recently. Based on the available evidence we conclude that in selected patients survival after heart transplantation in patients bridged with VAD is comparable to those who did not receive the device.     

Use of a Paracorporeal Pneumatic Ventricular Assist Device for Postoperative Cardiogenic Shock in Two Children with Complex Cardiac Lesions

Pneumatic ventricular assist device (VAD) was utilized for cardiogenic shock after intracardiac operation in two children with complex cardiac anomalies based with single ventricle. In the first case (a 10-year-old), after a modified Fontan operation, VAD was placed between the functional left atrium and ascending aorta, serving as a "artificial single ventricle" with neither pumping chamber nor artificial support in the right side of the heart. The systemic circulation was maintained by keeping relatively high central venous pressure. In another child (a 3-year-old) who underwent repair of incompetent atrioventricular valve leaving intracardiac lesions, VAD was placed between the common atrium and ascending aorta, serving as a pump for both pulmonary and systemic circulation with regulation of pulmonary blood flow through an aortopulmonary Gore-Tex shunt. The circulatory assist with VAD was utilized for 5 and 6 days, respectively. Although weaning from the device was not feasible in both patients because of the pulmonary dysfunction, these experience showed the possible use of VAD for cardiogenic shock after surgery in patients with complex cardiac anomalies.     

Development and evaluation of ventricular assist blood pump to salvage patients with profound heart failure

One of the most important characteristics of a ventricular assist device (VAD) is good antithrombogenicity such that the circulating blood does not clot on the surface even when the bypass flow through the device is reduced at the time of weaning-off. A pneumatic and diaphragm-type VAD with excellent antithrombogenicity was developed for clinical use. The pump is made of Japanese-made segmented polyether polyurethane and the maximum output is 7.0 L/min. If the bypass flow was maintained above 2.0 L/min during early postoperative period, thrombus formation was rarely observed even when the flow rate decreased afterwards in chronic animal experiments using 30 goats. Experimental analyses suggested that a biolization mechanism of the material surface covered by absorbed plasma protein might play a major role in the establishment of antithrombogenicity of the pump. No mechanical failure, thrombosis, calcification, and complication in experimental animals occurred when the VAD manufactured under our good quality control system was driven adequately. These results proved that the VAD could be used reliably for at least 3 months. In conclusion, the VAD is safely applicable to clinical cases and contributes to treatments of profound heart failure patients.     

First successful Italian clinical experience with DeBakey VAD.

The growing number of patients waiting for heart transplantation more than tripled between 1989 and 1998. Various non-pulsatile mechanical circulatory support devices have been developed as bridge to heart transplantation in recent years. We report the first successful Italian clinical experience with an axial-flow pump, DeBakey VAD, in a patient supported as bridge to transplantation for 55 days.     

Balloon-pump-induced pulsatility improves coronary and carotid flows in an experimental model of BioMedicus left ventricular assistance

The aim of this study is to evaluate the benefit of the simultaneous use of a BioMedicus left ventricular assistance device (Medtronic, Minneapolis, MN, U.S.A.) and an intra-aortic balloon pump on regional blood flows, pressure, and pulsatility. Twelve pigs are studied. A BioMedicus pump was placed between the left atrium and the ascending aorta and an intra-aortic balloon pump was inserted through the left femoral artery. Blood flow and pressure were measured in the carotid, femoral, and coronary arteries and in the thoracic aorta below the intra-aortic balloon in the basal experimental condition with a full-flow BioMedicus pump and with a full-flow BioMedicus pump + intra-aortic balloon. The BioMedicus pump eliminates pulsatility in all sites and significantly decreases coronary and carotid blood flow. The adjunction of an intra-aortic balloon restores pulsatility to values comparable to those recorded in basal conditions. Coronary and carotid flows even increase to values higher than in the basal conditions. The simultaneous use of an intra-aortic balloon combined with the BioMedicus pump provides a pulsatile flow and increases coronary and carotid blood flows in pigs. An intra-aortic balloon can easily be combined with a BioMedicus pump whenever possible and may improve myocardial recovery in patients with postcardiotomy ventricular failure.     

Low‐Cost Pulsatile Cardiac Assist Device With Compliant Input Chamber

We propose a new, low‐cost pulsatile ventricular assist device (VAD) for short‐term applications. The new device could prove very useful in emergency ventricular failure in which patient survival is not assured. In these cases, the device allows ventricular function to be maintained as the patient's situation is evaluated and a decision is made on whether to perform a heart transplant or to replace the device with a long‐term VAD. The device has a pneumatic tubular blood chamber, clip valves over the cannulae, and a compliant input chamber that improves filling of the pump. Clip valves and all other functions of the device are controlled by means of a computerized console. The use of clip valves reduces the cost of the disposable part of the device.     

Numerical simulations of blood flow in artificial and natural hearts with fluid-structure interaction

This article describes two ongoing numerical studies of fluid-structure interaction in the cardiovascular system: an idealized pulsatile ventricular assist device (VAD), consisting of two fluid chambers separated by a flexible diaphragm; and blood flow and heart wall motion during passive filling of a canine heart. Simulations have been performed for the VAD and compared with the results of a previous study and to our own preliminary experimental results. Detailed measurements of the flow field in the VAD model and additional simulations are in progress. Preliminary simulations using both an idealized model of the natural heart as well as a realistic model have identified the limitations of the current numerical methods in dealing with large three-dimensional deformations. Ongoing research aims at extending the range of simulations to include large deformations and to incorporate an anisotropic material model for the heart wall to account for the muscle fibers.     

The Impella Recover microaxial left ventricular assist device reduces mortality for postcardiotomy failure: a three-center experience

BACKGROUND: We evaluated patient outcomes and complications associated with the microaxial Impella Recover left ventricular assist device (Impella Cardiosystems AG, Aachen, Germany) for postcardiotomy low-output syndrome. This low-cost device is inserted across the aortic valve through a 10-mm vascular graft sewn to the ascending aorta. METHODS: Impella patients were compared with 198 patients treated with an intraoperative intra-aortic balloon pump between January 2000 and December 2002. Three risk scores were used: the Hausmann score, the Texas Heart Institute score, and the Cleveland intensive care unit score. Between September 2001 and March 2003, 24 patients were treated with the Impella Recover for low-output syndrome. Before device insertion, 21 could not be separated from cardiopulmonary bypass, and 3 had postoperative hemodynamic instability despite high-dose catecholamines. Sixteen were treated with the Impella and intra-aortic balloon pump and 8 with the Impella alone (no intra-aortic balloon pump because of peripheral vascular disease or because deemed unnecessary). RESULTS: No technical problems with device insertion occurred. Pump flow was 3.3 +/- 0.7 L/min at 28,000 +/- 4500 RPM. Support time was 61 +/- 56 hours (range, 7-228 hours). Four devices required repositioning. One device failed (leaking purge line) and was removed. Hemolysis was minimal (lactate dehydrogenase levels of 540 +/- 260 U/dL for Impella survivors). Mortality for Impella patients was 54% (13/24), similar to that for high-risk intra-aortic balloon pump patients (Hausmann score > or =2 [57%], intensive care unit score > or =2 [51%], Texas Heart Institute score > or =0.75 [55%], and cardiac index < or =2.3 [45%]). Cardiac output data were available in 19 Impella patients. Impella patients able to increase their cardiac output to 1 L/min or more above the pump flow of the Impella Recover had a 10% (1/10) mortality, versus 88% (8/9) in patients with a residual cardiac function of 1 L/min or less (P =.001). Comparison of high-risk intra-aortic balloon pump patients with Impella patients with residual cardiac function of 1 L/min or more showed a significant reduction in mortality, regardless of the high-risk definition used. Residual cardiac function was the strongest predictor of survival in Impella patients. CONCLUSIONS: The Impella Recover device provides 3 to 4 L/min flow. It improves survival in patients with low-output syndrome if the heart is able to pump 1 L/min or more above device flow.