HeartWare Ventricular Assist Device Implantation for Pediatric Heart Failure—A Single Center Approach

While pediatric HeartWare HVAD application has increased, determining candidacy and timing for initiation of pediatric VAD support has remained a challenge. We present our experience with a systematic approach to HVAD implantation as a bridge to pediatric heart transplantation. We performed a retrospective, single center review of pediatric patients (n = 11) who underwent HVAD implantation between September 2014 and January 2018. Primary endpoints evaluated were survival to heart transplantation, need for right ventricular assist device (RVAD) at any point, ongoing HVAD support, or death. Median patient age was 11 years (range: 3–16). Median BSA was 1.25 m² (range: 0.56–2.1). Heart failure etiologies requiring support were dilated cardiomyopathy (n = 8), myocarditis (n = 1), congenital mitral valve disease (n = 1), and single ventricle heart failure (n = 1). Median time from cardiac ICU admission for heart failure to HVAD placement was 15 days (range 3–55), based on standardized VAD implantation criteria involving imaging assessment and noncardiac organ evaluation. The majority of patients (91%) were INTERMACS Level 2 at time of implant. Three patients (27%) had CentriMag RVAD placement at time of HVAD implantation. Two of these three patients had successful RVAD explanation within 2 weeks. Median length of HVAD support was 60 days (range 6–405 days). Among the 11 patients, survival during HVAD therapy to date is 91% (10/11) with 9 (82%) bridged to heart transplantation and one (9%) continuing to receive support. Posttransplant survival has been 100%, with median follow‐up of 573 days (range 152–1126). A systematic approach to HVAD implantation can provide excellent results in pediatric heart failure management for a variety of etiologies and broad BSA range.     

Initial Clinical Experience With the HeartMate II Ventricular Assist System in a Pediatric Institution

In many adult cardiac programs, intracorporeal mechanical circulatory support has become a routine treatment for end‐stage cardiac failure. For the pediatric population, options are often limited by a small body habitus. Even when an adolescent's weight may suggest adequate space for device implant, most intracorporeal adult devices remain too large for adolescents. The Thoratec HeartMate II (HM II) (approved by the FDA in April of 2008) is a small, noiseless device that is easily operated and monitored. By having an uncomplicated operating system and small percutaneous drive line, the HM II provides an opportunity for these patients to aggressively rehabilitate to become a better transplant candidate and also provides the potential to be discharged home. The two youngest patients ever to utilize the HM II are also the first two cases of using the HM II at a freestanding pediatric hospital. A 12‐year‐old, 53 kg, girl with dilated cardiomyopathy was supported for 85 days before receiving her heart transplant. The second patient, a 13‐year‐old, 149 kg, Hispanic male suffering from morbid obesity and dilated cardiomyopathy, was supported for 128 days. The HM II allowed for rehabilitation and nutritional education, resulting in this patient losing 50 kg before heart transplant. Despite both of these patients' size, their thoracic cavities were that of a preadolescent and thus techniques were developed to avoid morbidities like chest wall abrasion and bleeding. Because of differences between adult and pediatric patients and institutions, these cases provided unique challenges. However, as pediatric device therapy is now maturing, pediatric programs such as Texas Children's Hospital have begun to develop strategies for mechanical support that factor in patient's size and need for long‐term or temporary support, utilizing the growing number of devices (i.e., Jostra Rotoflow, Tandem Heart PTVA, Thoratec CentriMag, Berlin Heart EXCOR, etc.) that are now available to children.     

Changes in Spirometry After Left Ventricular Assist Device Implantation

Left ventricular assist devices (LVADs) are increasingly being used as life‐saving therapy in patients with end‐stage heart failure. The changes in spirometry following LVAD implantation and subsequent unloading of the left ventricle and pulmonary circulation are unknown. In this study, we explored long‐term changes in spirometry after LVAD placement. In this retrospective study, we compared baseline preoperative pulmonary function test (PFT) results to post‐LVAD spirometric measurements. Our results indicated that pulmonary function tests were significantly reduced after LVAD placement (forced expiratory volume in one second [FEV₁]: 1.9 vs.1.7, P = 0.016; forced vital capacity [FVC]: 2.61 vs. 2.38, P = 0.03; diffusing capacity of the lungs for carbon monoxide [DLCO]: 14.75 vs. 11.01, P = 0.01). Subgroup analysis revealed greater impairment in lung function in patients receiving HeartMate II (Thoratec, Pleasanton, CA, USA) LVADs compared with those receiving HeartWare (HeartWare, Framingham, MA, USA) devices. These unexpected findings may result from restriction of left anterior hemi‐diaphragm; however, further prospective studies to validate our findings are warranted.     

Implantable Ventricular Assist Systems

A major goal of the Circulatory Support Program of the National Heart, Lung, and Blood Institute (NHLBI) is the development of a tether-free implantable ventricular assist system (VAS) to rehabilitate patients with advanced heart disease. In 1980, the NHLBI initiated a targeted program to develop and integrate implantable electromechanically powered VASs capable of operating for at least 2 years. The objectives of the program are to complete the development of the VAS and perform in vitro and in vivo evaluation studies. This article summarizes the research status of this NHLBI-sponsored program. It defines the VAS system requirements, describes the systems under development, identifies progress achieved to date, and identifies research challenges.     

The Use of Ventricular Assist Device Support in Children: The State of the Art

Improved survival, recognition, and management of patients with congenital heart disease have increased the number of pediatric patients with ventricular dysfunction. Many of these patients require mechanical support to bridge to transplant or recovery. Development of pediatric ventricular assist devices has lagged behind adult devices. Until recently, adult devices were used in pediatric patients, with suboptimal results in the smaller patient population. Extracorporeal membrane oxygenation can be life saving, but is a poor choice for long‐term support. The Berlin Heart EXCOR (Berlin Heart AG, Berlin, Germany) is a paracorporeal device with a variety of pumps for patients of all sizes. The PumpKIN Trial will compare this device to the Infant Jarvik 2000 (Jarvik Heart, New York, NY, USA) in a prospective, randomized study. The single ventricle population presents unique challenges to placement and proper functioning of assist devices. Data are anecdotal and mortality is high. A registry has been developed to assist in caring for this challenging population.     

Design Method of a Foldable Ventricular Assist Device for Minimally Invasive Implantation

To date, ventricular assist devices (VADs) have become accepted as a therapeutic solution for end‐stage heart failure patients when a donor heart is not available. Newer generation VADs allow for a significant reduction in size and an improvement in reliability. However, the invasive implantation still limits this technology to critically ill patients. Recently, expandable/deployable devices have been investigated as a potential solution for minimally invasive insertion. Such a device can be inserted percutaneously via peripheral vessels in a collapsed form and operated in an expanded form at the desired location. A common structure of such foldable pumps comprises a memory alloy skeleton covered by flexible polyurethane material. The material properties allow elastic deformation to achieve the folded position and withstand the hydrodynamic forces during operation; however, determining the optimal geometry for such a structure is a complex challenge. The numerical finite element method (FEM) is widely used and provides accurate structural analysis, but computation time is considerably high during the initial design stage where various geometries need to be examined. This article details a simplified two‐dimensional analytical method to estimate the mechanical stress and deformation of memory alloy skeletons. The method was applied in design examples including two popular types of blade skeletons of a foldable VAD. Furthermore, three force distributions were simulated to evaluate the strength of the structures under different loading conditions experienced during pump operation. The results were verified with FEM simulations. The proposed two‐dimensional method gives a close stress and deformation estimation compared with three‐dimensional FEM simulations. The results confirm the feasibility of such a simplified analytical approach to reveal priorities for structural optimization before time‐consuming FEM simulations, providing an effective tool in the initial structural design stage of foldable minimally invasive VADs.     

In Vivo Preclinical Anticoagulation Regimens After Implantation of Ventricular Assist Devices

Ventricular assist devices (VADs) have demonstrated successfully their ability to treat failing circulation of patients with end-stage heart failure. Among the main obstacles with these VADs is thromboembolic events that increase device-related morbidity and mortality. Prior to the clinical application of any newly developed VAD, the feasibility of the device is tested on animal models. Animal species have different hemostatic properties than human patients, and this factor creates a margin of error when comparing the occurrence of VAD-induced thrombosis in an animal versus a human. This detailed literature review provides a thorough documentation of various preclinical anticoagulation protocols used to date, including their outcomes and recommendations for future anticoagulation management strategies. In summary, the outcomes favor a sheep or pig model over other animal models, and discourage the application of a single anticoagulative agent to improve outcomes with any of the currently available devices.     

The PUCA Pump: A Left Ventricular Assist Device

Abstract: Left ventricular assist devices (LVADs) that are being used clinically still have specific drawbacks. Therefore, a new concept for mechanical circulatory support was developed, the pulsatile catheter (PUCA) pump. It consists of an extracorporeally placed, pneumatically driven membrane pump that is connected to a valved catheter. Ther catheter is introuced into an easily accessible artery and positioned with its distal tip in the left ventricle. Blood is aspirated from the left ventricle and ejected into the ascending aorta. Potential advantages of the catheter pump are its simple design and its fast application with minimal surgery. Preliminary in vitro tests with a first prototype showed that it is possible to create a pulsatile flow of 3 L/min and proved that further developing the PUCA pump will be worthwhile.     

Driving After Left Ventricular Assist Device Implantation

Literature on driving capacities of ventricular assist device patients is rare and driving restrictions differ from center to center. Currently, no guidelines exist on whether and when left ventricular assist device (LVAD) patients are allowed to begin driving cars after device implantation. In this study, we assess the driving abilities of patients after LVAD implantation. Three hundred and ninety LVAD patients have been surveyed in a worldwide, multicenter study. The single survey followed a multi‐method design, including online, phone, and face‐to‐face interviews. Out of 390 patients, 72% are still driving and 28% did not continue driving after LVAD implantation. Reasons for discontinuation were capability (24%), insecurity (17%), and disapproval by family members (9%) or doctors (5%). Ninety percent of the patients describe their ability to drive as perfect or adequate. Sixty‐nine percent state that they are not restricted in their general driving capacity. Forty‐nine percent report not to be restricted in agility to drive by the device equipment. The majority of patients have not been involved in car accidents or major complications (94%). Eight accidents were reported (3%). Out of those, all were minor collisions. No patient reported the occurrence of a fatal accident or casualties. LVAD alarms did occur in six incidents (2%) with the majority being low battery alarms. The results of this study suggest that driving with a left ventricular assist device is safe for stable patients and driving can be resumed 3 months after LVAD implantation after careful patient assessment.     

B‐Type Natriuretic Peptide Levels Predict Ventricular Arrhythmia Post Left Ventricular Assist Device Implantation

B‐type natriuretic peptide (BNP) levels have been shown to predict ventricular arrhythmia (VA) and sudden death in patients with heart failure. We sought to determine whether BNP levels before left ventricular assist device (LVAD) implantation can predict VA post LVAD implantation in advanced heart failure patients. We conducted a retrospective study consisting of patients who underwent LVAD implantation in our institution during the period of May 2009–March 2013. The study was limited to patients receiving a HeartMate II or HeartWare LVAD. Acute myocardial infarction patients were excluded. We compared between the patients who developed VA within 15 days post LVAD implantation to the patients without VA. A total of 85 patients underwent LVAD implantation during the study period. Eleven patients were excluded (five acute MI, four without BNP measurements, and two discharged earlier than 13 days post LVAD implantation). The incidence of VA was 31%, with 91% ventricular tachycardia (VT) and 9% ventricular fibrillation. BNP remained the single most powerful predictor of VA even after adjustment for other borderline significant factors in a multivariate logistic regression model (P < 0.05). BNP levels are a strong predictor of VA post LVAD implantation, surpassing previously described risk factors such as age and VT in the past.     

Implantation of the Left Ventricular Assist Device

Development of mechanical devices for support of the failing heart is a major goal in cardiac surgery. The application of left ventricular assist device (LVAD) is a promising approach in the case of severe and otherwise untreatable cardiac failure. In our experience we have used two external centrifugal pumps for the extracorporeal biventricular cardiac support in a post-transplantation patient who experienced severe rejection six months after heart transplantation. Our own series includes a total of ten implantations of LVAD's with six patients who could be weaned from the device but only one long-term survivor. The clinical results are not encouraging which suggests that the heart of the patient who needs an LVAD has been damaged beyond any chance for later recovery. Obviously timing is the most crucial aspect of the decision to implant the device. It would appear that orthotopic implantation of the transplanted heart remains the method of definitive treatment.     

Continuous Monitoring of Cardiac Rhythms in Left Ventricular Assist Device Patients

Monitoring of cardiac rhythms is of major importance in the treatment of heart failure patients with left ventricular assist devices (LVADs) implanted. A continuous surveillance of these rhythms could improve out‐of‐hospital care in these patients. The aim of this study was to investigate cardiac rhythms using available pump data only. Datasets (n = 141) obtained in the normal ward, in the intensive care unit, and during bicycle ergometry were analyzed in 11 recipients of a continuous flow LVAD (59.1 ± 9.7 years; male 82%). Tachograms and arrhythmic patterns derived from the pump flow waveform, and a simultaneously recorded ECG were compared, as well as heart rate variability parameters such as: the average heart beat duration (RR interval), the standard deviation of the beat duration (SDNN), the root‐mean‐square of the difference of successive beat durations (RMSSD), and the number of pairs of adjacent beat duration differing by >50 ms divided by the number of all beats (pNN50). A very good agreement of cardiac rhythm parameters from the pump flow compared with ECG was found. Tachycardia, atrial fibrillation, and extrasystoles could be accurately identified from the tachograms derived from the pump flow. Also, Bland–Altman analysis comparing pump flow with ECG indicated a very small difference in average RR interval of 0.3 ± 1.0 ms, in SSDN of 0.5 ± 2.7 ms, in RMSSD of 1.0 ± 5.6 ms, and in pNN50 of 0.3 ± 1.0%. Continuous monitoring of cardiac rhythms from available pump data is possible. It has the potential to reduce the out‐of‐hospital diagnostic burden and to permit a more efficient adjustment of the level of mechanical support.     

Chronic Survival of Calves Implanted with the DeBakey Ventricular Assist Device

The DeBakey ventricular assist device (VAD) is a miniaturized, electromagnetically driven axial flow pump capable of generating in excess of 10 L/min output. The VAD was evaluated in 19 calves during experiments designed to test iterative modifications in the system and to determine the safety of the DeBakey VAD for intermediate to long-term implant. Five of the animals died or were euthanized during the perioperative period (i.e., Days 1-5) due to complications associated with bleeding (n = 3), sudden cardiac arrest (n = 1), or pump occlusion due to a muscle remnant associated with coring (n = 1). The remaining 14 animals survived from 7-145 days. Ten of the 14 animals survived 30 or more days, and 2 animals survived 93 and 145 days before elective euthanasia. Pump function was evaluated in the 14 calves that survived beyond the perioperative period. Pump output at implantation averaged 3 L/min while output at 100 days (n = 2) averaged 4.22 L/min. The electrical current did not change across time during the study, indicating normal operation of the bearings. Pumps consumed less than 10.5 W of power for all support durations. Hemolysis did not occur; the average daily plasma free hemoglobin varied from 2.0 to 8.0 mg/dl. Evaluation of serum biochemical data showed that implantation of the DeBakey VAD in calves with normal hearts did not impair end organ function; BUN, creatinine, and total bilirubin varied minimally within the normal range. The white blood cell count of implanted animals remained within the normal range throughout the study.     

Pump Speed Waveform Analysis to Detect Aortic Valve Opening in Patients on Ventricular Assist Device Support

As the aortic valve (AV) opens, the pump pressure head remains constant, which is reflected as a “notch/plateau” in pump pressure and flow signals. However, instantaneous flow estimation may be influenced by friction and is particularly difficult in axial pumps. Therefore, a new method to determine the duration of AV opening based on the area under the curve (AUC) of the power spectral density analysis of pump speed signal was developed. Data from patients implanted with HeartWare HVAD left ventricular assist device were studied at different pump speeds, with simultaneous transthoracic echocardiography in two cohorts. In the first group, pump data of 15 patients were used to investigate the ability to discriminate between an open and closed AV. In the second cohort of a further 13 patients, the duration of AV opening was measured from digitized M‐mode images, and the relationship between the AV opening time and the new method assessed. In 14 of the initial 15 patients, AV status could be discriminated using only one threshold for all patients. In the second cohort, gradual speed reduction resulted in aortic valve opening in 12 of the 13 patients. The correlation between AV opening duration and AUC was 0.96 ± 0.03. Regression analysis indicated a linear relationship in each of the patients with a small error between the fit and the measured opening time (root mean square error = 11.0 ± 7.6 ms). However, the slopes (69.0 ± 52.8) and intercepts (?31.4 ± 78.0) varied widely between patients. The sensitivity and specificity for the new method using AUC threshold of 0.95 for aortic valve closure was 95% and 91%, respectively. The newly developed method to detect AV opening not only provides information on the AV status during LVAD support (open/closed) but also gives insight into the duration of AV opening. Because the slope of the relationship varies from patient to patient, initial training and adaptation of the method to each patient seems to be required.     

HeartWare Ventricular Assist Device Implantation in Patients With Fontan Physiology

We aim to describe the clinical course of a series of patients with hypoplastic left heart syndrome and refractory systolic heart failure supported with a HeartWare ventricular assist device (HVAD) following Fontan palliation. This is a retrospective review of three consecutive patients supported with a HVAD following Fontan palliation through February 2016. Data include patient characteristics, operative variables, postimplantation hemodynamic/device parameters, event outcomes, and duration of HVAD support. Patient ages were 11.7, 13.5, and 17.5 years, respectively, at the time of HVAD implant. The duration of HVAD support was 148, 272, and 271 days, respectively, of which 86, 222, and 211 were outpatient days. Inflow cannula position was the morphologic right ventricle with depth adjustment and manipulation of the tricuspid subvalvar apparatus to ensure good inflow. Echocardiographic, hemodynamic, and noninvasive oximetric monitoring resulted in high RPM settings for all patients. Despite various complications, all patients were successfully transplanted and discharged home alive. We present three patients bridged to transplantation using the HVAD following Fontan palliation. We demonstrate potential for durable support with transition to outpatient care while awaiting heart transplantation in a subset of patients status post Fontan surgery.     

Motor Feedback Physiological Control for a Continuous Flow Ventricular Assist Device

The response of a continuous flow magnetic bearing supported ventricular assist device, the CFVAD3 (CF3) to human physiologic pressure and flow needs is varied by adjustment of the motor speed. This paper discusses a model of the automatic feedback controller designed to develop the required pump performance. The major human circulatory, mechanical, and electrical systems were evaluated using experimental data from the CF3 and linearized models developed. An open-loop model of the human circulatory system was constructed with a human heart and a VAD included. A feedback loop was then closed to maintain a desired reference differential pressure across the system. A proportional-integral (PI) controller was developed to adjust the motor speed and maintain the system reference differential pressure when changes occur in the natural heart. The effects of natural heart pulsatility on the control system show that the reference blood differential pressure is maintained without requiring CF3 motor pulsatility.     

Third Generation Ventricular Assist Device: Mid‐Term Outcomes of the HeartWare HVAD in Pediatric Patients

The HeartWare HVAD is a small, third generation continuous flow pump that is intracorporeally placed for support of a failing ventricle in adult patients. This device is small in size when compared to other left ventricular assist devices and can therefore be used in smaller sized pediatric patients. We present our initial experience using the HVAD as a bridge to heart transplantation in the pediatric population. We performed a retrospective, single center, nonrandomized review of 17 pediatric patients who underwent HVAD implantation between June 2013 and March 2016. The primary endpoints evaluated in this study were overall survival to heart transplantation, ongoing device support, or death. In this patient cohort, nine (53%) of 17 patients were male. The median age of the patients was 13.4 ± 3.8 (range 5–17) years. The median body surface area was 1.4 ± 0.4(0.7–2) m². Etiologies of heart failure requiring HVAD support were dilated cardiomyopathy (n = 8), myocarditis (n = 5) and noncompaction cardiomyopathy (n = 4). The overall mean length of HVAD support was 254 ± 298 (range 2–804) days. A successful outcome (bridge to transplant and ongoing mechanical support) was achieved in 13 patients (76.5%). Of the 13 patients, nine (69.2%) were bridged to heart transplantation and four continue to receive support (30.7%) and are eligible for transplantation. Post‐transplant survival has been 100%, with a mean follow‐up of 296 ± 264.5 (range 18–785) days. The most common complication was pump thrombosis (23.5%) in follow‐up. Four patients (23.5%) experienced no complications. The HVAD continuous flow ventricular assist device can be safely used to bridge pediatric patients to cardiac transplantation. Favorable outcomes of this device are comparable to the adult population. This analysis demonstrated safe and effective implantation of the HVAD System in a child with a BSA of 0.7 m².