Numerical simulation of cardiovascular dynamics with left heart failure and in-series pulsatile ventricular assist device

This article presents a numerical model for investigations of the human cardiovascular circulation system response, where the function of the impaired left ventricle is augmented by the pumping action of a pulsatile ventricular assist device (VAD) connected in series to the native heart. The numerical model includes a module for detailed heart valve dynamics, which helps to improve the accuracy of simulation in studying the pulsatile type VAD designs. Simulation results show that, for the case with left ventricular (LV) failure, the VAD support successfully compensates the impaired cardiovascular response, and greatly reduces the after-load of the diseased ventricle, thus assisting possible recovery of the ventricle from the diseased condition. The effects of these conditions on pulmonary circulation are also shown. To investigate the effect of different pumping-activation functions (VAD motion profiles) on the cardiovascular response, three different VAD motion profiles are investigated. The numerical results suggest that Hermitian type motion profiles (smooth curves skewed toward early systole) have the advantage of requiring minimum power to the VAD, and producing the minimum after-load to the left ventricle, minimum ventricular wall stress, and minimum ventricular work to the diseased ventricle; while sawtooth type motions need slightly more power input, and induce slightly increased aortic pressure in diastole, thus improving coronary perfusion.     

Development of totally implantable pulsatile biventricular assist device

Approximately 10% to 15% of all patients implanted with left ventricular assist devices (LVADs) have required right heart support with another device. The necessity of aggressive biventricular support has already been proposed. Therefore, the totally implantable biventricular assist device (BVAD) was developed. The width of the BVAD main body was 87 mm, the thickness 67 mm, and the height 106 mm, while the weight was 785 g. The automatic control algorithm was developed to prevent lung edema and atrial rupture.     

Development of a totally implantable pulsatile centrifugal pump as a ventricular assist device

The Taita No. 1 ventricular assist device (T-VAD) is a totally implantable pulsatile impeller centrifugal pump driven by a magnetically suspended motor. The flow can achieve 2.01 +/- 0.17 L/min against a pressure of 100 mm Hg under 0.266 +/- 0.017 amp and 13.55 +/- 0.41 voltage. The speed was around 3,500 rpm. It consumed less than 6 W of power, resulting in less heat production and mechanical bearing complications. The impeller vane was designed to have both radial and axial curves according to the stream surface and stream lines to reduce thrombosis and hemolysis. Eight calves weighing 80 to 100 kg (mean 87 +/- 12 kg) were used for experiments. With the calves under general anesthesia, left posterolateral thoracotomy was performed to connect the inflow tube with the atrial appendage and to anastomose the outflow tube with the descending aorta. The calves usually awoke and stood up within hours after discontinuation of anesthetics. The mean survival of the calves was 75 +/- 42 days (range 33-148 days). The terminations of experiments were mainly due to infection. During the course of pumping, no significant deterioration of liver or renal function was noted. The evaluation of serum samples from the implanted calves indicated that hemolysis was not associated with use of the T-VAD. The average daily free hemoglobin level was 8.08 +/- 3.05 mg/dl, which was less than the set limit of 20 mg/dl. The red blood cell and platelet count and hemoglobin of implanted animals were within the normal range. In our results, the T-VAD provided competent pulsatile function without severe blood damage or organ dysfunction.     

Left ventricular circulatory support as bridge to heart transplantation in Chagas' disease cardiomyopathy

This study was performed to assess the safety and feasibility of the implantation of ventricular assist devices (VADs) as a bridge to heart transplantation in patients with advanced biventricular failure due to Chagas' disease. Six patients were submitted to paracorporeal left VAD implantation, while right ventricular dysfunction was managed clinically. The mean time of circulatory support was 27 days. Two patients were bridged to heart transplantation successfully, while the other four patients died under assistance with complications that correlated with the final situation of multiple organ failure. Nevertheless, persistent right ventricular dysfunction was observed only in one patient who survived more than 15 days, despite the general significant preoperative compromise of the right ventricle. This paradoxical observation indicates that left VAD implantation may be regarded as a valuable treatment option for patients with Chagas' disease cardiomyopathy who evolve with decompensated heart failure or cardiogenic shock.     

Mechanical bridge with extracorporeal membrane oxygenation and ventricular assist device to heart transplantation

The aim of this study was to evaluate the effect of double bridges with extracorporeal membrane oxygenation (ECMO) and ventricular assist devices (VADs) in clinical heart transplantation. Between May 1994 and October 2000, 134 patients underwent heart transplantation at the National Taiwan University Hospital. Ten patients received ECMO or VAD support as bridges to transplantation. The ages ranged from 3 to 63 years. The indications included cardiac arrest under cardiopulmonary resuscitation in 2 and profound cardiogenic shock refractory to conventional therapy in 8 patients. Usually ECMO was first set up as rescue therapy. If ECMO could not be weaned off after short-term (usually 1 week) support, suitable VADs (HeartMate or Thoratec VAD) were implanted for medium-term or long-term support. Five patients received ECMO support as emergency rescue for 2 to 9 days, and then moved to Thoratec VAD for 8, 49, and 55 days, respectively, or centrifugal VAD for 31 days, or HeartMate VAD for 224 days. They all survived. The survival rate of double bridges with ECMO and VAD was 100%. In postcardiotomy cardiogenic shock, circulatory collapse from acute myocardial infarction or myocarditis, ECMO is the device of choice for short-term support. If heart transplantation is indicated, VADs should replace ECMO for their superiority as a bridge to heart transplantation. Our preliminary data of double bridges with ECMO and VAD revealed good results and were reliable and effective bridges to transplantation.     

Destiny of candidates for heart transplantation in the Eurotransplant heart allocation system

OBJECTIVE: We analyzed the prognosis of candidates for heart transplantation (HTx) after being listed with 'urgent status' for donor heart allocation or after ventricular assist device (VAD) implantation without application for urgent status. METHODS: Urgent status as used in this study refers to both the high urgency (HU) status awarded by Eurotransplant until August 31, 2005 and the urgent (U) status that replaced it from then on. Patients who underwent primary VAD implantation between January 2001 and December 2006 and who were listed as transplantable (T) (group VAD-prim, n=159), and patients listed primarily in urgent status before VAD implantation and/or HTx during the same period (group U-prim, n=168) were enrolled in the study. Group U-prim consists of subgroups: group U-HTx (n=123), who underwent primarily HTx in urgent status; group U-VAD (n=25), who underwent primarily VAD implantation in urgent status; patients who died in urgent status before HTx or VAD implantation (n=6); and patients in urgent status without HTx or VAD implantation (n=14). The survival rate in each group was studied. RESULTS: Survival rates after VAD implantation in group VAD-prim were comparable to those after urgent status listing in group U-prim (67.0% vs 68.5% for 1-year survival, 56.6% vs 65.8% for 2-year survival, respectively). Actuarial survival after listing for urgent status in group U-HTx was significantly better than that in group U-VAD (73.7% vs 46.0% for 1-year survival, p<0.05, log-rank test). Actuarial survival during mechanical circulatory support after the VAD implantation (censored at HTx or weaning from the device) in group VAD-prim was significantly better than that in group U-VAD (80.7% vs 56.2% for 3-month survival, p<0.001, log-rank test). CONCLUSIONS: In order to receive urgent HTx, HTx candidates may choose urgency listing without primary VAD implantation at the risk of failed donor heart allocation in urgent status. However, the prognosis of the patients in the latter situation is poor.     

Short-term bridge to heart transplant using the BVS 5000 external ventricular assist device.

From January 1995 to April 2001, 71 patients with cardiogenic shock using the BVS 5000 were treated or accepted in transfer. Of the 24 transplanted, nine had dilated cardiomyopathy, ischemic cardiomyopathy, acute myocardial infarction, giant cell myocarditis and previous Fontan procedure (group I, n = 13). The others had postcardiotomy shock (group II, n = 11); seven were transferred to our center after device implantation. Age ranged from 8 to 67 years. Ten (77%) patients in group I were implanted without cardiopulmonary bypass. The mean duration of support was 6.7 (2-24) d. Twelve patients were extubated before transplantation and 13 (five in group I, eight in group II) received nonstandard donor organs. Survival to discharge and 1-year actuarial survival was 85 and 77% for group I and 73 and 64% for group II, respectively. Patients with post-implant serum bilirubin levels > 10 mg/dL had a tendency to expire from multiple systemic organ failure. Patients not ventilator-dependent at the time of transplant had the best outcomes. Short-term bridge to transplantation using the BVS 5000 is feasible in selected patients. Caution is recommended when directing such patients to transplant if they need ventilator support and have high serum bilirubin levels.     

Incidence of healthcare-associated infections in a pediatric population with an extracorporeal ventricular assist device

During the last decade, ventricular assist devices (VADs) have become a precious tool to support children with end-stage heart failure. However, thromboembolic events, bleeding, and infections may have a considerable impact on outcome. We retrospectively analyzed the incidence of healthcare-associated infections (HAIs) in nine patients supported by EXCOR Pediatric (Berlin Heart [BH]) VAD in a pediatric cardiosurgical intensive care unit between January 1, 2009 and March 31, 2011 (27 months). Median age was 8 months (interquartile range [IQR] 6-11), median weight 7.5 kg (IQR 4.5-8.5). Seven patients were supported with a left VAD, two with a biventricular VAD (BiVAD). Six patients with a left VAD underwent heart transplant after 89 days (median, IQR 41-143) of support. One patient is still on the waiting list. All patients with BiVAD died after 12 days of assistance due to VAD malfunction. Sixteen HAIs were reported in five out of nine patients (56%). All infected patients were supported by a left VAD. When compared with noninfected patients, they had a longer mechanical support period (median 131 days, IQR 75-164, vs. 25 days, IQR 11-61, P = 0.03), a longer intensive care unit stay (median 159 days, IQR 85-188, vs. 48 days, IQR 17-87, P = 0.06) and a longer length of hospital stay (median 186 days, IQR 105-222, vs. 64 days, IQR 34-113, P = 0.06). Overall, nine mechanical devices were replaced for thromboembolic issues, most of them (67%) in patients with VAD-related infections. Overall, infection rate was 17.6 per 1000 patients days, 1.3 BH endocarditis per 1000 BH days, 4.0 surgical sites infections per 1000 BH days, 12.5 central line-associated blood stream infections per 1000 central venous catheter days, 5 catheter-associated urinary tract infections per 1000 urinary catheter days, and 13.5 ventilator-associated pneumonia cases per 1000 mechanical ventilation days. Overall, VAD-related infections were 5.4 per 1000 BH days. Of the 17 isolated pathogens, 53% were Gram-negative rods, with a prevalence of Pseudomonas aeruginosa (35.3%). Four bacteria were multidrug resistant (25%), three were carbapenem-resistant P. aeruginosa (50% of all isolated pseudomonads), and one was a methicillin-resistant S. aureus. VADs used as a bridge to cardiac transplantation are associated with a large number of HAIs. Patients with infected VADs were admitted for longer time in intensive care and in hospital with increased healthcare costs but with no impact on survival.     

The PediPump: a new ventricular assist device for children

Options for mechanical circulatory support for the treatment of end-stage heart failure in children are limited. Ventricular assist devices (VADs), which have revolutionized cardiac care in adults, remain largely unavailable for pediatric applications. The PediPump is a new rotary dynamic VAD designed to provide support for the entire range of patient sizes encountered in pediatrics. Despite being much smaller than currently available VADs, which makes it suitable for even newborn circulatory support, the PediPump demonstrates excellent hemodynamic performance.     

Atrial versus ventricular cannulation for a rotary ventricular assist device

The ventricular assist device inflow cannulation site is the primary interface between the device and the patient. Connecting these cannulae to either atria or ventricles induces major changes in flow dynamics; however, there are little data available on precise quantification of these changes. The objective of this investigation was to quantify the difference in ventricular/vascular hemodynamics during a range of left heart failure conditions with either atrial (AC) or ventricular (VC) inflow cannulation in a mock circulation loop with a rotary left VAD. Ventricular ejection fraction (EF), stroke work, and pump flow rates were found to be consistently lower with AC compared with VC over all simulated heart failure conditions. Adequate ventricular ejection remained with AC under low levels of mechanical support; however, the reduced EF in cases of severe heart failure may increase the risk of thromboembolic events. AC is therefore more suitable for class III, bridge to recovery patients, while VC is appropriate for class IV, bridge to transplant/destination patients.     

Techniques for optimization of pulsatile ventricular assist device support

For some time now researchers have argued the efficacy of pulsatile versus nonpulsatile hemodynamic support. Pulsatile systems, while providing a more physiological pumping source, are burdened with a multiparametric output function that can greatly affect the utility of such ventricular assist device (VAD) support. A simplified approach to the optimization of the pulsatile VADs' output function has been developed. This approach yields device outputs of approximately 5.5 L/min at physiologic pressures while demonstrating clinically acceptable blood chemistry. Obtaining this optimal operating point involves the determination of the VAD system output function for a range of fill-enhancing vacuum settings. A quantitative method for evaluating synchronous versus asynchronous pumping modes as related to coronary perfusion is also demonstrated.     

Numerical model of flow in a sac-type ventricular assist device

This article addresses the growing need for comprehensive tools to investigate the hemodynamics of ventricular assist devices (VADs) in general and sac-type VADs in particular. Numerical simulations can be very helpful in these efforts. However, full simulation of flow inside sac-type VADs poses several key problems, among them simulation of the mechanical heart valves and calculation of the motion of flexible walls. We present a simplified three-dimensional (3D) numerical model of a sac-VAD chamber. The walls in the simplified model are defined to move according to experimental measurements, and the valves are modeled in fully open or fully closed positions. The model is validated by comparison to a fully coupled fluid-structure interaction numerical simulation and to experimental measurements using continuous digital particle image velocimetry. Our results demonstrate that the flexible wall motion is sensitive to changes in pressure distribution inside the chamber. However, small variations in wall motion do not significantly affect the global features of flow inside the chamber. Therefore, the simplified model can be used to predict the 3D time-dependent flow field in the VAD.     

One hundred days or more bridged on a ventricular assist device and effects on outcomes following heart transplantation

BACKGROUND: Successful bridging to transplantation (BTT) with ventricular assist devices (VAD) is an alternative to mitigate the effects of end-stage heart failure on organ function while awaiting a heart. The effects of long-term VAD BTT on patient outcomes following transplantation are poorly studied. METHODS: A retrospective chart review identified 145 patients BTT with a VAD between November of 1996 and June of 2005 at the Cleveland Clinic. Patients were divided into two groups and outcomes were compared: group 1 was supported for <100 days (median=44 days) and group 2 was supported for > or =100 days (median=161 days). RESULTS: Patients in group 1 were less likely to be blood type O (33% vs 68%, p<0.0001). BTT <100 days trended towards independently predicting improved survival by multivariate proportional hazards analysis (risk ratio=0.75, 95% CI=0.52-1.08, p=0.12), largely due to reduced in-hospital mortality in this group (2% vs 11%, p=0.055); however, no significant difference with respect to long-term survival was observed by Kaplan-Meier analysis (p=0.14). Furthermore, causes of death differed between groups: group 1 more commonly died of coronary artery vasculopathy (26% vs 0%, p=0.022) and group 2 more commonly died of sepsis (60% vs 26%, p=0.026). Ultimately, 21% of all group 2 patients died from sepsis (compared to 7% of group 1 patients, p=0.018). CONCLUSIONS: This study suggests that prolonged BTT with a VAD is a viable treatment strategy but may lead to significantly more post-transplant deaths from sepsis and higher in-hospital mortality. These data may inform management of this high-risk patient population.     

Implantable left ventricular assist device for treatment of pulmonary hypertension in candidates for orthotopic heart transplantation—a preliminary study

Objectives: Elevated pulmonary vascular resistance (PVR) unresponsive to pharmacological intervention is a major limitation in heart transplantation (HTX). The post-operative course of these patients is associated with an increased risk of life-threatening right heart failure. We evaluated the efficiency of an implantable left ventricular assist device (LVAD) to decrease PVR by unloading the left ventricle and to lower the risk of later orthotopic HTX. Methods: Six patients with end-stage heart failure (NYHA class IV) and ’fixed‘ pulmonary hypertension (PVR 5.7±0.7, range 4.4–6.5 Wood units) were analyzed. Despite maximal pharmacological intervention at initial evaluation (oxygen inhalation, nitrates, alprostadil infusion) PVR could not be reduced to under 2.5 Wood units. Four patients received a TCI Heartmate, one patient a Novacor, and one patient a Jarvik 2000. Results: All patients survived the LVAD implantation, four patients could be discharged from hospital. Cardiac index and pulmonary artery pressure values returned to normal during the early post-operative phase. After a mean support time of 191±86 days PVR had fallen to 2.0±1.2 (range 0.8–3.6) Wood units. All patients could be bridged to transplantation, one patient died 3 months after transplant, five patients are still alive after a mean follow-up of 16.2±10.5 months. Conclusions: Mechanical support using an implantable LVAD is a very efficient approach with an acceptable risk to treat severe pulmonary hypertension in end-stage heart failure patients before HTX. Adequate reduction of PVR can be expected within 3–6 months. Subsequent HTX is associated with a good outcome.     

Clinical outcome and bridge to transplant rate of left ventricular assist device recipient patients: comparison between continuous-flow and pulsatile-flow devices

BACKGROUND: Long-term implantable continuous axial-flow pumps are increasingly used in bridging heart failure patients to heart transplant. Compared to pulsatile left ventricular assist devices (LVADs), they offer smaller dimensions, less surgical trauma and less thromboembolisms. However concerns still remain about the long-term effects of continuous-flow on patients' outcome. The aim of this study was to review our mechanical bridge to transplant experience to compare pre- and post-transplant outcomes between pulsatile and continuous-flow LVAD recipients. METHODS: Thirty-six patients with a continuous-flow device (Micromed DeBakey, Houston, TX or InCor Berlin Heart, Berlin, Germany--group A) were compared with 41 patients supported with a pulsatile device (Novacor, WorldHeart, Oakland, CA--group B). RESULTS: Mean age (48.6+/-12.4 vs 47.2+/-12.5) and LVAD duration (119.3+/-115.4 vs 128.3+/-198.3) were similar in the two groups. Group A recipients were smaller compared to group B (mean body surface area=1.77+/-0.18 vs 1.93+/-0.16; p<0.001). Idiopathic dilated cardiomyopathy was not significantly greater between the two groups (78% vs 58.3%; p=0.085). Successful bridging to transplantation was similar in group A compared to group B (52.8% vs 63.4%; p=non significant). On-VAD mortality was similar between the two groups (A vs B=33.3% vs 36.6%; p=non significant). Thirty-day mortality after HTx in group A was 10.5% compared to 7.7% in group B (p=non significant). First year post-transplant incidence of treated rejections (36.8% vs 46%; p=non significant) as the mean number of rejection/patient (0.38+/-0.5 vs 0.53+/-0.83; p=non significant) were similar in group A compared to group B. CONCLUSIONS: In our experience, when compared to pulsatile LVAD, continuous-flow pumps are similarly effective in transplant rate and post-transplant outcome.     

Laparoscopic sleeve gastrectomy in patients with heart failure and left ventricular assist devices as a bridge to transplant

Background

Obesity is an epidemic that is closely associated with heart failure. The ultimate treatment for end-stage heart failure is cardiac transplantation. Patients with morbid obesity are often excluded from receiving donor organs. Many transplant centers use body mass index (BMI) >35 kg/m² as a contraindication to listing for heart transplant. Left ventricular assist devices (LVADs) were developed as a bridge to transplant for many heart failure patients, but bariatric surgery for LVAD patients has not been well described.