Success rates of long-term circulatory assist devices used currently for bridge to heart transplantation

Simulation of motor current waveforms in monitoring aortic valve state during ventricular assist device support

Monitoring of aortic valve (AV) opening and closure during left ventricular assist device (LVAD) heart pump support is crucial in preventing AV abnormalities and remodeling caused by anomalous resirculation. In this study, simulations of LVAD motor current waveforms were undertaken to investigate AV response to rotary blood pump assistance, as well as to detect AV open and close status under heart failure conditions. A two-dimensional fluid-structure interaction finite-element model is presented to predict AV state during LVAD outflow. The data will be useful in the development of a pump speed controller for optimal management of pump outflow.

Simulation of motor current waveform as an index for aortic valve open-close condition during ventricular support

Monitoring of aortic valve (AV) opening and closure during heart pump support by a left ventricular assist device (LVAD) is crucial in preventing adverse events such as thrombus formation near the AV. In preventing adverse events such as thrombus formation near the AV. In this paper, simulations of LVAD motor current waveform were undertaken to evaluate its suitability for ascertaining aortic valve status. A two-dimensional fluid-structure interaction finite-element model is presented to predict AV closure during LVAD outflow, useful in the development of a pump speed controller.

Computational analysis of the importance of flow synchrony for cardiac ventricular assist devices

This paper presents a patient customised fluid-solid mechanics model of the left ventricle (LV) supported by a left ventricular assist device (LVAD). Six simulations were conducted across a range of LVAD flow protocols (constant flow, sinusoidal in-sync and sinusoidal counter-sync with respect to the cardiac cycle) at two different LVAD flow rates selected so that the aortic valve would either open (60mLs(-1)) or remain shut (80mLs(-1)). The simulation results indicate that varying LVAD flow in-sync with the cardiac cycle improves both myocardial unloading and the residence times of blood in the left ventricle. In the simulations, increasing LVAD flow during myocardial contraction and decreasing it during diastole improved the mixing of blood in the LV cavity. Additionally, this flow protocol had the effect of partly homogenising work across the myocardium when the aortic valve did not open, reducing myocardial stress and thereby improving unloading.

Modeling aortic valve closure under the action of a ventricular assist device

The support of a failing heart with pump devices has been an essential element in cardiac health care for several decades. It is therefore important to understand the left ventricular response to the pumping action of these devices when connected to the native heart. Furthermore, monitoring of aortic valve opening and closure is important in avoiding valve stenosis and thrombogenesis during pump support. This paper reports the first steps in simulating the effects of outlet pump pressure on aortic valve closure of the heart assisted by an implantable blood pump. A two-dimensional fluid structure interaction aortic valve model is presented with blood flow in left ventricular chamber using the Arbitrary Lagrangian-Eulerian Finite Element Method formulation to predict the AV closure during outflow of blood from the left ventricle into the left ventricular assist device (LVAD).

The impact of bridge-to-transplant ventricular assist device support on survival after cardiac transplantation

OBJECTIVE

To determine the impact of bridge-to-transplant ventricular assist device support on survival after cardiac transplantation.

METHODS

From January 1, 1993, to April 30, 2009, a total of 525 cardiac transplants were performed. Ventricular assist devices were placed as a bridge to transplant in 110 patients. We focused our analysis on the 2 most common causes of end-stage heart failure requiring transplantation: idiopathic dilated cardiomyopathy (n = 201) and coronary artery disease (n = 213). Data including gender, age, date of transplant, cause of heart failure, prior heart transplant, placement of a ventricular assist device, type of ventricular assist device, and panel-reactive antibody sensitization were analyzed to derive Kaplan-Meier survival probabilities and multivariable Cox regression models.

RESULTS

In patients with idiopathic dilated cardiomyopathy who received a ventricular assist device as a bridge to transplant, survival was decreased at 1 year (P = .008) and 5 years (P = .019), but not at 10 years, posttransplant. In patients with coronary artery disease, the use of a ventricular assist device as a bridge to transplant did not influence survival at 1, 5, and 10 tears posttransplant. In patients with idiopathic dilated cardiomyopathy who received a Heartmate I (Thoratec Corp, Pleasanton, Calif) ventricular assist device as a bridge to a cardiac transplant, elevation in the pretransplant panel-reactive antibody correlated with a decrease in long-term survival.

CONCLUSION

In patients with idiopathic dilated cardiomyopathy, placement of a Heartmate I ventricular assist device as a bridge to a cardiac transplant is associated with an elevation in the pretransplant panel-reactive antibody and a decrease in 1- and 5-year survivals after cardiac transplantation.

Levitronix Ventricular Assist Devices as a Bridge to Recovery After Profound Biventricular Heart Failure Associated With Pulmonary Aspergillosis

A patient with multisystem organ failure and refractory cardiopulmonary shock stemming from Aspergillus pneumonia was treated with 2 Levitronix ventricular assist devices as a bridge-to-recovery. After ventricular assist device placement, the patient recovered myocardial function. The ventricular assist devices were removed on post-implant Day 7, and the patient made a full long-term recovery. Ventricular assist devices should be strongly considered, as bridges to recovery, to support patients with acute myocardial dysfunction associated with sepsis while the underlying infection is treated.

Importance of luxury flow for critically ill patients receiving a left ventricular assist system

The presence of a significant organ dysfunction does not immediately exclude patients from consideration for treatment with a left ventricular assist system (LVAS). However, in treating morbid circulatory shock patients with multiple organ failure, it is important to know the preoperative and postoperative factor or factors related to the recovery of the damaged organ function. In this study, we retrospectively analyzed patients receiving a LVAS at our institution and tried to determine the important factors related to the survival of patients with multisystem failure. Twenty-seven patients who underwent LVAS placement at Saitama Medical School Hospital between 1993 and 2003 were included in this study. The preoperative risk factors analyzed were renal dysfunction, respiratory dysfunction, hepatic dysfunction, the existence of active infection, and the combination of all four factors. As a postoperative factor, the pump flow index (mean LVAS pump flow during the first 2 weeks after LVAS surgery divided by the body surface area) was analyzed. None of the analyzed preoperative factors could predict survival after LVAS surgery, but a pump flow index of less than 2.5 l/min/m2 had a significant relationship with death after LVAS surgery. Further analysis revealed that all the patients with a pump flow index of 3.0 l/min/m2 or more could overcome preoperative organ dysfunction. Congestive heart failure patients with multisystem failure need luxury pump flow for successful LVAS surgery; this factor could be especially important in device selection and postoperative management.

Cellular and Hemodynamics Responses of Failing Myocardium to Continuous Flow Mechanical Circulatory Support Using the DeBakey-Noon Left Ventricular Assist Device: a Comparative Analysis With Pulsatile-Type Devices

BACKGROUND

An increasing number of continuous flow pumps are currently under clinical studies, however very little data exist on the hemodynamic and cellular responses of the failing heart to continuous flow support. The purpose of this investigation was to characterize the response of the failing myocardium to continuous flow support.

METHODS

We compared echocardiographic and cellular markers of failing myocardium at the time of left ventricular assist device (LVAD) implantation and explantation in 20 consecutive patients (12 pulsatile flow [Novacor] and 8 continuous flow [DeBakey-Noon]).

RESULTS

The use of mechanical support with both continuous- or pulsatile-type LVADs resulted in a reduction of left ventricular end-diastolic dimension (LVEDD), end-diastolic volume (EDV), end-systolic volume (ESV) and left atrial volume (LAV), as well as a decrease in mitral E/A ratio, tricuspid regurgitation velocity (TRV) and pulmonary valve acceleration time (PVAT). Comparative analyses for patients treated with a continuous- vs pulsatile-type LVAD support showed a greater degree of unloading with the latter type, as shown by the effect on LVEDD (-13.7% vs -33.7%, p = 0.0.004), EDV (-23.5% vs -41.2%, p = 0.015), ESV (-25.6% vs -57.6%, p = 0.001) and LAV (-25.2% vs -40.4%, p = 0.071). The hemodynamic effects of continuous vs pulsatile LVAD support were similar, as shown by their effect on mitral E/A ratio (-23.9% vs -39.9%, p = NS), TRV (-26.4% vs -23.8%, p = NS) and PVAT (28.5% vs 38.5%, p = NS). Only pulsatile support demonstrated a statistically significant percent change in mass (-6.3% vs -20.6%, p = 0.038). Continuous and pulsatile forms of mechanical support demonstrated equivalent reductions in myocardial tumor necrosis factor-alpha (TNF-alpha), total collagen and mycocyte size.

CONCLUSIONS

Our findings show that, although there are differences between these 2 devices in magnitude of unloading, both forms of support effectively normalize cellular markers of the failing phenotype.

Imaging of Left Ventricular Assist Devices

Left ventricular assist devices are used as a bridge to recovery, a bridge to transplant, or a permanent alternative to cardiac transplant. This exhibit demonstrates the imaging appearance of commonly used left ventricular assist devices and their complications.

Neurological Events During Long-Term Mechanical Circulatory Support for Heart Failure

BACKGROUND

Progression of heart failure can lead to cardiac transplantation, but when patients are ineligible, long-term mechanical circulatory support may improve survival. The REMATCH trial showed that left ventricular assist devices (LVADs) prolonged survival in patients with end-stage disease, but with a significant number of adverse events. We report on the neurological outcomes in the REMATCH trial.

METHODS AND RESULTS

We examined new neurological events in the 129 patients randomized to either LVAD placement (n=68) or medical management (n=61), classified as stroke, transient ischemic attack, toxic-metabolic encephalopathy, and other. There were 46 neurological events: 42 in 30 LVAD patients and 4 in 4 patients in the medical arm (chi2, 30/68 versus 4/61, P<0.001). Sixteen percent of the LVAD patients had a stroke, with a rate of 0.19 per year (95% CI, 0.10 to 0.33), many occurring in the postoperative period. The stroke rate in the medical arm was 0.052. A Kaplan-Meier survival analysis showed a 44% reduction in the risk of stroke or death in the LVAD group versus the optimal medical group (P=0.002). The mean interval from implantation to stroke was 221.8 days (+/-70.4 days). History of stroke, age, and sepsis were not stroke risk factors in the LVAD group.

CONCLUSIONS

Fewer than half of the patients in the LVAD group had a neurological event, and there were few neurological deaths. Survival analysis combining stroke or death demonstrated a significant benefit for long-term circulatory support with an LVAD over medical therapy. Future trials will need to address prospectively all neurological outcomes, including neurocognitive function, and the role of long-term neuroprotection.

The response of the failing heart to chronic mechanical unloading

PURPOSE OF REVIEW

The authors present a comprehensive analysis of the evidence in support of improvements at the cellular, structural, and hemodynamic levels after left ventricular assist device support.

RECENT FINDINGS

The use of left ventricular assist devices as a strategy to bridge patients to cardiac transplantation and, more recently, as a form of destination therapy has provided a great opportunity to study failing myocardium at various time points. Specifically, myocardial samples can be obtained from patients at the time of left ventricular assist device implantation and again at explant, thereby allowing comparisons between paired samples of failing myocardium obtained before and after mechanical unloading.

SUMMARY

A body of knowledge has been generated that illustrates the ability of the myocardium to "heal." This information may give us better insight into cellular and molecular mechanisms of heart failure and potential new therapies for patients with end-stage heart failure.

Outcome of patients surviving to heart transplantation after being mechanically bridged for more than 100 days

OBJECTIVE

The effect of long-term mechanical support on subsequent heart transplantation is still debated.

METHODS

We report the outcome of 41 patients (42 +/- 12 years) bridged with left ventricular assist devices (VAD; 28 Novacor, 9 HeartMate, 2 Thoratec, and 2 DeBakey) for >100 days (218 +/- 76 days) between April 1994 and March 2000). We compared follow-up with 146 patients (55 +/- 13 years) who underwent heart transplantation during the same time without prior long-term mechanical support.

RESULTS

Thirty-two of the 41 patients (78%) underwent heart transplantation, 9 patients (22%) died of multi-organ (n = 5), cardiac (n = 2), or cerebral failure (n = 2). Thirty-day post-transplant mortality includes 5 cases (3 graft failures). Within the following 2 years, another 5 patients expired, 2 of cardiac failure/sudden death. Currently, 21 of 41 patients (51%) are still alive 10 to 77 months (41 +/- 22 months) after heart transplantation (1 patient was lost for follow-up). One-year and 5-year survival rates were compared with the control group (VAD vs control, 1-year survival was 75% vs 74% and 5-year survival was 60% vs 66%). Fifteen patients are doing well in New York Heart Association Class I), and 6 are NYHA Class II despite normal left ventricular ejection fraction. Episodes of moderate acute rejection (International Society for Heart and Lung Transplantation Grade 3) occurred in 10 patients (1.3 episodes per patient), not significantly different from that of the control group (1.2 episodes per patient). Scintigraphy showed regional myocardial ischemia/transplant vasculopathy in 4 patients, and coronary angiography detected the same in 2. One patient has undergone successful retransplantation. Two patients had increased right ventricular pressure. Six patients had impaired kidney function, and 3 had impaired liver function. Seven patients experienced cytomegalovirus infection.

CONCLUSIONS

Our data indicate that patients who underwent heart transplantation after long-term mechanical support have a similar survival rate and comparable cardiac morbidity associated with acute rejection episodes.

Percutaneous intervention for unprotected left main disease prior to explantation of a left ventricular assist device

Percutaneous coronary intervention of unprotected left main coronary arterial disease is an alternative to surgical revascularization in selected patients. In this report, a patient with an implanted left ventricular assist device (LVAD) underwent successful coronary intervention prior to its planned removal. The implanted LVAD clearly assisted the technical performance of the intervention.

Newly developed ventricular assist device with linear oscillatory actuator

The goal of this study was to develop a new direct electromagnetic left ventricular assist device (DEM-LVAD) with a linear oscillatory actuator (LOA). The DEM-LVAD is a pulsatile pump with a pusher plate. The pusher plate is driven directly by the mover of the LOA. The LOA provides reciprocating motion without using any movement converter such as a roller screw or a hydraulic system. It consists of a stator with a single winding excitation coil and a mover with two permanent magnets. The simple structure of the LOA is based on fewer parts to bring about high reliability and smaller size. The mover moves back and forth when forward and backward electric current is supplied to the excitation coil. The pump housings have been designed using three-dimensional computer aided design software and fabricated with the aid of computer aided manufacturing technology. Monostrut valves (Bjork-Shiley #21) were used for the prototype. The DEM-LVAD dimension is 96 mm in diameter and 50 mm thick with a mass of 0.62 kg and a volume of 280 ml. An in vitro test (afterload 100 mm Hg; preload 10 mm Hg; input power 10 W) demonstrated more than 6 L/minute maximum output and 15% maximum efficiency at 130 beats per minute (bpm). Dynamic stroke volume ranged between 40 and 60 ml. The feasibility of the DEM-LVAD was confirmed.

Revised screening scale to predict survival after insertion of a left ventricular assist device

BACKGROUND

We previously calculated a risk factor summation score that successfully predicted survival after insertion of a left ventricular assist device. We sought to validate our previous score by using a single center's clinical experience and to determine emerging risk factors for mortality after device insertion.

METHODS

The clinical records of 130 consecutive patients who received the HeartMate VE left ventricular assist device (Thoratec Corp, Pleasanton, Calif) at our institution between June 1996 and March 2001 as a bridge to transplantation were reviewed. Univariate and multivariable analyses were performed to determine the predictors of operative mortality after device insertion. Using the relative risks for each identified variable, we devised a new risk factor summation score. The new and old scores were then compared by using linear regression analyses to determine whether the revised score improved statistical accuracy.

RESULTS

Overall operative mortality was 25% (n = 33). The old score successfully predicted operative mortality in the current patient population (operative mortality of 38% for score >5 vs 13% for score < or =5). However, the revised score improved risk discrimination (operative mortality of 46% for a score >5 vs 12% for a score < or = to 5). Statistical accuracy was comparable between scores, but the relationship between observed and predicted outcomes was improved with the revised score.

CONCLUSIONS

The changing demographic profile and management of patients presenting for mechanical circulatory support has led to a change in the predictors of mortality after device insertion. Periodic remodeling and recalibration of risk indices helps to accurately predict outcomes in high-risk patient groups and identifies emerging risk factors for mortality.

Prologue: ventricular assist devices and total artificial hearts. A historical perspective

In the 1960s, when LVADs and TAHs were introduced into clinical use, researchers estimated that, with this technology, the problem of heart failure could be solved within 20 years. Unfortunately, the evolution of these devices has taken much longer than anticipated. Nevertheless, significant advances have been achieved in both cardiac assistance and replacement, and today's cardiac surgeons have a wide range of devices from which to choose (Table 4). This progress has largely been due to the support of the NHLBI, especially the Devices and Technology Division headed by John Watson, and of the devoted commitment of the investigators. Because of the long-term commitment required for both basic and clinical research, commercial medical technology companies are unable to assume this burden. Advances in mechanical circulatory support and replacement have benefited numerous patients worldwide who would otherwise have died of heart failure, and devices now exist for use as bridges to recovery, bridges to transplant, and destination therapy. The current challenge is to refine what we have and to apply these technologies to broader patient populations with maximal safety and at a reasonable cost.

Neurologic complications of the Novacor left ventricular assist device

BACKGROUND

The left ventricular assist device (LVAD) is a bridging mechanism for patients with severe heart failure to remain viable until heart transplantation. The rate of cerebral embolism has been reported as high as 47% in some studies but the rate of other neurologic complications in patients with LVADs is not known.

METHODS

Retrospective chart review of all patients who had LVADs implanted at our hospital from September 1993 until September 1997. Complications from the time of implantation until heart transplantation or death and functional outcome were assessed.

RESULTS

Twenty-three patients had LVADs placed in the four-year period. Of 23 patients, 9 had neurologic complications after placement of the LVAD. These included four strokes, three seizures, and two cases of delirium. The 3 patients with seizures all died from multiorgan failure. All of the patients with strokes received a transplant. One patient with delirium died from multiorgan failure and another received a transplant. The most devastating medical complication was renal failure, which occurred in 7 patients and was associated with 100% mortality. All surviving patients with neurologic complications went on to transplant and good functional outcome.

CONCLUSIONS

Neurologic complications are common in patients with LVADs, occurring in 9 out of 23 patients in our series. Seizures are a poor prognostic indicator and were associated with 100% mortality. Strokes did not have a negative impact on outcome. Patients with delirium had a mixed outcome, which reflects the multifactorial nature of delirium. Further study needs to be done to limit the neurologic complications associated with LVADs and further improve outcomes.

Estimation of left ventricular recovery level based on the motor current waveform analysis on circulatory support with centrifugal blood pump

In a mock circulatory loop simulating the left heart bypass using a centrifugal blood pump, analysis of the motor current waveform of the centrifugal pump was performed to derive a useful parameter to evaluate the status of ventricular function. The relationship between the peak, amplitude, and the peak of the fundamental frequency of the power spectral density of the periodic motor current waveform (MCpsdP) that reflected the pulsatile ventricular pressure, and the peak of the left ventricular pressure (LVP) was examined. Although both peak and amplitude of the motor current waveform showed an excellent correlation with the peak LVP, they failed to predict the opening of the aortic valve. The MCpsdP that corresponds to the frequency of the heart rate showed an excellent correlation with the peak LVP throughout the LVP levels, but the slope between them changed with the opening of the aortic valve. Thus, it is possible to follow the change in the LVP and detect even the opening of the aortic valve, and, hence, the recovery of the left ventricle. However, the slope of the linear regression equation varied, depending on the pump speed. This result implies that the MCpsdP can be possibly used to follow the change of ventricular function during circulatory assistance with a centrifugal blood pump as well as to control the pump speed in response to varying ventricular function.

Intracranial bleed during bridge to transplant may not preclude a successful result

We report the case of a 29-year-old man who suffered sub-arachnoid bleeding while stabilized on a biventricular assist device as a bridge to cardiac transplantation. We adjusted his anti-coagulation therapy to control the bleeding and to concurrently minimize thrombosis while on support. He underwent 2 craniotomy operations to evacuate sub-arachnoid hematomas, and he underwent a subsequent operation to debride and close the dura. Eighteen days later, he underwent successful orthotopic heart transplant and was discharged to home 3 weeks post-transplant.

Surgical management of valvular disease in patients requiring left ventricular assist device support

BACKGROUND

Success with long-term implantable left ventricular assist devices (LVAD) has led to increased use in patients previously thought to be unsuitable for mechanical circulatory assistance. Patients with preexisting or newly diagnosed valvular disease have been traditionally excluded from device placement. The purpose of this study was to review our experience with LVAD support in patients with valvular disease and to develop a management algorithm for these difficult patients.

METHODS

We reviewed the clinical records of 199 consecutive patients who received the ThermoCardiosystems, Inc, HeartMate Pneumatic or Vented Electric LVAD. There were 18 patients (9%) who required surgical management of native or prosthetic valvular disease during LVAD implantation.

RESULTS

Suture or patch closure of the aortic valve was performed in 6 patients, aortic valve plication and repair in 1 patient, mitral valve repair in 4 patients, and tricuspid valve annuloplasty in 5 patients. Two patients with mechanical mitral valve prostheses were treated with postoperative warfarin anticoagulation. Fifteen of the 18 patients with valvular pathology survived the immediate postoperative period (17% mortality). Eleven patients have either undergone transplantation or continue to be supported with an LVAD (61%). Operative mortality in LVAD patients without concomitant valve repair was 18% (n = 33) with a late mortality of 7% (n = 13). Seven of these late deaths occurred in patients who received a device as destination therapy. In the remaining 6 patients, the cause of death was sepsis (n = 2), multisystem organ failure (n = 2), driveline rupture (n = 1), and massive gastrointestinal bleed (n = 1).

CONCLUSIONS

Preexisting native or prosthetic valve pathology does not increase the immediate perioperative risk of LVAD insertion; however, these patients continue to pose a challenge for postoperative management while awaiting transplantation.

Update on the total artificial heart

There has been a quest for an artificial organ that can replace the heart for decades. Remarkable advances were made in the second half of the twentieth century in the fields of medicine and engineering that led to the development of several devices with the intention of totally replacing the human heart. Some of these devices, like the Jarvik artificial heart, were utilized initially as a permanent replacement for the failing heart. It became more successful as a bridge to heart transplantation (BTT) in the years that followed its introduction. Currently the CardioWest total artificial heart (TAH) is the only device in clinical use with the intention of bridging patients to heart transplantation. Two new TAHs are being developed with the intention of being used as an alternative to transplantation (ATT) or on a permanent basis. The next 100 years will bring revolutionary new designs and advances in the field of end stage heart disease that may only be ideas at the present time.

Multicenter experience with the thoratec ventricular assist device in children and adolescents

BACKGROUND

Patient size is 1 determinant in selecting a mechanical circulatory support device. The current pulsatile ventricular assist devices (VADs) were designed primarily for average-sized adults. The flexibility of the Thoratec VAD, however, has encouraged physicians to use it in a significant number of intermediate-sized older children and adolescents.

METHODS

We conducted a retrospective study in 58 children and adolescents <18 years (41 boys, 17 girls) who had been supported with the Thoratec VAD in 27 centers worldwide as of December 1999. Mean patient age was 13.8 years (range, 7 to 17 years), and mean patient weight and body surface area were 51.6 kg (range, 17 to 93 kg) and 1.5 m(2) (range, 0.7 to 2.1 m(2)), respectively.

RESULTS

Thirty-five patients (60%) survived to transplantation and 6 (10%) to recovery of the native heart, respectively; 38 were discharged from the hospital (66%). In the transplanted group, post-transplantation survival was 97%. Patient age and size were not associated with significantly increased risk for death or adverse events. Fifteen patients (27%) had 18 neurologic events during support, and 6 of these were fatal. Left atrial cannulation proved a risk factor for neurologic complications.

CONCLUSIONS

The Thoratec VAD has successfully been used in a large number of children and adolescents with similar morbidity and mortality results as with adults. The risk of neurologic complications may be increased, particularly in patients cannulated in the left atria.

The LPD-II: a modified locked percutaneous device that permits safe subcutaneous access

A locked percutaneous device, the LPD-I (previously described as LPD), is effective in overcoming the problems of skin downgrowth and local tissue infection; however, it can only be implanted at a site providing adequate subcutaneous adipose tissue to attach to the subcutaneous connector of the LPD-I. A modified device, the LPD-II, has been developed that has a thin dome and skin connector but does not have a subcutaneous tissue connector. In addition, a newly designed structure called the skin stop collar (SSC) has been developed. It is positioned just beneath the mesh collar described in the LPD-I to further improve the function of the LPD-II. Six rabbits were implanted with one LPD-II without the SSC (group 1) and five rabbits were implanted with one LPD-II with the SSC (group 2). For more than 6 months, two of the implants in group 1 rabbits were successful. Four of the implants in group 2 rabbits were successful for more than 1 year. One of the animals in group 2 died of causes unrelated to the device. We conclude the following: the mesh collar skin connector can function well as a locked percutaneous device without the subcutaneous tissue connector; the LPD-II can be implanted in any site and does not require the presence of subcutaneous adipose tissue; and the SSC may increase the success rate of LPD-II implantation provided the mesh collar is made of soft material.

Bridging patients to cardiac transplantation

Potential recipients of heart transplants have the most advanced form of congestive heart failure, in which standard therapy fails to maintain clinical stability. In the absence of guidelines derived from evidence obtained in clinical trials, caring for these patients becomes a challenge. A successful approach requires the proper coordination of surgical and nonsurgical strategies, including revascularization and valvular surgery as well as mechanical ventricular support and medical strategies. Intensive medical therapy is the most commonly used approach for prolonged bridging to transplantation. Although carefully individualized regimens are necessary to achieve desired goals, most centers adopt a fairly standardized approach involving vasodilators, diuretics, and inotropic support. Bridging patients with cardiac decompensation to transplantation presents a major therapeutic challenge. Appropriate strategies will maximize patients' chances that the bridge from decompensation to transplantation remains intact. (c)2000 by CHF, Inc.

Alterations in coagulation after implantation of a pulsatile Novacor LVAD and the axial flow MicroMed DeBakey LVAD

BACKGROUND

The MicroMed DeBakey left ventricular assist device (LVAD) is a chamber and valveless axial flow blood pump. We investigated parameters of the coagulation system in patients after implantation of the axial flow LVAD and patients following implantation of a pulsatile Novacor LVAD.

METHODS

Six consecutive patients of both groups were investigated over a period of 6 weeks after implantation. beta-Thromboglobulin, platelet factor 4, factor XIIa, thrombin/antithrombin complexes, plasmin/alpha2-antiplasmin complexes, and D-Dimer levels were measured.

RESULTS

With the exception of the plasmin/alpha2-antiplasmin levels in the Novacor group, all parameters were elevated in both groups. The levels of beta-thromboglobulin, platelet factor 4, factor XIIa, and plasmin/alpha2-antiplasmin were significantly increased in the axial flow LVAD group.

CONCLUSIONS

The axial flow LVAD strongly influences the systems of contact activation and fibrinolysis. The elevation of platelet proteins appears to follow platelet damage. Although no thromboembolic events were observed in both groups, elevation of thrombin/antithrombin complexes provides convincing evidence of an increased activation of the coagulation system and the concomitant risk for the development of thromboembolism.

Wound complications after left ventricular assist device implantation

BACKGROUND

Wound necrosis and infection pose a tremendous risk for patients with left ventricular assist devices.

METHODS

We analyzed our database of patients with left ventricular assist devices for those who developed wound dehiscence and concomitant infection after left ventricular assist device implantation.

RESULTS

Three of our 66 patients (4.5%) with implantable ventricular assist devices had had severe wound complications with necrosis of the abdominal or thoracic wall uncovering part of the device. The predominant impact on the development of these complications was presumably related to multiple surgical interventions on the same site.

CONCLUSIONS

Nevertheless, these patients can recover and undergo successful heart transplantation if adequately managed.

Clinically available extracorporeal assist devices

Mechanical circulatory support has been shown to be of benefit to allow recovery after conventional heart surgery and as a successful bridge to heart transplantation. Recent clinical trials with implantable left ventricular assist devices (LVADs) have been completed with these devices showing restoration of normal hemodynamics and successful bridge to transplantation. A major advantage of the implantable devices is the ability for the patient to be discharged and followed up at an outpatient setting. However, multiple advantages to extracorporeal devices still remain, which are the focus of this review. One advantage of the extracorporeal devices is that they can be placed in much smaller patients than currently available implantable LVADs. Also, because of differences in design of the assist devices, the extracorporeal devices can be placed without the need for the cardiopulmonary bypass and with decreased operative time and dissection. Perhaps the biggest advantage of the extracorporeal devices is that they can provide a support for both the right and left side of the heart as opposed to the implantable LVADs, which are only used as left ventricular assist devices. This article describes in detail the advantages and disadvantages of the extracorporeal devices as well as the operative techniques used to implant them. As the number of patients with heart failure continues to rise, so will the need for mechanical circulatory support. Though the majority of these patients will be served by a long-term implantable device, there will remain a subset of patients that will be best suited for treatment with extracorporeal devices.

Implantation technique for the CardioWest total artificial heart

The CardioWest total artificial heart is a pneumatically driven device that totally replaces the failing ventricles. It is currently undergoing clinical investigation as a bridge to heart transplantation in several centers throughout the world. A bilateral ventriculectomy is performed and the device is implanted. Blood flows are usually maintained at 6-8 L/min. Approximately 130 patients have undergone bridge to transplant with this device. Patient selection and excellent surgical technique are required for a successful outcome. A detailed description of the implantation technique is presented to facilitate the use of this technology.

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.

Evaluation of an implantable motor-driven left ventricular assist device

A console based implantable motor-driven left ventricular assist device (LVAD) was developed and tested. Ten sheep weighing 42-73 kg (mean, 54.4 kg) were used as the experimental animals. Four animals survived 5-12 h (mean, 9.5 h). The mean pump flow was 1.63 L/min, ranging from 0.8 to 2.5 L/min. The cause of termination was respiratory failure in 3 animals, bleeding in 2, ventricular fibrillation in 2, vent tube obstruction in 1, thrombus formation in 1, and mechanical failure of the driving console in 1. Following the in vivo studies, the computer regulated controller was tested in a mock circulatory system. The LVAD provided 5.34 L/min of maximum output against a mean afterload of 80 mm Hg with a filling pressure of 15 mm Hg when the pump rate was 80 bpm in the fixed rate mode. With an increase in the pump afterload from 80 to 140 mm Hg, the total system efficiency varied from 7.81 to 8.34% when the pump preload was 15 mm Hg. An ultracompact, completely implantable electromechanical VAD has been under development. This device should fit in a 60 kg adult. As the next step, we are preparing to implant this ultracompact implantable VAD with an electronic controller in an animal model with better results being expected.

CardioWest total artificial heart: a retrospective controlled study

The CardioWest total artificial heart (TAH) is a pneumatic device that is used as a bridge to heart transplantation and the only TAH available that totally replaces the failing ventricles. It has been utilized in selected centers in the U.S.A. with approval from the Food and Drug Administration. Strict criteria have been developed to select candidates to be bridged with the TAH. The patient must be a heart transplant candidate of age >18 and <59 years with a body surface area (BSA) > or = 1.7 m2, cardiac index (CI) <2.0 L/min/m2, and 2 inotropic agents or 1 plus an intraaortic balloon pump (IABP). A total of 24 heat transplant candidates (Group A) met the entry criteria and underwent placement of the TAH between January 1993 and July 1996. Group A consisted of 23 males; 16 patients had an IABP. The control group (Group B) consisted of 18 heart transplant candidates who met the TAH entry criteria but never received a TAH. Group B consisted of 15 males; 14 patients had an IABP. Preimplantation pulmonary vascular resistance (PVR) (Wood units), serum creatinine (mg/dl), and total bilirubin (mg/dl) were determined in both groups. The mean values for Groups A and B were, respectively, age: 47 and 47 years, BSA: 2.01 and 1.93 m2, CI: 1.5 and 1.8 L/min/m2, PVR: 2.88 and 2.47 Wood units, creatinine: 1.5 and 1.6 mg/dl, and bilirubin: 1.8 and 1.4 mg/dl. In Group A, 1 patient died on the TAH, 1 patient died after transplant, and 22 patients reached transplant and were discharged home for a survival rate of 91.7%. In Group B, 10 patients died while waiting for a heart transplant. Of the 8 patients transplanted, 7 survived and were discharged home for a survival rate of 38.9% (p = 0.0003). In summary the CardioWest TAH provided an excellent and successful method of bridging patients to heart transplantation with a reasonable risk.