(Circulation. 1997;95:1844-1852.)
© 1997 American Heart Association, Inc.
Articles |
Bridge Experience With Long-term Implantable Left Ventricular Assist Devices
Are They an Alternative to Transplantation?
the Department of Surgery (M.C.O., M.A., K.A.C., M.T.G., D.J.G., R.C.A., A.C.G., E.A.R.) and the Division of Circulatory Physiology (H.R.L.), Columbia-Presbyterian Medical Center, New York, NY.
Correspondence to Mehmet C. Oz, MD, Division of Cardiothoracic Surgery, Milstein Hospital Building, 177 Fort Washington Ave, New York, NY 10032. E-mail mco2{at}columbia.edu
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Abstract |
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Background If long-term use of left ventricular assist devices (LVADs) as bridges to transplantation is successful, the issue of permanent device implantation in lieu of transplantation could be addressed through the creation of appropriately designed trials. Our medium-term experience with both pneumatically and electrically powered ThermoCardiosystems LVADs is presented to outline the benefits and limitations of device support in lieu of transplantation.
Methods and Results Detailed records were kept prospectively for all patients undergoing LVAD insertion. Fifty-eight LVADs were inserted over 5 years, with a survival rate of 74%. Mean patient age was 50 years, and duration of support averaged 98 days. Although common, both preexisting infection and infection during LVAD support were not associated with increased mortality or decreased rate of successful transplantation. Thromboembolic complications were rare, occurring in only three patients (5%) despite the absence of anticoagulation. Ventricular arrhythmias were well tolerated in all patients except in cases of early perioperative right ventricular failure, with no deaths. Right ventricular failure occurred in one third of patients and was managed in a small percentage by right ventricular assist device (RVAD) support and/or inhaled nitric oxide therapy. There were no serious device malfunctions, but five graft-related hemorrhages resulted in two deaths. Finally, a variety of noncardiac surgical procedures were performed in LVAD recipients, with no major morbidity and mortality.
Conclusions Over all, our medium-term experience with implantable LVAD support is encouraging. Although additional areas of investigation exist, improvements in patient selection and management together with device alterations that have reduced the thromboembolic incidence and facilitated patient rehabilitation lead us to believe that a prospective, randomized trial is indicated to study the role that LVADs may have as an alternative to medical management.
Key Words: heart failure • assist device • transplantation
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Introduction |
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With a national prevalence of more than 3 million victims1 and more than 400 000 new cases per year,2 congestive heart failure (CHF) is a major public health problem. Severe heart failure unresponsive to even maximal medical therapy occurs in
60 000 patients per year.3 Cardiac transplantation as treatment for CHF has been remarkably successful, with a 5-year survival in these patients of 60%4 compared with 20% to 30% 2-year survival in patients with NYHA class 4 heart failure.1 5 6 However, because of a limited donor organ supply, cardiac transplantation is an effective treatment for only 20007 8 of these patients per year. This vast discrepancy has led to the successful development of left ventricular assist devices (LVADs) as a bridges to transplantation. In addition to avoiding the immunosuppression and rejection complications of transplantation and the long-term limitations imposed by accelerated atherosclerosis, LVADs could be produced in the large numbers required to support this population who might otherwise die while awaiting transplantation. If long-term use of LVADs as bridges to transplantation is successful, the issue of permanent device implantation in lieu of transplantation9 could be addressed through the creation of appropriately designed trials. Our medium-term experience with both pneumatically and electrically powered ThermoCardiosystems LVADs is presented to outline the benefits and limitations of device support in lieu of transplantation.
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Methods |
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Device
The TCI Heartmate, a pusher-plate device with a maximum stroke volume of 85 mL, can be either pneumatically or electrically actuated and weighs
1 kg (Fig 1
). The sintered-titanium microspheres on the pump housing and the integrally textured polyurethane on the flexing pusher-plate diaphragm allow formation of a tenacious thrombus that evolves into a stable pseudointimal layer that does not embolize, thus reducing the need for systemic anticoagulation.10 FDA approval for the pneumatic version was obtained in November 1994.11 The device is implanted through a median sternotomy with an inflow cannula inserted into the ventricular apex and a woven Dacron outflow graft anastomosed to the ascending aorta (Fig 2). We place the pumping chamber in a preperitoneal position, although other centers advocate intraperitoneal placement. The driveline(s) exits through the left lower quadrant.
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Patient Screening and Selection
As in many other novel interventions, success with LVAD placement hinges on correct patient selection. These devices have often been used in patients who are extremely ill, with predictably poor results. The LVAD recipient population overlaps with that awaiting heart transplantation, and the choice between these therapies is often difficult. We have developed a screening scale, which, through the use of a scoring system based on criteria obtainable at the time of initial evaluation, is both predictive of successful early outcome and is easy to apply (Table 1). Oliguria, requirement for ventilatory support, and hepatic dysfunction resulting in coagulopathy are clear end points reflecting major end-organ injury and are assigned risk factor scores accordingly. Reoperation and right heart failure present technical limitations during device insertion and are also assigned risk points.
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In our experience, this practical screening scale accurately predicted patients unlikely to survive device insertion and in whom intervention would likely be futile.12 Physicians at our facility used the scale to guide discussions about the suitability of individual patients, but not as an absolute criteria for device insertion. Most of the later patients in our series (and particularly the survivors) scored less than 5 points on the screening scale.
Implantation Technique
Before heparinization, a plane is developed in the properitoneal plane by dividing the linea alba and sharply separating properitoneal fat and peritoneum from the posterior rectus sheath and the transversalis muscle at its diaphragmatic insertion.13 Drivelines are tunneled to an exit point in the left lower quadrant. After heparization, the aorta and right atrium are cannulated and cardiopulmonary bypass instituted. We have used the serine protease inhibitor Aprotinin (Miles Incorporated) in almost all cases to reduce bleeding and the consequent incidence of transfusion-related right-sided failure.14 In cases of recent aprotinin therapy, readministration is delayed until arterial access is established to avoid the sequelae of anaphylaxis. A vent is placed through the apex of the left ventricle and, without placing a cross-clamp or administering cardioplegia, device implantation is initiated. The inflow cannula is brought through the diaphragm and secured to a Teflon cuff that has been attached to the ventricular apex with a series of horizontal mattress, Teflon-pledgeted Dacron sutures. The outflow graft is anastomosed to the right lateral aspect of the ascending aorta using a running 4-0 polypropylene suture. As the patient is separated from cardiopulmonary bypass, the device is activated with the patient in a steep Trendelenberg position to reduce the risk of air embolism.
Blood products, if required, are administered through leukocyte filters15 to reduce antigen exposure of the patient, which could complicate later donor organ cross-matching. Inhaled nitric oxide (NO) is used when needed to reduce pulmonary hypertension, which is often associated with chronic left ventricular failure and is exacerbated by cardiopulmonary bypass-related generation of thromboxane A216 and transfusion-induced cytokine activation.17 Arginine vasopressin in low doses (0.04 units/min) has been useful in patients with catecholamine-resistant vasodilatory hypotension.
Data Collection and Analysis
Detailed records were kept prospectively for all patients undergoing LVAD insertion. For purposes of data analysis, a variety of end points were followed. LVAD survival was defined as survival during LVAD support; complications and deaths occurring after transplantation were not included in LVAD morbidity and mortality calculations. Preoperative infections were defined as clinical evidence of infection (leukocytosis and/or fever) in the presence of a positive culture; infections during LVAD support were similarly defined. Malignant arrhythmias were defined as documented cases of ventricular tachycardia or fibrillation. Thromboembolic events were defined as clinically verifiable cases of thromboembolism to the coronary, cerebral, or peripheral arterial systems. Perioperative right ventricular failure (RVF) was defined as indexed LVAD output <1.8 L/min/m2 in the setting of elevated central venous pressure (>20 mm Hg) and a decompressed left ventricle. In addition, patients requiring inotropic support for impaired right ventricular function for >10 days were included in the postoperative RVF group. Finally, a registry of subsequent noncardiac surgical procedures performed on LVAD recipients was maintained. Data were analyzed using SAS system software (SAS Institute, Inc). Kaplan-Meier product limit estimates were used to graphically display survival, providing actuarial estimates and 95% confidence intervals.
Cost Analysis
Assuming an average length of stay of 26 days, which is the median predicted time to discharge in our LVAD population and the true average stay for heart transplant recipients, we created a model that estimated the costs of LVAD insertion and postoperative care.18 The 21 patients in our study population had an average age of 53 years, with a range of 19 to 66 years. The immediate post-LVAD outcomes for this population included 1 explantation, 3 deaths, and 17 transplants. Although for purposes of the model, we projected a 26-day hospitalization in the absence of FDA regulations regarding hospital discharge, the actual mean LVAD support duration was 128 days, with a range of 35 to 324 days.
Patient care costs were estimated from the total time the patient spent in the intensive care unit (ICU) and the routine care floors. A calculation based on the intensity of nursing services provided to the patient and the nursing salaries allowed determination of the nursing cost per patient. Overhead charges, including capital, plant operations, laundry, housekeeping, meals, and administration were applied based on ICU and routine care room utilization.
To determine operating room (OR) costs, all OR supplies used in the operation were identified and valued at the unit price paid. A per-minute labor charge was developed that incorporated all nursing and perfusionist labor costs. The anesthesia records for each patient were audited and total case minutes were obtained. The per-minute labor costs were then applied to the total case minutes and summed with the supply costs to obtain the total OR labor cost. When possible, billable items were retrieved from the hospital patient management system and categorized into departments such as chemistry and radiology. The costs of supplies (including the device) were estimated by multiplying the number of units expended times the unit price of the materials. Any remaining resource expenditures were calculated using the ratio-of-costs-to-charges (RCC) method. No costs related to physician time and fees are included in this analysis.
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Results |
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Demographics and Survival
Fifty-eight patients underwent insertion of the TCI Heartmate left ventricular assist device (LVAD) at our institution between August 1990 and November 1995. Forty-five patients (78%) were men, and mean age at time of implant was 50±13 years. Indications for LVAD insertion were end-stage heart failure resulting from ischemic cardiomyopathy (52%), idiopathic cardiomyopathy (41%), myocarditis (5%), and idiopathic hypertrophic subaortic stenosis (2%). Devices used were either of the pneumatically driven (76%) or vented electric (24%) type. Mean duration of support has been 98±84 days, with an overall survival of 74%. Hemodynamic parameters as well as indices of renal and hepatic perfusion improved significantly after LVAD insertion (Table 2
). Thirty patients have undergone successful cardiac transplantation, 2 were weaned off LVAD support, and 11 currently await transplantation. Fifteen patients (26%) have died during LVAD support from various causes, including sepsis, right ventricular failure, stroke, pulmonary embolus, small bowel obstruction, and mechanical complications (Table 3). The nature and sequelae of complications occurring during LVAD support will be addressed in detail in subsequent sections.
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Costs
The costs of LVAD care in each category were summed to provide an estimated expense per 18-day hospitalization of $141 000, with a standard deviation of $19 000. Comparative analysis of a similar number of the heart transplant recipients with a projected 26-day hospitalization demonstrates almost identical expenditures.18 These results are not surprising since the cost of the device in the LVAD population is offset in the transplant cohort by the organ procurement and necessary endomyocardial biopsy expenses. Once LVADs can be used as alternatives to transplantation, decisions regarding the choice of LVAD insertion versus heart transplantation in individual patients should rely on criteria based on outcome rather than cost.
Infection
Preexisting Infection
Systemic infection has been considered a contraindication for placement of LVADs. However, in patients with end-stage congestive heart failure, sepsis is often the factor that precipitates hemodynamic decompensation and the need for mechanical cardiac assistance. If the additional circulatory demands of sepsis could be provided by LVAD support without prohibitive subsequent infection, this group of patients could be salvaged. Of 55 LVAD recipients operated on before October 1995, 14 patients (25%) had culture-proven infections before LVAD insertion, defined as fever and/or leukocytosis with positive bacterial cultures of blood (9 patients), urine (3 patients), previous LVAD (1 patient), or stool (1 patient). In these patients, rates of successful transplantation (57% versus 54% for patients without preexisting infection) and survival (Fig 3) were not different from the group of patients free of infection before LVAD placement. Three patients received LVADs for acute CHF associated with severe, life-threatening systemic infection (1 lung abscess with pneumococcal sepsis, 1 fungal LVAD endocarditis with sepsis, and 1 klebsiella bacteremia), each of whom was successfully transplanted after a mean support time of 109 days. Our experience suggests that patients with end-stage heart failure who develop systemic infections do not demonstrate an increased incidence of septic complications or death during LVAD support and should not be denied LVAD insertion.
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Infections During LVAD Support
Because patients receiving LVADs are critically ill, they are at increased risk for infection during LVAD support. But do these infections preclude successful transplantation? Of 55 LVADs recipients with >2 months' follow-up, 29 (53%) developed clinical infections (fever/leukocytosis) with positive cultures of blood, stool, LVAD drivelines, central venous catheters, urine, sputum, or abscess cavities. Most infections were bacterial in nature, although severe fungal infections of blood, urine, drivelines, and an LVAD diaphragm did occur (Table 4). Although patients with infections had longer support times than patients without infections (122 days versus 77 days, respectively), rates of successful transplantation (55% versus 54% in noninfected patients) and survival (Fig 4) did not significantly differ in the two groups. Only four patients with vented electric (VE) devices (28.%) experienced infections during LVAD support, despite a mean support time of 101 days.
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Our results indicate that although systemic infections in patients with LVADs are associated with prolonged support time, they do not result in consequential differences in mortality or rate of successful transplantation. Of special interest is the decreased rate of driveline infection in the vented electric LVAD (7%) versus that in the pneumatic device (20%), perhaps due to the decreased weight and caliber of the VE driveline.
LVAD Endocarditis
Infection of the LVAD surface or valves, when associated with persistent bacteremia or fungemia, has been termed LVAD endocarditis. Diagnosis of this entity can be difficult, since distinction from other sources of infection is often impossible. Of 45 patients who have undergone LVAD explantation, 11 (24%) had positive LVAD cultures. Eight of these had clinical manifestations of infection, and thus LVAD endocarditis, while in three the positive cultures were not associated with clinical sequelae. Manifestations of LVAD endocarditis included persistent fever with positive blood cultures, progressive cachexia, septic cerebral embolization, LVAD inlet obstruction, and LVAD outflow rupture. Infections were managed successfully in 4 patients by LVAD replacement, transplantation, LVAD explantation without transplantation, and antibiotic suppression, respectively. The remaining 4 patients died from septic cerebral emboli, outflow graft rupture, or multiple organ failure (Table 5).
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LVAD endocarditis may present with symptoms that resemble those of classic endocarditis but also may include mechanical complications. In our experience, 8 of 58 LVAD recipients (14%) developed this infection, with 4 deaths (50%). Although antibiotic suppression therapy was successful in 1 patient, 3 others required emergent device removal or replacement.
Thromboembolic Complications
One major limitation to the widespread use of LVADs as bridges to transplantation has been the high rate of associated thromboembolic complications. LVADs, like many other biomechanical devices, activate the coagulation cascade resulting in device-related thrombus formation. Unstable thrombus exposed to the shearing force of blood flow predisposes to thromboembolic events including stroke and end-organ or extremity ischemia. Despite rigorous anticoagulation, thromboembolic complication rates of 
30% are commonly reported for patients on LVAD support.19 20 21 22 The morbidity rate is further compounded by the high incidence of bleeding complications associated with necessary systemic anticoagulation.
In sharp contrast to previously used devices, the ThermoCardiosystems HeartMate 1000 IP LVAD uses unique design features that decrease the rate of thromboembolic events. In addition to a short inflow cannula and a "cornerless" pumping chamber, textured interior surfaces are used to promote formation of a densely adherent pseudointima that acts as a biological lining, eliminating direct contact between prosthetic surfaces and blood elements.
A recent multicenter study of 132 HeartMate LVAD recipients10 reported thromboembolic complications in 3% of patients, with an overall incidence of 0.014 events per patient-month. In our experience with 58 LVAD recipients over 5 years, representing a total of 187.3 patient-months of support, there have been 3 thromboembolic events (5.2%), with an event rate of 0.016 per patient-month. Complications that occurred in our series were 1 case of retinal microembolization associated with partial monocular visual loss and 2 cerebrovascular accidents (CVAs) in patients with LVAD endocarditis, a known predisposing factor for thromboembolism. One CVA resulted in temporary disability with eventual functional recovery, while the other, which resulted in death, occurred in a patient with overwhelming sepsis. If the two infected patients are excluded, the thromboembolic incidence and event rate in patients without predisposing factors are 1.7% and 0.005 events per patient-month, respectively.
In summary, the thromboembolic complication rate in our population of HeartMate LVAD recipients is acceptably low despite the absence of systemic anticoagulation. Studies are currently under way using transcranial Doppler technology to evaluate the incidence and potential long-term neurocognitive sequelae of asymptomatic microembolic events, which have been shown to be more common in patients during LVAD support than after transplantation.10
Ventricular Arrhythmias
The incidence of malignant ventricular arrhythmias is high in patients with cardiomyopathy and remains so after LVAD implantation,23 perhaps secondary to ischemia, intrinsic arrhythymogenicity associated with ventricular dilatation, or effects of necessary inotropic agents. The sewing ring used to secure the LVAD inflow cannula to the ventricular apex may also serve as a local focus of abnormal electrical activity. It has been suggested that a major limitation of univentricular assist devices (LVADs) may be their inability to maintain adequate pump output during episodes of serious arrhythmias24 due to decreased right ventricular output. We reviewed the courses of our LVAD patients to identify the incidence of malignant ventricular arrhythmias and determine whether univentricular support was adequate to maintain sufficient cardiac output during these events.
Of 58 patients receiving LVADs, 9 (16%) had ventricular tachycardia (VT) or fibrillation (VF) before device implantation, and 11 (19%) had these malignant arrhythmias after LVAD insertion. A study of the first 9 of the latter group of patients25 revealed mild hemodynamic changes during the course of the arrhythmia (mean arterial blood pressure decrease of 3±16 mm Hg), with significant decreases in LVAD flow of 1.6±0.9 L/min. Two patients with early arrhythmias and severe perioperative right ventricular dysfunction had dangerous decreases in LVAD flow (to 2.3 and 3.0 L/min), which improved with correction of the arrhythmia by electrical cardioversion. Six patients (67%) were fully ambulatory and although most reported lethargy, there were no syncopal episodes. All patients were placed on low-dose heparin during their arrhythmias, and 7 patients underwent successful electrical cardioversion. The others responded to pharmacological therapy and/or overdrive pacing. No deaths or thromboembolic events occurred in the 11 patients with arrhythmias after LVAD insertion.
Our experience demonstrates that malignant ventricular arrhythmias are remarkably well tolerated with left ventricular support alone, especially after the decreases in pulmonary vascular resistance that ensue after LVAD insertion.26 Arrhythmias should be suspected in patients who demonstrate sudden decreases in LVAD flow, with or without changes in arterial blood pressure. Although malignant ventricular arrhythmias are usually not life threatening in LVAD patients, especially after the early postoperative period, this complication should be managed aggressively to improve LVAD output and the clinical status of the patient and to avoid the potential adverse sequelae of thrombus formation or further right ventricular myocardial injury from prolonged fibrillation.
Right Ventricular Failure
Although native left ventricular function does not significantly contribute to cardiac output after LVAD placement, factors influencing right ventricular function, including intrinsic contractility, pulmonary vascular resistance, the presence of arrhythmias, and volume status, are critical in the maintenance of adequate right ventricular output, and therefore LVAD output. As already mentioned, perioperative myocardial stunning as well as the presence of ventricular arrhythmias impair right ventricular function, resulting in decreased LVAD flows. The ability of the impaired right ventricle to adequately supply volume to the left heart is critically related to pulmonary vascular resistance (PVR), which is usually elevated in longstanding congestive heart failure and further increased in the early postoperative period by the effects of cardiopulmonary bypass16 and blood product administration.14 After LVAD insertion, decompression of the left heart results in improvement of the reversible component of pulmonary hypertension,26 with gradual increases in right ventricular and therefore LVAD output. During periods of right ventricular dysfunction and/or elevated PVR, aggressive volume loading can be effective in improving LVAD flows, utilizing the right ventricle as a passive conduit to the left heart, analogous to Fontan physiology.
We defined right ventricular failure (RVF) as decreases in right ventricular function and/or output requiring insertion of a right ventricular assist device (RVAD), administration of inhaled NO for elevated PVR, and/or pharmacological inotropic support for >10 days after LVAD insertion. In our experience, 19 of 58 patients undergoing LVAD insertion (33%) met one of the above criteria for RVF. Thirteen patients required only medical inotropic support, while RVAD insertion was required in 4 cases and inhaled NO in 3 cases (Table 6). Four patients (21%) died from RVF and 3 died from other causes. Overall, 12 patients (63%) survived RVF; of these, 9 have been transplanted and 3 await transplantation. RVAD insertion was life saving in 2 of 4 cases, and administration of inhaled NO resulted in dramatic decreases in PVR and improvements in LVAD flows in 3 instances.
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In summary, although transient right ventricular dysfunction with or without pulmonary hypertension is common after LVAD insertion, medical inotropic support is usually successful in maintaining adequate right ventricular output and LVAD flows until right ventricular recovery and reductions in PVR occur. In the 6 cases of RVF refractory to inotropic agents, we have used RVAD support and/or inhaled NO to salvage 4 patients.
Graft Complications
Graft-related complications were defined as bleeding events at LVAD inflow or outflow sites. In 58 patients, there were 5 such complications, with 2 deaths. One patient experienced inflow graft bleeding, survived device explantation, and is currently well. In two cases, aortic rupture at the distal anastomotic site required emergent operation and Gore-tex patch repair, with one subsequent death. Finally, of 2 outflow graft hemorrhages requiring operative intervention, 1 patient died as the result of complications of an intraoperative neurological insult.
Device Malfunctions
Device malfunctions were defined as problems with the console/diaphragm unit, pump sensor system, interconnect cable/battery unit, or vented electric controller unit. In the pneumatic devices, the most common problem was interconnect cable malfunction, which required cable replacement in 23 cases. Consoles were exchanged on 6 occasions because of console hardware or diaphragm malfunction, and the pump sensor system required adjustment in 4 cases. Finally, premature battery fatigue occurred in 3 patients, requiring replacement. None of these malfunctions resulted in morbidity or mortality. There were 30 controller malfunctions in the VE group, with no serious device malfunctions or complications.
Noncardiac Surgery in Patients With LVADs
As the number of patients chronically supported by LVADs increases, general surgical diagnoses that are commonly seen in other hospitalized patients are becoming manifest. In our series, 13 LVAD recipients have undergone 17 noncardiac surgical procedures over 5 years, including wound debridement and flap coverage, thoracotomy, tracheostomy, laparotomy, peripheral revascularization, tooth extraction, and central venous access. Thirteen procedures were performed under general endotracheal anesthesia, 3 under local anesthesia, and 1 under monitored anesthesia care (Table 7). All patients received prophylactic antibiotics before skin incision. In addition, those patients deemed at high risk for fungal infection (recent or current use of broad-spectrum antibiotics or multiple indwelling lines) received antifungal prophylaxis. Since anticoagulation is not used for the TCI HeartMate LVAD, these patients were not anticoagulated perioperatively.
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Intraoperatively, all patients undergoing general anesthesia underwent uneventful induction. One patient required inotropic and vasopressor support during decortication for empyema, and two patients required exogenous blood products during three procedures (plication of a bleeding gastric ulcer, sternal debridement, and LVAD pocket debridement). Four patients became hypotensive with decreases in LVAD flow while being placed in the lateral decubitus position, and two patients became hypotensive during intraoperative hemorrhage (bleeding gastric ulcer and LVAD pocket debridement). Aggressive fluid therapy (and in one case vasopressor therapy) was successful in reestablishing hemodynamic stability in all cases. Minor problems encountered were abrupt power loss due to LVAD battery exhaustion and electrocautery-induced sensor interference with the LVAD in the "auto" mode. There were no perioperative complications or deaths.
In our experience, patients on LVAD support tolerated general surgical procedures without perioperative morbidity or mortality.27 Special considerations do need to be made in order for these patients to successfully undergo noncardiac surgical procedures. First, since right ventricular and subsequent LVAD output are dependent on preload, patients should be well hydrated before the induction of anesthesia to decrease the risk of hypotension from venous pooling. Particular attention should also be paid to the effects of intraoperative positioning on LVAD flow. Second, transport and preoperative preparation should be expedited in order to limit the period of time that the device is disconnected from the AC power source, and the device should be placed in the fixed-rate mode to avoid electrocautery-induced sensor interference. Finally, conventional anesthetic induction and maintenance protocols can be used, often without invasive monitoring, since the LVAD facilitates intraoperative fluid management by providing a continuous measure of cardiac output.
Rehabilitation
As LVAD insertion becomes more common and LVAD recipients are discharged from the hospital setting, early mobilization and functional rehabilitation become essential components of perioperative care. The deleterious effects of bed rest are well described,28 29 and since LVADs are capable of maintaining adequate output during changes in heart rate and loading conditions, we use an aggressive program of postoperative cardiac rehabilitation in our LVAD recipients. Our physical therapy protocol is initiated in the ICU on the first postoperative day and continues until explantation. Initially, chest physiotherapy, range of motion exercises, and positioning techniques are implemented, and once the patients are hemodynamically stable (postoperative day 2 to 7), ambulation is initiated, usually while still in the ICU. Upon transfer from the ICU, our program focuses on the goals of functional independence in activities of daily living and hallway ambulation. Once the latter is achieved, patients undergo progressive conditioning in the gym on the treadmill and/or bicycle, which progresses using the Borg Scale of Perceived Exertion, aiming for a rating of 11 to 13 on the 6 to 20 scale.30 Of the first 53 LVAD recipients, 45 participated in progressive mobilization. Twenty-seven of these initiated ambulation between postoperative days 7 and 10, and 37 (82%) tolerated treadmill exercise. Factors that impaired patients' ability to achieve these goals included infection, neurological complications, reoperation, and prolonged inotropic support. In 2571 physical therapy sessions lasting 1814 hours, only 8 minor incidents (all involving decreases in pump flow) occurred, representing 4.4 incidents per 1000 patient-hours.31 There was no resultant morbidity or mortality.
In addition to the general improvement in functional recovery seen after aggressive rehabilitation, there are several additional potential benefits to this approach. Lower extremity strengthening, weight-bearing exercise, and aerobic conditioning during the LVAD support period may lessen the severity of proximal muscle weakness, osteoporosis, and obesity, respectively, frequent problems in the transplant population. Chronic physical activity has been shown to lessen the chronotropic response to exercise by increasing cardiac output and stroke volume, while promoting increased cellular oxygen extraction and utilization.32 Early progressive mobilization of the LVAD recipient is safe and promotes functional independence and independent ambulation, often by the second postoperative week. As such, an aggressive rehabilitation program, initiated on the first postoperative day, is an integral part of our perioperative management protocol.
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Discussion |
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The unsatisfied need for donor organs has led to the advance of alternative cardiac replacement options. The textured surface device used at our institution over the past 5 years has resulted in a satisfactory survival rate in a cohort of patients in whom death would be uniformly expected in the absence of a donor organ.33 The improved results are in part due to lessons learned as we gained experience.
Routine intraoperative transesophageal echocardiography, which is obtained in all patients, allows early determination of appropriate LVAD inflow cannula placement by ensuring that the left ventricle is adequately decompressed. In addition, the presence of a patent foramen ovale and aortic insufficiency and the severity of tricuspid regurgitation can be quickly determined.
Pharmacological support with aprotinin to reduce perioperative bleeding and NO to provide selective pulmonary vasodilation have been used successfully. We have also found arginine vasopressin to be helpful in providing vasoconstriction in patients with catecholamine-resistant vasodilatory shock. In doses one tenth of that used to treat esophageal variceal bleeding, substantial elevations in peripheral blood pressure can be obtained without compromising renal function.
Early and prolonged use of mechanical right-sided support has reduced mortality from the major early complication of LVAD insertion, right heart failure. Identification of the relationship between bleeding and right-sided circulatory failure has been helpful in reducing the absolute incidence of profound pulmonary hypertension. Selection scales have also identified patients who are more likely to bleed and less likely to tolerate the consequences of hemorrhage, thus avoiding potential catastrophies.
Early ambulation and rehabilitation after LVAD insertion has expedited patient recovery and potential discharge status. Patients are able to return to work or school and live functional lives while awaiting heart transplantation. In this regard, the vented electric system appears superior to the pneumatically driven device with regard to quality of life and ease of ambulation. Overall, the low number of significant device-related complications and the high quality of life experienced by LVAD patients support continued investigations on long-term mechanical support using implantable devices.
A prospective, controlled trial has been proposed that would randomize patients who are not transplant candidates between LVAD support and standard medical management. If after randomization of 120 patients and a follow-up of 2 years, an improvement in survival from 25% to 50% is observed with an appropriate quality of life, the usefulness of LVADs as an alternative to medical therapy will have been demonstrated. The remaining question of whether society is willing to pay for a new life-saving operation will have to be answered, keeping in mind that we expect LVADs to eventually cost the same as a heart transplant.
Additional unanswered questions remain that must be addressed as the LVAD experience grows. Many patients have elevated panel reactive antibody (PRA) titers after LVAD insertion. The fear of aggressive hyperacute or chronic humoral rejection delays the transplantation of these patients and mandates a prospective crossmatch. The incidence of elevated PRA titers may be reduced by using leukocyte depletion filters, especially for platelets; however, some patients will still develop antibodies. Specifically designed combinations of cytolytic agents with plasmapheresis may allow quicker and safer transplantation in this patient population, although a formal study remains to be done.
An additional potential improvement would involve identification of LVAD recipients whose hearts have remodeled and who may be able to undergo successful device explantation without transplantation.34 We have explanted devices on 2 such patients (one died 4 months later with rapidly recurring heart failure and the other is still alive with an ejection fraction of 55%). Remodeling of a dilated heart or prevention of further dilation after a large myocardial infarction may have long-term beneficial effects and can be accomplished with several months of LVAD support.
Over all, the medium-term experience with implantable LVAD support is encouraging. Although additional areas of investigation exist, improvements in patient selection and management together with device alterations that have reduced the thromboembolic incidence and facilitated patient rehabilitation lead us to believe that a prospective, randomized trial is indicated to study the role LVADs may have has an alternative to medical management.
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Acknowledgments |
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Dr Oz is an Irving Fellow of Columbia University.
Received June 20, 1996; revision received November 11, 1996; accepted November 21, 1996.
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References |
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