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Ann Thorac Surg 1999;68:1187-1194
© 1999 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Columbia-Presbyterian Medical Center, Columbia University College of Physicians and Surgeons, New York, New York, USA
b Division of Cardiology, Columbia-Presbyterian Medical Center, Columbia University College of Physicians and Surgeons, New York, New York, USA
Address reprint requests to Dr Oz, Division of Cardiothoracic Surgery, Columbia-Presbyterian Medical Center, MHB 7-435, 177 Fort Washington Ave, New York, NY 10032
e-mail: mco2{at}columbia.edu
Presented at the Thirty-fifth Annual Meeting of The Society of Thoracic Surgeons, San Antonio, TX, Jan 25–27, 1999.
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Abstract |
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Methods. A referral network based upon the use of implantable LVADs as a bridge to transplantation in patients with postcardiotomy heart failure was established in the New York City region. Cardiac surgery centers were encouraged to contact our center early following any failed cardiotomy.
Results. Forty-four patients entered our postcardiotomy network: 12 recovered without an implantable LVAD, 23 received implantable LVADs, and six expired without long-term LVAD support. Of the 44 referrals, 29 (66%) survived to hospital discharge. Of the 23 patients receiving implantable LVADs, two recovered myocardial function and underwent LVAD explant, 14 were bridged to heart transplant, one underwent an emergent heart transplant, and six expired. Of the 23 implantable LVAD patients, 17 (74%) survived to hospital discharge.
Conclusions. Regional networks centered around bridge-to-transplant facilities that have an aggressive approach to implantable LVAD placement may substantially improve the survival rate of patients with postcardiotomy heart failure.
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Introduction |
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The advent of implantable devices provides an alternative solution to the problem of postcardiotomy heart failure and allows dedicated centers experienced in the care of this critically ill group of patients to potentially improve outcomes. Based on our initial results with the use of implantable left ventricular assist devices (LVADs) in patients with PCCS [12], we hypothesized that the survival rate of patients with postcardiotomy heart failure could be improved by the establishment of a postcardiotomy referral network based on the use on an implantable LVAD as a bridge to heart transplantation.
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Material and methods |
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Left ventricular assist devices
The TCI HeartMate LVAD (Thermo Cardiosystems, Inc, Woburn, MA) was utilized in patients determined to be in need of long-term cardiac support. The TCI LVAD is an implantable, pusher-plate assist device that has been described in detail previously [13]. The early patients in this study received the pneumatic version of this device (8 patients) while the more recent implants were of the wearable, vented-electric version (15 patients). A hemodynamic benefit over extracorporeal LVAD systems is provided by a short inflow cannula allowing effective pumping with the benefit of a lower left atrial filling pressure requirement. Left ventricular (LV) apical cannulation reduces the likelihood of blood stasis in an infarcted LV resulting in thrombus formation.
Patients
The patients considered in this series had undergone cardiac surgical procedures at hospitals in the New York City region in whom PCCS developed and were subsequently cared for at our institution. PCCS was defined as either the inability to wean a patient from cardiopulmonary bypass (CPB) or postcardiotomy hemodynamic instability despite maximal inotropic support and the use of an IABP [12]. The medical records of patients meeting these criteria at Columbia-Presbyterian Medical Center from April 1993 to December 1998 were reviewed.
Preoperative clinical characteristics of the 44 patients who entered our postcardiotomy network are shown in Table 1, which is delineated into patients that ultimately received a TCI LVAD and those that did not. Twenty-three of the 44 patients underwent placement of a TCI LVAD.
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The type of extracorporeal VAD in place and the specific cannulation technique utilized were reviewed to ensure adequate decompression of the LV and adequacy of systemic blood flow. Systemic and mixed venous pO2 levels were analyzed to screen for the presence of intracardiac shunts, biventricular assist device (BiVAD) mismatch, inadequate LVAD flow, and adult respiratory distress syndrome. An arterial pO2 of less than 100 mm Hg on 100% oxygen was considered a contraindication to transfer due to the potential for prolonged hypoxia during transport.
The potential for myocardial recovery was estimated with a review of precardiotomy LV function, electrocardiograms (ECGs), serum creatinine phosphokinase (CPK) levels, and echocardiograms (if not on VAD support). Basic neurologic function was considered to be present if the patient moved all extremities, even if purposeful movement could not be ascertained. Assessment of renal function was based primarily on urine output, rather than serum creatinine levels. Ongoing postoperative hemorrhage would delay transfer frequently, although once hourly chest tube drainage was less than 100 cc, we would expeditiously transport the patient.
Transfer to hub and secondary VAD screening
An important objective of the network was to transfer the patient to our facility within 72 hours of the initial surgical procedure. Upon patient arrival at our center, a secondary screening checklist was reviewed which included the elements in the primary screen in addition to those outlined in Step 2 (Fig 1). We also employed a screening scale predictive of successful LVAD use that we have reported previously that includes reoperation status, intubation status, central venous pressure (CVP) less than 16 mm Hg, urine output greater than 30 cc per hour, and prothrombin time (PT) less than 16 seconds as a means of predicting successful LVAD implantation [14].
Technical issues were considered that would have a bearing on the possibility of myocardial recovery or the utility of an implantable LVAD. The presence of infarcted LV apex tissue can compromise the placement of the LVAD inflow cannula and has been reported to be a major risk factor prohibiting device insertion [15]. We have not had difficulty with this connection, partly due to decreased LV pressure as a result of decompression by the LVAD. The desired placement of the LVAD outflow graft is on the right lateral aspect of the ascending aorta and can be complicated by the location of prior aortocoronary bypass grafts. The aorta is sometimes cross-clamped to facilitate an aortotomy curving around the prior proximal anastomoses.
Wean from temporary LVAD versus implantable LVAD
A decision regarding the potential for myocardial recovery was made within 24 hours of the patient’s arrival at our center and was based on a number of factors (Step 3, Fig 1). Precardiotomy preserved left ventricular ejection fraction (LVEF), low postcardiotomy serum CPKs, and lack of new Q waves on ECGs were encouraging predictors. An assessment of the technical success of the cardiotomy procedure was made in addition to determining if any surgically correctable problems existed. Patients with extracorporeal VADs underwent echocardiography with VAD support reduced to 2 L/min to assess myocardial function. An evaluation was also made of the capacity of the end-organs to tolerate suboptimal cardiac output.
Long-term LVAD implantation
The TCI LVADs were implanted in a pocket fashioned in the left upper quadrant of the abdomen in the properitoneal space, ideally before systemic heparinization. Following the administration of the serine protease inhibitor aprotinin (Bayer, West Haven, CT) to minimize bleeding and subsequent right heart failure [16], CPB was established and the LV was vented through the apex. The LVAD was implanted without the use of cardioplegia or aortic cross-clamping. The LVAD inflow cuff was sewn to the LV apex with pledgeted sutures taking wide bites of the LV myocardium. If the apex was necrotic, a 1-cm strip of bovine pericardium was secured to the base of the cuff. We have reinforced this connection with fibrin glue or cyanoacrylate glue in rare circumstances. Sutures were tied gently as this is a low pressure connection and bleeding is unlikely unless the sutures pull through the LV muscle. No patient bled from this site in this series, in part due to low LV pressures in the setting of decompression by the LVAD. The LVAD outflow graft was sewn to the right lateral aspect of the ascending aorta.
The presence of an extracorporeal cardiac assist device complicates long-term LVAD implantation for several reasons (Step 4, Fig 1) and usually results in significant bleeding. The inflow cannula site is opened widely to allow pressurized blood to expel out the rind of clot often coating the inflow cannula, thus minimizing the risk of an embolic event. The anastomosis from the outflow tract of the TCI LVAD can be made to a preexisting aortic outflow graft already in place from a temporary LVAD, although the size mismatch is 4 mm to 6 mm and bleeding often results.
At the completion of the inflow and outflow anastomoses, LVAD pumping was initiated and the patient was placed in steep Trendelenburg position during the termination of CPB to minimize the risk of air embolism. If an IABP was present at the time of TCI LVAD insertion, it was not removed until coagulation parameters normalized postoperatively.
Early postoperative management
Issues pertinent to management early in the period following LVAD placement are listed in Step 5 (Fig 1). Patients received antibiotic prophylaxis before LVAD implantation and for a minimum of three days post-LVAD implant. Right heart failure was treated with inhaled nitric oxide (NO) [17] and vasodilatory hypotension was treated with intravenous arginine vasopressin (Parke-Davis, Morris Plains, NJ) [18]. Malignant ventricular arrhythmias were managed with pharmacologic agents and cardioversion if necessary.
Late postoperative management
Late postoperative care focused on rehabilitation as well as monitoring the state of immunologic changes induced by the LVAD in anticipation of heart transplantation (Step 6, Fig 1). Patients receiving the wearable, vented-electric version of the TCI LVAD were eligible for discharge home with the LVAD in place while awaiting transplantation [19]. Once discharged, they were followed with weekly visits to our LVAD clinic. Panel-reactive antibody levels were followed in TCI LVAD patients on a biweekly basis.
LVAD explant versus transplant
All of the patients receiving TCI LVADs were identified as heart transplantation candidates. The decision to explant a long-term LVAD without subsequent transplantation was made only if significant native myocardial recovery during the period of LVAD support occurred as assessed by an exercise testing protocol. With the TCI LVAD flow reduced to 2 L/min, patients were placed on a treadmill and right heart catheterization pressure measurements and echocardiography during exercise were used to determine the adequacy of left and right ventricular function [20].
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Results |
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Fourteen of the 23 patients supported with TCI LVADs were supported to heart transplantation. One patient underwent emergent heart transplantation after LVAD placement due to an inability of the device to generate adequate systemic flows as a result of a congenitally small LV. Six of the long-term LVAD patients expired with their devices in place. Of the 23 patients receiving TCI LVADs, 17 (74%) survived to hospital discharge.
Data pertaining to the timing and duration of TCI LVAD support as well as duration of intensive care unit stays is shown in Table 4. Post-LVAD implantation treatment strategies and complications are outlined in Table 5. Inhaled NO and arginine vasopressin were not available for all patients, as we began to use these therapies after the start of the study period. End-stage renal disease did not develop in any of the survivors.
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Causes of death in the TCI LVAD patients were as follows:
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a Denominators indicate the number of patients for whom the specific treatment was available at the time of LVAD implantation.
CVVHD = continuous venovenous hemodialysis.
Overall actuarial survival in the TCI LVAD patients (including follow-up after heart transplantation or LVAD explantation) is shown in Figure 3. The 2-year and 5-year probabilities of survival were 70% and 61%, respectively. Of the 9 patients that left the intensive care unit with a wearable LVAD, 7 (78%) were discharged home while awaiting heart transplantation.
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Comment |
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We now have the capability of providing long-term ventricular assistance with several Food and Drug Administration (FDA)-approved devices to patients with heart failure in an efficacious manner with the possibility of discharge home while awaiting transplantation. With this in mind, we endeavored to establish a postcardiotomy bridge to transplantation network based on the use of long-term implantable LVADs.
The postcardiotomy network concept was based on the realization that many cardiac surgical centers have the capability of implementing short-term cardiac assist devices but do not have long-term ventricular assist or heart transplantation programs in place. We also hoped to preserve the scarce resource of donor hearts by absorbing the high risks of heart transplantation in sick patients during the LVAD implantation procedure and eventually presenting a healthy, relatively stable patient for heart transplantation. In addition, since some patients may recover LV function, device implantation provides a potential bridge to recovery. Finally, creation of a large ventricular assist center encouraged the interaction of health care professionals and support staff specially qualified to provide aggressive care to critically ill patients with multiple organ system failure. The expertise of this program could be utilized to resuscitate critically ill patients even if LVAD support was not required. Organization of a network provides centers with a programmed approach to managing PCCS, including a comfort level with early device support and knowledge that rapid transport to a hub facility is easily achieved.
Reports in the literature on the use of postcardiotomy mechanical assistance have pointed to the importance of minimizing the delay between the time at which PCCS is identified and the institution of adequate mechanical circulatory support [21, 22]. In the operating room, prolonged attempts at weaning from CPB compound the deleterious effects of exposure to the bypass circuit. Delays in implementing circulatory support in postcardiotomy patients who have left the operating room may result in end-organ damage resulting from periods of hypoperfusion and result in hospital discharge rates of less than 10% if associated with cardiovascular collapse [23]. A primary VAD screening within 12 hours of the recognition of postcardiotomy failure avoided these errors and helped teams stabilize patients optimally, eventually facilitating safe inter-hospital transfer and improving the rate of long-term survival. Discussions between surgeons at our hub center and the spoke hospitals initially covered the adequacy of temporary mechanical support that had been instituted and the status of end-organ function. The results of this screening step established the status of patient resuscitation and dictated the urgency of subsequent transfer to our institution.
Once the decision to transfer the patient to the hub had been finalized, we attempted to achieve this within 72 hours of the initial surgical procedure to reduce the chance of sepsis and to avoid the usual multiple organ system failure which eventually occurs in this sick patient population.
An important branch point in our management algorithm was based on our assessment of the potential recovery of the heart. However, we have been unable to identify reliable objective indicators to predict whether a perioperative insult has resulted in stunned [24] or necrosed myocardium. Decisions were based on preoperative cardiac function, technical success of the initial cardiotomy procedure, indicators of perioperative myocardial injury, and postcardiotomy myocardial function.
The usual factors that complicate LVAD placement are exacerbated in this group of very ill postcardiotomy patients. Right heart failure can result from either perioperative myocardial injury or a mismatch between right ventricular contractility and increased pulmonary vascular resistance (PVR). PVR may rise acutely in PCCS due to immunologic activation resulting from blood product transfusions and the inflammatory response known to be associated with CPB [25, 26]. In general, we have used two strategies to manage post-LVAD right heart failure, first inhaled NO, and if not successful, placement of a temporary RVAD [17], although the latter was not required in this patient population. In 2 patients, RVAD use may have allowed patient survival although the sudden decompensation in both patients prevented timely intervention.
Vasodilatory shock is encountered frequently in patients undergoing LVAD placement. We have used intravenous arginine vasopressin in the past as a treatment for vasodilatory hypotension [18]. The use of arginine vasopressin as a vasoconstrictive agent reduces the dependence on catecholamines, such as dopamine and epinephrine, which may increase the arrhythmogenicity of myocardial tissue in patients already prone to malignant ventricular rhythms. An additional benefit of vasopressin may be realized as a result of its effect on the kidneys. Possibly due to constriction of the glomerular efferent arteriole without constriction of the afferent arteriole, vasopressin has been shown to increase urine output rates in patients with septic shock [27].
Post-LVAD implant hemorrhage continues to be an important complication, often requiring reexploration. We have used aprotinin in all of our implantable LVAD patients [16] and sometimes leave the chest open in the immediate postoperative period to facilitate prompt identification of any significant hemorrhage and to reduce mechanical compression of the right ventricle. Contrary to concerns about leaving the chest open with a prosthetic device in place, we have not noted an increased incidence of postoperative infections.
Our overall results for the 44 patients referred to our postcardiotomy network show that 29 of these patients (66%) survived to hospital discharge. In the cohort of patients implanted with TCI LVADs, the survival rate to hospital discharge was 74%.
Through the establishment of an implantable LVAD-based bridge-to-transplant network, a significant improvement in survival after failed cardiotomy can be achieved. An additional benefit of long-term LVAD use is the preservation of scarce donor hearts. We would encourage centers, with established mechanical circulatory support and heart transplantation programs, to develop similar regional networks and actively identify postcardiotomy patients in whom implementation of long-term LVADs, in a timely fashion, may dramatically increase survival rates.
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Acknowledgments |
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