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Ann Thorac Surg 2001;71:S67-S72
© 2001 The Society of Thoracic Surgeons

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Session 1: acute heart failure

Management of acute cardiac failure with mechanical assist: experience with the ABIOMED BVS 5000

^a MCP Hahnemann University, Department of Cardiothoracic Surgery, Hahnemann University Hospital, Philadelphia, Pennsylvania, USA

Address reprint requests to Dr Samuels, Department of Cardiothoracic Surgery, Hahnemann University Hospital, Mailstop #111, Philadelphia, PA 19102
e-mail: Abiosam{at}aol.com

Presented at the Fifth International Conference on Circulatory Support Devices for Severe Cardiac Failure, New York, NY, Sept 15–17, 2000.

Abstract

Background. Mechanical circulatory assist industries have developed ventricular assist devices (VAD) for short-, intermediate-, and long-term use. The purpose of this report is to describe the progress made with the ABIOMED Biventricular System (BVS) 5000 (ABIOMED, Inc, Danvers, MA) short-term VAD.

Methods. From June 1994 through August 2000, all cardiogenic shock patients who required short-term mechanical assist were supported with the ABIOMED BVS 5000. Insertion criteria included any condition that may potentially result in cardiac recovery. A formal algorithm for timing of insertion was established to standardize implantation criteria.

Results. A total of 45 patients were supported at Hahnemann University Hospital, Philadelphia, PA. There were 26 male and 19 female patients, with a mean age of 57.9 years (range 33 to 80 years). Devices were inserted for postcardiotomy shock in 36 patients (80%) and precardiotomy shock in 9 patients (20%). The average duration of support was 8.3 days (range 1 to 31 days). Overall, there were 22 (49%) patients weaned from support and 14 (31%) discharged from the hospital. For patients in whom the device was implanted in accordance with an established protocol (group A), the wean and discharge rates were 60% and 43%, respectively. The most common morbidities included bleeding and adverse neurologic events.

Conclusions. The ABIOMED BVS 5000 VAD continues to be a valuable form of short-term mechanical assist for acute cardiogenic shock. The formation of a uniform VAD insertion algorithm has helped to standardize protocols in management.

Ever since the intraaortic balloon pump (IABP) was introduced and made clinically available in the 1960s, the use of mechanical circulatory assist had altered the management of acute cardiac failure. Over the course of the next several decades, efforts at providing additional support was brought about by the research and development of the ventricular assist device (VAD). Several industries have made products that translated into myocardial support devices for short-term (days to weeks), intermediate-term (weeks to months), and long-term (months to years) use. The purpose of this article is to describe our experience with the use of the ABIOMED BVS 5000 VAD (ABIOMED, Inc, Danvers, MA) for both pre- and postcardiotomy acute cardiogenic shock. The information presented here represents a single-center experience that has been published and updated since initiating a VAD program in 1994 [1–4]. National [5] as well as international [6] experience with the ABIOMED BVS 5000 has been described and is discussed in the Comments section for completeness.

Material and methods

The ABIOMED BVS 5000 VAD became available at Hahnemann University Hospital, Philadelphia, PA, in 1994. At that time, patients considered for support were in accordance with ABIOMED’s advisory council guidelines and the US Food and Drug Administration (FDA)–approved indication for postcardiotomy shock. The typical patient profile was failure to wean from cardiopulmonary bypass (CPB) after coronary artery bypass grafting (CABG). More recently, patient selection has expanded into precardiotomy shock states in accordance with the change in the US Food and Drug Administration-approved conditions to include any cardiac situation that is potentially reversible. As such, patients with viral myocarditis, myocardial infarction, and intractable arrhythmia have been recently added to the list of candidates for acute short-term mechanical assist (Table 1).

View larger version (30K): [in this window] [in a new window]   Fig 1. Algorithm for short-term VAD implantation for acute cardiogenic shock. (IABP = intraaortic balloon pump; VAD = ventricular assist device.)

In general, VAD management followed the guidelines described in the ABIOMED training manual. Alterations in management were made with respect to anticoagulation, antibiotic, physical therapy, and weaning. Beginning in October 1999, a VAD team with a lead nurse practitioner (E.C.H) position was created with the responsibility to oversee and supervise all VAD protocols. As such, alterations in management have been in collaboration with other experienced institutions. The traditional anticoagulation protocol using heparin remains the primary method of anticoagulation except in conditions of heparin-induced thrombocytopenia or studies examining alternative agents such as enoxaparen, dalteparin, or clopidogrel. As indicated in the training manual, heparin is completely reversed with protamine in the operating room and withheld for 24 hours after insertion. Every effort is made to correct coagulopathy with antifibrinolytics and coagulation factors during the first 24 hours. Once bleeding is controlled, an intravenous infusion of heparin is begun at 1000 units/h, adjusting the activated clotting time to approximately 200 seconds. Antibiotic regimens include standard gram-positive coverage with cefazolin and/or vancomycin, with the addition of broader spectrum coverage with ciprofloxacillin or piperacillin/tazobactam if fever, elevated white blood cell count, lung infiltrate, sputum production, or cloudy urine is demonstrated. Physical therapy is encouraged in the bed with range-of-motion and isometric exercises. If the patient’s condition is stable, transfer to a chair is attempted. Escorted ambulation at the bedside has been performed in 1 case. All patients remain in the cardiothoracic intensive care unit during BVS support.

Weaning is not begun before day 3 of support, and is started only when extracardiac organ recovery (eg, lungs, liver, kidneys) is demonstrated clinically, chemically, or radiographically. The weaning protocol requires a stable cardiac rhythm and minimal inotropic drug support. The VAD flows are decreased by 0.5 L every 10 minutes until a flow of 2 L · min^-1 · m^-2 is achieved with stable hemodynamics or stopped earlier if hemodynamics become unstable. Inotropic drugs may be added or titrated upward to determine whether myocardial reserve is satisfactory at moderate doses¹ of chemical support. In some cases, an IABP is inserted for additional support to successfully wean. Simultaneously, transplant evaluation is undertaken in all ABIOMED BVS patients aged less than 70 years. If recovery is not achieved within the first week of support, then the decision to convert to long-term mechanical assist versus extended BVS support is based on transplant candidacy. Patients who are considered transplant candidates are converted to an implantable system such as the Novacor (Oakland, CA) or the Heartmate (ThermoCardiosystems Inc, Woburn, MA) LVAS. Patients who were not transplant candidates but did not recover after 1 week were supported for longer periods until recovery occurred or a complication resulted in the need for explantation or in death. It is our policy to perform bedside blood pump exchange at weekly intervals for long-term (> 1 week) support patients.¹

Results

A total of 45 patients were supported at our institution from June 1994 through August 2000. There were 26 male and 19 female patients with a mean age of 57.9 years (33 to 80 years). In all, 43 patients were placed on support at our institution and 2 were transported on support from regional facilities. There were 25 left, 10 right, and eight biventricular assist devices placed. Two patients were placed on a BVS-ECMO (biventricular system-extra-corporeal membrane oxygenation) circuit, consisting of an oxygenator placed in-line with the outflow tubing of a right VAD to the pulmonary artery. Five patients were converted from short-term to long-term assist devices. Devices were inserted for postcardiotomy shock in 36 cases (80%) and precardiotomy shock in 9 cases (20%). In most cases (n = 40), the VAD was placed while the patient was on CPB. A minority (n = 5) of devices were placed without CPB, including four left VADs and one right. A summary of the conditions for device implantation is depicted in Table 3. The average duration of support was 8.3 days (range, 1 to 31 days). In all, 32 (71%) patients were supported for 10 days or less.

View larger version (20K): [in this window] [in a new window]   Fig 2. Outcome of BVS patients.

Comment

Tremendous progress has been made in the management of acute cardiogenic shock, whether pre- or postcardiotomy in nature. Medical management including antiplatelet and lytic therapy, as well as interventional management involving early angioplasty of culprit vessels has resulted in the survival of patients who would otherwise have died of cardiac failure [9]. However, a subset of patients remain problematic because of the inability to reverse cardiogenic shock or the sequelae of intractable arrhythmia that are so often associated with myocardial damage. Irrespective of whether the low cardiac output state occurs before or after cardiac surgery, the concept of mechanical support has become an established method by which to manage patients refractory to medical and interventional measures. Centers all over the world have described the versatility of the BVS 5000 in a variety of conditions, including right ventricular (RV) support after heart transplantation [10] and implantable LVAD placement; left ventricular (LV) support after valve replacement [11], LV aneurysmectomy [12], spontaneous postpartum coronary artery dissection [13], acute myocarditis [14], acute myocardial infarction [15], intractable arrhythmia [16], and postinfarction ventricular septal defect (personal communication, Louis Samuels, Hahnemann University Hospital, Philadelphia, PA, 1995). An additional potential therapy includes ventricular support for the damaged ventricle after trauma.

In 1987 (1992 in the United States), the ABIOMED corporation marketed the BVS 5000 with the approach that this pneumatically driven device could easily be implanted in the postcardiotomy shock patient and managed at the bedside by the nursing and house staff. Several other features made this device attractive; pulsatility, automatic console, and the ability to reverse anticoagulation completely within the first 24 hours of implantation. The advantages of pulsatility in the setting of acute cardiogenic shock have been described by Jett [17]; as opposed to chronic heart failure, improved end-organ perfusion and enhanced lymphatic flow with pulsatile versus centrifugal flow is beneficial in acute shock. In addition, the BVS is an asynchronous unit such that the pump output is a function of preload and afterload and is not dependent on cardiac rhythm, making support through a life-threatening arrhythmia a possibility [18]. As a result of these features, the device has been well received worldwide—particularly in the United States, where 365 of the 769 (47%) nontransplant cardiac centers and 111 of the 129 (86%) cardiac transplant centers currently have access to this technology [19]. Equally impressive is the growth in the number of patients in whom this device has been implanted over the past decade. At present, more than 4,000 patients have been supported with the BVS worldwide.

The success of the ABIOMED program has been the recognition of several factors associated with favorable as well as unfavorable results. The timing of insertion and proper patient selection are the two most important determinants of outcome. As the ABIOMED registry has shown, wean and discharge rates can be doubled (40% vs 20%) by adhering to the principle of early insertion [19]. Over the past several years, the timing of postcardiotomy shock insertion has decreased from 6 hours to 3 hours from the first attempt to wean from CPB. In our opinion, the decision to implant can be made even earlier. At our center, we make the decision within 1 hour of the first attempt to wean from CPB. In fact, the decision is often made sooner than 60 minutes. After a trial of inotropic drugs and IABP, preparation for device insertion is made instantly, thereby wasting little time and often avoiding the need for biventricular support. In our opinion, the majority of cases being with univentricular failure, usually involving the left side. If this condition is not corrected, biventricular failure ensues. It is our position to begin with LV support uniformly, unless an isolated RV problem can be identified with certainty. An LVAD is inserted, left atrial and pulmonary artery pressures reduced, and the right ventricle can usually be supported with low to moderate dose inotropic drugs. If the LVAD flows are unsatisfactory, then an RVAD is added. On rare occasions, both cardiac and pulmonary failure has forced the unconventional application of an in-line oxygenator. Although both patients in our series died, one patient successfully recovered pulmonary function to permit explantation of the RVAD and its oxygenator. Laboratory animal experiments have encouraged us to continue to clinically pursue the application of an in-line oxygenator with the BVS [20, 21].

An interesting transition that has taken place is the application of VAD technology to precardiotomy shock states such as acute myocarditis, acute myocardial infarction, and intractable arrhythmia. We have had experience with these conditions and have been impressed by the ability to support these patient populations. Some of the same experience in postcardiotomy shock has now been applied to precardiotomy shock. For example, the concept of maximal inotropic drug support in the setting of the failing ventricle has now been applied to patients in the coronary care unit and cardiac catheterization laboratory. We began a campaign of educating our cardiology colleagues with the knowledge that use of two to three inotropic drugs at maximal dosages is associated with an unacceptable mortality if hemodynamics are not rapidly improved. As a result of this education, we now receive consultations for mechanical assist before multiple organ system failure occurs. Finally, we have made the regional nontransplant cardiac centers aware of the resources available at our institution, such that pre- and postcardiotomy shock patients can be referred for consultation or management. The model for this approach has been well described by the program at Columbia Presbyterian in New York City [22] and elsewhere.

One of the most challenging issues with short-term mechanical assist has been the inability to predict sustained recovery. We have been very successful with determination of device explantation. However, there is a large difference between the percentage of patients successfully weaned versus successfully discharged. In an attempt to help understand these findings, we studied a subset of patients on short-term assist devices with serial cardiac nuclear studies to determine whether there was a means of quantifying myocardial viability. The results were inconclusive. Similarly, serial echocardiography was excellent for supporting the likelihood of successful explantation but was insensitive to predicting stable myocardial function over time. One area of research that we are examining includes myocardial biopsy to assess the degree of apoptosis and other elements of cardiac cell death and reprogramming. One of the authors (J.N.) has studied these reactions in chronically supported patients and is now attempting to do so in the acute model. Although histologic changes favoring cell reprogramming have been demonstrated in the chronically unloaded ventricle supported with a long-term implantable LVAD, it is unknown whether these cellular changes can be determined in a shorter time interval and whether they can predict sustained functional recovery [23].

In conclusion, the ABIOMED BVS 5000 has enjoyed more than a decade of excellent acceptance and application. The pace with which technology has progressed has resulted in the pursuit of even better devices for cardiac mechanical assist. There is great anticipation for smaller, more efficient devices for long-term support. Equally exciting is the day of the totally implantable replacement heart. Acute cardiogenic shock remains a medical challenge that requires rapid recognition and resuscitation. We are at the point at which we are beginning to accept the technology for both pre- and postcardiotomy shock. We must now learn to bridge the gap between successful wean and successful discharge. In our opinion, this step will require either conversion to long-term devices (implantable LVAD or total heart replacement), or application of compounds to limit cell death and to promote cell recovery and function.

Footnotes

Dr Samuels is a consultant with ABIOMED, Inc.

¹ Definition of inotropic drug doses: dopamine (µg · kg^-1 · min^-1): low 1 to 4, moderate 5 to 9, high 10; dobutamine (µg · kg^-1 · min^-1): low 1 to 4, moderate 5 to 9, high 10; epinephrine (µg · kg^-1 · min^-1): low 1 to 4, moderate 5 to 9, high 10; epinephrine (µg · kg^-1 · min^-1): low 0.05 to 0.09, moderate 0.10 to 0.14, high 0.15; milrinone (µg · kg^-1 · min^-1): low 0.125 to 0.24, moderate 0.25 to 0.49, high 0.50.

References

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3. Samuels LE, Kaufman MS, Morris RJ, Brockman. Early vs. late insertion of the ABIOMED BVS 5000 for postcardiotomy heart failure. Heart Failure Society of America, First Annual Meeting, Baltimore, MD, September 21–24, 1997.
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9. Hochman J.S., Sleeper L.A., Webb J.G., et al. Early revascularization in acute myocardial infarction complicated by cardiogenic shock. N Engl J Med 1999;341:625-634.[Abstract/Free Full Text]
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11. Samuels L.E., Kaufman M.S., Ravishankar R., Morris R.J., Strong M.D., Brockman S.K. Successful bridge to transplantation with the ABIOMED BVS 5000 VAD following double valve replacement. J Extra-Corpor Technol 1998;30:91-94.
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13. Samuels L.E., Kaufman M.S., Morris R.J., Brockman S.K. Postpartum coronary artery dissection: emergency coronary artery bypass with ventricular assist device support. Coron Artery Dis 1998;9:457-460.[Medline]
14. Chen J.M., Spanier T.B., Gonzalez J.J., et al. Improved survival in patients with acute myocarditis using external pulsatile mechanical ventricular assist. J Heart Lung Transplant 1999;18:351-357.[Medline]
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16. Thomas N.J., Harvey A.T. Bridge to recovery with the ABIOMED BVS-5000 device in a patient with intractable ventricular tachycardia. J Thorac Cardiovasc Surg 1999;117:831-832.[Free Full Text]
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19. ABIOMED Registry as of June 2000.
20. Entwistle JWC III, Samuels LE, Thomas MP, Wechsler AS. Adult ECMO using the ABIOMED BVS 5000i and Sarns Turbo membrane oxygenator. Presented at the 37th Annual Meeting of the Pennsylvania Association for Thoracic Surgery, Skytop, PA, Sept 16–19, 1999.
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