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Ann Thorac Surg 1996;61:291-295
© 1996 The Society of Thoracic Surgeons
Department of Surgery, Baylor College of Medicine, The Methodist Hospital, Houston, Texas
Abstract
Background. Bio-Medicus centrifugal ventricular support has been used widely for postcardiotomy cardiac failure. The purpose of this study was to review a large series of support patients examining complications and outcomes.
Methods. One hundred twenty-nine patients undergoing cardiac operations at The Methodist Hospital in Houston, Texas, were placed on Bio-Medicus centrifugal ventricular support for postcardiotomy cardiac failure; 102 were male and 27 were female with a mean age of 61.6 years. These patients were selected for ventricular support based solely on failure to be weaned from cardiopulmonary bypass or progressive postcardiotomy cardiac failure shortly after arrival in the intensive care unit.
Results. These patients experienced numerous complications including coagulopathy, renal insufficiency or failure, sepsis, neurologic deficits, ventricular failure, arrhythmias, and death; 56.3% of patients were weaned from mechanical support and 21.0% were discharged alive. Causes of death included ventricular failure (62.4%), arrhythmias (12.9%), triage (6.9%), perioperative myocardial infarction or cardiac arrest (5.0%), coagulopathy (4.0%), sepsis syndrome (4.0%), cardiac graft failure (3.0%), and device related (1.0%). The one device-related death was a venous cannula dislodgment in the intensive care unit with subsequent exsanguination. Device-related complications were seen in only 1.6% of patients.
Conclusions. Bio-Medicus centrifugal ventricular support can be implemented rapidly and relatively easily. There are few device-related complications and the cost is relatively inexpensive compared with other assist systems. This series demonstrates that a substantial number of patients who experience reversible postcardiotomy myocardial injury will benefit from temporary centrifugal ventricular support.
This study examines complications and outcomes in patients placed on Bio-Medicus centrifugal ventricular support.
Material and Methods
During a period from January 1986 through June 1994, 14,462 cardiac operations using cardiopulmonary bypass were performed at The Methodist Hospital in Houston, Texas, and 129 patients (0.89%) were placed on Bio-Medicus centrifugal ventricular support for postcardiotomy cardiac failure. One hundred two were male and 27 were female with ages ranging from 15 to 86 years and a mean age of 61.6 years. These patients were selected for ventricular support based solely on failure to wean from cardiopulmonary bypass or progressive ventricular failure in the intensive care unit. There were no other inclusion or exclusion criteria.
These patients underwent a variety of procedures, with coronary artery bypass being the most prevalent, constituting 62.8% of operative procedures. The operative procedures were as follows:
Left ventricular support was used in 100 patients, whereas right ventricular support and biventricular support was used in 7 and 22 patients, respectively.
One hundred four patients had a ventricular assist device (VAD) inserted at the time of the primary operation due to inability to be weaned from cardiopulmonary bypass despite maximum pharmacologic support and in most cases intraaortic balloon pump (IABP) insertion (68.8%). Twenty-five patients had VAD placement after the primary surgical procedure because of progressive ventricular failure in the intensive care unit.
Left ventricular support was usually achieved by cannulating the left atrium via the right superior pulmonary vein for inflow to the pump and the ascending aorta for outflow from the pump. Right ventricular support was implemented by cannulating the right atrium for inflow to the pump and the pulmonary outflow tract either directly through the pulmonary artery or through the right ventricle for outflow from the pump. Currently we are using cannulas and tubing that are Carmeda-coated (Medtronic, Minneapolis, MN) and anticoagulation is not used as long as VAD flow remains greater than 2.0 L/min. At the conclusion of VAD insertion and weaning from cardiopulmonary bypass, the sternotomy was closed in 72.2% of patients and left open in 27.8% of patients. Intraoperative complications other than low cardiac output syndrome included coagulopathy, arrhythmias, renal dysfunction, cardiac arrest, and death. Hemofiltration was used in 35.6% of patients either for massive fluid overload or for renal dysfunction.
Patients were evaluated daily for the possibility of weaning from mechanical ventricular support. Weaning and assessment of myocardial recovery were accomplished in the following manner: VAD flows were reduced in decrements of 1.0 L/min while hemodynamics were observed. In these patients, a cardiac index of greater or equal to 2.0 L•min-1•m-2 and a stable mean arterial pressure of greater than 60 mm Hg with little or no increase in filling pressures indicated evidence of improving myocardial function and the possibility of device explantation. After these initial criteria were met, some patients underwent radionuclide scanning or echocardiography with similar decrements in VAD flow to visualize ventricular function. Patients who maintained adequate hemodynamics and who had evidence of improving ventricular function with decreasing VAD flows were considered for device explantation [1, 2]. Figure 1
shows improving ventricular function with decreasing left VAD flows. For VAD flows less than 2.0 L/min full anticoagulation was used. Currently, after weaning criteria are met, a period of observation for 6 to 12 hours on minimal VAD support (0.5 to 1.0 L/min) is used to identify those patients who might deteriorate after VAD removal [2, 3].
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In this series 72 patients (56.3%) were weaned from mechanical assistance and 56 patients (43.7%) were not weaned. Twenty-seven patients (21.0%) were discharged from the hospital. Results by type of support are given in Table 2. These patients experienced multiple complications:
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The triage category includes patients who had life support discontinued at the request of family members usually because of profound neurologic injury, thus making it impossible to evaluate the possibility of ventricular recovery. The one mechanical cause of death was a venous cannula dislodgment in the intensive care unit with subsequent exsanguination. Causes of death for patients who were weaned from the device and those who were not weaned were as follows:
Comment
Numerous devices have been used for mechanical cardiac assistance, with the most common of these being the IABP. Other clinically applied devices have included pulsatile pumps (Thoratec [Berkeley, CA], Novacor [Novacor Division, Baxter Healthcare, Oakland, CA], ABIOMED [Danvers, MA], and TCI [Thermo Cardiosystems, Inc, Woburn, MA]), nonpulsatile pumps (roller pump, Bio-Medicus centrifugal [Eden Prairie, MN], and Sarns centrifugal [Sarns 3M Healthcare, Ann Arbor, MI]), and the total artificial heart. Currently, at The Methodist Hospital, Baylor College of Medicine, in Houston, Texas, the Bio-Medicus centrifugal ventricular assist device is the device of choice for patients with postcardiotomy cardiac failure. To date we have used this device in 173 patients requiring ventricular support, with the largest group requiring assistance for postcardiotomy cardiac failure (129 patients). It has been reported that postcardiotomy cardiogenic shock occurs in 2% to 6% of all patients undergoing revascularization or valvular procedures and less than 1.0% of postcardiotomy patients will require advanced mechanical cardiac assistance other than the IABP [4–8].
In this large series of patients, overall hospital discharge (21.0%) and weaning from VAD (56.3%) are within the ranges reported by other investigators [4, 9, 10]. Complications were frequent, but very few of these were exclusively device-related (1.6%). Although it has been noted that most of these patients experienced multiple complications, the causes of death were judged to reflect the primary factor contributing directly to patient death after an extensive review of each patient's hospital course. Ventricular failure was the single overwhelming cause of death in the majority of these patients (62.4%). For our purposes, ventricular failure was defined as cardiac index less than 2.0 L•min-1•m-2 with progressively deteriorating hemodynamics (mean arterial pressure less than 60 mm Hg) despite maximal pharmacologic support and in most cases IABP counterpulsation. This is a situation similar to that for which the VAD was inserted. Ventricular failure in patients who had been weaned from VAD support would indicate either premature discontinuation of mechanical support or irreversible myocardial injury.
Theoretically, if we are providing adequate mechanical support, then ventricular failure should not be a cause of death in patients still on mechanical support. However, situations do occur where despite maximal pharmacologic support, IABP counterpulsation, and VAD manipulation, the patient is unable to maintain a cardiac index greater than or equal to 2.0 L•min-1•m-2 or a mean arterial pressure greater than 60 mm Hg. Once this point is reached, a progressive cycle of acidosis and multisystem organ failure ensues resulting in rapid patient demise. It has been our experience that simply increasing pump speed will not always increase pump flow. This may be due to a variety of reasons including cannula size, cannula placement, preload (inflow to the pump), and afterload. In univentricular systems there may also be an imbalance between the assisted and the unassisted ventricle resulting in suboptimal flow. All of these factors influence pump flow and performance. In Bio-Medicus ventricular support, the ventricle is not always completely decompressed. As a direct consequence of this, when ventricular contraction occurs with sufficient residual volume the outflow valve opens. Figure 1
shows that at 3.5 L/min of left VAD flow the aortic valve can still open.
Therefore, some flow through the ascending aorta occurs, resulting in a reduction of inflow to the pump. Cannula size and placement may also be factors limiting pump flow. Our methods of cannulation have been previously described in this article. Currently, we are using 32F or 40F cannulas for venous return to the pump in left VADs and right VADs. In the left VAD, a 26F cannula is placed in the ascending aorta for outflow from the pump, and in the right VAD, a 28F or 26F cannula is placed in the pulmonary artery for outflow from the pump. These are relatively small conduits for flow when compared with the approximately 20-mm grafts used for inflow and outflow in a device like the Novacor left ventricular assist system. The size of the inflow conduit in the Novacor left ventricular assist system and its low resistance allow for complete left ventricular decompression, and with ventricular systole there is no volume to eject and open the aortic valve.
We have noted in some patients that efforts to maintain adequate pump flow and support by increasing pump speed have resulted in ``chattering'' of the conduit systems indicating a reduction of inflow to the pump. This phenomenon may be due to small cannula sizes, atrial or ventricular partial occlusion of the inflow cannulas, inadequate preload, or a combination of these factors. Therefore, using larger cannulas, ventricular cannulation, and optimizing preload may alleviate this problem and allow improved pump flow. Ease of device explantation also has to be considered in relation to cannula size and placement.
Although hemofiltration was used in only 35.6% of patients in this series, we have recently noted substantial improvement in the early postoperative period when hemofiltration was instituted in the operating room. Because most of these patients receive large amounts of fluids and blood products, we have noted that early use of hemofiltration can help reduce this fluid overload with third-space fluid accumulation as well as decrease pulmonary and other complications.
Controversy still exists over the advantages of univentricular or biventricular support. It has been shown that univentricular support in selected patients provides adequate ventricular support, and morbidity does not differ in the two groups [11]. We have seen right ventricular failure occur in the operating room shortly after left VAD insertion, necessitating the additional placement of a right VAD. Inotropic support could be further reduced with biventricular support, thereby minimizing the deleterious properties of many inotropes.
Finally, the most important factor in successful mechanical ventricular support is most likely related to the timing of VAD insertion. If the first attempt to wean the patient from cardiopulmonary bypass is unsuccessful, then manipulations including volume optimization, pharmacologic therapy, and a search for surgically correctable problems are performed. If these adjustments prove unsuccessful, then IABP insertion is often the next step for left ventricular failure. After all the above measures fail to achieve weaning from cardiopulmonary bypass, then the only alternative is VAD insertion (Fig 2).
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In summary, this series shows that a substantial number of patients who experience reversible postcardiotomy myocardial injury will benefit from temporary support with the Bio-Medicus centrifugal ventricular assist device. There are few exclusively device-related complications. Equipment for Bio-Medicus support is readily available in most cardiovascular surgery centers, and insertion can be achieved rapidly and easily. The cost is also relatively inexpensive when compared with other ventricular support systems. For successful ventricular support, timing is everything. Early VAD implementation may well be the key to improved patient outcome. Larger cannulas, biventricular support, minimizing inotropic requirements, and starting hemofiltration intraoperatively may also improve outcome. Research is currently ongoing to develop criteria for VAD implementation, weaning, and explantation that will improve patient survival.
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Presented at The Third International Conference on Circulatory Support Devices for Severe Cardiac Failure, Pittsburgh, PA, Oct 28-30, 1994.
Address reprint requests to Dr Noon, Department of Surgery, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030.
References
This article has been cited by other articles:
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  E. C. McGee Jr., P. M. McCarthy, and N. Moazami Temporary Mechanical Circulatory Support Card. Surg. Adult, January 1, 2008; 3(2008): 507 - 534. [Full Text]
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 M. Mert, A. Akcevin, C. E Yildiz, and K. Suzer Postoperative Mechanical Circulatory Support with Biomedicus Centrifugal Pump Asian Cardiovasc Thorac Ann, March 1, 2005; 13(1): 38 - 41. [Abstract] [Full Text] [PDF]
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 S. Taghavi, A. Zuckermann, J. Ankersmit, G. Wieselthaler, A. Rajek, G. Laufer, E. Wolner, and M. Grimm Extracorporeal Membrane Oxygenation is Superior to Right Ventricular Assist Device for Acute Right Ventricular Failure After Heart Transplantation Ann. Thorac. Surg., November 1, 2004; 78(5): 1644 - 1649. [Abstract] [Full Text] [PDF]
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 M. P. Siegenthaler, K. Brehm, T. Strecker, T. Hanke, A. Notzold, M. Olschewski, M. Weyand, H. Sievers, and F. Beyersdorf The Impella Recover microaxial left ventricular assist device reduces mortality for postcardiotomy failure: a three-center experience J. Thorac. Cardiovasc. Surg., March 1, 2004; 127(3): 812 - 822. [Abstract] [Full Text] [PDF]
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N. Moazami and P. M. McCarthy Temporary Circulatory Support Card. Surg. Adult, January 1, 2003; 2(2003): 495 - 520. [Full Text]
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 C Gobel, A Arvand, G Rau, H Reul, B Meyns, W Flameng, R Eilers, and O Marseille A new rotary blood pump for versatile extracorporeal circulation: the DeltaStreamTM Perfusion, September 1, 2002; 17(5): 373 - 382. [Abstract] [PDF]
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F. B.Y. Hoy, D. K. Mueller, D. M. Geiss, J. R. Munns, L. M. Bond, C. E. Linett, and R. C. Gomez Bridge to recovery for postcardiotomy failure: is there still a role for centrifugal pumps? Ann. Thorac. Surg., October 1, 2000; 70(4): 1259 - 1263. [Abstract] [Full Text] [PDF]
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A K Mahmood, J M Courtney, S Westaby, M Akdis, and H Reul Critical review of current left ventricular assist devices Perfusion, September 1, 2000; 15(5): 399 - 420. [PDF]
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B. Meyns, P. Sergeant, P. Wouters, F. Casselman, P. Herijgers, W. Daenen, K. Bogaerts, and W. Flameng Mechanical support with microaxial blood pumps for postcardiotomy left ventricular failure: Can outcome be predicted? J. Thorac. Cardiovasc. Surg., August 1, 2000; 120(2): 393 - 400. [Abstract] [Full Text] [PDF]
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H. M Reul and M. Akdis Blood pumps for circulatory support Perfusion, July 1, 2000; 15(4): 295 - 311. [PDF]
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J. J. Curtis, J. T. Walls, C. C. Wagner-Mann, R. A. Schmaltz, T. L. Demmy, C. A. McKenney, and F. A. Mann Centrifugal pumps: description of devices and surgical techniques Ann. Thorac. Surg., August 1, 1999; 68(2): 666 - 671. [Abstract] [Full Text] [PDF]
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 N. G. Smedira, C. C. Hlozek, and P. M. McCarthy Mechanical Support After Cardiac Surgery Seminars in Cardiothoracic and Vascular Anesthesia, March 1, 1998; 2(1): 66 - 77. [Abstract] [PDF]
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