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Ann Thorac Surg 2008;85:1639-1644. doi:10.1016/j.athoracsur.2008.01.052
© 2008 The Society of Thoracic Surgeons
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Original Articles: Adult Cardiac

Risk Factor Analysis for Bridge to Transplantation With the CardioWest Total Artificial Heart

Jack G. Copeland, MDa,*, Richard G. Smith, MSEEb, Raj K. Bose, MDa, Pei H. Tsau, MDa, Paul E. Nolan, PharmDc, Marvin J. Slepian, MDa

a Sarver Heart Center, University of Arizona, Tucson, Arizona
b Marshall Foundation Artificial Heart Program, University of Arizona, Tucson, Arizona
c Department of Pharmacy, University of Arizona, Tucson, Arizona

Accepted for publication January 17, 2008.

* Address correspondence to Dr Copeland, University of Arizona Sarver Heart Center, 1501 N Campbell Ave, Tucson, AZ 85724-6071 (Email: jackcope3{at}aol.com).


Drs Copeland and Slepian, and Mr Smith declare that they have a relationship with SynCardia Systems, Inc.

 

   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
Background: Safety and efficacy studies of various mechanical circulatory support devices are important, but may not be strictly comparable. Lacking prospective randomized studies for different devices, we believe that comparison of risk factor analyses may give the surgeon a tool more powerful than current studies for matching a patient with an appropriate device. In this paper, we report risk factor profiles for bridge to transplantation with the CardioWest total artificial heart and summarize reports for other devices.

Methods: A multiinstitutional risk factor analysis of the CardioWest total artificial heart, as a bridge to transplantation in 81 patients, was conducted. Univariate analyses were performed on 43 preimplantation prognostic factors. From this group, eight factors were chosen for multivariate analysis. Our results were compared with all recent risk factor analyses for other devices.

Results: Independent predictors for death at three intervals by multivariate analysis were as follows: "implant to transplant": history of smoking (odds ratio, 34); "implant to 30 days after transplant": history of smoking (odds ratio, 10.00), prothrombin time greater than 16 seconds (odds ratio, 4.76); and "implant to 1 year after transplant": prothrombin time greater than 16 seconds (odds ratio, 3.85). The major difference between this experience and multiple reported experiences with left ventricular assist devices is that for left ventricular assist devices, but not for the temporary CardioWest total artificial heart, right heart failure, high central venous pressure, and being on a ventilator (with or without sepsis) were independent predictors of mortality.

Conclusions: Risk factors for bridge to transplantation with the CardioWest total artificial heart are different from those reported for left ventricular assist devices. Recognition of these risk factor differences may facilitate appropriate device selection.

The CardioWest temporary total artificial heart (TAH-t; SynCardia, Inc, Tucson, AZ) was approved as a temporary device for bridge to cardiac transplantation by the US Food and Drug Administration in October 2004 [1]. It is an orthotopic pneumatic biventricular cardiac prosthesis that replaces the ventricles and all four valves as well as the proximal portion of each great vessel. The entire device weighs 150 g and displaces 400 mL, with each ventricle having a maximal stroke volume of 70 mL. It allows for immediate and complete control of blood circulation and pumps up to 9 L/min with a central venous pressure (CVP) of less than 15 mm Hg. More than 700 CardioWest TAH-ts have been implanted worldwide in 30 hospitals. In the US Food and Drug Administration Investigational Device Exemption study conducted in five US centers from 1993 to 2002 [2], hemodynamics were immediately improved by CardioWest TAH-t implantation with a sustained rise in cardiac index from a baseline value of 1.9 to 3.2 L · min–1 · m– 2. Other measurements of hemodynamic recovery that occurred immediately after implantation and persisted included mean systolic arterial pressure rise from 93.8 to 122 mm Hg, mean CVP fall from 19.8 to 13.6 mm Hg, and organ perfusion pressure (mean arterial pressure minus CVP) rise from 49 to 68 mm Hg. Mean support time was 79.1 days, and 79% of the implanted patients survived to transplantation. Survival to 1 year after transplantation was 85.9%.

Safety and efficacy end points from that study and others have been documented in previous reports [3–9]. All of these suggest that the CardioWest TAH-t safety is comparable to currently used biventricular assist devices (BiVADs) and left ventricular assist devices (LVADs).

Irreversible biventricular heart failure, acute decompensation after cardiotomy, cardiogenic shock after acute myocardial infarction, stone heart, irreversible cardiac rejection, failed LVAD or BiVAD, decompensating heart failure with left ventricular thrombus, acquired ventricular septal defect, prosthetic or incompetent native aortic valve in cardiogenic shock, or unresponsive ventricular arrhythmias are conditions appropriate for use of a TAH. The latter six indications are specific for a TAH. Biventricular failure and stone heart could be treated with a BiVAD, whereas acute decompensation after cardiotomy and cardiogenic shock could be treated with a TAH, a BiVAD, or an LVAD. Left heart decompensation in the absence of right heart failure and potentially reversible myocardial failure such as viral myocarditis are indications that are specific for LVAD or BiVAD therapy. There have never been randomized prospective studies to compare the three types of devices. There have been single-institution retrospective comparisons of LVAD versus LVAD [10], LVAD versus BiVAD [11], and LVAD versus BiVAD versus TAH [7]. Currently available registries [12, 13] have documented institutional results without being able to adjust for individual institutional patient selection, implantation, and management biases. Greater rationale and guidance for selection of a specific device for a given patient is needed.

Our hypothesis is that risk factor analysis provides a rationale for device comparison and selection. In the absence of randomized prospective trials, it may be the best method of characterizing specific patient populations at higher and lower risk for survival with various devices. Just as the classic studies of Norman and associates [14] defined a population of patients that was too sick to be helped by the intraaortic balloon pump, risk factor analysis of current mechanical circulatory support devices may help us make better selection choices by understanding device-specific independent risk factors for death. On the basis of this notion, we analyzed prognostic factors from the CardioWest TAH-t multiinstitutional US Food and Drug Administration Investigational Device Exemption study for comparison with contemporary studies for other devices to provide insight into device selection.


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 Acknowledgments
 References
 
Data were obtained from a multiinstitutional (5 centers) trial of the CardioWest TAH-t [2]. Risk factors were recorded within a 24-hour window before device implantation for the purpose of this analysis (Table 1). There were 81 study patients. All signed consent forms were approved by their respective institutional review boards.


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  		Table 1 Preimplantation Risk Factors in Total Artificial Heart Study
 
Patient accrual averaged nine cases per year (median, 9 per year; range, 2 to 18) during the period from January 1993 to September 2002.

Patients selected for this study were candidates for cardiac transplantation and were at high risk for imminent death from irreversible biventricular cardiac failure (Table 2). All were deteriorating in spite of maximal inotropic therapy. Many were more precarious. Table 1 lists all characteristics examined in the study with mean values and standard deviations. Odds ratios (OR) were calculated for increased risk of death.


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  		Table 2 Selection Criteria for Total Artificial Heart Implantation in US Food and Drug Administration Study
 
Total artificial heart recipients in this study were excluded from LVAD implantation for the following reasons: 15 were judged to have irreversible biventricular damage and could not be weaned from cardiopulmonary bypass (12 of those had prebypass cardiac arrests), 51 had CVPs greater than 18 mm Hg, 11 had right ventricular ejection fractions of less than 0.20, 2 had ventricular tachycardia, 1 had an aortic prosthesis, and 1 had right ventricular damage at sternotomy.

CardioWest TAH-ts were implanted using simplified fitting, implantation, and explantation techniques [3, 15, 16]. Patient management, coagulation monitoring, and anticoagulation [3] have previously been documented.

Statistical analyses were performed by Synteract, Inc (Carlsbad, CA). Only those implanted patients meeting all study entry criteria were included in the analyses. End points for univariate and multivariate analyses included survival to transplantation, survival to 30 days after transplantation, and survival to 1 year after transplantation. Probability values of less than 0.05 were considered statistically significant.


   Results
Top
 Abstract
 Introduction
 Material and Methods
 Results
Comment
 Acknowledgments
 References
 
Preoperative characteristics of the study group are shown in Table 1. This was a predominantly male (86%) population with a mean age of 51 years and a mean body surface area of 2 m2. Nearly half (53%) had ischemic cardiac disease, and nearly all of the others had dilated cardiomyopathies. This population was very sick, with 37% having cardiac arrests within 24 hours of implantation, 32% on intraaortic balloon pumps, 43% on mechanical ventilation, and 19% on cardiopulmonary bypass (Table 3). Hemodynamically, they either had essentially no cardiac function or were deteriorating on maximal support with inotropic agents. The mean cardiac index was 1.9 L · min–1 · m– 2, the mean pulmonary artery and wedge pressures were 41 and 30 mm Hg, respectively, and the mean CVP was 20 mm Hg. Laboratory values were compatible with onset of multiple organ failure with the following mean values: serum sodium, 132 mmol/L; serum creatinine, 1.7 mg/dL; total bilirubin, 2.0 mg/dL; and prothrombin time, 16.4 seconds (international normalized ratio of 2.0).


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  		Table 3 Univariate Analysis for Preimplant Factors Increasing Risk of Death
 
Survival rates for the CardioWest TAH-t patients from the time of implantation were 79% to transplantation, 71.6% to 30 days after transplantation, and 70.4% to 1 year after implantation (86% for those transplanted). The mean duration of device support was 79.1 days (median, 47 days; range, 1 to 414 days).

In the univariate analysis (Table 3), three factors were significantly associated with death from the time of TAH implantation until transplantation: history of smoking (OR, 3.45), patient being on the heart-lung machine at the time of selection for TAH implantation (OR, 3.33), and prior mediastinal operation (OR, 4.00). Four factors were found for the period from implantation to 30 days after transplantation: cause of ischemic cardiomyopathy (OR, 3.45), history of smoking (OR, 3.23), prior mediastinal operation (OR, 3.70), and prothrombin time of 16 seconds or longer (OR, 3.03). Four factors were found for the period from implantation to 1 year after transplantation: cause of ischemic cardiomyopathy (OR, 2.70), prior mediastinal operation (OR, 3.33), presence before implant of an automatic internal defibrillator (OR, 2.70), and age of 55 years or older (OR, 2.56).

Factors used in the multivariate analysis (Table 4) included ischemic cause of heart failure, history of smoking, on heart-lung machine at time of decision to implant, prior mediastinal surgery, pulmonary artery systolic pressure of 50 mm Hg or greater, central venous pressure of 20 mm Hg or greater, platelet count of 150,000/mL or greater, and prothrombin time of 16 seconds or longer. Significant risk factors for death for the three time intervals were from implant to transplant: history of smoking (OR, 34); from implant to 30 days after transplant: history of smoking (OR, 10) and prothrombin time of 16 seconds or longer (OR, 4.76); from implant to 1 year after transplant: prothrombin time of 16 seconds (OR, 3.8). None of the other factors were significant predictors of death. Platelet count of 150,000/mL or greater was a predictor of survival to transplant (OR for risk of death, 0.04; 95% confidence interval, 0.002 to 0.67; p = 0.03).


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  		Table 4 Multivariate Analysis
 

   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
Acknowledgments
 References
 
Patients receiving the CardioWest TAH-t in this study were unstable on maximal support. All were rapidly deteriorating with 42% on ventilators, 37% with cardiac arrests within 24 hours, 32% on intraaortic balloon pump, and 19% on full pump oxygenator support with failure to wean. Two thirds were on support ranging from three inotropic drugs to five drugs plus intraaortic balloon pump to full cardiopulmonary bypass.

Surprisingly few preimplant factors were found to be associated with increased risk by univariate analysis (Table 3). From a total of 43 prognostic factors tested at three time intervals, some continuous, some dichotomous, with two tested at different levels (CVP and total bilirubin), only 12 were significant. Univariate analyses for the bridge to transplant period identified increased risk associated with a history of smoking, being on a heart-lung machine at the time of accrual, and prior mediastinal operation. In this, the time when the patients were exposed to the TAH and thus the most important period for assessing efficacy and safety of device support, preimplant markers of right heart failure (elevated CVP, elevated pulmonary artery pressure and resistance, and low cardiac index) and markers of multiple organ failure and sepsis (ventilator support, elevated white blood cell count, elevated bilirubin, and elevated creatinine) were not significantly associated with increased risk of death.

Because of the increasing number of confounding influences at the time of transplantation such as donor-related risks and because of the relatively small number of patients in this study, the importance of the factors identified for the time periods after transplantation (implant to 30 days after transplantation and implant to 1 year after transplantation) may be less important than those for the bridge to transplant period.

The only independent predictor by multivariate analysis of risk for the implant to transplantation time interval was a history of smoking. If more patients had been included in this study, it is possible that more univariate and multivariate predictors would have been identified.

The appearance of history of smoking as a strong and unique negative predictor was initially surprising. History of smoking, history of alcoholism, and history of hypertension were incorporated in the study design because these profiles are common in the end-stage heart disease population. Such factors have not typically been examined in risk factor analysis for bridge-to-transplantation or transplantation. However, the Nantes (France) group [17], in a 20-year retrospective report of 148 cardiac recipients, found a history of smoking to be the only negative predictor for long-term survival. We are left with the impression that a smoking history is a powerful predictor of high risk in patients with end-stage heart disease.

Most data points in the previously published risk factor analyses for other devices summarized in Table 5 were acquired retrospectively. The largest studies published were multiinstitutional, with two (Deng and colleagues [20] and Farrar [22]) focusing on a single device and one looking at all devices implanted [13]. The numbers of patients in those studies ranged from 32 to 464 (mean, 145; median, 56). The chronology of these studies ranges from 1991 to 2004. In our prospective multiinstitutional study there were 81 patients accrued from 1993 to 2002. Forty-three prognostic factors were recorded prospectively and evaluated in this study.


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  		Table 5 Reported Risk Factors for Bridge to Transplantation
 
When necessary for consistency among all studies in Table 5, ORs for multivariate analyses were converted to risk of death. In all five papers considering LVAD support [13, 18–21], CVP of 16 mm Hg or greater and right heart failure were found to be independent predictors of death. In three of those papers [13, 18, 21], mechanical ventilation or respiratory failure and sepsis were found to be predictors of death. Other BiVAD and LVAD predictors mentioned were patient age, timing of implantation (emergent versus elective), postcardiotomy status, and indices of liver dysfunction. Comparing risk factor analyses provides a different perspective than direct comparison of published clinical series. Risk factor analyses subject raw data to careful statistical scrutiny often absent from institutional and even in US Food and Drug Administration–approved reports.

Risk factor profiles for LVADs include right heart failure, high CVP, and markers of multiple organ failure such as need for mechanical ventilation, elevated total bilirubin, and serum creatinine. Extracorporeal BiVAD support has been associated with increased risk with increased age, previous mediastinal operation, elevated blood urea nitrogen, elevated bilirubin, and mechanical ventilation before implantation.

By multivariate analysis in this study, none of those factors influenced survival of patients bridged with the CardioWest. We conclude the CardioWest TAH-t fills a therapeutic gap that is not covered by LVADs or extracorporeal BiVADs. This gap appears to include those failing patients carrying essentially all or many of the predictors defined by recent multivariate analyses of LVADs and BiVADs. There are different risk factor profiles for LVADs, BiVADs, and the TAH. Recognition of these risk factor profile differences may assist the clinician in making safer specific mechanical support device selections for a given patient.


   Acknowledgments
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
References
 
This study was funded by SynCardia Systems Inc.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 

  1. US Food and Drug Administration New Device Approval—SynCardia temporary CardioWest total artificial heart (TAH-t): P030011http://www.fda.gov/cdrh/mda/docs/p030011.htmlPosted: 11-03-2004.
  2. Copeland JG, Smith RG, Arabia FA, et al. Cardiac replacement with a total artificial heart as a bridge to transplantation N Engl J Med 2004;351:859-867.[Abstract/Free Full Text]
  3. Copeland JG, Arabia FA, Tsau PH, et al. Total artificial hearts: bridge to transplantation Cardiol Clin 2003;21:101-113.[Medline]
  4. Copeland JG, Arabia FA, Banchy ME, et al. The CardioWest total artificial heart bridge to transplantation: 1993–1996 National Trial Ann Thorac Surg 1998;66:1662-1669.[Abstract/Free Full Text]
  5. Copeland JG, Pavie A, Duveau D, et al. Bridge to transplant with the CardioWest total artificial heart: the international experience 1993 to 1995 J Heart Lung Transplant 1996;15:94-99.[Medline]
  6. Copeland JG, Arabia FA, Smith RG, Sethi GK, Nolan PE, Banchy ME. Arizona experience with CardioWest total artificial heart bridge to transplantation Ann Thorac Surg 1999;68:756-760.[Abstract/Free Full Text]
  7. Copeland JG, Smith RG, Arabia FA, et al. Comparison of the CardioWest total artificial heart, the Novacor left ventricular assist system, and the Thoratec ventricular assist system in bridge to transplantation Ann Thorac Surg 2001;71(Suppl):S92-S97.[Medline]
  8. Leprince P, Bonnet N, Rama A, et al. Bridge to transplantation with the Jarvik-7 (CardioWest) total artificial heart: a single-center 15-year experience J Heart Lung Transplant 2003;22:1296-1303.[Medline]
  9. El-Banayosy A, Arusoglu L, Morshuis M, et al. CardioWest total artificial heart: Bad Oeynhausen experience Ann Thorac Surg 2005;80:548-552.[Abstract/Free Full Text]
  10. El-Banayosy A, Arusoglu L, Kizner L, et al. Novacor left ventricular assist system versus HeartMate vented electric left ventricular assist system as a long-term mechanical circulatory support device in bridging patients: a prospective study J Thorac Cardiovasc Surg 2000;119:581-587.[Abstract/Free Full Text]
  11. El-Banayosy A, Arusoglu L, Kizner L, et al. Predictors of survival in patients bridged to transplantation with the Thoratec VAD device: a single-center retrospective study on more than 100 patients J Heart Lung Transplant 2000;19:964-968.[Medline]
  12. Mehta SM, Aufiero TX, Pae Jr WE, Miller CA, Pierce WS. Combined registry for the clinical use of mechanical ventricular assist pumps and the total artificial heart in conjunction with heart transplantation: sixth official report-1994 J Heart Lung Transplant 1995;14:585-593.[Medline]
  13. Deng MC, Edwards LB, Hertz MI, et al. Mechanical circulatory support device database of the International Society for Heart and Lung Transplantation: second annual report—2004 J Heart Lung Transplant 2004;23:1027-1034.[Medline]
  14. Norman JC, Cooley DA, Igo SR, et al. Prognostic indicis for survival during postcardiotomy intra-aortic balloon pumping: methods of scoring and classification, with implications for left ventricular assist device utilization J Thorac Cardiovasc Surg 1977;74:709-720.[Abstract]
  15. Arabia FA, Copeland JG, Pavie A, Smith RG. Implantation technique for the CardioWest total artificial heart Ann Thorac Surg 1999;68:698-704.[Abstract/Free Full Text]
  16. Copeland JG, Arabia FA, Smith RG, Covington D. Synthetic membrane neo-pericardium facilitates total artificial heart explantation J Heart Lung Transplant 2001;20:654-656.[Medline]
  17. Roussel JC, Baron O, Pattier S, et al. Outcome of heart transplants 15 to 20 years ago: graft survival, post-transplant morbidity, and risk factors for mortality J Heart Lung Transplant 2007;26(2S):S152(abstract).
  18. Oz MC, Goldstein DJ, Pepino P, et al. Screening scale predicts patients successfully receiving long-term implantable left ventricular assist devices Circulation 1995;92(Suppl):II-16973.
  19. Mehta S, Souza D, Boehmer J, et al. Comparison of Pierce-Donachy (PD) and TCI left ventricular assist systems as bridge to transplant: an institutional experience [Abstract] ASAIO J 1999;45:148.
  20. Deng MC, Loebe M, El-Banayosy A, et al. Mechanical circulatory support for advanced heart failure: effect of patient selection on outcome Circulation 2001;103:231-237.[Abstract/Free Full Text]
  21. Rao V, Oz MC, Flannery MA, Catanese KA, Argenziano M, Naka Y. Revised screening scale to predict survival after insertion of a left ventricular assist device J Thorac Cardiovasc Surg 2003;125:855-862.[Abstract/Free Full Text]
  22. Farrar DJ. Preoperative predictors of survival in patients with Thoratec ventricular assist devices as a bridge to heart transplantation. Thoratec Ventricular Assist Device Principal Investigators. J Heart Lung Transplant 1994;13:93-101.[Medline]
  23. Pavie A, Muneretto C, Aupart M, et al. Prognostic indices of survival in patients supported with temporary devices (TAH, VAD) Int J Artif Organs 1991;14:280-285.[Medline]
  24. Deng MC, Weyand M, Hammel D, et al. Selection and outcome of ventricular assist device patients: the Muenster experience J Heart Lung Transplant 1998;17:817-825.[Medline]

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