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Ann Thorac Surg 2006;82:28-33
© 2006 The Society of Thoracic Surgeons
a Department of Cardiac Surgery, Innsbruck Medical University, Innsbruck, Austria
b Department of Cardiology, Innsbruck Medical University, Innsbruck, Austria
c Department of Anesthesiology and Intensive Care Medicine, Innsbruck Medical University, Innsbruck, Austria
d Department of General and Transplantation Surgery, Innsbruck Medical University, Innsbruck, Austria
Accepted for publication February 27, 2006.
* Address correspondence to Dr Hoefer, Department of Cardiac Surgery, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria; (Email: daniel.hoefer{at}uibk.ac.at).
| Abstract |
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METHODS: One hundred thirty-one patients were supported with ECMO between March 1995 and November 2005. Reasons for ECMO implantation were acute heart failure, acute or chronic heart failure, and postcardiotomy heart failure. In 28 patients, subsequent VAD implantation was necessary (bridge to bridge concept).
RESULTS: Fourteen bridge to bridge patients (50%) became long-time survivors with a mean follow-up of 39 months. Risk factors for mortality were status postcardiopulmonary resuscitation and elevated lactate and bilirubin levels before VAD implantation. Complications after ECMO and VAD implantation were bleeding and thromboembolic events. The most common cause of death was multiorgan failure.
CONCLUSIONS: Bridge to bridge is a successful concept for selected patients with cardiogenic shock. During ECMO support, patients can be evaluated for comorbidities. For patients with a combination of risk factors (status postcardiopulmonary resuscitation, elevated lactate levels, and impaired liver function), VAD implantation should be considered very carefully.
| Introduction |
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Despite these advantages, ECMO support has several disadvantages that limit its applicability as a long-term support for a bridge to heart transplant: hemolysis, impossibility of patient mobilization, bleeding, stroke, infection, and limited ability to adequately decompress the left ventricle in poorly functioning hearts are the major problems associated with ECMO support. In addition, ECMO increases left ventricular afterload and wall stress [14, 811].
With the increasingly successful application of long-term implantable ventricular assist devices (VAD), the limitations of ECMO could be overcome by bridging patients to a long-term implantable VAD after initial ECMO resuscitation (bridge to bridge) [1, 2, 7]. In some patients suffering from myocarditis or postcardiotomy cardiogenic shock, weaning from VAD is possible (bridge to recovery). In all other patients, heart transplantation remains the only viable option (bridge to transplant).
The objective of this study is to evaluate the outcome of the bridge to bridge concept and to identify risk factors indicating adverse outcome.
| Patients and Methods |
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One hundred and thirty-one patients were stabilized with ECMO during this period at our center. Etiologies for conservatively intractable cardiogenic shock were acute heart failure (including acute coronary ischemia, myocarditis, and near drowning), acute on chronic heart failure (known ischemic or dilative cardiomyopathy), and postcardiotomy heart failure (inability to wean from cadiopulmonary bypass after cardiac surgery or postoperative acute heart failure; Table 1).
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Maintainance of adequate systemic blood flow was monitored by mean arterial pressure, blood lactate concentrations, central or mixed venous oxygen saturation, and urine output. Mean arterial pressure was maintained between 50 and 80 mm Hg with vasopressor or vasodilator administration. A pulsatile arterial pressure tracing indicated residual left ventricular myocardial contractility facilitating left ventricular drainage, while being supported with a right atrial to aortic extracorporeal system. Maintaining residual left ventricular ejection was also expected to reduce the risk of intracardiac clot formation. Whenever pulsations disappeared, volume expansion or inotropic support were immediately started until pulsatile systemic blood flow reappeared.
After ECMO implantation, early assessment of neurologic status was initiated with serial neurologic examination and computed tomography of the brain to assess for hypoxic injury or relevant cerebral hemorrhage. In patients who demonstrated sufficient cerebral, hepatic, renal, and pulmonary function, major contraindications for heart transplantation were excluded by serology for HIV and hepatitis C virus and total body computed tomography scan to exclude malignancy.
After an initial stabilization (minimum 24 hours), weaning attempts from ECMO were monitored by means of transesophageal echocardiography and measurement of central venous pressure, wedge pressure, arterial blood pressure, and mixed venous oxygen saturation. If weaning from ECMO support was not possible, another attempt was performed 12 to 24 hours later. In case of weaning failure, VAD implantation was usually considered after 72 hours.
Contraindications for VAD implantation were absolute contraindications to heart transplantation (malignancies, HIV infection), severe neurologic dysfunction (stroke, cerebral hemorrhage, diffuse hypoxic lesions after CPR), multiorgan failure, and sepsis.
In all patients receiving VAD support, a paracorporeal pulsatile VAD was implanted (Thoratec Corp, Pleasanton, CA, or Berlin Heart, Berlin, Germany). Left heart support was achieved by cannulating the apex of the left ventricle and the ascending aorta; for right heart support, the right atrium and the pulmonary artery were cannulated. Postoperative anticoagulation consisted of coumarins together with a platelet aggregation inhibitor at low dosage.
After stabilization, patients either went for recovery of myocardial function and weaning from VAD support (bridge to recovery) or for heart transplantation (bridge to transplant).
Data Analysis
Data analysis was performed with SPSS for Windows. Comparison of means was performed using the independent sample t test and Mann-Whitney test for nonparametric data. Categorical variables were analyzed with the
2 test or Fisher's exact test. Multivariate analysis was performed using the Cox regression model. Survival curves were compared by the log-rank test. Statistical significance was defined as p value less than 0.05.
| Results |
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Fifty-two patients (40%) died during ECMO support (mean ECMO support, 2.44 days), in most cases owing to multiorgan failure or sepsis. Forty-six patients (35%) were successfully weaned (acute heart failure 22.4%; acute on chronic heart failure 0%; postcardiotomy heart failure 53.2%), 5 patients (4%) were successfully transplanted during ECMO support, and in 28 patients (21%) a VAD was implanted (bridge to bridge). There was no significant difference in ECMO duration for these four groups.
Complications after ECMO implantation were uncontrollable bleeding after perforation of the femoral artery with subsequent death (n = 2), local bleeding requiring surgical revision (n = 8), intrathoracal bleeding requiring surgical revision (n = 5), retrograde aortic dissection with subsequent stent implantation (n = 2), leg ischemia due to thrombosis requiring surgical revision (n = 2), formation of an atrial thrombus left untreated (n = 1), and necessity of multiple oxygenator changes due to clot formation (n = 5).
In 28 patients, weaning from ECMO was not possible for hemodynamic reasons. As they fulfilled our criteria for either recovery or heart transplantation, a VAD was implanted; mean assist time was 49.9 days (Table 2).
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Fourteen patients (50%) died during VAD support. In 12 cases, multiorgan failure together with sepsis was the cause of death; 1 patient died from intracranial bleeding, and one from bleeding during VAD explantation and attempted heart transplantation. Fourteen patients (50%) became long-term survivors with a mean follow-up of 39 months. Eleven patients underwent heart transplantation (bridge to transplant), and in 3 patients weaning from VAD was possible (bridge to recovery). Twelve survivors have no impairments in daily life (New York Heart Association [NYHA] class I); 2 patients are in NYHA class II. One patient recovered after myocarditis, and she recently became a mother 3 years after weaning.
Complications after VAD implantation involved bleeding requiring surgical revision in 10 patients. Two patients died from bleeding complications, one of intracerebral hemorrhage, and 1 from uncontrollable bleeding during explantation of VAD and heart transplantation. One patient survived an intracranial bleeding, and 1 patient experienced a thrombembolic insult; both of them recovered without sequelae and were succefully transplanted. In 1 patient, multiple changings of VAD ventricles were necessary owing to clot formation, after which the patient was transplanted without any further problems.
Outcome analysis was performed using clinical data and laboratory values before ECMO implantation and VAD implantation (Table 3). Significant differences between survivors and nonsurvivors were found for status post-CPR, bilirubin level before ECMO, cardiac output before ECMO, bilirubin level before VAD implantation, and lactate level before VAD implantation. All other clinical variables and laboratory values, as well as the etiology of heart failure (Fig 1), did not show significant influence on survival.
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| Comment |
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However, the use of ECMO for cardiac failure has its limitations. One major concern is the limited duration of support and the poor outcome associated with long-term support in adults. Patients cannot be mobilized with cannulas implanted in femoral vessels. Furthermore, patients with these devices in place have a risk for complications such as bleeding, infection and sepsis, severe neurologic injury, limb ischemia, and technical problems (pump failure) [16]. Left ventricular decompression may be inadequate, thus requiring catecholamine therapy to prevent pulmonary hypertension, edema, and hemorrhage [1, 3, 4, 6]. In addition, ECMO increased left ventricular afterload, thus negatively affecting myocardial recovery in several animal studies [811]. To overcome this special problem, additional use of an intra-aortic balloon pump is discussed for decreasing left ventricular afterload and therefore reducing wall stress, especially during the critical initial period [9]. The combined use of ECMO and intra-aortic balloon pump under clinical conditions resulted in weaning rates from 56.7% to 69% in patients with postcardiotomy heart failure [16, 17].
In our patients, ECMO and intra-aortic balloon pump were not used together. Weaning rates were satisfactory, especially in the postcardiotomy heart failure group. It can be speculated that the additional use of intra-aortic balloon pump might have further improved ventricular function and might have led to a higher weaning rate.
In the literature, the bridge to bridge concept is still controversially discussed. Magliato and associates [1] report on not acceptable survival rates in the bridge to bridge population and favor primary VAD implantation. Other authors prefer primary ECMO support and favor the bridge to bridge concept [24, 7, 1315, 1820]. In detail, the immediate transfer to VAD would allocate resources to patients who would not have survived or been good candidates for transplantation. In addition, direct transfer to VAD would have prolonged time to reestablishment of sufficient cardiac output and thus may have affected perfusion of all vital organs in these critically ill patients.
The aim of this study was to evaluate the outcome of bridge to bridge patients and to evaluate clinical variables and laboratory tests for their impact on outcome.At our center, all patients presenting with otherwise intractable cardiogenic shock are stabilized with ECMO support, as we do not use primary VAD implantation for these patients, for the reasons discussed above.
Duration of ECMO support had no influence on outcome after ECMO implantation (weaning, subsequent VAD implantation, heart transplantation, or death) and outcome after VAD implantation. At least two weaning attempts were performed before implanting a VAD: hemodynamic monitoring in these patients showed no or only little improvement despite ECMO support. Therefore, early VAD implantation was attempted to avoid complications associated with prolonged ECMO support when no improvement in cardiac function was observed.
Data analysis of our patients revealed successful immediate circulatory support: blood lactate levels were lower before VAD implantation than before ECMO support. However, as a sign of advanced cardiogenic shock in nonsurvivors, not only lactate blood levels but also liver function tests were elevated in comparison with survivors; multivariate analysis revealed status post-CPR and lactate levels as independent risk factors. This was true for the time before ECMO implantation as well as before VAD implantation. Red and white blood cell count as well as renal function parameters showed no difference between survivors and nonsurvivors, as blood products were substituted as required, and in case of renal failure continuous hemofiltration was initiated.
Overall survival was 50%, which is satisfactory in comparison with other series [14, 21].
From our experience, we would recommend that initial stabilization with ECMO support should be attempted for all patients presenting with severe cardiac failure or cardiogenic shock. Extracorporeal membrane oxygenation implantation is less expensive than other forms of mechanical circulatory support and can be performed without major complications in the majority of patients and provides immediate sufficient organ perfusion. If implanted in an early state of refractory heart failure, it may prevent deleterious multiorgan failure. Additional use of intra-aortic balloon pump can be beneficial; experimental as well as clinical studies have revealed positive impact due to reduction of afterload.
Before VAD implantation, patients should be screened exactly for possible risk factors. In this study, clinical variables could be identified that were associated with a poor outcome: the mortality rate was high if blood lactate levels and liver function tests were still significantly elevated after ECMO support as a sign of advanced organ malperfusion and already severely affected liver function. In addition, patients after CPR had a significant higher mortality rate.
The combination of these risk factors might be detrimental as the general condition of such patients seems to be too poor, so that they do not tolerate VAD implantation anymore. At our center, we have refused VAD implantation recently for a patient whose liver function did not recover after ECMO support, because of the poor prognosis.
In summary, our results show that ECMO support can immediately stabilize circulation and provide organ perfusion in patients presenting with intractable cardiogenic shock. However, the mortality rate is extremely high among patients with persisting lactic acidosis and severely impaired liver function despite VAD support. Therefore, VAD implantation for patients after CPR together with elevated lactate and bilirubin levels despite ECMO support should be considered very carefully.
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