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Ann Thorac Surg 1996;61:684-691
© 1996 The Society of Thoracic Surgeons
Departments of Thoracic and Cardiovascular Surgery and Perfusion Services, The Cleveland Clinic Foundation, Cleveland, Ohio
Accepted for publication October 17, 1995.
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Abstract |
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 TopFootnotes Abstract IntroductionMaterial and MethodsResultsCommentAddendumReferences |
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Methods. During the 22-month period September 1992 through July 1994, 23 patients in cardiogenic shock were placed on venoarterial ECLS using a heparin-bonded circuit. These patients' charts were retrospectively reviewed. A logistic regression analysis of the variables collected was performed to identify clear-cut predictors of ability to be weaned from ECLS.
Results. Average patient age was 47.3 ± 16.4 years (range, 5 to 72 years). There were 17 male patients. Average time on ECLS was 58.4 ± 35.1 hours (range, 0.5 to 144 hours). Statistical analysis revealed that patients unable to be weaned from ECLS were more likely to have a critically dilated left ventricle on echocardiography and were female. Ten patients (43.5%) died while on ECLS. Four patients were transferred to an implantable left ventricular assist device, and 3 underwent successful transplantation. The 9 other patients were successfully weaned from ECLS, and 4 were discharged home from the hospital. Overall, 7 patients (30.4%) who were placed on ECLS were successfully discharged home.
Conclusions. Extracorporeal life support using an extracorporeal membrane oxygenation system provides excellent cardiac support with similar hospital survival rates as centrifugal mechanical support. Extracorporeal life support has complications unique to itself, but with time, these are likely to be overcome. Women and patients with persistent left ventricular dilatation are less likely to be weaned.
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Introduction |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAddendumReferences |
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However, there are no reliable methods of immediately distinguishing infarcting myocardium, which is unlikely to recover, from ``stunned myocardium,'' which may recover after operation [13]. We [14] have reported our previous experience with centrifugal mechanical ventricular assist devices in 91 patients seen between August 1979 and August 1991. Forty-nine (62%) of the 79 patients receiving assist for postcardiotomy ventricular failure were successfully weaned, and 20 (25.3%) were hospital survivors. Nevertheless, the high morbidity associated with the use of centrifugal blood pumps (bleeding, 87.3% of patients; mean transfusion requirement, 53.2 units; renal failure, 46.8%) persuaded us to pursue other forms of postcardiotomy cardiac support.
Extracorporeal membrane oxygenation (ECMO) circuits have recently been introduced for extracorporeal life support (ECLS) in adult patients in cardiogenic shock and have been shown to provide excellent oxygenation and hemodynamic support [15–17]. The incorporation of heparin coating of the extracorporeal circuit provides a more biocompatible surface, which has been shown to minimize early surface-induced complement activation and platelet dysfunction [18]. Moreover, the heparin-coated surface has been purported, in experimental and clinical reports, to reduce or obviate the need of systemic heparinization, and this has been demonstrated to reduce bleeding [19, 20]. Superb clinical results have been reported using heparin-bonded ECLS circuits without systemic heparinization [17]. This report reviews our experience in 23 patients placed on ECMO to treat postcardiotomy cardiogenic shock using minimal to no systemic anticoagulation.
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Material and Methods |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAddendumReferences |
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The hospital records, ECLS records, cardiopulmonary bypass records, and blood transfusion records of the 23 patients were respectively reviewed. In addition, transesophageal echocardiographic studies before and during ECLS were evaluated specifically for presence of intracardiac clot formation, spontaneous contrast (representing stagnant blood flow), and left ventricular dilatation (left ventricular end-diastolic diameter greater than 6 cm). Complications including intracardiac clot formation, stroke, oxygenator failure, pump head failure, infection, need of reexploration for bleeding, limb ischemia (limb discoloration, coolness to touch, loss of sensation), need of hemodialysis or ultrafiltration, and blood transfusion requirements were recorded. Complications were analyzed with respect to age, mode of cannulation, time of bypass, length of time on ECLS, height, weight, body surface area, time of initiation of support (intraoperatively, postoperatively), use of intraaortic balloon pump, use of systemic heparinization, and average pump flows. Timing of oxygenator changes were recorded. Univariate logistic regression analysis of these variables was performed to identify clear-cut predictors of ability to be weaned from ECLS.
ECMO Circuit
Our extracorporeal oxygenation circuit consists of several commercially available products. Specifically, the system is composed of a hollow-fiber microporous membrane oxygenator (Maxima, Medtronics, Inc), a heat exchanger (Cincinnati Sub Zero; Cincinnati, Ohio), a Sechrist oxygen blender, and an arteriovenous loop made from standard 
-inch (0.94-cm) Tygon tubing. A centrifugal pump (Medtronics, Inc) is used to provide blood flow. All components of the system in contact with blood including the cannulas are heparin coated (Carmeda Bioactive Surface). Wire-wound Carmeda-coated arterial and venous cannulas were used for arterial return from the ECMO circuit and for venous return, respectively (Medtronics, Inc). Arterial cannula sizes used in our patients ranged from 17F to 21F and venous cannulas, from 18F to 20F. The decision to cannulate the femoral vessels (which were preferred) or the right atrium and aorta directly was based on the size of the femoral artery and the presence of peripheral vascular disease. If femoral venous return was poor, then the right atrium was cannulated. The specific method of cannulation was left to the surgeon's preference, and six surgeons were responsible for initial ECMO cannulation.
Arterial and venous access for ECMO support was obtained by using the femoral vessels in the majority of patients (74%). We did not use distal leg perfusion. In 17 patients, ECMO cannulas were placed percutaneously into the femoral artery and vein, and in each, the mediastinal incision was closed to help control bleeding and prevent infection. Five patients were cannulated exclusively in the mediastinum: venous return was from the right atrium, and oxygenated blood was returned by way of the ascending aorta. The sternal incisions were not closed. One patient was managed by having the venous return from the femoral vein and the arterial return through the ascending aorta; the sternal incision was also not closed. Patients with signs of tamponade or with persistent excessive mediastinal hemorrhage despite correction of clotting variables (prothrombin time, partial thromboplastin time, activated clotting time, platelets) underwent exploration either in the intensive care unit if the chest had been left open or in the operating room if the sternotomy incision had been closed. Seventeen patients (73.9%) had insertion of an intraaortic balloon pump prior to being placed on ECLS. This was in an effort to decrease afterload as described by Lazar and associates [21]. The 6 patients not treated with intraaortic balloon pump support included 4 patients in whom ECMO was instituted postoperatively in the intensive care unit (14 to 77 hours postoperatively), 1 pediatric patient, and 1 patient in postcardiotomy cardiogenic shock in whom the surgeon chose not to use it.
Transesophageal echocardiography was routinely performed in all patients multiple times during the period of ECLS. Further, transesophageal echocardiography was used during attempts to wean patients from the life support circuit. Patients demonstrating intracardiac clot thrombus formation while on ECMO were managed by surgical removal of the clot (3 patients) or if this was considered too dangerous, initiation of systemic heparinization (3 patients).
In patients placed on ECLS for postcardiotomy cardiogenic shock, the systemic heparinization was reversed with protamine sulfate intraoperatively after the ECLS circuit was running. Patients placed on life support postoperatively in the intensive care unit were heparinized with 5,000 units of heparin sodium at the time of insertion of the life support circuit, and no protamine was given. All patients received 5,000 units of heparin intravenously during periods of low pump flow (ie, changing of an oxygenator or pump head). Similarly, 5,000 units of heparin was given during weaning from the life support circuit. In only 3 patients was systemic heparinization used (average dose, 750 U/h) because of the surgeon's concern about not using systemic heparin while they were on the extracorporeal circuit. In these 3 patients, the activated clotting time was kept greater than 200 seconds. In the 20 remaining patients, activated clotting times were not measured routinely. 
-Aminocaproic acid was used in 6 patients having redo open heart procedures (4, bypass; 2, valve). Aprotinin was not used in any patient. Bleeding was treated by transfusion of packed red blood cells, fresh frozen plasma, platelets, and cryoprecipitate when necessary. Selective left ventricular decompression was not used. While the patients were on ECMO, they were weaned from inotropic agents if possible (except for renal dose dopamine hydrochloride) to prevent further myocardial ischemia. Average pump flows on ECLS were 3.76 ± 1.01 L/min (range, 1.6 to 5.8 L/min). No effort beyond intraaortic balloon pump use was made to ensure that pulsatile flow was maintained. Average oxygen tension on ECMO was 154 ± 68 mm Hg (range, 100 to 304 mm Hg).
With the aid of a transesophageal echocardiogram to visually inspect the heart, weaning attempts were made when cardiac recovery was evident after 24 hours of assist. Pump flow was gradually reduced as cardiac function was determined using transesophageal echocardiography. If good ventricular ejection was maintained during weaning from the ECLS machine and the patient could maintain a cardiac index of 2.2 L•min-1•m-3, ECLS was discontinued. Four patients who were considered to have irreversible left ventricular dysfunction and who otherwise were candidates for cardiac transplantation were converted from the ECMO system to an implantable left ventricular assist device (LVAD) (HeartMate; Thermo Cardiosystems, Inc, Woburn, MA). These patients were less than 65 years old and had failed to demonstrate adequate improvement in left ventricular function for weaning from the ECMO circuit. All patients were accepted for potential cardiac transplantation before being transferred to the implantable LVAD.
Statistical Analysis
Results are recorded as the mean ± the standard deviation. Continuous variables were analyzed by Student's t test or Wilcoxon two-sample test. Fisher's exact test for 2 x 2 tables was used for categoric variables. Analysis was considered significant at a p value of less than or equal to 0.05. Univariate logistic regression analysis was performed for the variables that converged and that were an end or significantly related (p 
0.05) to the outcomes. Multivariate analyses were not performed because of the small sample size.
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Results |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAddendumReferences |
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. There was no difference in transfusion requirements between patients cannulated through the femoral or mediastinal vessels.
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). There was no correlation between the presence of stagnant intracardiac blood flow, left ventricular distention, and intracardiac clot formation.
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Seven patients (30.4%) had development of infectious complications: bacteremias (all gram-positive cocci) in 6 and mediastinitis (Staphylococcus epidermidi) in 1. All but one bacteremia was transient and cleared with antibiotics and changing of central lines. One progressed to endocarditis (S epidermidis), which eventually was the cause of death of the patient.
In 10 patients, the oxygenator had to be changed. The mean time to the first change was 35.0 ± 27.43 hours (range, 5 to 103 hours). The extracorporeal membrane oxygenator pump head was changed in 3 patients: in 1 because clot was detected in the pump head and in 2 prophylactically because of excessive noise and vibration of the pump potentially signaling impending pump failure. Table 6 lists complications and causes of death.
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Three patients underwent surgical removal of the clot using a left atrial incision. Two patients with intracardiac clot were able to be weaned from ECMO, and 1 was transferred to an implantable left ventricular support device. Only 1 had signs of a new cerebrovascular accident, but all 6 died. Two patients had development of intracardiac thrombus during administration of protamine to reverse systemic heparinization immediately after cardiopulmonary bypass. Both were being monitored with transesophageal echocardiography at the time of clot formation. One patient had clotting of the entire extracorporeal membrane oxygenator circuit and died in the operating room. In 4 patients, postoperative intracardiac thrombus formation was noted after 37.5 ± 28.7 hours (range, 6 to 72 hours) of ECLS. Intracardiac clot formation appeared to be a random event. Although it did not occur in patients maintained on systemic heparinization, it did not appear to be associated with the type of procedure performed or -aminocaproic acid use.
Survival
Ten patients (43.5%) died while on ECLS. Four patients (17.4%) were transferred to an implantable LVAD for possible heart transplantation. Three of the patients bridged to a LVAD did subsequently undergo heart transplantation, and all were discharged home after 88.7 ± 11.8 days of LVAD support. Nine other patients were successfully weaned from ECLS, and 4 were discharged home. Overall, 7 patients (30.4%) who were placed on ECLS were discharged home. There did not appear to be any relationship between preoperative left ventricular function, chronic congestive heart failure, or cardiogenic shock with respect to ability to be weaned from the ECMO circuit or hospital survival.
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Comment |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAddendumReferences |
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The major question surrounding the use of ECMO for postcardiotomy support is whether or not it is better than other methods of life support. Our mortality with ECMO is similar to results obtained in patients given centrifugal pump ventricular support. Another study [14] from this institution reported a similar death rate (25.3%) with use of centrifugal devices during the period just prior to our use of ECMO. Both that result and our current results with ECMO are similar to the 24.6% survival rate in 965 patients supported with ventricular assist devices in the Ventricular Assist Device National Registry as reported by Pae and associates [23]. Other authors [24, 25] using ECMO for ECLS have obtained results similar to ours; Kawahito and colleagues [24] had a 39% survival rate in 13 patients in postcardiotomy cardiogenic shock, and the national Extracorporeal Life Support Organization Registry [25] reported in 1994 a 33% survival rate in patients unable to be weaned from cardiopulmonary bypass.
Our results, however, are not as good as those recently reported by Magovern and co-workers [17], who had a 55% survival rate with ECMO in patients in postcardiotomy cardiogenic shock. This difference may be related to both how patients were selected and how the ECLS systems were used. In the experience of Magovern and colleagues [17] with 21 patients, 1% of all patients undergoing open heart operation were placed on ECLS using an ECMO circuit. In our experience, only 0.38% of all patients undergoing open heart procedures were placed on ECLS. This compares with 0.2% of all patients having cardiac operations who were placed on postcardiotomy centrifugal mechanical ventricular support during the years 1979 to 1991 at our institution as reported by Golding and associates [14]. Therefore, we applied ECLS less than half as frequently as Magovern's group, and perhaps this indicates that ECLS was underused in our experience. Moreover, we did not exclude from ECLS patients undergoing emergency procedures or patients older than 70 years, factors known to negatively influence survival [13]. Only 4 of our patients had primary coronary artery bypass grafting versus 10 from Magovern's group (79% survival).
Another difference between our results and those of Magovern's group is that 45% of their patients were placed on ECLS in the intensive care unit from 4 to 60 hours postoperatively. In our experience, only 35% of patients were placed on ECLS in the postoperative period. Such patients are known to have an improved survival (54% in the Extracorporeal Life Support Organization database [25]) compared with patients in whom ECMO is required to separate them from bypass. Another potential explanation for the differences in hospital survival rate is that we preferentially cannulate patients percutaneously through the femoral vessels unlike Magovern's group. Although similar flow rates were obtained in both series using peripheral versus mediastinal cannulation, it is unclear whether peripheral cannulation provides as good left ventricular decompression as mediastinal cannulation, a factor shown to inhibit weaning in our study.
There are several possible explanations for our inability to demonstrate an improved survival in patients in postcardiotomy cardiogenic shock compared with historical controls using centrifugal devices. Bavaria and colleagues [26] demonstrated that ECLS increases left ventricular wall stress and oxygen consumption in the postischemic heart by increasing afterload. Thus, ECMO actually adds to the mechanical burden of the poorly contracting left ventricle without improving contractility and may delay functional recovery of the myocardium. The elevated afterload inherent to ECMO support likely results in left ventricular dilatation. Despite the use of intraaortic balloon pumping as a method of decreasing afterload in these patients as advocated by Lazar and co-workers [21], patients with persistent ventricular dilatation did poorly. Presumably, better left ventricular drainage would have improved our results.
These findings seem to support the fact that mechanical circulatory support that drains only the right atrium cannot effectively decompress the left heart. The efficacy of left heart bypass for hemodynamic support in patients with ventricular dysfunction after cardiac surgical intervention has been demonstrated by many researchers [7, 8, 9, 12]. However, left heart bypass can be instituted only in the operating room and therefore not rapidly in emergency situations. Such practical problems constitute limiting factors for left heart bypass that may select out patients in more stable condition. In contrast, ECLS can be initiated on an emergency basis with rapid and relatively simple implementation, which makes ECMO very attractive. However, methods to decompress the left ventricle may be beneficial. Our preferred method of left heart decompression involves placing a separate venous cannula into the left atrium through the right superior primary vein permitting decompression back into the ECMO circuit by means of a Y connector linked to the venous line. In our experience, air has not been drawn into the heart using this technique, but this is a risk.
In addition to left ventricular distention, we found female sex to be a risk factor for inability to wean from ECLS. It is unclear why female sex increases mortality. Female sex is known to be a risk factor for coronary artery bypass grafting, which was the procedure most often performed in our series and therefore may have resulted in a higher mortality in female patients. It is also possible that the smaller body size of women does not allow adequate cardiac decompression because of limitations of cannula size. We were unable to demonstrate a correlation between female sex and increased risk of left ventricular distention.
Perhaps another factor that limited patient survival in our study was that all patients placed on ECMO intraoperatively were given protamine at the end of the bypass run. Heparin-coated ECLS circuits have been shown to reduce blood cell trauma [27], complement activation [18, 28, 29], and granulocyte activation [30]. Therefore, improvement in biocompatibility with heparin-coated ECLS systems may produce better outcomes. Von Segesser and associates [31], however, recently demonstrated that reversing systemic heparinization with protamine in animals supported by heparin-coated extracorporeal circuits markedly increases fibrin formation in the circuit and also promotes platelet and red cell deposition. Protamine administration effectively neutralized the heparin surface coating and presumably its biocompatability. This may have negated any potential advantage of the heparin-coated ECLS circuit.
The incidence of complications in our patients given ECLS for postcardiotomy cardiogenic shock was similar to that reported previously by our group [14] using centrifugal mechanical ventricular support. Although the incidence was similar, the complications appeared to be of a different nature. Our most frequent complication was leg ischemia, which is potentially reversible by using different cannulation techniques. We recently added distal limb perfusion through a separate catheter and have eliminated leg ischemia as a problem. The incidence of intracardiac clot formation is also very concerning and may potentially limit the use of ECLS systems at least without systemic anticoagulation. Magovern and co-workers [17] reported a 14.2% incidence of thrombus formation using a strategy similar to ours. Two patients had clot in cannulas, and 1 sustained a cerebrovascular accident, which was retrospectively noted to have been caused by intracardiac thrombus after the ECLS system had been removed. It is very likely that the incidence of intracardiac clot formation has been underestimated in most series using ECLS, as transesophageal echocardiography results are not reported routinely.
It appears prudent not to reverse heparin with protamine, if possible, in the operating room, and once bleeding has subsided to institute intravenous heparin. Not reversing the heparin effect with protamine is impractical in this patient population because of the frequent presence of coagulopathic bleeding. Following a protocol similar to ours (where protamine was used to reverse intraoperative heparin), Kawahito and colleagues [24] used intravenous heparin postoperatively, maintaining activated clotting times of approximately 150 s/min during ECMO. They had no episodes of clinical stroke. All patients who died underwent postmortem examination, and no evidence of thromboembolism or hemorrhage was found. In that study, circuits were inspected after bypass for clot formation using scanning electron microscopy. The tubing material, cannulas, and centrifugal pump showed no evidence of clot. However, minor clots were found in the areas of stagnant flow in the oxygenator in 7 patients. The clots appeared in the upper part of the housing and were limited to the stagnant-flow areas. As observed by the naked eye, there were no clots in the tubing material or cannulas, and scanning electron microscopy showed that the surface platelets exhibited minimal activation of pseudopod formation without aggregating. It is important to note that patients were not studied with transesophageal echocardiography to look for intracardiac clot.
Early and aggressive temporary hemodynamic support for patients in profound cardiogenic shock can be used to sustain them until a more long-term form of LVAD can be placed. Given the severe degree of cardiogenic shock, it is unlikely that our patients would have survived to LVAD implantation had ECMO not been used for hemodynamic support. Moreover, given their dire status, none would have been accepted as a transplant candidate. The most frequent cause of patient death when LVADs are used as a bridge to transplantation has been multiorgan failure [32–36]. Patient selection and early LVAD implantation are the most important factors for successful support [34–36]. We think ECMO can be useful in this process. First, ECMO provides early, adequate end-organ perfusion and oxygenation and therefore may help prevent multiorgan failure. Second, during this period of hemodynamic stability, the transplantation evaluation can be undertaken to determine whether the patient is a candidate for transplantation. Further, those patients not approved for transplantation will not be placed on an implantable LVAD, and ECMO can be used for temporary support in the hope of cardiac recovery [37].
In conclusion, we have found that ECLS using an ECMO system provides excellent cardiac support with similar hospital survival as centrifugal mechanical ventricular support. Extracorporeal life support, however, has complications unique to itself, which, with time, may be overcome. It appears that care must be taken to treat left ventricular distention, which occurs frequently and is associated with failure of myocardial recovery. The practice of reversing systemic heparinization at the end of a bypass run when ECLS has been instituted must be reassessed if patients are to benefit from the improved biocompatability of heparin-coated circuits. However, the use of systemic anticoagulation after bleeding has subsided seems more practical and may be beneficial in preventing intracardiac clot formation.
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Addendum |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAddendumReferences |
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