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Ann Thorac Surg 2001;71:S60-S66
© 2001 The Society of Thoracic Surgeons

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Session 1: acute heart failure

Postcardiotomy mechanical support: risk factors and outcomes

^a Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation, Cleveland, Ohio, USA

Address reprint requests to Dr Smedira, Department of Thoracic and Cardiovascular Surgery, 9500 Euclid Ave, Desk F25, Cleveland, OH 44195
e-mail: smedirn{at}ccf.org

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

Abstract

Background. The need for postcardiotomy mechanical support is uncommon, with an incidence of 0.5%.

Methods. Multivariable logistic regression analysis of factors associated with postcardiotomy extracorporeal membrane oxygenation (ECMO) support was investigated in 19,985 patients, of whom, 97 required ECMO.

Results. Younger age, number of reoperations, emergency operation, higher creatinine, greater left ventricular dysfunction, and history of myocardial infarction were significant predictors. Overall survival was 35%, but significantly better (72%) in the subgroup converted to an implantable system and then bridged to transplantation.

Conclusions. Patients at increased risk for mechanical support can be identified preoperatively and patient management modified as indicated. Improvement in postcardiotomy survival has been realized by bridging to transplantation. In nontransplant candidates, permanent support may be the only option for increasing survival.

Fortunately, the need for postcardiotomy mechanical circulatory support is uncommon and likely declining in incidence. Postcardiotomy support in the form of intraaortic balloon pump (IABP) counterpulsation is reported to occur in 4%, and more advanced support is necessary in 0.2% to 1.2% [1]. At the Cleveland Clinic Foundation between 1992 and 1999, 19,985 patients have undergone cardiac procedures, with 107 (0.5%) requiring postcardiotomy support. The preoperative predictors, intraoperative management, and results of postcardiotomy support with extracorporeal membrane oxygenation (ECMO) at the Cleveland Clinic Foundation, as well as published experiences with the ABIOMED BVS 5000 (ABIOMED Cardiovascular, Danvers, MA) and the Thoratec VAD (Thoratec Laboratories Corporation, Berkeley, CA), will be described below.

Material and methods

Predictors of postcardiotomy pump failure and ECMO support
Most reports of postcardiotomy mechanical support have included small numbers of patients and have focused on patient outcomes after support. There are little data detailing the patient’s preoperative characteristics, which may help identify patients at increased risk for mechanical support after cardiovascular procedures.

The best information about postoperative myocardial dysfunction comes from a careful review by Rao and associates of 4,558 consecutive patients who underwent coronary revascularization at the Toronto Hospital [2]. Although they did not look directly at postcardiotomy mechanical support, low output syndrome (LOS) as defined by the requirement for intraaortic balloon counterpulsation or inotropic support for longer that 30 minutes after arrival in the intensive care unit to maintain a systolic blood pressure greater than 90 mm Hg and the cardiac index greater than 2.2 L/min/m² is a useful surrogate for the potential need for advanced support. Multivariate analysis identified reduced ejection fraction (< 20%), reoperation, emergency surgery, and female gender as strong predictors of low output syndrome after CABG (Table 1). The likelihood of developing LOS for various combinations of predictors is shown in Figure 1. Additionally, there was a greater incidence of LOS after incomplete revascularization, 14.6% versus 8.1% with complete revascularization and after a perioperative myocardial infarction, 14.3% compared with 1.8% without a myocardial infarction. To see if similar factors were related to the need for postcardiotomy mechanical support, we compared patients undergoing cardiovascular procedures who did and did not need ECMO support postcardiotomy.

View larger version (32K): [in this window] [in a new window]   Fig 1. Probability of developing low output syndrome after coronary artery bypass grafting. Left ventricular grade (LV Grade) scored 1 to 4. (ACB Redo = reoperation; timing: E = elective; S = semi-elective; U = urgent; TVD = triple vessel disease.) (Tabular material from Rao and colleagues [2]; reprinted with permission from Mosby/Harcourt Brace, Inc.)

Conduct of ECMO
All 107 patients received veno-arterial ECMO. Peripheral cannulation (common femoral artery and vein) was used in 67% of the patients, and central cannulation (ascending aorta and right atrium or common femoral vein) in 33%. The ECMO circuit and cannulation protocols have been described in detail previously [3, 4].

Method of data analysis
Descriptive
Descriptive statistics are summarized as the mean and standard deviation for continuous variables when they were approximately normally distributed, and as range. Categorical variables are expressed as percentages.

Outcomes
Complications during ECMO that were examined included infection, dialysis, neurologic events (encephalopathy, intracranial bleeding, stroke), pump thrombus, and limb complications. The highest values for BUN, creatinine, AST, and total bilirubin were recorded. We recorded whether the patient was bridged with the intent of transplantation, was weaned with the intent for survival, or withdrawn from support.

Risk factors for ECMO
The question of what factors were associated with the decision to use ECMO after cardiovascular surgery was investigated by multivariable logistic regression. Initial screening of variables possibly related to survival utilized contingency table methods and simple t testing. Continuous and ordinal variables were assessed univariably by decile analysis to suggest transformation of scale to incorporate these into the multivariable analysis in a way that ensured that the relation of these variables to outcome was well calibrated with respect to model assumptions. Variables were identified using a directed technique of entry of variables into the multivariable models [5]. The p value criterion for retention of variables in the final model was 0.05.

This directed technique of entry of variables into the model was verified by bootstrap resampling variable selection [6, 7]. All variables found by ordinary multivariable regression composed a complete set of variables appearing in at least 50% of the 500 resamplings.

Presentation
Tables of risk factors are presented with their coefficients and standard deviations rather than as odds ratios because of the use of data transformation that makes these derived statistics difficult to interpret. All confidence limits are equivalent to 1 SE for consistency with the presentation of mean values.

Results

Variables associated with need for ECMO
Patients who required ECMO after cardiovascular surgery differed in a number of respects from patients who did not require ECMO (Appendix). They were older, they were in more advanced clinical status, they often had come to operation on an emergent basis, they had more severe left ventricular dysfunction, two-thirds had a history of myocardial infarction, they were more likely to have had a reoperation, they were more likely to be in renal failure, they were more likely to have left main disease and three-system disease, and they were less likely to have received an internal thoracic artery graft. By both multivariable and bootstrap reliability analysis, eight factors were found to be the common denominators for ECMO: younger age, more cardiac reoperations, emergency operation, higher creatinine, left main disease, greater left ventricular dysfunction, a history of previous myocardial infarction (MI), and a more recent date of operation (Table 3, Figs 2, 3). The correspondence between actual use of ECMO and that predicted on the basis of the above variables was strong and in the predictive range (C = 0.83).

View larger version (23K): [in this window] [in a new window]   Fig 2. ECMO use after cardiac surgery according to age of patients and clinical conditions. This is a so-called nomogram of the multivariable logistic regression equation shown in Table 3. It has been solved for patients with a median preoperative serum creatinine level of 1.3 mg/dL. Three different patient profiles are shown. The lowest curve relates to patients undergoing elective operations, without prior MI, normal ventricular function, and no left main (LM) disease, but undergoing a first reoperation. The other 2 patients are also undergoing first reoperations, but in an emergency setting with poor left ventricular function from a history of prior myocardial infarction. One of these patient profiles includes left main disease and the other does not.

View larger version (22K): [in this window] [in a new window]   Fig 3. ECMO use after cardiac surgery according to level of preoperative serum creatinine (mg/dL). The depictions represent patients 60 years of age (median). The patient profiles are otherwise the same as in Figure 2.

Complications
Complications occurring while patients were on ECMO included infections in 48%, requirement for dialysis in 39%, neurologic events in 29%, pump thrombus in 5%, and limb complications in 27% (Table 4). The infections were pneumonia, line-related bacteremia, and surgical wound infections and not related to the ECMO system or cannulation site. Distal limb ischemia was seen early in our experience and has been eliminated by inserting a 10 French pediatric aortic cannula into the superficial femoral artery [4]. The median number of transfused units of packed red blood cells was 18 (25th percentile, 11; 75th percentile, 28; minimum, 0; maximum, 99). All measures of renal and hepatic function were elevated during ECMO compared with pre-ECMO placement.

Wean and survival rates
ECMO
Eighteen of the patients supported with ECMO were bridged to transplantation, and 42 were weaned with intent for survival. ECMO support was withdrawn from 47 patients. This yielded an overall survival to discharge of 35%.

ABIOMED BVS 5000
The ABIOMED BVS 5000 is a simple, easy-to-use extracorporeal pulsatile pump capable of biventricular support. Its ease of use is reflected by the fact that it is available in over 450 centers in the US, with the majority being utilized in nontransplant centers. From the postmarket data recorded on 78 patients averaging 57.5 years of age, overall wean and discharge rates were 55% and 31%, respectively. Samuels and associates found similar wean and discharge rates and noted a substantial survival benefit, 40% versus 0% in patients whom the device was placed less than 3 hours of the first wean attempt from cardiopulmonary bypass, compared with patients’ support after 3 hours [12].

Thoratec VAD
The Thoratec VAD is a versatile paracorporeal device capable of biventricular and both short- and long-term support. Wean rates of 43% with survival of 27% have been reported [9].

Increasing survival with transplantation and advanced support
Overall survival and wean rates after postcardiotomy support have remained static over the past decade. The most significant improvement has been seen at transplant and assist centers, where appropriate transplant candidates are bridged to transplantation using an implantable system or the ABIOMED and Thoratec VADS. ECMO support was converted to an implantable left ventricular assist device (LVAD) in 18 patients at the Cleveland Clinic. Of these, 72% survived to transplant, with 92% 1-year survival (Fig 4). The successful use of an implantable LVAD for postcardiotomy support has been described by DeRose and associates from Columbia Presbyterian Medical Center [13]. In their series, 12 patients after elective or emergency coronary artery grafting requiring IABP, Biomedicus, or ABIOMED LVAD support were converted to the TCI Heartmate (ThermoCardio Systems, Inc, Woburn, MA) at a mean of 3.5 days. Of these, 8 were transplanted, 1 was explanted, and all discharged for an overall survival of 75%. Similar results have been described by Korfer and associates [10]. In their experience with 68 patients supported with the ABIOMED BVS 5000, the majority with postcardiotomy failure, 32 were weaned and 13 patients transplanted, with an overall survival of 47%. Thoratec VADs were used in another 17 patients at their institution for postcardiotomy support, with 8 survivors (47%): 7 patients transplanted and 1 successfully weaned (Farrar DJ, Personal communication, 2000).

View larger version (21K): [in this window] [in a new window]   Fig 4. Survival after ECMO following cardiac surgery. Two groups of patients are depicted, those bridged from ECMO with intent of heart transplantation, and those weaned from ECMO with intent of surviving without assistance. Patients who were bridged are represented by circles and those weaned are represented by squares. The symbols are nonparametric survival estimates, and the vertical bars represent confidence limits equivalent to 1 SE. The numbers in parentheses are the number of patients still being traced at the various time intervals. The solid lines are parametric survival estimates and are accompanied by confidence limits equivalent to 1

Risk analysis and careful review of patients developing LOS and needing ECMO support postcardiotomy reveal a consistent patient profile. In general, the patient at risk has a long history of coronary atherosclerosis with previous myocardial infarctions resulting in reduced cardiac reserve, had one or more coronary revascularizations, and is unstable, requiring an emergency operation. Incomplete revascularization and perioperative myocardial infarctions are common. In fact, McBride and Golding and associates found that over two-thirds of patients dying after postcardiotomy support and undergoing an autopsy had evidence of extensive MI [9, 10]. This information is important as it allows for perioperative identification of a high-risk patient and can be used to select a device intraoperatively.

At the Cleveland Clinic Foundation, a patient identified as being at increased risk for postcardiotomy support is admitted to the Heart Failure Service and is assessed and managed by a heart failure cardiologist. This expertise is utilized to prepare the patient for surgery by improving hemodynamics and functional class and reducing myocardial ischemia. In the appropriate patient, transplant screening is begun and discussions are initiated with the patient and the family about transplantation and use of assist devices. This approach reduces the difficulties of transplantation assessment in a patient already committed to an assist device.

With the knowledge that myocardial ischemia and damage, often irreversible, account for the majority of cases requiring postcardiotomy support, technical steps such as complete revascularization, meticulous myocardial protection, and avoiding vein graft atheroembolization will likely minimize its occurrence.

In the patient at high risk, with baseline severe limitation in cardiac function, the development of postcardiotomy low output favors the use of a "long-term" device such as the Thoratec VAD or an implantable system at the initial operation. The Thoratec VAD’s versatility is particularly useful in this setting, as the patient can be supported for prolonged periods, bridged to transplant, or weaned. However, it is not possible to discharge the patients supported on the Thoratec while awaiting transplant. At the Cleveland Clinic Foundation, our approach to device selection has evolved over the past few years. In patients with acute MIs with cardiogenic shock or postcardiotomy pump failure who have been cleared for transplantation, we utilize an implantable LVAD as the first choice and the ABIOMED or Thoratec devices if biventricular support is needed or for smaller patients. We believe this avoids the blood trauma of ECMO support and may promote myocardial recovery through direct apical cannulation. At this time, there is no evidence to directly support this contention. For the remainder of patients requiring postcardiotomy support, ECMO and IABP support remain our initial choices.

Overall, postcardiotomy survival has only recently begun to improve. From the literature, postcardiotomy survival averages between 25% and 30%. By utilizing VADs and transplantation more frequently, survival has improved to approximately 50%.

At the Cleveland Clinic Foundation, patients are supported for 48 to 72 hours with ECMO and then converted to an implantable device if they are an appropriate candidate for transplantation and if myocardial function has not improved. This approach avoids the high-risk emergency heart transplantation and provides the time necessary for improvement in organ function and patient status. Samuels, Körfer, DeRose, and Pagani and associates have published similar guidelines [10, 12–14].

With the knowledge that extensive myocardial injury is present in the majority of nonsurvivors of postcardiotomy support, it is unlikely that a specific device or mode of support will improve outcome. In the nontransplant candidate, consideration of permanent device support, when available, may offer a life-saving alternative.

Acknowledgments

The authors thank Colleen Vahcic for her help with manuscript preparation and Lucinda Mitchin for her invaluable advice and technical assistance.

Appendix

Comparison of patients receiving or not receiving ECMO

Variable No ECMO ECMO p N n % N n % Demography Women 19,888 5795 29 97 28 29 0.95 Age (years, mean ± SD) 19,888 63 ± 12 97 59 ± 11 0.0009 Weight (kg, mean ± SD) 19,807 81 ± 17 97 81 ± 19 0.9 BSA 19,753 1.97 ± 0.25 95 1.95 ± 0.21 0.4 BMI 19,753 28 ± 7.5 95 28 ± 4.7 0.4 Clinical condition NYHA class 19,875 97 0.0005 I 3,270 16 20 21 II 9,225 46 26 27 III 3,132 16 17 18 IV 4,248 21 34 35 Emergency operation 19,888 628 3.2 97 25 26 < 0.0001 LV dysfunction 19,094 84 0.0005 None 11,137 58 40 48 Mild 3,832 20 13 15 Moderate 2,563 13 14 17 Severe 1,562 8 17 20 History of MI 19,886 9,156 46 97 64 66 < 0.0001 Prior cardiac operation 19,888 97 < 0.0001 0 15,224 77 41 42 1 3,763 34 33 34 2 734 3.7 14 14.4 3 135 0.7 7 7.2 4 or more 32 0.2 2 2.1 Noncardiac comorbidity Diabetes 18,902 4,281 23 91 23 25 0.6 Smoker 19,760 11,980 61 92 59 64 0.5 Peripheral vascular disease 19,886 5,360 27 97 27 28 0.8 COPD 19,886 3,329 17 97 11 11 0.16 Hypertension 18,661 11,953 64 88 52 59 0.3 Renal failure 19,886 1,115 5.6 97 15 15 < 0.0001 Coronary disease Left main 50% 17,145 3,061 18 78 29 37 < 0.0001 LAD 50% 19,115 13,629 71 84 66 79 0.14 LCx 50% 19,115 11,618 61 84 58 69 0.12 RCA 50% 19,115 12,352 65 84 65 77 0.01 Three-system disease 19,115 9,214 48 84 50 60 0.04 Operative category 19,888 97 CABG only 11,911 60 57 59 0.8 Valve ± CABG 7,245 36 35 36 0.94 Thoracic aorta 732 3.7 5 5.2 0.4 Operative procedures 19,888 97 CABG 14,778 74 77 79 0.3 Use of ITA 10,425 52 32 33 0.0001 Aortic procedure 4,185 21 22 23 0.7 Mitral procedure 4,177 21 20 21 0.93

BSA = body surface area; BMI = body mass index; CABG = coronary artery bypass grafting; COPD = chronic obstructive pulmonary disease; ECMO = extracorporeal membrane oxygenation; ITA = internal thoracic artery; LAD = left anterior descending coronary artery; LCx = left circumflex coronary artery; LV = left ventricle; MI = myocardial infarction; NYHA = New York Heart Association; RCA = right coronary artery.

Variables examined as potential predictors of need for ECMO
Demography
Gender, age (years), weight (kg), height (cm), body surface area (m²), body mass index (kg/m²).

Clinical status
New York Heart Association functional class, emergency surgery.

Cardiac comorbidity
Atrial fibrillation, previous percutaneous coronary intervention, number of cardiac operations/reoperations.

Noncardiac comorbidity
Diabetes, insulin-treated diabetes, orally treated diabetes, smoker, lipid levels (cholesterol, LDL and HDL cholesterol, triglycerides), peripheral vascular disease, COPD, hypertension, chronic renal failure, BUN, creatinine.

Coronary anatomy
Left main, left anterior descending, circumflex, and right coronary artery disease (percent diameter reduction, 50%, 70%, 100%, and any obstruction >0).

Operation
Coronary artery bypass grafting (CABG) alone, valve surgery (with or without CABG), thoracic aorta operation, use of CABG, aortic valve repair or replacement, mitral valve repair or replacement, use of internal thoracic artery (ITA) conduit, date of operation (years since September 1, 1992).

References

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