Interact CardioVasc Thorac Surg 2009;9:291-294. doi:10.1510/icvts.2008.196105
© 2009 European Association of Cardio-Thoracic Surgery
Institutional report - Assisted circulation |
Prophylactic intra-aortic balloon pump in high-risk patients undergoing coronary artery bypass grafting: a propensity score analysis
Antonio Miceli*,
Brenno Fiorani,
Tommaso Hinna Danesi,
Giovanni Melina and
Riccardo Sinatra
Department of Cardiac Surgery, St. Andrea Hospital, University of Rome La Sapienza, Rome, Italy
Received 8 October 2008;
received in revised form 25 March 2009;
accepted 26 March 2009
 Poster communication form at XXIV meeting of Italian Society for Cardiac Surgery, Rome, Italy, November 8–11, 2008.
*Corresponding author. Department of Cardiothoracic Surgery, St. Andrea Hospital, Rome 00189, Italy. Tel.: +390633775310; fax: +390633775483.
E-mail address: antoniomiceli79{at}alice.it (A. Miceli).
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Abstract
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The optimal use of prophylactic intra-aortic balloon pump (IABP) to prevent postcardiotomy low cardiac output syndrome (LCOS) is still debated and poorly defined. The aim of this study was to evaluate whether prophylactic IABP reduces the rate of postcardiotomy LCOS and improves the early outcome in hemodynamically stable, high-risk patients undergoing coronary artery bypass grafting (CABG). From May 2004 to August 2007, 141 consecutive risk patients underwent CABG. Of these 38 (27%) received prophylactic IABP. The remaining 103 patients underwent operation without preoperative insertion of the device. Prophylactic IABP patients were more likely to be younger (P<0.0001), had a recent myocardial infarction (P<0.0001), lower ejection fraction (P=0.006), and higher New York Heart Association (NYHA) functional class (P=0.05). After risk-adjusting for propensity score, prophylactic IABP patients had a lower incidence of postcardiotomy LCOS (adjusted OR 0.07, P=0.006), postoperative myocardial infarction (adjusted OR 0.04, P=0.04), a shorter length of hospital stay (10.4±0.8 vs. 12.2±0.6 days, P<0.0001) than those who did not receive IABP. This study shows that prophylactic IABP treatment for hemodynamically stable high-risk patients undergoing CABG may improve postoperative course reducing postcardiotomy LCOS, postoperative myocardial infarction and length of hospital stay.
Key Words: Intra-aortic balloon pump; Low cardiac output syndrome; High-risk patients
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1. Introduction
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Postcardiotomy low cardiac output syndrome (LCOS) occurs in 2–9% of patients undergoing open-heart surgery, and is related to increased hospital mortality, morbidity, and costs [1–3]. Its occurrence is more frequent in patients with severe preoperative left ventricular dysfunction, inadequate myocardial protection, perioperative myocardial infarction, prolonged cardiopulmonary bypass (CPB) and intraoperative ischemic times, technical difficulties with the conduct of the operation or incomplete revascularization [3]. In these clinical conditions, patients may benefit from intra-aortic balloon pump (IABP). Preoperative IABP is an established tool in unstable patients undergoing urgent myocardial revascularization for an acute myocardial infarction and/or its mechanical complications [3], but the optimal use of preoperative prophylactic IABP in cardiac operations to prevent postcardiotomy syndrome is still not clearly defined. Several studies [4–6] demonstrated the efficacy of preoperative IABP in terms of postoperative mortality and morbidity. However, others did not confirm these findings [7, 8]. Difficulty concerns the definition of preoperative high-risk patients who could develop postcardiotomy LCOS after coronary artery bypass grafting (CABG). According to Christenson and colleagues, high-risk coronary patients have been previously described [5, 6]. Applying these criteria, we selected retrospectively a series of consecutive hemodynamically stable patients at risk for postcardiotomy low output syndrome. The aim of our study was to analyze the role of prophylactic IABP in these patients on early outcome.
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2. Materials and methods
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2.1. Indications
From May 2004 to August 2007, a total of 141 consecutive hemodynamically stable high-risk patients underwent CABG at our Institution. Isolated on-pump CABG was performed on 127/141 patients (90%), while 14/141 (10%) underwent off-pump CABG. According to Christenson et al. [5, 6], high-risk coronary patients requiring CABG presented with two or more of the following: 1) refractory unstable angina despite intravenous administration of heparin sodium and nitro-glycerine; 2) left ventricular ejection fraction (LVEF)  40%; 3) left main stenosis  70%; 4) previous CABG; 5) diffuse coronary artery disease (defined as a patient requiring four or more distal anastomoses to achieve complete revascularization). Exclusion criteria were: preoperative IABP insertion for hemodynamic instability, mechanical complications of acute myocardial infarction, emergent or urgent operations, myocardial infarction within three days, failed PTCA within the 6 h preceding CABG, poorly controlled preoperative ventricular arrhythmias. Patients with unstable angina with ongoing myocardial infarction were also excluded. The decision to use prophylactic preoperative IABP was made by the preference of individual surgeons. Cardiac index, left ventricular stroke, pulmonary capillary wedge pressure and central venous pressure were calculated by Swan–Ganz catheter in all patients.
2.2. Definitions
Postcardiotomy LCOS was defined as the requirement for IABP and/or inotropic support for inability to discontinue CPB or for longer than 30 min after the patient was returned to intensive care unit to maintain the systolic blood pressure >90 mmHg and the cardiac index >2.2 l/min/m2 [1]. Perioperative myocardial infarction was defined as elevation of creatinine kinase MB fraction and/or troponin I with the development of new electrocardiographic Q-wave. Postoperative renal dysfunction (PDR) was defined as patients with postoperative creatinine level >2.3 mg/dl or patients requiring dialysis. Neurological complications were defined as transient or persistent postoperative hemiparesis or neurological dysfunction with morphological substrate confirmed by computer tomography or nuclear magnetic resonance imaging. Postoperative mortality was defined as death occurring within 30 days from surgery. The threshold for blood transfusion was hemoglobin values <8 mg/dl in a stable situation and <9 mg/dl in an unstable situation.
2.3. IABP support and timing
A total of 38/141 (27%) patients received IABP support prophylactically two hours before the operation. Indication for therapeutic IABP after CABG was postcardiotomy LCOS. The intra-aortic balloon (Datascope FidelityTM, New Jersey, USA) was inserted percutaneously into the common femoral artery. After IABP insertion, all patients were anticoagulated with heparin IV as soon as the mediastinal drainage subsided (bleeding <50 ml/h), in order to keep an activated partial thromboplastin time (APPT) 1.5–2 times the normal value. In the control group, a postcardiotomy IABP was used for weaning from CPB or for low cardiac output in the intensive care unit. Patients were weaned from IABP when the cardiac output was satisfactory on minimal inotropic support. Before removing IABP, an echocardiogram was performed to evaluate the ejection fraction, global and regional wall contractility.
2.4. Statistical analysis
Continuous data with normal distribution are given as mean±S.D., otherwise as median and interquartile range (25–75%). The normality of data distribution was tested by the Kolmogorov–Smirnov test. Comparisons were performed with Student's test or Mann–Whitney tests or with  2-test or Fisher's exact test, when appropriate. Selection bias was addressed developing a propensity score [9]. Propensity score was the probability that a patient would receive prophylactic IABP and was computed using a logistic regression modelling including the covariates which are present in Table 1. The C-statistic for this model was 0.9. To control for selection bias, the variable propensity score was included along with the comparison variable (prophylactic or not) in multivariable analyses of outcome producing adjusted OR with 95% CI. Due to the low number of events and the sample size in our study, using a propensity score as the sole means for adjusting outcomes was preferable and provides better adjustment for those factors driving treatment selection bias. A P-value of 0.05 or less was considered statistically significant. All statistical analysis was performed with SPSS 13.0 (SPSS Inc, Chicago, IL, USA).
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3. Results
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3.1. Patient characteristics
A total of 141 patients were considered at high-risk for developing a LCOS. Thirty-eight out of 141 patients (27%) received a prophylactic IABP, the remaining 103/141 patients (73%) underwent myocardial revascularization without preoperative IABP insertion (control). Table 1 shows the baseline characteristics of the study population. Prophylactic IABP patients were more likely to be younger (P<0.0001), with a higher incidence of recent myocardial infarction (P<0.0001), a higher NYHA functional class (P=0.05) and a lower preoperative ejection fraction (P=0.006). No difference was found between groups with regard to EuroSCORE.
3.2. Crude and risk-adjusted outcomes
The median duration of IABP usage in the prophylactic IABP group was 2 (range interquartile 1–2). In the control group, a total of 37/103 patients (35.9%) developed a postcardiotomy LCOS (P<0.0001). All these patients received pharmacologic support and IABP was inserted postoperatively in the operating room for difficulties during weaning from CPB (n=27) or in intensive care for an acute low cardiac output (n=10). The 30-day mortality rate was 11.7% (12/103) in the control group vs. 2.6% (1/38) in the prophylactic IABP group (P=ns). Intensive care unit and ward stay were also significantly lower in the prophylactic IABP group (P=0.02 and 0.01, respectively). No association was noted between groups with regard to postoperative acute renal failure, neurological complications, atrial fibrillation, transfusions and ventilation time (Table 2). There was no conversion to CPB in off-pump CABG procedures. No major complications related to IABP insertion were reported. As shown in Table 3, after adjusting for the propensity score, prophylactic IABP patients had a significantly lower incidence of postcardiotomy LCOS (adjusted OR 0.07; 95% CI 00.1–0.5, P=0.006), and a lower rate of postoperative myocardial infarction (adjusted OR 0.04; 95% CI 0.0002–0.8, P=0.04). Prophylactic IABP patients had a shorter intensive care unit (ICU) (3.8±1.1 vs. 5.2±0.9 days, P0.0001) and ward stay (10.4±0.8 vs. 12.2±0.6 days, P0.0001).
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4. Discussion
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The main finding of this propensity-score based study is that prophylactic IABP insertion, in hemodynamically stable high-risk patients, is safe and effective in reducing postcardiotomy syndrome, perioperative myocardial infarction, as well as length of stay.
IABP is a well-established temporary device for weaning from CPB and for postoperative LCOS. As it has favorable hemodynamic effects on left ventricular performance and coronary arterial blood flow [3], preoperative IABP support may have beneficial hemodynamic and anti-ischemic effect. There are evidences for preoperative IABP use in CABG patients with low ejection fraction undergoing non-elective operation, re-operation, and NYHA class III–IV symptoms [10]. However, indications are less clear in patients hemodynamically stable at high risk to develop postcardiotomy syndrome. The present study, as the consequence of a better preoperative cardiac performance and myocardial revascularization, shows that high-risk stable patients treated with prophylactic IABP have a significant lower morbidity rate and a shorter hospital stay. Inserted at least 2 h before operation, the prophylactic use of IABP might play a key role in the better performance of myocardial muscle [11].
Our study did not demonstrate a significant mortality reduction, even if the control group showed a trend toward a higher mortality rate. Several studies confirm our data showing advantage in terms of outcomes compared to intra- or postoperative insertion in high-risk patients. Christenson et al. [5, 6] showed that preoperative IABP in high-risk patients lowers postoperative mortality and morbidity and shortens the length of hospital stay. Christenson's trials were recently analyzed in a meta-analysis by Field et al. [12], who showed a significant benefit of preoperative IABP with regard to in-hospital mortality and low postoperative cardiac index. Although these studies are conducted on a small population of patients and there is a lack of distinction between prophylactic and therapeutic preoperative insertion of IABP, they are the only randomized trials in the literature. Conversely, Baskett et al. evidenced a lack of evidence of effectiveness in benefit of preoperative IABP insertion, reporting a higher in-hospital mortality with the use of IABP [8]. These results could be correlated to a very high proportion of urgent operations. Excluding patients receiving preoperative IABP for hemodynamic instability, recent myocardial infarction (at most three days before CABG) and those undergoing emergent operations, Holman et al. did not find any survival advantage for patients who received a prophylactic IABP insertion compared to risk-matched patients control showing only a shorter post-CABG length of hospital stay [7]. On the other hand, Gutfinger and colleagues reported that high-risk patients older than 70 years undergoing CABG who received a preoperative IABP had a lower mortality compared to control group [4]. Controversies on mortality data could be related to the heterogeneity of definitions of high-risk patients, to whom are applied liberal criteria dictated by experience and which are not considered conventionally accepted prognostic factors in the EuroSCORE. Recently, Etienne et al. demonstrated that preoperative IABP support associated with off-pump operations was effective in reducing hospital mortality compared with EuroSCORE-predicted mortality [13].
Our patients undergoing off-pump CABG who received prophylactic IABP had no complication and no conversion to CABG procedure was necessary. In order to prevent hemodynamic instability in off-pump CABG, Suzuki et al. reported favorable results in patients with left main coronary artery disease, unstable angina, left ventricular dysfunction and congestive heart failure requiring medical treatment [14]. Regarding the timing of preoperative insertion, we inserted IABP two hours before operation in all cases. Christenson and colleagues did not find any difference in outcome whether the IABP is inserted 2, 12, 24 h preoperatively [11]. In the Benchmark counterpultation outcomes registry, the percentage of IABP-related mortality was 0.053%, major limb ischemia was 0.9% and severe bleeding was 0.9% [15]. We had no IABP-related mortality or morbidity.
There are some limitations to our study. Firstly, the small sample size and the nature of retrospective design. Propensity score is simply a method for reducing bias in observational studies when randomization to treatment groups is not possible. The adjustment with propensity scoring was limited by available variables, which underlines the fact that selection bias could not be completely eliminated. Secondly, in the selection of high-risk patients, unstable angina refractory to medical therapy is at borders between elective and urgent operation.
In conclusion, prophylactic IABP treatment for hemodynamically stable high-risk patients undergoing CABG is safe, reduces LCOS, improves postoperative course showing a trend of survival advantage.
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Abstract
1. Introduction
