Ann Thorac Surg 2003;76:1988-1992
© 2003 The Society of Thoracic Surgeons
Original article: cardiovascular
A multicenter comparison of intraaortic balloon pump utilization in isolated coronary artery bypass graft surgery
Roger J. F. Baskett, MDa*,
Gerald T. O'Connor, PhDb,
Gregory M. Hirsch, MDa,
William A. Ghali, MDc,
Kathy Sabadosa, MPHb,
Jeremy R. Morton, MDd,
Cathy S. Ross, MSb,
Felix Hernandez, MDe,
William C. Nugent, Jr, MDf,
Stephen J. Lahey, MDg,
Donato A. Sisto, MDb,
Lawrence J. Dacey, MDf,
John D. Klemperer, MDe,
Robert E. Helm, Jr, MDh,
Andrew Maitland, MBi Northern New England Cardiovascular Disease Study Group
a The Maritime Heart Center, Halifax, Nova Scotia, Canada
b Departments of Medicine and Community and Family Medicine and the Center for the Evaluative Clinical Sciences, Dartmouth Medical School, Hanover, New Hampshire, USA
c Department of Medicine, Health Sciences Centre, Department of Medicine, University of Calgary, Calgary, Alberta, Canada
d Department of Surgery, Maine Medical Center, Portland, Maine, USA
e Department of Surgery, Eastern Maine Medical Center, Bangor, Maine, USA
f Department of Cardiology, Dartmouth Hitchcock Medical Center, Lebanon, New Hampshire, USA
g Department of Surgery, University of Massachusetts Memorial Health Care, Worcester, Massachusetts, USA
h Department of Surgery, Portsmouth Regional Hospital, Portsmouth, New Hampshire, USA
i Division of Cardiac Surgery, University of Calgary, Calgary, Alberta, Canada
Accepted for publication June 30, 2003.
* Address reprint requests to Dr Baskett, The Maritime Heart Center, Room 2269 NHI, QE II HSC, 1796 Summer St, Halifax, Nova Scotia, Canada, B3H 3A7
e-mail: rogerbaskett{at}hotmail.com
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Abstract
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BACKGROUND: Single-center studies suggest substantial variation in intraaortic balloon pump (IABP) utilization. Our purpose is to examine IABP utilization over time and across medical centers.
METHODS: This was a prospective cohort of 29,961 consecutive patients undergoing isolated coronary artery bypass graft surgery, between 1995 and 2000, at 10 centers (eight in northern New England and two in Canada).
RESULTS: A total of 2,678 (8.9%) patients received an IABP. The rate of preoperative IABP insertion was 6.3%, and that of intra- or postoperative insertion was 2.6%. During the 6 years, IABP use increased from 7.0% to 10.3% (ptrend <0.001). Preoperative IABP insertion increased from 5.4% to 7.8% (ptrend < 0.001). There was no significant increase in intra-/postoperative IABP insertion 1.7% to 3.4% (ptrend = 0.34). Adjustment for changes in patient and disease characteristics did not substantially alter these results. The rate of IABP use varied substantially by center, from 5.9% to 16.4% (p < 0.001). Adjustment for patient and disease characteristics resulted in variation from 4.8% to 12.8% across the 10 centers (p < 0.001). The adjusted rates of preoperative IABP insertion varied from 3.6% to 13.7% (p < 0.001), and the rates of intra-/postoperative IABP insertion ranged from 1.0% to 5.2% (p < 0.001). There was no significant correlation between the rates of preoperative and intra-/postoperative IABP use (rs = 0.085, p = 0.815).
CONCLUSIONS: During the 6 years, there was a 47% increase in the rate of IABP utilization. Even after adjustment, there was almost threefold variation in IABP use across centers. This variation likely reflects lack of consensus on the appropriate use of the IABP in CABG patients.
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Introduction
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The intraaortic balloon pump (IABP) was first employed clinically in 1968 for supporting patients with cardiogenic shock after acute myocardial infarction [1]. Soon, its use was expanded to postoperative support, and as an aid in weaning from cardiopulmonary bypass[2, 3]. More recently, the IABP has been increasingly used for the preoperative support of patients with unstable coronary syndromes and cardiogenic shock [4]. These remain the three principal indications for its use in the cardiac surgical patient.
Numerous single-center reports suggest that there are different patterns of IABP use in cardiac surgery [4–8]. One multicenter comparison using administrative data has also found considerable variation in use between centers, even after risk adjustment [9]. Large-scale multicenter studies with detailed clinical data have not yet been done. Thus current patterns of IABP use in cardiac surgery are not well described.
Our purpose was to examine the trends in IABP use in isolated coronary artery bypass graft (CABG) patients over time, and across 10 tertiary care cardiac surgical centers in the United States and Canada.
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Patients and methods
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A prospective cohort study of IABP use in CABG was conducted. There were 10 participating medical centers; eight were members of the Northern New England Cardiovascular Disease Study Group (NNECDSG) and two were from Canadian heart centers (Halifax, Nova Scotia, Calgary, Alberta). The Internal Review Boards of the participating institutions approved this study. The population consisted of 29,961 consecutive patients undergoing isolated CABG between 1995 and 2000; 2,678 (8.9%) received an IABP during the index hospitalization. Patients undergoing CABG surgery, which was incidental to heart valve repair or replacement, resection of a ventricular aneurysm, or other surgical procedure, were not included in these analyses.
Data were collected on the following variables: patient gender and age; body surface area; presence of comorbidities (diabetes mellitus, chronic obstructive pulmonary disease, peripheral vascular disease renal insufficiency [creatinine >177 µmol/L]); cardiac catheterization results (ejection fraction [EF], number of diseased coronary arteries [10], and the percentage stenosis of the left main coronary artery).
The use of an IABP was coded as none, preoperative insertion, and intra- or postoperative insertion. Cardiac catheterizations were performed at the participating or referring institutions using their own methods during the course of regular clinical care. Priority at surgery (elective, urgent, emergent) was assessed by the cardiothoracic surgeons using definitions previously described [11]. Briefly, "emergent" meant that medical factors relating to the patient's cardiac disease dictated that surgery should be performed within hours to prevent morbidity or death, "urgent" meant that medical factors required the patient to stay in the hospital for an operation before discharge, and "elective" meant that medical factors indicated the need for operation, but the clinical situation permitted discharge from the hospital with readmission at a later date. There were no differences in the NNECDSG and Canadian data sets except in priority at surgery. Canadian data were recoded to match the NNECDSG definitions of "urgent" and "elective."
Statistical methods
Standard statistical methods were used for the calculation of differences in means (one-way analysis of variance), a nonparametric test of the linear component of trend, Spearman's rank order correlation statistic (rs) and the 
2 test [12]. Logistic regression techniques were used for multivariate analysis and for the calculation of adjusted rates. Rates of IABP use were adjusted for observed differences in preoperative patient and disease characteristics [13]. All analyses were performed using the STATA statistical program [14]. Statistical significance was defined as a two-tailed p value less than or equal to 0.05.
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Results
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Figure 1
shows the proportion of patients receiving an IABP by year of surgery for all 10 centers. During this time period, the crude cumulative rate (preoperative plus intra- or postoperative placement) of IABP usage increased monotonically from 7.0% to 10.3% (ptrend < 0.001). The rate of preoperative IABP insertion also increased, from 5.4% to 7.8% (ptrend < 0.001). The rate of intra- or postoperative insertion of IABP varied by year from 1.7% to 3.4%, but there was no evident trend (ptrend < 0.34).
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Fig 1. Crude rates of intraaortic balloon pump use among Northern New England Cardiovascular Study Group and Canadian centers organized by year. Dark bars = preoperative; shaded bars = intra-/postoperative.
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During this 6-year time period, several patient or disease characteristics changed. The proportion of patients at least 80 years of age increased somewhat (ptrend < 0.01) and the proportion of patients with comorbid conditions (diabetes, peripheral vascular disease, and renal failure [for renal failure, p = 0.17]) also increased significantly. The proportion with prior CABG or with chronic obstructive pulmonary disease decreased significantly (Table 1).
However, adjustment of the cumulative rates of IABP use for changes in patient or disease characteristics (including age, gender, ejection fraction, priority at surgery, prior CABG surgery, diabetes, peripheral vascular disease, renal failure, chronic obstructive pulmonary disease, and body mass index) did not substantially change these results (ptrend < 0.001) (Table 1). Even after accounting for changes in patient and disease characteristics, during these 6 years, there was nearly a 50% increase (from 7.0% to 10.6%) in the rate of IABP use among CABG patients. This increase was largely the result of increased use in the preoperative period (Fig 1).
Figure 2
shows the variation in IABP use by medical centers. The crude cumulative rate of IABP usage (preoperative plus intra- or postoperative placement) varied from 5.9% to 16.4% (p < 0.001). After adjustment for differences in patient and disease characteristic (as described above), the rates ranged from 4.8% to 12.8% (p < 0.001) (Table 2).
The crude rate of preoperative IABP insertion varied from 4.5% to 15.2%. The adjusted rates range from 3.6% to 13.7% (both p < 0.001). Crude rates of intra- or postoperative IABP insertion ranged from 1.2% to 4.5%, and the adjusted rates range from 1.2% to 5.2% (both p < 0.001) (Fig 2).
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Fig 2. Crude rates of intraaortic balloon pump use among Northern New England Cardiovascular Study Group and Canadian centers organized by center. Dark bars = preoperative; shaded bars = intra-/postoperative.
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The relationship between the rates of preoperative and intra- or postoperative IABP insertion by center is shown in Figue 3. On this bivariate plot, each symbol represents one of the 10 participating medical centers, the horizontal axis shows the rate of preoperative IABP usage, and the vertical axis shows the rate if intra- or postoperative IABP usage. The figure does not show any obvious correlation between preoperative and intra- or postoperative IABP usage. Spearman's rank order correlation coefficient showed only a very weak positive correlation that did not reach statistical significance (rs = 0.085, p = 0.815).
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Fig 3. Correlation between preoperative and intra- or postoperative IABP use by centers. Diamonds indicate individual centers.
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Comment
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There was a trend to increasing use of the IABP over time, which persisted after adjustment for patient and disease characteristics. The increased use was largely in the preoperative period (Fig 1). This may be a reflection of the increased use of cardiac catheterization in the setting of acute coronary syndromes. A similar trend has been observed in some institutions [4, 15], although several centers still report quite low rates of preoperative IABP utilization in contemporary series (0.8% and 0.6% of all cases) [7, 8]. A series of small randomized controlled trials from a single institution demonstrated a protective effect of preoperative IABP insertion in high-risk patients [16–19]. This also may have had an impact on the increased use of preoperative IABPs in our centers.
The variation in IABP use between different centers is dramatic, and is not accounted for by patient factors (Table 2). This range is similar to that seen in the previous multicenter comparison by Ghali and associates (7.8% to 21.8%), and also that reported in single centers (5.2% to 17%) [4, 8]. This wide variation in use likely reflects a lack of consensus on the indications for IABP use. As such, it represents differing philosophies of management, in the absence of adequate data on IABP effectiveness [5, 9, 20].
One might hypothesize that a higher proportion of preoperative IABP use would reduce the need for intra- or postoperative balloon insertion. However there was no correlation between the proportion of patients receiving intra- or postoperative IABP support, and the proportion in receipt of preoperative IABPs, across centers (Fig 3). Intraoperatively or postoperatively, the IABP is used more often for low cardiac output rather than ischemia (as is the case with the majority of preoperative insertions), and thus represents a different group of patients [21, 22]. The relatively constant rate of intra- and postoperative use over time may reflect a background rate of intra- and postoperative complications, rather than a group of patients who may have benefited from a preoperative IABP [15]. Intra- and postoperative IABP use is much harder to predict than preoperative use because intra- and postoperative insertion is usually in response to unexpected difficulties [5, 6]. Presumably, these patients were considered lower risk, and or, were more stable preoperatively than those receiving a preoperative IABP.
Limitations
Our 10 centers may not be representative of practices in other regions. However, the rates of use we have found are similar to those published by single institutions [4, 5, 8]. The variation in IABP use was not explained by the preoperative patient factors examined. Much of the variation in utilization is likely determined by the practice patterns of different institutions and physicians. We were not able to examine the impact of individual cardiologists and surgeons on IABP use. In addition, the specific indication for IABP placement was not captured in our databases, and would be useful to examine.
Conclusions
This study demonstrates an increased use of the IABP over time, and a wide variation in the use of the IABP across centers. This likely reflects a lack of consensus on the use of the IABP in cardiac surgery. Despite over 30 years of clinical experience, the optimal use of the IABP is unknown. In particular, the optimal rate of preoperative IABP use, and the identification of those patients who derive the greatest benefit from the IABP, are yet to be determined. Further work is required to examine the association between patient outcomes and the various rates of IABP utilization. This would allow for evidence-based criteria for IABP use, and lead to the optimization of IABP utilization.
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References
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Abstract
Introduction
