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Eur J Cardiothorac Surg 2005;27:887-892
© 2005 Elsevier Science NL
a Department of Cardiothoracic Surgery, The Cardiothoracic Centre, Liverpool, UK
b Department of Clinical Governance, The Cardiothoracic Centre, Thomas Drive, Liverpool L14 3PE, UK
Received 9 November 2004; received in revised form 31 January 2005; accepted 2 February 2005.
* Corresponding author. Tel.: +44 151 293 2336; fax: +44 151 288 2371. (E-mail: tony.grayson{at}ctc.nhs.uk).
| Abstract |
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Key Words: IABP support CABG Valve surgery Mortality
| 1. Introduction |
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There exists a clear distinction between those haemodynamically stable patients with a high estimated pre-operative risk who have an IABP inserted prophylactically and those patients who are haemodynamically compromised who require therapeutic IABP support to enable them to survive until surgery. The requirement for IABP support to wean from bypass or in the post-operative period suggests that severe cardiac injury has already occurred.
This study was undertaken on patients who had coronary revascularisation and/or valvular heart surgery over the last 5 years in a single institution. We performed an evaluation of the effect timing of IABP support had on 1-year survival.
| 2. Methods |
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Preoperative (Table 1), operative (Table 2) and post-operative (Table 3) data were collected prospectively in our cardiac surgery registry, as part of routine clinical practice. Methods of data collection have previously been published [2]. A retrospective case note review was carried out to collect additional information on indication for, timing of and complications of IABP support.
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2.2. IABP support and timing of insertion
A total of 237 (3.08%) patients received IABP support. They were allocated into groups based on the timing of the IABP insertion:
All IABPs were supplied by Datascope (New Jersey, USA). The balloon size was either 34 or 40ml and were all either 8.5 or 9 French. Open and percutaneous techniques via the femoral artery were used for IABP insertion in all cases.
2.3. One-year survival
Patient records were linked to the National Strategic Tracing Service (NSTS), which records all deaths in the United Kingdom. To establish current vital status for the patient population at 1-year, patients were matched to the NSTS based on patient name, National Health Service number, date of birth, gender, and postcode. Follow-up at 1-year was complete.
2.4. Statistical methods
Due to the non-normality of continuous variables, data are shown as median, except for number of grafts and valves which are shown as a mean value (because of the low averages). Categorical variables are shown as a percentage. Comparisons were made with KruskalWallis and Chi-square tests as appropriate. The European System for Cardiac Operative Risk Evaluation (EuroSCORE) was derived to assess differences in patient case-mix [5]. Deaths occurring as a function of time are described using KaplanMeier survival curves [6]. A multivariate forward stepwise Cox proportional hazards regression analysis was undertaken to identify independent predictors for 1-year mortality [7]. All the variables listed in Tables 13 were offered as potential risk factors, including the timing of IABP support. The final risk model was used to risk adjust the KaplanMeier survival curves. All statistical analysis was performed retrospectively with SAS for Windows Version 8.2.
| 3. Results |
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The numerous differences that existed between the groups is best illustrated by the Additive EuroSCORE (Table 1). The two preoperative IABP support groups (Groups B and C) had significantly higher estimated risk than those not requiring support (Group A). Those patients who required intra- and post-operative IABP support (Groups D and E) also had significantly higher estimated risk than those not requiring support. This preoperative risk was not as high as for those in Group B or C.
3.2. Indications for IABP support
The indications for IABP support are shown in Table 4. All but one patient in Group C had coronary artery bypass grafts performed and 12 patients had mitral valve replacement or repair. Fifteen patients had unstable angina. The other 10 patients had suffered from myocardial infarctions within the previous month and were haemodynamically unstable and thus required IABP support.
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In Group E the IABP was inserted after post-operative low cardiac output did not improve with judicious fluid loading and inotropic support.
3.3. IABP complications
Major IABP-related complications occurred in seven patients (2.9%). Four of these patients were women, two patients had peripheral vascular disease and none were diabetic.
One patient required femoral artery repair and another required femoral embolectomy. Two patients developed limb ischemia that resolved when the IABP was removed. Two patients developed IABP insertion site infection that responded to antibiotics and one patient developed a false aneurysm of the femoral artery that resolved with conservative management.
There were also three cases in which the IABP developed a leak and no clinical complication resulted.
3.4. Survival
Four-hundred and fifty (5.8%) deaths occurred during the 1-year follow-up, this included 230 (3.0%) deaths that occurred within 30 days of surgery. The number of patients at risk of death at 1-year in Groups A, B, C, D, and E were 7112, 23, 15, 76, and 28, respectively. Freedom from death at 30-days and 1-year for Groups AE are shown in Fig. 1. Patients who received IABP support at any time were more likely to die within the first 30 days. Patients who received post-operative IABP support had the lowest 30-day survival at 55.4%.
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| 4. Discussion |
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Other studies [810] have suggested this but not analysed the effect timing of IABP support had on patient survival. Patients who require post-operative IABP support are known to have high hospital mortality. However, these patients also have a higher adjusted mortality up to 1-year after the initial operation.
The relative benefits of pre-operative IABP support have only recently been quantified [11]. Cardiac surgery often results in some degree of temporary myocardial dysfunction and inotropes are used to provide temporary haemodynamic support. Escalating inotropic requirements usually preceed commencement of IABP support. In this series because of procedural complications during surgery, some haemodynamically stable patients were identified as having an increased risk of developing low cardiac output. Post-operative IABP support was commenced prophylactically before escalating inotropic requirements. Alternately, an arterial line was inserted into the femoral artery to facilitate IABP insertion if it became necessary. These patients may have benefited from this early intervention, but the numbers were too small to analyse.
The risks of vascular injury with the IABP cannot be ignored [4,1216] and opinions vary regarding the relative costs of escalating pharmacologic therapy or of using an IABP. These factors may affect the decision to use an IABP, but they have been minimised as a result of decreased IABP cost, improvements in IABP timing software (making them easier to use) and smaller catheter sizes. The smaller IABP catheter size may have also contributed to the lower incidence of vascular complications requiring surgical intervention in this series than in earlier series.
In our experience when haemodynamic instability occurs during OPCAB surgery, IABP support is preferred over the use of inotropes or cardiopulmonary bypass. Of interest is that all of the patients in whom the IABP was used to provide OPCAB support were free of serious complications and were alive at 1 year. This is a relatively recent trend [17] and suggests a greater acceptance of the IABP as a means of cardiac support with only a small associated risk.
Prophylactic IABP support in high-risk patients in this study resulted in 1-year survival that did not differ significantly from that of patients who did not require IABP support. This corroborates the evidence from Christenson [18] who showed that preoperative IABP insertion in high-risk cases reduced the cost of inpatient treatment, the length of stay in the intensive care and the in-hospital mortality. However, Holman et al. [19] used an adjusted case-matched model to show no survival benefit at 1-year in 550 high risk CABG patients with preincision IABP compared to controls matched using a propensity-score. Dunning and Prendergast reviewed the published evidence [20] and showed that there is evidence to support preoperative IABP insertion in patients with two of LVEF <30 or 40%, left main stem disease, unstable angina or redo-operation.
In Groups CE some degree of cardiac insult occurred that caused haemodynamic compromise sufficiently great to require IABP support. The trend for a significant, but gradual decrease in the risk-adjusted survival at 1-year among the groups suggests that the cardiac insult suffered was sufficient enough to have a prolonged negative impact. Therefore, the requirement for mechanical haemodynamic support should be considered as a negative long-term prognostic indicator.
The observed 30-day mortality for all patients treated with an IABP was 34%. This is comparable to the 3661% in other reported series [21]. In this series, major IABP-related complications only occurred in 2.9% of patients. This compared favourably with the morbidity reported in other series [12,13,2224] that varied between 8 and 18%. The smaller catheters used in this series (8 and 9.5 French) could have been responsible for the apparent reduced complication rate. Recognised risks for IABP-related complications include female gender, peripheral vascular disease, older age and obesity [14,15]. None of these associations were found to be significant in this study.
However, although almost all insertions were percutaneous, a complete record of method of insertion (percutaneous or open surgical) was not kept. Method of insertion appears to have a significant effect on the complication rate [16], however, we cannot comment on this effect.
Arafa et al. [21] reported a 10-years series of cardiac surgery patients operated on during the 1980s in which IABP use was associated with an early mortality rate of 52.6% and the actual survival rates at 1, 5 and 10 years was 40, 32 and 22%, respectively. Both Benchmark registry [4,25] data and Baskett's review of IABP use in cardiac surgery [9] have demonstrated the evolution of the indications for IABP use. Whereas the conclusions that were made in these early studies were valid, patient selection and improvements in peri-operative management may influence the results in a more recent cohort of patients.
This is a retrospective analysis involving data collected prospectively and validated and is subject to the limitations of all such studies. Patients with a recognised high-risk (such as post-infarction ventricular septal defect repair) were not included. Selection bias is likely to have affected our results because the timing of insertion was based on clinical judgement and was not controlled by protocol. Controversy persists regarding the indications for IABP use [16]. It would be impossible to arrange a randomised trial involving intra- and post-operative IABP insertion mainly because of issues related to consent and sample size. This study, however, gives an accurate picture of current clinical practice.
Because patients with a high estimated pre-operative risk are more likely to require IABP support we attempted to analyse the effect timing of IABP support had on patients with good estimated pre-operative ventricular function. Unfortunately, the patient numbers were too small to allow adequate analysis. The 1-year study period was chosen in order to obtain complete follow-up. A longer study period may further highlight the differences identified.
In conclusion, patients who require unplanned peri-operative IABP support appear to have an increased mortality at 1-year. Therefore, earlier IABP support as part of surgical strategy would appear to be a strategy worth pursuing.
| Acknowledgments |
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| References |
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