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© 2004 European Association of Cardio-Thoracic Surgery
Does off-pump coronary artery surgery reduce the incidence of postoperative atrial fibrillation?Department of Cardiac Surgery, Alder Hey Hospital, Liverpool L12 2AP, UK * Corresponding author. Address: Department of Cardiothoracic Surgery, Freeman Hospital, Freeman Road, Newcastle, NE7 7DN, UK. Tel./fax: +44-780-1548-122. (E-mail: joeldunning{at}doctors.org.uk). Received July 23, 2004; accepted July 27, 2004
A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether off-pump coronary artery surgery reduces the incidence of postoperative atrial fibrillation. Altogether 107 papers were found using the reported search, of which 18 presented the best evidence to answer the clinical question. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results, and study weaknesses of these papers are tabulated. We conclude that off-pump coronary artery surgery significantly reduces the incidence of postoperative atrial fibrillation with a number needed to treat of 20 to prevent one case of AF.
A best evidence topic was constructed according to a structured protocol. This protocol is fully described in the ICVTS [1].
You are about to attend a cardiothoracic conference in Leipzig and you are interested in possible intra-operative interventions that you could perform to reduce the incidence of atrial fibrillation. You have seen papers on bi-atrial pacing, posterior pericardotomy, and ventral cardiac denervation, which you think may reduce the incidence of AF. You present this to a colleague who tells you that you do not need to bother with any of these manoeuvres, which have very little evidence for them, as there is outstanding evidence that off-pump surgery alone will greatly reduce your incidence of AF. You are sceptical of his view and therefore resolve to look up the evidence for this.
In [patients undergoing coronary artery surgery] does [off-pump surgery compared to on pump surgery] reduce the incidence of [postoperative atrial fibrillation].
Medline 1966–July 2004 using the Ovid interface. [exp Cardiovascular surgical procedures/ OR cardiovascular surgical procedures.mp OR exp Thoracic surgery/ OR Thoracic surgery.mp OR exp Coronary Artery bypass/ OR coronary artery bypass.mp OR CABG.mp OR coronary surgery.mp OR cardiac surgery.mp OR revascularization.mp] AND [off-pump coronary artery surgery.mp OR beating heart surgery.mp OR off-pump.mp OR off pump.mp OR midcab.mp OR midcabg.mp OR opcab$.mp] AND [atrial tachyarrhythmia$.mp OR exp atrial fibrillation/ OR exp atrial flutter OR atrial flutter.mp OR atrial fibrillation.mp OR supraventricular arrhythmia$.mp OR expTachycardia, Supraventricular/ OR AF.mp] OR [meta-analysis.af AND exp Thoracic surgery/].
One hundred and seven papers were found of which 7 were deemed to be relevant. In addition cross-checking of the reference lists, suggestions from Journal Club members and hand checking Cardiothoracic Journals published this year revealed a further nine papers. These papers are presented in Table 1.
Reston et al. [2] performed a comprehensive and well-balanced meta-analysis in 2003 of the short term and mid-term outcomes of ‘off-pump coronary bypass surgery’ (OPCAB) versus conventional coronary arterial bypass surgery (CABG). Using comprehensive search strategies and strict entry criteria, they selected 28 studies from 180 reviewed papers that reported the incidence of AF in these patients. They found that there was a highly significant reduction in AF in the OPCAB group (Odds ratio of 0.69 in favour of OPCAB). There was, however, significant heterogeneity (or disagreement that cannot be explained by chance) between these studies that they could not account for. However, if only the randomised controlled trials were included, the difference was increased rather than decreased. They did caution that most studies excluded patients such as non-elective surgery, re-operation, renal failure and impaired ejection fraction. While Reston et al. also found significant benefits in terms of stroke, MI and mortality, a meta-analysis by Van der Heijden et al. in 2004 [3] that assessed only RCTs disagreed with their meta-analysis, finding that there was no significant difference in the combined end-point of MI, death or stroke. Although this study did not look at AF it is interesting to note that this meta-analysis also included, the Octopus study [4], the SMART study [5] and an RCT from Hawaii [6]. This calls into question whether the meta-analysis by Reston et al. is already outdated. In addition, yet another meta-analysis by Parolari et al. in 2003 [7], also found no difference in this composite outcome measure of stroke, MI, or death. Again this meta-analysis did not extract data on AF but calls into question the findings by Reston et al. due to the marked difference in their findings. Ascione and Angelini performed a pooled meta-analysis of BHACAS 1 and 2 [8]. They showed that the incidence of AF reduced from 37% to 13%, which was a highly significant finding. This was despite showing no difference in mortality or cardiac events. A meta-analysis by Athanasiou et al. in 2004 [9] specifically asked the question of whether OPCAB reduced the incidence of AF in elderly patients undergoing coronary arterial surgery. They found that in the eight studies that they identified, the incidence in the OPCAB group was 22% but in the CABG group it was 28%, which was significant. However, this study had many flaws. It only included cohort studies from 1999 to 2003 identified from Medline although the reasons for this narrow timeframe were not explained. More importantly no attempt was made to contact the authors of the many RCTs in this area to ask for their data on AF in the over 70s age group. Thus, this is a small meta-analysis of non-randomised patients only. Of the recent randomised trials not included in the Reston et al. meta-analysis. The SMART Trial [5] of 200 patients randomised to either OPCAB or CABG found no significant difference in AF but with an incidence of 16% in the OPCAB group and 22% in the CABG group there was a trend towards reduced incidence in OPCAB surgery. In contrast, the PRAGUE-4 trial [10] that randomised 400 patients to OPCAB or CABG found no difference at all in the incidence of AF. The OPCAB group had an incidence of 20% compared to an incidence of 24% in the CABG group. Unfortunately, the PRCT by Khan, Pepper et al. published in the New England Journal of Medicine in 2004 [11] and a PRCT by Taggart et al. in 2004 [12] published in Circulation did not report their findings of post-operative AF. The OCTOPUS trial [13] found no difference in AF between the two groups with a 20% incidence in the OPCAB group and a 21% incidence in the CABG group. Muneretto et al. performed a PRCT in 176 patients comparing total arterial OPCAB with total arterial CABG [14]. They found that the incidence of AF was 22% in the OPCAB group and 35% in the CABG group, which showed a strong trend towards a lower incidence in the OPCAB group but had a P value of 0.06. Gerola et al. [19] performed an RCT in 2004 in Brazil in 160 patients and found a low incidence of AF in both groups. The finding of 9% in the OPCAB group and 5% in the CABG group was far lower than other studies, and calls into question the measurement of AF in their study, which was not described in the protocol. Lee et al. in 2003 [6] performed a small RCT in 60 patients, and found an incidence of AF of 23% in OPCAB group and 39% in the CABG, but this was not statistically significant. Although not an RCT, Salamon et al. performed a retrospective cohort study in 2003 [15] that specifically looked at whether OPCAB reduced the incidence of AF. The 252 patients having OPCAB had an incidence of 8.8%, whereas the incidence of AF in 1470 CABG pts receiving prophylactic B-Blockers was 11.6%. When a matched group for number of grafts was found the CABG AF frequency of AF reduced to 9.4%. It should be remembered that there are many weaknesses inherent to the retrospective cohort design of this study including intergroup demographic differences and possible variation in AF definition. Therefore, although we found further cohort studies we excluded these from this topic. Thus in summary three meta-analyses were found that assessed AF in OPCAB versus CABG. They all found a significant reduction in AF with OPCABG. Six further RCTs were identified that were published after several of these meta-analyses. None of them identified a significant difference individually however if you summate their findings there was a 17.8% AF rate in the OPCAB group (114/642) but a 23% rate of AF in the CABG group (144/620). This corresponds to an odds of 0.76 (using a random effects model) with a probability of 1.6% that the results are non-significant (Fig. 1). This finding, therefore, agrees with the already performed meta-analyses that found significant differences. Our summary of the recent RCTs gives a number needed to treat of 20 to avoid one incidence of AF.
OPCAB reduces the incidence of postoperative atrial fibrillation with a number needed to treat of 20 to prevent one case of AF.
Author: Dr. John Pepper, Royal Brompton Hospital, Department of Surgery, Sydney Street, London SW3 6NP, UK Date: 23-Aug-2004 Message: This is a very interesting systematic review. As the authors point out, AF is very rarely the primary outcome measure in randomised controlled trials of on versus off-pump in coronary artery surgery. Furthermore, off-pump is a heterogeneous group, not only with respect to the conduct of the operation but to the use of prophylactic antiarrhythmic agents. An important unanswered question is to what extent does a reduction in the incidence of AF in OPCAB lead to a reduction in stroke? It is probably in the over 70 age group that this difference will be detectable, but dissecting out AF from other causes of stroke will be very difficult.
doi:10.1016/j.icvts.2004.07.016
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Abstract
1. Introduction
