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Interact CardioVasc Thorac Surg 2005;4:33-40. doi:10.1510/icvts.2004.097121 © 2005 European Association of Cardio-Thoracic Surgery
Bi-atrial pacing significantly reduces the Incidence of atrial fibrillation post cardiac surgery
Aberdeen Royal Infirmary, Aberdeen, AB25 2ZN, UK *Corresponding author: Tel.: +44 780 154 8122.E-mail address: joeldunning{at}doctors.org.uk (J. Dunning). Received 2 September 2004; accepted 3 September 2004
A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether either right atrial or bi-atrial pacing effectively reduces the incidence of Atrial fibrillation post cardiac surgery. Altogether 458 papers were found using the reported search, of which 16 represented the best evidence on this topic. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results, and study weaknesses were tabulated. We conclude that Right atrial pacing is of no benefit but bi-atrial pacing significantly reduces the incidence of atrial fibrillation with an odds ratio for benefit of 0.51 (95%CI 0.36–0.72) from 11 studies.
Key Words: Thoracic surgery; Atrial fibrillation; Review; Meta-analysis; Pacing
A best evidence topic was constructed according to a structured protocol. This protocol is fully described in the ICVTS [1].
You are concerned to note that the incidence of postoperative atrial fibrillation in your unit is almost 40% after elective cardiac surgery. You have read a recent review that suggests that postoperative atrial pacing may protect patients against atrial fibrillation and as all patients receive right atrial wires in your unit intra-operatively this seems to be a simple opportunity to reduce the incidence of AF without the inherent complications of pharmacological prophylaxis. Thus you resolve to explore the literature further with a view to implementing a departmental policy for post-operative atrial pacing.
In [patients who have undergone cardiac surgery] does [atrial pacing] decrease the incidence of [postoperative atrial fibrillation]?
Medline 1966-August 2004 and EMBASE 1980 to August 2004 using the OVID interface. [exp Cardiac Pacing, Artificial/ OR exp Pacemaker, Artificial/ OR pacing.mp] AND [atrial.mp or biatrial.mp or bi-atrial.mp or bachman$.mp] AND [Atrial fibrillation.mp OR exp Atrial Fibrillation/ OR Atrial flutter.mp OR exp Atrial Flutter/ OR AF.mp OR supraventricular tachycardia.mp OR exp Tachycardia, Supraventricular/] AND [CABG.mp OR Coronary art$ bypass.mp OR Cardiopulmonary bypass.mp OR exp Cardiovascular Surgical Procedures/ OR exp Cardiac Surgical Procedures/ OR exp Coronary Artery Bypass/ OR Cardiac Surgery.mp].
A total of 229 papers were found in Medline and exactly 229 papers were also found in Embase of which 14 were relevant. An additional 2 papers were found by checking reference lists (Table 1).
Crystal et al. [2] performed a meta-analysis in 2002 that looked at pharmacological and pacing strategies for the reduction of AF after Cardiac Surgery. They identified 10 of the 13 completed trials that we identified by our search strategies. They found that Biatrial pacing significantly reduced the likelihood of AF with an Odds ratio of 0.46 (95%CI 0.30–0.71), which was a significant result. They also identified that right atrial and left atrial pacing reduced the odds of AF but that these results were not significant (RA pacing OR 0.68, 95%CI 0.39–1.19 and LA pacing OR 0.57, 95%CI 0.28–1.16). The reported studies varied markedly, however, in their protocols and pacing strategies, with definitions of AF from 1 min of AF to 1 h. In addition, the placing of the wires varied, and the pacing strategies from fixed rates to complex flexible algorithms were used. A more recent review in this area identified 13 studies but did not perform an update of the meta-analysis [18]. We therefore elected to include all the individual trials in this topic so that all these various strategies could be compared. Debrunner in 2004 [3] studied 80 patients undergoing valve surgery with or without CABG. Patients were randomized to Biatrial pacing with an algorithm to keep pacing >10 bpm over the intrinsic rhythm for 3 days. Control patients received right atrial pacing with pacing set to 80 bpm. They demonstrated a reduction in AF from 45% to 20% in the biatrial pacing group, although the administration of beta-blockers was not controlled in this study, and a large number of patients had beta-blockers withdrawn post-operatively. Goette et al. [4] randomized 161 patients with a history of AF undergoing cardiopulmonary bypass. They randomized the patients into 3 groups, controls who had right atrial pacing, which was only used if clinically indicated, a right atrial pacing group with active pacing for 5 days and biatrial pacing with wires placed at Bachmann's Bundle and active pacing used for 5 days. They found no statistically significant results although 24 patients were withdrawn from the study for clinical reasons. Gerstenfeld et al. published 2 studies in 1999 and 2001 [5,12], studying Biatrial pacing, right atrial pacing and controls in 61 patients, and later just comparing biatrial pacing with controls in 188 patients. In the smaller study no significant differences were found although there were only 6–7 occurrences of AF in each group. In their second larger study, the incidence of AF in the control group was 35% but in the biatrial pacing group the incidence was only 19%. On further analysis this difference was attributable only to patients over 70 years of age. Levy et al. [6] performed a large study in 130 patients undergoing first time CABG. Patients were randomized to biatrial pacing with wires in the right atrium and a second pair of wires at Bachmann's Bundle, set to pace at 80 bpm. The control group had a rate of AF of 40% but the biatrial paced group had an incidence of only 15%. This was significant for both monitored and clinically detected AF. Unfortunately, the study protocol required all patients on beta-blockers pre-operatively to have these withdrawn post-operatively. Daoud published a study in Circulation in 2000 [7] that compared control right atrial pacing, right atrial pacing at 85 bpm or 10 bpm above the intrinsic rhythm or biatrial pacing in a double blind fashion. The control group had an incidence of 28% and the right atrial pacing group had an incidence of 32% but the biatrial pacing group had an incidence of only 10%. This was a statistically significant finding. Of note 60% of right atrial wires and 80% of left atrial wires failed by the 5th post-operative day. Fan et al. in 2000 published a study in Circulation [8] that randomized 137 patients to 4 groups, Biatrial, Right atrial, left atrial and a control group. The protocol was a fixed rate of 90 pbm with the rate increased to 10 bpm above the underlying rhythm up to 120 bpm for 5 days. They found that the incidence of AF in the biatrial pacing group was 12.5% but the incidence in the RA, LA and control groups were 36%, 33% and 42%, respectively. Thus they concluded that Biatrial pacing was significantly superior to the other 3 strategies. In addition they found that adequate pacing was possible in all patients for the full 5-day duration of the study. Greenberg et al. [9] studied 154 patients, randomizing them to right atrial, left atrial, biatrial pacing and a control group. Pacing was set to 100 bpm, if the native rhythm was over 80, rate was increased to either 105 or 110 bpm, for 3 days. Assessment of ECG recordings was by blinded cardiologists. They found that the incidence of AF was 8% in the right atrial pacing group, which was significantly lower than left atrial pacing 20%; Biatrial pacing 26% or control 37.5%. Unfortunately, they had considerable problems with the left atrial and biatrial pacing, with 23% and 33% of patients unable to maintain pacing either due to diaphragmatic pacing or high thresholds. Blommaert et al. [10] investigated 96 patients undergoing CABG, randomized to a control group or a right atrial wire group. They used a novel programmed dynamic pacing strategy where the pacemaker had a lower rate of 80 bpm but if the native rhythm rose above this, the pacemaker automatically increased the rate up to a rate of 125 bpm, but kept the rhythm just above that of the native rhythm. This strategy was started on day 2 and continued for 24 h. The control group had an incidence of AF of 27% compared to an incidence of 10% in the pacing group (P=0.036). Chung et al. [11] studied 100 patients who were at least 6 h post elective CABG. Forty-nine patients received AAI pacing at 90 bpm or 10 bpm above the native rhythm up to a rate of 110 bpm for 4 days. They found that the rate of AF was 26% for the AF group and the incidence in the control group was 29%, which was a non-significant finding. In addition they found that there was a significant increase in the atrial ectopic frequency in the paced group. This study had several problems in the pacing group. Eleven patients did not have successful overdrive pacing, and 5 of the 13 patients who went into AF in this group were not actually receiving pacing at the onset of AF. In 1999 Kurz et al. [13] set out to perform a randomized controlled trial in 200 patients, randomized to biatrial pacing with a single wire in the left atrium and two wires on the right atrium. However, they had considerable problems in the pacing group mainly due to sensing failure in 50% of studied patients. In 5 or the 6 patients with pacing failure, this induced atrial fibrillation. In addition 2 patients were withdrawn due to excessive diaphragmatic stimulation and one withdrawn as a wire dislocated and started to cause ventricular stimulation. Schweikert published an abstract in the Journal of the American College of Cardiology [15]. They used atrial pacing with advanced overdrive pacing capabilities to study 86 patients undergoing CABG. They found that there were 11 patients in each group that developed AF and thus concluded that right atrial pacing does not prevent AF. Orr et al. [14] performed a study in 230 patients, randomized to biatrial pacing or controls. They found that the incidence of AF was 17.9% in the biatrial pacing group compared to an incidence of 33.9% in the control group, which was a highly significant result. Au et al. [16] performed a small case-control study that showed no difference between biatrial pacing and controls in two groups of 52 patients. This study was however very small and non-randomized. The AFIST-II trial [17] performed a 2x2 factorial design study in 160 patients looking at both post-operative Amiodarone prophylaxis and also Atrial Pacing at Bachmann's Bundle. They used a pacing rate of 80 bpm increasing to 110 bpm, but pacing was stopped if the native rhythm increased to above 100 bpm. While they showed a significant improvement in AF for amiodarone, they showed no benefit for atrial pacing. The Pacing groups had an incidence of 27% and the control groups had an incidence of 33%. They also had many problems with the pacing algorithm, as 54% of patients had pacing stopped for a period during the trial including 17% stopped due to technical difficulties with the wires. Thus, in summary, of the 11 biatrial pacing studies (including 2 that used Bachmann's Bundle pacing), 6 found significant benefit and 5 found no significant benefit. We combined these results using the DerSimonian and Laird Random Effects Model (Fig. 1a and 1b). This showed that there was a significant benefit to biatrial pacing with an odds ratio of 0.51 (95%CI 0.36–0.72). Of the 8 right atrial pacing studies, 2 found a significant benefit and 6 found no benefit. When the results were again combined by meta-analysis no benefit was found.
While there is a significant benefit to biatrial pacing, several of the papers reported technical difficulties, with loss of sensing, diaphragmatic pacing and LV pacing which led to a number of patients being withdrawn from their respective studies. Thus, if biatrial pacing is used, much care must be used when placing the wires. In addition there were many different algorithms for pacing, although most seemed to pace at 80–90 bpm, raising this higher if the native rhythm went above 80 bpm. Also the number of days that pacing was used varied. AF incidence generally peaked around day 2, thus 3–5 days of pacing may be prudent.
Right atrial pacing is of no benefit but biatrial pacing significantly reduces the incidence of Atrial fibrillation.
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Abstract
1. Introduction
