Pericardial effusion in the post-operative period has been reported to precipitate atrial fibrillation (AF) after cardiac surgery [1, 2]. The occurrence of mild to moderate pericardial effusion is seen in more than half the patients undergoing cardiac surgery [3]. It is therefore axiomatic that by reducing the incidence of pericardial effusion it may be possible to reduce the occurrence of post-operative atrial fibrillation (POAF). Left posterior pericardiotomy, a simple procedure, allows pericardial collection to be drained into the left pleural cavity thereby reducing the incidence of pericardial collection and therefore POAF. This hypothesis has been examined in “the Effect of Posterior Pericardiotomy on the Incidence of Atrial Fibrillation After Cardiac Surgery (PALACS)” trial [4].
The PALACS trial was a single-centre trial that included patients undergoing coronary artery bypass graft (CABG), aortic valve replacement, or aortic surgery in isolation or in combination. Only elective patients were included in the study. Patients undergoing mitral or tricuspid valve surgery or with prior history of cardiac arrythmias were excluded from the study. The intervention was a left posterior pericardiotomy that consisted of 4–5-cm vertical incision posterior to the phrenic nerve and extending from the left inferior pulmonary vein to the diaphragm. Adaptive randomization technique was used and 209 patients in the left posterior pericardiotomy group were compared with 211 patients where no intervention was carried out. The primary outcome was POAF and was measured using continuous cardiac rhythm monitoring or standard 12-lead electrocardiogram (ECG). AF was defined as absence of p waves lasting for greater than 30 s. The strength of the study lies in the fact that it followed an adaptive randomized design. The study was adequately powered with a pre-trial sample size of 322. Following an interim analysis, the POAF rate was found to be lower than expected and the sample size was recalculated at 420. Besides, there were no missing data or loss to follow-up. Patients as well as assessors were blinded to the intervention received.
The incidence of POAF was significantly lower at 17%(37) in the pericardiotomy group compared to 32%(66) in the no-intervention group (p = 0.0007). There were two deaths in the pericardiotomy group and one in the no-intervention group within 30 days after hospital discharge. The need for post-operative antiarrhythmic medications as well as systemic anticoagulation was significantly higher in the no-intervention group. Need for post-operative electrical cardioversion was also higher in the no-intervention group, but not significantly so. The duration for which the AF persisted in the no-intervention group was also much longer than that in the pericardiotomy group (2277 versus 1262 hours). There were no differences in terms of hospital length of stay between the 2 groups. The pericardiotomy group had significantly lower incidence of post-operative pericardial effusion (12% versus 21%) and similar incidence of left pleural effusion (30% versus 32%). Five (2%) of the patients in the no-intervention group were readmitted to the hospital with pericardial effusion while none of the patients in the pericardiotomy group was readmitted due to pericardial effusion. Similar number of patients got readmitted with left pleural effusion, four (2%) in the pericardiotomy group and five (2%) in the no-intervention group. A sub-group analysis carried out showed that while the lower incidence of POAF seen in the overall group was replicated in aortic surgery as well as aortic valve surgery, no significant difference in the rates of POAF was seen in the CABG group. The statistical difference was also seen only in patients < 70 years of age and those with left ventricular ejection fraction < 50%. However, this lack of statistical difference could be because the sub-group analysis was not powered to detect a difference. Apart from left pericardiotomy, age, gender, number of diseased vessels, and post-operative usage of beta blockers were also independent predictors of POAF in the study [4].
The hypothesis that a left posterior pericardiotomy may reduce the incidence of POAF was first assessed in a prospective study quarter of a century ago [1]. Since then, several randomized controlled studies have been carried out and at least 4 meta-analyses on the subject have been published [5–8]. While most of the studies favoured left posterior pericardiotomy for reduction of POAF, the methodology of these studies was sub-optimal, with not all of them reporting the method of randomization. None of the studies reported if blinding was undertaken. There was considerable heterogeneity between the studies and the definitions used for POAF also differed among studies. Besides, patients who did not take β-blockers before the operation were also included in this analysis [7]. The largest meta-analysis included only 1723 patients undergoing left posterior pericardiotomy. There was, thus, a need for an adequately powered and rigorously conducted, randomized trial, a lacuna that was fulfilled by the PALACS trial.
The mechanism by which pericardial collection triggers POAF has been examined in previous studies [2, 9]. Inadequate drainage of the mediastinal blood leads to what is described as “retained blood syndrome”. This constitutes a number of mechanical and inflammatory complications [9]. After surgery, presence of blood clots and fluid in the pericardium can apply a mechanical pressure on the atrium and induce POAF. Apart from this, local inflammation and oxidative stress also play an important role. It has been shown that after cardiac surgery a highly inflammatory and pro-oxidant environment is present within the pericardium which acts as an important trigger for POAF [2]. Shed mediastinal blood undergoes modifications that promote inflammation. Activation of the clotting cascade in the intrapericardial blood produces thrombin and fibrin, which provoke inflammatory responses through release of cytokines and interleukins. Besides, haemolysis of the shed mediastinal blood also occurs in the intrapericardial space, leading to release of free haemoglobin which once oxidized to methaemoglobin further facilitates inflammatory activation [2]. Previous meta-analyses have confirmed that reduced retention of mediastinal blood results in reduced rates of POAF.
Left posterior pericardiotomy is a relatively safe intervention. However, there are theoretical risks of injury to the left phrenic nerve that lies close by, formation of adhesions, and herniation of heart and grafts through the pericardiotomy incision. The transfer of pericardial collection from the pericardium to the left pleura may lead to increased left-sided pleural effusion. However, in the current study, no evidence of any of these complications was seen.
There are few important limitations of the trial. Firstly, the cases included in the study were at lower risk of developing POAF. The study only included patients operated electively. Patients requiring mitral and tricuspid valve surgery were excluded from the study, who are generally at a higher risk of developing AF. The study was also quite heterogenous with valve surgery, aortic surgery, and isolated and combined CABG all included in the study. Not only did the study not show any significant benefit in the CABG group, none of the patients had off-pump coronary artery bypass (OPCAB) graft. Thus, extrapolation of the study findings to those undergoing OPCAB surgery will be erroneous. In fact, the only study that compared the effect of left posterior pericardiotomy on POAF in patients undergoing OPCAB surgery showed no difference in POAF rates between the 2 groups [10].
The PALACS trial provided confirmatory evidence that prevention of pericardial collection reduces rates of POAF. The technique is simple and appears to be a useful non-pharmacological technique to reduce rates of POAF. Despite being an adequately powered study, it only included 420 patients. The total number of reported patients undergoing left posterior pericardiotomy in randomized studies is thus still less than 2000 spread over the last 25 years. Considering that POAF has a major impact on outcomes and resource utilization, poor uptake of the left posterior pericardiotomy technique appears perplexing. The PALACS trial is an important step in the right direction and hopefully will lead to further studies from different parts of the world as the evidence base needs to be increased. A multi-centre study, with much larger number of patients undergoing surgical procedures not included in the PALACS trial, may be the way forward.
Funding
None.
Declarations
Ethics approval
Not applicable as a review article.
Informed consent
Not applicable as a review article.
Conflict of interest
None.
Footnotes
Publisher's note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
References
- 1.Mulay A, Kirk AJ, Angelini GD, Wisheart JD, Hutter JA. Posterior pericardiotomy reduces the incidence of supra-ventricular arrhythmias following coronary artery bypass surgery. Eur J Cardiothorac Surg. 1995;9:150–152. doi: 10.1016/S1010-7940(05)80063-6. [DOI] [PubMed] [Google Scholar]
- 2.St-Onge S, Perrault LP, Demers P, et al. Pericardial blood as a trigger for postoperative atrial fibrillation after cardiac surgery. Ann Thorac Surg. 2018;105:321–328. doi: 10.1016/j.athoracsur.2017.07.045. [DOI] [PubMed] [Google Scholar]
- 3.Pepi M, Muratori M, Barbier P, et al. Pericardial effusion after cardiac surgery: incidence, site, size, and haemodynamic consequences. Br Heart J. 1994;72:327–331. doi: 10.1136/hrt.72.4.327. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Gaudino M, Sanna T, Ballman KV, et al. Posterior left pericardiotomy for the prevention of atrial fibrillation after cardiac surgery: an adaptive, single-centre, single-blind, randomised, controlled trial. Lancet. 2021;398:2075–2083. doi: 10.1016/S0140-6736(21)02490-9. [DOI] [PubMed] [Google Scholar]
- 5.Biancari F, Mahar MAA. Meta-analysis of randomized trials on the efficacy of posterior pericardiotomy in preventing atrial fibrillation after coronary artery bypass surgery. J Thorac Cardiovasc Surg. 2010;139:1158–1161. doi: 10.1016/j.jtcvs.2009.07.012. [DOI] [PubMed] [Google Scholar]
- 6.Hu X-L, Chen Y, Zhou Z-D, Ying J, Hu Y-H, Xu G-H. Posterior pericardiotomy for the prevention of atrial fibrillation after coronary artery bypass grafting: a meta-analysis of randomized controlled trials. Int J Cardiol. 2016;215:252–256. doi: 10.1016/j.ijcard.2016.04.081. [DOI] [PubMed] [Google Scholar]
- 7.Xiong T, Pu L, Ma Y-F, et al. Posterior pericardiotomy to prevent new-onset atrial fibrillation after coronary artery bypass grafting: a systematic review and meta-analysis of 10 randomized controlled trials. J Cardiothorac Surg. 2021;16:233. doi: 10.1186/s13019-021-01611-x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Gozdek M, Pawliszak W, Hagner W, et al. Systematic review and meta-analysis of randomized controlled trials assessing safety and efficacy of posterior pericardial drainage in patients undergoing heart surgery. J Thorac Cardiovasc Surg. 2017;153:865–875.e12. doi: 10.1016/j.jtcvs.2016.11.057. [DOI] [PubMed] [Google Scholar]
- 9.Boyle EM, Jr, Gillinov AM, Cohn WE, Ley SJ, Fischlein T, Perrault LP. Retained blood syndrome after cardiac surgery: a new look at an old problem. Innovations (Phila) 2015;10:296–303. doi: 10.1097/imi.0000000000000200. [DOI] [PubMed] [Google Scholar]
- 10.Haddadzadeh M, Motavaselian M, Rahimianfar AA, Forouzannia SK, Emami M, Barzegar K. The effect of posterior pericardiotomy on pericardial effusion and atrial fibrillation after off-pump coronary artery bypass graft. Acta Med Iran. 2015;53:57–61. [PubMed] [Google Scholar]