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Atrial fibrillation (AF) after cardiac surgery is a common phenomenon reaching an incidence of 20-50% with a significant toll on postoperative complications, hospital stay, readmission and utilization of resources. Such patients have increased morbidity from stroke, myocardial infarction, congestive heart failure, arrhythmias from antiarrhythmic drugs and bleeding caused by anticoagulant use. Although there have been multiple studies done in the past to address post cardiac surgery atrial fibrillation majority of them focused on prevention strategies using prophylactic measures. The AFFIRM trial7 addressed rate vs rhythm control in nonsurgical patients, however conclusive evidence of whether this could be extrapolated to post cardiac surgery atrial fibrillation was lacking. This article explores the current literature on post cardiac atrial fibrillation rate versus rhythm control.
In addition to the mechanisms already known for AF, there are other pathophysiological changes that come into play post cardiac surgery. These include dispersion of atrial refractoriness, prolonged phase 3 depolarization, prolonged interatrial conduction time but decreased conduction velocity, escalated automaticity and electrolyte imbalances in the perioperative period that augment pre-existing degenerative myocardial changes in the atria.
Perioperative Risk Factors
Although the usual risk factors for atrial fibrillation apply, some perioperative factors increase the propensity to develop AF. Pericarditis, atrial injury from suturing or cannulation, acute atrial enlargement from volume or pressure overload, ischemia, prolonged aortic cross-clamp and bypass times, excessive use of postoperative inotropes, pulmonary comorbidities are some of the additional insults that can predispose to AF in post cardiac surgery population. Off pump CABG and preservation of the anterior fat pad are two negative risk factors, nonetheless.
The recently published study ‘Rate Control versus Rhythm control for Atrial Fibrillation after Cardiac Surgery’ by Gillinov et al1 is the largest multicenter, randomized, prospective trial on rate vs rhythm control in elective post cardiac surgery AF patients consisting of a sample size of 523 patients who were randomly assigned into rate and rhythm control groups. The baseline demographics of the patients in the two groups were similar with regards to pre-existing comorbidities, medications and the type of cardiac surgery they underwent. Patient who remained in atrial fibrillation or had recurrent atrial fibrillation 48 hours after randomization were started on anticoagulation with warfarin. 24% of the patients in the rhythm control group could not complete the full course of amiodarone largely due to side effects and 26.7% in rate control group received amiodarone or DC cardioversion mostly due to ineffectiveness of rate control or side effects.
The mean hospital days (6.4 days vs 7.0 days) and length of stay in index admission (5.5 days vs 5.8 days) for rate control vs rhythm control respectively were not significantly different. A separate sensitivity analysis in addition to intention-to-treat analysis did not show any significant difference between the two groups in terms of total number of hospital days (primary end point) or readmission for any reason (secondary end point). Also important was the finding that 93.8% patients in the rate-control group and 97.9% in the rhythm-control group were in a stable heart rhythm without atrial fibrillation from the 30 day to 60 day landmark post discharge. Complications and adverse effects including thromboembolism and bleeding did not show significant difference
In short, no significant difference was found between the two groups in terms of primary, secondary end points and complications. Although rate control drugs were used in the rhythm control group, this reflected the usual clinical practice where rapid ventricular rate needs to be controlled despite being on an antiarrhythmic. On the other hand hemodynamic deterioration usually warranted rhythm control either pharmacological or DC cardioversion which accounted for the switch from the rate to rhythm control group. The fact that risk of bleeding and thromboembolism was 3% and 2% respectively raises the question if anticoagulation is causing more harm than benefit in such patients when anticoagulation ended up being used only for median of 45 days in each group.
A few limitations of the study are not including outcomes such as stroke, serious bleeding episodes and effect on quality of life measures. Also there was a relatively high rate of switch between the two groups due to clinical necessity however the sensitivity analyses did take that into account.
Lee et al2,3 did a pilot study by randomly assigning 50 post cardiac surgery AF patients to rate versus rhythm control and measured time to sinus rhythm as well as hospital stay. This study demonstrated no significant difference between an antiarrhythmic conversion strategy (n =27) and a rate-control strategy (n = 23) in time to conversion to sinus rhythm (11.2 ± 3.2 vs 11.8 ± 3.9 hours; p= 0.8). The length of hospital stay was reduced in the antiarrhythmic arm
compared with the rate-control strategy (9.0 ± 0.7 vs. 13.2 ± 2.0 days; p = 0.05).
Other studies inspecting the effectiveness of antiarrhythmic therapy in postoperative AF have been small. Cochrane et al4 compared digoxin with amiodarone in the postoperative setting. After 24 hours, 93% and 86% of patients who received amiodarone and digoxin respectively were in sinus rhythm which were not statistically significant. Similarly another study by Hjelms et al5 showed procainamide to be superior to digoxin in restoring sinus rhythm but did not show difference in complications or hospital stay. In a trial by Al-Khatib SM et al,6 physicians were more inclined to use rhythm control over rate control and warfarin of the 663 patients who developed post CABG AF. Overall the efficacy of antiarrhythmic agents has been between 60-90% depending on the drug used.8
Although post cardiac surgery AF ablation has been managed per combined guidelines from ACC, AHA and HRS to begin with betablockers and rate control, recently published data shows no statistically significant difference in hospital stay, readmissions and complications in rate versus rhythm control. Most of the patients will revert to sinus rhythm by two months regardless of undergoing rhythm versus rate control. About 95% of the patients were free of atrial fibrillation by the end of the study by Gillinov et al. Therefore clinical judgement will need to guide therapy based on tolerance of medications side effects, urgency of conversion to sinus rhythm, hemodynamic status or difficulties with prolonged anticoagulation. as to which patients need to have antiarrhythmic for immediate conversion to sinus rhythm or those who cannot tolerate.
1. Gillinov M, Bagiella E, Moskowitz A, Raiten J, et al. Rate Control versus Rhythm Control for Atrial Fibrillation after Cardiac Surgery. N Engl J Med 2016:1-12.
2. Lee JK, Klein GJ, Krahn AD, et al. Rate-control versus conversion strategy in postoperative atrial fibrillation: a prospective, randomized pilot study. Am Heart J 2000;140:871-877.
3. Lee JK, Klein GJ, Krahn AD, et al. Rate-control versus conversion strategy in postoperative atrial fibrillation: trial design and pilot study results. Card Electrophysiol Rev 2003;7:178-184.
4. AO Cochrane, M Siddins, R. Rosenfeldt. A comparison of amiodarone and digoxin for treatment of supraventricular arrhythmias after cardiac surgery. Eur J Cardiothorac Surg, 8;1994:194–198.
5. E. Hjelms. Procainamide conversion of acute atrial fibrillation after open-heart surgery compared with digoxin treatment. Scan J Thorac Cardiovasc Surg, 26;1992:193–196.
6. Al-Khatib SM, Hafley G, Harrington RA, et al. Patterns of management of atrial fibrillation complicating coronary artery bypass grafting: results from the PRoject of Ex-vivo Vein graft ENgineering via Transfection IV (PREVENT-IV) Trial. Am Heart J 2009;158:792-798.
7. The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) Investigators. A comparison of rate control and rhythm control in patients with atrial fibrillation. N Engl J Med 2002;347:1825-1833.
8. B. Olshansky. Management of atrial fibrillation after coronary artery bypass graft. Am J Cardiol, 78;1996:27–34.
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