Interactive Cardiovascular and Thoracic Surgery 3:503-509(2004)
© 2004 European Association of Cardio-Thoracic Surgery
Best evidence topic - Cardiac general |
What is the optimal anticoagulation management of patients post-cardiac surgery who go into atrial fibrillation?
Joel Dunning*,1,
Darbhamulla V. Nagarajan,
Munir Amanullah and
Seyed Mahmoud Nouraei
Department of Cardiothoracic Surgery, Freeman Hospital, Freeman Road, NE7 7DN, Newcastle upon Tyne, UK
* Corresponding author
joeldunning{at}doctors.org.uk smnouraei{at}yahoo.co.uk
Received May 6, 2004;
accepted May 10, 2004
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Abstract
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A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether anticoagulation is indicated for patients in atrial fibrillation (AF) following coronary artery bypass grafting. Altogether 166 papers were found using the reported search, of which 10 presented the best evidence to answer the clinical question. In addition the American Heart Association guidelines for management of atrial fibrillation were reviewed. 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 patients post-cardiac surgery require warfarinisation while in atrial fibrillation with an INR of 2–3, and full anticoagulation should be commenced within 48 h of the onset of AF as their risk of stroke is doubled by the onset of AF.
Key Words: Evidence-based medicine; Thoracic surgery; Atrial fibrillation; Anticoagulation; Review
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1. Introduction
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A best evidence topic was constructed according to a structured protocol. This protocol is fully described in the ICVTS [1].
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2. Clinical scenario
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You are the cardiothoracic registrar on call and you are asked to review a 65-year-old gentleman who underwent coronary artery bypass grafting 3 days ago. He has gone into atrial fibrillation with a ventricular rate of 130 beats/min, but his blood pressure is good at 105/70. You commence him on Metoprolol, and the nurse asks you if you would like to fully anticoagulate him with full dose tinzaparin. He suffered a stroke 4 years ago and getting a repeat CVA was one of his main concerns prior to his operation and you are tempted to give him this anticoagulation right away. However, you are unsure if this is safe in someone so recently post-cardiac surgery and you are aware of no evidence for a reduction in stroke risk with anticoagulation post-cardiac surgery, so you resolve to check up on the literature that night.
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3. Three-part question
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In [patients with atrial fibrillation following coronary arterial bypass graft] is [anticoagulation] of any benefit in terms of [stroke prevention].
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4. Search strategy
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Medline 1966–Mar 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 surgery.mp OR CABG.mp OR coronary surgery.mp OR cardiac surgery.mp OR revascularization.mp] AND [exp anticoagulation/ OR anticoagulation.mp OR exp warfarin/ OR warfarin.mp OR exp heparin/ OR heparin.mp.] AND [exp atrial fibrillation/ OR atrial fibrillation.mp OR AF.mp OR exp atrial flutter/ OR atrial flutter.mp OR exp supraventricular tachycardia/]. This search was repeated in Cochrane Central Register of Controlled Trials.
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5. Search outcome
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A total of 166 papers was found of which only 2 relevant papers were relevant (both reviews). The American Heart Association guidelines for management of atrial fibrillation were reviewed. No direct studies were relevant looking at the reduction of stroke after AF post-cardiac surgery, thus the reference lists of these reviews and the AHA guidelines were checked which identified 4 further papers. Finally 2 papers were suggested by journal club colleagues. These 11 papers are presented in Table 1.
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6. Results
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There are several issues that must be addressed for this topic: does anticoaculation reduce the incidence of stroke in patients with atrial fibrillation?; In the subgroup of patients who get AF just after cardiac surgery is their stroke rate significantly increased?; If the stroke risk is increased in patients post CABG who go into AF, can anticoagulation reduce the risk of stroke without a significant increase in the risk of bleeding cmplications?
Addressing the issue of reduction in stroke risk in patients with atrial fibrillation, Hart et al. [2] analysed results from 16 trials by meta-analysis, 5 of which used warfarin against a placebo, 6 trials looked at antiplatelet therapy vs placebo and 5 trials looked at warfarin against aspirin. They demonstrated that warfarin reduced the relative risk of stroke both in comparison to placebo and aspirin and that warfarin is therefore by far the best long-term treatment in patients with atrial fibrillation. The numbers needed to treat to prevent 1 stroke per year was 37 in the primary prevention group and 12 in the secondary prevention group (patients with a history of stroke) when compared to the placebo. These results were consistent for disabling and non-disabling strokes. It is interesting to note that though the incidence of intracranial haemorrhages was twice that of placebo, the difference was not statistically significant. The mean INR achieved was 2.0–2.6 in primary prevention trials and 2.9 in a single secondary prevention trial. Aspirin reduced the incidence of stroke by 22% when compared to the placebo and numbers needed to treat per year to prevent a stroke were 67 in the primary prevention group and 40 for secondary prevention. The difference of intracranial and extracranial haemorrhages in both groups was not statistically significant and all cause mortality was not significantly reduced by aspirin. In addition, since the above meta-analysis was performed, Hylek et al. [3] published a cohort study of 13,600 patients in the New England Journal of Medicine, showing that an INR above 2.0 significantly improved survival among patients with AF who suffer a stroke.
The next issue is whether AF post-cardiac surgery significantly increases the risk of stroke. Lahtinen et al. [7] reported that 19 of 52 strokes (37%) in their cohort of patients undergoing CABG were preceded by atrial fibrillation, an average of 21 h previously. However, this is a small study and the incidence of AF in their patients who did not have a stroke was not reported.
Villareal et al. [8] reported that in a cohort of 6500 patients undergoing CABG, patients who went into AF had a much higher incidence of stroke (5.2 vs 1.7%) and also an increased risk of short and long-term mortalities. These patients were, however, significantly higher risk in a large range of categories including age, heart failure, COPD and underlying coronary arterial disease and thus some caution should be used when analysing these figures. However, adverse long-term mortality persisted after case-control matching.
Stamou et al. [9] performed a retrospective analysis of 19,500 patients who had undergone CABG, of whom 333 had suffered a stroke. Multivariate analysis showed that atrial fibrillation was an independent predictor of stroke, increasing the odds of stroke by 1.7. However, other multiple high-risk factors also predicted stroke and thus the stroke group was a much higher risk group than those who did not suffer a stroke. Almassi [10] also showed a 5% stroke rate in patients with AF compared to 2.5% in the sinus rhythm group, performing a similar study to Stamou in a cohort of 3855 patients. Creswell et al. [11] found that the incidence of stroke was 3.3% if the patient was in AF compared to 1.4% in those with sinus rhythm in a cohort of 3983 patients.
Unfortunately there are no studies that demonstrate that immediate or delayed anticoagulation of patients post-cardiac surgery who go into AF significantly reduce this increased risk of stroke. However, addressing the issue of the safety of immediate anticoagulation, Malouf et al. [12] performed a cohort study on 144 cardiac surgical patients, performing an echocardiogram on all these patients. They found a 16% incidence of tamponade requiring drainage in patients receiving early warfarinisation, with no such tamponades in controls. In addition 32% of the anticoagulated patients had a large pericardial effusion on echocardiography, compared to 4% in controls. As a caveat, these patients received warfarin not heparin, and a large number of these patients suffered a period of excessive anticoagulation at some stage; however, despite this, their figures are a cause for concern.
The American college of cardiology/American heart association/European society of cardiology guidelines for management of patients with atrial fibrillation suggest managing post-CABG AF in a similar fashion to atrial fibrillation in non-surgical patients [4]. They recommend use of antithrombotic treatment in high-risk patients and a target INR of 2.0–3.0.They further recommend that anticoagulation with heparin or an oral anticoagulant is appropriate when AF persists for more than 48 h. However, they only quote two pre-1990 papers in support of this statement.
Emile Daoud [5] supported these recommendations in a review published in 2004, stating that warfarin should be started after 48 h. He further recommends that in higher risk patients even if sinus rhythm returns, warfarin should be continued for 4 weeks as there is a delay in return of atrial contractility post-AF. Maisel et al. [6] performed a review in 2001 where the AHA guidelines were also supported for warfarinisation, but caution is advised in heparinisation, quoting anxiety over an increased risk of pericardial effusions Heparinisation is recommended only for the highest risk patients for stroke.
Thus it is clear that chronic atrial fibrillation increases the risk of stroke and warfarinisation provides the optimal protection from this risk, with a number needed to treat of only 37 to save a stroke and this number drops to 12 if there is a history of stroke. It is clear that AF post-cardiac surgery doubles the risk of stroke, but there are as yet no studies that have demonstrated a drop in this risk with immediate anticoagulation. In addition one study provides some evidence that there is a risk of pericardial effusions with early anticoagulation. The American Heart association supported by several other authors thus recommends warfarinisation while in AF, with an INR of 2–3 and anticoagulation within 48 h of the onset of AF post-cardiac surgery.
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7. Clinical bottom line
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Patients post-cardiac surgery require warfarinisation while in atrial fibrillation with an INR of 2–3, and full anticoagulation should be commenced within 48 h of the onset of AF due to a doubling of their risk of stroke.
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Footnotes
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1 Other address: Department of Cardiology, Stepping Hill Hospital, Stockport, Manchester, UK. 
doi:10.1016/j.icvts.2004.05.004
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References
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- Dunning J, Prendergast B, Mackway-Jones K. Towards evidence-based medicine in cardiothoracic surgery: best BETS. Interact Cardiovasc Thorac Surg. 2003;2:405–409[Abstract/Free Full Text]
- Hart RG, Benavente O, McBride R, Pearce LA. Antithrombotic therapy to prevent stroke in patients with atrial fibrillation: a meta-analysis. Ann Intern Med. 1999;131:492–501[Abstract/Free Full Text]
- Hylek EM, Go AS, Yuchiao C, Jensvold NG, Henault LE, Selby JV, Singer DE. Effect of intensity of oral anticoagulation on stroke severity and mortality in atrial fibrillation. N Engl J Med. 2003;349:1019–1026[Abstract/Free Full Text]
- A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines and Policy Conferences ACC/AHA/ESC Guidelines for the Management of Patients With Atrial Fibrillation. J Am Coll Cardiol, 2001; 38: 1266i–1266ixx.
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- Lahtinen J, Biancari F, Salmela E, Mosorin M, Satta J, Rainio P, Rimpila J, Lepoja M, Juvonen T. Postoperative atrial fibrillation is a major cause of stroke after on-pump coronary artery bypass surgery. Ann Thorac Surg. 2004;77:1241–1244[Abstract/Free Full Text]
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- Creswell LL, Schuessler RB, Rosenbloom M, Cox JL. Hazards of postoperative atrial arrhythmias [see comment]. Ann Thorac Surg. 1993;56:539–549[Abstract]
- Malouf JF, Alam S, Gharzeddine W, Stefadouros MA. The role of anticoagulation in the development of pericardial effusion and late tamponade after cardiac surgery [Erratum appears in Eur Heart J, 1994 15(4):583–4]. Eur Heart J. 1994;14:1451–1457
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Abstract
1. Introduction