Atrial fibrillation overview of treatment
Atrial Fibrillation Microchapters
Atrial fibrillation overview of treatment On the Web
Goals of Atrial Fibrillation Treatment
The two main goals in managing the patient with atrial fibrillation are:
- Prevent hemodynamic instability due to a low cardiac ouptut associated with poor ventricular filling as a result of rapid and chaotic contractions of the atrium. Rhythm control via antiarrhytmics is used to reduce the risk of developing recurrent atrial fibrillation, and rate control is used to reduce the heart rate when atrial fibrillation dues occur. If hemodynamic collapse has or is about to occur, then immediate cardioversion may be indicated.
- Prevent embolic stroke. Anticoagulation with antiplatelets such as aspirin and/or clopidogrel or antithrombins such as warfarin or dabigatran are used to reduce the risk of embolic stroke.
General Principals of Atrial Fibrillation Treatment
The primary determinants of the appropriate treatment of atrial fibrillation treatment are:
- Duration of atrial fibrillation and evidence of hemodynamic instability. Cardioversion is indicated if the AF is of new onset (the AF present for less than 48 hours) and if there is hemodynamic instability.
- Risk of systemic embolization and risk of bleeding. The risk of stroke can be ascertained using the CHADS2 Score or the more sophisticated CHA2DS2-VASC Score and the risk of bleeding can be asceratined using the HAS-BLED score as described below. The relative risk versus benefit of anticoagulation can then calculated.
- Durability of rate and rhythm control. If rate and rhythm control cannot be maintained by medication or cardioversion, electrophysiological studies with ablation may be required.
Risk of Cardioversion Due to Electrical and Mechanical Dissociation
Despite the restoration of sinus rhythm on the ECG following cardioversion (either spontaneous, pharmacologic or electrical or after radiofrequency catheter ablation of atrial flutter), in some patients there is a persistent lack of atrial contractility. This state is known as electrical mechanical dissociation and may be sue to mechanical stunning in the atrium and the atrial appendage.   The lack of atrial contraction can be diagnosed on echocardiography by the appearance of spontaneous echo contrast.  In general, the longer the patient was in atrial fibrillation, the longer the time it takes for the recoery of atrial mechanical function. The period of recovery can be quite variable, and it can take several weeks in total. Recovery of mechanical function can be delayed for several weeks, depending in part on the duration of AF before restoration of sinus rhythm This kind of electrical mechanical dissociation may explain in part the observation that some patients develop thromboembolic events following cardioversion despite the fact that they had no visible left atrial clot on TEE.  It has been hypothesized that the low shear state and turbulent nature of left atrial hemodynamics during this period leads to the development of clot which then embolizes once there is restoration of sufficient mechanical force. It is in part due to the presence of atrial mechanical dissociation and the risk of clot formation and embolization that oral anticoagulation is recommended for 3 to 4 weeks following successful electrical cardioversion in patients in whom the duration of Afib is unknown or in whom the duration of atrial fibrillation has been documented to be longer than 48 hours. Among patients in whom the duration of atrial fibrillation is less than 48 hours, the necessity for anticoagulation is not as clear, although it should be noted that stroke has been observed in these patients as well. No matter what the duration of atrial fibrillation, if a patient becomes hemodynamically unstable, this is an indication for immediate cardioversion.
Maintenance of Rhythm Control
Avoidance of stimulants such as caffeine, alcohol withdrawal, binge drinking, and holiday heart syndrome may be critical in reducing the recurrence of atrial fibrillation. Drugs such as digoxin and hyperthyroidism, hypokalemia, sleep apnea and pheochromocytoma are all associated with atrial fbrillation. Antiarrhythmics may also be critical to maintaining normal sinus rhythm. Recommendations for specific populations of patients are provided below:
New diagnosed or First Episode of Atrial Fibrillation
In patients who have self-limited episodes of paroxysmal AF, antiarrhythmic drugs to prevent recurrence are usually unnecessary, unless the AF is associated with severe symptoms related to hypotension, myocardial ischemia, or heart failure. Whether these individuals require longterm or even short-term anticoagulation is not clear, and the decision must be individualized for each patient based on the intrinsic risk of thromboembolism. Recommendations for specific patient populations follow:
Vagally mediated Atrial fibrillation
Adrenergically induced Atrial Fibrillation
Congestive Heart Failure
Patients with atrial fibrillation, even lone atrial fibrillation without other evidence of heart disease, are at increased risk of stroke during long term follow up. A systematic review of risk factors for stroke in patients with nonvalvular atrial fibrillation concluded that a prior history of stroke or TIA is the most powerful risk factor for future stroke, followed by advancing age, hypertension, diabetes. The risk of stroke increases whether the lone atrial fibrillation was an isolated episode, recurrent, or chronic. The risk of systemic embolization (atrial clots migrating to other organs) depends strongly on whether there is an underlying structural problem with the heart (e.g. mitral stenosis) and on the presence of other risk factors, such as diabetes and high blood pressure. Finally, patients under 65 are much less likely to develop embolization compared with patients over 75. In young patients with few risk factors and no structural heart defect, the benefits of anticoagulation may be outweighed by the risks of hemorrhage (bleeding). Those at a low risk may benefit from mild (and low-risk) anticoagulation with aspirin (or clopidogrel in those who are allergic to aspirin). In contrast, those with a high risk of stroke derive most benefit from anticoagulant treatment with warfarin or similar drugs.
In the United Kingdom, the NICE guidelines recommend using a clinical prediction rule for this purpose. The CHADS/CHADS2 score is the best validated clinical prediction rule for determining risk of stroke (and therefore who should be anticoagulated); it assigns points (totaling 0-6) depending on the presence or absence of co-morbidities such hypertension and diabetes. In a comparison of seven prediction rules, the best rules were the CHADS2 which performed similarly to the SPAF and Framingham prediction rules. 
To compensate for the increased risk of stroke, anticoagulants may be required. However, in the case of warfarin, if a patient has a yearly risk of stroke that is less than 2%, then the risks associated with taking warfarin outweigh the risk of getting a stroke. 
If anticoagulation is required urgently (e.g. for cardioversion), heparin or similar drugs achieve the required level of protection much quicker than warfarin, which may take several days to reach adequate levels.
In the initial stages after an embolic stroke, anticoagulation may be risky, as the damaged area of the brain is relatively prone to bleeding (hemorrhagic transformation). As a result, a clinical practice guideline by National Institute for Health and Clinical Excellence recommends that anticoagulation should begin two weeks after stroke if no hemorrhage occurred.
Among patients with "non-valvular" atrial fibrillation, anticoagulation with warfarin can reduce stroke by 60% while antiplatelet agents can reduce stroke by 20%. . There is evidence that aspirin and clopidogrel are effective when used together, but the combination is still inferior to warfarin.
Warfarin treatment requires frequent monitoring with a blood test called the international normalized ratio (INR); this determines whether the correct dose is being used. In atrial fibrillation, the usual target INR is between 2.0 and 3.0 (higher targets are used in patients with mechanical artificial heart valves, many of whom may also have atrial fibrillation). A high INR may indicate increased bleeding risk, while a low INR would indicate that there is insufficient protection from stroke.
An attempt was made to find a better method of implementing warfarin therapy without the inconvenience of regular monitoring and risk of intracranial hemorrhage. A combination of aspirin and fixed-dose warfarin (initial INR 1.2-1.5) was tried. Unfortunately, in a study of AF patients with additional risk factors for thromboembolism, the combination of aspirin and the lower dose of warfarin was significantly inferior to the standard adjusted-dose warfarin (INR 2.0-3.0), yet still had a similar risk of intracranial hemorrhage.
Use of the CHADS Score to Risk Stratify Patients and Determine the Appropriate Anticoagulation Strategy
|C||Congestive heart failure|
|H||Hypertension: blood pressure consistently above 140/90 mmHg (or treated hypertension on medication)|
|A||Age >/=75 years|
|S2||Prior Stroke or TIA|
CHADS score or CHADS2 score is a clinical prediction rule for estimating the risk of stroke in patients with non-rheumatic atrial fibrillation (AF), a common and serious heart arrhythmia associated with thromboembolic stroke. It is used to determine whether or not treatment is required with anticoagulation therapy or antiplatelet therapy, since AF can cause stasis of blood in the upper heart chambers, leading to the formation of a mural thrombus that can dislodge into the blood flow, reach the brain, cut off blood supply to the brain, and cause a stroke. A high CHADS2 score corresponds to a greater risk of stroke, while a low CHADS2 score corresponds to a lower risk of stroke. The CHADS2 score was validated by a study of nonrheumatic atrial fibrillation patients aged 65 to 95 who were not prescribed the anticoagulant warfarin.
How to Calculate the CHADS2 Score
The CHADS2 scoring table is shown above:
Adding together the points that correspond to the conditions that a patient has will result in the CHADS2
score. This score is used in the next section to estimate stroke risk.
Risk of stroke
|CHADS2 Score||Stroke Risk %||95% CI|
According to the findings of the validation study, the risk of stroke as a percentage per year is shown in the table titled Annual Stroke Risk:
While the CHADS2 score provides prognostic information regarding the natural history of non-valvular atrial fibrillation (NVAF) in the absence of warfarin therapy, it should be noted that warfarin therapy also has an associated stroke risk (particularly hemorrhagic stroke) and a risk of major bleeding, and these considerations were taken into account in the development of the recommendations in the next section.
The CHADS2 score has various limitations, which have been debated . Notably, many stroke risk factors have not been included, and whilst simple, the score has only modest predictive value for thromboembolism.
In order to improve upon the prognostic utility of the CHADS2 score and to incorporate additional stroke risk factors, the CHA2DS2-VASc score has been proposed . These additional 'clinically relevant non-major' stroke risk factors include age 65-74, female gender and vascular disease. In the CHA2DS2-VASc score, 'age 75 and above' also has extra weight, with 2 points.
The CHA2DS2-VASc score has been used in the new European Society of Cardiology guidelines for the management of atrial fibrillation .
The European Society of Cardiology (ESC) guidelines recommend that if the patient has a CHADS2 score of 2 and above, oral anticoagulation (OAC) therapy is recommended. OAC options include warfarin with an INR target of 2-3 or dabigatran.
If the CHADS2 score is 0-1, other stroke risk modifiers should be considered: (i) If there are 2 or more risk factors (essentially a CHA2DS2-VASc score score of 2 or more), OAC is recommended; and (ii) If there is 1 risk factor (essentially a CHA2DS2-VASc score score=1), then antithrombotic therapy with either OAC or aspirin (OAC preferred) is recommended.
If patients have a CHA2DS2-VASc score of 0, then such patients are ‘truly low risk’. The ESC guidelines recommend either aspirin or no antithrombotic therapy, but 'no antithrombotic therapy' is preferred.
Anticoagulation based on the CHADS2 score
|1||Moderate||Aspirin or Warfarin||Aspirin daily or INR to 2.0-3.0, depending on factors such as patient preference|
|2 or greater||Moderate or High||Warfarin||INR to 2.0-3.0, unless contraindicated (e.g. clinically significant GI bleeding, inability to obtain regular INR screening)|
For detailed recommendations on how the treatment recommendations based on the CHADS2 score are modified by considering additional 'stroke risk modifier' risk factors using the CHA2DS2-VASc score, see ESC guideline recommendations.
Assessment of Bleeding Risk with Anticoagulation
The decision to anticoagulate a patient should also be based upon an assessment of the risk of bleeding using a score such as the HAS-BLED score.
Anticoagulation in Special Populations
The very elderly (patients aged 75 years or more) may benefit from anticoagulation provided that their anticoaguation does not increase hemorrhagic complications, which is a difficult goal. Patients aged 80 years or more may be especially susceptible to bleeding complications, with a rate of 13 bleeds per 100 person-years. A rate of 13 bleeds per 100 person years would seem to preclude use of warfarin; however, a randomized controlled trial found benefit in treating patients 75 years or over with a number needed to treat of 50. Of note, this study had very low rate of hemorrhagic complications in the warfarin group.
Vote on and Suggest Revisions to the Current Guidelines
- 2011 ACCF/AHA/HRS Focused Updates Incorporated Into the ACC/AHA/ESC 2006 Guidelines for the Management of Patients With Atrial Fibrillation 
- ACC/AHA/Physician Consortium 2008 clinical performance measures for adults with nonvalvular atrial fibrillation or atrial flutter 
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