Pulmonary vein isolation
In a procedure that can potentially cure atrial fibrillation, catheters are inserted into the left atrium and rings of scar tissue are created around the ostia of the pulmonary veins using radiofrequency energy, electrically isolating them from the rest of the left atrium.
Some debate exists as to whether this procedure may be reasonable as a first-line therapy for some patients with atrial fibrillation.18,19 It may be considered as an early treatment strategy in a small subset of patients, specifically young patients with symptomatic, recurrent atrial fibrillation, especially if they are averse to long-term antiarrhythmic therapy.
Because patients may still be more prone to atrial arrhythmias for several weeks to months after the procedure, they must be able to tolerate anticoagulation with warfarin for at least several months.
Rate control vs rhythm control
The choice between a rate control strategy or a rhythm control strategy in the long term is not always straightforward. While atrial fibrillation is clearly associated with higher morbidity and mortality rates, there are few data to date showing that restoring and maintaining sinus rhythm in patients with atrial fibrillation reduce the incidence of morbid complications or the likelihood of death.
Thus, current guidelines recommend a rate control strategy in patients who have no symptoms, and a rhythm control strategy if rate control cannot be achieved or if symptoms persist despite adequate control of the heart rate.7 The circumstances and preferences of the individual patient should carry weight in this decision.
Trials are under way that may shed more light on the relative benefits of rhythm control with ablation or antiarrhythmics and rate control.
PREVENTING THROMBOEMBOLIC EVENTS
In the short term, warfarin therapy may be dictated by plans to restore sinus rhythm. Patients need warfarin for at least 4 weeks after cardioversion unless it is performed within 48 hours of the onset of atrial fibrillation.
The CHADS2score (1 point each for congestive heart failure, hypertension, age 75 or older, and diabetes mellitus; 2 points for prior stroke or transient ischemic attack) is useful when deciding whether to give long-term anticoagulation.
For patients with a score of 0, the risk of stroke is lower than the risk of a major bleeding complication while on therapeutic warfarin.20,21 For these patients, aspirin 81 to 325 mg daily is recommended for stroke prophylaxis.
For those with a score of 2 or greater, the risk of stroke without warfarin is greater than the risk of a major bleeding complication with warfarin. These patients should receive warfarin with a goal INR of 2.0 to 3.0.7
Patients with a CHADS2 score of 1 present a dilemma, as their risk of stroke without warfarin is about the same as their risk of a major bleeding complication with warfarin. They can be managed with either warfarin or aspirin, according to the physician’s judgment.7 In these cases, factors such as hobbies or professions that might increase the risk of bleeding, perceived frequency of atrial fibrillation episodes, and even patient preconceptions about warfarin are often used when deciding between aspirin and warfarin.
Patients with a CHADS2 score of 2 or greater with a single episode of atrial fibrillation and a likely reversible cause may also pose a dilemma when deciding whether to start warfarin. These patients have demonstrated they at least have the substrate to maintain atrial fibrillation. This situation again calls for physician judgment. Bear in mind that asymptomatic recurrences are common in patients with atrial fibrillation.22,23 A higher CHADS2 score denotes a greater risk of stroke and may influence this decision. It is usually beneficial to enlist the patient in this decision-making process, as patients often have very strong opinions about tolerance of the risk of stroke or of warfarin therapy itself.
Another strategy is to start anticoagulation with warfarin and aggressively monitor for recurrences. If the patient has no recurrences of atrial fibrillation after 6 to 12 months and the reversible cause is resolved, one can then revisit the need for warfarin.
Role of aspirin and clopidogrel
Aspirin, alone or in conjunction with clopidogrel (Plavix), may provide an alternative for stroke prophylaxis in patients in whom warfarin is contraindicated. While inferior to warfarin, the combination of aspirin and clopidogrel has been shown to decrease the incidence of major thromboembolic events, especially stroke.24 However, the risk of a major bleeding complication was also significantly increased.
This combination may be a reasonable strategy in select patients with a CHADS2 score of 2 or greater in whom warfarin cannot be used for reasons such as personal aversion to the medication, side effects, or nonbleeding complications or in patients whose INR is exceedingly difficult to keep within the therapeutic range.
Dabigatran, a new anticoagulant
The newest option for anticoagulation in patients with atrial fibrillation is a direct thrombin inhibitor, dabigatran (Pradaxa).
In the Randomized Evaluation of Long-Term Anticoagulation Therapy (RE-LY) trial,25 dabigatran was studied head-to-head with warfarin. The doses of dabigatran studied were 110 mg and 150 mg twice a day. At 150 mg twice a day, patients on dabigatran had a lower rate of stroke than with warfarin (1.11% vs 1.69%, P < .001), as well as a lower rate of central nervous system bleeding (0.10% vs 0.38% with warfarin, P < .001). The rates of major bleeding were comparable in the patients receiving warfarin or dabigatran 150 mg twice a day, but the rate of gastrointestinal bleeding was higher in the dabigatran group (1.51% vs 1.02% with warfarin, P < .001).25
Dabigatran was recently approved by the US Food and Drug Administration for use in patients with atrial fibrillation. Doses of 150 mg and 75 mg are available.
Dabigatran is renally excreted, and the 150 mg twice-a-day dosing is intended for patients with a creatinine clearance greater than 30 mL/min. The 75-mg twice-a-day dosing is intended for patients with a creatinine clearance of 15 to 30 mL/min. However, it should be noted that currently there are no data to support the 75-mg twice-a-day dosing.
Dabigatran does have several advantages over warfarin. Patients do not need to avoid foods containing vitamin K, and routine serial monitoring does not appear to be needed. As with any new medication, patients who are started on dabigatran should be observed closely for any side effects, and these should be reported to assist in the development of the drug’s safety profile.