First Detected Episode Duration Known >48 Hours or Duration Unknown
Key Points:
- Anticoagulation with warfarin (INR greater than or equal to 2.0 for three weeks) is recommended before electrical or pharmacologic cardioversion back to sinus rhythm. An alternative is transesophageal echocardiography (TEE)-guided cardioversion without the traditional pre-cardioversion anticoagulation, although this cannot be routinely recommended.
- TEE-guided cardioversion without traditional pre-cardioversion anticoagulation cannot be routinely recommended
- Amiodarone is the most effective antiarrhythmic drug for maintenance of normal sinus rhythm. However, it also is associated with the highest potential for non-cardiac toxicity, and absolutely requires regular scheduled medical follow-ups.
- Angiotensin-converting enzyme (ACE)-inhibitors and angiotensin receptor blockers (ARBs) have an emerging role as adjunctive medical therapies to antiarrhythmic drugs for maintenance of normal sinus rhythm.
General Recommendations
When the duration of A Fib or A Flutter is unknown, the risk of thromboembolic complications is as high as 7% following cardioversion without anticoagulation. Thus, in this setting, anticoagulation with warfarin is required (INR greater than or equal to 2.0 for three consecutive weeks). Though not a consistent clinical practice, the American College of Chest Physicians (ACCP) also recommends anticoagulation with warfarin (INR greater than or equal to 2.0 for three consecutive weeks) prior to the initiation of antiarrhythmics.
As A Fib persists for longer periods of time, the efficacy of pharmacologic cardioversion decreases. Though DC cardioversion requires conscious sedation, pharmacologic cardioversion is less effective and may cause serious arrhythmias including torsades de pointes. Antiarrhythmics like ibutilide or propafenone may be administered prior to DC cardioversion to increase the likelihood of its success.
Alternatively, the patient and/or physician may also opt for chronic anticoagulation (see Annotation #10) and chronic rate control (see Annotation #15). However, if this represents the first episode of persistent atrial fibrillation for the patient, there is general consensus that most patients deserve one trial of conversion back to normal sinus rhythm, given the high likelihood of initial success.
There is an emerging role for statin therapy following electrical cardioversion.
Evidence supporting this recommendation is of classes: A, D
Specific Anticoagulation Issues
Whenever possible, cardioversion should be undertaken with conventional anticoagulation prior to and following cardioversion.
When anticoagulation is temporarily contraindicated (such as acute gastrointestinal [GI] bleeding), cardioversion should be delayed if possible until appropriate anticoagulation can be given prior to and following cardioversion.
When anticoagulation is contraindicated and cardioversion cannot be delayed, TEE may identify high-risk patients but may not change therapeutic decisions.
However, if TEE is used to guide anticoagulant therapy, the patient must be anticoagulated with therapeutic (not prophylactic) levels of heparin and warfarin. Heparin should be continued until the INR is greater than or equal to 2.0 for 2 consecutive days. Warfarin should be continued a minimum of four weeks following successful cardioversion.
At this time, there is insufficient evidence to recommend routine TEE to guide anticoagulant therapy prior to or following cardioversion [Conclusion Grade III: See Conclusion Grading Worksheet A - Annotation #12 (Treatment Options) in the original guideline document.]
There is little experience reported on the use of low-molecular-weight heparins prior to or following cardioversion (with or without TEE). A pilot study of TEE-guided enoxaparin plus warfarin versus TEE-guided unfractionated heparin plus warfarin (ACUTE II) is in progress. Unfortunately, this trial does not include a conventional therapy group, which is a significant omission in light of the ACUTE trial results.
For additional information on anticoagulation with warfarin, refer to the NGC summary of the ICSI Antithrombotic Therapy Supplement guideline.
Evidence supporting this recommendation is of classes: A, C, D, M, R
DC Cardioversion
DC cardioversion has been used to treat a variety of rhythm disturbances including A Fib and A Flutter since the early 1960s. The success of external DC cardioversion depends on patient selection and cardioversion technique. Success rates range from 65 to 95%. Success of cardioversion is increased if the left atrium is less than 60 mm (3 cm/m2 body surface area [BSA]) and if the arrhythmia is of short duration.
Transthoracic cardioversion of A Fib may now be performed with biphasic waveform defibrillation. It typically uses less energy and may have greater efficacy than monophasic waveforms.
A recent study has shown that an anterior-posterior (A-P) paddle position is superior to an anterior-lateral position in success of cardioversion. The A-P position also required lower energy levels for success. If the first position is unsuccessful, paddle relocation should be considered.
Complications of DC cardioversion are uncommon but include embolization, pulmonary edema, and arrhythmias including ventricular fibrillation and asystole. DC cardioversion should be avoided in patients with known or suspected digoxin toxicity. It is unnecessary to interrupt digoxin therapy for cardioversion in patients without manifestations of toxicity.
See the original guideline document for specifics on DC cardioversion technique and information on comparing electrical and chemical cardioversion.
Evidence supporting this recommendation is of classes: A, D, R
Antiarrhythmic/Chemical Cardioversion
All antiarrhythmics used to treat A Fib/A Flutter can cause serious complications including the life-threatening arrhythmia torsades de pointes in up to 8% of patients. Therefore, antiarrhythmics should be initiated in the presence of a physician or nurse with expertise in the administration of antiarrhythmics with telemetry monitoring for at least 4 hours, or longer if QT remains prolonged.
Risk factors for proarrhythmia include:
- Pre-existing bradycardia or AV block
- Underlying structural heart disease
- Active heart failure or ischemia- hypokalemia or hypomagnesemia, and
- Drug dosages (e.g., lower doses for quinidine and higher doses for sotalol)
Pharmacologic therapy aimed at restoring sinus rhythm is often helpful in patients with A Fib. Conversion is much more common in patients with A Fib of less than 48 hours duration as conversion rates drop off considerably after this time.
As a general rule, regardless of the agent or route used, the conversion rate of A Fib of less than 48 hours duration is 60%-90%. Conversion rates drop to 15%-30% if present 48 hours or longer. Successful conversion of A Flutter is generally higher than for A Fib.
Agents that have been studied for conversion of A Fib to sinus rhythm include quinidine, procainamide, propafenone, flecainide, sotalol, ibutilide, and amiodarone. No single agent has emerged as the drug of choice for acute conversion of A Fib. Ibutilide is available only in the IV form and has been approved by the Food and Drug Administration (FDA) specifically for this purpose. All other agents used for acute pharmacologic conversion of A Fib are done "off-label."
Reported success rates vary in part because of the heterogeneity of patient populations– particularly with respect to the duration of A Fib in the published trials. Of the intravenous agents, only ibutilide is approved by the FDA for this indication.
Torsades de pointes (TDP) is a potentially life-threatening arrhythmia and requires prompt evaluation and treatment. See Figure 3 in the original guideline document for treatment of TDP.
Refer to Annotation #20, Table 7, "Antiarrhythmic Agents" in the original guideline document for more information on antiarrhythmic agents.
Ibutilide has been studied extensively for the conversion of recent onset A Fib and A Flutter. Efficacy rates between 30%-40% have been quoted in acute reversal of recent onset A Fib. Generally patients convert within 30 minutes. Significant adverse effect of torsades de pointes (TDP) was noted in 4.3% of patients, 1.7% requiring electrical termination. There were no deaths or severe morbidities.
Refer to Figure 2 in the original guideline document for more information on use of ibutilide.
Proarrhythmia associated with initiation of membrane antiarrhythmic agents relates to the presence of underlying structural heart disease as well as the type of drug initiated. The drugs sotalol, dofetilide, and quinidine should be initiated in all patients under telemetry guidance. These drugs should not be allowed to prolong QTc (similar to sotalol and dofetilide) to longer than 500 msec.
Amiodarone, the other class III drug, is the subject of several articles regarding its efficacy in conversion of recent onset and permanent A Fib. Amiodarone is effective in converting A Fib both acutely and chronically. It has been studied for both the oral and intravenous routes. Amiodarone can be started at maintenance doses in the outpatient setting; when high-dose loading is required or the drug is initiated in patients with structural heart disease, hospitalization should be advised. The Class I-C drugs propafenone and flecainide can also be initiated in the outpatient setting with appropriate follow-up of QRS duration that should not lengthen longer than 25%. For patients with structural heart disease, these agents should also be initiated in the inpatient setting. A new Class III agent, azimilide, may enhance future flexibility in the outpatient initiation of antiarrhythmic agents.
Oral flecainide (300 mg single dose) has similar conversion rates compared to oral propafenone (600 mg single dose) when used in patients with A Fib of acute onset (approximately 72%-78% conversion rate at eight hours).
Evidence supporting this recommendation is of classes: A, D, R
Failed Cardioversion Treatment Options
If initial attempts to restore normal sinus rhythm for A Fib fail, cardioversion can be repeated following a parenteral or oral loading dose of an appropriate antiarrhythmic agent. However, this approach should be avoided in patients with ejection fractions less than 30% because of the increased risk of torsades de pointes.
Furthermore, it should be noted that this is not a strategy to maintain normal sinus rhythm but only a means to enhance conversion back to sinus rhythm. Appropriate anticoagulation practices are required prior to and following cardioversion if the duration of A Fib exceeds 48 hours. If A Fib continues despite these attempts, cardiology consultation is advised.
The patient and/or physician may also opt for chronic anticoagulation and chronic rate control at this point - though the general consensus is that most patients with a first episode of A Fib or A Flutter have a high likelihood of successful conversion back to normal sinus rhythm.
Transthoracic cardioversion of A Fib may be achieved by applying biphasic waveform for defibrillation. It has been shown to be equally effective and to use less energy than monophasic waveforms.
Evidence supporting this recommendation is of class: A, R
Maintenance of Sinus Rhythm Following Conversion
Several antiarrhythmic drugs have been demonstrated to improve sinus rhythm maintenance following cardioversion, including amiodarone, propafenone, disopyramide, sotalol, flecainide, dofetilide, and quinidine. Amiodarone has been shown to be the single most effective agent of the lot, although it also contributes the most to noncardiac drug related toxicity. When administered at 800 mg per day for 2 weeks prior to elective cardioversion, amiodarone chemically converts one-fifth of patients with persistent AF, and when continued for 8 weeks at 200 mg per day, doubled the number of patients in normal sinus rhythm at that time. Both the ACE inhibitor, enalapril, and angiotensin receptor blocker, irbesartan, have been demonstrated to enhance the maintenance of normal sinus rhythm after cardioversion when added to amiodarone.
Evidence supporting this recommendation is of class: A