The acute management of patients with atrial fibrillation ( AF ) is driven by acute protection against thrombo-embolic events and acute improvement of cardiac function. The severity of AF-related symptoms should drive the decision for acute restoration of sinus rhythm ( in severely compromised patients ) or acute management of the ventricular rate ( in most other patients ).
Acute rate control
An inappropriate ventricular rate and irregularity of the rhythm can cause symptoms and severe haemodynamic distress in atrial fibrillation patients.
Patients with a rapid ventricular response usually need acute control of their ventricular rate. In stable patients, this can be achieved by oral administration of beta-blockers or nondihydropyridine calcium channel antagonists.
In severely compromised patients, i.v. Verapamil or Metoprolol can be very useful to slow atrioventricular node conduction rapidly.
In the acute setting, the target ventricular rate should usually be 80–100 bpm. In selected patients, Amiodarone may be used, especially in those with severely depressed left ventricular function.
Atrial fibrillation with slow ventricular rates may respond to Atropine ( 0.5–2 mg i.v. ), but many patients with symptomatic bradyarrhythmia may require either urgent cardioversion or placement of a temporary pacemaker lead in the right ventricle.
Acute initiation of rate control therapy should usually be followed by a long-term rate control strategy.
Pharmacological cardioversion
Many episodes of atrial fibrillation terminate spontaneously within the first hours or days. If medically indicated ( e.g. in severely compromised patients ), in patients who remain symptomatic despite adequate rate control, or in patients in whom rhythm control therapy is pursued, pharmacological cardioversion of atrial fibrillation may be initiated by a bolus administration of an antiarrhythmic drug.
The conversion rate with antiarrhythmic drugs is lower than with DCC ( direct current cardioversion ), but does not require conscious sedation or anaesthesia, and may facilitate the choice of antiarrhythmic drug therapy to prevent recurrent atrial fibrillation.
Most patients who undergo pharmacological cardioversion require continuous medical supervision and ECG monitoring during the drug infusion and for a period afterwards ( usually about half the drug elimination half-life ) to detect proarrhythmic events such as ventricular proarrhythmia, sinus node arrest, or atrioventricular block.
Repeat oral pharmacological cardioversion ( pill-in-the-pocket therapy ) may be appropriate for selected ambulatory patients once the safety of such an intervention has been established.
Several agents are available for pharmacological cardioversion.
Flecainide given i.v. to patients with atrial fibrillation of short duration ( especially, 24 h ) has an established effect ( 67–92% at 6 h ) on restoring sinus rhythm. The usual dose is 2 mg/kg over 10 min. The majority of patients convert within the first hour after i.v. administration. It is rarely effective for termination of atrial flutter or persistent atrial fibrillation. Oral administration of flecainide may be effective for recent-onset atrial fibrillation. Recommended doses are 200–400 mg. Flecainide should be avoided in patients with underlying heart disease involving abnormal left ventricular ( LV ) function and ischaemia.
Several placebo-controlled randomized studies have demonstrated the efficacy of Propafenone in converting recent-onset atrial fibrillation to sinus rhythm. Within a few hours, the expected conversion rate was between 41 and 91% after i.v. use ( 2 mg/kg over 10–20 min ). The corresponding early conversion rates in placebo-treated patients were 10–29%. Propafenone has only a limited efficacy for conversion of persistent atrial fibrillation and for atrial flutter. Similar to Flecainide, Propafenone should be avoided in patients with underlying heart disease involving abnormal LV function and ischaemia. In addition, owing to its weak beta-blocking properties, Propafenone should be avoided in severe obstructive lung disease. The time to conversion varies from 30 min to 2 h. Propafenone is also effective if administered orally ( conversion between 2 and 6 h ).
Cardioversion with Amiodarone occurs several hours later than with Flecainide or Propafenone. The approximate conversion rate at 24 h in placebo-treated patients was 40–60%, with an increase to 80–90% after Amiodarone treatment. In the short and medium term, Amiodarone does not achieve cardioversion. At 24 h the drug has demonstrated better effect compared with control in some but not all randomized studies.
In patients with recent-onset atrial fibrillation, Ibutilide in one or two infusions of 1 mg over 10 min each, with a wait of 10 min between doses, has demonstrated conversion rates within 90 min of approximately 50% in several well-designed randomized studies, placebo controlled or with a control group of drugs with known little effect. The time to conversion is approximately 30 min. The most important side effect is polymorphic ventricular tachycardia, most often non-sustained, but DCC may be needed, and the QTc interval is expected to increase by approximately 60 ms. Ibutilide is, however, more effective for conversion of atrial flutter than atrial fibrillation.
One study comparing the effect of placebo vs. two different dosages of Sotalol found conversion rates of 14% ( 2/14 patients ), 11% ( 2/11 patients ), and 13% ( 2/16 patients ). These differences were not significant.
In one study in 79 patients with atrial fibrillation ( but no control group ), 13% converted to sinus rhythm after i.v. b-blocker ( Metoprolol ) treatment.
No relevant reports have been published for Atenolol, Carvedilol, Bisoprolol, Propranolol, Timolol, or Esmolol.
No randomized controlled trial of sufficient size comparing Verapamil with placebo has been published. In studies comparing Verapamil with Flecainide, Esmolol, or Propafenone, 6, 12, and 14%, respectively, converted to sinus rhythm, in 17, 24, and 29 patients given Verapamil.
Digoxin is ineffective for atrial fibrillation termination. In one study in 239 patients with atrial fibrillation of less than 7 days duration, the conversion rate at 16 h was 46% in placebo-treated patients and 51% in patients given Digoxin; two other studies, in 40 and 82 patients, found conversion rates ( placebo vs. Digoxin ) of 40% vs. 47% and 14% vs. 32%, respectively.
In conclusion, there is good evidence that Digoxin has no effect. Although evidence is less comprehensive for Verapamil, the reported conversion rates point to a negligible effect. In one study Sotalol did not have any effect, and there are no data for Ajmaline. Metoprolol did not have any effect in the one study reported, and there are no data for the other b-blocking agents.
Comparisons between drugs
Several comparisons have been made between Flecainide and Propafenone, but only one study demonstrated better conversion rates of Flecainide ( 90 and 64%, respectively ). Ibutilide converted 71% of patients compared with 49% on Propafenone, but 10% in the Ibutilide group experienced non-sustained ventricular tachycardia.
From these studies, no clear conclusions can be drawn regarding the difference in the effect on conversion of these drugs. The choice may therefore be made on the basis of contraindications, side effects, and/or costs.
In suitable patients with recent-onset atrial fibrillation ( generally less than 48 h duration ), a trial of pharmacological cardioversion to sinus rhythm can be offered with i.v. Flecainide or Propafenone ( when there is little or no underlying structural heart disease ) or Amiodarone ( when there is structural disease ). The anticipated conversion rate is greater than or equal to 50% within approximately 15-120 min. Ibutilide is effective, but the risk of serious proarrhythmia is not negligible.
Pill-in-the-pocket approach
In-hospital oral Propafenone converted 55 of 119 ( 45% ) patients at 3 h compared with 22 of 121 ( 18% ) patients on placebo. In smaller studies, both Propafenone and Flecainide demonstrated a similar effect.
According to one medium-size trial, oral Propafenone ( 450–600 mg ) or flecainide ( 200–300 mg ) can be administered by the patient safely ( 1/569 episodes resulting in atrial flutter with rapid conduction ) and effectively ( 94%, 534/569 episodes ) out of hospital.
This approach may be used in selected, highly symptomatic patients with infrequent ( e.g. between once per month and once per year ) recurrences of atrial fibrillation. In order to implement the pill-in-thepocket technique, patients should be screened for indications and contraindications, and the efficacy and safety of oral treatment should be tested in hospital. Patients should be instructed to take Flecainide or Propafenone when symptoms of atrial fibrillation occur.
Direct current cardioversion
a) Procedure - DCC is an effective method of converting AF to sinus rhythm. Unless adequate anticoagulation has been documented for 3weeks or atrial fibrillation is less than 48 h from a definite onset, a TOE should be performed to rule out atrial thrombi. A pacing catheter or external pacing pads may be needed if asystole or bradycardia occurs.
Successful DCC is usually defined as termination of atrial fibrillation, documented as the presence of two or more consecutive P waves after shock delivery.
Evidence favours the use of biphasic external defibrillators because of their lower energy requirements and greater efficacy compared with monophasic defibrillators.
Trials have demonstrated a significant increase in the first shock success rate of DCC for atrial fibrillation when biphasic waveforms were used. Currently, two conventional positions are commonly used for electrode placement. Several studies have shown that anteroposterior electrode placement is more effective than anterolateral placement.
If initial shocks are unsuccessful for terminating the arrhythmia, the electrodes should be repositioned and cardioversion repeated.
Outpatient/ambulatory DCC can be undertaken in patients who are haemodynamically stable and do not have severe underlying heart disease. At least 3 h of ECG and haemodynamic monitoring are needed after the procedure, before the patient is allowed to leave the hospital.
Internal cardioversion may be helpful in special situations, e.g. when a patient undergoes invasive procedures and cardioversion catheters can be placed without further vascular access, but has been largely abandoned as a means for cardioversion, except when implanted defibrillation devices are present.
b) Complications - The risks and complications of cardioversion are associated primarily with thrombo-embolic events, post-cardioversion arrhythmias, and the risks of general anaesthesia. The procedure is associated with 1–2% risk of thromboembolism, which can be reduced by adequate anticoagulation in the weeks prior to cardioversion or by exclusion of left atrium thrombi before the procedure.
Skin burns are a common complication.
In patients with sinus node dysfunction, especially in elderly patients with structural heart disease, prolonged sinus arrest without an adequate escape rhythm may occur.
Dangerous arrhythmias, such as ventricular tachycardia and fibrillation, may arise in the presence of hypokalaemia, Digitalis intoxication, or improper synchronization.
The patient may become hypoxic or hypoventilate from sedation, but hypotension and pulmonary oedema are rare.
c) Cardioversion in patients with implanted pacemakers and defibrillators - The electrode paddle should be at least 8 cm from the pacemaker battery, and the anteroposterior paddle positioning is recommended. Biphasic shocks are preferred because they require less energy for atrial fibrillation termination.
In pacemaker-dependent patients, an increase in pacing threshold should be anticipated. These patients should be monitored carefully. After cardioversion, the device should be interrogated and evaluated to ensure normal function.
d) Recurrence after cardioversion - Recurrences after DCC can be divided into three phases: (1) immediate recurrences, which occur within the first few minutes after DCC; (2) early recurrences, which occur during the first 5 days after DCC; (3) late recurrence, which occur thereafter.
Factors that predispose to atrial fibrillation recurrence are age, atrial fibrillation duration before cardioversion, number of previous recurrences, an increased LA size or reduced LA function, and the presence of coronary heart disease or pulmonary or mitral valve disease.
Atrial ectopic beats with a long–short sequence, faster heart rates, and variations in atrial conduction increase the risk of atrial fibrillation recurrence.
Pre-treatment with antiarrhythmic drugs such as Amiodarone, Ibutilide, Sotalol, Flecainide, and Propafenone increases the likelihood of restoration of sinus rhythm.
Some highly symptomatic patients in whom atrial fibrillation occurs infrequently ( e.g. once or twice a year ) strongly prefer to undergo repeated cardioversions as a long-term rhythm control strategy, rather than opting for rate control or other rhythm control modalities which they may find uncomfortable.
Source: European Society of Cardiology, 2010
XagenaMedicine2010
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