Management of atrial fibrillation based on guidelines – part III
Anticoagulation prior to cardioversion in atrial fibrillation: Role of TEE
In atrial fibrillation (AF) which has lasted more than 48 hours, there is always a chance for the presence of left atrial appendage thrombus and anticoagulation prior to cardioversion is an important strategy. In those presenting within 48 hours, which may be in fact difficult to document in first diagnosed AF, heparinization [unfractionated heparin (UFH) IV bolus followed by infusion or weight adjusted therapeutic dose of low molecular weight heparin (LMWH)] followed by cardioversion can be considered. If sinus rhythm is achieved, they need be put on oral anticoagulation depending on risk factors. A minimum of four weeks anticoagulation is ideal to tide over the possibility of post cardioversion atrial stunning (lack of mechanical activity in spite of electrical activity). Long term anticoagulation is needed depending on the previously described scoring systems (CHADS2 score and CHA2DS2-VASc).
In AF which is known to have existed more than 48 hours (or if the duration is unknown, to be on the safer side), three weeks of therapeutic oral anticoagulation is recommended prior to an attempt of cardioversion. Further management is as mentioned above.
An alternate strategy is to have a transesophageal echocardiogram (TEE) done prior to cardioversion to look for thrombi in the left atrial appendage. If a thrombus is found, therapeutic anticoagulation is needed for three weeks prior to cardioversion. If the thrombus is persisting after three weeks, a rate control strategy is adopted and long term anticoagulation continued. If no thrombus is found initially or after three weeks, cardioversion is considered after heparinization. Further anticoagulation is as described in the first paragraph. It may be noted that though TEE is useful in detecting left atrial appendage (LAA) thrombus, it cannot totally exclude a LAA thrombus.
Cardioversion for atrial fibrillation
Cardioversion of atrial fibrillation can be achieved either by electrical therapy or pharmacological therapy. When atrial fibrillation is of less than 48 hours duration, those with hemodynamic instability will be taken for electrical cardioversion. In the absence of hemodynamic instability, if pharmacological cardioversion is opted for in those with structural heart disease, intravenous amiodarone will be the drug of choice. In those without structural heart disease, intravenous flecainide, propafenone or ibutilide may be given for pharmacological cardioversion.
Rhythm vs rate control
Rhythm control strategy may be considered in those who remain symptomatic despite adequate antithrombotic therapy and rate control measures, in all sub types (paroxysmal or persistent) of atrial fibrillation. By definition, permanent AF is redesignated as long standing persistent AF when rhythm control strategy is planned. If rhythm control strategy fails, they are again switched back to rate control. Catheter ablation is considered in those with recurrent symptomatic atrial fibrillation who has not responded to at least one anti arrhythmic drug. It is better suited for those with no or minimal left atrial enlargement/left ventricular dysfunction. Initial rhythm control strategy is a class Iia recommendation in the young as well in those with atrial fibrillation and heart failure as per the ESC guidelines.
Lenient vs strict rate control
If there are only few tolerable symptoms, lenient rate control is sufficient. Those who are more symptomatic may be considered for strict rate control. Exercise testing may be done if excessive rise in heart rate during exercise is anticipated. 24 hour Holter ECG monitoring is advisable to document safety while opting strict rate control to avoid bradycardic episodes.
Drugs for long term rate control in AF
If there are no associated heart diseases, beta blockers, verapamil, diltiazem or digitalis or a combination can be given for rate control. Beta blockers will be preferred in those with heart failure. In those with obstructive airways disease, the options would be diltiazem, verapamil, digitalis or beta one selective agents.
Drugs for acute rate control in AF
In those without heart failure or pre-excitation, intravenous beta blocker or non-dihydropyridine calcium channel blockers can be given for acute rate control in AF. For those in heart failure, intravenous digoxin or amiodarone will be considered. In those with AF and pre-excitation, class I anti arrhythmic agents or amiodarone are given for acute rate control. Beta blockers, non-dihydropyridine calcium channel blockers and digitalis are contraindicated in this group.
AV node ablation for rate control in AF
AV node ablation and pacing is a strategy reserved for drug refractory symptomatic atrial fibrillation. They will receive conventional pacing or cardiac resynchronization therapy depending on whether the left ventricular function is normal or not. This is because of the potential for right ventricular pacing to cause left ventricular dysfunction on the long term.
Principles of rhythm control in AF
The main aim of rhythm control strategy is to reduce symptoms related to atrial fibrillation. It should be remembered that the efficacy of antiarrhythmic drugs to maintain sinus rhythm is only modest. If one anti arrhythmic drug fails, another may succeed. Proarrhythmia and extra cardiac side effects of anti arrhythmic drugs have to be borne in mind while choosing rhythm control strategy. Safety rather than efficacy should be the primary concern.
Choice of antiarrhythmic drugs
The choice of antiarrhythmic drug would depend on associated structural heart disease and also whether the AF is vagally mediated, adrenergically mediated or undetermined. In those with no or minimal structural heart disease, adrenergically mediated AF will be treated with beta blockers, sotalol or dronedarone. Vagally mediated AF may be treated with disopyramide while the undetermined ones can be treated with dronedarone, flecainide, propafenone or sotalol. Those who do not respond to these agents may respond to amiodarone.
Among those with heart disease, those with hypertension, but no left ventricular hypertrophy, can be treated as those without heart disease. If there is left ventricular hypertrophy, dronedarone may be the first choice, followed by amiodarone. Dronedarone or sotalol may be the first choice in coronary artery disease and dronedarone becomes the first choice in those with stable heart failure. In NYHA class III/IV or unstable heart failure, amiodarone will be the first choice. Amiodarone is the second choice if dronedarone fails in those with left ventricular hypertrophy, coronary artery disease or stable heart failure.