Initial approach to atrial fibrillation
The immediate priority in a patient presenting with atrial fibrillation is the control of ventricular rate to reasonable range. Then the need for anticoagulation has to be assessed depending on the duration and risk factors. Whether to opt for a rhythm control strategy is the next consideration. Finally the treatment of underlying heart disease is very important in over all management of the patient with atrial fibrillation.
Upstream therapies in atrial fibrillation
‘Upstream’ therapy for prevention of atrial remodelling has been evaluated in a few prospective and retrospective studies, but the concept is still controversial. Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, statins, fish oils, glucocorticoids and moderate physical activity have all been considered in this upstream therapy and found to useful to a variable extent in both primary and secondary prevention of atrial fibrillation.
Oral anticoagulation in atrial fibrillation
Since thromboembolism and resultant strokes are an important risk of atrial fibrillation, oral anticoagulation is an important consideration. CHADS2 score was developed to assess the risk of thromboembolism in non rheumatic atrial fibrillation and has been discussed earlier. CHADS2 is short for congestive heart failure, hypertension, age, diabetes mellitus and stroke (doubled). Each component except stroke are alloted one point each while stroke or TIA is alloted two points. Total possible score is 6. The risk of stroke increases steadily from 1.9% to 18.2% as the score reaches 6, though there were only few patients with the highest score in the index study. Oral anticoagulation is indicated if the score is two or more. CHA2DS2-VASc risk factor based point scoring system for atrial fibrillation is meant for assessing the risk of thromboembolism in non-valvar atrial fibrillation in a better way than CHADS2. CHA2DS2-VASc considers previous stroke/TIA/systemic embolism and age 75 years and above as major risk factors with 2 points each. Other clinically relevant non-major risk factors alloted 1 point each are congestive heart failure/left ventricular dysfunction, hypertension, diabetes mellitus, vascular disease (prior myocardial infarction, peripheral arterial disease or aortic plaque), age between 65-74 years and female sex. Total score possible is 9 in the CHA2DS2-VASc scoring system. Just as in the CHADS2 score, the age adjusted stroke risk rises from 0% with a score of zero to 15.2% with a CHA2DS2-VASc score of 9. The lower number of individuals in the highest scores were also noted in the index study for this scoring system as well. If the CHADS2 score is two or more, the patient needs long term oral anticoagulation. If the score is lesser, age is considered. If age is 75 years or more, the patient still needs anticoagulation. If the age is less than 75 years, presence of two or more other risk factors from the CHA2DS2-VASc score is considered as an indication for anticoagulation. If patient has only one other risk factor, oral anticoagulation or aspirin (preferably the former) is given. If there are no risk factors, no anti thrombotic therapy or aspirin (preferably the former) is recommended.
Assessment of bleeding risk while planning oral anticoagulation
Potential bleeding risk has always been a worry especially when anticoagulating elderly with atrial fibrillation. In fact this often leads to deferring of anticoagulation, most often in the elderly who also have a higher benefit in terms of prevention of stroke. The HAS BLED [Hypertension, Abnormal renal/liver function, Stroke, Bleeding history or predisposition, Labile international normalized ratio, Elderly (>65 years), Drugs (anti platelet agents or non-steroidal anti inflammatory drugs)/alcohol concomitantly] bleeding risk score has been introduced to counter this problem. Maximum number of points possible on the HAS BLED score is 9.
HAS BLED scoring is based on the EuroHeart Survey involving about four thousand subjects with atrial fibrillation [Pisters R, Lane DA, Nieuwlaat R, de Vos CB, Crijns HJ, Lip GY. A novel userfriendlyscore (HAS-BLED) to assess one-year risk of major bleeding in atrialfibrillation patients: The Euro Heart Survey. Chest 2010; 138:1093-100]. In this study, number of bleeds per 100 patient years ranged from 1.13 to 12.5 when scores increased from 0 to 5. There were only two patients with a score of 6 and no patient had scores above 6.
While deciding on long term oral anticoagulation the risk of bleeding should be less than the risk due to stroke for a beneficial effect of anticoagulation to be obtained.
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, heparinisation [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 trans esophageal echocardiogarm (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 heparinisation. 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, permanant 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 anti arrhythmic 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 anti arrhythmic drugs
The choice of anti arrhythmic 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.
CHA2DS2-VASc scoring system for atrial fibrillation
CHA2DS2-VASc risk factor based point scoring system for atrial fibrillation is meant for assessing the risk of thromboembolism in non-valvar atrial fibrillation. Major risk factors (previous stroke, TIA or systemic embolism and age 75 years or more) are given a score of two points while other clinically relevant non-major risk factors ( congestive heart failure or moderate to severe left ventricular systolic dysfunction [left ventricular ejection fraction of 40% or less], hypertension, diabetes mellitus, age between 65-74 years, female sex and vascular disease [prior myocardial infarction, peripheral artery disease or aortic plaque]) are given one point each.
Congestive heart failure / LV dysfunction : 1
Hypertension : 1
Age 75 or more : 2
Diabetes mellitus : 1
Stroke/TIA/thromboembolism : 2
Vascular disease : 1
Age 65-74 : 1
Sex category (female sex) : 1
Maximum score : 9
CHA2DS2-VASc score is an improvement from the CHADS2 score. The risk increases as the score increases from 0 to 9. In a study involving over 7300 patients stroke rate was 0 when the score was 0, though there was only one patient in that category. There were fourteen patients with a score of nine and they had stroke rate of 15.2%. Maximum number of patients scores of 3 and 4 with 1730 and 1718 patients in these categories. Score 3 had a stroke rate of 3.2% and score 4 had a stroke rate of 4% [Cited from Eur Heart J. 2010; 31: 2369-2429].