Back to CARDIOLOGYAtrial fibrillation (AF) is the most common sustained disorder of cardiac rhythm presenting with many prognostic and therapeutic implications. It is a manifestation of many different cardiac and systemic disorders, the most common being coronary heart disease, hypertension, cardiomyopathies, vauvular heart desease, thyrotoxicosis, acute infections, excess alchool intake, pulmonary thromboembolism, lung carcinoma, postoperative problems and the idiopathic form.
AF is common in the community, affecting up to 5% of those aged 75 or over. Because of its serious implications, namely heart failure, angina, peripheral embolism and stroke, clinicians in all specialties must know how to recognize and treat AF as well as to detect its cause.
AF represents innumerable electrical atrial firings causing electrical and mechanical disarray. This is a result of multiple independent microreentrant wavelets of electrical activity. Because there is no single, organized atrial wavefront, no p wave is seen on the ECG, reflecting the loss of effective atrial contribution to ventricular filing during diastole.
Treatment of AF is currently the subject of many controversies, and can be divided depending on whether it is acute ou chronic and is based on two main objectives, namely restoration of sinus rhythm (and hence of atrial contraction) and control of heart (ventricular) rate. We should never forgett that at the same time we are trying to treat AF we are always looking for a reversible cause that should be treated and for preventing the thromboembolic complications related to it.
In patients with acute AF our initial goal is to control ventricular rate to avoid signs of congestion and hemodinamic decompensation in the stable patient. This can be done by pharmacologic means, with drugs that slow the conduction at the level of the AV node, like Digoxin, Verapamil, Diltiazen and Beta-bloquers((Propanolol, Atenolol,...).When rapid managment of heart rate is desired, the IV route should be used. A caveat as to the use of these drugs is their potencial for serious toxicity, with most problems arising not from the drugs themselves but from their simultaneous, rapid or overzealous administration, crating the potencial for such cumulative effects dangerously slow ventricular rates, sometimes requiring the use of a temporaty ventricular pacemaker.
In the hemodimicaly unstable patiente (hipotensive, with signs of impending circulatory collapse), the goal is immediate restoration of sinus rhythm, for wich the best means is electrical cardioversion, usually with 100-200J. In the patient who tolerates well the acute loss of AV sinchrony, restoration of sinus rythm after or concomitantly with rate control can be pursued with drugs such as Amiodarone, Quinidine, Procainamide, Sotalol and other Beta-bloquers and even Digoxin itself.
In patients with chronic AF our goals are the same, but special precautions should be undertaken. Because of the blood stasis in the noncontractile atria, clots are formed inside of it that can result in systemic and cerebral embolization, specially at the time we are attempting to restore sinus rythm, as the atria start to contract again (risk is about 7%). So it is imperative that anticoagulant therapy be installed in patients with AF, specially those with underlying cardiac disease and those with other risk factors for stoke (eg. the elderly).
The anticoagulation is made with either oral Warfarin or parenteral Heparin, the goal being a 1.5 times (INR 2-3) the prothrombin control value and twice the aPTT control value, respectively. If restoration of sinus rhythm is desired the therapy should be started 3 weeks prior and maintaned for a couple of weeks after the procedure (either electrically or pharmacologicaly). Otherwise anticoagulant therapy should be maintained indefinetly.
Some recents studies are trying to evaluate the role of Transesophageal Ecocardiography (TEE) in predicting the presence of atrial clots before cardioversion, thereby avoiding the need to run the risks of anticoagulation. Some authors advocate their use routinely whereas others still feel more secure proceding with anticagulation, as blood stasis still persists some time after restoration of sinus rhythm because of atrial stunning, maintaining a high risk of thromboembolic phenomena wich otherwise couldn't be prevented.
Some new interventional therapies of AF are becoming stablished slowly as experience is increasing, such as surgery (Maze produce, the Corridor procedure) and ablation with radiofrequency (RF) energy either remodeling of the AV node ou the resemblance of the Maze procedure with catheters inside the heart chambers). However these are still not widely used, although studies demonstate a high frequency of success in the short term.
Lastly, because some patients develop dilated heart failure because of the high ventricular rates associates with chronic AF (the so called Taquicardiomyopathy), some centers use ablation of the AV node (via RF) with pacemaker implantation in selected patients wich rates are not adequately controled pharmacologicaly and cadioversion failed.
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