Treating Atrial Fibrillation:
The treatment of atrial fibrillation must take into account the clinical situation, the chronicity of the fibrillation, the patients level of anti-coagulation and other stroke risk factors, the patients symptoms, the ventricular rate, and most importantly, the hemodynamic status of the patient. There are several treatment strategies depending on the above factors and also partly on patient preference. If the patient is hemodynamically stable, and the atrial fibrillation is new in onset, an attempt is made to convert the patient out of the rhythm, with either anti-arrhythmics or electrical cardioversion. If the rhythm is persistent or chronic, a strategy of ventricular rate control and anti-coagulation to prevent complications is generally used. If the patient is unstable, emergent cardioversion is warranted. Surgical catheter ablation therapy or AV node ablation with ventricular pacing are other options for patients with persistent atrial fibrillation and more bothersome symptoms.
Up to 2/3 of patients with new onset atrial fibrillation will spontaneously revert to sinus rhythm in 24 hours, so temporary rate control is appropriate. However, if it persists longer than a week, spontaneous conversion is unlikely and other measures should be attempted to either terminate the rhythm or control the rate.
For new onset atrial fibrillation, especially if it is thought to be of recent onset, termination of the rhythm is generally attempted with elective cardioversion during short-acting anesthesia using a 200 joule biphasic synchronized shock. It may also be attempted in patients with bothersome symptoms despite adequate rate control. Elective cardioversion must follow at least 4 weeks of anti-coagulant therapy with warfarin to prevent embolization of a thrombus with the cardioversion. The recurrence rate after elective cardioversion is significantly high, so anti-coagulation therapy is generally maintained until sinus rhythm can be proven for at least 6 months straight. Pharmacological therapy to convert the rhythm is less reliable than cardioversion. It can be instituted to maintain sinus rhythm after it has been achieved either by spontaneous conversion or cardioversion or it can be started in anticipation of cardioversion. The agents most commonly used are sotolol, amiodarone, procainamide, ibutilide or dofetilide. In the absence of structural heart disease or hypertensive heart disease, the use of class IC anti-arrhythmics flecainide or propafenone is well tolerated. Many of the anti-arrhythmic agents are associated with an increased risk of arrhythmias and many other adverse effects and these risks must be weighed against the benefit to the patient of maintaining sinus rhythm.
In the setting of chronic atrial fibrillation that has recurred despite the attempts described above, a strategy of ventricular rate control and anti-coagulation is used. Rate control is generally achieved with beta-blockers, non-dihydropyridine calcium channel blockers, and/or digoxin. In older, less active patients, control can generally be achieved with one agent, but in younger more active people, a combination may be necessary. Hypertensive patients should receive either a beta-blocker or calcium channel blocker and coronary disease patients and patients with heart failure should receive a beta-blocker. Heart rates over 80 beats per minute are an indication that rate control is inadequate. Anti-coagulation with warfarin to a target INR of 2-3 is necessary to prevent embolic events and stroke. An exception to the need for anti-coagulation is the patient with “lone atrial fibrillation” (no known heart disease, hypertension, atherosclerotic coronary disease, or diabetes) who is under 65 years old. These patients should however be treated with aspirin.
The AFFIRM and RACE trials compared outcome with respect to survival and thromboembolic events in patients with atrial fibrillation and risk factors for stroke in the above to treatment approaches. They favored the rate control strategy over the rhythm control strategy. There was no higher risk of death or stroke in the rate control group. There was only a mildly increased risk of hemorrhagic events in the rate control and anti-coagulation group. However, the decision of which strategy should be used is still controversial and many times is the patient’s preference.
Atrial Fibrillation very commonly co-exists with congestive heart failure, either as an exacerbating factor or as a cause. Some recent studies have suggested that atrial fibrillation is an independent predictor of mortality in patients with CHF with an ejection fraction of less than 35%. As such, a recent study has examined the relationship between atrial fibrillation and the incidence of death due to congestive heart failure. This study by Talajic et al, examined the relationship between the presence of sinus rhythm and outcomes in patients with a history of CHF and atrial fibrillation. In the study, patients were randomized into either a rate control or rhythm control group and their symptoms and EKG’s were monitored to determine the effects of both treatment strategies and sinus rhythm on the course of CHF. It was found that atrial fibrillation is not predictive of cardiovascular mortality, total mortality, or worsening heart failure. There was not a significant difference in mortality or worsening heart failure found between patients that had a high versus low prevalence of sinus rhythm. The most probable explanation for the findings of this study is that atrial fibrillation is a marker of more advanced heart failure but that it is not etiologically linked to a poorer outcome.
In the acute setting urgent cardioversion is usually indicated for patients with shock or severe hypotension, pulmonary edema, or ongoing myocardial infarction or ischemia. There is a potential risk of a thromboembolic event with this treatment if atrial fibrillation has been present for over 48 hours, but the need for immediate rate control outweighs the risk. Just like stable patients, an initial shock of 100-200 joules of synchronized, biphasic cardioversion is applied and if rhythm is not restored, an additional shock at 360 joules is indicated. If this still fails, cardioversion may be successful after loading with IV ibutlide over 10 minutes. If the onset of atrial fibrillation is acute and the conditions that precipitated it are expected to spontaneously resolve over a period of a few days (post-surgery, pericarditis, alcohol) a strategy of rate control is appropriate. Again, beta-blockers are generally first line. However, if hypertension is present or beta-blockers are contraindicated, calcium channel blockers are used. If rate control is still inadequate, digoxin may be used; however, rate control is generally slow, may affect the bronchial tree, and may be inadequate. Amiodarone may also be used if rate control is still inadequate or if cardioversion is planned in the near future.
If cardioversion and drugs are not successful in controlling the symptoms of atrial fibrillation or left ventricular function is worsening due to persistent tachycardia despite rate control treatment, radiofrequency AV nodal ablation may be performed with permanent ventricular pacing to ensure rate control. Another option is catheter ablative therapy of foci around the pulmonary veins that initiate atrial fibrillation. Elimination of atrial fibrillation generally occurs in 50-80% of individuals after catheter ablation. Catheter ablation even holds promise in patients with persistent atrial fibrillation, even those with severe atrial dilation. It does carry risks of pulmonary vein stenosis, atrioesophageal fistula, embolic events, or perforation and tamponade. These risks must be weighed against the benefit to the patient. Surgical ablation is typically only performed at the time of other necessary cardiac surgery.
Future options for the control of atrial fibrillation include, surgical elimination or isolation of the left atrial appendage where most thrombi form or by endovascular insertion of a left atrial appendage-occluding device. These strategies are currently undergoing investigation and may eliminate the need for anti-coagulation.
Fauci, Anthony S., and Tinsley Randolph Harrison. Harrison’s Principles of Internal Medicine. New York [etc.: McGraw-Hill, Medical Division, 2008. Print.
Talajic, Mario, Paul Khairy, Sylvie Levesque, and Stuart J. Connolly. “Maintenance of Sinus Rhythm and Survival in Patients with Heart Failure and Atrial Fibrillation.” Journal of the American College of Cardiology 55.17 (2010): 1796-802. 27 Apr. 2010. Web. 23 Jan. 2011. <www.sciencedirect.com>.
Ferry, David R., and David R. Ferry. ECG in 10 Days. New York: McGraw-Hill, Medical Pub. Division, 2007. Print.