Atrial fibrillation is the most common arrhythmia in clinical practice, affecting around 33 million people worldwide. The incidence and prevalence of atrial fibrillation increases with age. Its pathogenesis is usually associated with an underlying cardiac disease that leads to changes in the anatomy or the physiology of the atrium. The most common risk factors and associated diseases are: Hypertension, coronary artery disease, rheumatic heart disease (poor countries), valvular heart disease, heart failure, congenital heart diseases, pulmonary embolism, obesity and CKD. Family history and genetic factors are also important.
Common triggers of atrial fibrillation include surgeries (cardiac or noncardiac), drug use (alcohol, medications or illegal drugs), acute cardiopulmonary diseases (pericarditis, pulmonary embolism), and hyperthyroidism, among other conditions.
It can be classified as:
Paroxysmal – Lasts less than 7 days (terminates spontaneously or with intervention).
Persistent – Episodes lasts more than 7 days.
Long-standing persistent – Lasts more than 12 months.
Permanent – Persistent atrial fibrillation in which a decision was made by the patient and doctor to no longer pursue a rhythm control strategy.
The term non-valvular atrial fibrillation is used when there are no rheumatic mitral valve diseases, a prosthetic heart valve, or mitral valve repair involved.
SIGNS AND SYMPTOMS:
Patients can either be asymptomatic or present with palpitations, shortness of breath, dyspnea on exertion, angina or lightheadness. Patients with paroxysmal atrial fibrillation have a high chance of recurrence (up to 70% in one year).
DIAGNOSES AND ELECTROCARDIOGRAM FINDINGS:
Diagnoses is done by the ECG.
ECG findings include:
Irregularly irregular RR intervals.
Absence of P waves.
Narrow QRS (except in cases where there is pre-excitation or electrical pathway blocks)
Fibrillatory waves (f waves) are present in variable rate.
Ventricular rate (90-170bpm).
Underlying conditions that may be triggering the atrial fibrillation should be identified and managed.
Regarding the atrial fibrillation itself the physician should take in consideration the number of episodes (is it the first one or is it a recurrent episode?), the symptoms, the hemodynamic status and the thromboembolic risk.
In the acute setting, if the patient is hemodynamically unstable (severe acute left heart failure, ongoing myocardial ischemia, or hypotension) direct current cardioversion should be performed (120 to 200 joules for biphasic devices and 200 joules for monophasic devices). If the patient is hemodynamically stable in the acute setting the provider should start rate control (with beta-blockers, non-dihydropyridine calcium channel blockers or digoxin).
Useful dosages on the acute setting:
Metoprolol can be used IV, 2.5 to 5mg over two minutes and may be repeated q5min (Max. 15mg)
Diltiazem IV bolus of 0.25mg/kg (usually 20mg) over 2 min. May be repetead after 15 min in a dose of 0.35mg/kg (average 25mg).
After the initial management (rate control to alleviate symptoms or DCC in case of unstable patients) a strategy for chronic management must be chosen.
In the long term, the provider can choose between continuing the rate control or trying rhythm control. Both strategies can be used and may have similar results (this is a very old debate in cardiology that is yet to end). For rhythm control, the cardioversion (DCC or medicamentous) may be tried without prior anticoagulation if the episode is recent (<48 hours). If the episode is >48h the patient needs to be anticoagulated for at least 3 weeks (and he should continue anticoagulation for at least 4 weeks after the cardioversion). A transesophageal echocardiogram (TEE), may be performed and can assess the presence or absence of thrombus in the heart regardless of this time frame, helping the provider in the decision. Drugs used for rhythm control include amiodarone, dofetilide, dronedarone, flecainide, propafenone and sotalol. Rhythm control can also be obtained by catheter ablation in patients with persistent atrial fibrillation that do not tolerate or do not respond to medication.
Regardless of the strategy (rate or rhythm control) the thromboembolic risk should be considered. To assess the thromboembolic risk, the physician can use the CHADS2 or the CHA2DS2-VASc scores, that can help in the decision to start oral anticoagulation or not. The risk of bleeding should also be taken into consideration (check HAS-BLED score).
REFERENCES & FURTHER READING:
- January CT. et al. 2014 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation. Journal of the American College of Cardiology Dec 2014, 64 (21) e1-e76..
- Markides V, Schilling RJ. Atrial fibrillation: classification, pathophysiology, mechanisms and drug treatment
- Boyle NG. Atrial Fibrillation Guidelines. Medscape. Updated: Nov 30, 2015